Photon's End Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Photon's End Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	16% 10% 3 9% 5% 5% 5% 4 5% 7% 31%	131215
	Night	17% 12% 4 9% 5% 5% 4 4 5% 6% 29%	129923
Transparency	Day	53% 3 11% 22% 10% 1	134680
	Night	56% 3 10% 20% 10% 1	134545
Seeing	Day	23% 12% 29% 22% 11% 3	16036
	Night	23% 10% 27% 28% 10% 1	25243

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% 16% 7% 14% 6% 4 5% 4 4 5% 20%	4661
	11th to 20th	Day	12% 18% 7% 14% 7% 5% 5% 3 4 5% 20%	4650
	21st to end	Day	8% 15% 6% 14% 8% 8% 6% 4 5% 6% 20%	5286
February	1st to 10th	Day	13% 15% 5% 13% 6% 5% 4 4 6% 5% 25%	1890
	11th to 20th	Day	13% 15% 4 11% 6% 5% 4 3 6% 6% 26%	1863
	21st to end	Day	18% 14% 4 9% 7% 5% 4 4 5% 5% 24%	1730
March	1st to 10th	Day	19% 12% 5% 11% 6% 5% 4 3 5% 5% 25%	4496
	11th to 20th	Day	12% 12% 4 9% 5% 5% 5% 4 6% 7% 30%	4933
	21st to end	Day	18% 11% 3 8% 5% 4 4 3 4 5% 35%	5802
April	1st to 10th	Day	22% 12% 3 6% 4 4 4 3 3 5% 34%	2400
	11th to 20th	Day	22% 9% 3 7% 4 4 3 3 4 6% 36%	2374
	21st to end	Day	22% 9% 4 8% 5% 4 5% 3 5% 5% 32%	2541
May	1st to 10th	Day	22% 10% 4 8% 5% 5% 5% 4 6% 6% 25%	6346
	11th to 20th	Day	17% 9% 3 9% 6% 5% 5% 4 5% 7% 31%	6318
	21st to end	Day	21% 8% 2 7% 5% 5% 4 4 6% 7% 32%	6949
June	1st to 10th	Day	22% 8% 3 8% 5% 4 4 4 6% 6% 30%	2800
	11th to 20th	Day	13% 7% 2 6% 5% 5% 6% 4 5% 8% 38%	2800
	21st to end	Day	19% 7% 2 7% 5% 4 5% 5% 7% 8% 31%	2800
July	1st to 10th	Day	13% 6% 3 8% 6% 5% 5% 4 7% 9% 34%	6360
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	6360
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 7% 10% 45%	6926
August	1st to 10th	Day	14% 6% 2 8% 5% 5% 5% 4 6% 8% 37%	4536
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 9% 38%	4094
	21st to end	Day	14% 5% 2 7% 4 4 5% 4 6% 9% 40%	4312
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 5% 8% 43%	2400
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 5% 8% 48%	2389
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 6% 40%	2152
October	1st to 10th	Day	19% 9% 3 6% 4 3 4 4 5% 7% 37%	2000
	11th to 20th	Day	21% 8% 3 8% 4 5% 5% 4 5% 6% 30%	2000
	21st to end	Day	24% 11% 2 7% 6% 4 4 3 4 6% 29%	2021
November	1st to 10th	Day	17% 9% 3 7% 5% 5% 5% 4 6% 6% 33%	1851
	11th to 20th	Day	18% 13% 3 9% 5% 5% 5% 4 5% 6% 28%	1701
	21st to end	Day	22% 14% 4 9% 7% 5% 5% 3 5% 5% 21%	1680
December	1st to 10th	Day	20% 20% 6% 10% 5% 5% 5% 4 6% 6% 14%	2680
	11th to 20th	Day	18% 15% 5% 12% 5% 4 4 3 4 4 25%	3066
	21st to end	Day	23% 16% 5% 11% 5% 4 5% 3 4 4 20%	4048
January	1st to 10th	Night	14% 20% 8% 15% 5% 4 4 3 4 4 20%	8234
	11th to 20th	Night	12% 18% 6% 15% 8% 6% 5% 3 4 5% 18%	8235
	21st to end	Night	11% 17% 6% 12% 7% 6% 5% 4 5% 6% 21%	8878
February	1st to 10th	Night	13% 15% 5% 11% 6% 6% 5% 4 5% 6% 24%	2730
	11th to 20th	Night	13% 14% 5% 11% 7% 6% 4 3 4 5% 28%	2642
	21st to end	Night	15% 14% 5% 9% 6% 5% 5% 4 5% 5% 29%	2076
March	1st to 10th	Night	22% 15% 4 9% 5% 4 4 3 4 4 28%	5389
	11th to 20th	Night	13% 13% 4 9% 6% 5% 5% 4 6% 8% 30%	5025
	21st to end	Night	19% 11% 3 9% 5% 4 4 3 5% 5% 33%	5128
April	1st to 10th	Night	22% 11% 3 7% 5% 4 3 3 4 6% 32%	2000
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 4 4 5% 35%	1975
	21st to end	Night	22% 9% 3 7% 5% 3 4 3 4 6% 35%	1874
May	1st to 10th	Night	22% 10% 3 9% 5% 5% 5% 4 6% 7% 24%	3594
	11th to 20th	Night	17% 7% 3 6% 5% 5% 5% 4 5% 7% 36%	3575
	21st to end	Night	17% 9% 4 8% 5% 4 5% 4 6% 6% 31%	3926
June	1st to 10th	Night	16% 6% 2 7% 5% 5% 5% 4 8% 9% 33%	1600
	11th to 20th	Night	14% 7% 2 7% 5% 4 4 4 6% 8% 41%	1600
	21st to end	Night	19% 7% 2 7% 4 4 5% 4 6% 7% 35%	1600
July	1st to 10th	Night	14% 7% 3 7% 5% 6% 6% 4 7% 8% 33%	3600
	11th to 20th	Night	11% 7% 3 6% 4 4 5% 4 6% 9% 42%	3600
	21st to end	Night	9% 6% 2 7% 5% 5% 4 4 6% 7% 46%	3926
August	1st to 10th	Night	11% 8% 3 7% 4 4 4 5% 7% 8% 38%	2610
	11th to 20th	Night	15% 6% 2 7% 4 4 5% 4 6% 7% 42%	2908
	21st to end	Night	12% 6% 3 8% 4 5% 5% 4 7% 8% 39%	3586
September	1st to 10th	Night	11% 5% 2 6% 5% 5% 4 4 5% 7% 46%	2000
	11th to 20th	Night	13% 4 2 5% 4 3 3 4 4 7% 50%	2010
	21st to end	Night	17% 6% 2 6% 4 4 4 3 4 6% 44%	2245
October	1st to 10th	Night	18% 6% 2 6% 4 4 5% 4 5% 6% 40%	2400
	11th to 20th	Night	19% 9% 3 7% 6% 5% 5% 3 5% 5% 33%	2400
	21st to end	Night	22% 9% 4 8% 5% 4 5% 3 4 6% 30%	2818
November	1st to 10th	Night	20% 10% 3 6% 5% 4 4 3 5% 6% 33%	2667
	11th to 20th	Night	18% 11% 3 9% 5% 5% 5% 4 4 6% 30%	2914
	21st to end	Night	21% 14% 4 9% 6% 4 4 4 5% 5% 24%	2940
December	1st to 10th	Night	18% 18% 5% 12% 7% 6% 5% 4 4 5% 16%	4720
	11th to 20th	Night	23% 15% 4 9% 5% 4 4 3 4 4 25%	5348
	21st to end	Night	28% 17% 3 9% 4 4 4 3 5% 5% 19%	7150

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	68% 2 10% 15% 5%	4662
	11th to 20th	Day	68% 2 7% 12% 10%	4680
	21st to end	Day	66% 4 10% 11% 9% 1	5286
February	1st to 10th	Day	61% 3 9% 20% 6% 1	1890
	11th to 20th	Day	59% 2 11% 18% 9% 1	1872
	21st to end	Day	62% 3 9% 14% 10% 2	1730
March	1st to 10th	Day	63% 2 8% 13% 11% 3	4499
	11th to 20th	Day	54% 3 16% 16% 11% 1	4933
	21st to end	Day	53% 1 5% 19% 18% 2	5802
April	1st to 10th	Day	55% 2 6% 20% 13% 3	2400
	11th to 20th	Day	52% 2 6% 22% 16% 2	2374
	21st to end	Day	56% 2 8% 16% 14% 4	2541
May	1st to 10th	Day	60% 3 6% 21% 9% 2	6357
	11th to 20th	Day	54% 3 12% 20% 10% 1	6322
	21st to end	Day	52% 3 10% 21% 12% 1	6949
June	1st to 10th	Day	54% 3 10% 20% 12% 1	2800
	11th to 20th	Day	44% 4 11% 25% 13% 2	2800
	21st to end	Day	49% 4 14% 21% 10% 1	2800
July	1st to 10th	Day	45% 5% 14% 27% 9%	6290
	11th to 20th	Day	39% 5% 12% 31% 12%	6285
	21st to end	Day	34% 5% 15% 36% 11%	6728
August	1st to 10th	Day	45% 4 16% 25% 9%	4522
	11th to 20th	Day	42% 5% 15% 30% 7% 1	4133
	21st to end	Day	40% 5% 16% 26% 12% 1	4312
September	1st to 10th	Day	40% 3 13% 31% 12%	2400
	11th to 20th	Day	35% 3 13% 34% 13% 1	2389
	21st to end	Day	44% 4 14% 26% 11%	2152
October	1st to 10th	Day	47% 4 11% 30% 8%	3260
	11th to 20th	Day	49% 4 14% 25% 7% 1	3240
	21st to end	Day	50% 4 18% 22% 7%	3246
November	1st to 10th	Day	51% 4 13% 25% 7% 1	1851
	11th to 20th	Day	58% 3 13% 17% 9% 1	1701
	21st to end	Day	66% 4 12% 11% 6% 1	1680
December	1st to 10th	Day	70% 4 12% 12% 2	2680
	11th to 20th	Day	64% 2 10% 16% 7%	3066
	21st to end	Day	69% 3 8% 16% 5%	4048
January	1st to 10th	Night	69% 2 10% 13% 5% 1	8234
	11th to 20th	Night	71% 2 8% 13% 6%	8280
	21st to end	Night	64% 3 7% 14% 12% 1	8878
February	1st to 10th	Night	61% 3 9% 18% 8% 1	2730
	11th to 20th	Night	59% 2 8% 21% 8% 1	2644
	21st to end	Night	58% 3 8% 20% 11% 1	2076
March	1st to 10th	Night	63% 1 5% 15% 12% 3	5399
	11th to 20th	Night	54% 3 15% 16% 9% 3	5026
	21st to end	Night	55% 2 5% 22% 14% 2	5128
April	1st to 10th	Night	55% 2 8% 18% 15% 2	2000
	11th to 20th	Night	51% 3 6% 22% 16% 1	1975
	21st to end	Night	52% 2 8% 18% 17% 3	1874
May	1st to 10th	Night	60% 3 8% 19% 8% 3	3600
	11th to 20th	Night	49% 3 12% 20% 14% 1	3576
	21st to end	Night	53% 3 10% 19% 14% 1	3927
June	1st to 10th	Night	47% 4 12% 25% 11% 1	1600
	11th to 20th	Night	42% 4 11% 25% 17% 2	1600
	21st to end	Night	47% 5% 13% 20% 15% 1	1600
July	1st to 10th	Night	47% 5% 16% 20% 11% 1	3560
	11th to 20th	Night	39% 5% 12% 34% 11%	3552
	21st to end	Night	37% 5% 12% 31% 16%	3809
August	1st to 10th	Night	42% 6% 16% 26% 10% 1	2600
	11th to 20th	Night	42% 4 14% 31% 8%	2935
	21st to end	Night	42% 5% 15% 24% 12% 2	3586
September	1st to 10th	Night	38% 4 11% 31% 15% 1	2000
	11th to 20th	Night	35% 3 13% 36% 11% 1	2010
	21st to end	Night	43% 3 11% 31% 12%	2245
October	1st to 10th	Night	42% 5% 13% 28% 12% 1	3920
	11th to 20th	Night	47% 4 13% 26% 10%	3899
	21st to end	Night	48% 4 17% 21% 10%	4543
November	1st to 10th	Night	53% 3 13% 21% 9%	2667
	11th to 20th	Night	57% 3 11% 18% 10% 1	2914
	21st to end	Night	62% 4 12% 17% 5%	2940
December	1st to 10th	Night	68% 4 12% 12% 3	4720
	11th to 20th	Night	64% 3 7% 15% 11% 1	5348
	21st to end	Night	69% 2 6% 13% 9%	7150

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	25% 14% 34% 22% 4	220
	11th to 20th	Day	25% 15% 38% 16% 5% 1	220
	21st to end	Day	21% 14% 36% 22% 6%	272
February	1st to 10th	Day	30% 15% 38% 13% 3 1	330
	11th to 20th	Day	26% 21% 37% 14% 1	350
	21st to end	Day	29% 15% 34% 19% 3	446
March	1st to 10th	Day	27% 14% 33% 19% 7%	508
	11th to 20th	Day	26% 15% 33% 22% 4 1	500
	21st to end	Day	29% 19% 28% 15% 8% 1	550
April	1st to 10th	Day	30% 19% 28% 17% 6%	500
	11th to 20th	Day	33% 16% 24% 17% 10% 2	492
	21st to end	Day	31% 15% 30% 15% 7% 2	500
May	1st to 10th	Day	26% 12% 31% 21% 7% 2	503
	11th to 20th	Day	21% 14% 30% 21% 11% 3	527
	21st to end	Day	21% 11% 31% 23% 12% 2	573
June	1st to 10th	Day	26% 9% 28% 24% 10% 2	530
	11th to 20th	Day	16% 12% 31% 25% 14% 2	530
	21st to end	Day	24% 9% 27% 25% 11% 3	530
July	1st to 10th	Day	15% 6% 28% 30% 15% 6%	525
	11th to 20th	Day	13% 6% 32% 29% 16% 4	524
	21st to end	Day	13% 6% 31% 30% 17% 4	576
August	1st to 10th	Day	15% 6% 24% 34% 17% 5%	526
	11th to 20th	Day	16% 6% 22% 28% 20% 8%	519
	21st to end	Day	15% 9% 26% 26% 16% 8%	583
September	1st to 10th	Day	19% 7% 28% 21% 15% 10%	530
	11th to 20th	Day	12% 6% 21% 24% 24% 13%	530
	21st to end	Day	20% 11% 28% 23% 15% 5%	530
October	1st to 10th	Day	22% 11% 25% 23% 14% 5%	530
	11th to 20th	Day	27% 16% 29% 18% 9% 1	530
	21st to end	Day	32% 10% 27% 23% 7%	484
November	1st to 10th	Day	27% 15% 28% 21% 8% 1	425
	11th to 20th	Day	25% 15% 37% 17% 4 2	241
	21st to end	Day	33% 16% 31% 15% 4 1	220
December	1st to 10th	Day	30% 13% 33% 19% 5%	220
	11th to 20th	Day	28% 19% 36% 15% 2	220
	21st to end	Day	34% 15% 34% 12% 4 1	242
January	1st to 10th	Night	28% 11% 32% 24% 5%	840
	11th to 20th	Night	29% 14% 28% 23% 7% 1	840
	21st to end	Night	20% 10% 33% 28% 8% 1	924
February	1st to 10th	Night	21% 13% 32% 30% 5%	840
	11th to 20th	Night	20% 15% 37% 24% 4	823
	21st to end	Night	24% 13% 29% 31% 3	692
March	1st to 10th	Night	25% 15% 30% 25% 4	809
	11th to 20th	Night	25% 12% 33% 25% 4 1	800
	21st to end	Night	25% 13% 28% 25% 8%	880
April	1st to 10th	Night	29% 11% 29% 26% 6%	800
	11th to 20th	Night	25% 12% 31% 23% 8% 1	791
	21st to end	Night	29% 9% 28% 26% 7% 1	674
May	1st to 10th	Night	26% 7% 28% 29% 9% 2	400
	11th to 20th	Night	23% 9% 25% 33% 10% 1	394
	21st to end	Night	17% 6% 35% 31% 11%	433
June	1st to 10th	Night	19% 3 28% 40% 10%	400
	11th to 20th	Night	17% 6% 26% 36% 14% 2	400
	21st to end	Night	20% 5% 26% 33% 15% 1	400
July	1st to 10th	Night	10% 3 27% 42% 17%	390
	11th to 20th	Night	13% 3 21% 45% 17% 1	388
	21st to end	Night	10% 4 24% 44% 17% 1	438
August	1st to 10th	Night	13% 4 18% 41% 22% 1	409
	11th to 20th	Night	14% 4 16% 37% 26% 3	614
	21st to end	Night	13% 6% 22% 35% 21% 2	880
September	1st to 10th	Night	14% 5% 25% 36% 19% 1	800
	11th to 20th	Night	17% 4 18% 32% 25% 4	800
	21st to end	Night	21% 7% 23% 28% 20% 2	800
October	1st to 10th	Night	21% 8% 25% 27% 17% 2	800
	11th to 20th	Night	25% 9% 30% 27% 9% 1	800
	21st to end	Night	28% 10% 26% 30% 6%	880
November	1st to 10th	Night	29% 10% 24% 27% 9% 1	820
	11th to 20th	Night	25% 14% 30% 20% 10%	840
	21st to end	Night	29% 15% 26% 24% 6%	840
December	1st to 10th	Night	30% 13% 28% 25% 4	840
	11th to 20th	Night	30% 12% 30% 21% 5% 1	840
	21st to end	Night	34% 11% 27% 22% 5%	924

Page generated at 2026-02-28 01:40:22. Version ac07

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