Antique Photons Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Antique Photons Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	12% 6% 2 6% 4 4 4 3 5% 7% 48%	120038
	Night	12% 6% 2 5% 3 3 3 3 5% 6% 52%	118435
Transparency	Day	35% 4 11% 25% 20% 5%	123718
	Night	32% 4 10% 25% 22% 7%	122885
Seeing	Day	15% 12% 28% 27% 15% 3	16230
	Night	14% 11% 32% 30% 12% 1	26146

By Month

Percentage Cloud Cover SE (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	14% 11% 4 7% 3 3 3 2 4 6% 42%	4077
	11th to 20th	Day	7% 6% 2 6% 5% 4 4 4 4 5% 55%	4080
	21st to end	Day	19% 10% 2 5% 3 2 2 2 4 4 48%	4488
February	1st to 10th	Day	17% 11% 3 6% 4 3 2 3 4 6% 41%	1800
	11th to 20th	Day	15% 7% 3 6% 4 4 3 3 4 6% 45%	1858
	21st to end	Day	15% 7% 2 6% 4 4 3 3 4 5% 45%	1714
March	1st to 10th	Day	12% 8% 2 5% 3 3 3 3 4 5% 52%	4936
	11th to 20th	Day	9% 5% 2 5% 3 3 3 3 5% 7% 55%	4980
	21st to end	Day	14% 8% 3 7% 5% 5% 4 4 6% 8% 37%	5462
April	1st to 10th	Day	14% 6% 3 5% 4 4 4 4 6% 6% 45%	2235
	11th to 20th	Day	16% 6% 2 6% 4 4 4 3 6% 6% 44%	2374
	21st to end	Day	20% 8% 3 7% 4 4 3 3 4 6% 39%	2528
May	1st to 10th	Day	20% 8% 2 7% 4 4 4 3 5% 6% 38%	5862
	11th to 20th	Day	11% 6% 2 7% 5% 4 5% 4 6% 7% 44%	5862
	21st to end	Day	19% 8% 3 7% 4 4 5% 4 6% 7% 34%	6434
June	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 4 6% 9% 47%	2588
	11th to 20th	Day	8% 4 2 5% 5% 5% 5% 4 6% 7% 50%	2470
	21st to end	Day	5% 3 1 4 4 4 4 4 6% 9% 56%	2470
July	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 9% 44%	4120
	11th to 20th	Day	5% 4 2 5% 3 4 4 4 6% 9% 54%	4120
	21st to end	Day	5% 4 2 5% 4 5% 5% 4 8% 11% 48%	4465
August	1st to 10th	Day	5% 3 1 4 3 3 4 4 6% 10% 57%	4104
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 7% 9% 48%	4041
	21st to end	Day	4 3 1 5% 4 4 5% 3 6% 8% 57%	4258
September	1st to 10th	Day	10% 5% 2 4 4 4 3 3 4 6% 54%	2183
	11th to 20th	Day	11% 4 2 5% 4 4 5% 4 6% 8% 47%	2090
	21st to end	Day	8% 3 2 4 4 3 4 3 5% 7% 55%	2090
October	1st to 10th	Day	10% 4 2 4 3 3 3 4 5% 6% 57%	1942
	11th to 20th	Day	12% 5% 1 4 2 1 3 3 3 5% 62%	1900
	21st to end	Day	18% 5% 2 4 2 2 3 2 3 5% 53%	2090
November	1st to 10th	Day	12% 3 1 4 3 3 3 3 4 6% 57%	1958
	11th to 20th	Day	14% 5% 1 4 2 3 3 3 3 5% 57%	1840
	21st to end	Day	15% 7% 1 4 3 2 3 2 4 7% 52%	1800
December	1st to 10th	Day	11% 9% 2 6% 4 3 3 2 4 5% 53%	2940
	11th to 20th	Day	14% 7% 2 6% 3 3 3 2 4 6% 50%	3391
	21st to end	Day	22% 14% 5% 7% 4 3 3 2 3 4 31%	4488
January	1st to 10th	Night	13% 7% 3 7% 4 3 3 3 6% 6% 45%	5888
	11th to 20th	Night	7% 5% 2 4 4 3 5% 4 5% 6% 55%	5900
	21st to end	Night	17% 8% 3 6% 3 3 3 2 4 5% 48%	6490
February	1st to 10th	Night	16% 9% 3 6% 3 3 2 3 4 6% 45%	2600
	11th to 20th	Night	15% 7% 3 6% 4 3 3 2 4 6% 48%	2444
	21st to end	Night	15% 6% 2 5% 3 3 4 3 4 4 51%	1915
March	1st to 10th	Night	15% 8% 2 5% 3 3 3 2 4 5% 50%	4919
	11th to 20th	Night	8% 5% 2 4 2 2 3 2 4 6% 61%	4980
	21st to end	Night	13% 5% 2 5% 4 3 4 3 6% 8% 47%	5467
April	1st to 10th	Night	13% 6% 2 4 3 3 3 3 5% 6% 52%	2164
	11th to 20th	Night	14% 5% 2 5% 3 3 2 3 5% 6% 50%	1975
	21st to end	Night	15% 7% 3 7% 3 3 3 3 4 6% 47%	1869
May	1st to 10th	Night	18% 7% 2 5% 3 3 4 3 4 6% 44%	4053
	11th to 20th	Night	14% 5% 2 5% 4 3 4 3 5% 8% 47%	4053
	21st to end	Night	16% 5% 2 5% 4 4 3 3 6% 8% 44%	4443
June	1st to 10th	Night	7% 4 2 5% 3 3 4 4 6% 8% 53%	1796
	11th to 20th	Night	4 3 1 4 3 4 4 5% 6% 11% 56%	1710
	21st to end	Night	4 3 1 3 3 4 3 3 5% 8% 65%	1710
July	1st to 10th	Night	8% 5% 2 5% 4 3 3 4 5% 9% 52%	2850
	11th to 20th	Night	3 2 1 4 3 3 4 3 6% 9% 62%	2850
	21st to end	Night	6% 4 1 4 4 3 3 3 5% 10% 57%	3098
August	1st to 10th	Night	2 2 1 3 3 3 4 3 6% 9% 64%	2836
	11th to 20th	Night	5% 4 1 5% 4 5% 5% 5% 6% 8% 52%	2798
	21st to end	Night	3 3 1 3 3 3 4 2 6% 8% 64%	3398
September	1st to 10th	Night	7% 4 2 5% 4 3 3 3 4 7% 59%	1992
	11th to 20th	Night	9% 5% 2 4 3 4 3 3 5% 7% 53%	2090
	21st to end	Night	8% 3 1 4 4 3 4 3 4 6% 59%	2090
October	1st to 10th	Night	7% 3 1 4 3 3 3 3 4 6% 64%	2218
	11th to 20th	Night	12% 4 1 3 3 3 3 2 3 5% 60%	2280
	21st to end	Night	14% 6% 2 4 3 3 3 3 4 5% 55%	2508
November	1st to 10th	Night	12% 5% 1 3 2 2 2 2 4 4 62%	2340
	11th to 20th	Night	10% 5% 2 5% 3 2 3 2 4 5% 59%	2555
	21st to end	Night	14% 6% 2 3 3 2 3 3 4 5% 55%	2600
December	1st to 10th	Night	9% 7% 2 4 3 3 4 3 4 6% 56%	4250
	11th to 20th	Night	16% 7% 2 5% 3 3 3 2 3 4 52%	4816
	21st to end	Night	19% 11% 4 6% 4 3 3 3 4 4 40%	6490

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	45% 2 9% 26% 16% 1	4078
	11th to 20th	Day	31% 3 12% 28% 22% 5%	4080
	21st to end	Day	42% 2 7% 21% 24% 4	4488
February	1st to 10th	Day	46% 4 10% 23% 14% 3	1800
	11th to 20th	Day	42% 4 9% 25% 17% 3	1867
	21st to end	Day	41% 3 7% 23% 18% 8%	1714
March	1st to 10th	Day	35% 3 5% 21% 18% 17%	4936
	11th to 20th	Day	29% 4 10% 21% 21% 15%	4980
	21st to end	Day	44% 5% 10% 29% 10% 1	5464
April	1st to 10th	Day	38% 6% 11% 22% 18% 5%	2235
	11th to 20th	Day	40% 5% 12% 22% 16% 5%	2374
	21st to end	Day	47% 4 10% 22% 16% 1	2528
May	1st to 10th	Day	47% 4 10% 21% 15% 2	5900
	11th to 20th	Day	38% 5% 12% 22% 20% 3	5866
	21st to end	Day	47% 7% 12% 16% 15% 2	6447
June	1st to 10th	Day	33% 8% 16% 26% 16% 2	2588
	11th to 20th	Day	32% 7% 13% 29% 17% 2	2470
	21st to end	Day	25% 6% 15% 30% 20% 5%	2470
July	1st to 10th	Day	34% 7% 17% 26% 14% 3	4056
	11th to 20th	Day	26% 5% 11% 35% 20% 3	4051
	21st to end	Day	27% 6% 19% 33% 15%	4325
August	1st to 10th	Day	23% 5% 14% 28% 25% 5%	4090
	11th to 20th	Day	31% 6% 20% 25% 16% 2	4080
	21st to end	Day	25% 6% 12% 40% 14% 3	4257
September	1st to 10th	Day	31% 5% 10% 23% 22% 10%	2183
	11th to 20th	Day	33% 7% 13% 21% 21% 5%	2090
	21st to end	Day	29% 5% 9% 23% 28% 6%	2090
October	1st to 10th	Day	18% 3 7% 15% 42% 14%	3228
	11th to 20th	Day	16% 2 4 20% 43% 15%	3140
	21st to end	Day	29% 2 7% 27% 28% 6%	3428
November	1st to 10th	Day	29% 4 8% 27% 25% 7%	1958
	11th to 20th	Day	31% 3 8% 26% 23% 8%	1840
	21st to end	Day	34% 3 8% 27% 24% 4	1800
December	1st to 10th	Day	35% 3 7% 33% 20% 1	2940
	11th to 20th	Day	37% 2 6% 28% 25% 3	3389
	21st to end	Day	57% 3 8% 20% 9% 2	4488
January	1st to 10th	Night	39% 4 11% 29% 15% 3	5888
	11th to 20th	Night	28% 5% 11% 20% 31% 5%	5900
	21st to end	Night	41% 3 8% 19% 26% 4	6490
February	1st to 10th	Night	42% 3 11% 23% 17% 4	2600
	11th to 20th	Night	39% 3 8% 26% 19% 5%	2445
	21st to end	Night	38% 4 6% 19% 24% 9%	1915
March	1st to 10th	Night	39% 3 6% 21% 19% 12%	4919
	11th to 20th	Night	26% 3 8% 24% 26% 14%	4980
	21st to end	Night	35% 5% 13% 31% 15% 2	5467
April	1st to 10th	Night	33% 5% 9% 23% 21% 9%	2164
	11th to 20th	Night	34% 5% 10% 23% 20% 8%	1975
	21st to end	Night	40% 4 11% 23% 20% 3	1869
May	1st to 10th	Night	42% 5% 11% 20% 19% 3	4080
	11th to 20th	Night	36% 5% 11% 24% 18% 6%	4054
	21st to end	Night	37% 7% 15% 23% 15% 3	4452
June	1st to 10th	Night	27% 9% 15% 29% 18% 3	1796
	11th to 20th	Night	21% 7% 15% 32% 21% 3	1710
	21st to end	Night	19% 5% 14% 32% 25% 7%	1710
July	1st to 10th	Night	29% 6% 17% 27% 17% 5%	2805
	11th to 20th	Night	18% 4 11% 38% 26% 3	2796
	21st to end	Night	23% 4 16% 38% 18% 1	2999
August	1st to 10th	Night	16% 5% 14% 31% 27% 6%	2826
	11th to 20th	Night	29% 6% 17% 26% 19% 3	2825
	21st to end	Night	19% 5% 11% 40% 21% 5%	3398
September	1st to 10th	Night	26% 5% 9% 26% 24% 10%	1992
	11th to 20th	Night	30% 6% 10% 22% 24% 7%	2090
	21st to end	Night	26% 4 9% 25% 30% 6%	2090
October	1st to 10th	Night	14% 3 6% 14% 38% 25%	3699
	11th to 20th	Night	20% 3 4 18% 37% 19%	3779
	21st to end	Night	28% 3 7% 27% 27% 8%	4120
November	1st to 10th	Night	27% 3 8% 24% 30% 8%	2340
	11th to 20th	Night	29% 3 7% 25% 26% 10%	2555
	21st to end	Night	32% 3 8% 23% 27% 6%	2600
December	1st to 10th	Night	31% 3 9% 37% 17% 2	4250
	11th to 20th	Night	38% 3 6% 23% 25% 6%	4817
	21st to end	Night	48% 3 9% 24% 12% 4	6490

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% 17% 34% 20% 3	300
	11th to 20th	Day	24% 24% 35% 14% 2	300
	21st to end	Day	21% 21% 36% 16% 5%	330
February	1st to 10th	Day	28% 19% 37% 12% 4	300
	11th to 20th	Day	24% 23% 39% 13% 1	300
	21st to end	Day	25% 27% 34% 12% 1	249
March	1st to 10th	Day	25% 23% 31% 18% 3	300
	11th to 20th	Day	25% 23% 34% 15% 3	300
	21st to end	Day	25% 27% 31% 13% 3	330
April	1st to 10th	Day	21% 26% 33% 16% 4	335
	11th to 20th	Day	22% 23% 36% 15% 4	492
	21st to end	Day	24% 18% 33% 17% 7% 1	628
May	1st to 10th	Day	17% 15% 37% 24% 6%	703
	11th to 20th	Day	18% 14% 32% 24% 10% 3	725
	21st to end	Day	17% 12% 33% 21% 13% 5%	789
June	1st to 10th	Day	8% 6% 25% 34% 22% 5%	726
	11th to 20th	Day	8% 4 29% 37% 18% 4	680
	21st to end	Day	4 4 28% 40% 20% 4	680
July	1st to 10th	Day	8% 2 15% 38% 28% 9%	671
	11th to 20th	Day	4 1 17% 41% 29% 6%	668
	21st to end	Day	8% 1 13% 35% 32% 12%	739
August	1st to 10th	Day	6% 3 17% 42% 28% 5%	676
	11th to 20th	Day	9% 2 18% 35% 30% 5%	665
	21st to end	Day	7% 2 12% 34% 35% 9%	591
September	1st to 10th	Day	10% 2 15% 31% 33% 9%	393
	11th to 20th	Day	6% 2 23% 37% 28% 4	300
	21st to end	Day	12% 6% 22% 35% 19% 6%	300
October	1st to 10th	Day	10% 8% 33% 28% 17% 5%	300
	11th to 20th	Day	9% 17% 38% 28% 7%	300
	21st to end	Day	24% 17% 32% 20% 7% 1	330
November	1st to 10th	Day	16% 15% 37% 22% 9% 1	300
	11th to 20th	Day	18% 16% 37% 20% 7% 3	300
	21st to end	Day	24% 16% 38% 19% 4	300
December	1st to 10th	Day	18% 20% 36% 18% 6% 2	300
	11th to 20th	Day	24% 18% 40% 13% 5%	300
	21st to end	Day	23% 23% 38% 13% 2	330
January	1st to 10th	Night	17% 16% 37% 25% 5%	1000
	11th to 20th	Night	17% 18% 39% 23% 4	1000
	21st to end	Night	14% 17% 38% 27% 4	1100
February	1st to 10th	Night	21% 17% 38% 21% 3	1000
	11th to 20th	Night	21% 19% 35% 22% 2	890
	21st to end	Night	19% 19% 36% 23% 2	595
March	1st to 10th	Night	18% 16% 36% 26% 3	600
	11th to 20th	Night	19% 16% 38% 25% 3	600
	21st to end	Night	20% 14% 40% 21% 4	660
April	1st to 10th	Night	17% 16% 42% 22% 4	600
	11th to 20th	Night	18% 14% 39% 24% 6%	593
	21st to end	Night	19% 12% 42% 21% 6%	600
May	1st to 10th	Night	14% 10% 40% 30% 6%	600
	11th to 20th	Night	14% 9% 31% 33% 13% 1	591
	21st to end	Night	14% 6% 31% 29% 18% 1	650
June	1st to 10th	Night	8% 3 21% 42% 26% 1	599
	11th to 20th	Night	3 3 31% 44% 18% 1	570
	21st to end	Night	3 2 27% 47% 19% 2	570
July	1st to 10th	Night	6% 1 16% 47% 27% 3	555
	11th to 20th	Night	2 1 17% 45% 32% 3	552
	21st to end	Night	6% 15% 43% 33% 3	624
August	1st to 10th	Night	3 2 17% 46% 30% 2	567
	11th to 20th	Night	7% 2 14% 48% 26% 3	564
	21st to end	Night	4 1 14% 40% 37% 4	627
September	1st to 10th	Night	11% 1 16% 44% 28% 1	570
	11th to 20th	Night	10% 2 19% 42% 23% 4	570
	21st to end	Night	10% 3 23% 38% 24% 3	570
October	1st to 10th	Night	8% 3 29% 36% 21% 3	698
	11th to 20th	Night	14% 9% 38% 29% 9%	760
	21st to end	Night	17% 13% 32% 28% 10% 1	836
November	1st to 10th	Night	14% 10% 40% 25% 11% 1	780
	11th to 20th	Night	13% 15% 36% 28% 7%	955
	21st to end	Night	18% 15% 36% 24% 7%	1000
December	1st to 10th	Night	16% 16% 35% 28% 5%	1000
	11th to 20th	Night	21% 14% 36% 25% 5%	1000
	21st to end	Night	19% 19% 34% 25% 3	1100

Page generated at 2025-06-07 09:28:14. Version ac07

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