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 2024-03-18.

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	14% 10% 4 7% 6% 4 5% 5% 6% 7% 33%	78497
	Night	15% 10% 4 7% 6% 3 4 5% 5% 7% 33%	81301
Transparency	Day	50% 7% 13% 19% 10% 1	78207
	Night	50% 7% 12% 20% 10% 1	81112
Seeing	Day	16% 11% 30% 24% 13% 6%	14387
	Night	18% 10% 30% 29% 11% 1	24141

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% 18% 7% 11% 7% 4 4 4 4 4 23%	2527
	11th to 20th	Day	15% 18% 7% 12% 11% 6% 4 4 5% 5% 14%	2530
	21st to end	Day	24% 20% 7% 9% 7% 3 4 3 3 5% 16%	3096
February	1st to 10th	Day	14% 13% 6% 13% 9% 4 6% 5% 4 5% 22%	1710
	11th to 20th	Day	13% 11% 6% 9% 9% 4 5% 6% 5% 7% 25%	1752
	21st to end	Day	14% 14% 5% 11% 8% 4 5% 5% 4 5% 26%	1570
March	1st to 10th	Day	16% 11% 6% 7% 7% 3 5% 4 4 7% 29%	1962
	11th to 20th	Day	12% 13% 5% 7% 7% 3 5% 4 5% 7% 32%	2058
	21st to end	Day	19% 12% 4 8% 7% 3 6% 4 4 6% 27%	2178
April	1st to 10th	Day	16% 12% 5% 7% 6% 3 5% 5% 5% 7% 29%	2067
	11th to 20th	Day	17% 10% 3 7% 6% 3 4 5% 5% 7% 34%	2309
	21st to end	Day	17% 8% 3 8% 6% 4 4 4 5% 6% 33%	2340
May	1st to 10th	Day	17% 7% 4 8% 7% 4 5% 5% 5% 7% 33%	2340
	11th to 20th	Day	19% 7% 3 6% 5% 3 4 5% 5% 7% 36%	2301
	21st to end	Day	13% 5% 3 6% 5% 3 6% 5% 6% 8% 40%	2569
June	1st to 10th	Day	10% 6% 3 6% 6% 4 5% 5% 7% 9% 41%	2682
	11th to 20th	Day	11% 5% 3 5% 6% 4 5% 6% 6% 8% 43%	2700
	21st to end	Day	10% 6% 2 6% 5% 3 5% 6% 7% 10% 39%	2700
July	1st to 10th	Day	7% 4 3 5% 4 3 6% 6% 6% 9% 47%	2536
	11th to 20th	Day	9% 5% 2 5% 5% 4 6% 6% 6% 10% 42%	2520
	21st to end	Day	8% 5% 3 5% 6% 3 6% 6% 7% 10% 41%	2582
August	1st to 10th	Day	9% 6% 2 5% 6% 4 5% 7% 8% 9% 39%	2327
	11th to 20th	Day	9% 5% 2 6% 7% 4 7% 6% 7% 9% 39%	2303
	21st to end	Day	12% 6% 3 5% 5% 4 5% 5% 6% 8% 42%	2574
September	1st to 10th	Day	10% 6% 3 6% 7% 4 6% 7% 6% 9% 38%	2042
	11th to 20th	Day	11% 5% 2 5% 4 4 4 5% 6% 8% 45%	1980
	21st to end	Day	15% 7% 3 5% 6% 3 5% 6% 7% 9% 35%	1980
October	1st to 10th	Day	13% 7% 2 7% 7% 4 5% 5% 5% 6% 39%	1904
	11th to 20th	Day	17% 9% 4 7% 6% 4 5% 4 5% 7% 32%	1800
	21st to end	Day	20% 11% 4 7% 6% 3 5% 4 6% 7% 28%	1852
November	1st to 10th	Day	14% 9% 3 7% 7% 4 4 5% 6% 8% 34%	1672
	11th to 20th	Day	13% 10% 4 9% 8% 4 5% 5% 6% 6% 30%	1696
	21st to end	Day	17% 13% 6% 8% 7% 3 4 5% 4 5% 28%	1520
December	1st to 10th	Day	14% 13% 7% 11% 9% 4 5% 5% 5% 6% 21%	1520
	11th to 20th	Day	16% 15% 5% 8% 6% 3 4 5% 6% 6% 26%	1761
	21st to end	Day	26% 21% 7% 8% 6% 3 4 4 4 5% 12%	2537
January	1st to 10th	Night	16% 14% 6% 10% 6% 3 4 4 5% 6% 25%	4428
	11th to 20th	Night	13% 16% 7% 13% 9% 5% 6% 4 5% 5% 16%	4440
	21st to end	Night	22% 17% 9% 8% 7% 3 4 3 3 5% 20%	4559
February	1st to 10th	Night	15% 14% 6% 10% 8% 5% 5% 4 5% 6% 23%	2470
	11th to 20th	Night	13% 13% 5% 10% 7% 3 5% 5% 5% 6% 28%	2309
	21st to end	Night	18% 11% 4 9% 8% 4 5% 5% 4 6% 28%	1884
March	1st to 10th	Night	15% 12% 5% 8% 6% 3 4 4 4 6% 33%	2218
	11th to 20th	Night	12% 8% 3 7% 6% 3 5% 6% 6% 7% 37%	2068
	21st to end	Night	19% 9% 4 7% 6% 3 4 5% 4 5% 34%	2178
April	1st to 10th	Night	18% 10% 4 6% 5% 3 4 4 5% 7% 35%	1908
	11th to 20th	Night	18% 7% 3 5% 6% 3 4 4 5% 8% 37%	1599
	21st to end	Night	16% 9% 3 5% 5% 3 4 5% 5% 9% 36%	1620
May	1st to 10th	Night	15% 8% 3 6% 6% 4 5% 6% 6% 7% 33%	1620
	11th to 20th	Night	17% 5% 3 5% 5% 3 4 5% 5% 7% 41%	1592
	21st to end	Night	11% 5% 2 4 5% 3 5% 6% 6% 8% 47%	1704
June	1st to 10th	Night	12% 5% 2 5% 4 2 5% 5% 7% 8% 46%	1274
	11th to 20th	Night	10% 6% 2 4 5% 2 5% 6% 7% 10% 45%	1260
	21st to end	Night	9% 4 2 5% 6% 3 5% 4 5% 9% 49%	1260
July	1st to 10th	Night	6% 5% 2 3 4 3 5% 4 5% 9% 54%	1419
	11th to 20th	Night	8% 5% 2 4 4 2 6% 5% 6% 9% 51%	1440
	21st to end	Night	6% 3 2 5% 5% 3 5% 6% 7% 9% 50%	1736
August	1st to 10th	Night	7% 4 3 5% 4 3 4 5% 7% 11% 48%	1611
	11th to 20th	Night	7% 3 2 4 5% 3 4 6% 7% 8% 50%	1598
	21st to end	Night	8% 5% 2 5% 5% 3 4 5% 4 8% 52%	1782
September	1st to 10th	Night	10% 6% 3 6% 5% 4 4 4 6% 7% 46%	1896
	11th to 20th	Night	10% 4 2 4 4 2 4 6% 5% 7% 52%	1980
	21st to end	Night	14% 6% 3 5% 6% 3 4 5% 5% 7% 44%	1980
October	1st to 10th	Night	15% 6% 2 5% 4 3 4 4 5% 8% 43%	2055
	11th to 20th	Night	19% 8% 3 6% 5% 4 4 5% 6% 6% 35%	2160
	21st to end	Night	22% 9% 3 7% 6% 4 4 5% 5% 6% 29%	2502
November	1st to 10th	Night	14% 8% 3 5% 4 3 4 4 5% 7% 43%	2406
	11th to 20th	Night	15% 10% 4 7% 6% 3 5% 6% 6% 7% 30%	2482
	21st to end	Night	19% 13% 4 7% 6% 3 4 4 5% 7% 28%	2660
December	1st to 10th	Night	17% 14% 6% 9% 7% 4 5% 5% 5% 7% 23%	2660
	11th to 20th	Night	14% 12% 6% 10% 7% 3 5% 5% 5% 6% 25%	3431
	21st to end	Night	25% 21% 7% 8% 6% 3 4 4 4 4 14%	5112

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	64% 8% 10% 13% 5% 1	2528
	11th to 20th	Day	71% 6% 12% 7% 3	2530
	21st to end	Day	73% 5% 12% 7% 3	3096
February	1st to 10th	Day	64% 6% 9% 13% 7%	1710
	11th to 20th	Day	58% 6% 11% 15% 9% 1	1761
	21st to end	Day	59% 6% 11% 15% 7% 2	1570
March	1st to 10th	Day	56% 7% 12% 17% 8% 1	1962
	11th to 20th	Day	52% 6% 10% 18% 11% 2	2058
	21st to end	Day	58% 5% 10% 18% 7% 1	2178
April	1st to 10th	Day	54% 6% 12% 18% 10% 1	2067
	11th to 20th	Day	48% 6% 12% 18% 14% 2	2309
	21st to end	Day	50% 7% 13% 16% 12% 2	2340
May	1st to 10th	Day	49% 6% 12% 20% 11% 2	2340
	11th to 20th	Day	47% 7% 11% 20% 13% 2	2305
	21st to end	Day	40% 8% 13% 21% 16% 2	2569
June	1st to 10th	Day	38% 7% 13% 24% 15% 2	2682
	11th to 20th	Day	37% 8% 14% 24% 15% 2	2700
	21st to end	Day	38% 9% 14% 24% 15% 1	2700
July	1st to 10th	Day	32% 8% 12% 27% 18% 3	2467
	11th to 20th	Day	35% 8% 15% 25% 16% 2	2445
	21st to end	Day	35% 9% 15% 21% 17% 3	2439
August	1st to 10th	Day	37% 10% 17% 23% 12% 1	2314
	11th to 20th	Day	39% 9% 15% 23% 13% 2	2303
	21st to end	Day	39% 7% 12% 27% 14% 1	2574
September	1st to 10th	Day	41% 10% 15% 21% 12% 2	2042
	11th to 20th	Day	36% 6% 14% 32% 12% 1	1980
	21st to end	Day	44% 7% 15% 24% 10% 1	1980
October	1st to 10th	Day	44% 7% 11% 24% 13% 1	1904
	11th to 20th	Day	52% 6% 13% 20% 9% 1	1800
	21st to end	Day	55% 6% 13% 17% 8%	1852
November	1st to 10th	Day	48% 6% 12% 22% 10% 1	1672
	11th to 20th	Day	52% 7% 14% 17% 9%	1696
	21st to end	Day	58% 6% 13% 17% 5% 1	1520
December	1st to 10th	Day	64% 7% 13% 12% 3	1520
	11th to 20th	Day	58% 6% 14% 16% 5%	1757
	21st to end	Day	74% 6% 10% 7% 2	2537
January	1st to 10th	Night	58% 7% 14% 15% 6% 1	4428
	11th to 20th	Night	68% 8% 10% 11% 3	4440
	21st to end	Night	68% 6% 9% 14% 3	4559
February	1st to 10th	Night	62% 7% 9% 14% 7% 1	2470
	11th to 20th	Night	56% 6% 10% 18% 9% 1	2311
	21st to end	Night	58% 5% 11% 17% 8% 1	1884
March	1st to 10th	Night	52% 5% 11% 22% 9% 1	2218
	11th to 20th	Night	44% 7% 12% 22% 13% 2	2068
	21st to end	Night	52% 6% 8% 21% 11% 1	2178
April	1st to 10th	Night	48% 6% 10% 21% 13% 2	1908
	11th to 20th	Night	44% 6% 11% 18% 19% 2	1599
	21st to end	Night	44% 7% 11% 19% 15% 3	1620
May	1st to 10th	Night	48% 7% 11% 21% 11% 3	1620
	11th to 20th	Night	42% 5% 11% 19% 18% 4	1593
	21st to end	Night	33% 8% 13% 24% 16% 4	1705
June	1st to 10th	Night	35% 8% 11% 27% 18% 2	1274
	11th to 20th	Night	32% 9% 14% 23% 19% 3	1260
	21st to end	Night	33% 6% 14% 26% 19% 2	1260
July	1st to 10th	Night	28% 5% 13% 27% 23% 4	1379
	11th to 20th	Night	28% 8% 15% 30% 16% 2	1392
	21st to end	Night	27% 11% 19% 22% 18% 3	1639
August	1st to 10th	Night	29% 9% 17% 31% 13% 2	1600
	11th to 20th	Night	29% 9% 17% 30% 12% 3	1598
	21st to end	Night	31% 8% 14% 29% 17% 1	1782
September	1st to 10th	Night	37% 7% 14% 26% 14% 2	1896
	11th to 20th	Night	31% 7% 12% 31% 18% 1	1980
	21st to end	Night	39% 7% 11% 30% 12% 1	1980
October	1st to 10th	Night	39% 6% 13% 24% 17% 1	2055
	11th to 20th	Night	49% 7% 13% 21% 10% 1	2160
	21st to end	Night	55% 6% 11% 19% 8% 1	2502
November	1st to 10th	Night	40% 7% 14% 26% 13% 1	2406
	11th to 20th	Night	52% 7% 14% 18% 8% 1	2482
	21st to end	Night	56% 5% 16% 17% 6%	2660
December	1st to 10th	Night	61% 7% 14% 15% 4	2660
	11th to 20th	Night	58% 7% 14% 15% 6%	3434
	21st to end	Night	73% 6% 10% 7% 3	5112

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	21% 17% 39% 17% 5% 1	270
	11th to 20th	Day	20% 17% 42% 17% 3 1	270
	21st to end	Day	25% 18% 34% 18% 4 1	297
February	1st to 10th	Day	22% 20% 41% 13% 3 1	270
	11th to 20th	Day	24% 17% 38% 19% 2	270
	21st to end	Day	23% 23% 39% 14% 1	225
March	1st to 10th	Day	24% 20% 36% 16% 3 1	332
	11th to 20th	Day	20% 14% 35% 21% 8% 1	449
	21st to end	Day	27% 11% 33% 22% 7% 1	462
April	1st to 10th	Day	18% 18% 33% 22% 8% 1	420
	11th to 20th	Day	26% 13% 28% 17% 9% 6%	412
	21st to end	Day	21% 13% 29% 25% 9% 2	420
May	1st to 10th	Day	20% 12% 33% 22% 11% 2	423
	11th to 20th	Day	21% 8% 30% 22% 13% 6%	447
	21st to end	Day	14% 9% 22% 28% 18% 8%	485
June	1st to 10th	Day	11% 7% 32% 31% 13% 5%	612
	11th to 20th	Day	12% 7% 31% 30% 15% 5%	630
	21st to end	Day	12% 7% 29% 32% 15% 5%	630
July	1st to 10th	Day	6% 6% 21% 31% 23% 13%	621
	11th to 20th	Day	11% 5% 27% 32% 17% 8%	618
	21st to end	Day	7% 4 28% 29% 23% 10%	523
August	1st to 10th	Day	9% 4 19% 28% 26% 14%	446
	11th to 20th	Day	10% 5% 20% 28% 23% 14%	439
	21st to end	Day	13% 5% 22% 24% 24% 11%	495
September	1st to 10th	Day	11% 7% 25% 26% 20% 11%	450
	11th to 20th	Day	11% 4 20% 24% 26% 14%	450
	21st to end	Day	15% 12% 23% 24% 18% 9%	450
October	1st to 10th	Day	15% 10% 29% 23% 16% 8%	450
	11th to 20th	Day	17% 18% 35% 22% 7% 1	450
	21st to end	Day	26% 14% 36% 19% 5% 1	367
November	1st to 10th	Day	15% 20% 35% 21% 8% 1	270
	11th to 20th	Day	21% 20% 36% 14% 7% 2	264
	21st to end	Day	26% 19% 38% 13% 4	180
December	1st to 10th	Day	21% 21% 36% 14% 7% 1	180
	11th to 20th	Day	24% 22% 37% 14% 3 1	180
	21st to end	Day	26% 20% 35% 16% 3	230
January	1st to 10th	Night	22% 15% 37% 20% 5% 1	950
	11th to 20th	Night	23% 17% 34% 21% 4 1	950
	21st to end	Night	21% 11% 36% 26% 6%	850
February	1st to 10th	Night	22% 14% 40% 21% 3	760
	11th to 20th	Night	21% 16% 33% 26% 4	743
	21st to end	Night	23% 16% 38% 20% 2	628
March	1st to 10th	Night	20% 13% 36% 26% 5%	760
	11th to 20th	Night	16% 13% 38% 26% 6% 1	752
	21st to end	Night	23% 11% 30% 29% 7% 1	792
April	1st to 10th	Night	22% 13% 35% 26% 4	648
	11th to 20th	Night	21% 10% 34% 25% 8% 2	533
	21st to end	Night	22% 6% 32% 32% 8%	540
May	1st to 10th	Night	18% 6% 32% 33% 11% 1	540
	11th to 20th	Night	19% 6% 27% 35% 13% 1	531
	21st to end	Night	12% 4 24% 37% 22% 2	544
June	1st to 10th	Night	13% 3 29% 42% 13%	360
	11th to 20th	Night	13% 5% 25% 42% 14%	360
	21st to end	Night	9% 5% 23% 46% 17%	360
July	1st to 10th	Night	8% 2 16% 42% 28% 4	504
	11th to 20th	Night	9% 3 19% 43% 22% 4	522
	21st to end	Night	7% 3 21% 45% 22% 2	591
August	1st to 10th	Night	8% 3 15% 42% 29% 3	537
	11th to 20th	Night	7% 1 17% 41% 31% 3	534
	21st to end	Night	11% 3 19% 36% 28% 4	594
September	1st to 10th	Night	11% 5% 20% 36% 23% 5%	662
	11th to 20th	Night	11% 4 20% 36% 25% 4	720
	21st to end	Night	16% 6% 23% 33% 19% 4	720
October	1st to 10th	Night	17% 9% 26% 28% 18% 2	720
	11th to 20th	Night	22% 14% 30% 26% 7% 1	720
	21st to end	Night	25% 13% 32% 26% 5%	792
November	1st to 10th	Night	18% 10% 31% 27% 12% 1	740
	11th to 20th	Night	19% 15% 37% 21% 7% 1	760
	21st to end	Night	25% 13% 36% 20% 6%	760
December	1st to 10th	Night	23% 13% 40% 18% 5%	760
	11th to 20th	Night	23% 14% 39% 21% 2	859
	21st to end	Night	29% 14% 34% 21% 2	1045

Page generated at 2024-03-15 14:01:43. Version ac07

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