Anderson University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anderson University 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	14% 10% 4 8% 5% 4 4 4 6% 7% 35%	95473
	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 36%	93596
Transparency	Day	48% 5% 12% 22% 12% 2	95232
	Night	49% 4 10% 22% 13% 2	93443
Seeing	Day	17% 9% 26% 24% 17% 7%	15327
	Night	19% 8% 28% 30% 14% 2	25127

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% 18% 9% 11% 5% 5% 4 3 4 4 22%	2527
	11th to 20th	Day	16% 15% 9% 12% 5% 7% 7% 7% 4 4 15%	2530
	21st to end	Day	26% 22% 9% 11% 3 3 3 2 3 3 14%	2948
February	1st to 10th	Day	17% 15% 7% 10% 7% 5% 4 3 4 4 23%	1862
	11th to 20th	Day	15% 13% 4 10% 7% 5% 4 3 5% 5% 29%	1848
	21st to end	Day	17% 15% 6% 9% 5% 4 3 3 5% 6% 29%	1570
March	1st to 10th	Day	20% 20% 5% 9% 4 3 2 2 4 4 26%	3120
	11th to 20th	Day	13% 9% 3 7% 4 4 3 4 5% 7% 41%	3402
	21st to end	Day	16% 11% 4 10% 6% 5% 4 3 5% 7% 29%	3929
April	1st to 10th	Day	15% 13% 3 8% 5% 5% 3 3 5% 6% 33%	2280
	11th to 20th	Day	18% 9% 3 7% 4 4 4 3 5% 6% 37%	2259
	21st to end	Day	20% 8% 3 8% 5% 5% 4 3 5% 7% 33%	2470
May	1st to 10th	Day	19% 10% 3 7% 5% 5% 4 4 6% 7% 28%	4082
	11th to 20th	Day	19% 8% 2 5% 4 4 4 3 6% 8% 37%	4081
	21st to end	Day	10% 7% 2 7% 5% 5% 5% 4 7% 10% 37%	4530
June	1st to 10th	Day	10% 7% 2 7% 6% 5% 5% 4 6% 8% 40%	2660
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 5% 7% 8% 43%	2660
	21st to end	Day	10% 6% 3 7% 5% 5% 4 4 6% 9% 41%	2660
July	1st to 10th	Day	13% 7% 3 8% 5% 5% 5% 5% 6% 10% 34%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 8% 11% 46%	4440
	21st to end	Day	9% 7% 2 7% 5% 5% 6% 5% 7% 10% 37%	4631
August	1st to 10th	Day	8% 5% 2 5% 4 4 5% 4 6% 10% 46%	2457
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 4 7% 10% 39%	2380
	21st to end	Day	7% 4 2 6% 4 4 5% 5% 7% 10% 47%	2485
September	1st to 10th	Day	12% 7% 3 5% 4 4 4 3 6% 8% 45%	2111
	11th to 20th	Day	10% 6% 2 5% 4 5% 4 4 7% 8% 47%	1980
	21st to end	Day	14% 6% 2 5% 4 3 3 3 4 7% 49%	1980
October	1st to 10th	Day	12% 6% 2 7% 4 4 3 3 4 7% 47%	1980
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 7% 43%	1837
	21st to end	Day	20% 11% 3 7% 4 4 4 2 6% 7% 33%	1782
November	1st to 10th	Day	9% 8% 2 6% 4 4 4 3 5% 7% 49%	1672
	11th to 20th	Day	15% 14% 4 8% 5% 3 3 3 6% 6% 32%	1710
	21st to end	Day	19% 12% 4 7% 5% 3 3 3 5% 6% 33%	1710
December	1st to 10th	Day	19% 16% 4 11% 5% 4 4 2 4 5% 24%	1710
	11th to 20th	Day	15% 18% 6% 12% 5% 4 3 3 4 4 26%	1967
	21st to end	Day	22% 22% 9% 12% 5% 4 3 2 4 4 13%	2783
January	1st to 10th	Night	17% 18% 9% 12% 5% 4 3 2 4 4 22%	4428
	11th to 20th	Night	14% 21% 8% 14% 6% 5% 5% 5% 4 3 17%	4440
	21st to end	Night	25% 19% 8% 8% 4 3 3 2 3 4 20%	4711
February	1st to 10th	Night	18% 15% 4 10% 5% 4 4 2 5% 4 27%	2318
	11th to 20th	Night	14% 12% 5% 10% 6% 5% 3 3 5% 6% 31%	2218
	21st to end	Night	19% 12% 4 11% 5% 5% 4 3 4 5% 29%	1884
March	1st to 10th	Night	19% 14% 3 6% 4 4 3 3 4 5% 34%	3733
	11th to 20th	Night	12% 8% 2 5% 5% 4 4 3 5% 7% 45%	3557
	21st to end	Night	18% 9% 3 7% 5% 4 3 3 5% 6% 36%	3732
April	1st to 10th	Night	14% 11% 2 6% 4 4 5% 4 5% 7% 38%	1900
	11th to 20th	Night	17% 8% 2 5% 5% 4 3 3 5% 8% 38%	1870
	21st to end	Night	17% 8% 3 6% 4 4 5% 4 7% 7% 35%	1710
May	1st to 10th	Night	18% 11% 4 8% 5% 5% 5% 4 5% 8% 27%	2813
	11th to 20th	Night	19% 7% 2 5% 4 3 3 4 5% 8% 39%	2812
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 8% 9% 42%	3022
June	1st to 10th	Night	8% 6% 2 6% 4 5% 5% 3 5% 7% 49%	1520
	11th to 20th	Night	8% 6% 2 6% 4 3 4 3 5% 9% 48%	1520
	21st to end	Night	8% 4 2 6% 5% 4 5% 6% 8% 10% 43%	1520
July	1st to 10th	Night	9% 5% 2 6% 5% 4 4 4 7% 9% 46%	2530
	11th to 20th	Night	6% 3 2 4 3 3 4 4 6% 9% 55%	2530
	21st to end	Night	10% 7% 2 7% 5% 4 5% 4 7% 10% 40%	2924
August	1st to 10th	Night	7% 4 1 5% 4 5% 4 4 6% 8% 49%	1701
	11th to 20th	Night	6% 6% 2 6% 3 4 5% 5% 5% 8% 51%	1737
	21st to end	Night	6% 4 2 5% 4 5% 4 4 6% 8% 52%	2080
September	1st to 10th	Night	12% 5% 2 6% 4 3 4 4 6% 8% 47%	1829
	11th to 20th	Night	9% 4 2 5% 3 3 4 3 5% 8% 54%	1980
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 6% 52%	1980
October	1st to 10th	Night	9% 5% 2 6% 4 4 3 3 4 6% 53%	1980
	11th to 20th	Night	19% 7% 2 6% 3 3 3 3 4 5% 44%	2117
	21st to end	Night	18% 9% 2 6% 5% 4 4 4 5% 6% 37%	2574
November	1st to 10th	Night	12% 9% 2 5% 3 3 3 3 5% 6% 48%	2406
	11th to 20th	Night	15% 10% 3 7% 5% 3 3 3 5% 7% 38%	2470
	21st to end	Night	19% 14% 4 7% 6% 4 4 3 4 5% 31%	2470
December	1st to 10th	Night	18% 13% 5% 9% 6% 4 4 3 5% 5% 27%	2470
	11th to 20th	Night	17% 15% 6% 9% 5% 3 4 3 4 5% 28%	3226
	21st to end	Night	23% 19% 8% 11% 5% 5% 4 3 4 5% 15%	4884

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	65% 2 8% 17% 7%	2528
	11th to 20th	Day	73% 3 10% 9% 5%	2530
	21st to end	Day	77% 2 7% 11% 3	2948
February	1st to 10th	Day	64% 3 9% 13% 10% 1	1862
	11th to 20th	Day	58% 3 10% 20% 8% 1	1858
	21st to end	Day	57% 4 11% 19% 7% 2	1570
March	1st to 10th	Day	63% 3 7% 17% 9% 1	3120
	11th to 20th	Day	43% 4 10% 31% 11% 1	3402
	21st to end	Day	55% 4 14% 22% 4	3929
April	1st to 10th	Day	51% 4 12% 20% 13% 1	2280
	11th to 20th	Day	47% 5% 10% 24% 11% 3	2259
	21st to end	Day	51% 4 10% 22% 10% 3	2470
May	1st to 10th	Day	53% 6% 13% 21% 7%	4120
	11th to 20th	Day	45% 6% 14% 24% 10%	4085
	21st to end	Day	39% 7% 13% 23% 16% 1	4543
June	1st to 10th	Day	41% 5% 12% 23% 16% 3	2660
	11th to 20th	Day	36% 6% 11% 25% 20% 2	2660
	21st to end	Day	39% 6% 16% 20% 16% 4	2660
July	1st to 10th	Day	44% 5% 12% 21% 16% 2	4371
	11th to 20th	Day	29% 5% 16% 29% 19% 1	4365
	21st to end	Day	41% 7% 16% 18% 15% 3	4484
August	1st to 10th	Day	32% 7% 15% 30% 14% 2	2444
	11th to 20th	Day	37% 7% 14% 27% 15% 1	2380
	21st to end	Day	32% 7% 12% 27% 16% 7%	2485
September	1st to 10th	Day	37% 6% 12% 24% 18% 4	2111
	11th to 20th	Day	34% 6% 12% 25% 20% 3	1980
	21st to end	Day	36% 4 9% 26% 23% 1	1980
October	1st to 10th	Day	38% 4 11% 26% 18% 3	1980
	11th to 20th	Day	39% 4 11% 25% 19% 2	1837
	21st to end	Day	52% 3 10% 22% 12% 1	1782
November	1st to 10th	Day	34% 4 13% 28% 18% 3	1672
	11th to 20th	Day	52% 3 10% 21% 11% 3	1710
	21st to end	Day	53% 4 10% 23% 8% 2	1710
December	1st to 10th	Day	64% 3 10% 16% 7%	1710
	11th to 20th	Day	61% 3 9% 21% 6%	1964
	21st to end	Day	76% 3 7% 9% 5%	2783
January	1st to 10th	Night	67% 4 9% 14% 7%	4428
	11th to 20th	Night	73% 3 7% 12% 5%	4440
	21st to end	Night	70% 2 7% 14% 6%	4711
February	1st to 10th	Night	61% 3 11% 16% 9% 1	2318
	11th to 20th	Night	54% 4 11% 18% 12% 1	2219
	21st to end	Night	57% 4 11% 16% 10% 2	1884
March	1st to 10th	Night	53% 4 8% 24% 10% 1	3733
	11th to 20th	Night	39% 5% 11% 27% 16% 2	3557
	21st to end	Night	49% 4 13% 26% 7% 1	3732
April	1st to 10th	Night	46% 5% 11% 24% 13% 1	1900
	11th to 20th	Night	44% 5% 10% 20% 16% 4	1870
	21st to end	Night	47% 6% 10% 20% 12% 4	1710
May	1st to 10th	Night	55% 5% 10% 21% 7% 1	2840
	11th to 20th	Night	44% 5% 13% 28% 9% 1	2813
	21st to end	Night	35% 7% 15% 25% 15% 3	3030
June	1st to 10th	Night	34% 5% 10% 27% 20% 3	1520
	11th to 20th	Night	33% 6% 12% 25% 21% 3	1520
	21st to end	Night	32% 8% 15% 25% 16% 5%	1520
July	1st to 10th	Night	34% 7% 11% 27% 16% 6%	2490
	11th to 20th	Night	24% 6% 14% 32% 22% 2	2482
	21st to end	Night	39% 5% 15% 20% 17% 4	2831
August	1st to 10th	Night	30% 7% 15% 28% 17% 2	1690
	11th to 20th	Night	31% 7% 13% 27% 20% 2	1737
	21st to end	Night	27% 6% 14% 26% 22% 5%	2080
September	1st to 10th	Night	35% 5% 11% 24% 19% 6%	1829
	11th to 20th	Night	29% 5% 9% 28% 25% 3	1980
	21st to end	Night	33% 6% 9% 25% 24% 3	1980
October	1st to 10th	Night	32% 5% 11% 26% 23% 3	1980
	11th to 20th	Night	43% 3 8% 25% 19% 2	2117
	21st to end	Night	48% 3 9% 24% 14% 2	2574
November	1st to 10th	Night	38% 4 9% 25% 21% 3	2406
	11th to 20th	Night	46% 3 10% 22% 16% 3	2470
	21st to end	Night	56% 4 10% 21% 9%	2470
December	1st to 10th	Night	58% 4 10% 18% 9% 1	2470
	11th to 20th	Night	59% 2 9% 21% 8% 1	3228
	21st to end	Night	73% 4 9% 10% 5%	4884

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	24% 18% 33% 19% 4 1	270
	11th to 20th	Day	21% 19% 38% 15% 5% 1	270
	21st to end	Day	30% 18% 28% 19% 5%	297
February	1st to 10th	Day	28% 15% 33% 20% 4	270
	11th to 20th	Day	23% 19% 34% 18% 6%	270
	21st to end	Day	24% 15% 40% 19% 3	225
March	1st to 10th	Day	23% 20% 36% 19% 2	270
	11th to 20th	Day	25% 14% 35% 17% 8% 1	408
	21st to end	Day	30% 14% 31% 17% 8% 1	506
April	1st to 10th	Day	18% 17% 32% 21% 9% 3	460
	11th to 20th	Day	19% 16% 30% 20% 12% 3	452
	21st to end	Day	24% 14% 33% 18% 8% 2	460
May	1st to 10th	Day	21% 13% 29% 25% 9% 4	463
	11th to 20th	Day	23% 6% 26% 24% 13% 8%	487
	21st to end	Day	14% 4 25% 27% 20% 10%	557
June	1st to 10th	Day	10% 6% 26% 31% 21% 6%	680
	11th to 20th	Day	11% 5% 23% 32% 23% 7%	680
	21st to end	Day	13% 4 24% 29% 20% 9%	680
July	1st to 10th	Day	13% 2 16% 24% 27% 18%	671
	11th to 20th	Day	7% 4 19% 32% 25% 13%	668
	21st to end	Day	11% 3 12% 30% 29% 14%	632
August	1st to 10th	Day	11% 1 12% 28% 29% 18%	486
	11th to 20th	Day	13% 3 18% 26% 27% 13%	479
	21st to end	Day	9% 2 11% 28% 32% 17%	532
September	1st to 10th	Day	13% 4 15% 24% 31% 12%	450
	11th to 20th	Day	10% 2 13% 27% 29% 19%	450
	21st to end	Day	14% 8% 21% 23% 23% 10%	450
October	1st to 10th	Day	12% 5% 25% 32% 18% 8%	450
	11th to 20th	Day	14% 14% 33% 26% 12% 1	410
	21st to end	Day	30% 13% 34% 20% 3	297
November	1st to 10th	Day	13% 15% 30% 24% 14% 3	270
	11th to 20th	Day	21% 14% 33% 19% 10% 2	270
	21st to end	Day	28% 10% 37% 21% 4	270
December	1st to 10th	Day	20% 21% 36% 17% 6% 1	270
	11th to 20th	Day	21% 16% 37% 19% 6% 1	270
	21st to end	Day	29% 19% 31% 17% 4	297
January	1st to 10th	Night	23% 15% 34% 22% 5%	950
	11th to 20th	Night	27% 13% 36% 20% 4	950
	21st to end	Night	24% 14% 35% 23% 4	937
February	1st to 10th	Night	27% 10% 35% 25% 3	760
	11th to 20th	Night	21% 12% 38% 27% 3	743
	21st to end	Night	26% 10% 39% 22% 3	628
March	1st to 10th	Night	21% 14% 33% 26% 5%	760
	11th to 20th	Night	20% 12% 36% 26% 5% 1	760
	21st to end	Night	25% 10% 31% 29% 5% 1	789
April	1st to 10th	Night	18% 11% 37% 28% 7%	570
	11th to 20th	Night	20% 10% 33% 28% 9% 1	563
	21st to end	Night	21% 7% 41% 21% 9% 1	570
May	1st to 10th	Night	23% 5% 34% 28% 10%	570
	11th to 20th	Night	20% 5% 24% 33% 17% 2	561
	21st to end	Night	11% 3 23% 38% 22% 3	617
June	1st to 10th	Night	9% 5% 23% 46% 18% 1	570
	11th to 20th	Night	11% 4 20% 41% 22% 1	570
	21st to end	Night	9% 2 23% 39% 25% 2	570
July	1st to 10th	Night	9% 2 10% 39% 33% 6%	555
	11th to 20th	Night	7% 3 13% 41% 31% 5%	552
	21st to end	Night	8% 3 9% 43% 34% 2	624
August	1st to 10th	Night	9% 2 10% 40% 34% 4	567
	11th to 20th	Night	8% 1 13% 40% 33% 6%	564
	21st to end	Night	6% 3 11% 36% 40% 4	624
September	1st to 10th	Night	15% 2 12% 34% 32% 5%	569
	11th to 20th	Night	10% 1 15% 34% 34% 6%	720
	21st to end	Night	13% 4 21% 35% 24% 3	720
October	1st to 10th	Night	12% 6% 23% 36% 18% 5%	720
	11th to 20th	Night	23% 9% 29% 26% 12% 1	720
	21st to end	Night	21% 10% 35% 26% 7%	792
November	1st to 10th	Night	16% 9% 34% 27% 13% 1	740
	11th to 20th	Night	20% 15% 30% 26% 8% 1	760
	21st to end	Night	26% 11% 29% 27% 8%	760
December	1st to 10th	Night	24% 12% 35% 24% 4	760
	11th to 20th	Night	25% 9% 35% 24% 6%	897
	21st to end	Night	30% 13% 31% 22% 4	1045

Page generated at 2024-08-27 09:49:38. Version ac07

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