Peters Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Peters Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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	18% 12% 4 8% 5% 4 4 4 5% 7% 29%	101487
	Night	19% 13% 5% 10% 5% 4 4 3 5% 5% 27%	97506
Transparency	Day	55% 5% 12% 20% 8% 1	101245
	Night	58% 4 11% 18% 8% 1	97368
Seeing	Day	27% 17% 28% 18% 8% 2	14693
	Night	26% 17% 27% 22% 8% 1	23821

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	13% 25% 8% 14% 5% 5% 4 2 3 4 17%	2517
	11th to 20th	Day	14% 21% 10% 18% 8% 3 3 3 3 3 14%	2520
	21st to end	Day	19% 25% 8% 10% 9% 5% 4 3 3 3 11%	3000
February	1st to 10th	Day	16% 18% 5% 17% 9% 5% 5% 4 4 4 15%	1710
	11th to 20th	Day	13% 18% 7% 16% 7% 5% 4 3 4 4 18%	1731
	21st to end	Day	19% 18% 6% 15% 6% 4 4 3 3 4 19%	1570
March	1st to 10th	Day	27% 14% 4 10% 4 3 3 3 4 4 24%	3116
	11th to 20th	Day	13% 23% 6% 9% 5% 4 3 3 4 5% 26%	3470
	21st to end	Day	19% 13% 5% 11% 4 3 3 3 4 5% 32%	4038
April	1st to 10th	Day	19% 16% 3 8% 5% 3 3 3 4 5% 30%	2280
	11th to 20th	Day	19% 12% 3 6% 4 4 4 3 6% 5% 34%	2254
	21st to end	Day	22% 12% 3 7% 5% 4 3 3 5% 5% 31%	2289
May	1st to 10th	Day	25% 10% 3 7% 4 3 4 3 4 6% 31%	4391
	11th to 20th	Day	18% 9% 3 7% 5% 5% 5% 4 6% 8% 31%	4398
	21st to end	Day	14% 6% 3 6% 5% 4 5% 4 6% 9% 39%	4837
June	1st to 10th	Day	18% 8% 3 7% 5% 5% 4 4 6% 8% 31%	2660
	11th to 20th	Day	19% 5% 2 6% 4 5% 6% 4 6% 9% 33%	2660
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 7% 8% 31%	2660
July	1st to 10th	Day	13% 6% 2 6% 5% 5% 6% 5% 7% 11% 34%	4440
	11th to 20th	Day	11% 6% 3 8% 5% 6% 5% 5% 8% 10% 35%	4440
	21st to end	Day	13% 6% 3 7% 5% 5% 6% 5% 7% 8% 36%	4814
August	1st to 10th	Day	18% 7% 2 6% 4 5% 5% 5% 6% 8% 35%	4239
	11th to 20th	Day	16% 7% 3 8% 5% 5% 6% 5% 8% 9% 30%	3867
	21st to end	Day	17% 6% 3 6% 5% 4 4 4 6% 8% 39%	4180
September	1st to 10th	Day	15% 6% 2 5% 4 4 5% 4 6% 8% 40%	2280
	11th to 20th	Day	15% 7% 2 6% 3 4 3 3 5% 7% 44%	2261
	21st to end	Day	17% 6% 3 7% 5% 5% 5% 4 6% 7% 35%	2062
October	1st to 10th	Day	20% 8% 3 8% 5% 5% 4 3 5% 7% 32%	1900
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 4 5% 6% 33%	1900
	21st to end	Day	27% 13% 3 7% 4 4 4 3 5% 6% 23%	1966
November	1st to 10th	Day	16% 13% 3 7% 4 5% 4 4 5% 6% 31%	1681
	11th to 20th	Day	16% 18% 4 10% 6% 4 3 3 4 4 27%	1638
	21st to end	Day	19% 18% 6% 10% 5% 4 4 3 5% 6% 21%	1520
December	1st to 10th	Day	19% 24% 7% 12% 5% 3 4 3 4 5% 15%	1520
	11th to 20th	Day	22% 18% 9% 11% 6% 4 3 3 3 4 17%	1906
	21st to end	Day	27% 22% 7% 10% 5% 3 3 3 3 4 14%	2772
January	1st to 10th	Night	17% 23% 8% 17% 6% 4 3 3 3 4 12%	4429
	11th to 20th	Night	13% 20% 8% 18% 8% 5% 3 3 4 4 14%	4440
	21st to end	Night	21% 20% 8% 16% 9% 4 3 2 3 3 11%	4651
February	1st to 10th	Night	16% 18% 6% 15% 8% 5% 4 4 4 4 17%	2470
	11th to 20th	Night	14% 16% 7% 16% 8% 6% 5% 4 4 5% 17%	2333
	21st to end	Night	17% 16% 7% 16% 7% 5% 4 2 4 5% 18%	1884
March	1st to 10th	Night	22% 12% 5% 12% 6% 4 4 3 4 5% 24%	3724
	11th to 20th	Night	17% 21% 6% 9% 5% 3 3 3 4 4 24%	3488
	21st to end	Night	20% 14% 4 10% 4 4 4 2 4 4 30%	3594
April	1st to 10th	Night	21% 16% 4 6% 4 4 4 3 5% 5% 28%	1900
	11th to 20th	Night	21% 11% 3 7% 5% 5% 4 4 4 6% 32%	1875
	21st to end	Night	21% 10% 3 7% 4 3 4 3 6% 5% 34%	1891
May	1st to 10th	Night	26% 9% 4 7% 5% 4 3 4 4 5% 29%	2578
	11th to 20th	Night	16% 10% 4 8% 6% 5% 4 3 5% 6% 32%	2495
	21st to end	Night	15% 6% 2 7% 5% 5% 4 5% 7% 7% 38%	2738
June	1st to 10th	Night	19% 6% 2 7% 4 5% 5% 3 5% 7% 36%	1520
	11th to 20th	Night	19% 6% 2 5% 4 4 4 3 6% 8% 39%	1520
	21st to end	Night	16% 6% 3 7% 4 4 5% 5% 6% 7% 39%	1520
July	1st to 10th	Night	12% 6% 2 7% 7% 6% 5% 5% 7% 7% 37%	2520
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	2520
	21st to end	Night	14% 7% 2 6% 4 4 4 4 5% 8% 42%	2739
August	1st to 10th	Night	22% 8% 2 6% 3 3 3 3 6% 7% 37%	2687
	11th to 20th	Night	16% 7% 3 7% 5% 5% 4 3 4 7% 38%	2928
	21st to end	Night	13% 6% 2 6% 4 4 5% 3 6% 7% 42%	3476
September	1st to 10th	Night	15% 6% 2 6% 4 4 4 4 5% 8% 43%	1900
	11th to 20th	Night	17% 6% 2 4 3 4 4 3 4 5% 48%	1918
	21st to end	Night	19% 6% 2 6% 4 4 5% 3 6% 8% 38%	2114
October	1st to 10th	Night	23% 7% 3 8% 5% 4 5% 3 5% 6% 32%	2280
	11th to 20th	Night	22% 9% 2 7% 4 4 5% 4 4 6% 31%	2280
	21st to end	Night	28% 13% 3 7% 5% 4 4 3 4 5% 24%	2631
November	1st to 10th	Night	18% 11% 3 9% 5% 5% 4 3 5% 5% 32%	2431
	11th to 20th	Night	19% 15% 4 8% 4 4 4 3 5% 6% 27%	2540
	21st to end	Night	17% 18% 6% 9% 6% 4 4 3 5% 6% 22%	2660
December	1st to 10th	Night	21% 22% 7% 11% 5% 4 4 3 4 4 15%	2660
	11th to 20th	Night	21% 17% 8% 12% 5% 3 4 4 4 5% 16%	3288
	21st to end	Night	28% 19% 8% 9% 5% 4 3 2 3 5% 14%	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	71% 3 10% 12% 3	2518
	11th to 20th	Day	77% 3 8% 9% 3 1	2520
	21st to end	Day	78% 2 10% 6% 3 1	3000
February	1st to 10th	Day	74% 4 7% 11% 3	1710
	11th to 20th	Day	70% 5% 7% 13% 4	1740
	21st to end	Day	71% 3 8% 11% 6%	1570
March	1st to 10th	Day	65% 2 11% 15% 7% 1	3119
	11th to 20th	Day	62% 2 15% 11% 9% 1	3470
	21st to end	Day	57% 2 8% 18% 14% 1	4038
April	1st to 10th	Day	59% 3 6% 21% 9% 2	2280
	11th to 20th	Day	53% 4 10% 21% 11% 1	2254
	21st to end	Day	55% 3 8% 20% 11% 2	2289
May	1st to 10th	Day	55% 2 10% 19% 12% 1	4405
	11th to 20th	Day	52% 3 13% 24% 7% 1	4402
	21st to end	Day	41% 5% 14% 28% 11% 1	4837
June	1st to 10th	Day	51% 6% 12% 19% 11% 1	2660
	11th to 20th	Day	47% 5% 14% 23% 9% 1	2660
	21st to end	Day	49% 6% 14% 21% 9%	2660
July	1st to 10th	Day	41% 7% 16% 25% 11%	4370
	11th to 20th	Day	40% 8% 16% 28% 8%	4365
	21st to end	Day	43% 8% 14% 25% 9%	4661
August	1st to 10th	Day	47% 6% 14% 21% 11%	4225
	11th to 20th	Day	47% 8% 19% 19% 6%	3906
	21st to end	Day	43% 6% 14% 31% 6% 1	4180
September	1st to 10th	Day	41% 6% 12% 29% 11% 1	2280
	11th to 20th	Day	42% 3 11% 27% 16% 1	2261
	21st to end	Day	48% 6% 10% 24% 11% 1	2062
October	1st to 10th	Day	53% 4 10% 22% 10% 1	1900
	11th to 20th	Day	51% 5% 14% 22% 7% 1	1900
	21st to end	Day	62% 5% 12% 13% 8% 1	1966
November	1st to 10th	Day	53% 5% 11% 19% 11% 1	1681
	11th to 20th	Day	60% 4 11% 16% 7% 2	1638
	21st to end	Day	65% 5% 14% 12% 4	1520
December	1st to 10th	Day	74% 3 9% 11% 3	1520
	11th to 20th	Day	71% 4 13% 8% 4	1906
	21st to end	Day	76% 3 7% 10% 3	2772
January	1st to 10th	Night	77% 4 9% 7% 3	4429
	11th to 20th	Night	74% 3 7% 10% 5%	4440
	21st to end	Night	80% 3 7% 7% 2 1	4651
February	1st to 10th	Night	71% 4 8% 12% 5%	2470
	11th to 20th	Night	71% 4 7% 12% 5%	2335
	21st to end	Night	70% 3 10% 11% 6%	1884
March	1st to 10th	Night	64% 2 10% 16% 8%	3734
	11th to 20th	Night	64% 2 11% 17% 5%	3489
	21st to end	Night	60% 3 4 21% 10% 2	3594
April	1st to 10th	Night	59% 5% 9% 18% 8% 2	1900
	11th to 20th	Night	54% 5% 9% 19% 13% 1	1875
	21st to end	Night	51% 3 10% 19% 13% 3	1891
May	1st to 10th	Night	57% 2 11% 16% 10% 2	2584
	11th to 20th	Night	51% 5% 14% 21% 8% 1	2496
	21st to end	Night	44% 4 13% 21% 16% 1	2739
June	1st to 10th	Night	47% 5% 11% 24% 12% 1	1520
	11th to 20th	Night	42% 6% 16% 23% 13% 1	1520
	21st to end	Night	44% 6% 12% 27% 11% 1	1520
July	1st to 10th	Night	44% 6% 14% 21% 15% 1	2480
	11th to 20th	Night	39% 8% 15% 25% 13%	2472
	21st to end	Night	40% 5% 12% 28% 14% 1	2651
August	1st to 10th	Night	47% 6% 14% 24% 9%	2677
	11th to 20th	Night	45% 6% 16% 25% 8%	2955
	21st to end	Night	37% 8% 14% 31% 9% 1	3476
September	1st to 10th	Night	41% 5% 13% 28% 12% 1	1900
	11th to 20th	Night	38% 4 12% 28% 17% 1	1918
	21st to end	Night	45% 5% 11% 26% 11% 1	2114
October	1st to 10th	Night	52% 5% 12% 20% 11%	2280
	11th to 20th	Night	52% 5% 15% 18% 10% 1	2280
	21st to end	Night	63% 4 11% 14% 8% 1	2631
November	1st to 10th	Night	55% 5% 10% 16% 11% 2	2431
	11th to 20th	Night	58% 5% 10% 19% 7% 2	2540
	21st to end	Night	64% 4 13% 15% 4	2660
December	1st to 10th	Night	73% 5% 10% 10% 2	2660
	11th to 20th	Night	71% 4 9% 11% 4	3288
	21st to end	Night	75% 3 9% 11% 2	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	33% 23% 26% 13% 5%	180
	11th to 20th	Day	41% 24% 27% 6% 2 1	180
	21st to end	Day	28% 27% 33% 10% 2	263
February	1st to 10th	Day	42% 27% 24% 7%	270
	11th to 20th	Day	35% 32% 27% 6%	338
	21st to end	Day	39% 24% 25% 9% 2	382
March	1st to 10th	Day	32% 25% 27% 13% 2	460
	11th to 20th	Day	36% 23% 26% 12% 3	460
	21st to end	Day	38% 22% 23% 13% 4 1	506
April	1st to 10th	Day	36% 24% 24% 12% 5%	460
	11th to 20th	Day	35% 23% 22% 12% 6% 3	452
	21st to end	Day	37% 16% 27% 13% 6% 2	460
May	1st to 10th	Day	32% 17% 28% 14% 8% 2	463
	11th to 20th	Day	25% 12% 33% 20% 9% 2	487
	21st to end	Day	18% 15% 31% 23% 11% 3	529
June	1st to 10th	Day	23% 14% 29% 23% 8% 2	490
	11th to 20th	Day	20% 13% 31% 23% 12% 2	490
	21st to end	Day	20% 17% 35% 20% 6% 2	490
July	1st to 10th	Day	14% 9% 32% 28% 13% 5%	485
	11th to 20th	Day	15% 8% 31% 31% 13% 3	484
	21st to end	Day	15% 10% 36% 26% 10% 3	532
August	1st to 10th	Day	16% 11% 28% 25% 15% 6%	486
	11th to 20th	Day	18% 9% 27% 28% 13% 5%	479
	21st to end	Day	16% 12% 28% 26% 12% 5%	539
September	1st to 10th	Day	18% 11% 26% 23% 16% 6%	490
	11th to 20th	Day	15% 10% 25% 22% 18% 10%	490
	21st to end	Day	21% 13% 28% 21% 13% 4	490
October	1st to 10th	Day	26% 13% 26% 18% 12% 5%	490
	11th to 20th	Day	26% 20% 29% 15% 9% 1	490
	21st to end	Day	37% 19% 25% 15% 5%	473
November	1st to 10th	Day	31% 20% 23% 19% 8%	369
	11th to 20th	Day	31% 28% 24% 14% 3	298
	21st to end	Day	39% 19% 32% 9%	180
December	1st to 10th	Day	37% 23% 28% 10% 1 1	180
	11th to 20th	Day	37% 26% 30% 7%	180
	21st to end	Day	38% 24% 32% 5% 1	198
January	1st to 10th	Night	30% 26% 30% 12% 1	760
	11th to 20th	Night	31% 25% 27% 15% 2 1	760
	21st to end	Night	24% 25% 32% 17% 2	836
February	1st to 10th	Night	31% 23% 30% 16% 1	760
	11th to 20th	Night	29% 26% 30% 13% 2	743
	21st to end	Night	31% 24% 28% 15% 2	628
March	1st to 10th	Night	28% 22% 30% 18% 2	760
	11th to 20th	Night	31% 23% 27% 18% 2	760
	21st to end	Night	31% 21% 24% 19% 5%	836
April	1st to 10th	Night	28% 19% 31% 20% 2	760
	11th to 20th	Night	28% 18% 28% 18% 7% 1	751
	21st to end	Night	29% 14% 27% 23% 6%	751
May	1st to 10th	Night	28% 11% 24% 29% 7%	418
	11th to 20th	Night	20% 8% 36% 29% 7% 1	374
	21st to end	Night	16% 7% 33% 32% 10% 1	411
June	1st to 10th	Night	18% 9% 25% 36% 12% 1	380
	11th to 20th	Night	19% 9% 23% 37% 11%	380
	21st to end	Night	16% 7% 28% 40% 10%	380
July	1st to 10th	Night	11% 5% 24% 43% 16% 1	370
	11th to 20th	Night	13% 4 24% 43% 15% 1	368
	21st to end	Night	16% 4 22% 43% 14% 1	416
August	1st to 10th	Night	15% 4 26% 34% 20% 1	481
	11th to 20th	Night	15% 5% 22% 33% 22% 3	642
	21st to end	Night	14% 7% 24% 35% 19% 1	836
September	1st to 10th	Night	17% 8% 25% 31% 18% 2	760
	11th to 20th	Night	19% 7% 20% 29% 22% 3	760
	21st to end	Night	19% 11% 25% 29% 14% 2	760
October	1st to 10th	Night	26% 11% 23% 22% 16% 2	760
	11th to 20th	Night	27% 16% 27% 24% 6%	760
	21st to end	Night	36% 15% 28% 19% 2	836
November	1st to 10th	Night	26% 18% 30% 19% 7%	748
	11th to 20th	Night	29% 21% 27% 15% 6% 1	760
	21st to end	Night	28% 23% 28% 16% 4	760
December	1st to 10th	Night	35% 24% 25% 13% 3	760
	11th to 20th	Night	35% 22% 27% 13% 3	760
	21st to end	Night	34% 26% 27% 11% 1	836

Page generated at 2024-10-30 13:19:22. Version ac07

Copyright © 2024 Attilla Danko.