Astraeus Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astraeus Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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	15% 8% 3 6% 5% 3 5% 5% 5% 7% 37%	79352
	Night	15% 8% 3 6% 5% 3 4 4 5% 7% 39%	80165
Transparency	Day	46% 4 10% 23% 14% 2	79069
	Night	46% 4 10% 22% 16% 3	79968
Seeing	Day	17% 8% 22% 25% 18% 9%	14172
	Night	18% 7% 23% 32% 18% 2	23875

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	15% 14% 6% 8% 6% 3 4 5% 5% 7% 28%	2836
	11th to 20th	Day	17% 12% 5% 14% 6% 4 5% 4 3 4 26%	2840
	21st to end	Day	27% 14% 7% 6% 4 2 4 3 4 5% 24%	3124
February	1st to 10th	Day	18% 12% 5% 9% 4 3 4 4 4 6% 31%	1881
	11th to 20th	Day	19% 9% 4 8% 5% 4 5% 4 4 6% 34%	1848
	21st to end	Day	19% 11% 4 7% 5% 3 5% 5% 6% 5% 30%	1570
March	1st to 10th	Day	20% 9% 3 5% 5% 2 4 5% 4 6% 38%	1850
	11th to 20th	Day	19% 8% 4 7% 5% 3 4 5% 6% 6% 32%	1976
	21st to end	Day	18% 10% 4 7% 6% 3 4 4 5% 6% 32%	2178
April	1st to 10th	Day	13% 6% 3 6% 6% 3 5% 5% 6% 7% 41%	2142
	11th to 20th	Day	17% 8% 3 6% 5% 3 4 3 5% 5% 41%	2138
	21st to end	Day	18% 6% 4 5% 6% 3 5% 5% 5% 7% 37%	2340
May	1st to 10th	Day	18% 6% 3 6% 6% 4 5% 5% 5% 7% 35%	2340
	11th to 20th	Day	17% 8% 3 7% 6% 3 4 5% 5% 7% 36%	2301
	21st to end	Day	8% 5% 3 7% 6% 4 6% 6% 7% 10% 36%	2531
June	1st to 10th	Day	12% 5% 2 5% 5% 5% 6% 5% 6% 6% 43%	2340
	11th to 20th	Day	7% 4 2 5% 6% 4 7% 7% 7% 10% 43%	2430
	21st to end	Day	8% 5% 3 4 5% 4 6% 7% 6% 10% 42%	2520
July	1st to 10th	Day	13% 6% 3 6% 6% 4 6% 6% 6% 11% 33%	2520
	11th to 20th	Day	9% 5% 2 6% 5% 4 6% 6% 8% 10% 39%	2365
	21st to end	Day	10% 6% 3 5% 5% 4 6% 6% 7% 9% 39%	2547
August	1st to 10th	Day	11% 5% 2 5% 5% 3 5% 5% 8% 11% 40%	2327
	11th to 20th	Day	9% 5% 3 6% 7% 4 6% 7% 8% 9% 37%	2246
	21st to end	Day	8% 5% 2 5% 6% 4 6% 5% 6% 10% 43%	2376
September	1st to 10th	Day	14% 6% 2 5% 5% 3 5% 5% 5% 8% 42%	2059
	11th to 20th	Day	11% 5% 3 5% 4 2 4 5% 6% 8% 47%	1980
	21st to end	Day	13% 5% 2 5% 4 3 4 4 4 7% 48%	1980
October	1st to 10th	Day	11% 4 2 4 4 3 5% 4 5% 6% 52%	1980
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 5% 6% 48%	1866
	21st to end	Day	20% 7% 2 5% 3 3 3 4 4 5% 44%	1842
November	1st to 10th	Day	11% 6% 2 5% 4 2 3 3 4 6% 54%	1672
	11th to 20th	Day	16% 8% 3 5% 5% 3 3 3 4 6% 44%	1710
	21st to end	Day	18% 8% 3 5% 4 2 4 5% 4 5% 41%	1710
December	1st to 10th	Day	22% 12% 4 6% 5% 3 4 4 5% 5% 31%	1710
	11th to 20th	Day	14% 13% 4 8% 6% 3 4 4 4 5% 33%	2153
	21st to end	Day	20% 15% 5% 7% 6% 3 5% 5% 4 6% 23%	3124
January	1st to 10th	Night	16% 15% 6% 8% 6% 4 4 4 4 6% 27%	4109
	11th to 20th	Night	18% 13% 5% 9% 9% 3 4 4 3 4 28%	4120
	21st to end	Night	24% 14% 4 6% 5% 3 3 4 4 5% 28%	4532
February	1st to 10th	Night	22% 9% 5% 8% 5% 3 5% 4 5% 6% 29%	2296
	11th to 20th	Night	20% 9% 4 8% 5% 2 4 4 5% 5% 35%	2218
	21st to end	Night	21% 12% 4 8% 6% 3 3 4 4 5% 30%	1884
March	1st to 10th	Night	18% 10% 3 6% 5% 3 3 4 4 5% 40%	2227
	11th to 20th	Night	20% 9% 3 6% 5% 3 4 4 5% 6% 35%	1984
	21st to end	Night	17% 10% 4 6% 6% 3 4 4 5% 7% 35%	2178
April	1st to 10th	Night	12% 5% 3 4 6% 3 5% 5% 6% 8% 43%	1832
	11th to 20th	Night	15% 7% 3 6% 5% 3 5% 4 4 7% 41%	1771
	21st to end	Night	15% 7% 4 6% 5% 3 5% 5% 4 7% 39%	1620
May	1st to 10th	Night	16% 6% 3 6% 6% 4 5% 6% 5% 7% 35%	1620
	11th to 20th	Night	15% 6% 3 5% 6% 3 5% 6% 6% 7% 38%	1592
	21st to end	Night	7% 4 2 7% 5% 4 6% 6% 9% 11% 39%	1744
June	1st to 10th	Night	8% 5% 3 5% 4 3 4 4 5% 12% 48%	1620
	11th to 20th	Night	5% 4 2 5% 5% 3 5% 5% 7% 11% 49%	1522
	21st to end	Night	6% 3 2 4 5% 3 5% 5% 8% 13% 45%	1440
July	1st to 10th	Night	9% 5% 2 6% 5% 3 6% 5% 7% 8% 43%	1440
	11th to 20th	Night	6% 3 3 4 5% 4 5% 5% 6% 10% 49%	1588
	21st to end	Night	9% 5% 2 4 5% 3 5% 5% 6% 10% 46%	1771
August	1st to 10th	Night	7% 5% 2 4 4 3 5% 4 7% 10% 50%	1611
	11th to 20th	Night	6% 5% 2 5% 5% 4 5% 6% 7% 11% 44%	1652
	21st to end	Night	5% 4 2 3 4 3 5% 5% 7% 10% 52%	1980
September	1st to 10th	Night	12% 5% 2 4 5% 3 4 4 5% 8% 48%	1882
	11th to 20th	Night	11% 4 2 5% 5% 3 3 4 5% 8% 51%	1980
	21st to end	Night	11% 5% 2 4 4 3 4 3 4 6% 54%	1980
October	1st to 10th	Night	10% 4 1 3 5% 2 3 4 4 6% 57%	1980
	11th to 20th	Night	14% 6% 3 4 5% 2 4 3 5% 7% 47%	2092
	21st to end	Night	17% 7% 2 5% 4 3 3 4 4 6% 44%	2510
November	1st to 10th	Night	11% 6% 3 4 5% 2 3 4 5% 6% 51%	2406
	11th to 20th	Night	14% 7% 4 5% 5% 2 3 4 4 6% 45%	2470
	21st to end	Night	17% 9% 3 5% 5% 3 3 3 4 6% 41%	2470
December	1st to 10th	Night	20% 11% 4 7% 4 3 4 4 5% 6% 32%	2470
	11th to 20th	Night	19% 11% 5% 7% 5% 3 4 3 4 6% 34%	3042
	21st to end	Night	18% 15% 5% 9% 8% 5% 6% 5% 4 5% 21%	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	58% 2 10% 19% 11% 1	2837
	11th to 20th	Day	64% 2 7% 19% 8% 1	2840
	21st to end	Day	65% 1 6% 22% 5% 1	3124
February	1st to 10th	Day	55% 3 7% 22% 11% 2	1881
	11th to 20th	Day	54% 3 8% 21% 12% 3	1858
	21st to end	Day	55% 3 8% 19% 11% 3	1570
March	1st to 10th	Day	49% 3 9% 22% 15% 1	1850
	11th to 20th	Day	53% 4 10% 19% 12% 2	1976
	21st to end	Day	53% 4 11% 22% 9% 1	2178
April	1st to 10th	Day	41% 5% 12% 25% 14% 3	2142
	11th to 20th	Day	46% 3 8% 22% 17% 3	2138
	21st to end	Day	48% 4 9% 24% 12% 3	2340
May	1st to 10th	Day	48% 4 12% 24% 10% 1	2340
	11th to 20th	Day	48% 4 14% 21% 12% 1	2305
	21st to end	Day	41% 7% 17% 21% 13% 1	2531
June	1st to 10th	Day	40% 5% 9% 27% 17% 2	2340
	11th to 20th	Day	36% 7% 15% 24% 17% 2	2430
	21st to end	Day	35% 6% 15% 22% 18% 4	2520
July	1st to 10th	Day	45% 6% 13% 19% 15% 2	2451
	11th to 20th	Day	39% 6% 15% 22% 14% 4	2294
	21st to end	Day	39% 6% 14% 26% 13% 3	2405
August	1st to 10th	Day	38% 7% 14% 27% 14% 1	2314
	11th to 20th	Day	41% 6% 12% 24% 16% 1	2246
	21st to end	Day	35% 6% 12% 27% 16% 5%	2376
September	1st to 10th	Day	40% 4 13% 21% 17% 5%	2059
	11th to 20th	Day	35% 5% 10% 24% 23% 3	1980
	21st to end	Day	36% 4 8% 25% 24% 3	1980
October	1st to 10th	Day	33% 3 8% 26% 27% 4	1980
	11th to 20th	Day	38% 2 7% 25% 23% 4	1866
	21st to end	Day	43% 3 9% 26% 17% 3	1842
November	1st to 10th	Day	33% 2 7% 30% 23% 4	1672
	11th to 20th	Day	43% 2 8% 23% 18% 5%	1710
	21st to end	Day	46% 3 8% 23% 20% 2	1710
December	1st to 10th	Day	57% 3 9% 22% 10% 1	1710
	11th to 20th	Day	55% 2 8% 20% 14% 1	2150
	21st to end	Day	63% 3 8% 18% 7% 1	3124
January	1st to 10th	Night	61% 2 7% 18% 11% 1	4109
	11th to 20th	Night	62% 2 6% 20% 9% 2	4120
	21st to end	Night	60% 2 8% 20% 10% 1	4532
February	1st to 10th	Night	57% 3 10% 19% 10% 1	2296
	11th to 20th	Night	53% 2 7% 21% 13% 2	2219
	21st to end	Night	59% 2 9% 15% 12% 3	1884
March	1st to 10th	Night	48% 3 6% 22% 19% 3	2227
	11th to 20th	Night	50% 3 10% 20% 14% 2	1984
	21st to end	Night	50% 4 11% 23% 10% 2	2178
April	1st to 10th	Night	39% 4 11% 25% 19% 3	1832
	11th to 20th	Night	44% 4 7% 19% 19% 6%	1771
	21st to end	Night	45% 5% 10% 23% 13% 3	1620
May	1st to 10th	Night	49% 5% 10% 24% 10% 3	1620
	11th to 20th	Night	43% 7% 13% 21% 13% 2	1593
	21st to end	Night	35% 8% 16% 24% 14% 3	1745
June	1st to 10th	Night	31% 4 14% 29% 18% 4	1620
	11th to 20th	Night	27% 6% 17% 25% 21% 4	1522
	21st to end	Night	29% 7% 19% 24% 15% 6%	1440
July	1st to 10th	Night	38% 7% 11% 25% 15% 4	1400
	11th to 20th	Night	30% 5% 17% 25% 20% 4	1536
	21st to end	Night	32% 7% 16% 27% 16% 2	1672
August	1st to 10th	Night	30% 5% 18% 28% 17% 2	1600
	11th to 20th	Night	33% 6% 14% 27% 17% 3	1652
	21st to end	Night	26% 7% 17% 28% 19% 4	1980
September	1st to 10th	Night	34% 5% 13% 22% 20% 6%	1882
	11th to 20th	Night	33% 4 10% 25% 25% 3	1980
	21st to end	Night	32% 3 7% 26% 26% 6%	1980
October	1st to 10th	Night	29% 3 10% 26% 27% 5%	1980
	11th to 20th	Night	39% 3 8% 24% 23% 3	2092
	21st to end	Night	43% 2 6% 24% 21% 4	2510
November	1st to 10th	Night	35% 3 7% 26% 24% 5%	2406
	11th to 20th	Night	41% 3 7% 21% 22% 6%	2470
	21st to end	Night	46% 3 8% 25% 17% 2	2470
December	1st to 10th	Night	53% 3 10% 21% 12% 1	2470
	11th to 20th	Night	52% 3 7% 22% 14% 2	3044
	21st to end	Night	66% 3 9% 15% 8%	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	23% 16% 33% 20% 6% 1	270
	11th to 20th	Day	28% 22% 30% 16% 4	270
	21st to end	Day	25% 16% 39% 16% 3	297
February	1st to 10th	Day	24% 16% 39% 17% 3	270
	11th to 20th	Day	29% 21% 35% 10% 4	270
	21st to end	Day	31% 16% 36% 13% 3	225
March	1st to 10th	Day	25% 13% 44% 13% 5%	255
	11th to 20th	Day	23% 12% 37% 20% 8%	416
	21st to end	Day	28% 13% 30% 21% 8% 1	462
April	1st to 10th	Day	18% 15% 26% 28% 12% 2	420
	11th to 20th	Day	22% 12% 24% 24% 13% 5%	412
	21st to end	Day	23% 11% 28% 24% 10% 4	420
May	1st to 10th	Day	21% 9% 29% 23% 12% 6%	423
	11th to 20th	Day	18% 6% 24% 26% 17% 9%	447
	21st to end	Day	12% 4 17% 28% 22% 17%	485
June	1st to 10th	Day	13% 4 14% 26% 29% 15%	450
	11th to 20th	Day	8% 3 18% 31% 26% 14%	540
	21st to end	Day	10% 4 19% 31% 23% 13%	630
July	1st to 10th	Day	13% 3 12% 23% 26% 24%	621
	11th to 20th	Day	10% 1 13% 26% 30% 20%	467
	21st to end	Day	11% 2 9% 28% 32% 18%	488
August	1st to 10th	Day	13% 1 11% 26% 28% 20%	446
	11th to 20th	Day	13% 3 9% 28% 32% 15%	439
	21st to end	Day	9% 2 8% 28% 30% 23%	495
September	1st to 10th	Day	14% 2 11% 27% 29% 18%	450
	11th to 20th	Day	10% 3 11% 23% 35% 17%	450
	21st to end	Day	13% 7% 17% 24% 26% 13%	450
October	1st to 10th	Day	14% 2 16% 33% 25% 9%	450
	11th to 20th	Day	14% 13% 25% 32% 12% 4	450
	21st to end	Day	21% 10% 32% 24% 13% 1	357
November	1st to 10th	Day	16% 6% 30% 29% 15% 5%	270
	11th to 20th	Day	22% 15% 26% 27% 8% 1	270
	21st to end	Day	24% 10% 30% 26% 8% 2	270
December	1st to 10th	Day	24% 17% 27% 24% 7% 1	270
	11th to 20th	Day	18% 13% 39% 19% 10% 1	270
	21st to end	Day	28% 17% 30% 19% 6%	297
January	1st to 10th	Night	23% 14% 31% 28% 5%	760
	11th to 20th	Night	29% 14% 32% 22% 4	760
	21st to end	Night	24% 10% 36% 28% 2	836
February	1st to 10th	Night	28% 10% 33% 28% 2	760
	11th to 20th	Night	28% 11% 35% 25% 2	743
	21st to end	Night	27% 11% 39% 20% 2	628
March	1st to 10th	Night	22% 12% 33% 27% 6%	743
	11th to 20th	Night	25% 8% 33% 26% 6% 1	720
	21st to end	Night	22% 11% 27% 31% 8%	792
April	1st to 10th	Night	15% 8% 32% 35% 9% 1	572
	11th to 20th	Night	18% 7% 29% 32% 13% 1	533
	21st to end	Night	19% 6% 31% 31% 11% 2	540
May	1st to 10th	Night	20% 6% 25% 32% 15% 2	540
	11th to 20th	Night	16% 6% 15% 39% 20% 4	531
	21st to end	Night	8% 2 14% 38% 31% 7%	584
June	1st to 10th	Night	9% 2 13% 42% 30% 3	540
	11th to 20th	Night	6% 2 13% 43% 32% 5%	540
	21st to end	Night	6% 2 13% 44% 31% 4	540
July	1st to 10th	Night	11% 1 9% 30% 40% 10%	525
	11th to 20th	Night	7% 2 8% 34% 43% 6%	522
	21st to end	Night	9% 3 6% 36% 40% 6%	591
August	1st to 10th	Night	10% 2 5% 35% 43% 5%	537
	11th to 20th	Night	7% 2 8% 39% 38% 6%	534
	21st to end	Night	6% 1 6% 33% 49% 5%	594
September	1st to 10th	Night	14% 2 7% 32% 39% 6%	622
	11th to 20th	Night	11% 3 11% 30% 38% 7%	720
	21st to end	Night	12% 3 16% 34% 32% 3	720
October	1st to 10th	Night	11% 3 17% 34% 28% 6%	720
	11th to 20th	Night	18% 6% 23% 34% 18% 2	720
	21st to end	Night	20% 7% 28% 32% 13% 1	792
November	1st to 10th	Night	14% 6% 24% 36% 17% 2	740
	11th to 20th	Night	18% 9% 32% 31% 11%	760
	21st to end	Night	22% 10% 23% 33% 12% 1	760
December	1st to 10th	Night	27% 9% 28% 30% 6%	760
	11th to 20th	Night	25% 8% 33% 26% 8% 1	760
	21st to end	Night	28% 12% 28% 28% 5%	836

Page generated at 2024-03-03 06:28:54. Version ac07

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