Blue Moon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Moon Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	13% 7% 2 6% 4 4 4 4 5% 7% 43%	100905
	Night	14% 7% 2 6% 4 3 4 3 5% 7% 46%	98161
Transparency	Day	38% 5% 10% 24% 19% 4	104608
	Night	37% 5% 9% 24% 20% 5%	102598
Seeing	Day	16% 10% 23% 25% 18% 8%	15328
	Night	16% 9% 25% 29% 18% 3	25081

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	13% 15% 4 8% 5% 3 3 3 4 6% 37%	2527
	11th to 20th	Day	20% 9% 2 6% 4 3 3 2 3 4 44%	2694
	21st to end	Day	23% 10% 3 5% 3 3 3 3 4 6% 37%	3228
February	1st to 10th	Day	19% 10% 4 6% 4 4 3 3 4 6% 37%	1900
	11th to 20th	Day	20% 9% 3 7% 4 3 3 3 4 5% 39%	1848
	21st to end	Day	22% 10% 3 6% 4 4 4 3 4 4 35%	1570
March	1st to 10th	Day	20% 13% 3 8% 4 4 4 3 4 5% 33%	3120
	11th to 20th	Day	14% 7% 2 6% 3 4 3 3 5% 6% 47%	3300
	21st to end	Day	13% 7% 3 7% 4 4 4 4 5% 6% 42%	4165
April	1st to 10th	Day	13% 6% 3 6% 4 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	16% 7% 2 7% 5% 3 4 3 4 5% 44%	2254
	21st to end	Day	15% 6% 2 6% 4 4 5% 3 5% 8% 42%	2280
May	1st to 10th	Day	17% 7% 2 6% 4 4 4 4 6% 9% 36%	3947
	11th to 20th	Day	16% 7% 3 6% 4 4 5% 4 6% 8% 37%	4081
	21st to end	Day	11% 7% 3 7% 5% 4 5% 5% 6% 9% 39%	4522
June	1st to 10th	Day	9% 6% 2 6% 5% 4 5% 4 6% 10% 42%	2660
	11th to 20th	Day	4 4 2 5% 5% 5% 5% 5% 7% 10% 48%	2660
	21st to end	Day	6% 4 1 5% 4 5% 6% 5% 8% 10% 46%	2660
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 6% 5% 7% 11% 39%	4440
	11th to 20th	Day	8% 6% 3 6% 4 5% 5% 5% 8% 12% 38%	4440
	21st to end	Day	14% 9% 4 9% 5% 5% 5% 4 6% 8% 30%	4495
August	1st to 10th	Day	3 3 1 4 3 4 5% 5% 6% 10% 55%	3785
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 4 7% 10% 46%	3729
	21st to end	Day	6% 4 2 4 4 4 4 4 5% 8% 56%	4180
September	1st to 10th	Day	11% 6% 1 6% 4 4 5% 3 6% 8% 46%	2280
	11th to 20th	Day	13% 5% 2 6% 4 4 3 3 5% 7% 47%	2147
	21st to end	Day	11% 7% 2 4 3 3 5% 4 6% 5% 49%	2090
October	1st to 10th	Day	9% 4 2 4 3 3 3 3 5% 6% 58%	2090
	11th to 20th	Day	13% 5% 2 4 3 3 3 4 5% 6% 54%	1910
	21st to end	Day	18% 7% 2 4 3 2 3 2 3 4 50%	2005
November	1st to 10th	Day	12% 5% 2 5% 2 3 3 3 5% 5% 56%	1708
	11th to 20th	Day	14% 6% 2 5% 4 2 4 3 4 6% 50%	1710
	21st to end	Day	17% 8% 3 5% 3 3 3 3 5% 5% 45%	1710
December	1st to 10th	Day	21% 9% 3 6% 4 3 4 3 5% 5% 38%	1710
	11th to 20th	Day	17% 9% 3 7% 4 4 4 3 4 5% 41%	1997
	21st to end	Day	15% 12% 4 7% 5% 4 5% 3 5% 6% 34%	2783
January	1st to 10th	Night	19% 10% 3 5% 3 3 3 3 4 6% 40%	4428
	11th to 20th	Night	17% 10% 3 8% 5% 4 3 2 3 4 40%	4274
	21st to end	Night	26% 9% 2 5% 3 2 3 3 4 5% 39%	4433
February	1st to 10th	Night	21% 10% 3 7% 5% 4 3 3 5% 5% 35%	2280
	11th to 20th	Night	20% 7% 3 8% 5% 4 4 3 3 4 39%	2218
	21st to end	Night	20% 8% 3 6% 4 4 4 2 4 5% 38%	1884
March	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 4 4 36%	3733
	11th to 20th	Night	15% 8% 2 6% 4 3 3 3 4 5% 48%	3688
	21st to end	Night	14% 8% 3 6% 4 4 3 4 5% 8% 40%	3466
April	1st to 10th	Night	12% 6% 3 5% 4 3 4 3 5% 6% 48%	1900
	11th to 20th	Night	16% 6% 2 6% 3 4 3 2 5% 6% 47%	1875
	21st to end	Night	13% 7% 2 5% 4 4 4 4 6% 7% 44%	1900
May	1st to 10th	Night	19% 8% 2 6% 4 3 3 3 5% 7% 41%	2948
	11th to 20th	Night	13% 7% 3 6% 4 3 4 3 5% 7% 45%	2812
	21st to end	Night	9% 5% 2 6% 5% 4 5% 4 8% 10% 43%	3031
June	1st to 10th	Night	9% 6% 2 7% 5% 4 5% 4 7% 9% 43%	1520
	11th to 20th	Night	4 4 1 4 3 3 4 5% 6% 9% 58%	1520
	21st to end	Night	3 2 1 5% 3 4 6% 4 7% 13% 53%	1520
July	1st to 10th	Night	7% 4 2 5% 5% 5% 6% 5% 8% 11% 41%	2530
	11th to 20th	Night	4 4 1 5% 4 4 4 4 6% 11% 53%	2530
	21st to end	Night	10% 8% 4 9% 5% 5% 5% 4 7% 8% 36%	3044
August	1st to 10th	Night	3 3 1 3 2 3 4 3 6% 8% 62%	3144
	11th to 20th	Night	4 3 2 5% 4 4 4 4 7% 10% 54%	3100
	21st to end	Night	5% 3 1 4 3 3 3 4 5% 9% 61%	3476
September	1st to 10th	Night	10% 4 2 4 4 3 4 3 4 8% 53%	1900
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 4 8% 52%	2014
	21st to end	Night	10% 4 1 4 4 3 3 3 5% 7% 55%	2090
October	1st to 10th	Night	9% 4 1 4 2 3 3 3 5% 6% 61%	2090
	11th to 20th	Night	12% 5% 1 4 3 3 4 3 4 5% 56%	2266
	21st to end	Night	17% 6% 2 5% 2 3 3 3 4 5% 50%	2590
November	1st to 10th	Night	11% 6% 2 4 3 3 2 3 4 6% 56%	2470
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 52%	2470
	21st to end	Night	17% 7% 2 5% 4 3 3 3 4 5% 47%	2470
December	1st to 10th	Night	21% 9% 3 7% 4 3 3 3 4 6% 39%	2470
	11th to 20th	Night	16% 9% 2 5% 3 3 3 3 4 5% 46%	3193
	21st to end	Night	17% 10% 3 9% 5% 4 5% 4 5% 7% 32%	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	48% 4 6% 22% 18% 2	2528
	11th to 20th	Day	45% 3 8% 23% 20% 1	2694
	21st to end	Day	49% 3 8% 23% 15% 2	3228
February	1st to 10th	Day	50% 3 9% 20% 16% 2	1900
	11th to 20th	Day	49% 4 7% 20% 16% 4	1858
	21st to end	Day	52% 3 8% 17% 15% 6%	1570
March	1st to 10th	Day	55% 4 5% 14% 14% 8%	3120
	11th to 20th	Day	39% 5% 7% 26% 17% 6%	3300
	21st to end	Day	42% 4 11% 23% 19% 1	4165
April	1st to 10th	Day	39% 5% 9% 23% 21% 3	2280
	11th to 20th	Day	43% 4 8% 20% 21% 5%	2254
	21st to end	Day	40% 5% 10% 26% 17% 2	2280
May	1st to 10th	Day	44% 7% 12% 23% 14% 1	3982
	11th to 20th	Day	44% 6% 13% 24% 13% 1	4085
	21st to end	Day	40% 7% 11% 23% 17% 1	4535
June	1st to 10th	Day	36% 7% 13% 22% 19% 2	2660
	11th to 20th	Day	29% 7% 15% 28% 18% 3	2660
	21st to end	Day	30% 9% 15% 26% 18% 4	2660
July	1st to 10th	Day	36% 9% 16% 28% 9% 2	4371
	11th to 20th	Day	34% 8% 14% 31% 10% 2	4365
	21st to end	Day	51% 8% 12% 21% 8% 1	4352
August	1st to 10th	Day	22% 6% 17% 30% 24% 2	3773
	11th to 20th	Day	33% 6% 16% 26% 18% 3	3765
	21st to end	Day	25% 6% 10% 31% 25% 2	4179
September	1st to 10th	Day	36% 6% 10% 25% 17% 5%	2280
	11th to 20th	Day	38% 5% 9% 22% 23% 3	2147
	21st to end	Day	35% 5% 8% 23% 23% 6%	2090
October	1st to 10th	Day	18% 3 6% 15% 46% 11%	3480
	11th to 20th	Day	22% 2 7% 25% 28% 16%	3150
	21st to end	Day	30% 2 5% 25% 32% 6%	3282
November	1st to 10th	Day	31% 4 8% 24% 28% 5%	1708
	11th to 20th	Day	37% 4 7% 21% 24% 7%	1710
	21st to end	Day	41% 3 7% 24% 20% 5%	1710
December	1st to 10th	Day	48% 5% 6% 22% 16% 3	1710
	11th to 20th	Day	45% 4 8% 23% 17% 3	1994
	21st to end	Day	51% 4 10% 22% 12% 1	2783
January	1st to 10th	Night	45% 4 6% 26% 17% 2	4428
	11th to 20th	Night	50% 3 6% 21% 16% 4	4274
	21st to end	Night	49% 3 7% 23% 16% 2	4433
February	1st to 10th	Night	53% 3 9% 16% 17% 2	2280
	11th to 20th	Night	49% 4 7% 19% 17% 5%	2219
	21st to end	Night	49% 4 8% 17% 17% 5%	1884
March	1st to 10th	Night	51% 4 7% 12% 17% 9%	3733
	11th to 20th	Night	39% 4 9% 22% 16% 10%	3688
	21st to end	Night	42% 5% 9% 21% 21% 1	3466
April	1st to 10th	Night	36% 5% 10% 25% 19% 5%	1900
	11th to 20th	Night	38% 4 7% 22% 22% 8%	1875
	21st to end	Night	40% 5% 9% 25% 18% 3	1900
May	1st to 10th	Night	44% 6% 11% 23% 14% 2	2978
	11th to 20th	Night	39% 6% 14% 23% 16% 1	2813
	21st to end	Night	34% 8% 14% 27% 15% 2	3039
June	1st to 10th	Night	38% 6% 12% 20% 22% 2	1520
	11th to 20th	Night	22% 5% 16% 32% 21% 4	1520
	21st to end	Night	23% 7% 18% 27% 18% 6%	1520
July	1st to 10th	Night	32% 9% 16% 29% 11% 2	2490
	11th to 20th	Night	25% 6% 13% 40% 13% 3	2482
	21st to end	Night	45% 7% 14% 22% 11%	2947
August	1st to 10th	Night	18% 6% 13% 39% 23% 1	3132
	11th to 20th	Night	23% 7% 17% 31% 19% 2	3130
	21st to end	Night	21% 6% 12% 33% 25% 4	3476
September	1st to 10th	Night	30% 5% 11% 27% 21% 6%	1900
	11th to 20th	Night	32% 6% 10% 22% 27% 4	2014
	21st to end	Night	29% 5% 8% 27% 24% 7%	2090
October	1st to 10th	Night	17% 3 5% 16% 44% 14%	3480
	11th to 20th	Night	19% 3 4 18% 37% 19%	3765
	21st to end	Night	26% 3 6% 26% 26% 13%	4263
November	1st to 10th	Night	31% 3 7% 24% 27% 7%	2470
	11th to 20th	Night	33% 3 7% 23% 25% 9%	2470
	21st to end	Night	40% 3 6% 23% 23% 5%	2470
December	1st to 10th	Night	48% 4 8% 19% 18% 3	2470
	11th to 20th	Night	42% 2 7% 24% 21% 4	3195
	21st to end	Night	51% 5% 8% 19% 13% 3	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	26% 22% 35% 13% 4	270
	11th to 20th	Day	30% 22% 31% 13% 3 1	270
	21st to end	Day	24% 24% 37% 11% 3	297
February	1st to 10th	Day	27% 20% 30% 18% 4 1	270
	11th to 20th	Day	34% 23% 33% 8% 2	270
	21st to end	Day	37% 24% 26% 9% 3	225
March	1st to 10th	Day	27% 19% 37% 12% 4	270
	11th to 20th	Day	27% 23% 34% 13% 3	279
	21st to end	Day	27% 16% 32% 18% 7%	506
April	1st to 10th	Day	23% 16% 30% 23% 7% 1	460
	11th to 20th	Day	21% 17% 30% 23% 9% 1	452
	21st to end	Day	20% 15% 29% 23% 9% 3	460
May	1st to 10th	Day	20% 14% 27% 25% 11% 4	463
	11th to 20th	Day	15% 8% 26% 27% 16% 8%	487
	21st to end	Day	10% 7% 21% 30% 18% 13%	549
June	1st to 10th	Day	11% 5% 20% 28% 23% 13%	680
	11th to 20th	Day	5% 1 17% 35% 29% 12%	680
	21st to end	Day	6% 3 18% 35% 24% 13%	680
July	1st to 10th	Day	8% 2 13% 29% 28% 20%	671
	11th to 20th	Day	9% 2 12% 27% 33% 16%	668
	21st to end	Day	9% 3 13% 28% 28% 19%	658
August	1st to 10th	Day	7% 3 11% 30% 31% 17%	486
	11th to 20th	Day	12% 3 15% 32% 30% 9%	479
	21st to end	Day	11% 3 7% 22% 38% 19%	539
September	1st to 10th	Day	9% 4 12% 29% 34% 12%	490
	11th to 20th	Day	13% 1 13% 25% 35% 13%	490
	21st to end	Day	16% 6% 17% 30% 20% 11%	490
October	1st to 10th	Day	9% 4 20% 35% 24% 8%	490
	11th to 20th	Day	12% 12% 35% 25% 13% 2	310
	21st to end	Day	24% 15% 31% 21% 8% 1	330
November	1st to 10th	Day	14% 10% 36% 27% 12% 1	282
	11th to 20th	Day	11% 19% 37% 26% 6% 1	270
	21st to end	Day	24% 16% 30% 18% 10% 2	270
December	1st to 10th	Day	29% 19% 27% 17% 6% 1	270
	11th to 20th	Day	23% 19% 31% 20% 6%	270
	21st to end	Day	27% 21% 35% 15% 2	297
January	1st to 10th	Night	23% 17% 33% 24% 4	950
	11th to 20th	Night	26% 18% 31% 21% 4	950
	21st to end	Night	22% 13% 40% 24% 1	985
February	1st to 10th	Night	25% 14% 35% 22% 3	760
	11th to 20th	Night	25% 16% 35% 21% 2	743
	21st to end	Night	27% 19% 34% 18% 2	628
March	1st to 10th	Night	21% 15% 33% 28% 3	760
	11th to 20th	Night	24% 13% 33% 24% 6% 1	709
	21st to end	Night	18% 11% 33% 29% 8%	627
April	1st to 10th	Night	15% 11% 36% 29% 8% 1	570
	11th to 20th	Night	19% 11% 28% 30% 12% 1	563
	21st to end	Night	15% 8% 36% 29% 9% 2	570
May	1st to 10th	Night	15% 7% 33% 29% 15% 2	570
	11th to 20th	Night	12% 6% 22% 37% 21% 2	561
	21st to end	Night	7% 3 20% 35% 29% 6%	617
June	1st to 10th	Night	12% 2 15% 35% 29% 6%	570
	11th to 20th	Night	5% 2 11% 40% 38% 4	570
	21st to end	Night	5% 1 14% 37% 37% 6%	570
July	1st to 10th	Night	8% 2 9% 31% 41% 10%	555
	11th to 20th	Night	7% 2 9% 28% 45% 10%	552
	21st to end	Night	7% 10% 31% 42% 9%	624
August	1st to 10th	Night	5% 1 8% 32% 45% 9%	567
	11th to 20th	Night	6% 1 9% 40% 39% 5%	564
	21st to end	Night	9% 1 8% 30% 43% 9%	627
September	1st to 10th	Night	10% 1 9% 31% 43% 6%	570
	11th to 20th	Night	10% 3 11% 32% 37% 6%	684
	21st to end	Night	12% 2 17% 34% 31% 4	760
October	1st to 10th	Night	10% 3 16% 35% 31% 4	760
	11th to 20th	Night	14% 7% 24% 34% 20% 1	760
	21st to end	Night	19% 8% 27% 30% 14% 2	836
November	1st to 10th	Night	15% 8% 26% 34% 16% 1	760
	11th to 20th	Night	14% 11% 33% 31% 11%	760
	21st to end	Night	20% 10% 30% 28% 11% 1	760
December	1st to 10th	Night	26% 11% 30% 26% 7%	760
	11th to 20th	Night	24% 11% 29% 29% 7%	864
	21st to end	Night	26% 14% 30% 26% 4	1045

Page generated at 2024-11-03 01:11:16. Version ac07

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