Moss Rock Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Moss Rock Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	5% 6% 2 5% 4 3 5% 5% 6% 9% 51%	74768
	Night	4 5% 2 4 4 2 4 4 5% 8% 59%	74995
Transparency	Day	27% 7% 13% 24% 21% 7%	74476
	Night	23% 6% 13% 26% 24% 8%	74809
Seeing	Day	9% 10% 34% 29% 15% 3	14430
	Night	8% 9% 35% 32% 14% 2	24598

By Month

Percentage Cloud Cover SW (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	4 4 5% 4 2 3 3 5% 10% 60%	1518
	11th to 20th	Day	1 6% 4 6% 4 3 4 3 4 6% 59%	1510
	21st to end	Day	1 5% 5% 6% 5% 2 4 4 6% 8% 54%	1782
February	1st to 10th	Day	1 6% 4 8% 5% 2 3 4 5% 8% 56%	1620
	11th to 20th	Day	4 3 5% 4 2 4 4 6% 9% 58%	1703
	21st to end	Day	1 7% 3 7% 4 3 4 4 5% 8% 56%	1480
March	1st to 10th	Day	3 5% 2 6% 5% 2 4 5% 6% 9% 52%	1800
	11th to 20th	Day	4 8% 4 5% 4 2 5% 4 5% 8% 50%	1972
	21st to end	Day	4 10% 3 5% 4 3 4 4 7% 11% 45%	2298
April	1st to 10th	Day	5% 7% 3 4 4 2 3 5% 7% 9% 53%	2160
	11th to 20th	Day	9% 9% 4 7% 5% 3 4 5% 5% 8% 42%	2131
	21st to end	Day	8% 9% 3 5% 5% 3 6% 5% 7% 8% 42%	2160
May	1st to 10th	Day	10% 9% 3 5% 5% 4 6% 5% 6% 8% 39%	2282
	11th to 20th	Day	15% 9% 3 4 4 3 5% 5% 7% 10% 35%	2478
	21st to end	Day	10% 6% 2 4 5% 4 7% 7% 7% 9% 40%	2724
June	1st to 10th	Day	5% 4 1 5% 4 3 7% 7% 8% 10% 47%	2520
	11th to 20th	Day	7% 4 1 4 5% 3 6% 6% 7% 8% 51%	2520
	21st to end	Day	5% 4 1 4 5% 3 6% 6% 8% 9% 47%	2520
July	1st to 10th	Day	8% 4 2 4 5% 3 6% 7% 8% 10% 43%	2520
	11th to 20th	Day	5% 4 2 4 4 3 6% 6% 7% 11% 48%	2520
	21st to end	Day	6% 4 2 5% 6% 4 6% 7% 8% 10% 41%	2682
August	1st to 10th	Day	6% 5% 2 6% 5% 4 6% 8% 8% 10% 41%	2328
	11th to 20th	Day	6% 3 2 4 4 3 5% 5% 7% 9% 51%	2148
	21st to end	Day	6% 4 1 4 5% 3 6% 7% 7% 9% 47%	2376
September	1st to 10th	Day	5% 4 1 4 4 2 4 5% 6% 7% 57%	2160
	11th to 20th	Day	5% 4 1 4 4 3 4 4 6% 8% 58%	2155
	21st to end	Day	7% 4 2 3 3 2 3 4 3 5% 63%	1972
October	1st to 10th	Day	6% 6% 1 4 3 2 4 5% 5% 7% 56%	1800
	11th to 20th	Day	4 4 1 4 3 2 4 2 4 6% 67%	1800
	21st to end	Day	4 7% 2 4 3 2 3 4 4 5% 62%	1926
November	1st to 10th	Day	1 4 1 3 3 2 3 2 4 9% 68%	1673
	11th to 20th	Day	2 5% 2 2 3 2 3 4 6% 8% 62%	1710
	21st to end	Day	2 5% 3 6% 3 2 3 3 5% 8% 60%	1580
December	1st to 10th	Day	5% 2 6% 4 2 3 4 6% 9% 59%	1520
	11th to 20th	Day	2 5% 2 3 3 2 3 4 6% 10% 60%	1926
	21st to end	Day	1 6% 4 7% 5% 3 4 4 5% 7% 53%	2794
January	1st to 10th	Night	1 4 2 5% 5% 2 3 4 5% 8% 62%	2647
	11th to 20th	Night	1 4 2 4 3 2 3 4 4 9% 64%	2521
	21st to end	Night	1 6% 3 5% 5% 3 4 5% 4 7% 58%	2574
February	1st to 10th	Night	1 5% 3 5% 4 2 5% 4 5% 8% 59%	2340
	11th to 20th	Night	1 4 2 6% 5% 2 4 5% 5% 7% 59%	2143
	21st to end	Night	1 6% 3 6% 3 3 4 3 4 7% 60%	1776
March	1st to 10th	Night	1 5% 2 5% 4 2 3 5% 6% 9% 59%	2160
	11th to 20th	Night	4 7% 3 4 3 2 3 3 5% 7% 59%	1984
	21st to end	Night	4 8% 3 4 4 3 4 3 5% 7% 56%	2057
April	1st to 10th	Night	3 7% 3 4 3 2 4 4 5% 8% 59%	1800
	11th to 20th	Night	7% 9% 3 4 3 2 4 4 4 8% 54%	1777
	21st to end	Night	10% 9% 2 5% 3 2 3 5% 5% 7% 49%	1800
May	1st to 10th	Night	11% 8% 2 4 4 3 5% 5% 6% 8% 45%	1673
	11th to 20th	Night	14% 8% 3 4 4 2 3 4 6% 8% 44%	1417
	21st to end	Night	7% 6% 1 3 3 3 4 5% 5% 8% 56%	1552
June	1st to 10th	Night	5% 3 1 3 3 2 4 5% 6% 9% 59%	1440
	11th to 20th	Night	6% 3 1 2 2 2 4 5% 6% 7% 63%	1440
	21st to end	Night	4 2 1 3 3 2 3 5% 5% 10% 62%	1440
July	1st to 10th	Night	6% 3 2 3 4 2 4 5% 7% 9% 54%	1440
	11th to 20th	Night	2 2 1 2 4 3 4 5% 6% 9% 62%	1440
	21st to end	Night	6% 3 1 3 4 3 6% 5% 7% 10% 51%	1633
August	1st to 10th	Night	5% 3 2 4 4 3 4 6% 7% 9% 54%	1611
	11th to 20th	Night	5% 3 1 3 3 3 4 5% 6% 9% 59%	1752
	21st to end	Night	4 2 1 4 4 3 5% 4 6% 7% 58%	1980
September	1st to 10th	Night	6% 3 1 3 3 2 4 4 5% 8% 60%	1800
	11th to 20th	Night	6% 2 1 2 3 2 3 3 4 7% 67%	1804
	21st to end	Night	7% 3 1 3 3 2 3 4 4 5% 64%	1985
October	1st to 10th	Night	6% 6% 2 3 3 1 4 4 4 6% 61%	2160
	11th to 20th	Night	3 4 2 3 2 1 2 3 3 6% 71%	2160
	21st to end	Night	5% 7% 3 4 4 2 3 4 3 6% 59%	2412
November	1st to 10th	Night	1 4 2 3 2 1 2 3 4 8% 68%	2405
	11th to 20th	Night	1 4 2 4 4 2 3 3 4 7% 66%	2470
	21st to end	Night	2 5% 2 5% 3 2 3 4 5% 7% 62%	2598
December	1st to 10th	Night	1 4 2 4 4 2 3 3 5% 9% 63%	2660
	11th to 20th	Night	1 6% 3 5% 4 2 4 5% 6% 9% 56%	3271
	21st to end	Night	2 5% 3 6% 4 3 5% 5% 6% 7% 54%	4873

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	21% 5% 17% 30% 22% 5%	1519
	11th to 20th	Day	25% 5% 11% 30% 22% 6%	1510
	21st to end	Day	27% 4 13% 31% 18% 6%	1782
February	1st to 10th	Day	27% 6% 16% 27% 18% 6%	1620
	11th to 20th	Day	22% 6% 13% 28% 25% 5%	1713
	21st to end	Day	28% 4 12% 27% 23% 6%	1480
March	1st to 10th	Day	27% 6% 13% 28% 23% 4	1800
	11th to 20th	Day	30% 5% 14% 27% 21% 4	1972
	21st to end	Day	31% 9% 13% 26% 17% 4	2298
April	1st to 10th	Day	26% 7% 13% 27% 19% 8%	2160
	11th to 20th	Day	37% 7% 13% 21% 18% 5%	2134
	21st to end	Day	36% 8% 14% 24% 16% 1	2160
May	1st to 10th	Day	40% 10% 13% 22% 13% 3	2282
	11th to 20th	Day	43% 9% 15% 21% 10% 2	2482
	21st to end	Day	36% 9% 16% 21% 13% 6%	2724
June	1st to 10th	Day	27% 10% 18% 21% 16% 7%	2520
	11th to 20th	Day	27% 9% 12% 16% 21% 14%	2520
	21st to end	Day	26% 9% 13% 20% 23% 10%	2520
July	1st to 10th	Day	30% 10% 14% 18% 19% 9%	2451
	11th to 20th	Day	26% 9% 13% 23% 19% 10%	2445
	21st to end	Day	31% 11% 18% 21% 14% 5%	2533
August	1st to 10th	Day	33% 12% 16% 20% 14% 6%	2313
	11th to 20th	Day	25% 9% 14% 20% 23% 10%	2148
	21st to end	Day	27% 8% 13% 20% 24% 7%	2376
September	1st to 10th	Day	23% 6% 10% 21% 23% 16%	2160
	11th to 20th	Day	22% 6% 13% 21% 26% 12%	2155
	21st to end	Day	23% 5% 6% 22% 35% 9%	1972
October	1st to 10th	Day	26% 7% 11% 20% 28% 8%	1800
	11th to 20th	Day	19% 4 10% 25% 31% 11%	1800
	21st to end	Day	24% 4 10% 27% 25% 10%	1926
November	1st to 10th	Day	16% 5% 13% 24% 30% 11%	1673
	11th to 20th	Day	18% 5% 10% 31% 29% 7%	1710
	21st to end	Day	24% 3 10% 26% 26% 11%	1580
December	1st to 10th	Day	21% 6% 17% 29% 21% 6%	1520
	11th to 20th	Day	19% 6% 13% 30% 29% 3	1924
	21st to end	Day	26% 6% 12% 24% 25% 6%	2794
January	1st to 10th	Night	21% 4 13% 31% 26% 5%	2647
	11th to 20th	Night	18% 4 15% 29% 27% 6%	2521
	21st to end	Night	26% 4 11% 31% 21% 7%	2574
February	1st to 10th	Night	24% 6% 15% 28% 21% 6%	2340
	11th to 20th	Night	25% 6% 11% 28% 25% 5%	2143
	21st to end	Night	25% 5% 9% 28% 24% 9%	1776
March	1st to 10th	Night	22% 6% 9% 29% 28% 5%	2160
	11th to 20th	Night	24% 6% 10% 27% 27% 5%	1984
	21st to end	Night	28% 6% 12% 29% 21% 4	2057
April	1st to 10th	Night	24% 7% 13% 24% 23% 8%	1800
	11th to 20th	Night	30% 5% 12% 26% 20% 6%	1777
	21st to end	Night	34% 6% 11% 26% 20% 3	1800
May	1st to 10th	Night	35% 9% 14% 22% 16% 4	1673
	11th to 20th	Night	37% 8% 18% 21% 14% 1	1418
	21st to end	Night	25% 8% 20% 24% 16% 7%	1552
June	1st to 10th	Night	22% 7% 19% 29% 15% 9%	1440
	11th to 20th	Night	19% 6% 14% 19% 23% 20%	1440
	21st to end	Night	16% 8% 12% 23% 29% 13%	1440
July	1st to 10th	Night	25% 9% 14% 22% 22% 9%	1400
	11th to 20th	Night	17% 7% 14% 28% 21% 13%	1392
	21st to end	Night	24% 10% 19% 27% 14% 6%	1542
August	1st to 10th	Night	24% 10% 20% 24% 15% 7%	1602
	11th to 20th	Night	20% 6% 13% 25% 26% 11%	1752
	21st to end	Night	23% 6% 13% 24% 25% 10%	1980
September	1st to 10th	Night	22% 6% 12% 20% 23% 18%	1800
	11th to 20th	Night	18% 4 12% 24% 26% 16%	1804
	21st to end	Night	21% 4 10% 22% 31% 11%	1985
October	1st to 10th	Night	23% 7% 11% 20% 28% 10%	2160
	11th to 20th	Night	17% 5% 11% 23% 30% 14%	2160
	21st to end	Night	27% 4 9% 24% 26% 9%	2412
November	1st to 10th	Night	17% 6% 10% 26% 28% 13%	2405
	11th to 20th	Night	19% 4 9% 30% 30% 8%	2470
	21st to end	Night	22% 5% 11% 23% 29% 10%	2598
December	1st to 10th	Night	21% 5% 15% 26% 25% 8%	2660
	11th to 20th	Night	20% 7% 12% 30% 26% 4	3272
	21st to end	Night	25% 8% 12% 25% 24% 6%	4873

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	11% 9% 38% 30% 10% 3	270
	11th to 20th	Day	6% 17% 46% 25% 5% 1	246
	21st to end	Day	3 14% 53% 27% 3	264
February	1st to 10th	Day	8% 28% 46% 15% 2 1	240
	11th to 20th	Day	11% 11% 55% 18% 4	240
	21st to end	Day	8% 16% 53% 21% 2	198
March	1st to 10th	Day	8% 14% 48% 23% 8%	240
	11th to 20th	Day	13% 16% 41% 25% 5%	412
	21st to end	Day	14% 23% 42% 18% 4	462
April	1st to 10th	Day	12% 23% 37% 23% 5%	420
	11th to 20th	Day	15% 23% 36% 21% 5% 1	412
	21st to end	Day	15% 14% 41% 23% 6% 1	420
May	1st to 10th	Day	15% 11% 39% 26% 8% 2	521
	11th to 20th	Day	18% 8% 31% 27% 13% 3	625
	21st to end	Day	12% 7% 32% 28% 19% 3	679
June	1st to 10th	Day	5% 5% 26% 34% 23% 7%	630
	11th to 20th	Day	6% 7% 34% 33% 16% 4	630
	21st to end	Day	6% 5% 30% 34% 18% 7%	630
July	1st to 10th	Day	7% 2 18% 36% 29% 7%	621
	11th to 20th	Day	4 2 21% 36% 29% 7%	618
	21st to end	Day	6% 3 17% 35% 31% 8%	624
August	1st to 10th	Day	6% 4 27% 37% 21% 6%	447
	11th to 20th	Day	5% 4 27% 35% 24% 5%	437
	21st to end	Day	6% 3 27% 40% 19% 5%	495
September	1st to 10th	Day	7% 4 28% 36% 20% 5%	450
	11th to 20th	Day	5% 4 31% 38% 18% 4	445
	21st to end	Day	6% 6% 32% 30% 21% 5%	270
October	1st to 10th	Day	10% 9% 28% 24% 21% 8%	270
	11th to 20th	Day	4 12% 39% 32% 10% 3	270
	21st to end	Day	9% 15% 38% 28% 9% 1	297
November	1st to 10th	Day	5% 12% 43% 25% 14% 1	270
	11th to 20th	Day	11% 14% 37% 29% 8% 2	270
	21st to end	Day	9% 15% 40% 29% 5% 1	270
December	1st to 10th	Day	11% 13% 44% 23% 8% 1	270
	11th to 20th	Day	5% 17% 51% 22% 4	270
	21st to end	Day	10% 16% 44% 23% 7%	297
January	1st to 10th	Night	10% 14% 41% 25% 8% 2	950
	11th to 20th	Night	11% 17% 43% 20% 8% 1	875
	21st to end	Night	9% 14% 49% 23% 4 1	792
February	1st to 10th	Night	10% 15% 54% 17% 4	720
	11th to 20th	Night	8% 15% 48% 23% 6%	704
	21st to end	Night	7% 15% 53% 23% 3	592
March	1st to 10th	Night	6% 13% 48% 27% 7% 1	720
	11th to 20th	Night	9% 10% 38% 34% 8% 1	720
	21st to end	Night	10% 11% 45% 29% 4 1	671
April	1st to 10th	Night	9% 9% 48% 30% 4	540
	11th to 20th	Night	12% 10% 41% 27% 9% 1	533
	21st to end	Night	14% 8% 38% 29% 11% 1	540
May	1st to 10th	Night	12% 7% 35% 33% 12% 1	540
	11th to 20th	Night	19% 3 21% 40% 15% 3	531
	21st to end	Night	9% 4 27% 36% 21% 3	584
June	1st to 10th	Night	6% 2 19% 44% 24% 4	540
	11th to 20th	Night	7% 2 25% 46% 18% 2	540
	21st to end	Night	4 2 17% 44% 30% 3	540
July	1st to 10th	Night	7% 2 9% 36% 40% 6%	525
	11th to 20th	Night	2 1 10% 41% 40% 6%	522
	21st to end	Night	7% 1 5% 38% 42% 7%	591
August	1st to 10th	Night	6% 1 8% 43% 38% 4	537
	11th to 20th	Night	5% 1 12% 44% 33% 5%	534
	21st to end	Night	5% 1 12% 40% 34% 7%	594
September	1st to 10th	Night	6% 1 14% 42% 29% 7%	540
	11th to 20th	Night	7% 3 20% 43% 20% 7%	540
	21st to end	Night	6% 3 23% 44% 18% 5%	545
October	1st to 10th	Night	8% 6% 32% 35% 15% 4	720
	11th to 20th	Night	7% 7% 36% 36% 12% 3	720
	21st to end	Night	10% 11% 40% 29% 9% 2	828
November	1st to 10th	Night	5% 9% 43% 31% 10% 2	925
	11th to 20th	Night	8% 14% 45% 27% 4 1	950
	21st to end	Night	7% 10% 45% 30% 7%	950
December	1st to 10th	Night	10% 14% 44% 27% 5%	950
	11th to 20th	Night	6% 13% 49% 25% 5% 1	950
	21st to end	Night	9% 16% 45% 23% 6% 1	1045

Page generated at 2024-01-10 08:16:12. Version ac07

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