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 2025-06-10.

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% 4 8% 5% 5% 5% 4 5% 7% 32%	119751
	Night	16% 9% 4 9% 5% 4 4 4 5% 6% 34%	118476
Transparency	Day	49% 6% 11% 21% 11% 2	123388
	Night	48% 6% 11% 21% 12% 2	122976
Seeing	Day	23% 13% 28% 21% 11% 4	15473
	Night	21% 12% 25% 29% 11% 1	25015

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% 16% 7% 18% 4 4 4 3 3 4 24%	3620
	11th to 20th	Day	10% 16% 10% 18% 9% 6% 4 3 4 4 15%	4060
	21st to end	Day	17% 18% 7% 11% 5% 4 3 3 4 5% 23%	4466
February	1st to 10th	Day	15% 16% 5% 10% 7% 5% 4 3 4 6% 24%	1800
	11th to 20th	Day	15% 12% 5% 11% 6% 5% 5% 4 7% 5% 26%	1753
	21st to end	Day	17% 12% 3 10% 5% 5% 5% 4 5% 6% 28%	1623
March	1st to 10th	Day	18% 13% 3 6% 4 4 4 3 4 6% 35%	4928
	11th to 20th	Day	13% 10% 4 9% 5% 4 4 4 5% 7% 36%	4980
	21st to end	Day	13% 10% 3 8% 6% 5% 5% 4 5% 5% 36%	5497
April	1st to 10th	Day	18% 11% 3 8% 6% 5% 4 4 5% 6% 31%	2400
	11th to 20th	Day	16% 11% 2 7% 4 5% 4 3 6% 6% 36%	2374
	21st to end	Day	20% 7% 3 6% 5% 5% 4 3 5% 6% 35%	2486
May	1st to 10th	Day	26% 6% 2 8% 5% 5% 5% 4 5% 7% 27%	5862
	11th to 20th	Day	25% 7% 2 7% 5% 5% 5% 3 5% 7% 29%	6212
	21st to end	Day	19% 6% 2 6% 5% 4 5% 5% 6% 8% 33%	6934
June	1st to 10th	Day	14% 6% 2 6% 6% 5% 5% 4 6% 8% 36%	2786
	11th to 20th	Day	15% 5% 2 6% 6% 6% 5% 4 6% 9% 36%	2660
	21st to end	Day	13% 5% 2 7% 4 5% 5% 4 7% 9% 39%	2660
July	1st to 10th	Day	8% 5% 3 7% 6% 6% 6% 4 8% 9% 38%	4440
	11th to 20th	Day	8% 5% 2 7% 6% 5% 6% 5% 7% 10% 39%	4376
	21st to end	Day	11% 7% 3 8% 5% 5% 5% 5% 6% 7% 38%	4466
August	1st to 10th	Day	20% 6% 3 6% 5% 5% 5% 5% 7% 8% 30%	4104
	11th to 20th	Day	14% 6% 2 7% 6% 7% 6% 4 7% 7% 35%	4017
	21st to end	Day	15% 5% 2 5% 3 5% 4 4 6% 8% 43%	4180
September	1st to 10th	Day	17% 5% 2 6% 5% 3 5% 3 4 6% 44%	2280
	11th to 20th	Day	15% 5% 2 4 4 3 4 3 5% 7% 48%	2256
	21st to end	Day	23% 6% 3 6% 4 4 3 4 6% 6% 35%	1995
October	1st to 10th	Day	17% 8% 3 6% 4 5% 4 3 5% 6% 39%	1900
	11th to 20th	Day	18% 7% 3 7% 4 4 5% 4 6% 6% 36%	1900
	21st to end	Day	17% 9% 2 7% 4 4 5% 3 5% 6% 37%	2090
November	1st to 10th	Day	11% 7% 3 6% 4 5% 4 5% 5% 6% 43%	1850
	11th to 20th	Day	15% 12% 3 7% 5% 5% 5% 3 6% 6% 31%	1646
	21st to end	Day	17% 12% 3 8% 7% 6% 4 4 6% 6% 28%	1600
December	1st to 10th	Day	15% 13% 8% 15% 5% 4 5% 3 5% 5% 21%	2600
	11th to 20th	Day	22% 16% 5% 8% 3 3 4 3 4 5% 26%	2990
	21st to end	Day	20% 16% 7% 10% 6% 5% 5% 4 5% 5% 17%	3960
January	1st to 10th	Night	12% 12% 7% 21% 6% 4 3 3 5% 5% 22%	6321
	11th to 20th	Night	12% 13% 6% 19% 6% 5% 4 3 5% 6% 20%	5900
	21st to end	Night	17% 13% 6% 11% 6% 6% 5% 3 5% 5% 23%	6490
February	1st to 10th	Night	15% 11% 5% 10% 6% 5% 4 4 4 7% 30%	2600
	11th to 20th	Night	16% 10% 3 9% 6% 5% 6% 5% 5% 6% 30%	2533
	21st to end	Night	15% 11% 3 11% 5% 6% 4 3 5% 5% 32%	2005
March	1st to 10th	Night	18% 11% 5% 7% 5% 4 4 3 4 5% 34%	4923
	11th to 20th	Night	11% 8% 5% 6% 4 4 4 4 5% 6% 43%	4980
	21st to end	Night	13% 10% 3 8% 5% 5% 4 4 4 5% 40%	5433
April	1st to 10th	Night	19% 12% 3 9% 5% 4 3 4 4 6% 32%	2000
	11th to 20th	Night	16% 9% 2 6% 5% 4 4 4 6% 6% 38%	1975
	21st to end	Night	18% 6% 2 6% 5% 4 4 4 5% 7% 38%	1930
May	1st to 10th	Night	28% 8% 2 6% 5% 4 5% 3 4 6% 28%	4033
	11th to 20th	Night	27% 8% 2 6% 3 3 3 3 5% 6% 33%	3677
	21st to end	Night	21% 7% 2 6% 4 4 4 3 6% 8% 36%	3920
June	1st to 10th	Night	13% 6% 2 7% 5% 4 3 3 6% 8% 44%	1598
	11th to 20th	Night	12% 6% 2 7% 4 4 4 4 8% 9% 40%	1520
	21st to end	Night	11% 5% 2 5% 3 4 5% 4 8% 10% 42%	1520
July	1st to 10th	Night	9% 5% 3 7% 6% 4 5% 4 6% 8% 42%	2520
	11th to 20th	Night	7% 4 2 6% 4 5% 5% 5% 7% 11% 45%	2580
	21st to end	Night	13% 6% 2 7% 5% 5% 4 4 5% 7% 42%	3087
August	1st to 10th	Night	17% 6% 3 6% 4 5% 4 4 6% 9% 37%	2825
	11th to 20th	Night	16% 6% 2 6% 4 4 5% 4 6% 6% 41%	2785
	21st to end	Night	15% 4 2 5% 3 4 4 3 6% 7% 47%	3471
September	1st to 10th	Night	17% 4 2 5% 4 4 4 3 5% 8% 45%	1900
	11th to 20th	Night	12% 6% 2 5% 2 3 3 3 4 8% 52%	1921
	21st to end	Night	20% 6% 2 6% 3 5% 4 3 4 7% 39%	2184
October	1st to 10th	Night	17% 6% 2 6% 3 3 4 3 4 7% 45%	2280
	11th to 20th	Night	16% 7% 2 6% 4 3 3 4 5% 6% 43%	2280
	21st to end	Night	20% 8% 3 5% 4 4 4 3 5% 6% 39%	2508
November	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 4 6% 50%	2446
	11th to 20th	Night	17% 10% 3 6% 5% 4 5% 3 5% 6% 35%	2750
	21st to end	Night	16% 11% 4 7% 4 4 5% 4 6% 6% 33%	2800
December	1st to 10th	Night	14% 11% 7% 12% 5% 4 5% 4 6% 7% 26%	4580
	11th to 20th	Night	21% 13% 5% 8% 5% 4 5% 3 4 5% 27%	5205
	21st to end	Night	19% 14% 5% 10% 6% 5% 5% 4 5% 5% 22%	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	62% 6% 10% 15% 6% 1	3621
	11th to 20th	Day	72% 5% 7% 10% 6% 1	4060
	21st to end	Day	63% 4 10% 15% 7% 1	4466
February	1st to 10th	Day	61% 4 11% 15% 7% 1	1800
	11th to 20th	Day	56% 5% 9% 22% 7% 1	1762
	21st to end	Day	57% 4 11% 19% 8% 2	1623
March	1st to 10th	Day	52% 4 11% 21% 10% 2	4928
	11th to 20th	Day	47% 5% 14% 22% 9% 2	4980
	21st to end	Day	48% 5% 10% 20% 14% 2	5497
April	1st to 10th	Day	53% 4 10% 19% 12% 2	2400
	11th to 20th	Day	48% 5% 10% 19% 16% 2	2374
	21st to end	Day	49% 4 8% 22% 14% 2	2486
May	1st to 10th	Day	56% 7% 10% 16% 10% 2	5897
	11th to 20th	Day	53% 7% 10% 20% 9% 1	6216
	21st to end	Day	46% 7% 12% 23% 11% 2	6949
June	1st to 10th	Day	45% 6% 10% 23% 15% 1	2786
	11th to 20th	Day	45% 6% 12% 21% 14% 2	2660
	21st to end	Day	40% 6% 13% 27% 14% 1	2660
July	1st to 10th	Day	40% 7% 14% 25% 11% 2	4370
	11th to 20th	Day	37% 9% 14% 25% 15% 1	4301
	21st to end	Day	42% 7% 10% 24% 16% 1	4324
August	1st to 10th	Day	49% 8% 13% 21% 9%	4091
	11th to 20th	Day	44% 7% 11% 27% 10% 1	4056
	21st to end	Day	39% 5% 11% 28% 15% 2	4180
September	1st to 10th	Day	42% 4 9% 24% 18% 3	2280
	11th to 20th	Day	36% 4 11% 27% 20% 2	2256
	21st to end	Day	48% 5% 10% 20% 16% 1	1995
October	1st to 10th	Day	41% 4 9% 25% 18% 3	3160
	11th to 20th	Day	42% 6% 8% 24% 17% 3	3140
	21st to end	Day	32% 5% 14% 31% 18% 1	3428
November	1st to 10th	Day	40% 5% 13% 21% 17% 3	1850
	11th to 20th	Day	53% 5% 10% 20% 11% 2	1646
	21st to end	Day	56% 4 12% 21% 7%	1600
December	1st to 10th	Day	61% 8% 10% 15% 6% 1	2600
	11th to 20th	Day	60% 5% 12% 18% 4	2986
	21st to end	Day	68% 6% 11% 10% 5% 1	3960
January	1st to 10th	Night	61% 5% 10% 16% 7% 1	6321
	11th to 20th	Night	60% 7% 13% 11% 7% 1	5900
	21st to end	Night	61% 4 10% 16% 7% 1	6490
February	1st to 10th	Night	54% 5% 11% 21% 8% 1	2600
	11th to 20th	Night	54% 5% 10% 19% 12% 1	2535
	21st to end	Night	55% 5% 9% 19% 11% 2	2005
March	1st to 10th	Night	52% 4 12% 20% 10% 2	4923
	11th to 20th	Night	39% 7% 16% 26% 8% 4	4980
	21st to end	Night	46% 5% 8% 20% 20% 2	5433
April	1st to 10th	Night	54% 4 9% 18% 14% 1	2000
	11th to 20th	Night	44% 7% 10% 22% 15% 2	1975
	21st to end	Night	45% 4 10% 24% 15% 3	1930
May	1st to 10th	Night	57% 6% 8% 15% 11% 3	4060
	11th to 20th	Night	51% 7% 11% 20% 11% 1	3678
	21st to end	Night	46% 7% 12% 20% 12% 3	3927
June	1st to 10th	Night	39% 5% 13% 26% 15% 2	1598
	11th to 20th	Night	38% 8% 14% 23% 15% 2	1520
	21st to end	Night	35% 8% 13% 29% 14% 1	1520
July	1st to 10th	Night	38% 8% 13% 21% 16% 3	2480
	11th to 20th	Night	32% 9% 15% 26% 17% 1	2532
	21st to end	Night	40% 7% 13% 18% 20% 2	2988
August	1st to 10th	Night	45% 8% 14% 23% 10%	2814
	11th to 20th	Night	41% 7% 11% 28% 13% 1	2812
	21st to end	Night	36% 6% 12% 32% 13% 2	3471
September	1st to 10th	Night	38% 5% 11% 24% 18% 3	1900
	11th to 20th	Night	32% 5% 10% 31% 20% 2	1921
	21st to end	Night	45% 5% 10% 22% 17% 1	2184
October	1st to 10th	Night	37% 5% 11% 26% 20% 1	3800
	11th to 20th	Night	34% 5% 9% 26% 20% 5%	3779
	21st to end	Night	33% 3 13% 28% 21% 2	4120
November	1st to 10th	Night	36% 4 13% 26% 19% 2	2446
	11th to 20th	Night	48% 4 9% 23% 13% 3	2750
	21st to end	Night	50% 4 13% 22% 9% 1	2800
December	1st to 10th	Night	53% 10% 14% 19% 4	4580
	11th to 20th	Night	58% 5% 14% 17% 6%	5208
	21st to end	Night	62% 6% 10% 15% 7%	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% 24% 31% 10% 4 1	205
	11th to 20th	Day	35% 21% 32% 11% 1	300
	21st to end	Day	27% 18% 37% 13% 4 1	330
February	1st to 10th	Day	31% 20% 34% 12% 3	300
	11th to 20th	Day	37% 20% 33% 8% 1	300
	21st to end	Day	34% 17% 31% 16% 2	387
March	1st to 10th	Day	29% 19% 28% 20% 4	500
	11th to 20th	Day	29% 20% 29% 15% 4 1	500
	21st to end	Day	29% 20% 31% 13% 5% 2	550
April	1st to 10th	Day	30% 18% 29% 17% 5% 1	500
	11th to 20th	Day	23% 21% 25% 18% 9% 3	492
	21st to end	Day	29% 16% 32% 15% 8% 2	500
May	1st to 10th	Day	30% 14% 30% 13% 10% 4	503
	11th to 20th	Day	26% 14% 27% 16% 13% 4	527
	21st to end	Day	22% 9% 26% 22% 15% 6%	573
June	1st to 10th	Day	19% 13% 26% 26% 12% 4	526
	11th to 20th	Day	20% 8% 24% 29% 15% 4	490
	21st to end	Day	16% 9% 30% 27% 14% 4	490
July	1st to 10th	Day	14% 6% 25% 27% 18% 10%	485
	11th to 20th	Day	9% 5% 29% 30% 20% 8%	484
	21st to end	Day	14% 6% 27% 30% 18% 5%	532
August	1st to 10th	Day	13% 6% 24% 27% 20% 9%	486
	11th to 20th	Day	13% 6% 23% 27% 19% 11%	479
	21st to end	Day	16% 5% 23% 28% 16% 13%	539
September	1st to 10th	Day	19% 6% 19% 28% 19% 9%	490
	11th to 20th	Day	16% 3 18% 28% 23% 11%	490
	21st to end	Day	29% 8% 22% 21% 14% 6%	490
October	1st to 10th	Day	22% 9% 20% 25% 19% 6%	490
	11th to 20th	Day	21% 14% 29% 23% 11% 2	490
	21st to end	Day	23% 14% 32% 24% 7% 1	539
November	1st to 10th	Day	17% 15% 29% 24% 12% 2	440
	11th to 20th	Day	24% 21% 31% 15% 8%	246
	21st to end	Day	28% 17% 36% 17% 2 1	200
December	1st to 10th	Day	33% 20% 34% 9% 5% 1	200
	11th to 20th	Day	30% 21% 31% 17% 2	200
	21st to end	Day	28% 19% 30% 17% 5%	220
January	1st to 10th	Night	24% 20% 33% 19% 3	800
	11th to 20th	Night	29% 14% 31% 23% 3	800
	21st to end	Night	22% 19% 34% 22% 3	880
February	1st to 10th	Night	26% 17% 29% 26% 2	800
	11th to 20th	Night	29% 21% 31% 18% 1	783
	21st to end	Night	27% 16% 33% 22% 2	660
March	1st to 10th	Night	25% 15% 33% 24% 3	800
	11th to 20th	Night	26% 16% 29% 23% 6% 1	800
	21st to end	Night	23% 15% 33% 22% 6%	880
April	1st to 10th	Night	27% 16% 30% 22% 5%	800
	11th to 20th	Night	21% 13% 32% 26% 7% 1	791
	21st to end	Night	23% 11% 28% 31% 7%	730
May	1st to 10th	Night	26% 7% 24% 32% 11% 1	600
	11th to 20th	Night	21% 7% 26% 35% 10%	444
	21st to end	Night	16% 6% 21% 36% 19% 2	433
June	1st to 10th	Night	15% 6% 20% 39% 19% 1	400
	11th to 20th	Night	15% 5% 22% 39% 19% 1	380
	21st to end	Night	12% 6% 22% 44% 17% 1	380
July	1st to 10th	Night	12% 6% 15% 44% 19% 4	370
	11th to 20th	Night	8% 2 16% 43% 28% 2	402
	21st to end	Night	11% 3 17% 45% 24% 1	624
August	1st to 10th	Night	10% 2 14% 43% 30% 2	567
	11th to 20th	Night	15% 5% 10% 39% 26% 5%	564
	21st to end	Night	14% 4 16% 34% 30% 3	831
September	1st to 10th	Night	18% 4 16% 35% 24% 4	760
	11th to 20th	Night	15% 4 15% 32% 29% 5%	760
	21st to end	Night	22% 8% 18% 30% 20% 3	760
October	1st to 10th	Night	20% 7% 20% 29% 21% 3	760
	11th to 20th	Night	20% 13% 24% 31% 11% 1	760
	21st to end	Night	24% 12% 23% 32% 8% 1	836
November	1st to 10th	Night	16% 10% 28% 34% 11% 1	780
	11th to 20th	Night	24% 17% 24% 26% 8% 1	800
	21st to end	Night	24% 15% 28% 27% 5% 1	800
December	1st to 10th	Night	28% 16% 30% 21% 5%	800
	11th to 20th	Night	27% 16% 28% 25% 4	800
	21st to end	Night	26% 16% 28% 28% 3	880

Page generated at 2025-06-07 10:28:18. Version ac07

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