Stella Nova Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stella Nova Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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% 6% 2 6% 4 4 4 4 6% 8% 40%	127216
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 42%	123823
Transparency	Day	40% 7% 12% 23% 16% 3	130805
	Night	40% 6% 11% 23% 17% 3	128304
Seeing	Day	19% 11% 27% 23% 14% 5%	16346
	Night	18% 9% 29% 31% 12% 1	25749

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	13% 7% 2 6% 4 4 4 4 5% 6% 46%	3597
	11th to 20th	Day	13% 9% 4 10% 5% 5% 4 2 4 5% 40%	3899
	21st to end	Day	16% 7% 3 8% 4 5% 5% 3 5% 5% 39%	4466
February	1st to 10th	Day	14% 10% 3 6% 5% 4 4 4 6% 8% 38%	1800
	11th to 20th	Day	16% 8% 3 5% 5% 4 4 3 6% 7% 39%	1840
	21st to end	Day	18% 11% 3 6% 4 4 3 2 4 5% 39%	1650
March	1st to 10th	Day	20% 5% 1 5% 3 4 4 3 4 6% 45%	4680
	11th to 20th	Day	11% 6% 3 7% 4 5% 4 4 5% 7% 44%	4980
	21st to end	Day	17% 7% 2 5% 4 5% 4 3 5% 5% 42%	5666
April	1st to 10th	Day	15% 8% 2 6% 5% 4 5% 4 5% 7% 39%	2400
	11th to 20th	Day	14% 7% 2 5% 5% 3 5% 4 6% 7% 43%	2374
	21st to end	Day	17% 6% 2 5% 4 4 4 4 6% 7% 41%	2400
May	1st to 10th	Day	25% 7% 2 6% 4 4 4 4 6% 8% 31%	5788
	11th to 20th	Day	25% 7% 2 7% 4 4 4 3 6% 8% 31%	6318
	21st to end	Day	17% 6% 2 6% 4 4 5% 4 6% 9% 38%	6934
June	1st to 10th	Day	13% 5% 2 5% 5% 5% 5% 4 7% 9% 40%	2800
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 9% 38%	2800
	21st to end	Day	10% 4 2 5% 5% 5% 5% 5% 6% 11% 43%	2800
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 5% 6% 11% 41%	6360
	11th to 20th	Day	10% 7% 3 8% 6% 6% 7% 5% 8% 11% 31%	6360
	21st to end	Day	9% 7% 2 6% 5% 6% 5% 5% 7% 9% 40%	6566
August	1st to 10th	Day	18% 5% 2 6% 5% 6% 6% 4 6% 8% 34%	4234
	11th to 20th	Day	12% 5% 3 6% 4 5% 5% 4 7% 9% 40%	3952
	21st to end	Day	11% 5% 2 5% 4 4 4 4 5% 7% 49%	4312
September	1st to 10th	Day	15% 6% 3 5% 4 4 4 3 4 7% 45%	2400
	11th to 20th	Day	14% 5% 2 4 3 4 4 2 5% 8% 49%	2400
	21st to end	Day	20% 7% 2 6% 4 4 4 4 5% 7% 37%	2131
October	1st to 10th	Day	17% 6% 2 4 4 3 3 4 5% 7% 45%	2000
	11th to 20th	Day	17% 5% 3 4 4 4 4 3 4 6% 46%	2000
	21st to end	Day	16% 6% 2 5% 3 3 4 4 6% 6% 46%	2200
November	1st to 10th	Day	12% 6% 2 5% 4 3 3 3 4 8% 51%	1856
	11th to 20th	Day	15% 6% 2 4 4 3 4 4 5% 6% 47%	1887
	21st to end	Day	15% 7% 2 6% 4 4 5% 3 5% 6% 44%	1680
December	1st to 10th	Day	13% 6% 2 7% 4 5% 4 3 5% 6% 44%	2680
	11th to 20th	Day	19% 10% 2 4 3 3 3 2 6% 7% 40%	3046
	21st to end	Day	15% 8% 3 8% 5% 5% 5% 4 6% 6% 36%	3960
January	1st to 10th	Night	12% 7% 2 6% 4 4 4 4 5% 7% 44%	6349
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 4 6% 48%	6057
	21st to end	Night	16% 8% 3 6% 4 3 3 3 4 5% 44%	6490
February	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 5% 6% 40%	2600
	11th to 20th	Night	17% 8% 2 6% 4 4 4 3 5% 5% 41%	2444
	21st to end	Night	16% 9% 3 6% 4 5% 4 3 4 6% 40%	1980
March	1st to 10th	Night	17% 8% 2 5% 4 3 3 3 4 5% 45%	5158
	11th to 20th	Night	10% 7% 3 5% 3 3 3 3 4 6% 52%	4980
	21st to end	Night	14% 8% 2 7% 4 4 4 3 4 5% 45%	5266
April	1st to 10th	Night	18% 8% 3 6% 4 4 4 3 6% 6% 38%	2000
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 6% 7% 43%	1975
	21st to end	Night	19% 6% 2 5% 4 2 3 4 5% 7% 44%	2000
May	1st to 10th	Night	23% 8% 2 6% 5% 4 5% 4 5% 8% 30%	4135
	11th to 20th	Night	24% 8% 3 6% 5% 3 3 3 5% 8% 31%	3575
	21st to end	Night	20% 6% 2 6% 4 4 4 3 6% 8% 38%	3920
June	1st to 10th	Night	13% 5% 2 4 4 4 3 6% 6% 8% 44%	1600
	11th to 20th	Night	13% 4 2 6% 5% 5% 5% 4 6% 10% 39%	1600
	21st to end	Night	11% 5% 2 5% 5% 3 6% 5% 7% 10% 43%	1600
July	1st to 10th	Night	8% 6% 3 7% 5% 5% 6% 5% 8% 9% 39%	3598
	11th to 20th	Night	10% 7% 3 8% 6% 6% 7% 5% 8% 9% 30%	3597
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 43%	4280
August	1st to 10th	Night	19% 5% 3 6% 4 5% 4 4 6% 8% 36%	2915
	11th to 20th	Night	12% 8% 2 7% 4 4 5% 4 6% 7% 41%	3062
	21st to end	Night	12% 6% 2 5% 4 3 5% 3 6% 7% 48%	3586
September	1st to 10th	Night	13% 6% 3 6% 4 4 3 4 5% 6% 48%	2000
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 7% 51%	2000
	21st to end	Night	20% 7% 2 5% 4 4 4 3 4 6% 39%	2264
October	1st to 10th	Night	19% 7% 3 5% 3 4 3 3 4 6% 44%	2400
	11th to 20th	Night	16% 5% 2 5% 3 3 4 3 4 6% 50%	2400
	21st to end	Night	17% 5% 2 4 3 3 4 3 5% 6% 49%	2640
November	1st to 10th	Night	11% 4 1 5% 4 4 4 4 4 6% 54%	2662
	11th to 20th	Night	15% 7% 2 5% 4 3 3 3 5% 5% 47%	2730
	21st to end	Night	13% 5% 2 6% 5% 4 4 4 5% 7% 45%	2940
December	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 6% 7% 45%	4720
	11th to 20th	Night	21% 7% 2 5% 3 4 4 3 5% 7% 40%	5304
	21st to end	Night	17% 8% 3 6% 4 5% 5% 4 5% 7% 36%	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	36% 6% 12% 25% 18% 3	3598
	11th to 20th	Day	46% 5% 8% 20% 16% 5%	3899
	21st to end	Day	45% 7% 10% 23% 14% 1	4466
February	1st to 10th	Day	44% 6% 13% 24% 11% 2	1800
	11th to 20th	Day	44% 5% 10% 24% 14% 2	1849
	21st to end	Day	48% 4 9% 21% 14% 4	1650
March	1st to 10th	Day	39% 5% 10% 24% 15% 6%	4680
	11th to 20th	Day	37% 6% 12% 26% 14% 5%	4980
	21st to end	Day	43% 6% 8% 18% 20% 5%	5666
April	1st to 10th	Day	43% 7% 11% 19% 16% 4	2400
	11th to 20th	Day	38% 8% 11% 22% 17% 4	2374
	21st to end	Day	40% 6% 11% 21% 18% 4	2400
May	1st to 10th	Day	50% 8% 12% 19% 10% 2	5821
	11th to 20th	Day	49% 7% 11% 22% 10% 1	6322
	21st to end	Day	41% 8% 13% 23% 15% 1	6949
June	1st to 10th	Day	38% 9% 13% 22% 16% 2	2800
	11th to 20th	Day	40% 9% 13% 23% 12% 3	2800
	21st to end	Day	34% 10% 15% 25% 16% 1	2800
July	1st to 10th	Day	35% 11% 15% 21% 16% 2	6290
	11th to 20th	Day	43% 11% 16% 21% 9% 1	6285
	21st to end	Day	37% 8% 10% 22% 21% 1	6378
August	1st to 10th	Day	46% 8% 12% 24% 10%	4221
	11th to 20th	Day	37% 8% 12% 28% 14% 1	3991
	21st to end	Day	32% 7% 11% 29% 19% 2	4312
September	1st to 10th	Day	39% 5% 11% 20% 20% 4	2400
	11th to 20th	Day	34% 5% 11% 26% 21% 4	2400
	21st to end	Day	46% 7% 8% 18% 18% 2	2131
October	1st to 10th	Day	35% 5% 9% 19% 27% 5%	3260
	11th to 20th	Day	28% 5% 11% 26% 22% 8%	3240
	21st to end	Day	24% 4 12% 29% 28% 4	3538
November	1st to 10th	Day	32% 5% 14% 24% 22% 4	1856
	11th to 20th	Day	37% 6% 11% 24% 20% 3	1887
	21st to end	Day	41% 5% 12% 29% 11% 2	1680
December	1st to 10th	Day	41% 5% 16% 25% 11% 2	2680
	11th to 20th	Day	44% 4 13% 29% 9% 1	3042
	21st to end	Day	45% 7% 15% 19% 13% 1	3960
January	1st to 10th	Night	37% 6% 11% 25% 17% 4	6349
	11th to 20th	Night	37% 4 12% 23% 17% 6%	6057
	21st to end	Night	41% 4 10% 26% 17% 2	6490
February	1st to 10th	Night	45% 5% 13% 24% 12% 1	2600
	11th to 20th	Night	44% 4 10% 21% 18% 3	2446
	21st to end	Night	45% 6% 9% 20% 15% 4	1980
March	1st to 10th	Night	41% 5% 9% 25% 12% 8%	5158
	11th to 20th	Night	32% 6% 13% 30% 13% 6%	4980
	21st to end	Night	41% 5% 8% 18% 25% 3	5266
April	1st to 10th	Night	44% 6% 10% 19% 17% 4	2000
	11th to 20th	Night	38% 7% 11% 20% 20% 4	1975
	21st to end	Night	39% 7% 10% 21% 18% 5%	2000
May	1st to 10th	Night	52% 8% 10% 16% 12% 3	4165
	11th to 20th	Night	50% 8% 11% 19% 11% 1	3576
	21st to end	Night	43% 8% 11% 23% 12% 3	3927
June	1st to 10th	Night	36% 9% 11% 23% 19% 2	1600
	11th to 20th	Night	38% 10% 13% 23% 15% 1	1600
	21st to end	Night	34% 8% 14% 25% 16% 2	1600
July	1st to 10th	Night	39% 11% 14% 18% 14% 4	3560
	11th to 20th	Night	45% 12% 15% 18% 9% 1	3552
	21st to end	Night	36% 9% 12% 23% 20% 1	4154
August	1st to 10th	Night	45% 8% 17% 21% 9% 1	2904
	11th to 20th	Night	40% 7% 11% 27% 14% 1	3089
	21st to end	Night	34% 8% 11% 29% 17% 2	3586
September	1st to 10th	Night	37% 8% 10% 22% 21% 4	2000
	11th to 20th	Night	33% 5% 10% 24% 24% 3	2000
	21st to end	Night	45% 6% 10% 18% 18% 3	2264
October	1st to 10th	Night	42% 6% 9% 20% 22% 2	3920
	11th to 20th	Night	26% 5% 10% 27% 27% 5%	3899
	21st to end	Night	25% 4 11% 32% 24% 4	4252
November	1st to 10th	Night	32% 5% 13% 25% 22% 5%	2662
	11th to 20th	Night	39% 4 9% 23% 19% 5%	2730
	21st to end	Night	37% 6% 12% 27% 16% 2	2940
December	1st to 10th	Night	39% 5% 13% 30% 12% 1	4720
	11th to 20th	Night	43% 5% 13% 23% 13% 3	5307
	21st to end	Night	45% 8% 12% 18% 16% 1	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% 22% 33% 14% 3 1	200
	11th to 20th	Day	29% 23% 31% 15% 2	265
	21st to end	Day	22% 23% 35% 14% 5% 1	330
February	1st to 10th	Day	28% 18% 37% 13% 3 1	300
	11th to 20th	Day	29% 24% 36% 10% 2	387
	21st to end	Day	28% 17% 34% 18% 3	414
March	1st to 10th	Day	22% 20% 32% 21% 5%	500
	11th to 20th	Day	21% 21% 35% 17% 5% 1	500
	21st to end	Day	24% 17% 33% 20% 5% 2	550
April	1st to 10th	Day	24% 16% 34% 18% 6% 2	500
	11th to 20th	Day	20% 18% 27% 20% 11% 4	492
	21st to end	Day	25% 12% 30% 22% 9% 2	500
May	1st to 10th	Day	26% 14% 26% 21% 11% 3	503
	11th to 20th	Day	22% 11% 29% 21% 13% 5%	527
	21st to end	Day	20% 5% 22% 24% 20% 9%	573
June	1st to 10th	Day	15% 7% 29% 24% 17% 8%	530
	11th to 20th	Day	17% 7% 24% 28% 18% 6%	530
	21st to end	Day	14% 3 26% 31% 19% 8%	530
July	1st to 10th	Day	13% 4 14% 30% 25% 14%	525
	11th to 20th	Day	6% 4 15% 33% 30% 11%	524
	21st to end	Day	13% 3 21% 32% 23% 7%	576
August	1st to 10th	Day	13% 2 20% 28% 25% 11%	526
	11th to 20th	Day	12% 5% 18% 27% 26% 12%	519
	21st to end	Day	11% 5% 19% 28% 24% 13%	583
September	1st to 10th	Day	18% 6% 19% 22% 22% 12%	530
	11th to 20th	Day	15% 4 20% 26% 24% 12%	530
	21st to end	Day	25% 8% 21% 25% 15% 6%	530
October	1st to 10th	Day	22% 6% 22% 24% 17% 9%	530
	11th to 20th	Day	20% 10% 27% 25% 14% 4	530
	21st to end	Day	18% 11% 34% 26% 10% 2	583
November	1st to 10th	Day	16% 12% 32% 25% 12% 3	428
	11th to 20th	Day	18% 16% 32% 24% 10%	427
	21st to end	Day	23% 19% 33% 17% 7%	220
December	1st to 10th	Day	25% 20% 32% 17% 4 2	220
	11th to 20th	Day	26% 21% 32% 14% 7%	214
	21st to end	Day	21% 18% 32% 21% 8%	220
January	1st to 10th	Night	19% 14% 41% 22% 3	800
	11th to 20th	Night	24% 14% 32% 26% 4	800
	21st to end	Night	18% 13% 43% 24% 2	880
February	1st to 10th	Night	20% 15% 37% 26% 2	800
	11th to 20th	Night	24% 17% 38% 19% 1	783
	21st to end	Night	22% 17% 39% 19% 3	660
March	1st to 10th	Night	19% 15% 38% 24% 5%	800
	11th to 20th	Night	20% 16% 36% 23% 6% 1	800
	21st to end	Night	21% 12% 38% 24% 5%	880
April	1st to 10th	Night	22% 14% 37% 23% 4	800
	11th to 20th	Night	18% 11% 32% 30% 8%	791
	21st to end	Night	22% 8% 32% 30% 8%	800
May	1st to 10th	Night	21% 8% 28% 34% 9%	653
	11th to 20th	Night	20% 6% 27% 36% 10%	394
	21st to end	Night	15% 3 20% 42% 19% 2	433
June	1st to 10th	Night	13% 3 23% 41% 20% 1	400
	11th to 20th	Night	15% 3 21% 43% 17% 1	400
	21st to end	Night	13% 3 16% 50% 18%	400
July	1st to 10th	Night	12% 3 15% 41% 27% 2	390
	11th to 20th	Night	8% 1 13% 44% 31% 3	388
	21st to end	Night	11% 1 16% 44% 26% 2	588
August	1st to 10th	Night	12% 2 10% 45% 29% 2	597
	11th to 20th	Night	13% 3 12% 40% 30% 2	703
	21st to end	Night	13% 3 14% 39% 27% 4	880
September	1st to 10th	Night	15% 4 19% 34% 25% 4	800
	11th to 20th	Night	13% 3 15% 37% 28% 4	800
	21st to end	Night	22% 4 18% 35% 20% 2	800
October	1st to 10th	Night	22% 4 21% 28% 21% 4	800
	11th to 20th	Night	18% 8% 27% 33% 13% 1	800
	21st to end	Night	18% 7% 33% 29% 12%	880
November	1st to 10th	Night	14% 6% 32% 35% 12% 1	820
	11th to 20th	Night	20% 13% 30% 30% 7% 1	840
	21st to end	Night	16% 13% 34% 29% 7%	840
December	1st to 10th	Night	22% 14% 34% 25% 5% 1	840
	11th to 20th	Night	19% 11% 39% 26% 5%	829
	21st to end	Night	20% 11% 37% 29% 3	880

Page generated at 2025-12-15 01:13:56. Version ac07

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