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 2026-11-13.

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% 46%	153341
	Night	12% 6% 2 5% 3 3 3 3 5% 7% 50%	148058
Transparency	Day	35% 5% 11% 23% 19% 8%	157031
	Night	33% 4 10% 21% 20% 10%	152434
Seeing	Day	13% 6% 19% 27% 25% 11%	17649
	Night	14% 6% 25% 35% 17% 2	27447

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	15% 8% 3 5% 3 3 3 3 4 7% 47%	5289
	11th to 20th	Day	12% 5% 2 6% 3 3 3 2 5% 6% 53%	5310
	21st to end	Day	26% 8% 3 6% 5% 3 3 2 3 4 37%	5812
February	1st to 10th	Day	21% 8% 3 6% 3 3 3 2 4 6% 41%	2046
	11th to 20th	Day	20% 8% 2 7% 4 3 4 3 4 6% 40%	2049
	21st to end	Day	19% 7% 2 5% 3 3 3 3 4 5% 46%	1824
March	1st to 10th	Day	15% 8% 3 7% 5% 4 4 3 4 6% 41%	5046
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 5% 6% 49%	5090
	21st to end	Day	16% 8% 2 6% 4 4 4 3 5% 7% 40%	5583
April	1st to 10th	Day	14% 8% 3 7% 5% 4 4 3 5% 7% 38%	2310
	11th to 20th	Day	14% 8% 3 7% 5% 5% 4 4 5% 7% 38%	2393
	21st to end	Day	14% 7% 3 6% 5% 5% 5% 3 5% 6% 43%	2530
May	1st to 10th	Day	21% 8% 3 7% 4 4 4 3 5% 6% 35%	7617
	11th to 20th	Day	11% 6% 3 8% 5% 5% 6% 4 6% 7% 40%	7627
	21st to end	Day	11% 7% 3 8% 6% 6% 6% 5% 7% 10% 33%	8392
June	1st to 10th	Day	5% 5% 2 6% 4 5% 6% 5% 7% 11% 44%	2730
	11th to 20th	Day	6% 4 1 6% 5% 4 5% 5% 7% 10% 46%	2730
	21st to end	Day	5% 5% 2 5% 6% 5% 6% 6% 8% 11% 42%	2730
July	1st to 10th	Day	7% 4 2 6% 4 5% 4 4 6% 11% 47%	7680
	11th to 20th	Day	6% 5% 2 6% 4 5% 6% 5% 7% 11% 42%	7680
	21st to end	Day	7% 4 2 5% 4 4 4 4 6% 9% 52%	8337
August	1st to 10th	Day	2 1 2 2 2 3 3 4 8% 73%	6014
	11th to 20th	Day	2 1 1 3 3 2 4 3 6% 12% 63%	5948
	21st to end	Day	4 2 1 4 4 4 5% 5% 7% 11% 54%	5731
September	1st to 10th	Day	6% 5% 2 6% 5% 5% 5% 5% 5% 10% 45%	2310
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 8% 46%	2310
	21st to end	Day	5% 3 1 5% 5% 5% 5% 4 6% 9% 51%	2310
October	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 4 6% 55%	3593
	11th to 20th	Day	8% 3 2 5% 3 4 4 3 5% 8% 55%	3358
	21st to end	Day	11% 5% 2 7% 4 4 4 3 4 6% 50%	3696
November	1st to 10th	Day	11% 7% 2 5% 4 3 4 3 4 6% 49%	2158
	11th to 20th	Day	11% 6% 2 5% 4 4 3 3 4 6% 53%	2120
	21st to end	Day	16% 7% 3 7% 4 3 4 3 4 7% 42%	1890
December	1st to 10th	Day	21% 7% 2 4 4 3 3 3 5% 5% 44%	3030
	11th to 20th	Day	19% 7% 3 5% 4 4 4 2 5% 6% 41%	3481
	21st to end	Day	15% 7% 2 6% 3 3 3 3 3 6% 47%	4587
January	1st to 10th	Night	16% 6% 2 5% 3 3 3 2 3 5% 52%	7634
	11th to 20th	Night	11% 5% 1 3 2 2 3 4 5% 5% 59%	7680
	21st to end	Night	28% 7% 2 6% 4 3 3 2 4 5% 36%	8402
February	1st to 10th	Night	19% 7% 2 6% 4 3 3 3 3 4 47%	2592
	11th to 20th	Night	20% 8% 3 5% 3 3 3 2 3 5% 45%	2458
	21st to end	Night	20% 7% 1 4 3 3 2 3 4 5% 47%	1979
March	1st to 10th	Night	17% 7% 2 7% 4 4 3 3 5% 7% 41%	5029
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 4 6% 49%	5090
	21st to end	Night	16% 9% 3 6% 3 3 3 3 4 5% 45%	5588
April	1st to 10th	Night	13% 5% 2 5% 5% 4 4 3 6% 6% 47%	2310
	11th to 20th	Night	13% 6% 3 5% 5% 4 3 3 6% 7% 46%	2175
	21st to end	Night	13% 7% 2 6% 3 3 4 3 5% 7% 46%	2084
May	1st to 10th	Night	19% 10% 3 8% 4 4 4 3 5% 7% 34%	5266
	11th to 20th	Night	12% 6% 3 7% 5% 5% 5% 4 6% 7% 40%	5265
	21st to end	Night	11% 7% 2 7% 5% 5% 6% 5% 6% 10% 37%	5793
June	1st to 10th	Night	7% 4 1 3 3 3 4 4 5% 10% 55%	1890
	11th to 20th	Night	5% 3 1 3 3 3 4 4 5% 9% 60%	1890
	21st to end	Night	4 4 2 5% 4 4 4 3 7% 9% 53%	1890
July	1st to 10th	Night	5% 3 2 5% 3 4 5% 4 7% 12% 50%	5308
	11th to 20th	Night	4 4 2 5% 4 4 4 4 7% 12% 50%	5307
	21st to end	Night	6% 4 2 4 3 3 4 4 5% 9% 57%	5770
August	1st to 10th	Night	1 1 1 1 1 2 2 2 3 8% 78%	4156
	11th to 20th	Night	2 1 1 3 2 3 3 3 5% 12% 66%	4118
	21st to end	Night	2 2 1 3 3 4 4 4 7% 12% 58%	5388
September	1st to 10th	Night	6% 5% 2 5% 4 5% 4 3 6% 8% 51%	2310
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 6% 7% 50%	2310
	21st to end	Night	5% 4 2 6% 4 4 4 3 5% 8% 57%	2310
October	1st to 10th	Night	11% 5% 1 4 2 3 3 2 5% 6% 59%	3773
	11th to 20th	Night	8% 4 1 3 2 3 3 3 4 6% 63%	4040
	21st to end	Night	11% 6% 3 5% 2 3 3 2 5% 6% 54%	4444
November	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 4 7% 55%	2580
	11th to 20th	Night	9% 5% 2 4 4 4 3 3 5% 7% 54%	2545
	21st to end	Night	16% 7% 2 5% 4 3 3 3 4 5% 48%	2725
December	1st to 10th	Night	21% 7% 3 5% 3 3 3 2 4 5% 43%	4380
	11th to 20th	Night	18% 9% 3 6% 3 3 3 2 3 4 45%	4946
	21st to end	Night	16% 6% 2 4 3 3 3 2 3 4 55%	6633

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	39% 3 6% 25% 21% 6%	5290
	11th to 20th	Day	33% 2 5% 19% 29% 12%	5310
	21st to end	Day	54% 2 4 12% 17% 11%	5812
February	1st to 10th	Day	46% 3 5% 14% 21% 11%	2046
	11th to 20th	Day	47% 3 8% 15% 18% 9%	2059
	21st to end	Day	42% 3 6% 18% 18% 13%	1824
March	1st to 10th	Day	44% 3 6% 14% 21% 11%	5046
	11th to 20th	Day	36% 4 7% 12% 18% 23%	5090
	21st to end	Day	43% 5% 8% 20% 18% 6%	5585
April	1st to 10th	Day	45% 4 8% 18% 14% 11%	2310
	11th to 20th	Day	45% 4 9% 16% 17% 9%	2393
	21st to end	Day	41% 5% 8% 19% 21% 6%	2530
May	1st to 10th	Day	49% 6% 9% 21% 13% 2	7655
	11th to 20th	Day	41% 6% 11% 17% 22% 3	7631
	21st to end	Day	43% 8% 13% 24% 11% 2	8405
June	1st to 10th	Day	31% 8% 14% 29% 16% 2	2730
	11th to 20th	Day	30% 7% 15% 28% 17% 4	2730
	21st to end	Day	33% 8% 15% 26% 16% 2	2730
July	1st to 10th	Day	29% 6% 27% 33% 5%	7616
	11th to 20th	Day	34% 8% 22% 24% 12%	7611
	21st to end	Day	28% 6% 14% 36% 16% 1	8155
August	1st to 10th	Day	11% 4 14% 40% 24% 7%	6000
	11th to 20th	Day	15% 5% 25% 41% 12% 2	5987
	21st to end	Day	23% 9% 15% 32% 20% 1	5730
September	1st to 10th	Day	33% 7% 13% 21% 18% 8%	2310
	11th to 20th	Day	34% 8% 14% 22% 17% 5%	2310
	21st to end	Day	29% 5% 12% 23% 18% 14%	2310
October	1st to 10th	Day	24% 2 5% 10% 24% 35%	4930
	11th to 20th	Day	20% 3 6% 17% 34% 19%	4600
	21st to end	Day	31% 3 5% 23% 28% 10%	5032
November	1st to 10th	Day	36% 4 7% 19% 23% 11%	2158
	11th to 20th	Day	33% 4 8% 19% 22% 15%	2120
	21st to end	Day	43% 3 7% 17% 20% 10%	1890
December	1st to 10th	Day	44% 2 7% 17% 22% 8%	3030
	11th to 20th	Day	45% 3 6% 12% 23% 11%	3479
	21st to end	Day	40% 3 5% 14% 28% 9%	4587
January	1st to 10th	Night	37% 3 6% 21% 23% 10%	7635
	11th to 20th	Night	28% 2 5% 17% 32% 16%	7680
	21st to end	Night	53% 2 3 12% 17% 12%	8402
February	1st to 10th	Night	43% 3 5% 13% 21% 16%	2592
	11th to 20th	Night	43% 3 7% 16% 19% 13%	2458
	21st to end	Night	41% 3 7% 14% 18% 16%	1979
March	1st to 10th	Night	44% 4 6% 13% 21% 12%	5029
	11th to 20th	Night	39% 3 6% 15% 14% 22%	5090
	21st to end	Night	44% 4 7% 17% 20% 9%	5588
April	1st to 10th	Night	38% 5% 9% 19% 17% 12%	2310
	11th to 20th	Night	38% 4 10% 17% 17% 13%	2175
	21st to end	Night	38% 4 10% 19% 22% 6%	2084
May	1st to 10th	Night	50% 5% 10% 20% 12% 3	5293
	11th to 20th	Night	41% 7% 11% 17% 20% 4	5266
	21st to end	Night	40% 8% 17% 24% 9% 2	5805
June	1st to 10th	Night	24% 6% 18% 30% 20% 2	1890
	11th to 20th	Night	20% 6% 18% 32% 20% 5%	1890
	21st to end	Night	27% 6% 17% 30% 19% 2	1890
July	1st to 10th	Night	27% 7% 27% 35% 4	5265
	11th to 20th	Night	28% 7% 25% 30% 10%	5256
	21st to end	Night	25% 6% 16% 34% 17% 2	5641
August	1st to 10th	Night	8% 3 16% 40% 26% 7%	4146
	11th to 20th	Night	14% 6% 25% 42% 12% 2	4145
	21st to end	Night	19% 9% 18% 32% 19% 2	5388
September	1st to 10th	Night	29% 7% 18% 21% 16% 9%	2310
	11th to 20th	Night	33% 6% 16% 22% 17% 6%	2310
	21st to end	Night	25% 5% 13% 24% 19% 13%	2310
October	1st to 10th	Night	21% 3 7% 12% 22% 35%	5202
	11th to 20th	Night	17% 2 4 19% 35% 23%	5539
	21st to end	Night	27% 2 5% 21% 30% 14%	6056
November	1st to 10th	Night	31% 3 9% 21% 24% 12%	2580
	11th to 20th	Night	30% 4 8% 21% 22% 15%	2545
	21st to end	Night	40% 3 8% 17% 20% 13%	2725
December	1st to 10th	Night	45% 2 5% 18% 22% 8%	4380
	11th to 20th	Night	44% 3 6% 9% 23% 14%	4947
	21st to end	Night	36% 3 4 16% 29% 13%	6633

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	21% 10% 35% 23% 9% 2	330
	11th to 20th	Day	20% 11% 33% 26% 9% 1	330
	21st to end	Day	25% 11% 38% 20% 7%	363
February	1st to 10th	Day	25% 12% 32% 23% 8%	330
	11th to 20th	Day	25% 17% 33% 18% 6%	330
	21st to end	Day	26% 12% 41% 15% 4 1	273
March	1st to 10th	Day	21% 14% 34% 25% 6%	330
	11th to 20th	Day	15% 18% 37% 21% 7% 2	330
	21st to end	Day	15% 12% 37% 25% 10% 2	363
April	1st to 10th	Day	22% 13% 34% 24% 8%	330
	11th to 20th	Day	23% 12% 34% 21% 9% 1	431
	21st to end	Day	20% 9% 31% 29% 9% 2	550
May	1st to 10th	Day	17% 8% 36% 29% 8% 1	753
	11th to 20th	Day	15% 7% 26% 30% 18% 4	775
	21st to end	Day	11% 5% 23% 36% 20% 5%	844
June	1st to 10th	Day	7% 2 12% 36% 32% 10%	780
	11th to 20th	Day	8% 2 13% 40% 29% 8%	780
	21st to end	Day	7% 2 8% 32% 36% 15%	780
July	1st to 10th	Day	8% 2 5% 26% 39% 20%	771
	11th to 20th	Day	4 2 4 27% 41% 22%	768
	21st to end	Day	5% 2 3 25% 45% 20%	849
August	1st to 10th	Day	4 1 1 21% 49% 24%	776
	11th to 20th	Day	6% 1 2 23% 47% 20%	765
	21st to end	Day	8% 2 3 14% 39% 34%	473
September	1st to 10th	Day	5% 1 4 22% 36% 32%	360
	11th to 20th	Day	6% 2 3 19% 41% 29%	360
	21st to end	Day	6% 2 8% 26% 36% 23%	360
October	1st to 10th	Day	6% 1 10% 33% 35% 15%	360
	11th to 20th	Day	8% 3 20% 35% 24% 10%	360
	21st to end	Day	20% 7% 21% 24% 20% 8%	396
November	1st to 10th	Day	15% 7% 21% 31% 20% 6%	360
	11th to 20th	Day	18% 5% 24% 31% 18% 4	336
	21st to end	Day	19% 13% 31% 23% 12% 2	330
December	1st to 10th	Day	22% 7% 30% 23% 12% 6%	330
	11th to 20th	Day	25% 9% 29% 26% 8% 2	330
	21st to end	Day	20% 9% 34% 25% 10% 1	363
January	1st to 10th	Night	20% 9% 35% 30% 7%	1050
	11th to 20th	Night	20% 11% 32% 29% 8%	1050
	21st to end	Night	21% 10% 32% 31% 6%	1155
February	1st to 10th	Night	23% 11% 35% 26% 4	912
	11th to 20th	Night	26% 10% 33% 27% 3	824
	21st to end	Night	26% 10% 42% 19% 3	595
March	1st to 10th	Night	23% 10% 39% 24% 5%	630
	11th to 20th	Night	16% 10% 40% 28% 7%	630
	21st to end	Night	14% 9% 44% 27% 5%	693
April	1st to 10th	Night	15% 8% 44% 28% 5%	630
	11th to 20th	Night	16% 10% 39% 30% 6%	623
	21st to end	Night	15% 10% 39% 27% 9%	630
May	1st to 10th	Night	13% 8% 42% 31% 6%	630
	11th to 20th	Night	13% 8% 30% 35% 13% 1	621
	21st to end	Night	8% 3 30% 42% 16% 2	683
June	1st to 10th	Night	9% 1 16% 45% 27% 2	630
	11th to 20th	Night	5% 2 21% 50% 20% 2	630
	21st to end	Night	4 2 12% 46% 33% 4	630
July	1st to 10th	Night	4 2 7% 44% 37% 6%	615
	11th to 20th	Night	4 1 5% 49% 38% 3	612
	21st to end	Night	5% 1 6% 48% 38% 4	690
August	1st to 10th	Night	2 1 4 48% 41% 4	627
	11th to 20th	Night	6% 2 50% 37% 4	624
	21st to end	Night	3 2 5% 37% 46% 7%	693
September	1st to 10th	Night	7% 2 7% 36% 41% 7%	630
	11th to 20th	Night	10% 2 5% 34% 44% 5%	630
	21st to end	Night	6% 2 10% 41% 36% 5%	630
October	1st to 10th	Night	6% 1 10% 48% 29% 5%	677
	11th to 20th	Night	11% 5% 20% 42% 21% 2	840
	21st to end	Night	13% 6% 26% 35% 18% 2	924
November	1st to 10th	Night	13% 3 24% 39% 20% 1	860
	11th to 20th	Night	12% 7% 26% 40% 15% 1	849
	21st to end	Night	19% 9% 29% 29% 14% 1	1045
December	1st to 10th	Night	21% 6% 30% 32% 10%	1050
	11th to 20th	Night	23% 9% 26% 35% 7%	1050
	21st to end	Night	20% 8% 30% 33% 8%	1155

Page generated at 2026-11-10 02:55:17. Version ac07

Copyright © 2026 Attilla Danko.