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 2024-11-02.

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	14% 8% 3 7% 4 4 5% 4 6% 7% 38%	101559
	Night	14% 9% 3 7% 5% 4 4 3 5% 7% 40%	97360
Transparency	Day	45% 4 10% 24% 15% 2	101365
	Night	45% 4 10% 24% 16% 3	97224
Seeing	Day	17% 8% 23% 25% 18% 9%	15149
	Night	18% 7% 23% 32% 18% 2	24680

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% 15% 6% 9% 5% 4 4 4 5% 7% 28%	2836
	11th to 20th	Day	17% 12% 5% 16% 5% 6% 4 3 3 4 26%	2840
	21st to end	Day	27% 15% 7% 7% 3 3 3 2 4 5% 24%	3124
February	1st to 10th	Day	17% 13% 4 9% 4 4 4 3 5% 6% 31%	1881
	11th to 20th	Day	18% 10% 3 9% 4 5% 5% 3 4 5% 34%	1848
	21st to end	Day	19% 12% 4 7% 5% 4 5% 3 6% 5% 30%	1570
March	1st to 10th	Day	25% 13% 3 7% 3 3 3 3 4 5% 31%	3120
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 5% 7% 45%	3476
	21st to end	Day	14% 9% 3 8% 5% 4 4 3 5% 7% 38%	3815
April	1st to 10th	Day	14% 7% 3 6% 5% 4 5% 4 5% 7% 40%	2261
	11th to 20th	Day	16% 9% 3 7% 4 4 4 2 5% 5% 41%	2259
	21st to end	Day	17% 7% 3 6% 5% 4 5% 4 5% 7% 37%	2470
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	4082
	11th to 20th	Day	17% 8% 3 8% 4 4 4 3 4 7% 37%	4081
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 5% 7% 10% 37%	4476
June	1st to 10th	Day	11% 6% 2 6% 5% 6% 5% 5% 6% 6% 42%	2470
	11th to 20th	Day	7% 4 2 6% 5% 5% 6% 5% 7% 9% 42%	2566
	21st to end	Day	8% 5% 3 5% 4 5% 6% 5% 7% 10% 42%	2660
July	1st to 10th	Day	10% 6% 3 8% 5% 5% 6% 4 6% 10% 37%	4440
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 5% 8% 11% 43%	4159
	21st to end	Day	13% 11% 4 9% 6% 6% 7% 5% 6% 7% 25%	4466
August	1st to 10th	Day	7% 4 2 5% 4 4 4 4 8% 12% 46%	4104
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 9% 11% 38%	3931
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 9% 54%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 43%	2173
	11th to 20th	Day	11% 5% 2 6% 3 3 4 4 6% 8% 47%	2090
	21st to end	Day	15% 6% 2 5% 5% 4 4 4 4 7% 46%	2090
October	1st to 10th	Day	10% 4 2 4 3 4 5% 3 5% 6% 54%	2090
	11th to 20th	Day	13% 6% 2 6% 3 3 4 3 5% 6% 49%	1969
	21st to end	Day	19% 7% 2 6% 2 4 3 3 5% 5% 45%	1944
November	1st to 10th	Day	11% 6% 2 5% 4 2 3 2 4 6% 54%	1681
	11th to 20th	Day	16% 8% 3 6% 5% 3 3 3 4 6% 44%	1710
	21st to end	Day	18% 9% 3 6% 4 3 4 4 4 5% 41%	1710
December	1st to 10th	Day	22% 13% 3 7% 4 4 3 3 5% 5% 30%	1710
	11th to 20th	Day	14% 14% 4 9% 5% 5% 4 4 4 5% 33%	2153
	21st to end	Day	19% 16% 5% 8% 5% 5% 4 4 4 6% 23%	3124
January	1st to 10th	Night	16% 16% 6% 9% 5% 5% 4 3 4 5% 26%	4109
	11th to 20th	Night	18% 14% 5% 11% 7% 4 3 3 3 4 28%	4120
	21st to end	Night	24% 14% 4 7% 4 3 3 3 4 5% 28%	4532
February	1st to 10th	Night	21% 10% 5% 9% 4 4 4 3 5% 5% 29%	2296
	11th to 20th	Night	20% 10% 4 8% 5% 3 4 3 5% 4 34%	2218
	21st to end	Night	21% 13% 4 9% 5% 3 4 3 4 5% 29%	1884
March	1st to 10th	Night	22% 14% 2 7% 4 4 3 3 4 5% 32%	3733
	11th to 20th	Night	14% 7% 2 5% 3 3 4 3 5% 6% 48%	3484
	21st to end	Night	14% 8% 3 6% 5% 5% 4 4 6% 6% 40%	3817
April	1st to 10th	Night	12% 6% 2 5% 5% 5% 5% 4 6% 7% 42%	1933
	11th to 20th	Night	15% 7% 3 7% 4 4 4 3 5% 6% 41%	1870
	21st to end	Night	15% 8% 3 7% 5% 4 4 4 5% 7% 39%	1710
May	1st to 10th	Night	19% 9% 3 8% 6% 5% 6% 4 5% 7% 28%	2813
	11th to 20th	Night	17% 7% 3 5% 4 4 4 4 6% 7% 39%	2812
	21st to end	Night	8% 5% 2 8% 4 5% 5% 4 8% 10% 41%	3079
June	1st to 10th	Night	8% 6% 2 5% 4 4 4 4 6% 11% 47%	1710
	11th to 20th	Night	5% 5% 2 5% 4 4 4 4 8% 10% 49%	1606
	21st to end	Night	6% 3 2 4 5% 5% 4 4 8% 13% 45%	1520
July	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 4 6% 10% 46%	2530
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 6% 9% 51%	2795
	21st to end	Night	11% 8% 3 10% 6% 6% 6% 5% 6% 9% 29%	3087
August	1st to 10th	Night	5% 5% 2 6% 3 5% 4 3 7% 10% 50%	2825
	11th to 20th	Night	6% 6% 2 7% 5% 5% 5% 4 6% 10% 43%	2881
	21st to end	Night	3 3 1 3 3 3 4 3 6% 9% 62%	3476
September	1st to 10th	Night	12% 6% 2 4 4 4 4 3 5% 8% 49%	1987
	11th to 20th	Night	10% 5% 2 6% 4 4 3 3 5% 8% 51%	2090
	21st to end	Night	12% 6% 1 5% 4 4 3 2 4 6% 52%	2090
October	1st to 10th	Night	9% 4 1 4 4 3 3 3 5% 6% 58%	2090
	11th to 20th	Night	14% 6% 3 5% 4 3 4 2 5% 6% 49%	2209
	21st to end	Night	16% 7% 2 5% 4 4 3 3 4 6% 45%	2650
November	1st to 10th	Night	11% 6% 3 5% 5% 3 3 3 5% 5% 51%	2420
	11th to 20th	Night	14% 8% 3 6% 4 3 3 4 4 6% 45%	2470
	21st to end	Night	17% 10% 3 6% 4 4 3 3 4 6% 40%	2470
December	1st to 10th	Night	20% 12% 4 7% 4 4 3 3 5% 6% 32%	2470
	11th to 20th	Night	19% 11% 4 7% 5% 3 3 3 5% 6% 34%	3042
	21st to end	Night	17% 15% 5% 10% 6% 6% 6% 3 4 6% 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	57% 2 7% 19% 11% 4	3120
	11th to 20th	Day	40% 3 10% 26% 19% 2	3476
	21st to end	Day	46% 3 11% 27% 12% 1	3815
April	1st to 10th	Day	42% 4 12% 25% 14% 2	2261
	11th to 20th	Day	46% 3 8% 23% 17% 3	2259
	21st to end	Day	47% 4 10% 25% 12% 2	2470
May	1st to 10th	Day	54% 3 13% 21% 9%	4120
	11th to 20th	Day	48% 3 12% 23% 13% 1	4085
	21st to end	Day	42% 5% 13% 19% 19% 1	4489
June	1st to 10th	Day	40% 5% 9% 27% 16% 2	2470
	11th to 20th	Day	35% 7% 15% 24% 17% 2	2566
	21st to end	Day	35% 6% 15% 21% 18% 4	2660
July	1st to 10th	Day	42% 6% 13% 22% 15% 1	4371
	11th to 20th	Day	33% 6% 12% 34% 13% 2	4088
	21st to end	Day	56% 6% 11% 16% 9% 1	4324
August	1st to 10th	Day	30% 6% 12% 38% 13% 1	4091
	11th to 20th	Day	36% 7% 12% 29% 15% 2	3970
	21st to end	Day	27% 6% 10% 37% 17% 3	4179
September	1st to 10th	Day	39% 4 12% 20% 19% 5%	2173
	11th to 20th	Day	35% 5% 10% 24% 23% 3	2090
	21st to end	Day	39% 4 7% 24% 22% 3	2090
October	1st to 10th	Day	31% 3 8% 25% 29% 3	2090
	11th to 20th	Day	37% 2 7% 26% 24% 4	1969
	21st to end	Day	41% 3 9% 27% 17% 4	1944
November	1st to 10th	Day	33% 2 7% 30% 24% 4	1681
	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	57% 2 6% 21% 13% 2	3733
	11th to 20th	Night	39% 2 9% 29% 17% 4	3484
	21st to end	Night	46% 2 10% 25% 15% 1	3817
April	1st to 10th	Night	41% 4 11% 24% 18% 3	1933
	11th to 20th	Night	44% 3 7% 19% 19% 6%	1870
	21st to end	Night	45% 5% 11% 24% 13% 3	1710
May	1st to 10th	Night	55% 4 10% 21% 8% 2	2840
	11th to 20th	Night	43% 5% 13% 27% 11% 1	2813
	21st to end	Night	36% 6% 13% 25% 17% 3	3087
June	1st to 10th	Night	32% 4 14% 29% 17% 4	1710
	11th to 20th	Night	27% 6% 17% 25% 21% 4	1606
	21st to end	Night	29% 7% 19% 23% 16% 6%	1520
July	1st to 10th	Night	34% 7% 11% 27% 18% 3	2490
	11th to 20th	Night	29% 5% 13% 34% 16% 2	2743
	21st to end	Night	50% 7% 13% 19% 11% 1	2988
August	1st to 10th	Night	29% 5% 15% 36% 14% 1	2814
	11th to 20th	Night	35% 6% 12% 29% 16% 2	2908
	21st to end	Night	19% 5% 14% 36% 21% 4	3476
September	1st to 10th	Night	34% 5% 13% 21% 21% 6%	1987
	11th to 20th	Night	32% 4 10% 25% 25% 3	2090
	21st to end	Night	34% 4 7% 25% 24% 5%	2090
October	1st to 10th	Night	28% 3 10% 25% 29% 5%	2090
	11th to 20th	Night	37% 3 8% 24% 24% 4	2209
	21st to end	Night	41% 2 6% 24% 22% 5%	2650
November	1st to 10th	Night	35% 3 7% 26% 24% 5%	2420
	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	26% 14% 43% 13% 5%	270
	11th to 20th	Day	21% 14% 38% 20% 7%	456
	21st to end	Day	27% 13% 32% 20% 7% 1	506
April	1st to 10th	Day	20% 15% 26% 27% 11% 2	460
	11th to 20th	Day	21% 13% 25% 25% 12% 4	452
	21st to end	Day	22% 11% 29% 25% 9% 4	460
May	1st to 10th	Day	20% 11% 28% 23% 12% 6%	463
	11th to 20th	Day	17% 6% 24% 26% 18% 9%	487
	21st to end	Day	12% 5% 19% 28% 21% 16%	529
June	1st to 10th	Day	13% 4 17% 25% 27% 14%	490
	11th to 20th	Day	8% 3 18% 31% 27% 14%	586
	21st to end	Day	10% 4 19% 31% 23% 13%	680
July	1st to 10th	Day	13% 3 13% 23% 26% 22%	671
	11th to 20th	Day	9% 1 14% 26% 30% 19%	508
	21st to end	Day	11% 2 10% 29% 31% 17%	532
August	1st to 10th	Day	13% 1 11% 26% 29% 20%	486
	11th to 20th	Day	13% 3 11% 28% 32% 14%	479
	21st to end	Day	8% 2 7% 27% 31% 25%	539
September	1st to 10th	Day	13% 2 11% 27% 28% 18%	490
	11th to 20th	Day	11% 3 11% 24% 36% 16%	490
	21st to end	Day	16% 7% 16% 23% 25% 12%	490
October	1st to 10th	Day	13% 2 16% 32% 27% 9%	490
	11th to 20th	Day	13% 13% 25% 30% 13% 7%	490
	21st to end	Day	19% 9% 32% 24% 15% 1	393
November	1st to 10th	Day	15% 5% 30% 29% 15% 5%	273
	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	23% 12% 33% 26% 6%	760
	11th to 20th	Night	24% 8% 34% 27% 6% 1	760
	21st to end	Night	22% 11% 29% 30% 8%	836
April	1st to 10th	Night	15% 10% 32% 34% 8%	603
	11th to 20th	Night	18% 8% 30% 31% 12% 1	563
	21st to end	Night	18% 6% 32% 31% 10% 2	570
May	1st to 10th	Night	19% 6% 25% 32% 15% 2	570
	11th to 20th	Night	16% 6% 14% 40% 20% 4	561
	21st to end	Night	8% 3 14% 39% 30% 6%	617
June	1st to 10th	Night	10% 2 13% 42% 29% 3	570
	11th to 20th	Night	5% 2 12% 44% 32% 4	570
	21st to end	Night	6% 2 14% 44% 31% 4	570
July	1st to 10th	Night	12% 1 9% 30% 39% 9%	555
	11th to 20th	Night	7% 2 8% 35% 42% 6%	552
	21st to end	Night	9% 3 6% 36% 39% 6%	624
August	1st to 10th	Night	9% 2 6% 34% 43% 5%	567
	11th to 20th	Night	7% 2 8% 40% 37% 5%	564
	21st to end	Night	6% 1 6% 32% 50% 6%	627
September	1st to 10th	Night	14% 2 7% 33% 39% 5%	657
	11th to 20th	Night	11% 3 11% 32% 37% 6%	760
	21st to end	Night	14% 3 16% 34% 31% 3	760
October	1st to 10th	Night	11% 3 16% 34% 30% 5%	760
	11th to 20th	Night	17% 6% 22% 34% 19% 1	760
	21st to end	Night	19% 6% 27% 33% 13% 1	836
November	1st to 10th	Night	15% 6% 23% 36% 17% 2	745
	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 2024-10-30 01:22:56. Version ac07

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