Shooting Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shooting Star Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	3 8% 3 8% 5% 5% 5% 4 6% 7% 46%	140673
	Night	3 8% 4 9% 5% 4 4 4 5% 7% 47%	137933
Transparency	Day	35% 8% 13% 21% 17% 7%	135401
	Night	35% 8% 14% 22% 15% 5%	134209
Seeing	Day	11% 17% 32% 26% 11% 2	17299
	Night	10% 10% 27% 37% 15% 1	27044

By Month

Percentage Cloud Cover SW (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	1 12% 7% 18% 8% 6% 6% 4 7% 7% 25%	4513
	11th to 20th	Day	1 8% 4 10% 5% 6% 4 3 4 6% 50%	5340
	21st to end	Day	1 11% 5% 10% 5% 4 4 3 6% 8% 43%	5844
February	1st to 10th	Day	2 17% 8% 15% 8% 6% 5% 4 7% 6% 23%	1890
	11th to 20th	Day	2 16% 8% 13% 8% 6% 6% 4 5% 6% 25%	1845
	21st to end	Day	2 18% 6% 17% 8% 5% 5% 4 4 6% 24%	1669
March	1st to 10th	Day	1 15% 6% 14% 7% 5% 4 3 5% 5% 34%	4888
	11th to 20th	Day	2 13% 5% 11% 6% 5% 5% 4 5% 6% 38%	5000
	21st to end	Day	2 18% 7% 13% 7% 7% 8% 6% 6% 7% 20%	5486
April	1st to 10th	Day	6% 16% 5% 10% 7% 6% 5% 4 6% 6% 28%	2300
	11th to 20th	Day	6% 13% 5% 13% 7% 6% 5% 4 5% 6% 31%	2516
	21st to end	Day	5% 14% 5% 10% 6% 5% 6% 5% 7% 8% 29%	2600
May	1st to 10th	Day	6% 10% 3 8% 4 5% 5% 4 6% 8% 42%	5880
	11th to 20th	Day	4 5% 3 7% 6% 6% 7% 5% 8% 8% 41%	6016
	21st to end	Day	5% 9% 3 7% 4 5% 4 4 6% 8% 44%	6925
June	1st to 10th	Day	9% 6% 3 7% 5% 5% 5% 4 7% 8% 42%	2800
	11th to 20th	Day	8% 7% 2 6% 4 4 5% 3 7% 7% 46%	2991
	21st to end	Day	2 2 1 3 3 4 4 3 5% 7% 65%	3000
July	1st to 10th	Day	1 2 1 3 3 3 4 4 6% 7% 66%	6779
	11th to 20th	Day	1 1 1 2 3 3 4 4 6% 7% 68%	6207
	21st to end	Day	2 2 1 4 4 4 5% 4 6% 9% 60%	6401
August	1st to 10th	Day	2 2 1 4 3 4 5% 5% 7% 9% 58%	5779
	11th to 20th	Day	2 1 1 3 3 4 4 4 6% 8% 64%	5798
	21st to end	Day	4 3 1 5% 3 4 4 3 5% 7% 61%	6392
September	1st to 10th	Day	3 4 1 5% 4 4 3 3 5% 6% 61%	2380
	11th to 20th	Day	5% 5% 2 6% 4 5% 5% 3 5% 7% 53%	2200
	21st to end	Day	6% 5% 2 5% 4 3 3 3 4 6% 60%	2200
October	1st to 10th	Day	5% 6% 2 4 3 3 4 3 4 4 63%	3321
	11th to 20th	Day	4 6% 2 6% 4 3 4 3 4 5% 58%	3250
	21st to end	Day	4 7% 3 7% 5% 5% 5% 4 7% 9% 44%	3496
November	1st to 10th	Day	8% 13% 4 9% 5% 4 4 4 5% 7% 39%	1833
	11th to 20th	Day	4 15% 4 11% 5% 5% 5% 4 5% 7% 35%	1680
	21st to end	Day	1 13% 5% 12% 6% 5% 4 4 5% 6% 39%	1680
December	1st to 10th	Day	2 10% 5% 9% 6% 5% 4 3 3 5% 49%	2700
	11th to 20th	Day	3 14% 7% 15% 8% 6% 6% 3 5% 6% 28%	3106
	21st to end	Day	3 14% 5% 14% 7% 6% 6% 4 7% 8% 27%	3968
January	1st to 10th	Night	1 10% 6% 17% 9% 7% 6% 5% 6% 7% 26%	8407
	11th to 20th	Night	1 8% 4 12% 6% 4 5% 3 6% 7% 45%	7650
	21st to end	Night	1 12% 4 9% 4 3 3 3 6% 8% 44%	8370
February	1st to 10th	Night	3 15% 7% 15% 7% 6% 6% 4 5% 7% 25%	2730
	11th to 20th	Night	2 14% 7% 13% 8% 6% 6% 3 5% 5% 31%	2662
	21st to end	Night	2 14% 7% 16% 8% 5% 5% 3 6% 5% 28%	2134
March	1st to 10th	Night	1 15% 6% 16% 5% 4 3 3 4 5% 37%	5050
	11th to 20th	Night	2 10% 5% 10% 5% 5% 5% 3 5% 7% 44%	5000
	21st to end	Night	3 12% 5% 11% 6% 6% 6% 6% 7% 7% 30%	5489
April	1st to 10th	Night	4 12% 4 9% 6% 5% 6% 4 6% 8% 36%	2100
	11th to 20th	Night	5% 11% 4 9% 6% 5% 5% 5% 6% 7% 38%	1830
	21st to end	Night	5% 10% 3 8% 5% 5% 5% 4 5% 9% 42%	1800
May	1st to 10th	Night	6% 10% 3 7% 3 3 4 3 4 7% 48%	4100
	11th to 20th	Night	5% 6% 2 6% 4 5% 5% 5% 7% 9% 47%	3896
	21st to end	Night	4 7% 2 5% 4 3 4 4 6% 9% 53%	3972
June	1st to 10th	Night	8% 5% 3 5% 4 4 4 4 8% 8% 47%	1600
	11th to 20th	Night	8% 5% 1 4 3 3 3 4 5% 9% 54%	1402
	21st to end	Night	2 1 3 2 3 4 3 5% 8% 70%	1400
July	1st to 10th	Night	1 1 1 2 2 3 4 4 6% 7% 70%	3180
	11th to 20th	Night	1 1 1 1 2 3 3 6% 9% 73%	3746
	21st to end	Night	1 1 1 2 2 2 4 4 7% 8% 69%	4472
August	1st to 10th	Night	2 2 1 3 2 3 4 4 6% 8% 65%	4033
	11th to 20th	Night	1 1 1 3 3 3 4 4 6% 8% 67%	4051
	21st to end	Night	5% 3 1 5% 2 3 3 3 5% 6% 65%	4583
September	1st to 10th	Night	4 3 1 3 3 2 3 4 5% 6% 66%	2015
	11th to 20th	Night	4 4 2 5% 3 5% 5% 4 6% 7% 56%	2200
	21st to end	Night	7% 5% 1 3 2 3 3 2 3 5% 65%	2200
October	1st to 10th	Night	5% 5% 2 4 3 2 3 3 3 4 67%	3869
	11th to 20th	Night	6% 7% 2 5% 3 4 4 3 4 6% 55%	3898
	21st to end	Night	3 8% 3 7% 4 3 4 4 6% 8% 50%	4301
November	1st to 10th	Night	7% 12% 3 8% 5% 4 3 4 5% 7% 42%	2665
	11th to 20th	Night	4 12% 4 10% 6% 5% 5% 5% 6% 6% 38%	2939
	21st to end	Night	3 11% 5% 9% 6% 4 5% 4 5% 7% 42%	2940
December	1st to 10th	Night	2 10% 4 8% 6% 5% 4 3 4 5% 47%	4710
	11th to 20th	Night	3 12% 6% 15% 8% 7% 5% 4 5% 6% 30%	5321
	21st to end	Night	3 14% 5% 13% 7% 6% 6% 5% 6% 7% 28%	7218

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	53% 11% 16% 13% 7%	4514
	11th to 20th	Day	32% 6% 23% 22% 11% 4	5340
	21st to end	Day	37% 9% 15% 23% 15% 2	5844
February	1st to 10th	Day	61% 9% 13% 13% 4 1	1890
	11th to 20th	Day	57% 10% 13% 12% 6% 2	1854
	21st to end	Day	60% 9% 8% 15% 6% 1	1669
March	1st to 10th	Day	48% 8% 12% 17% 11% 4	4888
	11th to 20th	Day	44% 8% 15% 24% 8% 1	5000
	21st to end	Day	59% 11% 14% 13% 2	5486
April	1st to 10th	Day	54% 9% 13% 15% 8% 1	2300
	11th to 20th	Day	52% 9% 11% 18% 9% 1	2519
	21st to end	Day	50% 10% 13% 21% 5%	2600
May	1st to 10th	Day	37% 9% 14% 27% 12% 1	5880
	11th to 20th	Day	33% 11% 14% 27% 12% 3	6019
	21st to end	Day	34% 10% 12% 31% 14%	6926
June	1st to 10th	Day	37% 9% 17% 26% 11% 1	2800
	11th to 20th	Day	35% 8% 10% 21% 19% 8%	2991
	21st to end	Day	17% 7% 8% 24% 32% 11%	3000
July	1st to 10th	Day	15% 4 8% 15% 34% 25%	6706
	11th to 20th	Day	14% 3 7% 17% 30% 29%	6130
	21st to end	Day	19% 5% 7% 19% 36% 15%	6217
August	1st to 10th	Day	21% 6% 8% 17% 31% 16%	4208
	11th to 20th	Day	18% 5% 8% 23% 33% 12%	4197
	21st to end	Day	17% 5% 7% 21% 31% 18%	4611
September	1st to 10th	Day	23% 5% 8% 19% 33% 12%	2380
	11th to 20th	Day	28% 7% 9% 23% 24% 8%	2200
	21st to end	Day	27% 5% 13% 27% 24% 5%	2200
October	1st to 10th	Day	26% 5% 7% 22% 33% 8%	3321
	11th to 20th	Day	30% 5% 10% 36% 16% 4	3250
	21st to end	Day	34% 8% 18% 29% 11% 1	3496
November	1st to 10th	Day	45% 8% 15% 22% 8% 2	1833
	11th to 20th	Day	46% 8% 20% 18% 7% 1	1680
	21st to end	Day	46% 9% 17% 19% 8% 1	1680
December	1st to 10th	Day	38% 6% 26% 21% 7% 2	2700
	11th to 20th	Day	55% 9% 20% 13% 3	3104
	21st to end	Day	49% 10% 14% 14% 7% 6%	3968
January	1st to 10th	Night	51% 12% 13% 18% 6%	8408
	11th to 20th	Night	38% 8% 21% 22% 9% 2	7650
	21st to end	Night	37% 7% 17% 24% 13% 2	8370
February	1st to 10th	Night	58% 10% 13% 13% 5%	2730
	11th to 20th	Night	55% 8% 12% 15% 8% 1	2663
	21st to end	Night	57% 9% 10% 15% 7% 2	2134
March	1st to 10th	Night	48% 8% 10% 18% 11% 4	5050
	11th to 20th	Night	38% 9% 15% 27% 10% 1	5000
	21st to end	Night	47% 15% 16% 20% 2	5489
April	1st to 10th	Night	43% 12% 16% 17% 10% 1	2100
	11th to 20th	Night	43% 11% 16% 21% 8% 1	1830
	21st to end	Night	38% 10% 16% 28% 8%	1800
May	1st to 10th	Night	34% 8% 14% 30% 14% 1	4097
	11th to 20th	Night	28% 10% 16% 32% 12% 2	3897
	21st to end	Night	24% 11% 15% 34% 15% 1	3972
June	1st to 10th	Night	33% 10% 18% 26% 13% 1	1600
	11th to 20th	Night	27% 7% 13% 25% 20% 8%	1402
	21st to end	Night	14% 4 11% 25% 32% 13%	1400
July	1st to 10th	Night	12% 4 9% 17% 37% 22%	3145
	11th to 20th	Night	8% 3 5% 20% 38% 26%	3700
	21st to end	Night	10% 6% 6% 20% 37% 20%	4344
August	1st to 10th	Night	17% 5% 9% 18% 36% 15%	2928
	11th to 20th	Night	17% 6% 9% 28% 26% 14%	2928
	21st to end	Night	15% 4 7% 23% 35% 16%	3295
September	1st to 10th	Night	18% 6% 8% 20% 32% 16%	2015
	11th to 20th	Night	24% 7% 12% 23% 25% 9%	2200
	21st to end	Night	24% 4 10% 29% 28% 5%	2200
October	1st to 10th	Night	21% 4 9% 27% 34% 5%	3869
	11th to 20th	Night	30% 6% 9% 36% 16% 3	3898
	21st to end	Night	31% 9% 15% 30% 14% 1	4301
November	1st to 10th	Night	42% 9% 15% 23% 9% 2	2665
	11th to 20th	Night	44% 9% 17% 21% 7% 1	2939
	21st to end	Night	41% 9% 17% 21% 9% 2	2940
December	1st to 10th	Night	38% 7% 26% 22% 5% 1	4710
	11th to 20th	Night	52% 10% 20% 14% 4	5322
	21st to end	Night	51% 9% 15% 15% 7% 3	7218

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	14% 22% 28% 27% 8% 1	258
	11th to 20th	Day	5% 16% 39% 28% 10% 2	330
	21st to end	Day	6% 15% 37% 33% 9% 1	363
February	1st to 10th	Day	18% 29% 32% 17% 3	330
	11th to 20th	Day	14% 25% 32% 23% 5%	330
	21st to end	Day	15% 28% 35% 16% 5%	385
March	1st to 10th	Day	14% 29% 33% 18% 4 1	509
	11th to 20th	Day	12% 25% 33% 23% 7%	500
	21st to end	Day	16% 27% 34% 19% 4	550
April	1st to 10th	Day	18% 25% 30% 20% 6% 1	500
	11th to 20th	Day	17% 26% 36% 16% 4 1	492
	21st to end	Day	16% 23% 30% 20% 9% 2	500
May	1st to 10th	Day	13% 21% 30% 26% 9% 2	503
	11th to 20th	Day	15% 16% 32% 24% 12% 2	599
	21st to end	Day	16% 13% 26% 27% 16% 3	789
June	1st to 10th	Day	8% 17% 26% 30% 16% 3	730
	11th to 20th	Day	13% 18% 34% 25% 9%	730
	21st to end	Day	6% 12% 32% 31% 16% 3	730
July	1st to 10th	Day	2 8% 32% 39% 17% 2	721
	11th to 20th	Day	4 10% 39% 32% 13% 2	614
	21st to end	Day	3 11% 32% 38% 14% 3	575
August	1st to 10th	Day	5% 10% 37% 32% 14% 2	527
	11th to 20th	Day	3 9% 35% 31% 18% 4	517
	21st to end	Day	6% 13% 31% 30% 15% 5%	583
September	1st to 10th	Day	5% 12% 32% 29% 18% 5%	530
	11th to 20th	Day	11% 17% 29% 26% 12% 4	530
	21st to end	Day	9% 13% 29% 29% 15% 4	530
October	1st to 10th	Day	10% 13% 30% 26% 17% 4	368
	11th to 20th	Day	10% 21% 23% 24% 15% 6%	330
	21st to end	Day	14% 18% 31% 28% 7% 2	363
November	1st to 10th	Day	15% 22% 29% 22% 9% 3	330
	11th to 20th	Day	11% 21% 37% 21% 9% 2	330
	21st to end	Day	8% 14% 38% 29% 10% 1	330
December	1st to 10th	Day	14% 18% 30% 27% 11% 1	330
	11th to 20th	Day	17% 20% 33% 23% 6%	330
	21st to end	Day	17% 20% 31% 21% 10% 2	333
January	1st to 10th	Night	9% 14% 30% 36% 10% 1	1008
	11th to 20th	Night	8% 12% 35% 33% 11% 2	840
	21st to end	Night	8% 8% 38% 36% 9% 1	924
February	1st to 10th	Night	10% 16% 35% 32% 6% 1	840
	11th to 20th	Night	9% 15% 32% 34% 9% 1	824
	21st to end	Night	11% 15% 37% 29% 8% 1	692
March	1st to 10th	Night	8% 18% 32% 33% 9% 1	808
	11th to 20th	Night	8% 12% 30% 37% 12% 1	800
	21st to end	Night	10% 13% 32% 33% 11%	880
April	1st to 10th	Night	11% 14% 30% 32% 11% 1	700
	11th to 20th	Night	12% 11% 34% 33% 9%	593
	21st to end	Night	11% 9% 27% 35% 16% 1	600
May	1st to 10th	Night	11% 11% 22% 37% 18% 1	600
	11th to 20th	Night	11% 7% 25% 35% 20% 2	591
	21st to end	Night	13% 8% 21% 38% 19% 1	650
June	1st to 10th	Night	12% 8% 22% 36% 21% 1	600
	11th to 20th	Night	10% 7% 26% 43% 14%	402
	21st to end	Night	3 1 19% 48% 28% 2	400
July	1st to 10th	Night	1 1 18% 47% 31% 2	390
	11th to 20th	Night	3 2 17% 51% 27%	525
	21st to end	Night	2 1 14% 51% 30% 2	657
August	1st to 10th	Night	5% 2 15% 48% 28% 2	597
	11th to 20th	Night	3 2 13% 50% 30% 2	594
	21st to end	Night	4 4 19% 39% 31% 3	660
September	1st to 10th	Night	6% 2 16% 44% 29% 2	615
	11th to 20th	Night	6% 4 18% 40% 28% 4	800
	21st to end	Night	11% 3 19% 39% 24% 4	800
October	1st to 10th	Night	11% 7% 24% 37% 20% 2	800
	11th to 20th	Night	13% 8% 20% 37% 19% 2	800
	21st to end	Night	9% 9% 25% 43% 11% 3	880
November	1st to 10th	Night	13% 12% 29% 34% 10% 2	820
	11th to 20th	Night	12% 14% 34% 33% 6% 1	1049
	21st to end	Night	9% 11% 33% 35% 10% 1	1050
December	1st to 10th	Night	14% 12% 32% 34% 7% 1	1050
	11th to 20th	Night	14% 15% 30% 34% 6%	1050
	21st to end	Night	14% 15% 32% 28% 8% 1	1155

Page generated at 2026-02-27 23:40:22. Version ac07

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