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 2024-01-31.

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% 6% 3 5% 5% 3 5% 5% 5% 7% 44%	75142
	Night	10% 6% 2 4 4 2 4 4 5% 7% 51%	75014
Transparency	Day	38% 7% 11% 22% 18% 5%	74866
	Night	32% 6% 10% 23% 22% 7%	74810
Seeing	Day	15% 12% 27% 26% 16% 4	14243
	Night	15% 11% 26% 30% 17% 2	24229

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% 9% 3 5% 4 2 4 4 4 6% 48%	1707
	11th to 20th	Day	10% 8% 3 5% 5% 3 5% 3 4 6% 48%	1710
	21st to end	Day	16% 9% 2 4 3 2 4 3 4 6% 47%	1872
February	1st to 10th	Day	18% 9% 4 6% 5% 3 4 3 4 4 41%	1620
	11th to 20th	Day	14% 9% 4 7% 6% 3 5% 4 4 5% 39%	1637
	21st to end	Day	19% 10% 4 5% 5% 2 3 3 4 5% 39%	1617
March	1st to 10th	Day	14% 8% 3 5% 4 3 4 4 4 6% 45%	1980
	11th to 20th	Day	17% 10% 3 5% 4 3 4 3 4 5% 41%	1980
	21st to end	Day	16% 9% 3 6% 5% 3 4 3 4 7% 38%	2178
April	1st to 10th	Day	11% 5% 3 6% 7% 3 5% 4 5% 7% 43%	2047
	11th to 20th	Day	14% 6% 3 5% 5% 4 4 4 5% 6% 44%	2134
	21st to end	Day	15% 7% 4 7% 6% 4 5% 4 5% 5% 40%	2160
May	1st to 10th	Day	13% 7% 3 6% 5% 3 6% 4 4 7% 43%	2316
	11th to 20th	Day	12% 6% 2 5% 7% 4 5% 6% 6% 8% 39%	2302
	21st to end	Day	11% 6% 3 8% 6% 3 6% 6% 7% 8% 37%	2531
June	1st to 10th	Day	8% 5% 3 6% 5% 4 6% 6% 7% 9% 42%	2340
	11th to 20th	Day	6% 3 3 5% 6% 5% 7% 6% 7% 8% 43%	2340
	21st to end	Day	4 3 2 4 5% 3 5% 6% 7% 9% 51%	2340
July	1st to 10th	Day	8% 6% 3 5% 7% 4 7% 7% 9% 10% 34%	2340
	11th to 20th	Day	4 3 2 4 5% 5% 6% 6% 7% 10% 48%	2340
	21st to end	Day	5% 4 2 5% 5% 5% 8% 7% 8% 10% 41%	2546
August	1st to 10th	Day	4 4 2 5% 6% 4 6% 8% 7% 10% 43%	2328
	11th to 20th	Day	9% 5% 2 5% 6% 3 6% 6% 7% 10% 42%	2265
	21st to end	Day	7% 3 2 5% 6% 4 7% 7% 7% 9% 42%	2376
September	1st to 10th	Day	11% 4 2 4 5% 3 5% 5% 6% 6% 50%	2138
	11th to 20th	Day	13% 4 2 5% 5% 3 5% 5% 7% 8% 45%	1980
	21st to end	Day	8% 4 2 5% 5% 2 4 4 6% 7% 54%	1978
October	1st to 10th	Day	7% 5% 1 4 5% 2 4 5% 4 7% 55%	1800
	11th to 20th	Day	13% 4 3 3 5% 2 3 3 3 4 57%	1800
	21st to end	Day	18% 6% 1 4 4 2 3 3 3 5% 50%	1980
November	1st to 10th	Day	9% 5% 2 5% 4 2 3 4 5% 7% 54%	1858
	11th to 20th	Day	8% 6% 2 4 5% 2 4 4 4 6% 56%	1886
	21st to end	Day	14% 7% 2 6% 3 2 4 4 4 5% 49%	1710
December	1st to 10th	Day	14% 5% 2 5% 4 2 3 4 4 7% 49%	1710
	11th to 20th	Day	11% 10% 4 7% 5% 3 4 4 4 5% 42%	2161
	21st to end	Day	13% 12% 6% 8% 6% 3 4 4 5% 6% 34%	3135
January	1st to 10th	Night	11% 9% 3 4 4 2 3 4 4 6% 51%	2458
	11th to 20th	Night	13% 7% 3 5% 4 2 4 3 3 7% 50%	2470
	21st to end	Night	13% 7% 2 4 3 2 3 3 5% 6% 52%	2711
February	1st to 10th	Night	16% 9% 3 6% 4 2 3 4 4 6% 45%	2340
	11th to 20th	Night	14% 9% 3 6% 4 2 4 4 5% 6% 44%	2224
	21st to end	Night	14% 9% 3 5% 4 2 4 4 4 6% 45%	1637
March	1st to 10th	Night	15% 7% 2 5% 4 2 4 4 5% 6% 45%	1980
	11th to 20th	Night	17% 9% 2 5% 4 3 4 3 5% 5% 44%	1980
	21st to end	Night	12% 8% 2 6% 5% 3 3 4 5% 6% 46%	2178
April	1st to 10th	Night	11% 5% 3 4 5% 3 4 5% 5% 8% 49%	1913
	11th to 20th	Night	10% 6% 2 4 4 3 4 3 6% 6% 50%	1775
	21st to end	Night	14% 6% 3 4 3 3 3 4 5% 8% 48%	1800
May	1st to 10th	Night	10% 4 2 4 5% 4 4 5% 6% 8% 47%	1639
	11th to 20th	Night	11% 5% 2 3 5% 3 5% 5% 6% 10% 45%	1593
	21st to end	Night	9% 4 1 5% 5% 3 5% 5% 6% 11% 46%	1745
June	1st to 10th	Night	4 3 2 4 3 3 4 4 7% 9% 56%	1620
	11th to 20th	Night	6% 3 2 4 3 2 3 5% 5% 9% 60%	1620
	21st to end	Night	4 3 1 2 2 2 3 3 6% 10% 65%	1620
July	1st to 10th	Night	4 3 2 4 4 3 6% 7% 8% 13% 46%	1620
	11th to 20th	Night	3 2 1 3 3 2 4 4 6% 11% 62%	1620
	21st to end	Night	3 2 1 3 4 3 4 5% 7% 11% 57%	1772
August	1st to 10th	Night	3 2 2 4 4 3 4 6% 6% 12% 55%	1611
	11th to 20th	Night	6% 4 2 4 4 3 5% 5% 7% 9% 51%	1635
	21st to end	Night	4 3 2 5% 5% 3 4 5% 6% 9% 54%	1980
September	1st to 10th	Night	7% 4 2 4 3 2 5% 5% 5% 7% 58%	1818
	11th to 20th	Night	10% 4 2 3 3 2 4 4 5% 9% 51%	1980
	21st to end	Night	7% 4 1 3 3 2 4 3 4 6% 62%	1980
October	1st to 10th	Night	7% 3 1 4 3 2 3 4 6% 8% 59%	2142
	11th to 20th	Night	11% 4 2 3 3 2 2 3 4 5% 59%	2160
	21st to end	Night	18% 6% 2 3 3 2 3 2 3 4 55%	2376
November	1st to 10th	Night	10% 5% 2 4 4 2 3 4 4 6% 58%	2220
	11th to 20th	Night	8% 6% 2 4 3 2 3 3 4 7% 57%	2289
	21st to end	Night	14% 6% 2 4 3 2 4 4 5% 6% 50%	2470
December	1st to 10th	Night	14% 7% 3 5% 3 2 3 3 4 6% 49%	2470
	11th to 20th	Night	11% 8% 3 7% 5% 3 4 4 4 5% 47%	3036
	21st to end	Night	11% 11% 6% 8% 5% 2 4 4 3 5% 40%	4532

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	38% 6% 8% 23% 19% 6%	1708
	11th to 20th	Day	38% 5% 11% 23% 20% 3	1710
	21st to end	Day	40% 3 5% 23% 23% 5%	1872
February	1st to 10th	Day	48% 4 10% 16% 18% 4	1620
	11th to 20th	Day	48% 4 6% 19% 18% 4	1646
	21st to end	Day	50% 3 6% 14% 19% 8%	1617
March	1st to 10th	Day	41% 5% 8% 17% 18% 11%	1980
	11th to 20th	Day	48% 5% 7% 19% 16% 5%	1980
	21st to end	Day	47% 6% 9% 22% 15% 2	2178
April	1st to 10th	Day	40% 6% 11% 20% 18% 5%	2047
	11th to 20th	Day	42% 6% 10% 21% 17% 5%	2134
	21st to end	Day	47% 6% 8% 18% 18% 2	2160
May	1st to 10th	Day	43% 6% 10% 21% 17% 3	2316
	11th to 20th	Day	41% 10% 13% 22% 13% 1	2306
	21st to end	Day	43% 10% 13% 22% 13% 1	2531
June	1st to 10th	Day	36% 9% 14% 24% 14% 2	2340
	11th to 20th	Day	36% 9% 14% 21% 18% 2	2340
	21st to end	Day	26% 8% 15% 28% 19% 3	2340
July	1st to 10th	Day	38% 11% 17% 22% 11%	2276
	11th to 20th	Day	27% 9% 13% 29% 20% 2	2271
	21st to end	Day	31% 12% 17% 28% 11% 1	2405
August	1st to 10th	Day	31% 9% 16% 29% 13% 1	2314
	11th to 20th	Day	35% 9% 13% 25% 16% 1	2265
	21st to end	Day	34% 9% 14% 26% 14% 3	2376
September	1st to 10th	Day	34% 8% 10% 22% 18% 8%	2138
	11th to 20th	Day	34% 8% 11% 22% 18% 6%	1980
	21st to end	Day	29% 6% 10% 19% 27% 8%	1978
October	1st to 10th	Day	29% 6% 11% 20% 24% 9%	1800
	11th to 20th	Day	33% 4 6% 16% 30% 13%	1800
	21st to end	Day	38% 5% 8% 19% 21% 10%	1980
November	1st to 10th	Day	31% 5% 10% 23% 25% 7%	1858
	11th to 20th	Day	31% 5% 8% 22% 26% 9%	1886
	21st to end	Day	38% 5% 6% 18% 26% 7%	1710
December	1st to 10th	Day	37% 5% 11% 23% 19% 6%	1710
	11th to 20th	Day	43% 5% 6% 16% 24% 6%	2159
	21st to end	Day	47% 9% 7% 16% 16% 5%	3135
January	1st to 10th	Night	35% 5% 9% 20% 26% 6%	2458
	11th to 20th	Night	36% 4 10% 21% 24% 5%	2470
	21st to end	Night	34% 4 7% 22% 26% 7%	2711
February	1st to 10th	Night	42% 5% 9% 21% 17% 6%	2340
	11th to 20th	Night	42% 6% 6% 22% 19% 5%	2225
	21st to end	Night	41% 4 9% 18% 19% 9%	1637
March	1st to 10th	Night	39% 6% 8% 15% 21% 11%	1980
	11th to 20th	Night	43% 6% 9% 18% 18% 7%	1980
	21st to end	Night	40% 5% 10% 22% 18% 4	2178
April	1st to 10th	Night	34% 7% 10% 20% 20% 9%	1913
	11th to 20th	Night	34% 6% 10% 21% 20% 9%	1775
	21st to end	Night	35% 6% 11% 22% 23% 2	1800
May	1st to 10th	Night	34% 8% 11% 23% 17% 6%	1639
	11th to 20th	Night	33% 10% 15% 26% 15% 1	1594
	21st to end	Night	32% 9% 17% 27% 14% 2	1746
June	1st to 10th	Night	24% 7% 17% 30% 20% 3	1620
	11th to 20th	Night	21% 6% 14% 34% 22% 3	1620
	21st to end	Night	17% 7% 13% 29% 29% 5%	1620
July	1st to 10th	Night	25% 12% 18% 28% 16% 2	1575
	11th to 20th	Night	16% 7% 16% 33% 26% 2	1566
	21st to end	Night	19% 9% 18% 34% 18% 1	1673
August	1st to 10th	Night	20% 9% 18% 33% 18% 2	1601
	11th to 20th	Night	26% 8% 14% 28% 21% 2	1635
	21st to end	Night	26% 7% 15% 27% 21% 3	1980
September	1st to 10th	Night	25% 7% 10% 26% 23% 9%	1818
	11th to 20th	Night	29% 9% 12% 20% 23% 7%	1980
	21st to end	Night	24% 4 9% 24% 30% 9%	1980
October	1st to 10th	Night	23% 6% 13% 23% 21% 13%	2142
	11th to 20th	Night	27% 6% 6% 16% 29% 16%	2160
	21st to end	Night	35% 3 7% 19% 24% 11%	2376
November	1st to 10th	Night	28% 5% 8% 22% 26% 11%	2220
	11th to 20th	Night	28% 4 9% 21% 27% 11%	2289
	21st to end	Night	36% 5% 8% 18% 26% 7%	2470
December	1st to 10th	Night	37% 5% 10% 19% 22% 8%	2470
	11th to 20th	Night	41% 5% 6% 18% 21% 9%	3037
	21st to end	Night	42% 9% 7% 18% 19% 5%	4532

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	23% 22% 36% 15% 4	270
	11th to 20th	Day	25% 27% 34% 10% 2 1	270
	21st to end	Day	25% 28% 31% 11% 5%	294
February	1st to 10th	Day	30% 20% 33% 14% 3	240
	11th to 20th	Day	29% 31% 31% 7% 1	240
	21st to end	Day	38% 24% 28% 7% 2	198
March	1st to 10th	Day	25% 29% 28% 17% 2	240
	11th to 20th	Day	35% 21% 31% 10% 3	240
	21st to end	Day	28% 25% 38% 8% 2	264
April	1st to 10th	Day	24% 22% 35% 11% 7% 1	307
	11th to 20th	Day	24% 19% 34% 16% 7%	412
	21st to end	Day	21% 24% 30% 18% 5% 1	420
May	1st to 10th	Day	15% 21% 38% 20% 5% 1	579
	11th to 20th	Day	16% 13% 35% 24% 10% 2	625
	21st to end	Day	11% 9% 39% 23% 14% 4	679
June	1st to 10th	Day	10% 5% 23% 35% 22% 6%	630
	11th to 20th	Day	5% 5% 29% 37% 19% 4	630
	21st to end	Day	3 6% 28% 35% 22% 7%	630
July	1st to 10th	Day	7% 1 19% 35% 28% 9%	621
	11th to 20th	Day	4 1 18% 37% 30% 9%	618
	21st to end	Day	4 2 11% 36% 36% 11%	684
August	1st to 10th	Day	6% 2 14% 41% 32% 5%	626
	11th to 20th	Day	12% 1 13% 38% 28% 8%	579
	21st to end	Day	8% 1 9% 32% 38% 13%	495
September	1st to 10th	Day	9% 2 10% 35% 36% 8%	428
	11th to 20th	Day	5% 2 22% 37% 28% 6%	270
	21st to end	Day	10% 7% 21% 33% 23% 6%	270
October	1st to 10th	Day	5% 10% 35% 30% 19% 1	270
	11th to 20th	Day	15% 17% 36% 24% 7% 1	270
	21st to end	Day	33% 12% 31% 19% 4 1	297
November	1st to 10th	Day	13% 20% 36% 21% 10%	270
	11th to 20th	Day	18% 19% 38% 20% 4 1	270
	21st to end	Day	26% 23% 27% 19% 5%	270
December	1st to 10th	Day	26% 21% 30% 17% 5% 1	270
	11th to 20th	Day	26% 23% 30% 16% 4	270
	21st to end	Day	24% 23% 38% 12% 3	297
January	1st to 10th	Night	19% 16% 31% 29% 5%	950
	11th to 20th	Night	20% 21% 31% 24% 5%	950
	21st to end	Night	17% 20% 31% 28% 4	1043
February	1st to 10th	Night	23% 17% 29% 25% 6%	900
	11th to 20th	Night	22% 20% 35% 21% 1	830
	21st to end	Night	26% 15% 35% 20% 3	453
March	1st to 10th	Night	23% 12% 31% 29% 5%	540
	11th to 20th	Night	22% 14% 33% 25% 6%	540
	21st to end	Night	19% 16% 36% 23% 6%	594
April	1st to 10th	Night	15% 20% 32% 26% 6%	540
	11th to 20th	Night	15% 17% 32% 25% 10%	533
	21st to end	Night	17% 15% 35% 23% 9% 1	540
May	1st to 10th	Night	11% 13% 32% 34% 10%	540
	11th to 20th	Night	13% 9% 30% 30% 17% 1	531
	21st to end	Night	9% 6% 31% 28% 24% 2	584
June	1st to 10th	Night	6% 3 16% 34% 38% 3	540
	11th to 20th	Night	6% 2 25% 40% 26% 2	540
	21st to end	Night	4 1 21% 36% 34% 5%	540
July	1st to 10th	Night	3 13% 35% 43% 6%	525
	11th to 20th	Night	3 1 10% 34% 45% 7%	522
	21st to end	Night	3 1 7% 38% 45% 7%	591
August	1st to 10th	Night	2 1 11% 38% 41% 6%	537
	11th to 20th	Night	7% 1 9% 38% 40% 4	534
	21st to end	Night	6% 1 8% 39% 39% 7%	594
September	1st to 10th	Night	8% 2 9% 39% 39% 4	540
	11th to 20th	Night	13% 1 10% 34% 38% 4	540
	21st to end	Night	9% 2 16% 34% 34% 5%	540
October	1st to 10th	Night	9% 3 22% 34% 29% 3	702
	11th to 20th	Night	14% 9% 31% 32% 13% 1	720
	21st to end	Night	22% 11% 25% 27% 14% 1	792
November	1st to 10th	Night	12% 10% 32% 34% 12% 1	740
	11th to 20th	Night	14% 13% 29% 33% 10% 1	769
	21st to end	Night	19% 15% 29% 27% 9%	950
December	1st to 10th	Night	20% 13% 30% 30% 6%	950
	11th to 20th	Night	19% 15% 31% 30% 5%	950
	21st to end	Night	19% 19% 29% 28% 6%	1045

Page generated at 2024-01-28 04:26:37. Version ac07

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