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 2026-10-14.

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	16% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	149602
	Night	16% 9% 4 9% 5% 4 4 4 5% 6% 34%	142137
Transparency	Day	49% 6% 11% 21% 12% 1	153198
	Night	48% 6% 11% 21% 12% 1	146612
Seeing	Day	23% 13% 28% 21% 11% 4	17270
	Night	21% 12% 25% 29% 11% 1	26686

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	14% 16% 6% 20% 5% 4 3 3 3 4 21%	4698
	11th to 20th	Day	9% 15% 9% 19% 9% 6% 4 3 4 4 16%	5280
	21st to end	Day	15% 15% 5% 11% 7% 5% 4 3 4 4 25%	5780
February	1st to 10th	Day	14% 16% 5% 10% 6% 5% 4 3 4 6% 26%	1890
	11th to 20th	Day	14% 12% 5% 11% 6% 5% 5% 4 7% 5% 26%	1843
	21st to end	Day	17% 13% 3 10% 5% 4 4 4 5% 6% 28%	1702
March	1st to 10th	Day	18% 13% 3 6% 4 4 4 3 4 5% 35%	5038
	11th to 20th	Day	13% 10% 3 9% 5% 4 4 4 5% 7% 35%	5090
	21st to end	Day	13% 10% 3 8% 6% 5% 5% 4 5% 5% 36%	5618
April	1st to 10th	Day	18% 11% 3 8% 6% 5% 4 4 5% 6% 32%	2520
	11th to 20th	Day	15% 11% 2 7% 4 5% 4 3 6% 6% 36%	2494
	21st to end	Day	20% 7% 3 6% 4 5% 4 3 5% 6% 34%	2610
May	1st to 10th	Day	24% 6% 2 7% 5% 5% 5% 4 6% 7% 29%	7616
	11th to 20th	Day	21% 7% 2 7% 5% 5% 5% 3 5% 8% 32%	8075
	21st to end	Day	23% 7% 2 6% 4 4 4 4 5% 6% 34%	9045
June	1st to 10th	Day	13% 6% 2 6% 6% 6% 5% 4 6% 8% 37%	2940
	11th to 20th	Day	16% 5% 2 7% 6% 5% 5% 4 6% 8% 35%	2940
	21st to end	Day	13% 5% 2 6% 4 5% 5% 4 6% 9% 39%	2940
July	1st to 10th	Day	12% 6% 3 7% 6% 5% 5% 4 6% 7% 40%	8280
	11th to 20th	Day	9% 5% 2 8% 5% 6% 6% 5% 7% 11% 36%	8160
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	8340
August	1st to 10th	Day	19% 7% 3 8% 6% 5% 5% 5% 7% 8% 27%	6014
	11th to 20th	Day	16% 5% 2 7% 5% 6% 6% 4 7% 8% 33%	5910
	21st to end	Day	12% 5% 2 5% 4 5% 5% 5% 7% 9% 40%	6080
September	1st to 10th	Day	16% 5% 2 6% 4 3 5% 3 4 7% 45%	2520
	11th to 20th	Day	15% 5% 2 4 3 3 4 3 5% 7% 48%	2494
	21st to end	Day	24% 7% 3 6% 4 3 3 4 6% 6% 34%	2205
October	1st to 10th	Day	16% 7% 3 6% 4 5% 4 3 5% 6% 42%	2100
	11th to 20th	Day	18% 7% 3 7% 4 4 5% 4 6% 6% 35%	2030
	21st to end	Day	17% 9% 2 7% 4 4 5% 4 5% 6% 37%	2200
November	1st to 10th	Day	11% 7% 3 6% 4 5% 4 5% 6% 6% 43%	1944
	11th to 20th	Day	15% 14% 3 8% 5% 5% 5% 4 6% 6% 30%	1728
	21st to end	Day	16% 13% 3 8% 7% 6% 5% 4 6% 6% 28%	1680
December	1st to 10th	Day	15% 14% 8% 15% 5% 4 5% 3 5% 5% 21%	2680
	11th to 20th	Day	22% 16% 5% 8% 4 3 4 3 4 5% 26%	3070
	21st to end	Day	20% 16% 7% 11% 6% 5% 5% 4 5% 5% 17%	4048
January	1st to 10th	Night	12% 15% 6% 21% 6% 5% 4 3 5% 5% 19%	8191
	11th to 20th	Night	11% 13% 6% 19% 7% 5% 5% 3 5% 6% 21%	7680
	21st to end	Night	15% 12% 5% 10% 9% 6% 5% 3 4 5% 26%	8401
February	1st to 10th	Night	15% 11% 5% 10% 6% 5% 4 4 4 7% 30%	2730
	11th to 20th	Night	16% 11% 3 10% 6% 4 6% 4 5% 6% 29%	2663
	21st to end	Night	15% 11% 3 11% 5% 6% 4 3 5% 5% 32%	2102
March	1st to 10th	Night	19% 11% 5% 7% 5% 4 3 3 4 5% 34%	5033
	11th to 20th	Night	11% 8% 5% 6% 4 4 4 4 5% 6% 42%	5090
	21st to end	Night	14% 10% 3 8% 5% 5% 4 4 4 5% 40%	5554
April	1st to 10th	Night	19% 12% 3 9% 5% 4 3 4 4 6% 32%	2100
	11th to 20th	Night	16% 9% 2 6% 5% 4 4 4 6% 7% 37%	2075
	21st to end	Night	18% 7% 2 6% 5% 4 4 4 5% 7% 38%	2027
May	1st to 10th	Night	24% 8% 2 6% 5% 4 5% 3 4 6% 31%	5237
	11th to 20th	Night	23% 8% 2 6% 3 4 4 3 5% 6% 36%	4781
	21st to end	Night	25% 7% 2 6% 4 4 3 3 5% 6% 35%	5108
June	1st to 10th	Night	13% 6% 2 6% 4 4 3 3 6% 8% 45%	1680
	11th to 20th	Night	13% 6% 2 7% 4 4 4 4 7% 8% 40%	1680
	21st to end	Night	12% 5% 1 5% 3 5% 5% 4 8% 10% 42%	1680
July	1st to 10th	Night	13% 6% 3 7% 5% 4 5% 4 5% 9% 40%	4678
	11th to 20th	Night	10% 5% 2 7% 5% 5% 5% 4 7% 11% 38%	4793
	21st to end	Night	12% 5% 2 7% 5% 4 4 4 5% 7% 45%	5736
August	1st to 10th	Night	17% 7% 3 8% 5% 6% 5% 4 6% 8% 32%	4135
	11th to 20th	Night	16% 6% 2 7% 4 5% 5% 4 6% 7% 38%	4095
	21st to end	Night	14% 4 2 5% 4 4 5% 3 6% 8% 45%	5040
September	1st to 10th	Night	16% 4 2 5% 4 4 4 3 5% 8% 46%	2100
	11th to 20th	Night	13% 6% 2 5% 3 4 4 3 4 8% 50%	2123
	21st to end	Night	21% 6% 2 6% 3 5% 4 3 5% 7% 38%	2414
October	1st to 10th	Night	16% 6% 2 5% 3 3 4 3 4 7% 47%	2520
	11th to 20th	Night	16% 7% 2 6% 4 4 3 4 5% 6% 42%	2437
	21st to end	Night	19% 8% 3 5% 4 4 4 3 5% 6% 40%	2640
November	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 4 6% 49%	2571
	11th to 20th	Night	17% 10% 3 6% 5% 4 5% 3 5% 6% 35%	2888
	21st to end	Night	17% 12% 4 7% 4 4 5% 4 6% 6% 32%	2940
December	1st to 10th	Night	13% 11% 7% 12% 5% 4 5% 4 6% 7% 25%	4720
	11th to 20th	Night	21% 12% 5% 8% 5% 4 5% 3 4 5% 27%	5345
	21st to end	Night	19% 14% 5% 11% 6% 5% 5% 4 5% 5% 22%	7150

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	66% 6% 11% 12% 5% 1	4699
	11th to 20th	Day	70% 4 7% 11% 6% 2	5280
	21st to end	Day	61% 4 11% 17% 6%	5780
February	1st to 10th	Day	60% 4 11% 17% 7% 1	1890
	11th to 20th	Day	57% 6% 9% 21% 7% 1	1852
	21st to end	Day	57% 4 11% 19% 7% 2	1702
March	1st to 10th	Day	52% 4 11% 22% 10% 2	5038
	11th to 20th	Day	48% 5% 14% 22% 8% 2	5090
	21st to end	Day	48% 5% 10% 20% 14% 3	5618
April	1st to 10th	Day	53% 4 10% 19% 12% 2	2520
	11th to 20th	Day	47% 5% 11% 19% 16% 2	2494
	21st to end	Day	50% 4 8% 23% 13% 2	2610
May	1st to 10th	Day	53% 7% 10% 19% 9% 2	7651
	11th to 20th	Day	49% 7% 10% 23% 10% 1	8079
	21st to end	Day	49% 6% 9% 22% 13% 2	9061
June	1st to 10th	Day	44% 6% 10% 23% 16% 1	2940
	11th to 20th	Day	45% 6% 12% 21% 14% 1	2940
	21st to end	Day	40% 6% 13% 26% 14% 1	2940
July	1st to 10th	Day	43% 6% 12% 25% 13% 1	8210
	11th to 20th	Day	38% 9% 13% 29% 10%	8085
	21st to end	Day	40% 6% 10% 25% 18% 1	8156
August	1st to 10th	Day	52% 8% 11% 16% 11% 1	6001
	11th to 20th	Day	45% 8% 14% 25% 8%	5949
	21st to end	Day	37% 7% 14% 26% 15% 1	6080
September	1st to 10th	Day	40% 5% 10% 24% 18% 3	2520
	11th to 20th	Day	36% 4 11% 28% 19% 2	2494
	21st to end	Day	49% 5% 10% 19% 16% 2	2205
October	1st to 10th	Day	39% 4 9% 26% 19% 3	3360
	11th to 20th	Day	42% 6% 9% 24% 17% 3	3270
	21st to end	Day	33% 5% 13% 30% 18% 1	3538
November	1st to 10th	Day	40% 5% 14% 21% 17% 3	1944
	11th to 20th	Day	54% 5% 10% 19% 10% 2	1728
	21st to end	Day	56% 4 12% 20% 7%	1680
December	1st to 10th	Day	62% 8% 10% 14% 5%	2680
	11th to 20th	Day	60% 5% 13% 19% 4	3066
	21st to end	Day	68% 6% 11% 10% 5% 1	4048
January	1st to 10th	Night	64% 6% 11% 14% 5%	8192
	11th to 20th	Night	59% 7% 12% 12% 9% 1	7680
	21st to end	Night	59% 4 10% 19% 7% 1	8401
February	1st to 10th	Night	53% 5% 11% 21% 9% 1	2730
	11th to 20th	Night	55% 5% 10% 19% 11% 1	2665
	21st to end	Night	55% 4 9% 20% 11% 2	2102
March	1st to 10th	Night	52% 4 12% 20% 10% 2	5033
	11th to 20th	Night	39% 7% 15% 26% 8% 4	5090
	21st to end	Night	46% 5% 8% 20% 19% 2	5554
April	1st to 10th	Night	54% 4 9% 18% 13% 1	2100
	11th to 20th	Night	45% 7% 10% 21% 15% 2	2075
	21st to end	Night	45% 4 10% 24% 14% 3	2027
May	1st to 10th	Night	52% 7% 10% 17% 12% 2	5264
	11th to 20th	Night	47% 7% 12% 23% 10% 1	4782
	21st to end	Night	48% 6% 10% 20% 13% 2	5115
June	1st to 10th	Night	38% 5% 13% 26% 16% 1	1680
	11th to 20th	Night	39% 8% 14% 22% 15% 2	1680
	21st to end	Night	35% 8% 13% 28% 15% 1	1680
July	1st to 10th	Night	40% 8% 13% 22% 15% 2	4640
	11th to 20th	Night	37% 9% 15% 26% 12% 1	4748
	21st to end	Night	36% 7% 11% 23% 21% 1	5606
August	1st to 10th	Night	50% 8% 12% 20% 9% 2	4124
	11th to 20th	Night	42% 8% 13% 26% 10%	4122
	21st to end	Night	36% 6% 13% 30% 12% 1	5040
September	1st to 10th	Night	38% 5% 11% 25% 18% 3	2100
	11th to 20th	Night	33% 5% 10% 31% 19% 1	2123
	21st to end	Night	47% 5% 9% 21% 17% 1	2414
October	1st to 10th	Night	36% 5% 10% 27% 21% 1	4040
	11th to 20th	Night	34% 5% 9% 26% 20% 5%	3936
	21st to end	Night	33% 4 13% 28% 21% 2	4252
November	1st to 10th	Night	37% 4 14% 25% 18% 2	2571
	11th to 20th	Night	48% 5% 10% 22% 12% 3	2888
	21st to end	Night	51% 4 13% 22% 9% 1	2940
December	1st to 10th	Night	53% 10% 14% 19% 4	4720
	11th to 20th	Night	57% 5% 13% 18% 6%	5348
	21st to end	Night	62% 6% 10% 15% 7%	7150

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	31% 24% 31% 9% 4 1	226
	11th to 20th	Day	37% 22% 30% 10% 1	330
	21st to end	Day	28% 20% 35% 12% 4 1	363
February	1st to 10th	Day	30% 20% 35% 12% 4	330
	11th to 20th	Day	37% 20% 33% 9% 1	330
	21st to end	Day	33% 18% 32% 16% 1	418
March	1st to 10th	Day	30% 20% 28% 19% 3	540
	11th to 20th	Day	31% 20% 28% 15% 4 1	540
	21st to end	Day	29% 20% 31% 14% 5% 2	594
April	1st to 10th	Day	31% 17% 29% 17% 5% 1	540
	11th to 20th	Day	22% 21% 27% 18% 9% 3	532
	21st to end	Day	29% 15% 32% 15% 8% 2	540
May	1st to 10th	Day	29% 15% 31% 12% 9% 3	543
	11th to 20th	Day	25% 14% 28% 17% 12% 4	567
	21st to end	Day	24% 9% 26% 21% 14% 5%	617
June	1st to 10th	Day	17% 15% 25% 25% 13% 4	570
	11th to 20th	Day	22% 10% 26% 25% 13% 4	570
	21st to end	Day	17% 9% 29% 28% 14% 4	570
July	1st to 10th	Day	13% 5% 24% 28% 19% 9%	565
	11th to 20th	Day	9% 5% 29% 29% 20% 8%	564
	21st to end	Day	14% 5% 27% 30% 18% 6%	620
August	1st to 10th	Day	14% 6% 25% 27% 20% 9%	566
	11th to 20th	Day	14% 6% 23% 27% 20% 10%	559
	21st to end	Day	14% 5% 25% 28% 15% 13%	627
September	1st to 10th	Day	17% 6% 21% 28% 19% 9%	570
	11th to 20th	Day	16% 3 18% 29% 24% 10%	570
	21st to end	Day	29% 8% 23% 21% 14% 5%	570
October	1st to 10th	Day	20% 10% 20% 25% 18% 6%	570
	11th to 20th	Day	22% 15% 30% 22% 10% 1	542
	21st to end	Day	22% 14% 33% 23% 7% 1	583
November	1st to 10th	Day	18% 16% 30% 23% 11% 2	474
	11th to 20th	Day	27% 21% 29% 15% 9%	268
	21st to end	Day	28% 16% 37% 16% 2 1	220
December	1st to 10th	Day	32% 21% 34% 8% 4 1	220
	11th to 20th	Day	30% 20% 31% 17% 2	220
	21st to end	Day	31% 19% 30% 15% 5%	242
January	1st to 10th	Night	24% 20% 33% 19% 3	840
	11th to 20th	Night	28% 16% 31% 22% 3	840
	21st to end	Night	23% 20% 34% 22% 2	924
February	1st to 10th	Night	25% 17% 30% 27% 2	840
	11th to 20th	Night	28% 21% 31% 19% 1	823
	21st to end	Night	27% 16% 33% 22% 2	692
March	1st to 10th	Night	25% 15% 33% 24% 3	840
	11th to 20th	Night	27% 16% 29% 23% 5%	840
	21st to end	Night	23% 16% 33% 22% 6%	924
April	1st to 10th	Night	28% 16% 29% 22% 5%	840
	11th to 20th	Night	21% 13% 32% 26% 7% 1	831
	21st to end	Night	22% 11% 27% 32% 7%	767
May	1st to 10th	Night	25% 7% 25% 32% 10% 1	630
	11th to 20th	Night	20% 7% 26% 36% 10%	467
	21st to end	Night	17% 6% 21% 36% 18% 2	455
June	1st to 10th	Night	15% 5% 20% 40% 19% 1	420
	11th to 20th	Night	16% 6% 22% 39% 17%	420
	21st to end	Night	12% 6% 21% 43% 18%	420
July	1st to 10th	Night	13% 5% 15% 42% 21% 3	410
	11th to 20th	Night	8% 2 16% 43% 28% 2	446
	21st to end	Night	11% 3 16% 45% 25% 1	690
August	1st to 10th	Night	9% 3 14% 41% 31% 2	627
	11th to 20th	Night	15% 5% 10% 39% 26% 4	624
	21st to end	Night	13% 4 16% 35% 29% 3	919
September	1st to 10th	Night	16% 4 16% 36% 24% 3	840
	11th to 20th	Night	15% 4 15% 33% 28% 4	840
	21st to end	Night	22% 8% 18% 31% 19% 3	840
October	1st to 10th	Night	19% 6% 19% 31% 21% 3	840
	11th to 20th	Night	20% 13% 24% 31% 11% 1	813
	21st to end	Night	24% 12% 24% 33% 7% 1	880
November	1st to 10th	Night	17% 11% 27% 34% 11% 1	820
	11th to 20th	Night	25% 17% 23% 26% 8% 1	840
	21st to end	Night	25% 15% 28% 27% 5% 1	840
December	1st to 10th	Night	27% 16% 31% 21% 5%	840
	11th to 20th	Night	28% 16% 28% 25% 4	840
	21st to end	Night	26% 16% 28% 27% 3	924

Page generated at 2026-10-11 05:06:33. Version ac07

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