DeepSkyEye Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DeepSkyEye Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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	22% 12% 4 9% 5% 4 4 3 4 6% 28%	138611
	Night	22% 13% 4 10% 5% 4 4 3 4 5% 25%	134456
Transparency	Day	39% 36% 6% 11% 7% 1	142175
	Night	41% 35% 6% 11% 6%	138981
Seeing	Day	31% 19% 30% 15% 5% 1	19142
	Night	29% 15% 29% 20% 6%	26845

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	17% 20% 9% 22% 7% 3 3 2 3 3 10%	4187
	11th to 20th	Day	19% 21% 10% 21% 6% 4 3 2 3 3 8%	5225
	21st to end	Day	16% 16% 6% 21% 14% 6% 3 2 2 3 12%	5781
February	1st to 10th	Day	19% 19% 6% 14% 8% 5% 3 2 4 5% 14%	1890
	11th to 20th	Day	17% 16% 6% 17% 9% 4 3 3 3 4 18%	1843
	21st to end	Day	13% 17% 7% 11% 6% 4 4 3 4 5% 26%	1678
March	1st to 10th	Day	26% 15% 6% 11% 8% 3 3 2 4 4 19%	4943
	11th to 20th	Day	19% 17% 3 7% 4 3 4 3 4 6% 28%	5090
	21st to end	Day	29% 14% 6% 9% 4 4 3 2 4 4 20%	5587
April	1st to 10th	Day	26% 14% 4 6% 4 3 3 2 4 4 30%	2417
	11th to 20th	Day	22% 11% 2 6% 3 3 3 3 5% 6% 35%	2670
	21st to end	Day	23% 11% 2 6% 3 3 3 3 5% 6% 36%	2730
May	1st to 10th	Day	30% 12% 3 7% 4 3 3 2 3 5% 26%	7639
	11th to 20th	Day	19% 11% 3 7% 4 4 4 3 5% 7% 33%	7913
	21st to end	Day	22% 10% 4 8% 5% 4 4 3 5% 7% 29%	9059
June	1st to 10th	Day	25% 8% 2 6% 4 4 3 3 4 6% 34%	2989
	11th to 20th	Day	22% 8% 2 6% 4 3 4 3 5% 7% 38%	3150
	21st to end	Day	27% 8% 2 6% 4 3 4 4 5% 6% 31%	3150
July	1st to 10th	Day	30% 9% 3 5% 3 3 4 3 5% 6% 29%	6970
	11th to 20th	Day	30% 9% 2 5% 3 3 3 3 4 7% 30%	6469
	21st to end	Day	16% 8% 2 6% 4 4 4 3 6% 8% 39%	6555
August	1st to 10th	Day	32% 9% 3 5% 3 3 4 3 4 6% 28%	4235
	11th to 20th	Day	19% 6% 3 8% 5% 5% 5% 4 4 7% 36%	4175
	21st to end	Day	14% 6% 2 5% 4 3 3 3 5% 8% 48%	4595
September	1st to 10th	Day	18% 6% 2 6% 3 4 3 3 5% 6% 45%	2390
	11th to 20th	Day	17% 6% 2 5% 4 4 3 2 4 6% 47%	2200
	21st to end	Day	20% 8% 2 6% 3 3 3 3 4 6% 42%	2200
October	1st to 10th	Day	20% 7% 2 6% 3 3 4 3 5% 7% 39%	2017
	11th to 20th	Day	21% 8% 2 7% 4 5% 5% 4 5% 6% 33%	2000
	21st to end	Day	21% 10% 3 8% 6% 5% 4 3 5% 6% 30%	2165
November	1st to 10th	Day	23% 10% 3 7% 4 4 3 4 4 5% 33%	1814
	11th to 20th	Day	21% 17% 5% 8% 5% 4 4 3 4 6% 21%	1680
	21st to end	Day	20% 20% 5% 10% 6% 4 4 3 3 6% 18%	1680
December	1st to 10th	Day	24% 16% 6% 14% 5% 4 4 3 4 6% 14%	2690
	11th to 20th	Day	27% 14% 5% 11% 6% 4 4 2 4 5% 17%	3076
	21st to end	Day	21% 16% 7% 12% 5% 4 3 3 3 4 22%	3759
January	1st to 10th	Night	15% 20% 10% 24% 8% 4 4 2 2 2 10%	8729
	11th to 20th	Night	23% 17% 8% 17% 6% 5% 4 2 3 3 11%	7640
	21st to end	Night	14% 15% 6% 22% 10% 7% 4 3 4 3 12%	8400
February	1st to 10th	Night	19% 17% 5% 14% 9% 5% 5% 4 4 4 15%	2730
	11th to 20th	Night	18% 14% 5% 14% 8% 6% 5% 3 5% 5% 18%	2663
	21st to end	Night	14% 13% 5% 10% 7% 6% 6% 4 5% 6% 25%	2123
March	1st to 10th	Night	24% 14% 6% 10% 9% 5% 3 3 3 4 20%	5115
	11th to 20th	Night	19% 16% 5% 8% 4 4 4 4 5% 6% 25%	5089
	21st to end	Night	30% 13% 4 7% 3 3 2 2 3 5% 27%	5587
April	1st to 10th	Night	24% 14% 2 6% 4 4 4 3 4 5% 28%	2201
	11th to 20th	Night	25% 9% 2 5% 4 3 4 3 5% 7% 31%	1895
	21st to end	Night	24% 10% 2 6% 4 4 4 4 4 6% 33%	1890
May	1st to 10th	Night	32% 12% 3 5% 4 4 4 2 4 5% 25%	5259
	11th to 20th	Night	24% 13% 3 6% 3 3 3 3 4 6% 31%	4958
	21st to end	Night	19% 13% 3 8% 4 4 4 3 4 6% 32%	5147
June	1st to 10th	Night	26% 9% 3 5% 3 4 4 3 5% 7% 31%	1646
	11th to 20th	Night	21% 10% 3 7% 3 3 4 3 5% 6% 34%	1470
	21st to end	Night	27% 11% 3 6% 4 4 5% 3 5% 6% 27%	1470
July	1st to 10th	Night	33% 12% 3 6% 5% 3 3 3 6% 6% 20%	3230
	11th to 20th	Night	32% 12% 3 6% 4 3 3 3 4 5% 25%	3654
	21st to end	Night	18% 8% 3 8% 5% 4 4 4 5% 7% 35%	4519
August	1st to 10th	Night	34% 9% 3 6% 3 3 2 2 4 6% 28%	2915
	11th to 20th	Night	21% 12% 4 9% 4 4 3 3 4 6% 31%	2872
	21st to end	Night	13% 9% 2 6% 3 3 3 3 5% 6% 45%	3289
September	1st to 10th	Night	19% 8% 2 4 3 4 4 3 6% 7% 40%	2008
	11th to 20th	Night	20% 6% 2 5% 4 3 3 3 5% 7% 44%	2200
	21st to end	Night	23% 8% 2 5% 4 3 4 3 4 6% 37%	2200
October	1st to 10th	Night	21% 6% 2 5% 3 4 3 3 5% 6% 41%	2381
	11th to 20th	Night	18% 9% 2 6% 5% 4 3 3 5% 7% 39%	2400
	21st to end	Night	24% 10% 3 6% 4 4 4 3 4 6% 32%	2672
November	1st to 10th	Night	20% 9% 3 7% 4 4 4 4 5% 6% 34%	2701
	11th to 20th	Night	20% 16% 4 9% 6% 4 4 4 6% 6% 23%	2940
	21st to end	Night	20% 16% 5% 8% 6% 5% 4 4 5% 6% 23%	2940
December	1st to 10th	Night	18% 17% 6% 15% 6% 5% 4 4 5% 6% 15%	4720
	11th to 20th	Night	23% 14% 5% 10% 5% 5% 5% 4 6% 6% 19%	5353
	21st to end	Night	23% 16% 5% 12% 5% 3 3 2 3 3 24%	7450

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	64% 22% 8% 5%	4188
	11th to 20th	Day	67% 23% 4 4 2	5258
	21st to end	Day	63% 23% 4 4 6%	5781
February	1st to 10th	Day	30% 59% 3 5% 3	1890
	11th to 20th	Day	28% 59% 3 7% 3	1851
	21st to end	Day	22% 60% 4 8% 5% 1	1678
March	1st to 10th	Day	54% 29% 5% 8% 4 1	4947
	11th to 20th	Day	42% 31% 10% 13% 4	5090
	21st to end	Day	54% 28% 3 8% 6% 1	5587
April	1st to 10th	Day	27% 58% 3 7% 6%	2417
	11th to 20th	Day	21% 60% 5% 9% 5% 1	2670
	21st to end	Day	21% 59% 3 9% 7% 1	2730
May	1st to 10th	Day	48% 25% 6% 15% 6%	7651
	11th to 20th	Day	42% 25% 10% 15% 7% 1	7917
	21st to end	Day	45% 26% 7% 10% 11% 1	9060
June	1st to 10th	Day	19% 59% 4 10% 7%	2989
	11th to 20th	Day	18% 59% 6% 9% 7% 1	3150
	21st to end	Day	22% 58% 5% 9% 6% 1	3150
July	1st to 10th	Day	45% 26% 8% 12% 8% 1	6895
	11th to 20th	Day	44% 26% 5% 16% 8%	6389
	21st to end	Day	31% 27% 11% 19% 10% 1	6372
August	1st to 10th	Day	40% 37% 5% 11% 7% 1	4222
	11th to 20th	Day	31% 39% 7% 18% 4	4214
	21st to end	Day	20% 37% 8% 18% 15% 2	4595
September	1st to 10th	Day	17% 58% 5% 12% 7% 1	2390
	11th to 20th	Day	19% 58% 4 9% 8% 1	2200
	21st to end	Day	18% 57% 4 11% 9% 2	2200
October	1st to 10th	Day	29% 38% 6% 18% 8% 1	3277
	11th to 20th	Day	26% 37% 5% 15% 16% 1	3240
	21st to end	Day	27% 36% 7% 19% 8% 3	3479
November	1st to 10th	Day	27% 55% 6% 9% 3 1	1814
	11th to 20th	Day	32% 54% 5% 6% 3	1680
	21st to end	Day	33% 55% 5% 7% 1	1680
December	1st to 10th	Day	46% 37% 8% 9% 1	2690
	11th to 20th	Day	48% 31% 9% 7% 4	3075
	21st to end	Day	46% 28% 11% 9% 6%	3759
January	1st to 10th	Night	66% 22% 5% 6% 1	8729
	11th to 20th	Night	62% 23% 5% 8% 2	7682
	21st to end	Night	59% 23% 6% 6% 5%	8400
February	1st to 10th	Night	31% 58% 4 4 3	2730
	11th to 20th	Night	26% 58% 3 9% 3	2666
	21st to end	Night	24% 59% 4 7% 5%	2123
March	1st to 10th	Night	53% 29% 4 6% 8%	5124
	11th to 20th	Night	45% 30% 9% 12% 4	5090
	21st to end	Night	49% 27% 4 11% 7% 1	5587
April	1st to 10th	Night	25% 58% 3 6% 6% 2	2201
	11th to 20th	Night	23% 60% 4 9% 4 1	1895
	21st to end	Night	22% 60% 4 8% 6% 1	1890
May	1st to 10th	Night	50% 25% 7% 11% 6%	5265
	11th to 20th	Night	44% 24% 8% 15% 7% 1	4959
	21st to end	Night	44% 24% 7% 17% 7%	5148
June	1st to 10th	Night	19% 60% 4 12% 5%	1646
	11th to 20th	Night	20% 59% 5% 11% 6%	1470
	21st to end	Night	22% 58% 4 9% 7% 1	1470
July	1st to 10th	Night	51% 27% 6% 10% 6%	3195
	11th to 20th	Night	48% 26% 6% 10% 10% 1	3611
	21st to end	Night	36% 28% 8% 17% 10% 2	4388
August	1st to 10th	Night	41% 37% 6% 11% 5%	2903
	11th to 20th	Night	34% 39% 10% 15% 2	2899
	21st to end	Night	23% 38% 7% 18% 14% 1	3288
September	1st to 10th	Night	18% 58% 3 12% 8% 1	2008
	11th to 20th	Night	20% 57% 4 11% 7% 1	2200
	21st to end	Night	20% 58% 2 12% 8%	2200
October	1st to 10th	Night	32% 37% 8% 14% 9% 1	3901
	11th to 20th	Night	21% 36% 8% 18% 17% 1	3899
	21st to end	Night	26% 36% 8% 20% 10% 1	4308
November	1st to 10th	Night	25% 54% 7% 9% 5%	2701
	11th to 20th	Night	28% 55% 6% 8% 3	2940
	21st to end	Night	29% 55% 7% 6% 3	2940
December	1st to 10th	Night	43% 37% 7% 12% 2	4720
	11th to 20th	Night	43% 32% 9% 9% 6%	5355
	21st to end	Night	47% 27% 7% 11% 7% 1	7450

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	42% 24% 27% 5% 2	220
	11th to 20th	Day	39% 19% 27% 12% 3	421
	21st to end	Day	27% 26% 34% 10% 2	473
February	1st to 10th	Day	35% 20% 31% 11% 3	430
	11th to 20th	Day	37% 25% 24% 11% 2	426
	21st to end	Day	32% 24% 29% 12% 2	419
March	1st to 10th	Day	34% 24% 31% 9% 2	540
	11th to 20th	Day	38% 24% 25% 8% 4 1	540
	21st to end	Day	36% 24% 25% 10% 4 1	594
April	1st to 10th	Day	42% 25% 24% 6% 2	540
	11th to 20th	Day	36% 23% 30% 9% 2	532
	21st to end	Day	34% 21% 30% 10% 4 1	540
May	1st to 10th	Day	36% 26% 27% 9% 2 1	543
	11th to 20th	Day	28% 23% 30% 15% 4 1	660
	21st to end	Day	31% 16% 31% 16% 4	845
June	1st to 10th	Day	31% 17% 28% 17% 5% 1	780
	11th to 20th	Day	26% 17% 31% 20% 6% 1	780
	21st to end	Day	34% 14% 29% 18% 4 1	780
July	1st to 10th	Day	29% 11% 31% 21% 8% 1	770
	11th to 20th	Day	28% 11% 31% 21% 8% 1	689
	21st to end	Day	24% 12% 38% 20% 5% 1	616
August	1st to 10th	Day	22% 10% 38% 22% 7% 2	526
	11th to 20th	Day	25% 11% 34% 19% 9% 2	519
	21st to end	Day	23% 15% 31% 19% 9% 3	583
September	1st to 10th	Day	20% 15% 35% 22% 7% 1	530
	11th to 20th	Day	22% 16% 32% 18% 8% 5%	530
	21st to end	Day	22% 15% 33% 19% 7% 3	530
October	1st to 10th	Day	26% 12% 31% 19% 9% 3	428
	11th to 20th	Day	27% 15% 31% 18% 6% 2	420
	21st to end	Day	28% 22% 28% 14% 7%	462
November	1st to 10th	Day	30% 20% 28% 14% 7% 1	425
	11th to 20th	Day	39% 19% 27% 11% 4	430
	21st to end	Day	36% 20% 31% 9% 3 1	430
December	1st to 10th	Day	36% 22% 29% 11% 2	430
	11th to 20th	Day	43% 24% 22% 9% 2	430
	21st to end	Day	40% 24% 24% 9% 3 1	331
January	1st to 10th	Night	33% 22% 29% 15% 2	931
	11th to 20th	Night	36% 17% 28% 15% 3	840
	21st to end	Night	28% 24% 30% 16% 3	924
February	1st to 10th	Night	34% 18% 30% 17% 1	840
	11th to 20th	Night	32% 25% 26% 15% 2	823
	21st to end	Night	23% 21% 35% 17% 4	692
March	1st to 10th	Night	29% 20% 33% 15% 2	840
	11th to 20th	Night	28% 20% 28% 19% 5%	840
	21st to end	Night	27% 19% 32% 16% 5% 1	924
April	1st to 10th	Night	36% 17% 31% 14% 2	731
	11th to 20th	Night	30% 18% 34% 15% 2	624
	21st to end	Night	32% 14% 29% 20% 5%	630
May	1st to 10th	Night	31% 15% 35% 16% 3	630
	11th to 20th	Night	29% 13% 33% 21% 4	622
	21st to end	Night	24% 14% 36% 22% 4 1	682
June	1st to 10th	Night	31% 9% 33% 22% 5%	596
	11th to 20th	Night	23% 9% 33% 30% 5% 1	420
	21st to end	Night	32% 4 30% 28% 6%	420
July	1st to 10th	Night	27% 5% 32% 27% 8%	410
	11th to 20th	Night	24% 8% 34% 25% 9%	517
	21st to end	Night	24% 6% 34% 30% 6%	687
August	1st to 10th	Night	24% 6% 29% 33% 8% 1	598
	11th to 20th	Night	26% 6% 29% 30% 9%	592
	21st to end	Night	19% 7% 30% 32% 11% 1	660
September	1st to 10th	Night	22% 7% 29% 30% 11%	608
	11th to 20th	Night	23% 9% 26% 25% 15% 2	800
	21st to end	Night	25% 11% 26% 25% 12% 2	800
October	1st to 10th	Night	26% 11% 26% 26% 12% 1	800
	11th to 20th	Night	25% 15% 26% 24% 9% 1	800
	21st to end	Night	31% 16% 25% 22% 6%	880
November	1st to 10th	Night	29% 13% 28% 22% 7% 1	839
	11th to 20th	Night	32% 18% 26% 19% 5%	950
	21st to end	Night	32% 21% 25% 16% 5%	950
December	1st to 10th	Night	35% 18% 27% 15% 3	950
	11th to 20th	Night	37% 21% 25% 14% 3	950
	21st to end	Night	35% 21% 24% 17% 3	1045

Page generated at 2026-07-28 04:25:27. Version ac07

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