Clear Sky Chart

2024 April 5: Showing eclipse tracks

I don't have time to make this look pretty. But when you click on a colored cloud, transparency, or seeing block on a clear sky chart page, your browser will show you the forecast map for that time. What's new is a link, on the left "Show Eclipse Track" which shows a bare page with same forecast map but with the eclipse track overlaid. This is handy if your favorite clear sky chart is clouded out and you want to know the closest clear spot that is still on the eclipse track. This new page, has zero other features (like clicking the forecast map to show other charts or goto a google map). Sorry, not enough time left to write that code.

Same is true for the "Near-Realtime Satellite Imagry of Clouds" link in the "nifty links" section of each clear sky chart page. There is a new link on the "Near-Realtime Satellite Imagry of Clouds" page called "Show Eclipse Track" which pops you into a bare page with the satellite image showing the eclipse track. I plan to use that page just an hour or so before the eclipse to make a final choice of observing location.

This only works with a browser. None of the apps which display clear sky charts have had enough time to pick up these features.

Best of luck to all chasing the eclipse.

2024 February 4: More Near-Realtime Satellite Imagry for Clouds

I've found a more efficeient way of showing chart locations on top of NESDIS cloud-satellite images. So I can now support them for all clear sky charts (not just sponsored ones). As a thank-you to sponsors who supported during this work, there will be no ads on cloud-satellite pages for sponsored charts.

2024 January 27: Near-Realtime Satellite Imagry for Clouds

NOAA/NESDIS is producing very interesting satellite images of clouds. They are composites of satellite images in many wavelengths. They identify different cloud types -- including fog at night, which as far as I know is unique among statellite images. I think these images show more detail of thin cloud that other satellite images. The color coding, however, is very complicated.

Fortunately for astronomy, the interpretation is simple: If it's moving: It's cloudy. It's not not moving: The sky is clear there.

The images rejoice in the name "Day Cloud Phase / Night Microphysics".

I have linked the appropriate image to some clear sky charts to make them easy to find. An example is here. My tiny contribution is putting a circle and cross on the exact location of chart on the statellite image so we know where to look.

For now, only sponsored clear sky charts have such pages. Look in the "nifty links" section. But for the 2024-05-08 solar eclipse, all charts located along the path of totality which have such satellite image pages. I suggest people use them to plan their eclipse-observing site in the last hour before the eclipse.

2023 December 29: Better map of charts along 2024 Eclipse Track

The map of charts along the eclipse track used to label chart locations with an icon representing the night-time lightpollution level. A completely useless for a daytime event. (Ok, I was re-using the code for mapping all charts).

Now the map of charts along the eclipse track, shows chart locations with a little box containing a percentage. That percentage is the number of times past cloud forecasts have predicted 20% or less cloud cover for the first 10 days of April.

Those precentages show a 3 to 1 range of probability of mostly-cloud-free skies for the eclipse.

I hope this map will help people plan their eclipse watching.

2023 December 14: New lightpollution maps

David Lorenz has recalculated his Light Pollution Atlas with 2022 satellite data. I have updated the lightpollution maps and lightpollution ratings for clear sky charts to use David's latest maps. David's previous maps based on 2020 satellite data are available on his website for those wishing to track the creeping horror of increasing lightpollution. :(

2023 October 5: More updates

CMC is now publishing two additional runs of the cloud, transparency and seeing models. So I've added extra chart updates that happen around 6am EDT and 6pm EDT. The 6pm update is particularly interesting because it may be more accurate for planning a night's observing than the previous closest update which is around noon EDT.

If you see new weirdnesses in the chart images or mouse click features, email me. It was a big code change, so bugs are possible.

2023 August 27: 2024 Eclipse data

Clear sky charts along the path of the 2024 April total solar eclipse are now on this map. More interesting perhaps, is this list which sorts charts along the eclipse path from south-west to north-east with summaries of cloud/transparency stats. As you scroll though the list, you can clearly see there is a much higher chance of good weather for the eclipse in the south-west of north america than the north west. (Use a desktop computer. There is too much data to show on a phone.)

Each clear sky chart page along the eclipse path now has a "nifty link" with eclipse timings and a copy of the weather stats for 2024 April. Charts sites which will only see a partial eclipse will have a "nifty link" for timing data too.

2023 June 7: new smoke colors

I had originally added the smoke forecast to the charts to warn reductions of transarency since the CMC cloud/transparency forecasts do not consider smoke.

Lately much of north america have experienced unprecedented, and unhealthy levels of forestfire smoke. I hadn't expected people to start using the smoke forecast on the chart as a health tool.

So I have changed the colors on the smoke line of the chart to more clearly indicate unhealthy levels. Levels over 35 micrograms per cubic meter (EPA's limit for 24 hour exposure) are now shown in red. The last two levels I show in brown because that's what the sky actually looks like at 200 to 500 micrograms per cubic meter. Yuck.

2023 May 2: clear sky charts and solar eclipses

I will soon be displaying timing of solar eclipse events on clear sky charts in the path of the 2023 October 14 annular solar eclipse. A link in the "nifty links" section of affected chart pages will link to a page with timing details. Plus link to a map of the charts along the eclipse path will appear on the clear sky chart home page in the "By popular keyword" section. In the same section will be a link to a page that lists charts along the eclipse path with snippets of cloud and transparney history for each chart for the time of the eclipse.

It's a beta release right now.

Also comming is the same for the total solar eclipse in 2024 April 8.

2023 February 17: Delays in handling chart requests and sponsorships.

Emails I receive after 12pm on February 20th, I may may only be able to handle after February 28th. So creating new charts or setting up new or renewed sponsorships may be delayed until the 28th. An exception is people who have setup paypal monthly-payment profiles to sponsor a chart every month. Those will be unaffected.

I hope this delay will not dampen anyone's enthusiasm for using the clear sky charts.

2023 January 24: New extended forecasts

I often get requests for forecasts more that a week into the future. Until now I didn't have the data.

I've added about another 5 days of the CMC cloud forecast and the ECMWF cloud forecast. But this data so far into the future is only available in every 3 hours for CMC and every 6 hours for ECMWF.

Each block in the extended portion of the chart represents 3 hours. Aside from the lower time resolution, one should consider the forecast accuracy to be lower. Still if ECMWF and CMC agree, it may mean a useful forecast.

Available for all sponsored clear sky charts.

2022 November 20: cleaning up unused charts

Each clear sky chart costs me money in server storage and excecution time. So I reserve the right to remove unused charts. I've recently removed charts who's web pages were not downloaded in the last 90 days. (For observatories, I removed chart pages only if the pages were not used in two separate 90-day intervals).

If you're missing your favorite chart page, email me. I can restore them quickly. No need to restate the latitude/longitude or other details. Just send me the url of chart you'd like restored.

Oh, and sponsored charts are never removed even if they are unused.

2022 June 8: Text alerts

A few weeks ago I lost main power for 6.5 days. I was unable to update charts every day. (Hard to buy gas for your generator when 170,000 of your neighbors, and all their local gas stations, also are without power.) It took a significant amount of time to answer all the users' emails complaining about "no update". Next time I need to rapidly tell all chart users about an update problem, a text alert will appear at the the top of chart pages. I'll warn users of whatever might be slowing chart updates (servers down, power outage, flood, zombie apocalypse, meteor strike, vacuum catastrophe ... okay maybe not the last one).

In the meantime I'm working on a better recovery plan for the next power outage.

2021 December 1: More Hourly Forecast Data

CMC forecast data more than 48 hours into the future used to be for 3-hour blocks. It's now hourly, except for seeing.

But one should still consider that forecasts more than 48 hours into the future are less accurate.

2020 October 31: Possible Aurora" warnings

If the NOAA Ovation forecast model predicts aurora for a clear sky chart within the next 1 to 1.5 hours, a text message, highlighted in green, appears below the chart image on appropriate clear sky chart pages.

But I'm guessing that if the southern-most extent of the aurora oval is futher south (and still east of) a clear sky chart location, there is a chance the aurora oval will stay that far south when the earth eventually rotates enough to put the chart location under the aurora oval. In those cases, I now display a note, highlighted in yellow, to warn for a possible aurora later tonight. This note can appear many hours before the actual aurora and sometimes the previous afternoon. I'm hoping this will give aurora watchers extra time to plan their trips.

2021 September 26: Updated Light Pollution map

David Lorenz has re-issed his Light Pollution Atlas with satellite data from 2020. The previous lightpollution map was based on 2016 data. The meaning of the colors is unchanged. But some charts have different light pollution ratings as a result.

2021 May 5: Small format change to chart pages

I've moved the "other charts" box from the right of the page to the left of the page. That results in a small reduction in the overall width of the page and slightly less furious thumb-panning for people using narrow screens.

2021 April 18: New colors on Light Pollution map

David Lorenz has re-issed his Light Pollution Atlas 2016 . I use his maps for the light pollution maps on clear sky charts.

David has changed the colors to make them more distinguishable. But he has not changed the quantity of light pollution (Bortle Class, magnitudes per square arcsecond etc) of each color band. If you like to use names of colors to describe your observing site, you'll probably keep using the same names. Ex: a site which was "light green in the light pollution map", is still light green. But David is now using a different shade of light green.

Personally, I can't rememeber bortle numbers or magnitudes per square arcsecond. I describe light pllution ratings with the names of David's colors. So if you hear me say "Take me to a black site!", that's actually a good thing.

2020 November 11:Cleaning up unused charts

I've been removing charts that my usage logs say have not been used in at least 2 months. I've kept the definitions, so I can quickly restore a removed chart. If you are using a chart that I removed, email me and I will restore it. If you were not the person who originally requested the chart, but were using it because it was nearby your location, feel free to ask me for a new chart for your actual location.

2020 October 5: Past Clear sky charts

I sometimes get asked for yesterday's clear sky chart, or one from last week. I used to reply that I don't keep past clear sky charts because I could not afford host the very large amount of data they'd require (or double my upload bandwith). But I going to try it anyway. To keep my webhosters from kicking me out, for now I will archive only past chart images and only for sponsored charts. I figure I can keep a couple of week's worth.

I'd appreciate users telling me how useful they find being able to retrieve past clear chart images.

They are linked from the "Nifty Links" section of sponsored clear sky chart page. The link is called "Past Charts". So far, I only have a few days of charts archived.

2020 September 18: Smoke forecasts

I've added environment Canada's smoke forecast to the clear sky charts. Their page is I'm using their "total in the atmosphere overhead" maps for the charts to estimate affect on transparency. (A ground level forecast should be used for health concerns.)

The smoke forecast predicts for only 48 hours. So it always looks shorter than the other (up to 84hrs) lines on the chart.

I find the colors on the smoke maps quite confusing. They use white to mean "no smoke" and blue to mean "rather a lot of smoke". But the cloud and transparency lines on the chart use white to mean "overcast" and blue to mean "clear sky". In an attempt to keep the clear sky chart a way to "tell if I can observe at a glance", I am showing a different set of colors on the chart for the smoke forecast than used on the map. I'm using blue-ish to mean no or low smoke, brown to mean lots of smoke and red to mean "stay indoors". So like before, lots of blue squares means you can observe.

I'm using such vague and qualitative terms because I haven't yet integrated the units of the smoke forecast (which is the total mass of 2.5micron particles in a column of air 1 meter square) with transparency.

As a final note, adding this forecast has broken one web feature of the charts which i'm still fixing. Please let me know if you notice. (I'm guessing it's no longer used.)

2020 September 11: More forecasts

CMC is now forecasting 84 hours into the future. Formerly it forecast only 48 hours into the future. From 3 to 48 hours, there is forecast data every hour (except for seeing). From 51 to 48 hours into the future, there is data every three hours.

There is currently no information as to how accurate the forecasts are for hours over 48. CMC belives their long range forecast is very good compared to other models. However, one should still assume the astronomy forecasts are most accurate for the first 12 hours.

I'm migrating the clear sky charts to use the new data from 51 hours to 84 hours. It will take a few days. Expect not all charts to show the new data, and a few bugs until then.

2020 June 16: Those annoying video ads

They were an experiment to see if I could supplement lagging sponsorships. (They never appeared on sponsored charts.) But they were very annoying. The powers that be assured me that they would eventually become targeted and cease advertising toothpase and shampoo.

I'm removing them. Apologies to all chart users who were annoyed.

2020 feb 21: chart icons on OSM now working on Android

The map versions of charts-in-state, and the map version of charts-within-x-miles now work on android. I'd appreciate if iOS users would let me know how the work on Apple devices.

For desktop users, mouse-ing over a marker reveals the name of the chart. It's a quicker way of finding the chart you want rather than having to click each marker.

2020 Feb 12 chart icons on OSM not working on iPhones/Safari

When you click on a icon on a page like, a little window should popup showing the chart's name, a small version of the chart image, and a link to the full chart page. This works on desktop Safari but, according to a report, not on mobile Safari.

Regrettably, I don't have an iPhone to test with. So if there are any savvy iPhone users who can send me error logs or have a clue as to why OpenLayers2 might not work on iPhone Safari, i'd appreciate any help.

2020 Feb 10: moving from Google Maps to OSM maps

Google has begun to invoice me whenever anyone looks at a map with chart locations marked. Sponsorships have declined so I am moving to using the free maps from Open Street Maps.

There may be bugs during the transition. Please email me with bug reports.

2020 Jan 23: forecast data is back

CMC is back online and I am updating the clear sky charts. The ECMWF cloud forecast data will stay on some charts for a few days.

2020 Jan 22: Missing forecast data

The Canadian Meterological Center is the source of the data that I use for the cloud cover, transparency and seeing lines on the clear sky charts. Last night, they replaced a supercomputer and they're having trouble with it. As a result, the astronomy forecasts 19 hours overdue as of 6pm EDT today. I'm not sure when they will resume publishing.

You can see "No data from CMC" warnings appearing on most clear sky charts. To mitigate the fact that I have no new astronomy-forecast data at all, i have added the ECMWF (aka 'the european model') cloud forecast to the busiest charts. It makes the charts look ugly because the ECMWF forecast predicts much further into the future. But the ECMWF forecast is usable. That's the best I can do on short notice until CMC resumes operations.

2020 Jan 15: Automatic search for nearby charts

On the search section of the charts home page, click on "search nearby" to show a list charts close to the geographic position that your browser thinks is your location. Much less tedious than typing latitudes and longitudes. It's more accurate on mobile devices with enabled GPS but still works on desktop browsers. You can decline to allow your browser to use your geographic location, if you like.

2019 Dec 10: Sun & Moon Data

I had removed the "Sun & Moon Data" page from the "Nifty Links" section of clear sky charts. It used to display rise and set times for the sun and moon and show a picture of the moon phase.

I removed it because I was pulling data from servers at the United States Naval Observatory (USNO). But most of USNO's website went dead. It now looks like they wont be back until April 2020. (A renovation of some sort.)

So I have re-implemented the Sun & Moon Data page. I'm no longer using USNO's data. The calculations do not depend on external servers, so it should never again hang halfway thru loading the page.

This method of calculation (javascript running in the user's browser) allows a sufficiently motivated hacker to find the exact latitude/longitude of charts that have "location privacy". So I have suppressed the calculation for charts with location-privacy. However, it will be possible for users to enter their own latitude and longitude in that case.

2019 May 10: Forecast back to normal.

CMC seems to be publishing their astronomy-weather forecast data at the normal times now.

2019 May 7: Forecast Delays

The Canadian Meteorological Centre (CMC) is having technical problems with their supercomputers. That has significantly delayed all of their forecast products, including the one I use to make the clear sky charts. The astronomy-forecast date is still being published, but appears between 5 and 13 hours later than it should.

I'm not sure how long these delays will continue, But CMC is working hard on the problem.

Meanwhile, the ECMWF Cloud forecast on sponsored charts is unaffected.

2019 April 12: paypal nastyness?

One of my sponsor's paypals went missing. It appears he sent to "Atilla Danko" at email address danko at potbox dot com. But that's not my email address. My email address is (no "t"). Also I spell my first name with two Ts: Attilla Danko.

It's possible that danko at potbox dot com is a real person. However, considering how rare the name "attilla danko" is, it possible something nasty is going on.

I acknowlege all sponsorships in email, usually on the same day. So if you have sponsored and haven't heard from me, please check the email address to which you sent paypal, and reverse the transaction if you think it went to the wrong person.

Many thanks to all my sponsors, who's support makes the clear sky charts possible.

2019 January 27: Addition cloud forecast plus cloud-forecast accuracy stats

For comparison to the CMC cloud forecasts, I have added a cloud forcast from the ECMWF ("european model") because it has a reputation (or PR) for being an accurate forecast.

To evaluate the "accurate forecast" rumours, I have been comparing both ECMWF and CMC cloud forecasts to Environment Canada's weather observations for 175 places in Canada and METARs for about 663 airports in both the USA and Canada. Differences appear to be real. I've listed accuracy measurements in the text portion of clear sky chart pages. I have only one month's worth of observation data so far. So the accuracy numbers may change. Also since i've averages over entire countries, local accuracy is likely to be different.

Because of limitations set by the Norwegian Meterologcal Office, from whom I get the ECMWF cloud data, I'm only displaying the ECMWF cloud forecast on sponsored chart pages for now.

2018 September 22: Reduced updates for a few days

Where I live, a few hundred thousand people are without power -- including me. I will probably only be able to update charts once a day. I will be giving preference to the afternoon updates. In the event that I cannot update all charts, I will give preference to sponsored charts. Local power utilities say the situation may last a few days.

2018 September 4. Tool tips not working in IE 11

The tool tips that explain the meaning of the colors when you hover your mouse over a colored block in a clear sky chart image do not appear if you are using Internet Explorer v11 on Windows 7.

This is a documented bug in IE 11. Earlier versions of Internet Explorer do not have this bug, but I've read that Microsoft will not let you downgrade IE11 to earlier versions.

Microsoft's solution to the bug is for users to run windows update. But they do not specify which update (out of bazillions, including the ones that force you to upgrade to windows 10) fixes the bug.

If you are unwilling to accept every Microsoft update, there is a workaround: In IE11 turn on the menu bar, then under "view" select 100% zoom. Any zoom factor other than 100% will prevent the appearance of tool tips on any website, not just clear sky charts.

Firefox, Opera and Chrome do not have this problem.

2018 August 2. Popup window gone

The popup data window on the clear sky chart webpage, the one that displays an explanation of a colored block, is getting increasing difficult to maintain. It seems that no one (not even the guys who write the html standard) like popups.

So i've removed the popup window.

Now, if you hold your mouse over a colored bar, words explaining the color will appear in a tool tip -- after a second. This now also works for the "darkness" bar. The limiting magnitude, sun altitude and moon altitude will appear as a tooltip.

Coincidentally, this change has also sped up the loading time for clear sky chart pages.

2017 October 21. Aurora Alerts

The NOAA has a nice map. For clear sky charts in green region of that map, i'm displaying a small text alert under the chart image on my web pages. Even though I can only update the chart forecasts twice a day, the aurora alerts on chart pages may update as often as every 15 minutes.

2017 October 17. Smoke Warnings

I had a warning to check's smoke and forest fire map on *every* clear sky chart page. Tedious.

I'm now displaying a warning on only those clear sky chart pages whoose location is close to fire or smoke on ospo's page.

I update the warning links much more often that I update the clear sky chart forecasts. Also, the warnings are only on the chart's web page. You will not see the warnings if you use an app.

2017 August 20. Back to regular forecasts

The regular forecast maps linked by each clear sky chart now forecast far enough to forecast for the eclipse. They are now more likely to be accurate than the long-range forecast map I posted yesterday. So I have removed the long-range map.

Long range cloud forecast for 2017 Eclipse

Allan Rahill has manually run the cloud model which normally feeds the clear sky chart for eclipse day. It's on the clear sky chart homepage. The reliablity of this map is lower than the maps displayed on the clear sky charts because it forecasts farther into the future. (No forecast model does well with clouds more than 44hours into the future.) For planning your eclipse trip, use all available forecasts and especially check realtime statellite images.

2017, August 15, Server Certificate problems

If you find that links to the clear sky charts nolonger work because of security certificate problems, the temporary work-around is to remove the "www." from the url.

so for example, if dosnt work, use instead:

I'm working on a permanent fix

2017, August 10: Eclipse track

I'm displaying the path of totality on all google maps on Though you might need to zoom out to see it sometimes.

The all charts map, which shows all 5300+ clear sky charts, is very slow. Can take a few minutes on mobile devices and is about a megabyte download. The map displays first, after a while the eclipse track appears. Somewhat later markers showing positions of clear sky charts appear. Tedious.

2017, June 27: Bug in eclipse times

The local time of eclipse in the "nifty links" section of chart pages was wrong. They will all be fixed by June 28 noon. So if you have written down eclipse times from the "nifty links", pease look them up again.

The times on the "details" page from USNO were always correct.

2017, June 19: Current Forecast and Weather History For 2017 Eclipse

I've listed the current forecast thumnail image, and weather history for late August, for all clear sky charts in one, extremely wide, web page. It's sorted by latitude from west to east. To plan an observing spot, you can scroll down the list looking for sites with the best weather stats. Close to eclipse day, you can scroll down the list looking for the best current forecast.

The page is here.

My disclaimer from May 7 below still applies. On eclipse day, I suggest checking realtime satellite images of clouds a few hours before the eclipse.

2017, May 7: Climate/History pages for all charts.

It took 265 hours of compute time, but I've finished making climate/history pages for all clear sky charts as of May 5th. Look for the "climate/history" link in the "nifty links" section of your chart's web page. I've done this to help people choose a site for the 2017 solar eclipse.

Previously i've only generated these pages for sponsored charts because of the very long time it takes to compute them. I will probably have time to keep the climate/history pages of only sponsored charts updated. But the current snapshot should have enough data points to give a good indication of the cloud cover and transparency we can expect for the eclipse for any currently existing chart site.

DISCLAIMER: The climate history pages are based from past forecast records, not from sky observations. So it's possible that the climate/history pages are not an accurate indication of weather for the eclipse. If you miss seeing the eclipse because you took a climate/history page for a clear sky chart too literally, your only recourse is to complain to me in email. Reminder: by using this website you agree to not sue me for any reason.

Experienced eclipse chaser tell me they check *all* available weather forecasts 48,24,12 and 6 hours before the eclipse and stay prepared to drive to an an observing location on short notice.

2015, Sept 3: Please edit your links.

Please consider changing your links and bookmarks from

The extra "www." will speed up your browser a little bit and will unload my servers a little bit.

2015, May 10: Daytime Seeing Forecasts

I'm now showing daytime seeing blocks on the clear sky charts. CMC is publishing them but is a hesitant about wanting us to them. That's because they don't model daytime convective heating well. (It's a chaotic physical process. No forecast can model can predict daytime convective heating well.) So consider the seeing forecast for daytime hours to be less accurate than for the night -- particularly for the afternoon.

2014, Mar 3: New iPad app uses Clear Sky Charts

Emerald Bay Sofware has written the iPad app, Star Log, for tracking and analysing astronomical observations. It integrates weather data taken from the Clear Sky Charts. Emerald Bay Sofware is using data from my clear sky charts with my permission (and small help). They are nice people. A small portion of their revenue from the Star Log app comes back to support the clear sky chart website.

2013, Oct 2: New Lightpollution maps.

David Lorenz, University of Winsconsin-Madison, has recalculated the lightpollution maps originaly created by Falci, Cinzano et al on the The World Atlas of the Artificial Night Sky Brightness.i David's version is called the Light Pollution Atlas 2006.

David recalculated with satellite data from 2006. David has also increased the number of color bands. Each color band is now 1.73 times the light pollution of the previous band. (The factor used to be 3.) David maps also have a larger coverage area.

I am now using David's maps for all the lightpollution maps linked to clear sky charts. The light pollution ratings of charts is now more accurate. Now all clear sky charts, even the ones near the arctic, have lightpollution maps.

Big thanks to David.

2013, Oct 1: iCSC app no longer works

People have been writing me to say that the iCSC app no longer works when they upgrade their Apple device to iOS7.

I did not write that app. It was written by Darryl of (with my permission).

A while ago Darryl wrote me to say that he was removing the app frome the app store. But you should send your questions directly to him.

If you are an app writer and would like to replace iCSC, please write me (attilla danko).

In the meantime you can create your own mini non-app by creating shortcuts for your favorite clear sky chart pages and placing them into a folder.

2013, May 23

Apparantly, the "donate" buttons on the sponsors page havent been working for some time. I humbly ask those of you who gave up in frustration trying to use the donate buttons to please try again.

I've changed the code of the donate buttons to conform to PayPal's lastest interface.

If you're a potential sponsor (great people, btw) who dislikes PayPal, please email me for a snail mail address.

2012, Aug 15

Both my primary and backup CSC generating computers have failed. I'm trying update clear sky charts from a cofffee shop 800km away with a laptop. I will update all sponsored charts, but I may not be able to update all charts untill I drive the 800km back to my faulty computers. But I hope to restore full service by friday morning. Sorry about the distruption.

2010, Mar 4: Server 3

I've brought a third server online to share the load, so CSCs should loading as a reasonable speed now. (Thanks to sponsors helping with costs.)

However I'm still denying search engines that appear to be ignoring my robots.txt file. So keep using Google.

2010, Feb 21: Slow Servers, or no access

If clear sky charts have been loading very slowly, or you can't reach them at all, please note:

My web servers are very slow. It appears to be because of heavy use. The problem appears to be certain search engines, like Yahoo, who are ignoreing my robots.txt file. (A file I write that tells search engines how to moderate their searches on my site.)

One of my web hosters has cancelled my account because of heavy use. To prevent my remaining web hosters from cancelling, and leaving me with no web site at all, I've had to do something drastic.

I have denied the yahoo search engine access to I've also denied accesses to several other ip addresses that appeared to clandesine search engines.


In the meantime, I'm buying more webhosting space to spread out the load.

Good thing it's cloudy now.

2009, Dec 31. "No Data" problem

All CSCs have been showing "No Data From CMC". It's wasn't CMC's fault. Problem is now fixed and I'm uploading fixed CSCs.

Just in case you might want to know why:

In 2001 when, I first wrote code to parse forecast data from CMC, I figured I should check for corrupt dates. Clearly anything after 2009-12-31 was a corrupt and ridiculous date.

I had made a teeny weeny little assumption --- that there was no possible way I'd still be doing this for 10 years. I figured, "in 10 years, someone, somewhere will be doing a much better forecast, which will replace the CSCs -- and I'll use it."

Seems I wrote my own Y2.01K bug, and then promptly forgot about it.

But really, we're overdue for a better forecast. And while we're at it, where the heck is my flying car?

2009, Aug 11. Email problems

I'm having email problems. if you've send me an email between 2009-08-10 18:00 and 2008-08-11 02:40, and havent gotten a reply from me by now, please re-send.

2008, Oct 17. Sever problems

I'm having server problems. It's causing many clear sky chart images to not display.

I have two load-sharing servers. One of my two webhosters moved my site to a new datacenter, breaking that copy of my site in the process. (Their motivation was to improve reliablity. ahem. ) So half the time, CSC users were looking at broken webpages.

I've switched the traffic over to the one working server, so CSCs should be displaying again.'

However, it might take me a couple of days to fix the root cause of the problem. During that time, if you can't see a CSC image, try using the url (instead of But don't book mark it. I reserve the right to stop supporting server2.

Time to shop for a new webhoster.

2008, Feb 29. Name Change

Due to potential trademark infringement litigation on the part of Skyclock Company of Michigan, who owns the USA registered trademark "SKYCLOCK," and unsuccessful attempts to resolve the situation, my lawyer has advised me to change the name "clear sky clock" to something else. It is my attorney's position that I am not infringing Skyclock's trademark, but he advises me that changing the name is the least expensive and least painful solution. (Which is *not* to say that it isn't painful.) (The long version of the story is here.)

In a moment of complete-lack-of-imagination, i've decide to call them "clear sky charts" instead.

Annoying. But this is the reality:

It's altered a lot of code to change the name. So it's possible I introduced a few bugs. Please email me if you find a bug. (Though my email response may be slow for a few days.)

Note: As you read the rest of this file, please replace any occurence of the word "clock" with "chart".
(I'd do it myself, but I hate re-writing history.)

2008, Jan 20. You may see a few bugs

I was thinking of using the title "possible service interruptions". But I don't wear suits. soo..

I'm re-writing a noticeable amount of infrastructure. So if you see some of my web pages garbled, or unreachable; or if some of the click or mouse-over features dont work: please wait 15 minutes and try again. If it's still hosed (that's the technical term), then please email me.

Aug 3, Transparency Forecast is back

Allan Rahill and his colleagues are CMC have been working hard to correct the problems that shutdown the transparency forecast for over a week. Not only is the forecast back, but Allan has also fixed the bug which sometimes caused a transparency forecast of all white, "too cloudy to forecast", while the cloud forecast was "clear".

Aug 1, email problems

Please note: I respond to all emails, if only briefly. If you have trouble reaching me at, please retry to, and let me know you had a problem with

July 25, Continuing forecast problems

CMC now says it will be next week before they can restore the transparency forecast. :(

July 23, forecast problems 3.

Expect the transparency forecast to either show "No data from CMC" or be completely absent for the next day or so as CMC works on restoring the transparency forecast.

July 21, forecast problems 2.

I've manged to get a one-shot download of good transparency data. I'm updating the CSCs with it. However, I wont get more data until sometime on Monday. So on Sunday, the CSCs will read "No Data From CMC" on the transparency line. Untill I get fresh data early next week, clicking on a transparency block on a CSC will at take you to an incorrect transparency map: it will be all white. I'm hopeful all will be restored to normal early next week.

July 19, Forecast problems

The transparency forecast fror this afternoon was corrupted. The problem originated at CMC. I've temporarily removed the transparency row from he CSCs so that no one will be confused by an incorrect forecast. I expect the problem is temporary. I will restore the tranparency row on the CSCs as soon as the data from CMC starts looking good again.

Legal Issues Clearing

I am still awed by the volume of support, advice and commiseration i've received over the last few days.

I'm still working though a large email backlog. But I will reply --eventually-- to everyone who has emailed me.

However many of you have been asking for details of my legal problems. Sorry about being vague earlier. I didnt want to say anything until I had found legal advice and figured out what to say to the complainant.

So this is what happened so far:

On June 28, I recevied an email from Skyclock company. I understood the email to mean legal action against me over the use of the word "skyclock" for which Skyclock company has a trademark registered in the USA. I have zero experience with trademarks or legal conflicts so it took me over a week to calm down enough to find legal advice. In the midst of all this angst, I received a second email from another individual at Skyclock company.

This email was polite, considerate and reasonable. Since then I've spoken with a Mr Rob Baxtresser of Skyclock company and find him to be a consderate and reasonable person. Since this was a sharp contrast to my first impressions of Skyclock company and since many of you were incensed at the thought of harm being done the CSCs, I thought CSC users should see Rob's words.

Reprinted with the permission of Rob Baxtresser.

So it would appear that Skyclock company an the CSCs will not be in conflict. (Now I can start regrowing my stomach-lining.) Even better, it looks like conflict will be replaced with cooperation.

I'll still have to add "legal bills" to the list of things that sponsorship help pay for. But my legal bills look like they will be finite and will mostly go towards perparing for the future.

Again I wish to thank everyone for their considerable and kind support. And I'm very glad to say that i'm still generating the CSCs.

July 10: Legal Issues Calming down

Relax: I'm not expecting any interruption in the updating of CSCs.

After a huge amount of stress, I can now say that it looks like I will not be sued by an USA trademark holder for trademark infringment. I will post details soon.

But for now I'd like to express my thanks and awe at the enormous support from CSC users. You guys are great. I have a very large number of people to thank. I will also reply to every email I've received, however I have a big backlog. Please forgive me for not following up in all newsgroups.

Special thanks to Norman Van Treeck.

July 5: CSC threatened

I wouldn't have thought that a weather forecast for amateur astronomers would attact opposition from anyone, never mind a company claiming to promote the understanding of science.

However, I've been threatened with legal action by a company in the USA over trademark infringement. Personally, I can't even figure out whether USA or Canadian law applies, or whether I need zero, one or two (one for each country) lawyers.

Legal fees are something I've never faced before in operating this site. It seems I must soon add "legal fees" to the list of things that sponsorships help pay for. So now is a time when sponsorships are particularly welcome.

Further reports, and possibly louder cries for help, as events develop. As always, I will continue to do my utmost to keep the CSCs updated.

June 13: the CSCs has not been "suspended"

Some users are getting "account suspended" error message, error 404 errors, or are being routed to weird websites unrelated to CSCs.

The CSC website is no danger. It's just a server problem, though it's an annoying one.

I buy hosting from two different webserver companaies. Someone is sustaning a denial-of-service attack on one of my webhoster servers, though not specifically on the CSCs website. That webhoster is responding by changing their ip addressess -- without telling clients like me. That explains why only some CSC users are having problems. It also explains why some CSC users are being routed to the wrong website.

I have manually switched all CSC traffic to the other sane server.

However, the problems may recurr for a few days as I experiment to fix the bad server. So if you continue have problems with the CSCs, try the url (But dont edit web page links to point to that url, since it is temporary). If you find doesnt work either, dont hestiate to email me.

May 15: Upload improvements and seeing database news

Over the last few weeks, the afternoon CSC updates were taking until about 18:00UT (4pm EDT) to complete. I've optimized the generation and upload of CSCs somewhat: sponsored CSCs are now being updated by about 16:30UT (12:30pm EDT) and the rest by 16:00UT (2pm EDT).

The analysis of new observations is on hold untill some database problems get fixed. You are still welcome to enter observations, but they wont be listed on maps untill the database problems are solved.

Mar 11: Daylight Saving Time

The USA and Canada are now on Daylight Saving Time. DST came a few weeks early this year. So I have switched all CSCs in the USA, Canada and the Bahamas, which are set to use DST in the summer, to DST.

CSCs in Saskatechewan and Arizona, and other places that never use DST are not affected.

CSCs in Mexico do use DST, but they start DST in April.

To check that a CSC is properly set up, look at upper left of a CSC image under the words "Local Time". You should see something like "GMT -4.0" for the eastern timezone with DST, "GMT -5.0" for Central, etc. Email me if you see an CSCs with the wrong GMT offset.

Feb 4: Climate / CSC History

The climate pages (aka CSC history pages), a feature of sponsored CSCs, have been damaged. I am regenerating them now. However the process is very compute-intensive and will take a day to complete.

Jan 7: Fahrenheit

It seems like a lot of USA CSC users were having trouble reading the temperature scales in Celsius. So I'm now displaying temperature legends on USA CSCs in degress F. If you look at a full temperature map from a USA CSC, the legend there will also be in degrees F. Canadian, Mexico and Carribean CSCs are unaffected, as are full temperature maps if you click to them from a non-USA map.

2007, Jan 4: yet another feep

On a CSC's legend page, it's just too hard to scoll up and down to try to read both the CSC image and the bars that define the meanings of the colored blocks.

Now you can make a color-legend appear just below the CSC image by clicking under "image control" (just to the left of the CSC image) on the check box labeled "Display color legend".

Dec 29: Server changes

Once upon a time, all the CSCs vanished because an overworked admin hit 'delete' at the wrong time. Since them i've been using two web servers from different webhosting companies. I'm also pretty picky about who I get hosting from. (I've fired hosters at least four times in the last few years.) I'm about to do it again. But the visible change to CSC users should be slight:

Sep 7

Astronmical Twilight times The USNO astronomcial twilight time webpages (linked off of the "Sun & Moon Data" pages of CSCs) were messed up. (That's the technical term.) They were displaying bogus times.

The problem is now fixed.

Aug 27: Some update bandwith restored

I've aquired a second upload link so the danger of possibly not being able to update the CSCs should be past. They should also update a bit more quickly. Special thanks to sponsors for helping with the extra costs.

Aug 21: Warning: Possible major outage.

There is a possibility that I will temporarily loose the ability to update the CSCs. (Ahhhh!) If it happens, the symptoms will be some or all of the CSCs will not be updated with a new forecast. My reponse to email will also likely be slow. I am working on getting a more robust infrastructure. but it will take time (and money). This urgent part of the situation should be resolved by August 28th. I will hold requests for new CSCs until then.

July 31: Slow updates

I've lost half of my upload bandwith. One of my DSL providers seem to have met a black hole. Luckily one remaining DSL link is still working. (This is why I duplicate everything, including the companies i get DSL from.) But I'll have to sign with a new provider to get my bandwith back. In the meantime, CSCs will take about 2 hours to update. As always, I'll be uploading the sponsored CSCs, and popular CSCs first to minimize the number of users affected.

July 25: Now works with Netscape

For those of you who were wondering why i'd annouce blank web pages as a google map plotting CSCs: Try them again. The per-state and per-province map pages were not working with Netscape, until now. If you still cant see a map (example) email me with your browser version.

July 24: CSCs on google maps

For those of you who've been using the coverage map to locate CSCs, and been annoyed because it can't zoom, now have a slightly better alternative.

I'm now plotting CSCs on zoomable an panable Google maps. There is one map per state or province. The maps for California and Ontario take about minute to display the map. Also, there is no single Google map that plots at 2800+ CSCs. That's because Google's api doesnt scale well. Such a page would take 10 minutes to draw the map.

To see CSCs plotted on a google map, goto any list of CSCs in a state or province, and click on the "Map (may be slow)" link.

June 12: More Sun & Moon Data

From the "sun & moon data" page for each CSC, i've added links to UNSO's year-long tables for the rise and send times fo the sun and moon, plus astronomical twilight. No need to tediously type in your latitude and longitude into USNO's forms. People planning observing more than two days in advance may find these useful for picking times.

May 5: Lightpollution corrections

The magnitudes-per-square-arcecond numbers in the legnd of the light pollution maps were mis-calculated. There were about 2 to 3 mags too bright. I am now reloading all the CSC lighpollution pages with the new numbers. They should now conform much better to what people are measuring with their SQMs.

Unfortuneately this does not mean that anybody's sky has gotten darker.

Thanks to Jack Liebenthal for pointing out the error.

Apr 20: Indiana Time Changes

Indiana changed over to using Daylight Saving Time on April 2. But I just found out about it now. So for the last two weeks all Indiana CSCs were out by an hour. Geeze, doenst anybody out there complain? :)

I've converted all Indiana CSCs to DST. However, some counties have also changed from the eastern timezone to the central timezone. I may not have found all the affected CSCs. So please let me know if you see a CSC with the wrong GMT offset. (It's written in small print in the CSC image under "Local Time".)

Mar 11: Forecast coverage restored

Thanks to the a quick action by Allan Rahill, the image production guys at CMC have restored coverage to south Texas and norther Mexico. All CSCs are now getting data again. Whew.

Mar 9.5 Still no coverage for south Texas

I'm still not getting data from CMC for south Texas and parts of northern Mexico. To prevent people from being misled, I've removed the forecast lines from the CSCs that were getting no data. So instead of showing all white, the affected CSCs will show only a darkness forecast line. I figure no forecast is better than an incorrect forecast of perpetual clouds.

No word yet if I can get coverage restored.

Mar 9: Coverage problem

We've lost coverage for a big chunk of south Texas. All forecasts are affected. The symptoms are that the CSCs will read all white. I'm trying to get CMC to notice the problem. I know nothing yet about possible solutions.

Nov 18: Update bandwidth restored

I've installed a new dual-wan router so CSCs should now be updated at their normal rate. Thanks very much to all CSCs sponsors for making that possible.

Nov 3: Conversion to new forecasts

I've just changed the CSCs to take data from a new series of astronomy-forecasts maps at CMC. These new maps are exactly the same numerical-forecast model from CMC that new know and love. However, there are a few changes to the CSCs as a consequence:

These new astronomy-forecasts at CMC are now officially one of their products. Check out their website.

2005 Nov 3: update problems

My router has failed. I'm now using a backup. That means i've also lost half my bandwidth for updating CSCs. I will still update CSCs, but the updates may be late. As always, I'll be updating sponsored CSCs first. So if your CSC is not updated on time, look for nearby sponsored CSC, it may be close enough for the forecast to be usable.

2005 June 19: new server

<rant> One of my webhosters thinks that the Cahsville CSC image, CshvllVA.gif, is a threat to their security so they are no longer allowing me to host it. I think that they have mod_security of their Apache server mis-configured.

In difference of opinion like this, the webhoster always wins. My only recourse is to buy webhosting space from another webhoster and move. I have done so.

</rant> If you use the official url to reach the CSCs,, you should see no change, other than the CSCs loading a bit faster. However there may be a few people using unoffical urls or IP addresses. If so, you should know that or it's ip address can no longer be used to reach the CSCs.

2005 June 16: It's officical.

Allan Rahill astronomy forecasts, the ones that provide data for all CSCs, are now an official product of Environment Canada. Special thanks go to the thousands of people who have emailed us so we could show Allan's bosses that his forecasts are important and are being used. They were a factor in the Canadian Meterologcal Centre deciding to make Allan's forecasts official.

The offical Environment Canada astronomy weather page is

It will take me a some time to convert the CSCs to use data from the new images. In the meantime, I will continue to generate the CSCs from the old stream of data.

2005 May 10: Server proboems

Over the last week i've had severe problems with the comptuers I use to generate the CSCs. Many CSCs were not updated or were updated a day late. However, all CSCs are now current.

Looks like I have a lot of work to do upgrading my computers.

The server outages and resulting email backlog means that there are a number or requests for new CSCs that I have not yet read. I'll start creating new CSCs as soon as I can.

Sorry about the mess.

2005 Apr 25: new CSC

I usually I respond to requests for new CSCs in a day or so. However the next time I'll be adding CSCs is May 13.

2005 Feb 3: Email problems

I make it a point to reply to all email. If you've sent me an email recently, and if I haven't replied in a few days, it's probably because I lost your email (spam filter problems). Please resend.

2004 Nov 20: Temperature and Humdity forecasts

I'm now displaying Allan Rahill's temperature and humidity forecasts on all CSCs. These forecasts are generated by the same high-accuracy model that generates the cloud, transparency and seeing forecasts.

To keep the new forecasts from cluttering the CSC images, I've made some format changes. I've also changed the legend pages a bit. So email me if you find broken links, bad splleing, or non-functional features.

I've also made changes to the machine-readable ascii CSC files. If you use them, email me for details.

I'd like to thank sponsors for helping me provide the extra computing power and hosting space needed to handle the new forecasts.

2004 Nov 12: Obsolete URLs

[..gritting teeth...surpessing diatribe on how webhosters are a pain in the neck...]
If by some weird chance you've been using

  •, or

    to access CSCs, please note that none of those urls work properly anymore.

    Please use the offical url: only, especially as I seems that I have to keep changing web servers. But I'll always keep pointing at the right server.

    2004 Nov 9: New Forecast

    Allan, at CMC, has added a wind forecast. I've just integrated it into the CSCs and will be regenerating the CSCs with the new forecast in a few hours. If you find some CSC feature not working as a result of the wind forecast, send me and email.

    In keeping with the notion that blue blocks are good, Allan has labeled calmer conditions with blue.

    2004 Oct 23: Server change

    I've retired one of my webhosters. It was identified as "server2" on the urls and server status page. Since I still have two other webhosters that are sharing the load for the domain, noone should notice the difference.

    However, it's just barely possible that the change to my name servers has not propagated througout the internet yet. So, if you get error 404 when you try to load any page from, try quiting and re-entering your browser. Also, if you have any direct links to the old server, like, replace them with

    2004 July 28: Transparency forecast change

    Thanks to many people who asked for better separation in the colors of the transparency maps, Allan Rahill has added a fifth color. The CSCs are now updated to display them.

    2004 July 6: Forecast History Tweak

    Not happy with my simplsitic "good/bad" summary of forecast conditions, I've replaced the summaries with the occurence of the combinations of forecasts (which I hope observers will agree) corresponding to planetary observing conditions, deep sky observing conditions, and conditions good enough for CCD imaging. Here is an example.

    The history pages just summarize past forecasts, but they sure make me wonder if there are better places to observe than where I am. To aid people, like me, who are looking for climate data for other CSCs, I've changed the coverage map to subtly indicate which CSCs have a forecast history page.

    2004 June 25: Forecast History

    I'm often asked if I have historical data of transparency, cloud cover or seeing -- in otherwords: climate data. The answer is always no: all my data is a forecast and shouldnt be confused with weather observations. However, many people, including me, are tempted to read a summary of past forecasts as an indication of climate data. Not very scientific, but fun.

    In the interests of fun, I've added a CSC history page to selected CSCs. For example.

    2004 June 12: Obsolete URLs

    Inspired by the email flood I get whenever the CSCs site goes down, I'm now serving CSCs out of two servers. Each is from a different webhosting company for the unltimate is robustness against administration errors (the cause of the last 3 major outages that occured on new-moon fridays). Most people fear disk crashes. I fear underpaid data-entry clerks hitting "delete".

    The url switches automatically to point to both servers, or just the working one, if the other fails. It's clever, but the switchover takes about an hour.

    To give people the choice, I used to publish direct urls to each server directly. One was

    Please dont use and any more. Because of obstruse software interactions, none of my PHPs, including the ones for displaying CSC images, will work via those urls.

    This page will always list the currently valid main and alternate urls for getting to the CSCs.

    2004 June 7

    Venus Transit

    This is probably the first time so many peope will use CSCs to forecast transparency for an event right on the horizon. So I'd like to remind people that the CSC colors represent a calculation of the transparency of a *vertical* column of air above the observer.

    To make sure you are reading conditions correctly for the transit, look at the full forecast map for the hour of your observation. Look at the few pixels immediately east of the cross marking your location. If that is clear, you may still be able to observe, even if the CSC is showing white.

    To see the full forecast map, goto the legend page for your CSC (browse or search from here) and click on the colored block for your hour of observation.

    And remember, never look at the sun without proper eye protection. If you don't have have a properly filtered solar telescope, watch the transit on the web.

    Readers unfamillar with the transit of venus might want to start here.

    2004 June 5

    I've fixed the seeing observations database.

    However the alias for the CSCs is gone. Use http:/ instead for the CSCs.

    2004 June 4

    I've done a lot of work to make sure the CSCs cant be taken down by an an administrative error at a webhoster. It' seem they ability to make a mess is still bigger than mine for fix it.

    The seeing observation database browser functions are down because of server config problems. I have no idea when I can get them fixed. In the meantime, it is still possible to enter new seeing observations. (I just cant re-display the them).

    The CSCs, however. Are still working.

    2004 May 13

    I've found a few CSCs setup with the wrong timezone. There is probably no easier way to make a CSC's forecsat innaccurate.

    To make it easier to see timezone errors, I've added the timezone to each CSC image. It's in small print just below the words "Local Time". Please email me if you see any CSC images with the wrong timezone.

    2004 April 12

    Massive move to new server complete

    I hope no one noticed.

    The new server is automatically load sharing with the old one. So no one should have noticed any changes.

    But this means that should one of my webhosting servers fail, (or get messed up by the administrators of a certain webhosting company I'm too polite to describe in more detail), the other hoster will take up the load.

    If that happens, you may see 404 or other weird error messages about half the time. That's because half of all CSC users would being sent to the dead server. But if you keep exiting and re-entering your browser, you will eventually be connected to the good server. After a few hours, I will automatically re-configure my name servers to point only to the good server. (Takes 15 minutes for me to switch, but a few hours to propagate through the internet.) That should cause all the errors to disappear. Some time later, the dead server will come back up and resume load sharing. It should be *very* unlikely that both servers will be down at the same time -- even on a new moon friday!

    People who dont want to reload pages in order to get to the good server when one is dead, may want to access them directly through alternate urls. Server status and alternate urls are posted here.

    2004 April 2

    Moving to a new server on April 6

    Don't panic. My plan is to move to a new webhoster with no interruption the the delivery of CSCs.

    I plan to do the switch over during the early hours of April 6th. Users should continue to use to get to the CSCs.

    Ok, for some that's not enough. Here's some more detail. I've rewritten my CSC generating infrastructure to upload to two mirror sites. The new server is already up and is being updated with CSC forecasts in parallel to the current server. I'm hopeful that the new server will be much more reliable than my current server which is difficult to describe in polite company.

    On April 6, I plan to switch DNS configurations to point to the new server. That means requests for CSCs will automatically be routed to the new server. In the event the new server fails, quit your browser and retry to load a CSC page. Eventually you'll be routed to the old server which will still be running as a backup.

    In the event that the DNS reconfiguration has problems, here are aliases to both servers. But I will be working to make to always point to the best server. So dont make permanent links to these;

    Aliases for New server:

    Aliases for Old server:

    I will fire^H^H^H^Hretire the old server sometime before Septempber, so dont keep permanent links to

    In the event of a total disaster, remember that you can still get the astronomy forecasts, in map form, from Allan Rahill's site:

    2004 March 29

    Some people using two alternate urls that I posted in September:

    Those alternate urls are not working properly. Please use instead:

    In the event of a total disaster, remember that you can still get the astronomy forecasts, in weather map form, from Allan Rahill's astronomy-weather site at CMC: .

    2004 March 25

    I've purchased space from a new, more expensive, and more reliable (I hope) web hoster. I'm working on transferring the site. My current plan is to do the switch with no visible change to any CSC users.

    Now that sounds like "famous last words".

    However, since I'm paranoid, I will post a switch over date here (when I'm ready). I'll also post work-around urls for both old and new servers.

    If you're even more paranoid than I, feel free to ask me to email you to remind you of the switchover a day before it happens.

    2004 March 21

    Webhosting Follies

    All CSCs were down for 24 hours. People who saw the "account cancelled" message should not take it personally. My webhoster was talking about my account with them.

    As I thought, the problem was simply the admin division of my webhoster being confused. They restored my service without explanation. This hasn't been the first time. [....unchartiable remrarks deleted in the interests of maintaining some semblance of decorum ... ]

    Soooooo. I've bought space on a new hoster and am working on transferring the site. I will try to do the transfer without an interuption in CSC service and without changing any urls -- I hope. I'll pick a time which isn't a weekend or a new moon! I'll post plans here when I have them.

    I've also changed registrars and am looking into getting a mirror site.

    I'd like to thank all of the many people who wrote to offer supprt.

    2004 March 9

    I've found a way of getting USNO's sun & moon data without revealing he latitude and longitude of a CSC site. So I've re-enabled the "sun & moon data" link for CSCs with location privacy.

    In other news the WAP or cell phone CSCs I released a few days ago are now obsolete. New model cellphones with WAP 2.0 browsers can display the graphical CSCs. So CSC users with the latest uber-geek equipment can dispense with the clunky WAP CSC and just use the preview (also called "icon CSC") images. However, since most of us still have WAP 1.0 cellphones, I'll be generating the text CSCs for cellphones for a while.

    2004 March 6

    Whenever I goto star parties, I'm frustrated by the lack of internet access. I need to see my CSCs. (No I'm not addicted. I can stop any time I want.... I just dont want.)

    A small step towards getting CSC forecasts to observing sites: the WAP or cell phone version. If you have a web-enabled cell phone (aka WAP capable cell phone) you can now read a simplified text version of CSCs whenever you are in a digital coverage area.

    Because of costs of generating and hosting an extra copy of the CSCs, only sponsored CSCs have a cell phone version at the moment.

    Look in the nifty links on your CSC's legend page.

    2004 February 3

    Desparate for photons? Clouded out? Willing to drive a 100 miles? You can see a tantalizing clear spot on the forecast map but cant tell exactly where it is?

    A new feep to help solve this problem:

    1. goto to your favorite CSC's legend page
    2. click on the block that corresponds to the hour you want to start observing -- nevermind that it's white
    3. In the full forecast map page, in the "Click on Map to:" section, select "link roadmap"
    4. from the cross hair marking your CSC, find the closet blue patch. Click on it
    5. You'll be popped into a road map for that point
    Only works from non location-privacy CSCs.

    As my S.O. would say "feep...feep...feep".

    2004 January 7

    The red "No Data From CMC" banners on all the CSCs is because of a problem with the astronomy-weather computer model running at the Canadian Meterological Center. CMC knows about the problem. As soon as they resume modeling, my software will detect the new data and will automatically update all the CSCs. Unfortuneately, I cant say exactly when that will happen.

    2004 January 4

    In legend pages, when you check "Show block details when you mouse-over" and then run your mouse over a colored block in the CSC image, a little text window pops up to show numerical details of the forecast for the hour of the block. However, browser incompatibilities have made it too frustrating to position that little window properly.

    So instead of automatically closing the popup after your mouse has left the colored block, I leave it open. That allows you to move or resize the popup window so you can see the numerical fields properly.

    You may need to uncheck and recheck the "Show block details when you mouse-over" to regenerate the popup window in some cases.

    2003 December 21

    A small feep: I'm now showing the locations of other CSCs on each CSC's lightpollution map. You can go to those CSCs by selecting "on click: find CSCs" in the lightpollution map page. Then click on the little crosses that mark the other CSCs.

    2003 November 30

    A couple of people tell me that the light pollution maps are wrong, being too pessimistic. In reviewing my own observing notes and the bortle scale, I conclude the maps are about right. But some of the descriptions on my light pollution pages were out by one whole catagory.

    I've rewritten the descriptions on the lightpollution pages. Feel free write me if you think your site's lightpollution is significantly different that what the maps show.

    2003 November 10

    I was originally inspired to create the first CSC because I was too lazy to download all of Allan Rahill's forecast maps. But I've been surpassed (in lazyness).

    A user has asked for a faster way of seeing the light pollution rating of a CSC. Apparently he got excited about the forecast for a friend's CSC only to realize later that it wasnt as dark as he thought. Clicking the "light pollution map" link would have been too much work.

    I've added a light pollution column to CSC listing pages and search outputs. But I'm not convinced it's it's worth increasing the clutter in the CSC images with another color code. So, I put the color code for the CSC's light pollution rating into the text portion fo the CSC's legend page.

    2003 November 6

    Mark Casazza (not affiliated with has written a web application that can email people when their favorite CSC shows a good forecast. He calls it the Alarm Clock. I have linked his registration page from each CSC's legend page. If you follow links to the Alarm Clock from a legnd page, the CSC will be auto selected. This saves a lot of time scrolling though huge CSC lists on Mark's site.

    For the tech weenies: Mark is using the machine readable versions of the CSCs. I wrote them just so 3rd parties, like Mark, could come up with new applications. If you have other ideas for machine-readable CSCs, let me know.

    2003 November 5

    To make the lightpollution maps more usable, you can now click on the map to display latitude/longitude or link to road/topo maps. (Sorry no panning.)

    This feep isnt available for CSCs that have been requested as "location private". It would have been easy to find the exact location of private CSCs otherwise.

    2003 October 28

    I've regained ownership of the domain. (Whew!) So, people with working links to CSCs though need not change them.

    Thanks for everyone's patience during this mess. Special thanks for the very many people who offered support, help and added new adjectives to my vocabulary.

    2003 September 28

    Mark Casazza has written an email interface to the CSCs. When you register on his web page he will automatically send you emails when the CSC, of your choice, is updated with a new forecast which is clear.

    (I knew the machine-readable version of the CSCs would come in handy some day.)

    I'm quite amused -- really. I started the CSCs because I was too lazy to download all of Allan Rahill's astronomy forecast maps. Mark has gone one step further.

    2003 September 20

    To each CSC's legend page, I've added a little link "CalSky". It links to a very sofphisticated website that can, among other things, compute a sky calendar for a specific latitude and longitude. When goto CalSky from a CSC page, the latitude and longitude of that CSC site are automatically set. It's a nice way of getting, for example, a list of lunar occulations visible from a CSC site. (Use the "Calendar" link from the CalSky main page.)

    2003 August 26

    1. I've resumed adding new CSCs.
    2. I've also added a questionable new page to the site.
    3. Allan Rahill and I will be speaking briefly at FAAQ in Montreal on September 6th. If you must express yourself by thowing things, please limit yourself to soft vegetables or pitted fruit.

    2003 June 28

    CSC images not displaying

    Some people have reported that, on CSC legend pages, the text appears, but the CSC image does not. In all cases so far, the problem has been that some ad-killer software, added by users to their browsers, have decided that the CSC images are advertisements.

    To see if you are having this problem, compare what you see with these two links: Link 1 and Link 2.

    If you can see the CSC with Link 1 but not Link 2, then you probably have ad-killer software that needs to be told not to nuke gifs from

    If you cant see the CSC with either link, then my webhoster is probably down.

    2003 May 27

    CMC is now generating hourly cloud-cover forecasts. (The transparency and seeing forecasts are still 3 hours apart.) That should make it easier for us to plan our obsering around sucker holes.

    I'm converting the CSC generation system to use the new hourly data. The CSCs will be updated this evening. There are a few bugs in the "next" "previous" links of the full-map display that should be fixed tormorrow evening.

    2003 May 26

    The world has not come to an end. The forecasts have not been cancelled. Not too many people were buying new telescopes.

    The problems with the numerical model at CMC have been fixed.

    2003 March 21

    When you click on a colored block in on a CSC in a legend page, the resulting full-forecast map now shows the location of the CSC with a cross hair. That should make it much easier to read the full maps. Because my webhost does not allow server-side graphics processing, I used a clever trick to make it work anyway. Unfortuneately, that means the trick wont work on all browsers, notably older versions of Netscape. If the map doesn't appear correct, click the "click here if map is mangled" link to restore the old map.

    2003 March 17

    I've added distance scales to the lighpollution maps. (Yes, those LP maps could use a lot more to make them more readable.)

    2003 March 9

    Limited French Languge support
    I can now display CSC images with French labels. (An example is here). It's limited because there can only be one version of each CSC and the legend page is not translated. Still, some have found just the translated images useful.

    Originators of existing CSCs are welcome to ask me to convert them to French.

    I could also support Spanish (same limitations) if anyone is interested.

    2003 March 6

    The Cached CSCs problem
    On rare occaisions, someone would complain that their CSC was not updated, while it looked perfectly fine to me. Others would say that the details pop-up window had the wrong numbers. Both problems are caused by some people's ISPs running transparent proxies which were caching the CSC .gifs.

    Now serveral users of one CSC have reported it not updating for as long 5 days.

    Here is my third and hopefully final attempt to prevent CSC .gifs from being cached. It appears effective. But people who want the fix for CSC images displayed on their own web pages need to change their html. Use the sample html at the bottom of the legend page for your CSC.

    If your CSC appears older than 12 hours, and you are using the current html to display CSC, please write me.

    2003 February 23

    On the legend page for each CSC, you can click on a colored block to goto CMC's full forecast-map for that time. I've added "previous" and "next" links to the pages that display CMCs maps so one can navigate them without returning to the CSC legend page.

    This change has also made the text of the legend page load about 1/3 faster.

    2003 January 5

    Minor policy change

    I have this feeling that the number of CSC requests that I am getting is about to increase. I figure I will eventually get requests for CSCs that will not really be used. So I reserve the right to delete CSCs that I believe have fallen into disuse. For the moment, by definition of "fallen into disuse" is "the legend page of the CSC hasnt been used in 30 days".

    If a CSC you care about has vanished, the remedy is simple: request it again and it will live for at least another 30 days.

    Sorry, I can't make all news items as exciting as the Oct 9th entry.

    2002 October 9

    Huge thanks to CSC users.

    Last week, news of the imminent cancellation of the CSCs made it to usenet and a number of astronomy mailing lists. That news was followed by calls for emails to be written to to certain civil servants, followed by news to not write civil servants, followed by the news that everything is fine. Now that we can breath again, here is the story:

    The struggle had been quitely going on for a year.

    I generate the CSCs from publicly available forecast maps from the Canadian Meterologial Service. They are the creation of Allan Rahill, CMC meterologist, and are incredibly accurate. But they are not an official product of the CMC. Allan created them on his lunch hour. Well, during a couple of years of lunch-hours. He always knew he was taking a chance releasing a unofficial forecast.

    In August, a department in a different division than Allan, told him that his forecast was in violation of Environment Canada's policy against specialty forecasts and unofficial use of government computers. Allan was told to take down his forecast. That would have starved the CSCs of data within 36 hours.

    The CSCs themselves were never in danger since and I have no connection to the CMC. However, Allan's forecasts are simply the best for astronomy. I don't believe I would have been able to find a replacement accurate enough for the hourly display of the CSCs to be useful.

    News of the status of Allan's forecast hit the net last week. The situation was exaggerated to appear to be a crisis and was followed by calls to write Allan's directors. In an attempt to keep Allan from getting fired, I posted request to re-direct the traffic to me. Allan posted that emails were in fact welcome, but that they should be sent to him. In the confusion each of Allan, I and two CMC directors each received between 100 and 200 emails over the course of three days.

    It turns out that it was not a crisis. Allan had been planning to present his directors user-written emails of support. Allan did not get in trouble. His directors actually expected to receive some emails directly, but not in the hundreds. Allan presented them with the full set of emails from people supporting his forecast. There were over 2000. Almost all of the people who wrote those emails said they used the astronomy forecasts though my CSC interface. (I think thats pretty cool.)

    The volume and geographical extent of the emailed support for the astronomy forecasts was a factor in the CMC directors deciding to work to make the Astronomy forecasts into an offical CMC product. That might take a year or so. In the meantime, they will leave Allan to continue to develop and tune his forecasts.

    So the short story is: Yes the CSCs were in danger of disappearing. They are safe now. Huge thanks to all those who wrote in support.

    As long as Allan can generate his astronomy forecasts maps (and as long as they are the best :) ), I will continue to create CSCs from them.

    We now return you to your regular, more boring, web site news.

    2002 September 2

    Distances to CSCs

    The "CSCs within 100km" page lists distances from the orgin CSC.

    Some may note that some distances are labeled as "<24km"or "<15mi". Those are CSCs for which the owners of the site requested that I not reveal their their precise location.

    2002 September 1

    Light Pollution Maps.

    I've added a "light pollution map" link to each CSC's legend page. It's a small exerpt from the 130meg tiff image of North America from The World Atlas of Artificial Night Sky Brightness centered on the CSC site. Used by the gracious premission of the authors: P. Cinzano, F. Falchi, and C. D. Elvidge.

    2002 August 27

    email list

    I've created a public mailing list about weather forecasting for astronomy. I've been inviting those few meterologist who I know are also astronomers to join in the hopes that I may bathe in their combined wisdom. Or maybe just get an answer or two. We can also use the list to discuss usage and accuracy of weather forecasting websites, like the CSC, if we feel like it.

    2002 August 6

    Astronomical Seeing Observations Database

    Help tune the seeing forecast used by the CSCs by submitting your observations of astronomical seeing. The database in currently in beta test. Everyone is welcome to play with it and report bugs or suggestions to me.

    I will reset the database and make it ready for real observations around August 20th.

    2002 August 4

    Worried about security?

    If you'd like a CSC for your observatory, but are worried that the CSC would make your site's latitude and longitude too public for comfort, there is a solution. Mention your desire for privacy in your email to me and I do my best to not reveal your latitude and longitude on

    I've added reminder in May I get my own CSC? and a link to the privacy policy that explains the choice.

    2002 July 20

    Night-vision colors for legend pages.

    The people at Observatoires du Mont Megantic have asked be for a less "pupil destroying" background color for the background of legend page for their CSC. Apparantly they've been projecting it onto a huge screen at night. They seem to prefer these colors which are a little easier on night vision.

    The orginal requestors of any CSC are welcome to ask me to set their legend page to the same color set. However, since having separate colors for each page is a pain, I will take each request as a vote to change them all. Even if you've never requested a CSC, email me if you'd like all CSC pages in night vision colors -- or not.

    CSC Home.