Stardust Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stardust 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	12% 8% 3 7% 5% 4 4 4 6% 8% 38%	127277
	Night	13% 9% 3 7% 4 4 4 3 5% 7% 40%	123987
Transparency	Day	43% 5% 12% 24% 15% 2	130811
	Night	43% 4 11% 24% 16% 2	128528
Seeing	Day	16% 9% 27% 26% 17% 5%	17230
	Night	17% 9% 29% 31% 13% 1	27075

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% 11% 7% 14% 6% 5% 5% 4 5% 6% 24%	3617
	11th to 20th	Day	10% 10% 6% 12% 8% 7% 8% 5% 6% 6% 24%	3638
	21st to end	Day	17% 16% 7% 10% 5% 5% 3 3 4 5% 27%	4488
February	1st to 10th	Day	15% 13% 4 11% 6% 4 4 3 4 6% 30%	1800
	11th to 20th	Day	13% 11% 4 7% 7% 6% 5% 4 5% 7% 31%	1938
	21st to end	Day	15% 12% 5% 10% 4 4 3 4 4 6% 34%	1650
March	1st to 10th	Day	19% 12% 3 6% 4 3 3 2 3 4 42%	4480
	11th to 20th	Day	7% 8% 3 5% 4 4 4 4 6% 9% 45%	4887
	21st to end	Day	17% 10% 4 10% 5% 4 5% 4 5% 7% 29%	5863
April	1st to 10th	Day	15% 9% 3 7% 5% 4 4 3 6% 7% 36%	2400
	11th to 20th	Day	14% 10% 3 7% 5% 4 4 4 5% 5% 39%	2374
	21st to end	Day	17% 8% 2 7% 5% 5% 5% 3 5% 6% 36%	2400
May	1st to 10th	Day	16% 9% 3 7% 5% 5% 5% 4 6% 9% 32%	5771
	11th to 20th	Day	14% 7% 3 6% 5% 5% 4 3 5% 7% 40%	6268
	21st to end	Day	12% 7% 3 7% 5% 4 5% 4 7% 8% 38%	6935
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 46%	2800
	11th to 20th	Day	9% 5% 2 6% 3 5% 4 4 6% 7% 49%	2800
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 7% 10% 43%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 4 4 4 7% 11% 42%	6360
	11th to 20th	Day	8% 7% 3 9% 5% 5% 5% 4 7% 10% 37%	6360
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 8% 11% 38%	6924
August	1st to 10th	Day	6% 4 2 5% 4 4 4 4 8% 11% 48%	4211
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 43%	3849
	21st to end	Day	5% 4 2 6% 4 5% 6% 5% 7% 10% 47%	4312
September	1st to 10th	Day	10% 5% 2 5% 4 4 4 4 5% 7% 50%	2400
	11th to 20th	Day	9% 4 2 5% 4 4 4 4 5% 7% 52%	2340
	21st to end	Day	9% 5% 2 5% 4 5% 4 3 6% 8% 49%	2200
October	1st to 10th	Day	10% 5% 2 5% 4 4 4 2 5% 6% 52%	2045
	11th to 20th	Day	15% 8% 3 6% 4 4 4 3 4 6% 45%	2000
	21st to end	Day	17% 10% 2 7% 3 3 3 3 5% 6% 40%	2094
November	1st to 10th	Day	11% 8% 2 5% 4 2 4 3 5% 6% 50%	1852
	11th to 20th	Day	16% 9% 4 7% 3 3 3 3 5% 7% 41%	1890
	21st to end	Day	16% 12% 4 9% 5% 3 3 3 4 5% 37%	1795
December	1st to 10th	Day	8% 9% 4 7% 5% 3 3 3 5% 7% 46%	2690
	11th to 20th	Day	13% 13% 6% 9% 5% 5% 5% 3 5% 7% 27%	3064
	21st to end	Day	26% 18% 7% 12% 4 3 3 3 3 4 16%	3982
January	1st to 10th	Night	14% 13% 7% 11% 5% 4 3 3 4 5% 32%	6348
	11th to 20th	Night	11% 15% 5% 13% 6% 5% 7% 4 4 3 26%	6337
	21st to end	Night	18% 14% 6% 10% 4 4 4 2 3 5% 30%	6490
February	1st to 10th	Night	16% 12% 5% 9% 5% 4 3 4 4 7% 31%	2600
	11th to 20th	Night	14% 10% 5% 8% 6% 3 4 3 5% 5% 37%	2347
	21st to end	Night	16% 10% 3 7% 6% 3 3 3 4 5% 39%	1980
March	1st to 10th	Night	18% 12% 4 7% 3 3 3 2 4 5% 40%	5373
	11th to 20th	Night	11% 7% 2 5% 4 3 3 3 5% 6% 50%	5102
	21st to end	Night	17% 11% 3 9% 6% 5% 5% 4 5% 6% 31%	5065
April	1st to 10th	Night	12% 7% 4 6% 5% 4 5% 4 5% 6% 42%	2000
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 44%	1975
	21st to end	Night	19% 7% 3 8% 5% 4 3 4 4 6% 38%	2000
May	1st to 10th	Night	18% 9% 2 7% 5% 4 5% 3 5% 7% 34%	4110
	11th to 20th	Night	13% 6% 3 5% 4 4 4 4 7% 8% 41%	3641
	21st to end	Night	12% 7% 2 7% 5% 4 5% 4 6% 9% 41%	3942
June	1st to 10th	Night	9% 5% 1 5% 4 3 3 3 7% 10% 51%	1600
	11th to 20th	Night	8% 5% 2 5% 3 5% 5% 4 6% 8% 49%	1600
	21st to end	Night	6% 5% 2 7% 5% 4 5% 4 7% 10% 46%	1600
July	1st to 10th	Night	9% 5% 2 7% 5% 5% 5% 4 6% 10% 43%	3618
	11th to 20th	Night	5% 4 2 6% 4 6% 5% 5% 7% 10% 46%	3617
	21st to end	Night	8% 6% 2 7% 4 4 5% 4 7% 9% 42%	3947
August	1st to 10th	Night	5% 3 1 5% 3 3 4 3 6% 11% 55%	2943
	11th to 20th	Night	7% 4 2 5% 5% 3 4 4 6% 9% 52%	3200
	21st to end	Night	4 4 2 4 3 5% 4 5% 7% 9% 53%	3586
September	1st to 10th	Night	10% 5% 2 5% 4 3 3 2 4 7% 56%	2000
	11th to 20th	Night	7% 5% 2 5% 4 4 3 3 5% 9% 54%	2039
	21st to end	Night	8% 6% 2 5% 4 3 4 3 5% 8% 51%	2200
October	1st to 10th	Night	10% 4 2 5% 3 3 4 3 4 6% 56%	2350
	11th to 20th	Night	14% 6% 2 4 3 3 4 2 5% 7% 51%	2400
	21st to end	Night	18% 9% 2 6% 4 4 4 3 4 5% 42%	2745
November	1st to 10th	Night	10% 8% 2 5% 4 3 3 3 5% 6% 52%	2666
	11th to 20th	Night	12% 8% 2 6% 4 4 4 3 5% 7% 45%	2730
	21st to end	Night	17% 11% 3 6% 4 4 4 3 4 6% 39%	2822
December	1st to 10th	Night	11% 10% 3 8% 4 4 4 3 4 6% 44%	4720
	11th to 20th	Night	15% 10% 4 10% 5% 5% 5% 3 5% 6% 34%	5298
	21st to end	Night	24% 19% 6% 10% 5% 4 4 3 4 4 17%	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	60% 4 9% 18% 8% 1	3618
	11th to 20th	Day	60% 4 10% 14% 10% 2	3638
	21st to end	Day	61% 4 8% 19% 7% 1	4488
February	1st to 10th	Day	57% 4 11% 19% 8% 1	1800
	11th to 20th	Day	52% 4 11% 20% 12% 1	1948
	21st to end	Day	52% 4 8% 22% 11% 2	1650
March	1st to 10th	Day	48% 3 7% 22% 18% 2	4480
	11th to 20th	Day	35% 5% 11% 30% 18% 1	4887
	21st to end	Day	54% 5% 14% 21% 6% 1	5865
April	1st to 10th	Day	47% 5% 11% 23% 13% 1	2400
	11th to 20th	Day	46% 5% 9% 25% 14% 2	2374
	21st to end	Day	48% 5% 13% 21% 12% 2	2400
May	1st to 10th	Day	48% 5% 13% 20% 12% 1	5807
	11th to 20th	Day	43% 6% 11% 25% 12% 3	6272
	21st to end	Day	42% 6% 11% 22% 18% 1	6949
June	1st to 10th	Day	34% 6% 14% 28% 16% 4	2800
	11th to 20th	Day	34% 5% 10% 26% 22% 3	2800
	21st to end	Day	35% 7% 14% 22% 18% 3	2800
July	1st to 10th	Day	34% 5% 14% 29% 16% 2	6291
	11th to 20th	Day	40% 6% 14% 25% 14% 1	6285
	21st to end	Day	37% 8% 20% 24% 11% 1	6728
August	1st to 10th	Day	28% 6% 20% 33% 11% 1	4196
	11th to 20th	Day	36% 7% 14% 30% 14% 1	3885
	21st to end	Day	30% 7% 16% 29% 15% 4	4311
September	1st to 10th	Day	33% 5% 10% 27% 20% 6%	2400
	11th to 20th	Day	31% 4 9% 26% 24% 6%	2340
	21st to end	Day	33% 4 8% 29% 23% 2	2200
October	1st to 10th	Day	24% 3 7% 20% 43% 3	3331
	11th to 20th	Day	28% 3 8% 22% 34% 5%	3240
	21st to end	Day	40% 3 8% 26% 21% 2	3358
November	1st to 10th	Day	35% 3 14% 26% 19% 4	1852
	11th to 20th	Day	44% 3 10% 26% 14% 3	1890
	21st to end	Day	52% 3 11% 22% 12%	1795
December	1st to 10th	Day	39% 4 15% 31% 10%	2690
	11th to 20th	Day	56% 4 10% 21% 6% 2	3061
	21st to end	Day	73% 3 10% 10% 4	3982
January	1st to 10th	Night	55% 4 11% 23% 7%	6348
	11th to 20th	Night	62% 3 8% 14% 11% 2	6337
	21st to end	Night	58% 3 8% 19% 11% 1	6490
February	1st to 10th	Night	53% 4 11% 19% 11% 2	2600
	11th to 20th	Night	49% 3 11% 22% 14% 2	2348
	21st to end	Night	48% 3 10% 23% 14% 3	1980
March	1st to 10th	Night	49% 3 8% 23% 16% 2	5373
	11th to 20th	Night	36% 4 8% 29% 19% 4	5102
	21st to end	Night	52% 5% 11% 22% 8% 2	5065
April	1st to 10th	Night	42% 4 12% 24% 15% 3	2000
	11th to 20th	Night	41% 4 9% 27% 16% 3	1975
	21st to end	Night	48% 4 10% 20% 15% 3	2000
May	1st to 10th	Night	48% 7% 11% 21% 10% 3	4137
	11th to 20th	Night	38% 5% 14% 26% 13% 3	3642
	21st to end	Night	39% 6% 12% 23% 17% 3	3950
June	1st to 10th	Night	28% 5% 15% 29% 17% 5%	1600
	11th to 20th	Night	31% 6% 12% 25% 23% 4	1600
	21st to end	Night	32% 7% 16% 23% 19% 4	1600
July	1st to 10th	Night	35% 6% 11% 30% 16% 2	3580
	11th to 20th	Night	31% 8% 15% 27% 18% 1	3572
	21st to end	Night	36% 7% 19% 23% 13% 2	3832
August	1st to 10th	Night	24% 6% 18% 32% 18% 1	2934
	11th to 20th	Night	29% 6% 14% 34% 17% 1	3230
	21st to end	Night	25% 6% 16% 33% 16% 4	3586
September	1st to 10th	Night	30% 4 9% 27% 23% 8%	2000
	11th to 20th	Night	28% 4 9% 26% 27% 5%	2039
	21st to end	Night	33% 4 9% 26% 23% 5%	2200
October	1st to 10th	Night	23% 3 6% 23% 42% 4	3844
	11th to 20th	Night	24% 2 8% 24% 36% 5%	3899
	21st to end	Night	36% 3 10% 23% 24% 4	4431
November	1st to 10th	Night	34% 4 11% 27% 20% 5%	2666
	11th to 20th	Night	40% 3 11% 26% 19% 2	2730
	21st to end	Night	48% 3 9% 24% 14% 1	2822
December	1st to 10th	Night	43% 3 12% 30% 12% 1	4720
	11th to 20th	Night	51% 4 11% 23% 10% 1	5300
	21st to end	Night	71% 4 9% 12% 4	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	24% 20% 29% 18% 8%	300
	11th to 20th	Day	25% 17% 38% 16% 4	300
	21st to end	Day	19% 18% 36% 22% 5%	330
February	1st to 10th	Day	24% 15% 41% 16% 4	300
	11th to 20th	Day	23% 22% 30% 20% 5%	300
	21st to end	Day	25% 15% 42% 16% 2	249
March	1st to 10th	Day	24% 17% 41% 16% 3	300
	11th to 20th	Day	26% 15% 37% 16% 6%	300
	21st to end	Day	31% 14% 34% 16% 4 1	498
April	1st to 10th	Day	23% 12% 33% 24% 7%	500
	11th to 20th	Day	21% 18% 28% 23% 8% 2	492
	21st to end	Day	24% 12% 35% 21% 8% 1	500
May	1st to 10th	Day	21% 10% 32% 25% 10% 2	503
	11th to 20th	Day	19% 10% 27% 25% 16% 3	700
	21st to end	Day	14% 7% 32% 27% 13% 7%	789
June	1st to 10th	Day	10% 5% 24% 30% 24% 7%	730
	11th to 20th	Day	10% 5% 21% 34% 24% 6%	730
	21st to end	Day	9% 5% 28% 32% 21% 5%	730
July	1st to 10th	Day	11% 2 13% 32% 26% 16%	721
	11th to 20th	Day	9% 3 21% 30% 28% 10%	718
	21st to end	Day	10% 3 15% 33% 32% 7%	794
August	1st to 10th	Day	8% 2 14% 36% 30% 10%	715
	11th to 20th	Day	9% 5% 15% 28% 27% 15%	519
	21st to end	Day	7% 2 16% 31% 34% 11%	583
September	1st to 10th	Day	12% 3 20% 29% 27% 9%	530
	11th to 20th	Day	8% 3 11% 29% 33% 15%	530
	21st to end	Day	12% 8% 20% 25% 25% 10%	530
October	1st to 10th	Day	10% 8% 25% 30% 21% 5%	375
	11th to 20th	Day	17% 18% 29% 25% 8% 3	330
	21st to end	Day	29% 14% 35% 17% 5%	363
November	1st to 10th	Day	13% 14% 35% 26% 8% 4	330
	11th to 20th	Day	21% 17% 33% 18% 9% 2	330
	21st to end	Day	30% 10% 32% 23% 5%	330
December	1st to 10th	Day	15% 19% 40% 18% 6% 2	330
	11th to 20th	Day	21% 16% 40% 19% 4	321
	21st to end	Day	28% 16% 38% 15% 3	330
January	1st to 10th	Night	17% 15% 38% 25% 5%	1000
	11th to 20th	Night	20% 15% 38% 21% 5%	1000
	21st to end	Night	22% 13% 36% 26% 3	1100
February	1st to 10th	Night	23% 14% 35% 24% 4	1000
	11th to 20th	Night	21% 14% 35% 27% 3	792
	21st to end	Night	22% 15% 38% 22% 2	660
March	1st to 10th	Night	21% 14% 36% 24% 4	800
	11th to 20th	Night	20% 11% 35% 28% 6%	657
	21st to end	Night	24% 11% 35% 24% 6%	660
April	1st to 10th	Night	17% 14% 36% 28% 6%	600
	11th to 20th	Night	19% 13% 32% 28% 8%	593
	21st to end	Night	23% 8% 34% 29% 6%	600
May	1st to 10th	Night	18% 7% 35% 31% 7% 1	600
	11th to 20th	Night	17% 5% 26% 38% 12% 2	591
	21st to end	Night	12% 4 26% 35% 21% 2	650
June	1st to 10th	Night	11% 3 22% 47% 18%	600
	11th to 20th	Night	10% 2 22% 45% 19% 2	600
	21st to end	Night	8% 3 27% 41% 21% 1	600
July	1st to 10th	Night	10% 3 10% 38% 34% 6%	585
	11th to 20th	Night	4 3 15% 45% 30% 3	582
	21st to end	Night	7% 2 13% 44% 33% 2	657
August	1st to 10th	Night	7% 1 11% 48% 30% 3	597
	11th to 20th	Night	8% 2 10% 43% 31% 5%	594
	21st to end	Night	5% 2 13% 37% 40% 2	660
September	1st to 10th	Night	11% 3 16% 38% 28% 4	600
	11th to 20th	Night	7% 3 15% 40% 30% 5%	639
	21st to end	Night	10% 7% 21% 33% 25% 4	800
October	1st to 10th	Night	11% 4 27% 35% 21% 2	800
	11th to 20th	Night	17% 11% 29% 30% 13% 1	800
	21st to end	Night	23% 10% 34% 26% 7%	880
November	1st to 10th	Night	13% 10% 40% 27% 10% 1	820
	11th to 20th	Night	18% 13% 36% 26% 6%	840
	21st to end	Night	22% 13% 35% 24% 5%	932
December	1st to 10th	Night	21% 10% 38% 25% 5%	1050
	11th to 20th	Night	23% 10% 34% 28% 5%	1036
	21st to end	Night	29% 15% 32% 22% 2	1100

Page generated at 2025-12-15 00:13:49. Version ac07

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