Starmere Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starmere Observatory clear sky chart from 2005-11-06 to 2024-05-14.

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	16% 8% 3 7% 5% 4 5% 4 6% 7% 35%	83404
	Night	17% 9% 3 7% 5% 4 4 3 5% 6% 35%	86083
Transparency	Day	45% 9% 14% 20% 11% 1	83109
	Night	46% 8% 13% 20% 11% 1	85912
Seeing	Day	21% 16% 30% 21% 9% 2	14189
	Night	21% 14% 32% 26% 7% 1	23406

By Month

Percentage Cloud Cover NE (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% 11% 3 7% 5% 4 5% 4 6% 7% 34%	2517
	11th to 20th	Day	15% 12% 4 10% 6% 6% 6% 4 5% 6% 27%	2520
	21st to end	Day	18% 11% 4 9% 7% 6% 5% 4 6% 6% 26%	2882
February	1st to 10th	Day	15% 11% 4 8% 6% 6% 5% 5% 7% 6% 28%	1710
	11th to 20th	Day	12% 11% 4 8% 6% 5% 5% 4 5% 7% 33%	1835
	21st to end	Day	19% 9% 4 8% 6% 4 4 3 5% 6% 32%	1570
March	1st to 10th	Day	23% 14% 4 9% 5% 3 3 2 3 4 29%	3116
	11th to 20th	Day	12% 12% 4 8% 5% 5% 5% 4 5% 7% 33%	3288
	21st to end	Day	20% 8% 3 7% 4 4 4 3 4 6% 36%	4161
April	1st to 10th	Day	18% 10% 3 8% 5% 4 4 4 4 6% 35%	2280
	11th to 20th	Day	16% 7% 2 7% 5% 4 5% 3 5% 6% 39%	2254
	21st to end	Day	20% 6% 3 6% 5% 4 5% 3 6% 7% 35%	2356
May	1st to 10th	Day	20% 9% 2 7% 5% 4 5% 4 5% 7% 32%	2492
	11th to 20th	Day	17% 6% 3 6% 5% 4 5% 4 5% 7% 39%	2520
	21st to end	Day	14% 6% 2 5% 4 4 5% 4 6% 9% 40%	2725
June	1st to 10th	Day	15% 7% 3 6% 5% 5% 6% 4 6% 9% 34%	2520
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 5% 7% 10% 35%	2520
	21st to end	Day	14% 6% 3 7% 5% 5% 6% 5% 6% 8% 35%	2520
July	1st to 10th	Day	10% 6% 2 6% 6% 5% 6% 5% 7% 8% 38%	2520
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 4 7% 11% 39%	2520
	21st to end	Day	11% 5% 2 6% 6% 6% 5% 6% 7% 8% 38%	2744
August	1st to 10th	Day	8% 6% 2 7% 5% 6% 6% 4 8% 9% 39%	2471
	11th to 20th	Day	11% 7% 3 7% 6% 5% 5% 4 8% 10% 35%	2126
	21st to end	Day	12% 5% 2 5% 5% 4 5% 5% 6% 9% 42%	2376
September	1st to 10th	Day	14% 5% 2 7% 4 5% 5% 3 5% 8% 43%	2160
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 4 8% 48%	2075
	21st to end	Day	15% 5% 2 5% 4 3 5% 4 6% 8% 42%	1980
October	1st to 10th	Day	21% 6% 3 7% 5% 4 5% 2 3 6% 37%	1886
	11th to 20th	Day	14% 8% 3 7% 4 3 4 4 5% 7% 40%	1800
	21st to end	Day	21% 10% 3 7% 5% 4 4 4 5% 6% 30%	1796
November	1st to 10th	Day	14% 8% 2 5% 4 3 3 3 5% 6% 45%	1671
	11th to 20th	Day	16% 8% 3 8% 5% 5% 4 3 6% 6% 37%	1710
	21st to end	Day	18% 9% 2 5% 5% 4 5% 4 6% 7% 35%	1585
December	1st to 10th	Day	17% 12% 4 8% 5% 5% 6% 5% 5% 6% 27%	1520
	11th to 20th	Day	23% 10% 4 7% 4 3 3 3 5% 5% 34%	1906
	21st to end	Day	24% 15% 4 9% 5% 4 3 3 5% 5% 23%	2772
January	1st to 10th	Night	15% 12% 4 8% 5% 4 4 3 4 5% 36%	4429
	11th to 20th	Night	13% 13% 5% 13% 6% 5% 4 3 4 6% 29%	4440
	21st to end	Night	23% 13% 4 8% 6% 4 4 3 5% 5% 26%	4756
February	1st to 10th	Night	16% 10% 3 9% 6% 5% 5% 4 5% 6% 31%	2470
	11th to 20th	Night	13% 11% 4 9% 6% 5% 5% 4 6% 6% 32%	2229
	21st to end	Night	18% 10% 3 7% 6% 4 5% 3 5% 6% 33%	1884
March	1st to 10th	Night	26% 10% 3 7% 5% 4 4 3 4 5% 30%	3724
	11th to 20th	Night	15% 13% 4 8% 5% 4 5% 4 5% 6% 32%	3653
	21st to end	Night	17% 12% 3 9% 5% 4 4 3 4 5% 35%	3471
April	1st to 10th	Night	17% 10% 4 8% 6% 4 5% 4 6% 7% 30%	1900
	11th to 20th	Night	21% 8% 3 6% 5% 4 3 3 5% 6% 37%	1875
	21st to end	Night	21% 7% 2 7% 4 3 4 3 6% 5% 38%	1823
May	1st to 10th	Night	20% 10% 4 8% 5% 5% 4 3 4 5% 32%	1704
	11th to 20th	Night	16% 10% 3 7% 4 4 4 4 4 8% 37%	1445
	21st to end	Night	13% 5% 2 7% 5% 5% 5% 5% 7% 7% 40%	1550
June	1st to 10th	Night	17% 6% 3 6% 4 3 4 4 6% 8% 39%	1440
	11th to 20th	Night	15% 7% 2 5% 5% 5% 4 4 6% 8% 38%	1440
	21st to end	Night	12% 5% 2 6% 4 5% 5% 4 5% 9% 43%	1440
July	1st to 10th	Night	13% 4 1 4 5% 3 4 5% 5% 10% 45%	1440
	11th to 20th	Night	12% 5% 2 6% 4 4 6% 4 8% 12% 38%	1440
	21st to end	Night	10% 5% 2 6% 5% 5% 6% 5% 6% 8% 42%	1574
August	1st to 10th	Night	8% 5% 2 8% 4 4 4 4 7% 8% 46%	1447
	11th to 20th	Night	11% 5% 3 8% 5% 5% 5% 5% 7% 9% 38%	1773
	21st to end	Night	15% 5% 2 6% 4 4 4 3 5% 7% 45%	1980
September	1st to 10th	Night	15% 6% 2 6% 4 5% 4 3 6% 7% 41%	1800
	11th to 20th	Night	14% 5% 1 4 3 3 4 2 4 6% 54%	1885
	21st to end	Night	14% 5% 3 6% 4 4 4 3 5% 6% 45%	1980
October	1st to 10th	Night	20% 7% 2 7% 4 4 4 4 5% 6% 38%	2070
	11th to 20th	Night	16% 7% 2 7% 4 4 5% 4 5% 7% 40%	2160
	21st to end	Night	24% 9% 2 7% 4 4 4 3 5% 6% 32%	2559
November	1st to 10th	Night	15% 7% 2 6% 4 4 3 3 6% 6% 43%	2407
	11th to 20th	Night	19% 8% 3 7% 5% 4 4 3 5% 6% 37%	2470
	21st to end	Night	16% 8% 3 7% 5% 5% 4 4 6% 6% 37%	2593
December	1st to 10th	Night	19% 11% 3 6% 6% 5% 5% 4 5% 7% 29%	2660
	11th to 20th	Night	21% 10% 4 8% 4 4 4 4 5% 6% 31%	3288
	21st to end	Night	23% 14% 4 9% 5% 5% 4 3 4 5% 24%	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	43% 7% 18% 26% 6% 1	2518
	11th to 20th	Day	53% 9% 15% 18% 5% 1	2520
	21st to end	Day	56% 10% 10% 17% 6% 1	2882
February	1st to 10th	Day	52% 9% 13% 16% 9% 1	1710
	11th to 20th	Day	48% 8% 11% 20% 11% 2	1844
	21st to end	Day	50% 7% 12% 19% 11% 1	1570
March	1st to 10th	Day	56% 6% 13% 16% 8% 1	3119
	11th to 20th	Day	40% 12% 20% 19% 8% 1	3288
	21st to end	Day	45% 7% 10% 17% 19% 3	4161
April	1st to 10th	Day	49% 7% 10% 20% 11% 3	2280
	11th to 20th	Day	43% 7% 12% 20% 14% 2	2254
	21st to end	Day	46% 7% 11% 19% 14% 3	2356
May	1st to 10th	Day	50% 8% 10% 18% 11% 2	2492
	11th to 20th	Day	42% 8% 12% 21% 15% 2	2524
	21st to end	Day	40% 10% 16% 22% 12% 2	2725
June	1st to 10th	Day	45% 9% 15% 19% 11% 1	2520
	11th to 20th	Day	42% 10% 15% 21% 11% 1	2520
	21st to end	Day	44% 9% 14% 22% 10% 1	2520
July	1st to 10th	Day	40% 11% 13% 20% 14% 2	2450
	11th to 20th	Day	36% 10% 18% 23% 12%	2445
	21st to end	Day	38% 10% 17% 19% 13% 2	2591
August	1st to 10th	Day	36% 12% 17% 22% 12% 1	2457
	11th to 20th	Day	40% 12% 17% 22% 8% 1	2126
	21st to end	Day	36% 8% 16% 24% 15% 1	2376
September	1st to 10th	Day	40% 8% 14% 23% 14% 1	2160
	11th to 20th	Day	35% 7% 12% 23% 21% 2	2075
	21st to end	Day	37% 8% 15% 23% 15% 2	1980
October	1st to 10th	Day	47% 7% 11% 20% 13% 2	1886
	11th to 20th	Day	41% 8% 15% 24% 10% 1	1800
	21st to end	Day	53% 8% 13% 15% 10% 2	1796
November	1st to 10th	Day	38% 6% 15% 25% 13% 2	1671
	11th to 20th	Day	45% 7% 13% 19% 14% 2	1710
	21st to end	Day	45% 8% 16% 23% 8% 2	1585
December	1st to 10th	Day	54% 9% 15% 13% 9%	1520
	11th to 20th	Day	49% 8% 16% 20% 7% 1	1906
	21st to end	Day	59% 9% 12% 15% 5%	2772
January	1st to 10th	Night	45% 8% 15% 22% 8% 1	4429
	11th to 20th	Night	52% 9% 13% 16% 9% 1	4440
	21st to end	Night	57% 7% 11% 17% 7% 1	4756
February	1st to 10th	Night	51% 8% 13% 19% 8% 2	2470
	11th to 20th	Night	49% 7% 13% 18% 12% 1	2231
	21st to end	Night	48% 7% 14% 18% 9% 3	1884
March	1st to 10th	Night	53% 8% 10% 19% 9% 1	3734
	11th to 20th	Night	44% 12% 16% 19% 8% 1	3654
	21st to end	Night	47% 6% 9% 16% 18% 3	3471
April	1st to 10th	Night	52% 6% 12% 18% 11% 2	1900
	11th to 20th	Night	47% 6% 11% 19% 16% 1	1875
	21st to end	Night	47% 6% 10% 19% 14% 3	1823
May	1st to 10th	Night	53% 7% 10% 16% 12% 3	1704
	11th to 20th	Night	45% 8% 11% 20% 14% 3	1446
	21st to end	Night	39% 10% 17% 19% 13% 1	1551
June	1st to 10th	Night	42% 7% 13% 24% 12% 2	1440
	11th to 20th	Night	40% 11% 15% 23% 10%	1440
	21st to end	Night	36% 11% 15% 24% 14% 1	1440
July	1st to 10th	Night	34% 9% 15% 24% 15% 2	1400
	11th to 20th	Night	36% 11% 19% 25% 10%	1392
	21st to end	Night	36% 9% 17% 22% 14% 2	1486
August	1st to 10th	Night	33% 10% 18% 25% 13% 1	1437
	11th to 20th	Night	39% 11% 17% 23% 10%	1773
	21st to end	Night	38% 7% 13% 25% 16% 1	1980
September	1st to 10th	Night	40% 8% 12% 25% 14% 1	1800
	11th to 20th	Night	33% 6% 12% 25% 23% 1	1885
	21st to end	Night	38% 6% 12% 24% 19% 1	1980
October	1st to 10th	Night	47% 6% 13% 20% 13% 1	2070
	11th to 20th	Night	40% 9% 15% 23% 12% 1	2160
	21st to end	Night	52% 6% 12% 19% 9% 1	2559
November	1st to 10th	Night	39% 8% 12% 21% 17% 2	2407
	11th to 20th	Night	46% 6% 14% 20% 11% 3	2470
	21st to end	Night	44% 8% 18% 22% 7% 1	2593
December	1st to 10th	Night	50% 9% 15% 18% 8%	2660
	11th to 20th	Night	50% 8% 16% 15% 10% 1	3288
	21st to end	Night	55% 9% 14% 16% 6%	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% 23% 33% 13% 5%	180
	11th to 20th	Day	27% 27% 32% 12% 3	180
	21st to end	Day	21% 26% 35% 14% 3 1	231
February	1st to 10th	Day	33% 24% 33% 8% 1	270
	11th to 20th	Day	27% 29% 31% 12% 1	443
	21st to end	Day	29% 24% 33% 12% 2	382
March	1st to 10th	Day	25% 22% 36% 15% 2	460
	11th to 20th	Day	24% 25% 33% 14% 2 1	460
	21st to end	Day	33% 20% 27% 12% 5% 2	506
April	1st to 10th	Day	30% 22% 27% 15% 6%	460
	11th to 20th	Day	26% 26% 27% 15% 5% 2	452
	21st to end	Day	27% 19% 32% 16% 5% 1	460
May	1st to 10th	Day	29% 18% 29% 17% 5% 2	463
	11th to 20th	Day	21% 15% 35% 21% 6% 2	459
	21st to end	Day	20% 11% 28% 26% 12% 3	485
June	1st to 10th	Day	20% 10% 32% 24% 12% 2	450
	11th to 20th	Day	17% 15% 30% 26% 10% 2	450
	21st to end	Day	15% 12% 32% 26% 12% 2	450
July	1st to 10th	Day	11% 8% 30% 31% 17% 3	445
	11th to 20th	Day	11% 5% 30% 33% 18% 2	444
	21st to end	Day	10% 8% 33% 31% 15% 2	488
August	1st to 10th	Day	9% 6% 28% 37% 15% 4	446
	11th to 20th	Day	13% 6% 27% 29% 17% 7%	439
	21st to end	Day	11% 9% 29% 29% 16% 6%	495
September	1st to 10th	Day	19% 8% 23% 30% 13% 7%	450
	11th to 20th	Day	14% 12% 29% 22% 14% 10%	450
	21st to end	Day	20% 10% 28% 25% 13% 5%	450
October	1st to 10th	Day	24% 13% 25% 20% 13% 5%	450
	11th to 20th	Day	18% 16% 34% 23% 8% 1	450
	21st to end	Day	27% 15% 32% 19% 6% 1	403
November	1st to 10th	Day	21% 18% 28% 22% 10% 1	365
	11th to 20th	Day	22% 24% 30% 17% 6% 1	370
	21st to end	Day	26% 20% 30% 22% 2	245
December	1st to 10th	Day	23% 25% 32% 14% 6%	180
	11th to 20th	Day	27% 31% 29% 9% 3	180
	21st to end	Day	22% 21% 40% 14% 3 1	198
January	1st to 10th	Night	21% 17% 40% 20% 2	760
	11th to 20th	Night	24% 20% 35% 20% 1	760
	21st to end	Night	19% 20% 39% 20% 2	836
February	1st to 10th	Night	23% 18% 37% 21% 2	760
	11th to 20th	Night	23% 21% 40% 16%	743
	21st to end	Night	27% 18% 36% 17% 3	628
March	1st to 10th	Night	24% 20% 35% 18% 3	760
	11th to 20th	Night	22% 21% 38% 16% 3	760
	21st to end	Night	24% 22% 31% 18% 5%	836
April	1st to 10th	Night	23% 21% 32% 20% 3	760
	11th to 20th	Night	24% 17% 33% 19% 6%	751
	21st to end	Night	25% 16% 32% 22% 5%	683
May	1st to 10th	Night	24% 16% 32% 22% 6%	564
	11th to 20th	Night	19% 13% 37% 27% 4	362
	21st to end	Night	15% 10% 29% 36% 9% 1	389
June	1st to 10th	Night	17% 9% 31% 34% 9% 1	360
	11th to 20th	Night	17% 8% 30% 33% 12% 1	360
	21st to end	Night	13% 5% 26% 44% 12% 1	360
July	1st to 10th	Night	15% 3 21% 42% 18% 1	350
	11th to 20th	Night	13% 4 21% 42% 18% 1	348
	21st to end	Night	12% 5% 21% 47% 13% 1	394
August	1st to 10th	Night	9% 3 22% 47% 17% 2	373
	11th to 20th	Night	13% 4 19% 40% 21% 2	709
	21st to end	Night	15% 4 23% 36% 19% 2	792
September	1st to 10th	Night	16% 5% 29% 34% 14% 1	720
	11th to 20th	Night	15% 9% 26% 28% 18% 4	720
	21st to end	Night	17% 8% 28% 33% 12% 2	720
October	1st to 10th	Night	24% 9% 25% 28% 13% 1	720
	11th to 20th	Night	18% 12% 33% 29% 7%	720
	21st to end	Night	29% 13% 32% 22% 4	792
November	1st to 10th	Night	21% 13% 32% 26% 7%	740
	11th to 20th	Night	24% 13% 35% 21% 7% 1	760
	21st to end	Night	19% 17% 35% 24% 5% 1	760
December	1st to 10th	Night	24% 18% 35% 18% 5%	760
	11th to 20th	Night	24% 18% 32% 24% 2	760
	21st to end	Night	27% 17% 36% 18% 2	836

Page generated at 2024-05-11 05:13:34. Version ac07

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