Stardom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stardom Observatory clear sky chart from 2005-11-06 to 2025-05-11.

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	15% 7% 2 6% 4 4 4 4 6% 7% 41%	113705
	Night	16% 7% 2 6% 4 4 4 3 5% 6% 44%	115205
Transparency	Day	41% 5% 11% 23% 17% 3	117294
	Night	40% 4 11% 23% 18% 4	119780
Seeing	Day	22% 16% 29% 21% 10% 3	15633
	Night	19% 14% 31% 26% 9% 1	25001

By Month

Percentage Cloud Cover NE (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	13% 7% 2 4 3 3 3 3 4 6% 52%	3597
	11th to 20th	Day	14% 8% 3 8% 4 4 4 3 4 5% 43%	3598
	21st to end	Day	19% 8% 3 6% 4 3 3 2 4 5% 42%	4466
February	1st to 10th	Day	15% 8% 2 7% 5% 5% 4 3 6% 6% 40%	1800
	11th to 20th	Day	18% 7% 2 6% 4 4 4 3 5% 6% 41%	1934
	21st to end	Day	17% 8% 3 6% 5% 4 3 3 5% 5% 40%	1650
March	1st to 10th	Day	21% 6% 2 4 3 3 3 3 4 5% 46%	4476
	11th to 20th	Day	11% 7% 2 6% 4 5% 4 4 5% 6% 45%	4906
	21st to end	Day	18% 5% 2 5% 4 4 4 3 5% 6% 43%	5848
April	1st to 10th	Day	17% 8% 3 5% 4 4 5% 3 6% 6% 40%	2400
	11th to 20th	Day	15% 6% 2 5% 4 5% 4 4 5% 7% 42%	2374
	21st to end	Day	16% 6% 2 6% 4 4 4 5% 7% 7% 40%	2400
May	1st to 10th	Day	26% 9% 3 6% 4 5% 4 3 5% 8% 29%	4161
	11th to 20th	Day	24% 8% 3 7% 5% 5% 4 3 5% 6% 30%	4394
	21st to end	Day	12% 6% 2 5% 4 4 5% 4 5% 9% 44%	4837
June	1st to 10th	Day	13% 5% 2 5% 6% 5% 5% 4 7% 9% 39%	2660
	11th to 20th	Day	11% 7% 2 6% 6% 5% 5% 4 7% 8% 39%	2660
	21st to end	Day	10% 5% 2 7% 4 5% 6% 4 6% 9% 41%	2660
July	1st to 10th	Day	8% 5% 3 7% 6% 6% 8% 6% 9% 10% 34%	4440
	11th to 20th	Day	11% 6% 2 6% 4 5% 6% 5% 8% 10% 37%	4440
	21st to end	Day	11% 9% 3 8% 6% 5% 7% 4 7% 8% 32%	4793
August	1st to 10th	Day	18% 6% 3 7% 5% 5% 5% 5% 7% 7% 31%	4052
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 5% 7% 9% 39%	3730
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 44%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 3 5% 7% 44%	2280
	11th to 20th	Day	12% 6% 1 5% 4 3 4 4 5% 7% 50%	2228
	21st to end	Day	18% 7% 3 7% 4 3 4 4 5% 6% 39%	2090
October	1st to 10th	Day	18% 6% 2 6% 3 4 4 3 5% 6% 45%	1938
	11th to 20th	Day	15% 5% 2 5% 3 3 3 3 4 6% 51%	1900
	21st to end	Day	17% 5% 3 6% 3 2 4 2 5% 6% 47%	1996
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 2 4 7% 52%	1761
	11th to 20th	Day	15% 6% 2 6% 3 3 4 3 5% 5% 48%	1800
	21st to end	Day	15% 5% 2 5% 5% 4 4 2 5% 7% 47%	1710
December	1st to 10th	Day	13% 7% 2 5% 4 3 3 3 6% 8% 45%	2600
	11th to 20th	Day	20% 9% 3 4 3 2 3 2 3 5% 45%	2986
	21st to end	Day	16% 6% 2 5% 4 4 5% 5% 6% 7% 41%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 4 6% 51%	6349
	11th to 20th	Night	15% 7% 2 6% 3 3 3 3 4 5% 49%	6269
	21st to end	Night	18% 8% 3 6% 4 3 4 3 4 6% 42%	6490
February	1st to 10th	Night	17% 8% 2 6% 4 4 4 3 5% 6% 41%	2600
	11th to 20th	Night	19% 8% 2 6% 4 3 3 3 5% 6% 42%	2350
	21st to end	Night	18% 8% 2 6% 4 3 3 4 5% 5% 42%	1980
March	1st to 10th	Night	19% 9% 2 5% 3 3 3 3 4 5% 45%	5364
	11th to 20th	Night	12% 9% 3 5% 3 3 3 3 4 6% 49%	5037
	21st to end	Night	16% 8% 3 6% 4 3 4 3 4 5% 43%	5083
April	1st to 10th	Night	17% 8% 2 7% 4 4 4 3 5% 5% 41%	2000
	11th to 20th	Night	16% 6% 3 6% 4 4 4 3 4 6% 42%	1975
	21st to end	Night	17% 6% 2 5% 3 4 4 3 5% 7% 45%	2000
May	1st to 10th	Night	22% 9% 4 8% 3 4 3 4 5% 8% 30%	2996
	11th to 20th	Night	24% 9% 3 7% 5% 4 4 3 4 6% 31%	2534
	21st to end	Night	14% 7% 2 5% 4 4 4 3 6% 10% 41%	2738
June	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 6% 8% 43%	1520
	11th to 20th	Night	10% 7% 2 6% 6% 5% 4 4 6% 6% 44%	1520
	21st to end	Night	8% 5% 2 4 5% 6% 5% 5% 8% 10% 41%	1520
July	1st to 10th	Night	8% 5% 3 7% 5% 6% 6% 5% 9% 10% 36%	2520
	11th to 20th	Night	11% 6% 2 6% 3 5% 5% 6% 7% 11% 38%	2520
	21st to end	Night	15% 7% 3 7% 4 5% 5% 4 6% 7% 35%	2756
August	1st to 10th	Night	22% 6% 2 7% 4 5% 5% 4 7% 8% 32%	2844
	11th to 20th	Night	12% 6% 2 7% 4 5% 4 3 6% 8% 42%	3097
	21st to end	Night	9% 6% 2 5% 4 3 4 4 6% 7% 50%	3476
September	1st to 10th	Night	14% 6% 2 5% 5% 5% 4 4 4 6% 45%	1900
	11th to 20th	Night	10% 6% 2 4 3 3 4 3 5% 8% 52%	1952
	21st to end	Night	18% 7% 2 6% 4 3 3 3 5% 7% 40%	2090
October	1st to 10th	Night	18% 6% 2 5% 4 4 3 3 5% 6% 44%	2237
	11th to 20th	Night	14% 5% 2 4 4 3 3 3 4 6% 52%	2280
	21st to end	Night	17% 6% 2 5% 4 3 3 3 5% 5% 47%	2599
November	1st to 10th	Night	11% 5% 2 5% 4 4 3 3 4 6% 53%	2537
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 4 4 48%	2600
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 7% 45%	2688
December	1st to 10th	Night	14% 7% 2 5% 3 3 3 3 5% 6% 48%	4580
	11th to 20th	Night	23% 7% 2 5% 3 3 3 3 5% 6% 41%	5208
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 6% 41%	6996

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	35% 3 8% 27% 23% 3	3598
	11th to 20th	Day	44% 3 7% 23% 17% 5%	3628
	21st to end	Day	46% 3 11% 24% 14% 2	4466
February	1st to 10th	Day	45% 4 11% 26% 12% 2	1800
	11th to 20th	Day	46% 4 9% 24% 15% 2	1943
	21st to end	Day	46% 3 8% 23% 15% 4	1650
March	1st to 10th	Day	43% 3 7% 24% 16% 7%	4479
	11th to 20th	Day	38% 3 8% 29% 16% 5%	4906
	21st to end	Day	42% 4 8% 17% 23% 6%	5848
April	1st to 10th	Day	44% 6% 9% 21% 15% 5%	2400
	11th to 20th	Day	40% 5% 12% 23% 17% 4	2374
	21st to end	Day	42% 5% 9% 20% 20% 4	2400
May	1st to 10th	Day	55% 6% 10% 18% 10% 2	4175
	11th to 20th	Day	54% 6% 11% 20% 8% 1	4398
	21st to end	Day	35% 8% 11% 27% 17% 2	4837
June	1st to 10th	Day	40% 8% 11% 24% 16% 2	2660
	11th to 20th	Day	40% 8% 12% 25% 13% 3	2660
	21st to end	Day	38% 7% 12% 23% 17% 2	2660
July	1st to 10th	Day	42% 9% 15% 18% 13% 2	4370
	11th to 20th	Day	41% 7% 16% 21% 14% 1	4365
	21st to end	Day	48% 7% 10% 18% 15% 1	4640
August	1st to 10th	Day	50% 6% 13% 21% 10% 1	4039
	11th to 20th	Day	40% 7% 12% 25% 14% 1	3766
	21st to end	Day	35% 6% 11% 27% 19% 2	4180
September	1st to 10th	Day	40% 6% 10% 19% 22% 3	2280
	11th to 20th	Day	34% 5% 9% 23% 25% 4	2228
	21st to end	Day	47% 5% 7% 19% 21% 2	2090
October	1st to 10th	Day	37% 3 9% 17% 29% 5%	3224
	11th to 20th	Day	25% 3 9% 24% 31% 8%	3140
	21st to end	Day	26% 3 11% 27% 28% 6%	3273
November	1st to 10th	Day	34% 3 12% 27% 22% 3	1761
	11th to 20th	Day	39% 3 8% 25% 22% 3	1800
	21st to end	Day	39% 4 12% 31% 13% 2	1710
December	1st to 10th	Day	39% 3 16% 26% 15% 2	2600
	11th to 20th	Day	45% 2 10% 30% 10% 3	2986
	21st to end	Day	41% 5% 11% 22% 18% 2	3960
January	1st to 10th	Night	35% 3 8% 25% 22% 7%	6349
	11th to 20th	Night	39% 3 9% 25% 18% 7%	6314
	21st to end	Night	44% 3 8% 24% 19% 2	6490
February	1st to 10th	Night	45% 3 13% 24% 13% 2	2600
	11th to 20th	Night	44% 5% 8% 21% 18% 5%	2352
	21st to end	Night	44% 4 7% 22% 17% 5%	1980
March	1st to 10th	Night	43% 3 7% 24% 13% 10%	5374
	11th to 20th	Night	39% 4 12% 26% 15% 5%	5038
	21st to end	Night	44% 4 7% 17% 24% 5%	5083
April	1st to 10th	Night	45% 5% 9% 19% 18% 4	2000
	11th to 20th	Night	43% 4 9% 21% 20% 4	1975
	21st to end	Night	39% 6% 9% 20% 21% 5%	2000
May	1st to 10th	Night	53% 6% 10% 19% 11% 1	3002
	11th to 20th	Night	54% 6% 13% 15% 10% 2	2535
	21st to end	Night	38% 7% 14% 22% 17% 2	2739
June	1st to 10th	Night	39% 7% 11% 22% 19% 2	1520
	11th to 20th	Night	39% 8% 12% 27% 13% 2	1520
	21st to end	Night	35% 8% 15% 24% 16% 2	1520
July	1st to 10th	Night	42% 9% 19% 18% 11% 2	2480
	11th to 20th	Night	38% 7% 18% 25% 10% 1	2472
	21st to end	Night	46% 6% 14% 19% 14% 1	2668
August	1st to 10th	Night	49% 6% 18% 17% 9% 1	2833
	11th to 20th	Night	40% 5% 12% 29% 13% 1	3127
	21st to end	Night	32% 5% 11% 28% 22% 2	3476
September	1st to 10th	Night	38% 7% 11% 20% 21% 3	1900
	11th to 20th	Night	31% 4 11% 24% 26% 4	1952
	21st to end	Night	43% 6% 8% 22% 20% 2	2090
October	1st to 10th	Night	38% 4 10% 23% 22% 2	3731
	11th to 20th	Night	24% 3 9% 27% 30% 6%	3779
	21st to end	Night	27% 3 10% 31% 25% 4	4272
November	1st to 10th	Night	33% 4 11% 25% 22% 5%	2537
	11th to 20th	Night	40% 4 8% 23% 21% 5%	2600
	21st to end	Night	38% 5% 12% 26% 17% 2	2688
December	1st to 10th	Night	38% 3 12% 30% 15% 3	4580
	11th to 20th	Night	45% 3 11% 24% 14% 4	5208
	21st to end	Night	45% 4 10% 20% 18% 3	6996

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	29% 26% 28% 14% 3 1	200
	11th to 20th	Day	38% 26% 24% 12% 1	207
	21st to end	Day	31% 26% 26% 14% 3 1	330
February	1st to 10th	Day	29% 30% 27% 11% 2	300
	11th to 20th	Day	36% 24% 30% 8% 1	482
	21st to end	Day	31% 23% 32% 12% 2	414
March	1st to 10th	Day	30% 22% 29% 15% 3	500
	11th to 20th	Day	27% 23% 33% 12% 3 1	500
	21st to end	Day	27% 25% 30% 14% 4 1	550
April	1st to 10th	Day	30% 25% 29% 11% 4 1	500
	11th to 20th	Day	25% 21% 33% 14% 5% 1	492
	21st to end	Day	29% 18% 32% 15% 5% 2	500
May	1st to 10th	Day	32% 19% 26% 15% 7% 1	503
	11th to 20th	Day	23% 15% 34% 20% 7% 2	487
	21st to end	Day	19% 11% 24% 29% 14% 4	529
June	1st to 10th	Day	16% 13% 32% 25% 12% 3	490
	11th to 20th	Day	15% 13% 30% 27% 11% 3	490
	21st to end	Day	12% 10% 32% 30% 12% 3	490
July	1st to 10th	Day	12% 6% 28% 29% 20% 6%	485
	11th to 20th	Day	8% 5% 29% 33% 21% 5%	484
	21st to end	Day	13% 7% 30% 30% 14% 5%	532
August	1st to 10th	Day	13% 6% 28% 31% 15% 7%	486
	11th to 20th	Day	13% 4 25% 32% 20% 5%	479
	21st to end	Day	13% 6% 29% 27% 17% 9%	539
September	1st to 10th	Day	16% 10% 26% 25% 16% 8%	490
	11th to 20th	Day	14% 8% 26% 30% 14% 9%	490
	21st to end	Day	27% 12% 24% 21% 11% 4	490
October	1st to 10th	Day	25% 10% 27% 20% 13% 6%	490
	11th to 20th	Day	20% 16% 28% 21% 11% 3	490
	21st to end	Day	19% 17% 34% 18% 11% 2	489
November	1st to 10th	Day	18% 14% 35% 19% 13% 1	395
	11th to 20th	Day	24% 20% 31% 18% 7%	400
	21st to end	Day	23% 21% 30% 19% 6% 1	310
December	1st to 10th	Day	26% 31% 29% 9% 6%	200
	11th to 20th	Day	37% 17% 32% 12% 3 1	200
	21st to end	Day	30% 18% 29% 17% 5% 1	220
January	1st to 10th	Night	22% 23% 34% 19% 3	800
	11th to 20th	Night	26% 19% 30% 21% 4	800
	21st to end	Night	19% 21% 37% 21% 2	880
February	1st to 10th	Night	22% 19% 36% 22% 2	800
	11th to 20th	Night	27% 25% 33% 14% 1	783
	21st to end	Night	26% 20% 34% 18% 2	660
March	1st to 10th	Night	24% 21% 32% 19% 4	800
	11th to 20th	Night	22% 23% 32% 17% 6%	800
	21st to end	Night	22% 16% 39% 18% 4	880
April	1st to 10th	Night	22% 23% 35% 16% 4	800
	11th to 20th	Night	21% 15% 37% 21% 5%	791
	21st to end	Night	21% 15% 34% 25% 5%	800
May	1st to 10th	Night	22% 14% 35% 24% 6%	646
	11th to 20th	Night	17% 14% 38% 26% 5%	396
	21st to end	Night	17% 7% 24% 40% 10% 2	411
June	1st to 10th	Night	17% 6% 31% 36% 10%	380
	11th to 20th	Night	12% 5% 29% 41% 12%	380
	21st to end	Night	10% 4 30% 45% 10% 1	380
July	1st to 10th	Night	10% 2 27% 43% 16% 2	370
	11th to 20th	Night	7% 3 23% 48% 17% 2	368
	21st to end	Night	11% 5% 27% 40% 16%	421
August	1st to 10th	Night	12% 3 19% 43% 21% 2	573
	11th to 20th	Night	13% 4 20% 40% 20% 3	750
	21st to end	Night	14% 3 20% 39% 22% 3	836
September	1st to 10th	Night	16% 5% 27% 34% 16% 2	760
	11th to 20th	Night	14% 4 23% 33% 23% 4	760
	21st to end	Night	23% 6% 25% 28% 17% 1	760
October	1st to 10th	Night	22% 7% 27% 27% 16% 3	760
	11th to 20th	Night	17% 11% 28% 30% 13% 1	760
	21st to end	Night	21% 12% 35% 23% 10%	836
November	1st to 10th	Night	15% 11% 35% 27% 10% 1	780
	11th to 20th	Night	20% 16% 29% 26% 9%	800
	21st to end	Night	18% 17% 36% 21% 7% 1	800
December	1st to 10th	Night	25% 17% 32% 19% 6% 1	800
	11th to 20th	Night	22% 18% 33% 23% 5%	800
	21st to end	Night	22% 16% 33% 26% 3	880

Page generated at 2025-05-08 09:33:54. Version ac07

Copyright © 2025 Attilla Danko.