Celestial Exploration Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Celestial Exploration Observatory clear sky chart from 2005-11-06 to 2024-07-16.

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	17% 7% 2 6% 4 4 4 4 6% 7% 39%	89791
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	89714
Transparency	Day	43% 7% 12% 22% 14% 2	89510
	Night	42% 7% 12% 23% 14% 2	89548
Seeing	Day	20% 14% 28% 23% 12% 4	14496
	Night	19% 9% 31% 30% 10% 1	23757

By Month

Percentage Cloud Cover NE (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% 8% 2 5% 4 4 4 3 5% 5% 45%	2517
	11th to 20th	Day	14% 10% 5% 10% 5% 6% 5% 4 5% 7% 30%	2552
	21st to end	Day	21% 11% 3 7% 4 3 3 3 5% 5% 34%	3124
February	1st to 10th	Day	16% 7% 3 7% 5% 5% 4 4 6% 7% 38%	1710
	11th to 20th	Day	15% 9% 2 6% 4 5% 5% 3 6% 6% 40%	1787
	21st to end	Day	19% 8% 3 7% 5% 4 4 4 5% 5% 36%	1570
March	1st to 10th	Day	26% 7% 2 5% 4 4 4 3 5% 6% 35%	3116
	11th to 20th	Day	10% 5% 2 7% 5% 5% 4 4 6% 8% 43%	3476
	21st to end	Day	21% 8% 2 5% 3 3 3 3 4 6% 42%	4038
April	1st to 10th	Day	17% 7% 3 6% 5% 4 5% 4 6% 7% 37%	2280
	11th to 20th	Day	16% 6% 3 6% 4 4 4 4 6% 7% 39%	2254
	21st to end	Day	17% 5% 2 7% 5% 3 4 4 5% 8% 39%	2280
May	1st to 10th	Day	27% 7% 3 6% 4 4 4 3 5% 8% 30%	4129
	11th to 20th	Day	24% 9% 3 7% 5% 5% 4 4 5% 6% 29%	4398
	21st to end	Day	13% 5% 2 5% 3 4 5% 4 7% 9% 44%	4837
June	1st to 10th	Day	14% 6% 2 6% 5% 5% 6% 5% 7% 9% 37%	2660
	11th to 20th	Day	14% 5% 2 6% 5% 5% 6% 4 7% 9% 37%	2660
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 42%	2660
July	1st to 10th	Day	9% 6% 2 6% 5% 6% 6% 5% 7% 9% 38%	2660
	11th to 20th	Day	9% 4 2 6% 4 5% 5% 5% 7% 11% 40%	2593
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 5% 7% 8% 37%	2728
August	1st to 10th	Day	11% 6% 2 7% 4 4 6% 5% 8% 8% 37%	2327
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 5% 6% 7% 40%	2148
	21st to end	Day	14% 7% 2 5% 4 4 5% 4 6% 7% 41%	2376
September	1st to 10th	Day	16% 5% 2 6% 4 6% 4 4 6% 7% 41%	2160
	11th to 20th	Day	14% 4 2 4 3 3 4 3 5% 7% 51%	2134
	21st to end	Day	18% 7% 2 6% 4 4 5% 3 5% 6% 41%	1976
October	1st to 10th	Day	19% 6% 3 5% 3 3 4 4 5% 7% 41%	1800
	11th to 20th	Day	17% 5% 2 5% 4 5% 4 3 5% 7% 44%	1800
	21st to end	Day	21% 6% 2 5% 4 5% 4 3 4 7% 39%	1904
November	1st to 10th	Day	15% 7% 2 4 3 3 3 3 4 6% 51%	1671
	11th to 20th	Day	17% 6% 1 5% 3 4 4 4 6% 5% 45%	1710
	21st to end	Day	17% 7% 2 5% 4 2 4 3 6% 8% 42%	1558
December	1st to 10th	Day	19% 7% 3 7% 5% 4 4 3 6% 7% 34%	1520
	11th to 20th	Day	20% 8% 2 5% 3 5% 4 3 6% 6% 39%	1906
	21st to end	Day	20% 8% 3 8% 6% 5% 5% 4 6% 6% 28%	2772
January	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	4429
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 4 5% 7% 38%	4406
	21st to end	Night	25% 10% 2 5% 3 3 3 3 4 6% 35%	4532
February	1st to 10th	Night	16% 9% 3 6% 4 3 4 4 5% 6% 40%	2470
	11th to 20th	Night	17% 7% 3 6% 4 5% 4 4 5% 5% 40%	2277
	21st to end	Night	18% 8% 2 5% 4 3 4 4 5% 5% 41%	1884
March	1st to 10th	Night	23% 10% 2 6% 3 3 4 3 4 5% 37%	3724
	11th to 20th	Night	12% 7% 3 6% 4 4 4 4 5% 6% 48%	3479
	21st to end	Night	17% 9% 3 7% 3 4 4 3 4 4 44%	3594
April	1st to 10th	Night	18% 7% 3 6% 6% 4 4 4 5% 7% 37%	1900
	11th to 20th	Night	16% 7% 2 7% 4 4 4 3 5% 7% 41%	1875
	21st to end	Night	21% 5% 2 4 2 3 4 3 6% 6% 45%	1900
May	1st to 10th	Night	27% 8% 2 6% 4 4 4 4 5% 7% 30%	2825
	11th to 20th	Night	25% 9% 3 8% 5% 3 3 3 5% 6% 30%	2495
	21st to end	Night	13% 6% 2 6% 4 3 4 3 6% 9% 41%	2738
June	1st to 10th	Night	16% 7% 1 5% 5% 3 4 3 5% 8% 43%	1520
	11th to 20th	Night	13% 4 2 6% 4 4 4 4 8% 8% 42%	1520
	21st to end	Night	12% 4 1 4 5% 4 6% 5% 6% 9% 44%	1520
July	1st to 10th	Night	11% 6% 2 6% 5% 5% 5% 4 8% 10% 38%	1520
	11th to 20th	Night	10% 5% 2 6% 5% 4 6% 4 7% 9% 44%	1488
	21st to end	Night	10% 5% 2 5% 4 4 5% 5% 7% 11% 41%	1586
August	1st to 10th	Night	12% 5% 3 6% 5% 4 5% 5% 7% 8% 42%	1611
	11th to 20th	Night	12% 6% 3 8% 5% 5% 5% 5% 6% 8% 37%	1735
	21st to end	Night	14% 5% 2 6% 5% 4 4 4 6% 10% 40%	1980
September	1st to 10th	Night	16% 6% 2 5% 5% 4 4 3 4 6% 46%	1800
	11th to 20th	Night	13% 5% 2 5% 4 4 3 3 5% 6% 52%	1825
	21st to end	Night	16% 6% 2 6% 3 4 4 3 5% 6% 45%	1980
October	1st to 10th	Night	21% 6% 2 5% 3 3 3 3 4 6% 43%	2160
	11th to 20th	Night	17% 6% 1 4 3 3 4 3 5% 6% 47%	2160
	21st to end	Night	21% 6% 2 4 3 3 3 3 4 6% 45%	2450
November	1st to 10th	Night	13% 5% 2 4 3 4 3 4 5% 5% 51%	2407
	11th to 20th	Night	17% 8% 2 5% 3 4 3 3 4 6% 46%	2470
	21st to end	Night	15% 6% 1 6% 4 4 4 4 6% 7% 44%	2622
December	1st to 10th	Night	20% 7% 2 6% 4 4 4 4 4 6% 37%	2660
	11th to 20th	Night	19% 7% 2 6% 5% 4 4 4 6% 6% 39%	3288
	21st to end	Night	20% 10% 3 6% 4 4 4 3 5% 5% 35%	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	40% 6% 14% 27% 11% 2	2518
	11th to 20th	Day	50% 7% 13% 18% 11% 2	2552
	21st to end	Day	51% 7% 11% 21% 9% 1	3124
February	1st to 10th	Day	45% 6% 14% 22% 11% 1	1710
	11th to 20th	Day	45% 6% 10% 23% 14% 2	1796
	21st to end	Day	49% 5% 10% 22% 11% 3	1570
March	1st to 10th	Day	49% 6% 10% 26% 8% 2	3119
	11th to 20th	Day	34% 9% 13% 28% 13% 2	3476
	21st to end	Day	44% 5% 10% 17% 21% 4	4038
April	1st to 10th	Day	45% 6% 10% 21% 14% 5%	2280
	11th to 20th	Day	41% 7% 12% 22% 15% 3	2254
	21st to end	Day	42% 7% 11% 20% 15% 4	2280
May	1st to 10th	Day	52% 8% 11% 17% 10% 2	4142
	11th to 20th	Day	54% 8% 12% 16% 8% 1	4402
	21st to end	Day	34% 8% 13% 27% 16% 2	4837
June	1st to 10th	Day	41% 8% 15% 22% 13% 1	2660
	11th to 20th	Day	41% 9% 16% 21% 10% 2	2660
	21st to end	Day	37% 9% 14% 25% 14% 1	2660
July	1st to 10th	Day	40% 9% 13% 20% 15% 1	2590
	11th to 20th	Day	32% 10% 16% 26% 13% 2	2518
	21st to end	Day	41% 9% 12% 21% 15% 3	2575
August	1st to 10th	Day	40% 10% 15% 21% 14% 1	2314
	11th to 20th	Day	39% 9% 15% 22% 14% 1	2148
	21st to end	Day	39% 8% 12% 21% 17% 3	2376
September	1st to 10th	Day	41% 8% 11% 21% 18% 2	2160
	11th to 20th	Day	32% 6% 13% 22% 24% 3	2134
	21st to end	Day	44% 5% 10% 19% 20% 2	1976
October	1st to 10th	Day	42% 7% 12% 22% 16% 2	1800
	11th to 20th	Day	40% 5% 11% 25% 17% 1	1800
	21st to end	Day	45% 6% 9% 23% 15% 2	1904
November	1st to 10th	Day	35% 5% 13% 24% 19% 3	1671
	11th to 20th	Day	39% 6% 10% 25% 18% 2	1710
	21st to end	Day	38% 7% 14% 28% 11% 2	1558
December	1st to 10th	Day	48% 6% 14% 19% 11% 1	1520
	11th to 20th	Day	45% 5% 17% 23% 9% 1	1906
	21st to end	Day	50% 9% 13% 20% 7%	2772
January	1st to 10th	Night	40% 7% 12% 28% 11% 3	4429
	11th to 20th	Night	45% 6% 14% 23% 10% 2	4406
	21st to end	Night	49% 5% 10% 24% 10% 2	4532
February	1st to 10th	Night	44% 6% 14% 24% 11% 2	2470
	11th to 20th	Night	45% 5% 10% 19% 16% 4	2279
	21st to end	Night	43% 5% 10% 22% 16% 3	1884
March	1st to 10th	Night	48% 6% 10% 23% 11% 2	3734
	11th to 20th	Night	34% 7% 14% 27% 15% 2	3480
	21st to end	Night	44% 4 7% 17% 22% 5%	3594
April	1st to 10th	Night	43% 7% 11% 21% 14% 4	1900
	11th to 20th	Night	42% 7% 10% 20% 19% 2	1875
	21st to end	Night	39% 5% 12% 21% 19% 4	1900
May	1st to 10th	Night	52% 9% 9% 19% 9% 1	2831
	11th to 20th	Night	53% 9% 14% 13% 10% 2	2496
	21st to end	Night	36% 11% 14% 23% 13% 3	2739
June	1st to 10th	Night	39% 7% 12% 22% 19% 2	1520
	11th to 20th	Night	36% 10% 16% 24% 13% 1	1520
	21st to end	Night	34% 10% 14% 27% 14% 1	1520
July	1st to 10th	Night	40% 10% 14% 20% 14% 2	1480
	11th to 20th	Night	33% 11% 16% 27% 12% 2	1440
	21st to end	Night	31% 12% 18% 20% 15% 2	1498
August	1st to 10th	Night	37% 10% 14% 21% 16% 1	1600
	11th to 20th	Night	42% 10% 14% 18% 15% 1	1735
	21st to end	Night	38% 8% 14% 19% 19% 2	1980
September	1st to 10th	Night	40% 6% 11% 22% 19% 2	1800
	11th to 20th	Night	32% 7% 10% 21% 26% 4	1825
	21st to end	Night	39% 6% 9% 22% 22% 1	1980
October	1st to 10th	Night	42% 6% 12% 24% 14% 2	2160
	11th to 20th	Night	37% 6% 12% 28% 15% 2	2160
	21st to end	Night	41% 5% 11% 26% 16% 1	2450
November	1st to 10th	Night	34% 6% 13% 24% 20% 4	2407
	11th to 20th	Night	40% 4 10% 24% 17% 4	2470
	21st to end	Night	38% 6% 14% 27% 14% 2	2622
December	1st to 10th	Night	46% 6% 13% 22% 12% 1	2660
	11th to 20th	Night	43% 6% 14% 20% 14% 3	3288
	21st to end	Night	48% 7% 13% 23% 9%	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	26% 23% 28% 21% 2 1	180
	11th to 20th	Day	29% 26% 29% 14% 3 1	189
	21st to end	Day	22% 23% 34% 13% 6% 1	297
February	1st to 10th	Day	24% 23% 38% 11% 3 1	270
	11th to 20th	Day	26% 18% 41% 14% 2	395
	21st to end	Day	30% 19% 28% 20% 3	382
March	1st to 10th	Day	23% 21% 31% 21% 4	460
	11th to 20th	Day	24% 21% 33% 18% 3 1	460
	21st to end	Day	27% 21% 30% 15% 6% 1	506
April	1st to 10th	Day	22% 23% 31% 17% 6% 1	460
	11th to 20th	Day	22% 21% 27% 19% 6% 4	452
	21st to end	Day	27% 16% 30% 19% 6% 2	460
May	1st to 10th	Day	29% 19% 25% 17% 7% 3	463
	11th to 20th	Day	21% 14% 29% 23% 10% 2	487
	21st to end	Day	19% 7% 24% 25% 21% 4	529
June	1st to 10th	Day	16% 14% 28% 24% 16% 3	490
	11th to 20th	Day	16% 11% 25% 27% 17% 4	490
	21st to end	Day	14% 10% 30% 28% 14% 3	490
July	1st to 10th	Day	10% 5% 23% 31% 23% 9%	485
	11th to 20th	Day	9% 5% 22% 31% 26% 7%	465
	21st to end	Day	15% 6% 26% 32% 17% 5%	488
August	1st to 10th	Day	11% 6% 23% 31% 22% 8%	446
	11th to 20th	Day	15% 5% 18% 33% 22% 8%	439
	21st to end	Day	13% 5% 25% 28% 18% 11%	495
September	1st to 10th	Day	19% 7% 21% 26% 18% 9%	450
	11th to 20th	Day	15% 4 25% 27% 17% 12%	450
	21st to end	Day	20% 11% 22% 27% 15% 5%	450
October	1st to 10th	Day	27% 6% 24% 24% 14% 6%	450
	11th to 20th	Day	19% 12% 30% 24% 12% 2	450
	21st to end	Day	23% 14% 35% 18% 10% 1	457
November	1st to 10th	Day	17% 13% 29% 26% 13% 3	365
	11th to 20th	Day	21% 18% 29% 25% 6% 1	370
	21st to end	Day	21% 19% 35% 18% 6% 1	218
December	1st to 10th	Day	26% 22% 32% 13% 6% 1	180
	11th to 20th	Day	32% 21% 26% 16% 6%	180
	21st to end	Day	25% 19% 30% 20% 5% 2	198
January	1st to 10th	Night	19% 14% 42% 22% 3	760
	11th to 20th	Night	24% 13% 34% 25% 3	760
	21st to end	Night	17% 14% 43% 24% 1	836
February	1st to 10th	Night	20% 13% 39% 26% 2	760
	11th to 20th	Night	21% 17% 43% 18% 1	743
	21st to end	Night	22% 17% 38% 21% 3	628
March	1st to 10th	Night	22% 13% 36% 27% 3	760
	11th to 20th	Night	21% 15% 38% 21% 5%	760
	21st to end	Night	22% 10% 40% 22% 5%	836
April	1st to 10th	Night	20% 15% 39% 21% 5%	760
	11th to 20th	Night	19% 12% 37% 25% 7%	751
	21st to end	Night	22% 10% 33% 28% 7%	760
May	1st to 10th	Night	25% 9% 31% 28% 6% 1	574
	11th to 20th	Night	20% 7% 35% 30% 8%	374
	21st to end	Night	16% 6% 21% 42% 15% 1	411
June	1st to 10th	Night	18% 4 27% 35% 16% 1	380
	11th to 20th	Night	13% 5% 27% 41% 14%	380
	21st to end	Night	13% 3 21% 49% 13%	380
July	1st to 10th	Night	12% 4 18% 45% 20% 1	370
	11th to 20th	Night	8% 4 20% 46% 21% 1	360
	21st to end	Night	12% 4 20% 42% 21% 1	406
August	1st to 10th	Night	11% 3 13% 47% 24% 2	537
	11th to 20th	Night	14% 3 17% 36% 28% 2	671
	21st to end	Night	14% 4 15% 41% 24% 2	792
September	1st to 10th	Night	17% 4 21% 36% 19% 2	720
	11th to 20th	Night	15% 5% 16% 39% 22% 4	720
	21st to end	Night	19% 4 23% 35% 18% 1	720
October	1st to 10th	Night	21% 6% 25% 28% 17% 3	720
	11th to 20th	Night	18% 8% 29% 35% 10%	720
	21st to end	Night	24% 7% 32% 28% 8%	792
November	1st to 10th	Night	16% 7% 35% 31% 11% 1	740
	11th to 20th	Night	21% 12% 31% 29% 7% 1	760
	21st to end	Night	17% 12% 37% 27% 6%	760
December	1st to 10th	Night	24% 11% 34% 25% 5% 1	760
	11th to 20th	Night	21% 11% 36% 27% 4	760
	21st to end	Night	22% 12% 38% 27% 2	836

Page generated at 2024-07-13 10:19:53. Version ac07

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