Rock Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rock Star Observatory clear sky chart from 2005-11-06 to 2024-08-30.

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% 6% 2 5% 4 4 4 3 5% 7% 48%	95580
	Night	12% 5% 2 5% 3 3 3 3 5% 7% 54%	93531
Transparency	Day	36% 3 9% 25% 21% 6%	95356
	Night	32% 3 9% 23% 23% 9%	93361
Seeing	Day	12% 6% 20% 28% 25% 8%	14930
	Night	13% 6% 26% 36% 18% 2	24741

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% 5% 1 5% 4 3 3 2 4 6% 54%	2847
	11th to 20th	Day	13% 5% 2 4 2 3 2 3 4 5% 57%	2850
	21st to end	Day	23% 10% 2 6% 2 2 2 2 2 5% 45%	3135
February	1st to 10th	Day	19% 8% 4 7% 4 3 2 2 3 5% 44%	1797
	11th to 20th	Day	18% 8% 3 5% 3 4 2 2 3 6% 45%	1849
	21st to end	Day	21% 6% 2 5% 3 3 3 2 3 4 49%	1627
March	1st to 10th	Day	16% 8% 2 4 3 3 3 3 6% 7% 46%	3436
	11th to 20th	Day	19% 7% 2 6% 5% 4 5% 4 5% 6% 39%	3480
	21st to end	Day	16% 8% 2 6% 4 3 4 3 6% 7% 41%	3814
April	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 4 7% 45%	2090
	11th to 20th	Day	15% 8% 2 6% 4 4 4 3 5% 6% 43%	2186
	21st to end	Day	12% 6% 2 6% 4 5% 4 5% 5% 6% 45%	2361
May	1st to 10th	Day	21% 9% 3 7% 5% 3 4 3 4 6% 36%	4082
	11th to 20th	Day	15% 6% 2 6% 4 4 4 3 5% 5% 46%	4082
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4477
June	1st to 10th	Day	6% 4 2 5% 5% 3 6% 4 7% 8% 50%	2470
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 4 7% 9% 52%	2470
	21st to end	Day	5% 4 2 5% 4 3 5% 4 6% 9% 54%	2470
July	1st to 10th	Day	6% 5% 2 5% 5% 5% 5% 4 6% 8% 50%	4120
	11th to 20th	Day	2 3 1 4 3 3 4 4 6% 10% 61%	4120
	21st to end	Day	7% 6% 3 6% 4 5% 5% 5% 8% 10% 40%	4465
August	1st to 10th	Day	2 1 1 2 2 3 4 4 5% 9% 65%	2458
	11th to 20th	Day	7% 3 1 5% 4 4 5% 4 6% 10% 50%	2431
	21st to end	Day	4 4 2 4 5% 5% 7% 4 7% 9% 49%	2434
September	1st to 10th	Day	7% 4 2 5% 4 4 4 3 5% 7% 53%	1980
	11th to 20th	Day	9% 4 2 7% 5% 5% 5% 4 6% 6% 47%	1980
	21st to end	Day	8% 4 2 4 3 3 3 2 5% 7% 58%	1980
October	1st to 10th	Day	6% 3 2 5% 4 3 3 3 4 6% 61%	1911
	11th to 20th	Day	13% 3 1 5% 3 2 3 3 3 6% 58%	1800
	21st to end	Day	14% 5% 2 4 2 2 2 2 3 4 59%	1980
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 5% 56%	1858
	11th to 20th	Day	8% 4 2 6% 4 3 3 3 5% 6% 56%	1824
	21st to end	Day	17% 6% 1 4 3 4 3 2 4 5% 51%	1710
December	1st to 10th	Day	15% 5% 2 5% 4 2 4 3 5% 6% 49%	1710
	11th to 20th	Day	15% 8% 2 6% 5% 4 3 3 4 5% 45%	2161
	21st to end	Day	17% 7% 2 6% 3 3 3 3 4 5% 49%	3135
January	1st to 10th	Night	14% 5% 2 4 3 3 3 3 4 5% 56%	4108
	11th to 20th	Night	13% 4 1 4 2 2 2 2 3 4 62%	4120
	21st to end	Night	21% 8% 2 5% 3 3 2 2 3 4 47%	4532
February	1st to 10th	Night	16% 7% 2 5% 3 3 2 2 3 6% 50%	2399
	11th to 20th	Night	18% 6% 2 5% 4 3 3 2 4 6% 48%	2218
	21st to end	Night	19% 5% 2 4 3 2 3 2 4 5% 50%	1827
March	1st to 10th	Night	16% 7% 3 7% 5% 4 3 3 4 6% 41%	3419
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 5% 6% 44%	3480
	21st to end	Night	15% 6% 2 5% 3 4 3 3 5% 6% 47%	3817
April	1st to 10th	Night	9% 5% 2 4 4 4 4 3 6% 7% 53%	2090
	11th to 20th	Night	13% 5% 2 5% 3 4 3 4 5% 7% 49%	1942
	21st to end	Night	12% 5% 2 4 2 2 3 3 5% 7% 53%	1815
May	1st to 10th	Night	20% 9% 3 7% 3 3 3 4 5% 7% 37%	2823
	11th to 20th	Night	11% 6% 3 6% 4 4 4 2 5% 7% 48%	2823
	21st to end	Night	11% 5% 2 6% 4 4 4 4 6% 7% 46%	3090
June	1st to 10th	Night	5% 2 1 3 4 3 4 4 6% 8% 60%	1710
	11th to 20th	Night	3 3 1 3 2 3 3 3 5% 8% 65%	1710
	21st to end	Night	4 2 1 3 4 4 4 4 7% 9% 58%	1710
July	1st to 10th	Night	4 3 1 4 3 4 4 3 6% 10% 57%	2850
	11th to 20th	Night	3 3 1 3 2 2 2 2 6% 10% 66%	2850
	21st to end	Night	4 4 2 5% 5% 4 5% 5% 7% 10% 50%	3098
August	1st to 10th	Night	1 1 1 2 1 1 2 3 5% 10% 72%	1701
	11th to 20th	Night	4 4 2 4 3 3 3 4 5% 9% 58%	1690
	21st to end	Night	3 3 1 3 4 4 4 3 7% 11% 56%	2124
September	1st to 10th	Night	6% 4 2 5% 3 3 4 3 4 8% 57%	1980
	11th to 20th	Night	9% 4 2 4 4 4 4 3 6% 7% 54%	1980
	21st to end	Night	6% 3 4 3 2 3 3 5% 7% 63%	1980
October	1st to 10th	Night	6% 3 1 3 2 3 3 3 5% 7% 64%	2029
	11th to 20th	Night	13% 4 1 3 2 2 3 2 3 5% 61%	2160
	21st to end	Night	16% 5% 1 4 2 2 2 2 3 3 60%	2376
November	1st to 10th	Night	10% 4 2 4 3 3 3 2 3 5% 61%	2220
	11th to 20th	Night	7% 5% 2 5% 3 3 2 3 5% 7% 57%	2352
	21st to end	Night	16% 6% 2 5% 3 3 3 2 4 5% 52%	2470
December	1st to 10th	Night	14% 5% 2 5% 3 3 3 3 3 7% 52%	2470
	11th to 20th	Night	13% 8% 2 5% 4 3 3 3 4 5% 50%	3036
	21st to end	Night	17% 6% 2 5% 3 2 2 2 3 4 53%	4532

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	34% 1 4 21% 34% 5%	2848
	11th to 20th	Day	32% 1 8% 24% 30% 5%	2850
	21st to end	Day	46% 1 4 19% 22% 8%	3135
February	1st to 10th	Day	45% 2 5% 18% 21% 10%	1797
	11th to 20th	Day	44% 2 5% 18% 21% 9%	1859
	21st to end	Day	41% 2 4 16% 23% 14%	1627
March	1st to 10th	Day	40% 2 5% 18% 28% 7%	3436
	11th to 20th	Day	48% 2 8% 21% 17% 4	3480
	21st to end	Day	43% 2 10% 21% 19% 5%	3814
April	1st to 10th	Day	39% 3 10% 20% 18% 10%	2090
	11th to 20th	Day	41% 3 8% 18% 22% 8%	2186
	21st to end	Day	39% 3 8% 22% 24% 5%	2361
May	1st to 10th	Day	51% 2 7% 23% 13% 4	4120
	11th to 20th	Day	40% 2 8% 26% 23% 1	4086
	21st to end	Day	47% 4 12% 21% 12% 4	4489
June	1st to 10th	Day	29% 5% 16% 31% 17% 3	2470
	11th to 20th	Day	28% 5% 13% 31% 19% 5%	2470
	21st to end	Day	26% 6% 12% 31% 22% 3	2470
July	1st to 10th	Day	30% 6% 18% 35% 11%	4056
	11th to 20th	Day	19% 4 12% 42% 21% 2	4051
	21st to end	Day	35% 7% 15% 32% 11%	4325
August	1st to 10th	Day	17% 3 15% 37% 25% 3	2444
	11th to 20th	Day	27% 6% 15% 30% 19% 3	2431
	21st to end	Day	28% 6% 14% 33% 16% 3	2434
September	1st to 10th	Day	30% 4 10% 25% 22% 9%	1980
	11th to 20th	Day	36% 5% 10% 20% 21% 8%	1980
	21st to end	Day	27% 3 8% 24% 25% 14%	1980
October	1st to 10th	Day	26% 3 10% 24% 22% 16%	1911
	11th to 20th	Day	29% 2 6% 18% 28% 17%	1800
	21st to end	Day	32% 2 6% 18% 27% 16%	1980
November	1st to 10th	Day	32% 3 7% 25% 25% 9%	1858
	11th to 20th	Day	30% 2 9% 20% 29% 10%	1824
	21st to end	Day	38% 2 4 22% 24% 10%	1710
December	1st to 10th	Day	37% 3 9% 20% 23% 7%	1710
	11th to 20th	Day	43% 2 5% 17% 25% 8%	2159
	21st to end	Day	40% 2 4 24% 22% 8%	3135
January	1st to 10th	Night	34% 1 4 19% 32% 10%	4108
	11th to 20th	Night	30% 1 6% 19% 30% 13%	4120
	21st to end	Night	45% 1 4 16% 26% 9%	4532
February	1st to 10th	Night	38% 3 6% 18% 22% 13%	2399
	11th to 20th	Night	40% 2 6% 17% 25% 10%	2218
	21st to end	Night	39% 3 7% 15% 21% 16%	1827
March	1st to 10th	Night	46% 2 5% 15% 22% 11%	3419
	11th to 20th	Night	43% 2 8% 20% 20% 6%	3480
	21st to end	Night	39% 2 8% 19% 26% 6%	3817
April	1st to 10th	Night	30% 3 11% 22% 19% 14%	2090
	11th to 20th	Night	36% 3 9% 20% 18% 14%	1942
	21st to end	Night	31% 3 9% 24% 28% 5%	1815
May	1st to 10th	Night	49% 3 8% 21% 14% 6%	2850
	11th to 20th	Night	37% 3 13% 21% 25% 2	2824
	21st to end	Night	38% 3 14% 27% 12% 6%	3099
June	1st to 10th	Night	22% 4 17% 32% 21% 4	1710
	11th to 20th	Night	18% 3 14% 37% 20% 8%	1710
	21st to end	Night	21% 5% 13% 30% 25% 6%	1710
July	1st to 10th	Night	22% 5% 18% 41% 12% 2	2805
	11th to 20th	Night	14% 3 12% 45% 22% 3	2796
	21st to end	Night	27% 7% 17% 35% 13% 1	2999
August	1st to 10th	Night	10% 2 14% 38% 31% 5%	1691
	11th to 20th	Night	25% 4 14% 29% 22% 6%	1690
	21st to end	Night	22% 4 15% 33% 22% 4	2124
September	1st to 10th	Night	27% 3 11% 25% 23% 10%	1980
	11th to 20th	Night	30% 5% 12% 21% 22% 10%	1980
	21st to end	Night	21% 3 8% 22% 30% 16%	1980
October	1st to 10th	Night	20% 2 10% 27% 21% 19%	2029
	11th to 20th	Night	27% 2 6% 17% 26% 22%	2160
	21st to end	Night	31% 2 4 18% 25% 21%	2376
November	1st to 10th	Night	28% 2 7% 22% 28% 14%	2220
	11th to 20th	Night	28% 2 7% 21% 28% 14%	2352
	21st to end	Night	37% 2 7% 17% 26% 12%	2470
December	1st to 10th	Night	34% 3 8% 21% 23% 11%	2470
	11th to 20th	Night	38% 2 5% 17% 27% 11%	3037
	21st to end	Night	37% 2 5% 18% 27% 11%	4532

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	19% 12% 33% 28% 7%	270
	11th to 20th	Day	18% 16% 34% 24% 6% 2	270
	21st to end	Day	22% 11% 34% 23% 10% 1	297
February	1st to 10th	Day	26% 9% 36% 21% 8%	270
	11th to 20th	Day	25% 13% 40% 17% 4 1	270
	21st to end	Day	31% 13% 39% 15% 2	225
March	1st to 10th	Day	22% 13% 32% 26% 6% 1	270
	11th to 20th	Day	20% 15% 36% 22% 5% 1	270
	21st to end	Day	15% 11% 45% 20% 8%	297
April	1st to 10th	Day	20% 13% 36% 23% 8%	270
	11th to 20th	Day	20% 12% 31% 27% 9% 1	384
	21st to end	Day	16% 12% 34% 27% 9% 2	541
May	1st to 10th	Day	14% 11% 31% 34% 9% 1	653
	11th to 20th	Day	16% 4 26% 32% 18% 4	675
	21st to end	Day	12% 5% 25% 35% 20% 4	734
June	1st to 10th	Day	8% 2 12% 36% 32% 10%	680
	11th to 20th	Day	5% 3 13% 41% 29% 9%	680
	21st to end	Day	5% 2 9% 34% 37% 13%	680
July	1st to 10th	Day	6% 3 7% 29% 41% 15%	671
	11th to 20th	Day	2 5% 29% 47% 16%	668
	21st to end	Day	4 1 5% 26% 47% 17%	739
August	1st to 10th	Day	4 1 3 28% 48% 17%	676
	11th to 20th	Day	7% 1 3 29% 46% 14%	665
	21st to end	Day	5% 1 4 21% 44% 25%	481
September	1st to 10th	Day	7% 5% 14% 47% 27%	270
	11th to 20th	Day	4 1 3 29% 35% 27%	270
	21st to end	Day	11% 3 7% 19% 37% 23%	270
October	1st to 10th	Day	3 1 15% 32% 36% 13%	270
	11th to 20th	Day	12% 4 24% 31% 22% 7%	270
	21st to end	Day	24% 10% 21% 22% 20% 3	297
November	1st to 10th	Day	17% 3 30% 26% 17% 6%	270
	11th to 20th	Day	13% 8% 25% 34% 17% 3	270
	21st to end	Day	19% 13% 31% 25% 12% 1	270
December	1st to 10th	Day	18% 8% 33% 26% 12% 4	270
	11th to 20th	Day	23% 13% 32% 24% 7%	270
	21st to end	Day	21% 9% 37% 24% 9% 1	297
January	1st to 10th	Night	15% 9% 35% 33% 7% 1	950
	11th to 20th	Night	19% 13% 30% 31% 6%	950
	21st to end	Night	18% 9% 35% 32% 7%	1045
February	1st to 10th	Night	21% 10% 34% 30% 5%	879
	11th to 20th	Night	20% 11% 39% 27% 3	744
	21st to end	Night	22% 13% 42% 21% 3	571
March	1st to 10th	Night	20% 10% 35% 30% 6%	570
	11th to 20th	Night	16% 10% 37% 31% 6%	570
	21st to end	Night	14% 12% 38% 30% 6%	627
April	1st to 10th	Night	10% 9% 45% 31% 5%	570
	11th to 20th	Night	15% 9% 37% 29% 9% 1	563
	21st to end	Night	15% 8% 39% 30% 8% 1	570
May	1st to 10th	Night	11% 8% 40% 33% 8% 1	570
	11th to 20th	Night	10% 4 31% 37% 16% 1	561
	21st to end	Night	8% 5% 27% 40% 19% 2	617
June	1st to 10th	Night	6% 2 15% 48% 27% 3	570
	11th to 20th	Night	3 1 19% 56% 20% 1	570
	21st to end	Night	4 2 12% 40% 38% 5%	570
July	1st to 10th	Night	4 1 8% 43% 39% 6%	555
	11th to 20th	Night	3 1 7% 43% 43% 4	552
	21st to end	Night	2 4 44% 44% 5%	624
August	1st to 10th	Night	3 3 42% 48% 4	567
	11th to 20th	Night	6% 1 4 39% 45% 6%	564
	21st to end	Night	4 1 3 38% 46% 8%	624
September	1st to 10th	Night	6% 1 8% 36% 44% 5%	540
	11th to 20th	Night	11% 2 6% 37% 39% 4	540
	21st to end	Night	8% 1 11% 40% 35% 6%	540
October	1st to 10th	Night	6% 2 15% 45% 28% 4	589
	11th to 20th	Night	14% 4 23% 40% 18% 2	720
	21st to end	Night	17% 6% 27% 32% 16% 2	792
November	1st to 10th	Night	10% 5% 26% 42% 16% 1	740
	11th to 20th	Night	9% 8% 31% 39% 13%	832
	21st to end	Night	19% 9% 31% 29% 11% 1	950
December	1st to 10th	Night	16% 7% 33% 37% 7%	950
	11th to 20th	Night	21% 8% 30% 35% 6%	950
	21st to end	Night	20% 8% 33% 33% 6%	1045

Page generated at 2024-08-27 08:49:37. Version ac07

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