Blue Moon Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Moon Astronomical Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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	11% 7% 2 6% 4 4 4 4 5% 7% 45%	109134
	Night	10% 6% 2 5% 3 3 3 3 5% 7% 51%	109335
Transparency	Day	36% 7% 10% 22% 20% 5%	112785
	Night	31% 7% 10% 23% 22% 7%	113824
Seeing	Day	15% 12% 27% 26% 16% 4	15623
	Night	14% 11% 26% 30% 17% 2	25590

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	12% 12% 4 5% 3 3 3 3 4 5% 45%	4077
	11th to 20th	Day	6% 7% 2 6% 4 4 4 2 4 5% 56%	4080
	21st to end	Day	20% 9% 2 4 2 2 3 2 3 4 48%	4488
February	1st to 10th	Day	17% 10% 3 6% 5% 3 3 3 4 4 41%	1755
	11th to 20th	Day	14% 10% 3 7% 5% 4 5% 3 4 5% 41%	1730
	21st to end	Day	18% 11% 4 6% 4 3 3 3 4 5% 39%	1715
March	1st to 10th	Day	15% 9% 2 6% 4 4 4 3 4 5% 45%	3436
	11th to 20th	Day	13% 8% 2 5% 4 5% 4 3 6% 7% 43%	3480
	21st to end	Day	17% 10% 3 7% 5% 4 3 3 4 7% 39%	3814
April	1st to 10th	Day	11% 5% 3 7% 6% 4 4 3 6% 7% 44%	2161
	11th to 20th	Day	15% 7% 3 5% 5% 4 4 3 5% 6% 43%	2254
	21st to end	Day	15% 8% 3 8% 6% 5% 4 3 4 6% 39%	2280
May	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 3 5% 6% 37%	4044
	11th to 20th	Day	12% 6% 2 7% 6% 5% 4 4 6% 7% 42%	4082
	21st to end	Day	14% 8% 3 9% 6% 5% 5% 5% 6% 6% 35%	4477
June	1st to 10th	Day	8% 6% 3 6% 5% 5% 6% 5% 7% 9% 42%	2470
	11th to 20th	Day	6% 4 2 6% 6% 6% 7% 5% 7% 8% 44%	2470
	21st to end	Day	3 4 1 4 5% 4 6% 5% 8% 9% 51%	2470
July	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 5% 7% 9% 43%	4120
	11th to 20th	Day	4 3 2 5% 4 5% 4 5% 7% 8% 54%	4120
	21st to end	Day	7% 5% 2 7% 6% 7% 8% 6% 9% 9% 35%	4465
August	1st to 10th	Day	3 3 1 4 4 4 5% 5% 6% 8% 56%	4104
	11th to 20th	Day	8% 4 2 5% 4 4 6% 5% 7% 10% 45%	3977
	21st to end	Day	5% 3 2 5% 5% 5% 7% 5% 7% 9% 48%	4180
September	1st to 10th	Day	11% 5% 2 5% 4 4 5% 3 5% 6% 49%	2256
	11th to 20th	Day	12% 4 2 5% 4 4 5% 4 7% 8% 44%	2090
	21st to end	Day	7% 4 2 5% 5% 3 4 4 6% 7% 53%	2087
October	1st to 10th	Day	7% 5% 1 5% 4 3 4 4 4 7% 57%	1900
	11th to 20th	Day	12% 4 2 4 4 3 3 2 3 4 59%	1900
	21st to end	Day	17% 6% 1 4 3 3 3 3 4 5% 50%	2090
November	1st to 10th	Day	10% 6% 2 5% 4 3 3 3 5% 7% 53%	1958
	11th to 20th	Day	8% 6% 2 5% 4 4 3 3 4 6% 56%	1985
	21st to end	Day	13% 7% 2 6% 3 3 4 3 4 5% 50%	1800
December	1st to 10th	Day	14% 6% 2 6% 4 3 3 2 4 6% 51%	2940
	11th to 20th	Day	9% 9% 3 6% 4 5% 5% 4 6% 6% 44%	3391
	21st to end	Day	14% 12% 4 8% 5% 4 4 3 5% 5% 38%	4488
January	1st to 10th	Night	11% 9% 3 9% 4 3 3 2 4 5% 47%	5888
	11th to 20th	Night	8% 5% 3 5% 3 3 3 2 3 5% 59%	5900
	21st to end	Night	16% 11% 3 5% 3 2 3 2 4 5% 46%	6490
February	1st to 10th	Night	15% 9% 3 6% 3 3 3 3 4 6% 45%	2536
	11th to 20th	Night	14% 10% 3 6% 4 3 3 3 4 5% 45%	2352
	21st to end	Night	13% 9% 3 5% 4 3 4 3 4 6% 47%	1737
March	1st to 10th	Night	18% 9% 2 6% 3 3 3 3 5% 6% 42%	3419
	11th to 20th	Night	14% 8% 2 5% 3 3 3 3 4 5% 50%	3480
	21st to end	Night	13% 9% 3 6% 5% 4 3 3 5% 6% 42%	3817
April	1st to 10th	Night	11% 6% 2 4 5% 4 4 3 5% 7% 48%	2019
	11th to 20th	Night	11% 7% 2 5% 4 4 3 3 6% 6% 49%	1875
	21st to end	Night	14% 6% 2 4 3 4 3 3 5% 8% 47%	1900
May	1st to 10th	Night	12% 7% 3 6% 5% 4 4 4 6% 8% 39%	2855
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 6% 9% 44%	2823
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 9% 43%	3090
June	1st to 10th	Night	4 3 2 5% 3 3 4 4 7% 9% 56%	1710
	11th to 20th	Night	5% 3 2 4 2 2 4 4 5% 9% 60%	1710
	21st to end	Night	3 3 1 3 2 3 3 3 6% 10% 64%	1710
July	1st to 10th	Night	7% 4 1 4 4 4 5% 4 7% 9% 50%	2850
	11th to 20th	Night	4 2 1 3 2 2 4 2 5% 8% 66%	2850
	21st to end	Night	4 3 2 5% 4 5% 5% 5% 8% 11% 48%	3098
August	1st to 10th	Night	2 1 1 4 3 3 4 3 5% 9% 65%	2836
	11th to 20th	Night	4 3 2 4 3 3 4 3 6% 8% 60%	2859
	21st to end	Night	3 2 1 4 3 4 3 3 6% 9% 61%	3476
September	1st to 10th	Night	7% 4 1 4 3 4 4 3 5% 7% 58%	1919
	11th to 20th	Night	10% 4 2 4 3 3 4 4 5% 9% 51%	2090
	21st to end	Night	8% 4 1 4 3 3 4 2 5% 6% 60%	2090
October	1st to 10th	Night	6% 3 1 4 3 2 3 3 5% 8% 61%	2262
	11th to 20th	Night	10% 5% 2 4 3 2 2 2 4 5% 61%	2280
	21st to end	Night	17% 6% 2 4 2 2 2 2 3 4 55%	2508
November	1st to 10th	Night	10% 5% 1 5% 3 2 3 3 4 6% 57%	2340
	11th to 20th	Night	8% 7% 2 4 3 2 2 3 5% 7% 57%	2410
	21st to end	Night	13% 7% 1 4 3 3 3 4 5% 6% 51%	2600
December	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 5% 53%	4250
	11th to 20th	Night	9% 7% 3 8% 4 5% 4 3 5% 5% 48%	4816
	21st to end	Night	11% 11% 5% 8% 4 3 4 3 4 5% 42%	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	41% 5% 9% 23% 19% 3	4078
	11th to 20th	Day	30% 4 12% 21% 28% 4	4080
	21st to end	Day	41% 3 4 18% 25% 8%	4488
February	1st to 10th	Day	47% 4 10% 17% 19% 4	1755
	11th to 20th	Day	47% 4 6% 19% 19% 5%	1739
	21st to end	Day	49% 3 6% 15% 19% 8%	1715
March	1st to 10th	Day	40% 6% 9% 14% 20% 10%	3436
	11th to 20th	Day	39% 9% 11% 19% 16% 6%	3480
	21st to end	Day	45% 6% 9% 22% 16% 1	3814
April	1st to 10th	Day	39% 6% 10% 19% 19% 6%	2161
	11th to 20th	Day	42% 6% 9% 20% 17% 5%	2254
	21st to end	Day	46% 6% 8% 18% 18% 2	2280
May	1st to 10th	Day	44% 9% 10% 21% 13% 2	4082
	11th to 20th	Day	38% 10% 11% 23% 18% 1	4086
	21st to end	Day	46% 10% 11% 17% 13% 2	4489
June	1st to 10th	Day	36% 9% 15% 25% 14% 2	2470
	11th to 20th	Day	35% 9% 14% 22% 19% 2	2470
	21st to end	Day	26% 8% 15% 29% 18% 3	2470
July	1st to 10th	Day	35% 8% 18% 26% 12% 2	4056
	11th to 20th	Day	24% 7% 10% 35% 22% 2	4051
	21st to end	Day	35% 12% 17% 25% 10% 1	4325
August	1st to 10th	Day	22% 7% 13% 28% 25% 5%	4090
	11th to 20th	Day	32% 8% 16% 32% 11% 1	4016
	21st to end	Day	29% 9% 14% 32% 14% 2	4179
September	1st to 10th	Day	34% 8% 10% 21% 18% 9%	2256
	11th to 20th	Day	34% 8% 10% 23% 19% 6%	2090
	21st to end	Day	29% 6% 11% 19% 27% 8%	2087
October	1st to 10th	Day	16% 4 6% 12% 33% 29%	3160
	11th to 20th	Day	20% 3 4 17% 37% 19%	3140
	21st to end	Day	27% 6% 8% 29% 23% 8%	3428
November	1st to 10th	Day	31% 5% 10% 22% 24% 8%	1958
	11th to 20th	Day	30% 5% 8% 22% 26% 10%	1985
	21st to end	Day	37% 5% 7% 19% 26% 7%	1800
December	1st to 10th	Day	36% 4 8% 28% 21% 4	2940
	11th to 20th	Day	38% 6% 7% 20% 25% 4	3389
	21st to end	Day	45% 8% 8% 20% 16% 3	4488
January	1st to 10th	Night	39% 5% 8% 24% 21% 3	5888
	11th to 20th	Night	27% 6% 9% 18% 31% 9%	5900
	21st to end	Night	42% 4 6% 16% 25% 7%	6490
February	1st to 10th	Night	41% 5% 9% 21% 17% 6%	2536
	11th to 20th	Night	41% 6% 6% 22% 19% 6%	2353
	21st to end	Night	39% 4 9% 18% 20% 9%	1737
March	1st to 10th	Night	41% 8% 8% 14% 18% 11%	3419
	11th to 20th	Night	36% 7% 9% 24% 16% 7%	3480
	21st to end	Night	40% 8% 10% 22% 18% 2	3817
April	1st to 10th	Night	35% 7% 10% 20% 19% 10%	2019
	11th to 20th	Night	34% 6% 10% 21% 20% 9%	1875
	21st to end	Night	35% 7% 11% 22% 22% 2	1900
May	1st to 10th	Night	37% 13% 10% 22% 13% 4	2882
	11th to 20th	Night	34% 10% 15% 24% 15% 1	2824
	21st to end	Night	36% 11% 15% 23% 12% 4	3099
June	1st to 10th	Night	23% 8% 17% 30% 19% 3	1710
	11th to 20th	Night	21% 6% 13% 34% 23% 3	1710
	21st to end	Night	17% 7% 14% 30% 28% 5%	1710
July	1st to 10th	Night	27% 10% 18% 27% 15% 3	2805
	11th to 20th	Night	16% 6% 11% 39% 27% 1	2796
	21st to end	Night	26% 10% 20% 29% 15% 1	2999
August	1st to 10th	Night	15% 7% 14% 29% 28% 7%	2826
	11th to 20th	Night	21% 6% 19% 34% 17% 2	2886
	21st to end	Night	20% 7% 15% 33% 23% 2	3476
September	1st to 10th	Night	25% 7% 10% 26% 23% 11%	1919
	11th to 20th	Night	30% 8% 12% 20% 23% 7%	2090
	21st to end	Night	26% 4 9% 24% 29% 9%	2090
October	1st to 10th	Night	13% 3 7% 13% 27% 36%	3782
	11th to 20th	Night	18% 4 4 15% 37% 23%	3779
	21st to end	Night	26% 4 6% 26% 27% 11%	4120
November	1st to 10th	Night	29% 5% 8% 21% 26% 11%	2340
	11th to 20th	Night	27% 4 9% 21% 28% 12%	2410
	21st to end	Night	35% 5% 8% 18% 26% 7%	2600
December	1st to 10th	Night	33% 5% 8% 30% 21% 4	4250
	11th to 20th	Night	37% 6% 6% 19% 21% 10%	4817
	21st to end	Night	40% 9% 8% 20% 19% 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% 22% 35% 14% 4	300
	11th to 20th	Day	24% 28% 34% 11% 2 1	300
	21st to end	Day	25% 27% 31% 11% 5%	330
February	1st to 10th	Day	29% 19% 34% 15% 3	285
	11th to 20th	Day	29% 29% 30% 10% 1	270
	21st to end	Day	39% 27% 27% 6% 2	225
March	1st to 10th	Day	24% 29% 29% 18% 1	270
	11th to 20th	Day	33% 23% 32% 10% 2	270
	21st to end	Day	29% 24% 36% 9% 1	297
April	1st to 10th	Day	26% 23% 34% 10% 6% 1	341
	11th to 20th	Day	25% 19% 36% 14% 6%	452
	21st to end	Day	21% 24% 30% 18% 5% 1	460
May	1st to 10th	Day	16% 21% 37% 21% 4 1	628
	11th to 20th	Day	15% 13% 35% 24% 9% 2	675
	21st to end	Day	12% 10% 39% 22% 13% 4	734
June	1st to 10th	Day	10% 5% 23% 36% 21% 5%	680
	11th to 20th	Day	5% 5% 30% 36% 20% 4	680
	21st to end	Day	3 6% 27% 36% 22% 6%	680
July	1st to 10th	Day	7% 2 19% 36% 27% 8%	671
	11th to 20th	Day	4 1 18% 39% 29% 9%	668
	21st to end	Day	4 2 13% 37% 34% 10%	739
August	1st to 10th	Day	6% 2 14% 42% 31% 5%	676
	11th to 20th	Day	11% 1 13% 39% 28% 7%	627
	21st to end	Day	7% 1 9% 32% 37% 14%	539
September	1st to 10th	Day	9% 3 11% 36% 34% 8%	466
	11th to 20th	Day	6% 3 23% 37% 26% 6%	300
	21st to end	Day	10% 8% 22% 33% 21% 6%	300
October	1st to 10th	Day	4 9% 33% 33% 19% 1	300
	11th to 20th	Day	14% 16% 36% 25% 8% 1	300
	21st to end	Day	30% 12% 32% 20% 5% 1	330
November	1st to 10th	Day	13% 21% 36% 21% 9%	300
	11th to 20th	Day	18% 18% 38% 21% 4 2	300
	21st to end	Day	25% 24% 27% 18% 5%	300
December	1st to 10th	Day	25% 21% 30% 18% 5% 1	300
	11th to 20th	Day	26% 24% 31% 15% 4	300
	21st to end	Day	25% 23% 36% 13% 3	330
January	1st to 10th	Night	19% 16% 31% 29% 5%	1000
	11th to 20th	Night	19% 21% 32% 24% 4	1000
	21st to end	Night	17% 19% 32% 28% 4	1100
February	1st to 10th	Night	23% 17% 30% 25% 5%	976
	11th to 20th	Night	22% 21% 35% 21% 1	878
	21st to end	Night	27% 15% 36% 20% 3	481
March	1st to 10th	Night	23% 13% 31% 29% 5%	570
	11th to 20th	Night	22% 15% 33% 26% 5%	570
	21st to end	Night	19% 16% 35% 23% 6%	627
April	1st to 10th	Night	17% 21% 31% 26% 6%	570
	11th to 20th	Night	16% 18% 32% 24% 10%	563
	21st to end	Night	17% 16% 34% 23% 9% 1	570
May	1st to 10th	Night	11% 13% 32% 35% 10%	570
	11th to 20th	Night	13% 10% 29% 31% 16% 1	561
	21st to end	Night	10% 7% 31% 28% 23% 1	617
June	1st to 10th	Night	6% 4 17% 34% 36% 2	570
	11th to 20th	Night	6% 2 25% 40% 26% 2	570
	21st to end	Night	3 1 20% 36% 35% 5%	570
July	1st to 10th	Night	4 13% 36% 42% 5%	555
	11th to 20th	Night	3 1 10% 36% 43% 6%	552
	21st to end	Night	3 1 8% 39% 42% 6%	624
August	1st to 10th	Night	2 1 11% 38% 42% 5%	567
	11th to 20th	Night	7% 1 10% 38% 40% 4	564
	21st to end	Night	6% 1 9% 38% 39% 7%	627
September	1st to 10th	Night	8% 2 9% 39% 38% 4	570
	11th to 20th	Night	13% 1 12% 34% 36% 4	570
	21st to end	Night	9% 2 16% 34% 33% 5%	570
October	1st to 10th	Night	8% 3 22% 35% 29% 3	742
	11th to 20th	Night	13% 9% 30% 33% 13% 1	760
	21st to end	Night	21% 11% 25% 27% 14% 1	836
November	1st to 10th	Night	13% 10% 31% 34% 11% 1	780
	11th to 20th	Night	13% 14% 29% 33% 10%	810
	21st to end	Night	19% 16% 30% 27% 9%	1000
December	1st to 10th	Night	20% 12% 31% 30% 6%	1000
	11th to 20th	Night	19% 15% 31% 30% 5%	1000
	21st to end	Night	19% 19% 29% 27% 6%	1100

Page generated at 2025-02-03 02:05:54. Version ac07

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