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 2024-07-03.

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	17% 10% 3 8% 5% 5% 5% 4 5% 6% 32%	89598
	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 31%	89596
Transparency	Day	53% 3 11% 21% 10% 1	89317
	Night	55% 3 11% 20% 10% 1	89431
Seeing	Day	23% 12% 29% 22% 11% 3	14000
	Night	24% 9% 27% 28% 10% 1	23115

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% 15% 6% 13% 7% 4 5% 4 4 4 20%	2517
	11th to 20th	Day	15% 12% 6% 13% 7% 6% 5% 3 5% 5% 23%	2520
	21st to end	Day	14% 18% 6% 11% 6% 6% 5% 4 5% 5% 18%	2850
February	1st to 10th	Day	13% 16% 4 13% 6% 5% 4 4 5% 5% 25%	1710
	11th to 20th	Day	14% 15% 4 11% 6% 5% 4 3 5% 6% 27%	1681
	21st to end	Day	19% 14% 3 9% 6% 5% 4 4 5% 5% 25%	1570
March	1st to 10th	Day	21% 12% 4 9% 5% 5% 4 3 5% 4 27%	3116
	11th to 20th	Day	13% 15% 5% 10% 5% 5% 6% 4 4 5% 27%	3447
	21st to end	Day	14% 7% 2 8% 5% 4 4 4 5% 6% 40%	4054
April	1st to 10th	Day	22% 12% 3 6% 4 4 4 3 3 5% 33%	2280
	11th to 20th	Day	22% 9% 3 7% 4 4 3 3 4 6% 36%	2254
	21st to end	Day	22% 10% 4 8% 5% 4 5% 3 4 5% 31%	2413
May	1st to 10th	Day	20% 9% 3 7% 4 5% 5% 4 6% 7% 30%	4426
	11th to 20th	Day	17% 9% 3 7% 5% 5% 4 4 5% 8% 33%	4398
	21st to end	Day	15% 7% 2 7% 5% 5% 4 4 6% 8% 37%	4837
June	1st to 10th	Day	22% 8% 3 7% 5% 4 4 4 6% 6% 30%	2660
	11th to 20th	Day	14% 7% 2 7% 5% 5% 6% 4 5% 8% 38%	2660
	21st to end	Day	20% 7% 2 6% 5% 4 5% 5% 7% 8% 30%	2660
July	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 8% 40%	2548
	11th to 20th	Day	12% 6% 2 7% 5% 5% 6% 5% 7% 8% 38%	2520
	21st to end	Day	12% 6% 2 7% 5% 3 5% 5% 7% 9% 38%	2744
August	1st to 10th	Day	12% 6% 2 8% 5% 5% 4 4 7% 8% 40%	2494
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 5% 5% 8% 40%	2267
	21st to end	Day	13% 6% 2 6% 4 4 5% 4 5% 9% 42%	2376
September	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 5% 8% 42%	2160
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 5% 8% 46%	2151
	21st to end	Day	17% 6% 2 6% 5% 4 4 3 5% 7% 40%	1938
October	1st to 10th	Day	20% 9% 3 7% 4 4 4 4 5% 7% 35%	1800
	11th to 20th	Day	23% 9% 3 9% 4 5% 5% 4 4 6% 28%	1800
	21st to end	Day	26% 10% 2 7% 6% 4 4 3 4 5% 28%	1819
November	1st to 10th	Day	17% 9% 3 6% 5% 5% 5% 4 6% 6% 34%	1671
	11th to 20th	Day	19% 12% 3 8% 5% 4 4 4 5% 6% 28%	1539
	21st to end	Day	22% 13% 3 9% 7% 5% 5% 4 5% 5% 21%	1520
December	1st to 10th	Day	22% 16% 5% 10% 6% 5% 4 3 5% 5% 18%	1520
	11th to 20th	Day	22% 14% 4 10% 5% 4 4 3 5% 4 25%	1906
	21st to end	Day	28% 19% 5% 10% 4 3 4 2 3 3 19%	2772
January	1st to 10th	Night	18% 18% 6% 12% 5% 4 4 2 4 5% 21%	4429
	11th to 20th	Night	13% 14% 5% 13% 8% 6% 5% 4 5% 6% 22%	4440
	21st to end	Night	17% 20% 6% 11% 5% 5% 4 2 4 5% 21%	4789
February	1st to 10th	Night	14% 15% 5% 11% 5% 6% 5% 4 4 6% 24%	2470
	11th to 20th	Night	13% 13% 5% 11% 7% 5% 4 4 4 5% 28%	2384
	21st to end	Night	16% 13% 4 9% 5% 4 5% 3 5% 5% 30%	1884
March	1st to 10th	Night	20% 13% 3 9% 5% 4 4 3 4 4 30%	3724
	11th to 20th	Night	17% 17% 4 10% 6% 4 4 3 4 5% 26%	3511
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 5% 39%	3576
April	1st to 10th	Night	22% 11% 3 6% 5% 4 3 3 4 6% 33%	1900
	11th to 20th	Night	19% 9% 3 7% 5% 4 4 4 5% 6% 35%	1875
	21st to end	Night	22% 9% 3 6% 5% 3 4 3 4 6% 34%	1781
May	1st to 10th	Night	20% 10% 3 9% 5% 4 4 4 6% 6% 29%	2514
	11th to 20th	Night	20% 8% 3 6% 4 5% 4 4 5% 6% 35%	2495
	21st to end	Night	15% 7% 3 6% 5% 4 5% 4 6% 7% 38%	2738
June	1st to 10th	Night	16% 7% 2 7% 5% 5% 5% 4 8% 9% 32%	1520
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 4 6% 8% 41%	1520
	21st to end	Night	19% 7% 3 7% 4 4 5% 4 6% 8% 35%	1520
July	1st to 10th	Night	11% 4 2 6% 5% 5% 6% 4 6% 7% 45%	1456
	11th to 20th	Night	11% 7% 2 5% 4 4 5% 4 7% 9% 43%	1440
	21st to end	Night	9% 6% 2 6% 5% 5% 4 5% 6% 8% 43%	1574
August	1st to 10th	Night	9% 7% 3 6% 4 4 5% 5% 7% 8% 43%	1441
	11th to 20th	Night	11% 6% 2 7% 4 4 5% 4 6% 7% 45%	1616
	21st to end	Night	11% 5% 2 7% 4 4 5% 4 7% 8% 43%	1980
September	1st to 10th	Night	12% 6% 2 6% 5% 5% 4 4 5% 7% 44%	1800
	11th to 20th	Night	15% 5% 2 5% 4 3 3 3 5% 7% 48%	1808
	21st to end	Night	17% 6% 2 7% 4 4 4 3 4 6% 43%	2020
October	1st to 10th	Night	19% 7% 2 6% 4 4 5% 4 5% 5% 37%	2160
	11th to 20th	Night	20% 9% 3 7% 6% 5% 5% 3 5% 5% 32%	2160
	21st to end	Night	23% 10% 4 7% 5% 4 4 3 4 6% 29%	2536
November	1st to 10th	Night	20% 10% 3 6% 5% 4 4 3 5% 6% 34%	2407
	11th to 20th	Night	19% 11% 3 8% 5% 5% 5% 4 4 6% 30%	2636
	21st to end	Night	22% 13% 4 9% 5% 4 4 3 5% 5% 25%	2660
December	1st to 10th	Night	21% 18% 5% 9% 7% 5% 4 4 4 5% 19%	2660
	11th to 20th	Night	23% 15% 4 8% 5% 3 4 3 4 4 27%	3288
	21st to end	Night	32% 17% 3 10% 3 4 4 2 4 3 18%	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	69% 1 12% 11% 6% 1	2518
	11th to 20th	Day	65% 2 10% 15% 8%	2520
	21st to end	Day	69% 4 11% 11% 5%	2850
February	1st to 10th	Day	61% 2 10% 20% 5% 2	1710
	11th to 20th	Day	59% 2 12% 17% 9% 1	1690
	21st to end	Day	61% 3 10% 14% 10% 2	1570
March	1st to 10th	Day	62% 2 9% 18% 9% 1	3119
	11th to 20th	Day	60% 1 11% 15% 11% 1	3447
	21st to end	Day	47% 1 6% 24% 19% 3	4054
April	1st to 10th	Day	56% 2 7% 20% 12% 3	2280
	11th to 20th	Day	52% 2 6% 23% 15% 2	2254
	21st to end	Day	57% 2 8% 16% 14% 4	2413
May	1st to 10th	Day	54% 2 7% 24% 11% 2	4440
	11th to 20th	Day	52% 2 13% 21% 10% 2	4402
	21st to end	Day	46% 3 11% 24% 15% 2	4837
June	1st to 10th	Day	54% 3 11% 20% 12% 1	2660
	11th to 20th	Day	45% 4 11% 25% 13% 2	2660
	21st to end	Day	50% 4 14% 21% 10% 1	2660
July	1st to 10th	Day	40% 4 13% 27% 15% 1	2478
	11th to 20th	Day	42% 4 15% 28% 12%	2445
	21st to end	Day	41% 5% 16% 27% 11%	2591
August	1st to 10th	Day	42% 4 17% 27% 10%	2480
	11th to 20th	Day	41% 5% 16% 28% 9% 1	2267
	21st to end	Day	40% 4 14% 29% 13% 1	2376
September	1st to 10th	Day	42% 3 13% 29% 13%	2160
	11th to 20th	Day	37% 4 13% 32% 13% 1	2151
	21st to end	Day	45% 4 15% 27% 9%	1938
October	1st to 10th	Day	49% 3 12% 24% 11% 1	1800
	11th to 20th	Day	59% 4 13% 18% 6% 1	1800
	21st to end	Day	60% 2 12% 17% 8% 1	1819
November	1st to 10th	Day	50% 4 14% 25% 7% 1	1671
	11th to 20th	Day	58% 3 13% 17% 9% 1	1539
	21st to end	Day	65% 4 13% 11% 6% 1	1520
December	1st to 10th	Day	68% 3 12% 12% 4	1520
	11th to 20th	Day	64% 2 13% 15% 5%	1906
	21st to end	Day	73% 2 7% 15% 3	2772
January	1st to 10th	Night	68% 1 14% 12% 4	4429
	11th to 20th	Night	65% 2 13% 15% 5%	4440
	21st to end	Night	68% 2 10% 12% 7% 1	4789
February	1st to 10th	Night	62% 3 9% 18% 7% 1	2470
	11th to 20th	Night	59% 3 9% 20% 9% 1	2386
	21st to end	Night	57% 3 8% 20% 11% 1	1884
March	1st to 10th	Night	59% 1 8% 20% 10% 2	3734
	11th to 20th	Night	62% 1 11% 15% 9% 2	3512
	21st to end	Night	49% 1 5% 22% 19% 3	3576
April	1st to 10th	Night	54% 2 8% 18% 16% 2	1900
	11th to 20th	Night	51% 3 6% 22% 16% 1	1875
	21st to end	Night	52% 2 8% 18% 17% 4	1781
May	1st to 10th	Night	56% 2 8% 21% 10% 3	2520
	11th to 20th	Night	52% 2 11% 21% 13% 2	2496
	21st to end	Night	46% 2 11% 22% 17% 2	2739
June	1st to 10th	Night	47% 4 12% 25% 11% 1	1520
	11th to 20th	Night	42% 4 11% 25% 17% 2	1520
	21st to end	Night	47% 5% 13% 20% 14% 1	1520
July	1st to 10th	Night	36% 5% 12% 27% 17% 2	1416
	11th to 20th	Night	38% 3 11% 33% 13%	1392
	21st to end	Night	39% 4 16% 26% 15%	1486
August	1st to 10th	Night	37% 6% 19% 24% 13% 1	1431
	11th to 20th	Night	38% 4 16% 30% 11%	1616
	21st to end	Night	38% 4 16% 29% 11%	1980
September	1st to 10th	Night	39% 4 11% 30% 15% 1	1800
	11th to 20th	Night	37% 3 13% 36% 10% 1	1808
	21st to end	Night	43% 3 10% 33% 10%	2020
October	1st to 10th	Night	48% 4 10% 25% 13% 1	2160
	11th to 20th	Night	55% 3 11% 22% 9%	2160
	21st to end	Night	58% 3 13% 18% 8%	2536
November	1st to 10th	Night	52% 3 14% 22% 9%	2407
	11th to 20th	Night	57% 2 11% 18% 10% 1	2636
	21st to end	Night	62% 3 13% 17% 5%	2660
December	1st to 10th	Night	69% 3 10% 13% 4	2660
	11th to 20th	Night	62% 2 9% 17% 8% 1	3288
	21st to end	Night	73% 2 7% 14% 4	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	28% 13% 31% 24% 4 1	180
	11th to 20th	Day	26% 14% 36% 18% 5% 1	180
	21st to end	Day	24% 12% 35% 23% 6%	222
February	1st to 10th	Day	32% 15% 37% 12% 2 1	270
	11th to 20th	Day	26% 21% 37% 14% 2	288
	21st to end	Day	31% 16% 31% 19% 3	382
March	1st to 10th	Day	26% 12% 35% 19% 8%	460
	11th to 20th	Day	26% 15% 33% 22% 3 1	460
	21st to end	Day	29% 18% 28% 15% 8% 2	506
April	1st to 10th	Day	29% 17% 29% 18% 6%	460
	11th to 20th	Day	33% 14% 24% 17% 10% 1	452
	21st to end	Day	30% 15% 29% 16% 7% 2	460
May	1st to 10th	Day	25% 11% 31% 22% 8% 3	463
	11th to 20th	Day	22% 13% 29% 22% 11% 3	487
	21st to end	Day	19% 12% 32% 23% 12% 2	529
June	1st to 10th	Day	27% 8% 27% 25% 11% 2	490
	11th to 20th	Day	16% 12% 30% 25% 15% 2	490
	21st to end	Day	25% 9% 26% 25% 12% 3	490
July	1st to 10th	Day	14% 5% 27% 32% 16% 6%	453
	11th to 20th	Day	13% 5% 31% 30% 16% 5%	444
	21st to end	Day	14% 5% 29% 31% 17% 4	488
August	1st to 10th	Day	15% 6% 25% 32% 17% 5%	446
	11th to 20th	Day	15% 5% 22% 28% 20% 10%	439
	21st to end	Day	14% 9% 25% 25% 17% 9%	495
September	1st to 10th	Day	19% 6% 27% 22% 15% 10%	450
	11th to 20th	Day	14% 8% 23% 23% 21% 11%	450
	21st to end	Day	20% 10% 27% 24% 14% 5%	450
October	1st to 10th	Day	24% 10% 25% 22% 14% 5%	450
	11th to 20th	Day	28% 14% 29% 18% 9% 1	450
	21st to end	Day	33% 10% 25% 24% 7%	414
November	1st to 10th	Day	25% 14% 28% 22% 10% 1	365
	11th to 20th	Day	28% 14% 36% 16% 4 2	199
	21st to end	Day	29% 16% 31% 17% 5% 2	180
December	1st to 10th	Day	31% 12% 34% 19% 4	180
	11th to 20th	Day	28% 20% 33% 18% 1 1	180
	21st to end	Day	34% 15% 34% 13% 3 1	198
January	1st to 10th	Night	29% 11% 31% 23% 5%	760
	11th to 20th	Night	29% 13% 28% 23% 7% 1	760
	21st to end	Night	21% 9% 33% 29% 8% 1	836
February	1st to 10th	Night	22% 13% 32% 28% 4	760
	11th to 20th	Night	21% 14% 35% 25% 4	743
	21st to end	Night	25% 13% 29% 31% 3	628
March	1st to 10th	Night	25% 14% 31% 26% 4	760
	11th to 20th	Night	26% 12% 33% 24% 5% 1	760
	21st to end	Night	24% 13% 29% 26% 8%	836
April	1st to 10th	Night	28% 11% 29% 26% 6%	760
	11th to 20th	Night	25% 13% 31% 23% 8% 1	751
	21st to end	Night	28% 10% 27% 27% 8% 1	641
May	1st to 10th	Night	26% 6% 28% 30% 9% 2	380
	11th to 20th	Night	24% 9% 24% 34% 9% 1	374
	21st to end	Night	16% 6% 36% 30% 11%	411
June	1st to 10th	Night	19% 3 27% 39% 11%	380
	11th to 20th	Night	17% 6% 24% 37% 14% 2	380
	21st to end	Night	21% 4 25% 33% 16% 1	380
July	1st to 10th	Night	10% 4 27% 42% 17%	354
	11th to 20th	Night	13% 2 22% 44% 18% 1	348
	21st to end	Night	10% 3 24% 44% 18% 2	394
August	1st to 10th	Night	14% 4 19% 40% 22% 2	367
	11th to 20th	Night	14% 3 16% 38% 26% 3	552
	21st to end	Night	13% 6% 22% 35% 21% 3	792
September	1st to 10th	Night	15% 4 26% 35% 19% 1	720
	11th to 20th	Night	19% 4 19% 33% 22% 3	720
	21st to end	Night	21% 7% 23% 27% 20% 2	720
October	1st to 10th	Night	23% 8% 25% 26% 17% 2	720
	11th to 20th	Night	26% 9% 29% 27% 9% 1	720
	21st to end	Night	29% 10% 26% 29% 6%	792
November	1st to 10th	Night	28% 9% 25% 27% 10% 1	740
	11th to 20th	Night	26% 14% 30% 19% 11%	760
	21st to end	Night	30% 13% 26% 24% 6%	760
December	1st to 10th	Night	31% 12% 28% 25% 4	760
	11th to 20th	Night	30% 12% 30% 21% 6% 1	760
	21st to end	Night	34% 11% 28% 22% 4	836

Page generated at 2024-06-29 22:08:53. Version ac07

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