Regina Caelorum Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Regina Caelorum Observatory clear sky chart from 2005-11-06 to 2025-07-21.

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	12% 6% 2 6% 4 4 4 4 5% 8% 45%	120419
	Night	13% 6% 2 5% 3 3 3 3 5% 7% 50%	118950
Transparency	Day	36% 5% 10% 21% 19% 8%	124152
	Night	34% 4 10% 20% 20% 11%	123347
Seeing	Day	13% 6% 19% 27% 25% 10%	15902
	Night	14% 6% 25% 35% 17% 2	25758

By Month

Percentage Cloud Cover SE (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	16% 9% 3 5% 3 3 3 3 4 7% 45%	4077
	11th to 20th	Day	14% 5% 2 6% 3 3 3 2 5% 6% 52%	4080
	21st to end	Day	27% 9% 3 6% 3 2 2 2 2 5% 40%	4488
February	1st to 10th	Day	21% 8% 3 6% 3 3 3 3 4 6% 40%	1948
	11th to 20th	Day	20% 8% 2 7% 4 3 4 3 4 5% 40%	1949
	21st to end	Day	20% 8% 2 5% 3 3 3 3 4 5% 44%	1740
March	1st to 10th	Day	14% 8% 3 7% 5% 4 4 3 4 6% 42%	4936
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 5% 6% 48%	4980
	21st to end	Day	16% 8% 2 7% 4 4 4 3 5% 7% 40%	5462
April	1st to 10th	Day	14% 8% 3 7% 5% 4 4 3 5% 7% 39%	2200
	11th to 20th	Day	13% 8% 3 7% 5% 5% 4 4 5% 7% 39%	2278
	21st to end	Day	12% 7% 2 6% 4 5% 5% 3 4 6% 45%	2410
May	1st to 10th	Day	18% 8% 3 7% 4 5% 4 4 6% 7% 34%	5862
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	5862
	21st to end	Day	10% 6% 3 7% 5% 6% 6% 5% 7% 10% 34%	6434
June	1st to 10th	Day	5% 5% 2 6% 4 5% 6% 5% 7% 11% 45%	2600
	11th to 20th	Day	6% 4 1 5% 5% 4 5% 5% 7% 10% 47%	2600
	21st to end	Day	5% 5% 2 6% 6% 5% 6% 6% 8% 11% 41%	2600
July	1st to 10th	Day	8% 4 2 5% 5% 5% 5% 4 7% 10% 46%	4250
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 5% 7% 10% 47%	4250
	21st to end	Day	13% 6% 3 7% 6% 5% 6% 4 6% 9% 35%	4466
August	1st to 10th	Day	2 2 2 2 2 3 3 4 8% 71%	4104
	11th to 20th	Day	3 2 1 3 3 3 4 3 6% 12% 59%	4041
	21st to end	Day	5% 3 1 5% 4 5% 6% 5% 8% 11% 47%	3937
September	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 5% 10% 45%	2090
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 5% 7% 7% 43%	2090
	21st to end	Day	6% 3 1 5% 4 5% 5% 4 6% 8% 52%	2090
October	1st to 10th	Day	6% 3 2 4 4 4 4 3 4 6% 60%	2028
	11th to 20th	Day	12% 4 2 5% 3 3 3 2 4 5% 57%	1900
	21st to end	Day	13% 4 1 4 3 3 3 3 3 5% 58%	2090
November	1st to 10th	Day	11% 8% 2 5% 4 3 4 4 5% 6% 48%	1958
	11th to 20th	Day	11% 6% 2 5% 4 4 3 3 4 6% 53%	2000
	21st to end	Day	16% 7% 3 7% 4 3 4 3 4 7% 43%	1800
December	1st to 10th	Day	21% 7% 2 4 4 3 3 3 5% 5% 44%	2940
	11th to 20th	Day	19% 7% 3 5% 4 4 4 2 5% 6% 41%	3391
	21st to end	Day	15% 8% 2 6% 3 3 3 3 3 6% 48%	4488
January	1st to 10th	Night	18% 6% 2 4 3 2 3 2 3 5% 53%	5888
	11th to 20th	Night	13% 6% 2 3 2 2 3 3 3 5% 59%	5900
	21st to end	Night	28% 7% 2 5% 3 3 3 2 4 4 39%	6490
February	1st to 10th	Night	19% 8% 2 6% 4 3 3 3 3 4 46%	2469
	11th to 20th	Night	20% 8% 3 5% 3 3 3 2 3 5% 45%	2338
	21st to end	Night	21% 7% 2 5% 3 3 2 3 4 5% 45%	1888
March	1st to 10th	Night	17% 7% 2 7% 4 4 3 3 5% 7% 41%	4919
	11th to 20th	Night	14% 6% 2 6% 4 3 4 3 4 6% 49%	4980
	21st to end	Night	17% 9% 3 6% 3 3 3 3 4 5% 44%	5467
April	1st to 10th	Night	13% 5% 2 5% 5% 4 4 3 6% 6% 48%	2200
	11th to 20th	Night	12% 5% 3 5% 5% 4 3 3 6% 7% 48%	2070
	21st to end	Night	12% 7% 2 5% 3 3 4 3 5% 7% 47%	1985
May	1st to 10th	Night	17% 10% 3 8% 4 4 4 3 5% 8% 34%	4053
	11th to 20th	Night	9% 6% 3 7% 5% 5% 5% 4 6% 8% 43%	4053
	21st to end	Night	9% 7% 2 7% 5% 5% 5% 5% 7% 10% 39%	4443
June	1st to 10th	Night	6% 4 1 3 3 3 4 4 6% 11% 56%	1800
	11th to 20th	Night	4 2 1 3 3 3 4 4 5% 10% 62%	1800
	21st to end	Night	4 4 2 5% 4 4 4 3 7% 9% 53%	1800
July	1st to 10th	Night	4 3 1 4 4 4 5% 4 7% 12% 50%	2940
	11th to 20th	Night	3 3 2 4 3 3 3 4 7% 12% 56%	2940
	21st to end	Night	9% 7% 2 6% 4 4 4 5% 7% 10% 41%	3098
August	1st to 10th	Night	1 1 1 1 1 2 2 2 3 10% 76%	2836
	11th to 20th	Night	3 2 1 4 2 3 3 3 6% 12% 61%	2798
	21st to end	Night	3 3 2 4 3 4 4 4 7% 12% 55%	3713
September	1st to 10th	Night	6% 6% 2 5% 4 4 4 3 6% 8% 51%	2090
	11th to 20th	Night	8% 5% 2 6% 5% 4 4 4 5% 7% 49%	2090
	21st to end	Night	5% 4 2 6% 3 3 4 3 4 8% 59%	2090
October	1st to 10th	Night	4 3 1 4 2 3 3 2 5% 6% 66%	2133
	11th to 20th	Night	10% 5% 1 4 2 3 2 3 4 5% 61%	2280
	21st to end	Night	12% 5% 2 4 2 3 3 2 3 4 61%	2508
November	1st to 10th	Night	12% 5% 1 5% 3 3 4 3 4 7% 54%	2340
	11th to 20th	Night	9% 5% 2 5% 4 4 3 3 5% 7% 54%	2400
	21st to end	Night	15% 7% 2 5% 4 3 3 3 4 5% 48%	2595
December	1st to 10th	Night	21% 7% 3 5% 4 3 3 3 4 5% 43%	4250
	11th to 20th	Night	18% 9% 3 6% 3 3 3 2 3 4 45%	4816
	21st to end	Night	16% 6% 2 4 3 3 3 2 3 4 55%	6490

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	41% 3 5% 25% 20% 7%	4078
	11th to 20th	Day	35% 2 4 20% 27% 12%	4080
	21st to end	Day	51% 2 3 11% 18% 15%	4488
February	1st to 10th	Day	47% 3 5% 14% 21% 11%	1948
	11th to 20th	Day	47% 3 7% 15% 18% 9%	1959
	21st to end	Day	44% 3 6% 17% 17% 13%	1740
March	1st to 10th	Day	44% 3 6% 14% 21% 12%	4936
	11th to 20th	Day	37% 4 7% 11% 18% 23%	4980
	21st to end	Day	43% 5% 8% 20% 18% 6%	5464
April	1st to 10th	Day	45% 4 7% 18% 14% 11%	2200
	11th to 20th	Day	44% 4 8% 16% 18% 9%	2278
	21st to end	Day	39% 5% 8% 20% 22% 6%	2410
May	1st to 10th	Day	47% 6% 10% 21% 12% 3	5900
	11th to 20th	Day	38% 6% 13% 17% 23% 3	5866
	21st to end	Day	40% 8% 12% 24% 14% 2	6447
June	1st to 10th	Day	30% 8% 14% 30% 16% 2	2600
	11th to 20th	Day	28% 7% 14% 29% 18% 5%	2600
	21st to end	Day	34% 8% 16% 26% 15% 2	2600
July	1st to 10th	Day	31% 7% 25% 31% 6%	4186
	11th to 20th	Day	31% 7% 17% 29% 15%	4181
	21st to end	Day	43% 8% 17% 25% 7%	4326
August	1st to 10th	Day	13% 4 14% 40% 28% 1	4090
	11th to 20th	Day	18% 5% 27% 38% 11% 2	4080
	21st to end	Day	28% 12% 19% 26% 14% 1	3936
September	1st to 10th	Day	33% 7% 12% 22% 17% 8%	2090
	11th to 20th	Day	36% 8% 13% 19% 18% 6%	2090
	21st to end	Day	29% 5% 11% 22% 19% 14%	2090
October	1st to 10th	Day	16% 2 7% 12% 22% 41%	3366
	11th to 20th	Day	19% 3 6% 17% 34% 22%	3140
	21st to end	Day	25% 3 4 21% 33% 14%	3428
November	1st to 10th	Day	37% 4 7% 19% 22% 11%	1958
	11th to 20th	Day	33% 4 8% 19% 22% 15%	2000
	21st to end	Day	43% 3 7% 17% 20% 11%	1800
December	1st to 10th	Day	44% 3 7% 17% 22% 8%	2940
	11th to 20th	Day	45% 4 6% 12% 23% 11%	3389
	21st to end	Day	40% 3 5% 14% 29% 9%	4488
January	1st to 10th	Night	37% 3 4 23% 25% 9%	5888
	11th to 20th	Night	30% 2 4 18% 32% 14%	5900
	21st to end	Night	51% 2 3 12% 18% 15%	6490
February	1st to 10th	Night	44% 3 5% 12% 20% 16%	2469
	11th to 20th	Night	43% 3 6% 15% 19% 13%	2338
	21st to end	Night	43% 3 8% 13% 17% 16%	1888
March	1st to 10th	Night	43% 4 6% 13% 22% 12%	4919
	11th to 20th	Night	39% 3 6% 15% 14% 23%	4980
	21st to end	Night	44% 4 7% 16% 20% 9%	5467
April	1st to 10th	Night	37% 4 9% 19% 18% 13%	2200
	11th to 20th	Night	36% 4 10% 18% 18% 14%	2070
	21st to end	Night	36% 4 10% 19% 23% 7%	1985
May	1st to 10th	Night	49% 5% 9% 22% 11% 4	4080
	11th to 20th	Night	37% 7% 12% 19% 22% 3	4054
	21st to end	Night	37% 8% 15% 26% 12% 3	4452
June	1st to 10th	Night	22% 6% 18% 31% 21% 2	1800
	11th to 20th	Night	19% 5% 18% 33% 20% 6%	1800
	21st to end	Night	27% 6% 17% 29% 19% 2	1800
July	1st to 10th	Night	26% 8% 26% 34% 6%	2895
	11th to 20th	Night	21% 8% 21% 36% 14% 1	2886
	21st to end	Night	37% 8% 21% 26% 8%	2999
August	1st to 10th	Night	8% 4 16% 39% 31% 3	2826
	11th to 20th	Night	17% 6% 26% 38% 11% 2	2825
	21st to end	Night	22% 11% 22% 29% 14% 2	3713
September	1st to 10th	Night	30% 7% 17% 22% 16% 9%	2090
	11th to 20th	Night	34% 6% 15% 20% 18% 7%	2090
	21st to end	Night	25% 4 12% 24% 21% 14%	2090
October	1st to 10th	Night	13% 2 7% 16% 19% 43%	3562
	11th to 20th	Night	17% 2 4 19% 33% 26%	3779
	21st to end	Night	22% 2 5% 22% 32% 17%	4120
November	1st to 10th	Night	31% 4 9% 20% 23% 13%	2340
	11th to 20th	Night	31% 4 8% 20% 22% 16%	2400
	21st to end	Night	39% 3 8% 17% 20% 13%	2595
December	1st to 10th	Night	45% 2 5% 18% 22% 8%	4250
	11th to 20th	Night	44% 3 7% 9% 23% 14%	4817
	21st to end	Night	36% 3 4 16% 30% 13%	6490

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	22% 10% 36% 22% 8% 2	300
	11th to 20th	Day	21% 11% 35% 24% 8% 1	300
	21st to end	Day	25% 10% 38% 20% 7%	330
February	1st to 10th	Day	26% 13% 32% 22% 7%	300
	11th to 20th	Day	27% 17% 33% 18% 5%	300
	21st to end	Day	28% 13% 41% 14% 3 1	249
March	1st to 10th	Day	20% 15% 34% 24% 7%	300
	11th to 20th	Day	17% 17% 39% 19% 6% 2	300
	21st to end	Day	16% 12% 40% 22% 8% 1	330
April	1st to 10th	Day	22% 14% 34% 22% 7%	300
	11th to 20th	Day	23% 11% 33% 22% 10% 2	396
	21st to end	Day	18% 9% 32% 30% 9% 3	510
May	1st to 10th	Day	16% 8% 37% 30% 9% 1	703
	11th to 20th	Day	16% 6% 25% 31% 18% 3	725
	21st to end	Day	12% 5% 23% 36% 19% 4	789
June	1st to 10th	Day	6% 2 12% 37% 33% 10%	730
	11th to 20th	Day	7% 2 13% 41% 30% 8%	730
	21st to end	Day	7% 2 8% 30% 38% 16%	730
July	1st to 10th	Day	9% 2 6% 26% 38% 20%	721
	11th to 20th	Day	3 2 3 28% 42% 23%	718
	21st to end	Day	5% 2 3 25% 45% 20%	740
August	1st to 10th	Day	4 1 1 22% 49% 23%	676
	11th to 20th	Day	7% 1 2 23% 47% 20%	665
	21st to end	Day	9% 1 3 12% 40% 35%	400
September	1st to 10th	Day	4 1 4 22% 36% 33%	300
	11th to 20th	Day	7% 3 4 20% 37% 29%	300
	21st to end	Day	7% 2 8% 23% 37% 23%	300
October	1st to 10th	Day	3 1 11% 32% 39% 13%	300
	11th to 20th	Day	9% 2 21% 36% 23% 9%	300
	21st to end	Day	21% 8% 22% 23% 19% 8%	330
November	1st to 10th	Day	16% 7% 20% 33% 18% 6%	300
	11th to 20th	Day	19% 5% 25% 28% 18% 4	300
	21st to end	Day	20% 13% 31% 22% 12% 3	300
December	1st to 10th	Day	20% 7% 30% 23% 14% 6%	300
	11th to 20th	Day	27% 9% 30% 26% 7% 2	300
	21st to end	Day	21% 10% 35% 23% 10% 1	330
January	1st to 10th	Night	20% 9% 34% 30% 7%	1000
	11th to 20th	Night	21% 11% 31% 29% 8%	1000
	21st to end	Night	20% 9% 33% 31% 6%	1100
February	1st to 10th	Night	24% 11% 35% 26% 4	869
	11th to 20th	Night	27% 11% 33% 27% 3	784
	21st to end	Night	27% 10% 42% 19% 2	568
March	1st to 10th	Night	23% 10% 38% 24% 5%	600
	11th to 20th	Night	15% 11% 40% 28% 7%	600
	21st to end	Night	15% 10% 45% 26% 5%	660
April	1st to 10th	Night	15% 9% 44% 28% 5%	600
	11th to 20th	Night	15% 10% 39% 31% 6%	593
	21st to end	Night	14% 9% 39% 28% 9%	600
May	1st to 10th	Night	12% 9% 41% 32% 6% 1	600
	11th to 20th	Night	12% 7% 31% 36% 13% 1	591
	21st to end	Night	9% 3 30% 41% 15% 2	650
June	1st to 10th	Night	8% 1 16% 46% 27% 2	600
	11th to 20th	Night	5% 1 21% 51% 20% 3	600
	21st to end	Night	4 2 11% 45% 34% 4	600
July	1st to 10th	Night	4 2 7% 44% 37% 6%	585
	11th to 20th	Night	3 1 5% 49% 37% 3	582
	21st to end	Night	5% 1 5% 48% 38% 4	624
August	1st to 10th	Night	2 1 4 49% 41% 4	567
	11th to 20th	Night	6% 3 49% 38% 4	564
	21st to end	Night	4 1 5% 36% 46% 8%	627
September	1st to 10th	Night	8% 2 7% 35% 42% 7%	570
	11th to 20th	Night	11% 2 5% 33% 43% 6%	570
	21st to end	Night	6% 2 9% 39% 38% 6%	570
October	1st to 10th	Night	6% 1 11% 48% 29% 6%	613
	11th to 20th	Night	11% 5% 20% 42% 20% 2	760
	21st to end	Night	13% 6% 27% 34% 18% 2	836
November	1st to 10th	Night	14% 3 24% 38% 19% 2	780
	11th to 20th	Night	12% 7% 26% 40% 15% 1	800
	21st to end	Night	19% 9% 29% 28% 14% 1	995
December	1st to 10th	Night	21% 6% 30% 33% 11%	1000
	11th to 20th	Night	23% 10% 26% 35% 7%	1000
	21st to end	Night	20% 8% 31% 33% 8%	1100

Page generated at 2025-07-18 00:09:58. Version ac07

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