Starlight Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starlight Hills Observatory clear sky chart from 2005-11-06 to 2026-08-30.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	4 5% 2 5% 4 4 5% 4 6% 8% 54%	152652
	Night	4 5% 2 5% 3 3 4 3 5% 7% 59%	147106
Transparency	Day	23% 7% 11% 23% 24% 12%	147627
	Night	22% 7% 11% 25% 25% 10%	143140
Seeing	Day	7% 11% 30% 29% 17% 6%	18055
	Night	6% 6% 32% 39% 15% 2	27983

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	1 6% 3 5% 3 3 3 3 5% 8% 61%	4720
	11th to 20th	Day	1 1 1 4 4 4 4 3 5% 7% 65%	4938
	21st to end	Day	1 3 2 8% 4 3 3 3 4 6% 62%	5844
February	1st to 10th	Day	1 6% 2 5% 5% 3 4 3 5% 7% 59%	1911
	11th to 20th	Day	1 3 2 5% 4 4 4 4 7% 9% 57%	2049
	21st to end	Day	1 5% 2 7% 4 3 4 3 5% 6% 60%	1730
March	1st to 10th	Day	1 4 2 5% 3 3 3 3 5% 7% 64%	4600
	11th to 20th	Day	2 9% 3 7% 4 4 4 3 6% 8% 50%	5007
	21st to end	Day	2 5% 3 5% 4 4 5% 4 6% 9% 53%	5981
April	1st to 10th	Day	3 6% 2 5% 3 4 4 4 6% 9% 54%	2520
	11th to 20th	Day	6% 6% 3 5% 3 4 4 4 7% 8% 50%	2491
	21st to end	Day	6% 8% 2 5% 3 4 5% 4 6% 9% 48%	2520
May	1st to 10th	Day	11% 8% 2 5% 3 4 4 4 6% 6% 47%	7413
	11th to 20th	Day	6% 6% 2 5% 3 4 5% 5% 7% 8% 48%	7982
	21st to end	Day	7% 6% 2 5% 3 4 5% 5% 8% 9% 45%	9026
June	1st to 10th	Day	5% 4 1 5% 4 4 6% 6% 9% 9% 47%	2940
	11th to 20th	Day	4 3 1 4 4 4 5% 5% 8% 9% 54%	2940
	21st to end	Day	3 3 2 5% 5% 5% 6% 6% 9% 8% 49%	2940
July	1st to 10th	Day	2 3 1 4 4 5% 5% 5% 7% 9% 56%	8249
	11th to 20th	Day	3 3 1 5% 4 5% 5% 5% 7% 8% 53%	8250
	21st to end	Day	4 4 2 7% 6% 6% 7% 6% 7% 9% 43%	8747
August	1st to 10th	Day	7% 5% 2 6% 6% 5% 6% 6% 9% 10% 40%	5805
	11th to 20th	Day	3 3 1 5% 5% 5% 7% 5% 8% 10% 49%	5486
	21st to end	Day	8% 4 2 5% 4 5% 6% 5% 8% 9% 44%	6093
September	1st to 10th	Day	5% 3 2 4 3 5% 5% 4 7% 7% 56%	2400
	11th to 20th	Day	5% 3 1 4 3 4 4 5% 6% 7% 58%	2360
	21st to end	Day	4 4 1 5% 3 3 3 3 4 7% 64%	2200
October	1st to 10th	Day	4 4 1 3 1 2 2 2 4 5% 73%	3344
	11th to 20th	Day	4 5% 2 6% 3 3 3 3 4 6% 60%	3250
	21st to end	Day	3 3 1 3 2 2 2 3 4 6% 72%	3425
November	1st to 10th	Day	2 4 1 3 3 2 3 2 6% 7% 67%	1853
	11th to 20th	Day	1 3 1 3 3 2 3 3 5% 7% 69%	1890
	21st to end	Day	1 4 2 6% 3 3 3 3 5% 7% 63%	1850
December	1st to 10th	Day	1 4 2 3 3 2 3 3 4 6% 70%	2700
	11th to 20th	Day	1 3 1 3 3 2 3 3 4 8% 69%	3106
	21st to end	Day	1 4 2 5% 3 3 4 4 5% 7% 61%	4092
January	1st to 10th	Night	6% 3 7% 4 3 3 3 5% 8% 58%	8201
	11th to 20th	Night	2 2 4 3 4 4 3 5% 6% 67%	8095
	21st to end	Night	1 3 2 7% 4 4 3 3 4 6% 65%	8370
February	1st to 10th	Night	1 5% 2 6% 4 3 3 3 5% 8% 60%	2707
	11th to 20th	Night	1 6% 3 7% 4 3 4 3 6% 7% 54%	2458
	21st to end	Night	1 4 2 6% 3 2 3 2 5% 4 67%	2076
March	1st to 10th	Night	1 5% 1 5% 3 4 4 3 5% 7% 63%	5494
	11th to 20th	Night	4 8% 2 5% 4 4 3 3 5% 6% 57%	5205
	21st to end	Night	3 7% 2 5% 3 3 4 3 5% 7% 57%	5218
April	1st to 10th	Night	3 5% 1 4 3 3 4 3 5% 8% 60%	2100
	11th to 20th	Night	6% 8% 2 4 2 4 3 4 6% 7% 54%	2077
	21st to end	Night	7% 7% 2 5% 3 4 4 3 5% 8% 52%	2100
May	1st to 10th	Night	11% 7% 2 4 3 3 4 3 5% 7% 51%	5532
	11th to 20th	Night	7% 6% 2 4 2 3 4 4 7% 9% 52%	4893
	21st to end	Night	12% 8% 2 5% 4 4 4 3 4 7% 48%	5181
June	1st to 10th	Night	5% 4 2 4 2 3 3 4 7% 10% 56%	1680
	11th to 20th	Night	4 3 1 3 3 3 3 3 6% 9% 64%	1680
	21st to end	Night	4 4 1 5% 4 3 5% 5% 8% 8% 53%	1680
July	1st to 10th	Night	3 3 1 5% 4 4 4 4 6% 7% 59%	4740
	11th to 20th	Night	3 3 1 4 4 4 4 5% 7% 10% 56%	4740
	21st to end	Night	4 4 2 6% 5% 5% 6% 6% 9% 10% 43%	5345
August	1st to 10th	Night	7% 5% 2 4 4 4 5% 4 8% 10% 46%	4227
	11th to 20th	Night	4 4 1 6% 4 5% 5% 5% 8% 10% 48%	4583
	21st to end	Night	7% 5% 2 6% 4 5% 5% 5% 8% 10% 43%	5083
September	1st to 10th	Night	5% 4 2 5% 4 5% 6% 4 7% 8% 53%	2000
	11th to 20th	Night	7% 4 1 4 3 3 3 3 4 7% 62%	2040
	21st to end	Night	5% 4 2 4 3 3 3 3 4 6% 64%	2200
October	1st to 10th	Night	5% 4 1 2 2 2 2 2 3 5% 72%	3841
	11th to 20th	Night	7% 5% 1 4 3 3 3 3 5% 6% 60%	3898
	21st to end	Night	3 3 2 3 2 2 2 2 3 6% 71%	4341
November	1st to 10th	Night	2 4 1 3 2 3 3 2 5% 7% 67%	2665
	11th to 20th	Night	1 2 2 3 3 2 3 3 5% 5% 71%	2730
	21st to end	Night	2 4 2 5% 3 3 2 3 5% 7% 63%	2767
December	1st to 10th	Night	2 1 4 3 2 2 2 3 5% 75%	4710
	11th to 20th	Night	1 3 2 4 3 3 3 3 5% 10% 65%	5321
	21st to end	Night	2 5% 2 5% 3 3 4 3 5% 7% 61%	7128

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	20% 4 8% 31% 27% 9%	4723
	11th to 20th	Day	16% 6% 11% 25% 32% 11%	4938
	21st to end	Day	22% 5% 7% 25% 29% 12%	5844
February	1st to 10th	Day	23% 5% 11% 26% 24% 11%	1911
	11th to 20th	Day	21% 7% 9% 26% 28% 9%	2059
	21st to end	Day	23% 5% 7% 21% 25% 19%	1730
March	1st to 10th	Day	17% 5% 8% 16% 33% 21%	4600
	11th to 20th	Day	27% 8% 10% 22% 27% 7%	5007
	21st to end	Day	21% 9% 12% 37% 18% 4	5981
April	1st to 10th	Day	23% 7% 13% 24% 23% 10%	2520
	11th to 20th	Day	29% 6% 12% 22% 20% 11%	2494
	21st to end	Day	30% 7% 13% 25% 20% 6%	2520
May	1st to 10th	Day	31% 7% 12% 27% 17% 6%	7413
	11th to 20th	Day	25% 8% 12% 21% 24% 9%	7986
	21st to end	Day	27% 10% 15% 22% 17% 9%	9027
June	1st to 10th	Day	26% 10% 15% 22% 17% 10%	2940
	11th to 20th	Day	21% 8% 12% 18% 24% 18%	2940
	21st to end	Day	25% 9% 12% 19% 21% 13%	2940
July	1st to 10th	Day	19% 8% 10% 18% 24% 20%	8181
	11th to 20th	Day	23% 8% 11% 21% 19% 18%	8175
	21st to end	Day	31% 10% 16% 17% 14% 11%	8552
August	1st to 10th	Day	36% 9% 17% 22% 11% 5%	4256
	11th to 20th	Day	26% 11% 13% 19% 19% 13%	4002
	21st to end	Day	26% 9% 14% 20% 25% 6%	4420
September	1st to 10th	Day	22% 7% 10% 22% 24% 14%	2400
	11th to 20th	Day	21% 7% 10% 18% 29% 16%	2360
	21st to end	Day	20% 5% 8% 21% 33% 14%	2200
October	1st to 10th	Day	15% 4 7% 16% 38% 22%	3344
	11th to 20th	Day	22% 6% 8% 21% 31% 12%	3250
	21st to end	Day	13% 3 6% 22% 39% 17%	3425
November	1st to 10th	Day	16% 4 9% 24% 29% 18%	1853
	11th to 20th	Day	15% 5% 5% 30% 33% 12%	1890
	21st to end	Day	20% 5% 8% 23% 29% 16%	1850
December	1st to 10th	Day	15% 5% 8% 30% 33% 10%	2700
	11th to 20th	Day	15% 4 6% 30% 31% 13%	3104
	21st to end	Day	18% 6% 10% 27% 26% 12%	4092
January	1st to 10th	Night	23% 5% 7% 31% 27% 6%	8202
	11th to 20th	Night	15% 6% 11% 26% 26% 15%	8095
	21st to end	Night	20% 6% 9% 23% 30% 12%	8370
February	1st to 10th	Night	23% 5% 9% 28% 25% 10%	2707
	11th to 20th	Night	26% 6% 10% 28% 21% 8%	2458
	21st to end	Night	19% 4 6% 25% 28% 17%	2076
March	1st to 10th	Night	19% 5% 7% 16% 38% 15%	5494
	11th to 20th	Night	25% 7% 10% 18% 28% 12%	5205
	21st to end	Night	22% 8% 12% 32% 22% 3	5218
April	1st to 10th	Night	21% 6% 13% 24% 25% 11%	2100
	11th to 20th	Night	27% 7% 12% 24% 21% 9%	2077
	21st to end	Night	29% 7% 14% 26% 18% 6%	2100
May	1st to 10th	Night	30% 8% 15% 31% 11% 5%	5530
	11th to 20th	Night	23% 10% 15% 26% 18% 9%	4894
	21st to end	Night	32% 9% 15% 21% 15% 7%	5182
June	1st to 10th	Night	23% 8% 21% 25% 14% 9%	1680
	11th to 20th	Night	16% 7% 15% 24% 20% 18%	1680
	21st to end	Night	24% 9% 12% 21% 22% 13%	1680
July	1st to 10th	Night	20% 8% 11% 21% 29% 11%	4700
	11th to 20th	Night	20% 9% 16% 22% 22% 11%	4692
	21st to end	Night	30% 11% 19% 18% 13% 9%	5228
August	1st to 10th	Night	36% 10% 19% 19% 10% 5%	3100
	11th to 20th	Night	26% 12% 19% 20% 19% 5%	3343
	21st to end	Night	24% 11% 19% 26% 16% 4	3687
September	1st to 10th	Night	26% 7% 11% 23% 22% 11%	2000
	11th to 20th	Night	20% 6% 10% 24% 26% 15%	2040
	21st to end	Night	21% 6% 8% 23% 31% 11%	2200
October	1st to 10th	Night	15% 5% 7% 21% 35% 17%	3841
	11th to 20th	Night	22% 5% 8% 27% 27% 10%	3898
	21st to end	Night	15% 4 7% 26% 33% 15%	4341
November	1st to 10th	Night	15% 5% 9% 26% 29% 16%	2665
	11th to 20th	Night	15% 4 8% 28% 32% 12%	2730
	21st to end	Night	20% 4 10% 24% 30% 12%	2767
December	1st to 10th	Night	13% 4 8% 33% 32% 10%	4710
	11th to 20th	Night	15% 5% 7% 28% 34% 11%	5322
	21st to end	Night	22% 6% 11% 22% 27% 12%	7128

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	7% 8% 33% 36% 12% 3	330
	11th to 20th	Day	6% 12% 35% 36% 9% 2	330
	21st to end	Day	3 13% 35% 35% 12% 2	363
February	1st to 10th	Day	4 16% 45% 25% 7% 2	330
	11th to 20th	Day	3 14% 47% 27% 9% 1	330
	21st to end	Day	1 18% 45% 29% 7% 1	273
March	1st to 10th	Day	4 15% 37% 32% 10% 3	330
	11th to 20th	Day	10% 18% 38% 21% 10% 3	489
	21st to end	Day	11% 21% 39% 21% 6% 2	594
April	1st to 10th	Day	11% 18% 39% 23% 8% 2	540
	11th to 20th	Day	11% 24% 36% 20% 6% 2	532
	21st to end	Day	14% 17% 35% 25% 7% 2	540
May	1st to 10th	Day	15% 16% 32% 25% 9% 3	667
	11th to 20th	Day	13% 12% 29% 29% 14% 3	775
	21st to end	Day	10% 11% 30% 27% 19% 4	844
June	1st to 10th	Day	7% 10% 22% 33% 21% 7%	780
	11th to 20th	Day	6% 11% 29% 32% 18% 5%	780
	21st to end	Day	4 9% 25% 34% 22% 6%	780
July	1st to 10th	Day	6% 5% 19% 32% 28% 9%	771
	11th to 20th	Day	5% 2 14% 34% 34% 11%	768
	21st to end	Day	6% 4 14% 28% 34% 14%	779
August	1st to 10th	Day	9% 2 20% 35% 26% 8%	567
	11th to 20th	Day	4 6% 21% 32% 23% 13%	557
	21st to end	Day	7% 3 22% 36% 21% 10%	620
September	1st to 10th	Day	7% 4 25% 33% 19% 11%	530
	11th to 20th	Day	5% 7% 30% 28% 22% 8%	490
	21st to end	Day	10% 8% 18% 27% 26% 12%	330
October	1st to 10th	Day	9% 12% 20% 26% 23% 10%	330
	11th to 20th	Day	3 9% 35% 31% 16% 6%	330
	21st to end	Day	6% 12% 35% 27% 18% 3	363
November	1st to 10th	Day	6% 13% 35% 27% 13% 6%	330
	11th to 20th	Day	3 7% 39% 33% 15% 3	330
	21st to end	Day	6% 12% 35% 32% 12% 4	330
December	1st to 10th	Day	3 14% 40% 26% 13% 3	330
	11th to 20th	Day	4 9% 42% 29% 14% 1	330
	21st to end	Day	3 13% 43% 31% 8% 2	363
January	1st to 10th	Night	3 6% 39% 36% 12% 3	1050
	11th to 20th	Night	3 7% 42% 37% 9% 2	999
	21st to end	Night	2 6% 39% 42% 10% 1	924
February	1st to 10th	Night	3 5% 52% 33% 6% 1	840
	11th to 20th	Night	3 7% 49% 33% 8%	824
	21st to end	Night	3 8% 50% 34% 4	692
March	1st to 10th	Night	3 7% 46% 34% 8% 1	840
	11th to 20th	Night	7% 8% 36% 38% 10% 1	840
	21st to end	Night	5% 10% 43% 35% 7%	752
April	1st to 10th	Night	7% 10% 43% 35% 5%	630
	11th to 20th	Night	13% 10% 35% 35% 7% 1	623
	21st to end	Night	12% 9% 35% 35% 8% 1	630
May	1st to 10th	Night	11% 9% 30% 37% 12% 1	630
	11th to 20th	Night	12% 7% 27% 40% 13% 1	621
	21st to end	Night	11% 7% 30% 34% 16% 2	683
June	1st to 10th	Night	6% 6% 21% 44% 20% 3	630
	11th to 20th	Night	4 4 26% 51% 14% 1	630
	21st to end	Night	5% 4 20% 48% 21% 2	630
July	1st to 10th	Night	6% 3 14% 43% 32% 2	615
	11th to 20th	Night	4 2 7% 46% 36% 5%	612
	21st to end	Night	8% 3 8% 36% 42% 3	690
August	1st to 10th	Night	8% 4 9% 41% 35% 4	627
	11th to 20th	Night	7% 2 10% 49% 30% 3	624
	21st to end	Night	5% 2 10% 44% 35% 4	687
September	1st to 10th	Night	6% 3 12% 46% 28% 6%	600
	11th to 20th	Night	8% 3 16% 48% 22% 4	600
	21st to end	Night	7% 4 20% 44% 22% 4	600
October	1st to 10th	Night	10% 4 24% 41% 17% 3	747
	11th to 20th	Night	5% 4 33% 39% 16% 4	800
	21st to end	Night	6% 5% 32% 37% 16% 3	933
November	1st to 10th	Night	4 4 35% 41% 14% 2	1025
	11th to 20th	Night	3 6% 38% 43% 9% 2	1050
	21st to end	Night	5% 7% 36% 39% 12% 2	1050
December	1st to 10th	Night	2 6% 42% 38% 10% 1	1050
	11th to 20th	Night	3 7% 40% 37% 11% 1	1050
	21st to end	Night	5% 8% 45% 34% 8% 1	1155

Page generated at 2026-08-27 02:07:11. Version ac07

Copyright © 2026 Attilla Danko.