Battersea Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Battersea 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	17% 10% 3 8% 5% 4 4 4 5% 7% 33%	101566
	Night	18% 11% 3 8% 5% 4 4 4 5% 6% 33%	97437
Transparency	Day	48% 7% 13% 22% 10% 1	105088
	Night	50% 6% 12% 21% 10% 1	102004
Seeing	Day	23% 16% 31% 20% 8% 3	14530
	Night	22% 14% 30% 24% 9% 1	23667

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	16% 17% 4 10% 6% 4 4 3 3 5% 28%	2517
	11th to 20th	Day	14% 17% 7% 13% 6% 6% 5% 3 4 5% 20%	2520
	21st to end	Day	17% 21% 7% 13% 7% 5% 4 3 4 4 17%	3000
February	1st to 10th	Day	16% 16% 5% 12% 5% 6% 5% 4 6% 4 22%	1710
	11th to 20th	Day	13% 16% 4 12% 6% 5% 5% 4 4 5% 27%	1663
	21st to end	Day	20% 15% 4 9% 6% 5% 6% 3 4 5% 23%	1564
March	1st to 10th	Day	22% 13% 3 9% 5% 4 4 2 3 5% 29%	3180
	11th to 20th	Day	12% 17% 5% 10% 6% 4 4 3 5% 5% 31%	3480
	21st to end	Day	13% 10% 3 8% 4 4 4 3 5% 6% 41%	3988
April	1st to 10th	Day	21% 13% 2 8% 4 4 4 3 4 5% 32%	2280
	11th to 20th	Day	22% 9% 3 5% 4 3 4 3 4 5% 37%	2254
	21st to end	Day	22% 10% 3 8% 4 4 4 3 4 5% 32%	2367
May	1st to 10th	Day	21% 9% 3 7% 5% 4 5% 4 5% 6% 32%	4421
	11th to 20th	Day	17% 9% 3 8% 5% 4 4 4 5% 8% 33%	4398
	21st to end	Day	13% 6% 2 6% 4 4 4 4 7% 9% 40%	4837
June	1st to 10th	Day	20% 7% 4 7% 4 4 5% 4 6% 8% 32%	2660
	11th to 20th	Day	15% 6% 2 5% 5% 5% 5% 4 6% 9% 38%	2660
	21st to end	Day	17% 8% 3 7% 4 4 5% 4 6% 7% 35%	2660
July	1st to 10th	Day	11% 6% 3 6% 4 5% 5% 5% 7% 10% 38%	4440
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 5% 7% 9% 42%	4440
	21st to end	Day	10% 5% 2 6% 4 5% 5% 5% 7% 9% 40%	4814
August	1st to 10th	Day	17% 7% 2 7% 4 4 5% 4 6% 8% 36%	4217
	11th to 20th	Day	17% 6% 2 6% 4 5% 5% 5% 7% 8% 36%	3998
	21st to end	Day	15% 6% 2 5% 4 4 4 4 7% 9% 40%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 3 4 4 6% 8% 43%	2280
	11th to 20th	Day	12% 6% 2 6% 3 4 4 3 5% 7% 49%	2280
	21st to end	Day	17% 7% 2 6% 4 4 5% 3 5% 7% 41%	2017
October	1st to 10th	Day	22% 7% 2 6% 5% 3 4 4 4 6% 37%	1900
	11th to 20th	Day	20% 9% 4 7% 5% 4 5% 3 5% 7% 32%	1900
	21st to end	Day	25% 10% 3 7% 4 5% 5% 3 4 5% 28%	1985
November	1st to 10th	Day	15% 9% 2 7% 6% 4 4 5% 6% 7% 34%	1708
	11th to 20th	Day	16% 12% 4 9% 5% 5% 4 3 4 6% 31%	1530
	21st to end	Day	21% 14% 5% 6% 6% 4 5% 4 5% 5% 23%	1520
December	1st to 10th	Day	23% 16% 5% 9% 5% 4 4 4 4 6% 20%	1520
	11th to 20th	Day	20% 16% 5% 11% 5% 4 4 3 5% 5% 23%	1906
	21st to end	Day	26% 18% 5% 10% 5% 4 3 3 3 4 20%	2772
January	1st to 10th	Night	18% 15% 5% 10% 6% 6% 5% 3 5% 5% 23%	4429
	11th to 20th	Night	14% 15% 6% 15% 7% 6% 5% 4 4 5% 19%	4440
	21st to end	Night	21% 16% 6% 12% 5% 5% 4 3 4 4 21%	4651
February	1st to 10th	Night	17% 15% 4 12% 6% 6% 5% 3 5% 5% 22%	2470
	11th to 20th	Night	14% 14% 5% 10% 6% 5% 4 3 4 5% 29%	2403
	21st to end	Night	17% 13% 3 9% 5% 5% 5% 3 4 6% 28%	1889
March	1st to 10th	Night	19% 11% 4 8% 5% 4 4 3 4 5% 32%	3642
	11th to 20th	Night	19% 15% 4 8% 5% 4 4 3 4 6% 27%	3479
	21st to end	Night	16% 10% 3 8% 4 4 3 3 4 5% 40%	3642
April	1st to 10th	Night	21% 10% 4 7% 4 3 4 4 4 5% 34%	1900
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 4 6% 37%	1875
	21st to end	Night	22% 9% 3 7% 5% 4 4 3 5% 6% 33%	1829
May	1st to 10th	Night	22% 10% 3 6% 5% 5% 4 4 5% 6% 31%	2518
	11th to 20th	Night	19% 9% 3 6% 4 4 4 4 4 7% 36%	2495
	21st to end	Night	13% 6% 2 5% 4 5% 5% 4 6% 8% 42%	2738
June	1st to 10th	Night	15% 7% 3 7% 6% 5% 5% 4 6% 7% 34%	1520
	11th to 20th	Night	14% 5% 2 5% 4 5% 4 5% 6% 9% 43%	1520
	21st to end	Night	18% 6% 2 6% 6% 4 5% 4 6% 8% 36%	1520
July	1st to 10th	Night	11% 6% 3 7% 5% 5% 6% 5% 6% 7% 39%	2520
	11th to 20th	Night	14% 6% 2 6% 4 3 3 3 6% 9% 45%	2520
	21st to end	Night	11% 6% 2 5% 4 4 4 3 6% 8% 46%	2739
August	1st to 10th	Night	11% 7% 2 7% 4 4 5% 3 6% 8% 43%	2695
	11th to 20th	Night	14% 8% 3 6% 4 3 3 4 6% 7% 43%	2785
	21st to end	Night	9% 5% 2 6% 5% 6% 5% 5% 8% 9% 41%	3476
September	1st to 10th	Night	12% 6% 2 7% 4 4 4 3 5% 6% 47%	1900
	11th to 20th	Night	12% 6% 2 4 3 3 3 4 6% 7% 51%	1900
	21st to end	Night	17% 7% 2 6% 3 4 3 4 6% 7% 42%	2160
October	1st to 10th	Night	17% 9% 3 7% 4 5% 4 3 6% 7% 37%	2280
	11th to 20th	Night	20% 9% 3 8% 5% 4 6% 3 5% 5% 33%	2280
	21st to end	Night	23% 10% 3 8% 5% 5% 4 3 4 5% 30%	2612
November	1st to 10th	Night	18% 9% 3 7% 5% 3 4 3 4 6% 37%	2470
	11th to 20th	Night	18% 10% 3 8% 4 4 5% 4 5% 6% 33%	2648
	21st to end	Night	21% 12% 3 8% 5% 5% 5% 3 5% 6% 25%	2660
December	1st to 10th	Night	20% 16% 5% 10% 6% 5% 4 3 4 5% 21%	2660
	11th to 20th	Night	21% 14% 4 9% 5% 4 3 3 4 4 27%	3288
	21st to end	Night	30% 15% 4 10% 4 4 4 3 5% 5% 17%	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	58% 9% 13% 13% 5% 2	2518
	11th to 20th	Day	66% 6% 13% 9% 6%	2520
	21st to end	Day	71% 6% 8% 9% 4 1	3000
February	1st to 10th	Day	63% 5% 10% 16% 5% 1	1710
	11th to 20th	Day	60% 5% 10% 15% 8% 1	1672
	21st to end	Day	62% 6% 9% 12% 9% 1	1564
March	1st to 10th	Day	58% 5% 10% 17% 9% 1	3183
	11th to 20th	Day	54% 6% 14% 15% 10% 2	3480
	21st to end	Day	42% 6% 8% 26% 15% 3	3988
April	1st to 10th	Day	54% 5% 8% 18% 12% 3	2280
	11th to 20th	Day	49% 5% 7% 22% 15% 2	2254
	21st to end	Day	54% 5% 8% 16% 13% 4	2367
May	1st to 10th	Day	51% 7% 10% 21% 10% 2	4435
	11th to 20th	Day	48% 7% 13% 22% 9% 1	4402
	21st to end	Day	38% 7% 15% 25% 13% 2	4837
June	1st to 10th	Day	49% 8% 11% 19% 12% 1	2660
	11th to 20th	Day	41% 6% 12% 26% 13% 2	2660
	21st to end	Day	45% 8% 14% 20% 11% 1	2660
July	1st to 10th	Day	38% 8% 13% 28% 12% 1	4370
	11th to 20th	Day	35% 9% 16% 32% 9%	4365
	21st to end	Day	37% 9% 15% 29% 10%	4661
August	1st to 10th	Day	44% 7% 15% 24% 10% 1	4203
	11th to 20th	Day	42% 8% 15% 25% 10%	4037
	21st to end	Day	38% 7% 16% 29% 11%	4180
September	1st to 10th	Day	37% 7% 16% 27% 12% 1	2280
	11th to 20th	Day	35% 5% 13% 31% 16% 1	2280
	21st to end	Day	43% 6% 13% 27% 10%	2017
October	1st to 10th	Day	41% 6% 13% 29% 9%	3160
	11th to 20th	Day	44% 6% 16% 27% 7%	3140
	21st to end	Day	48% 6% 15% 23% 8%	3249
November	1st to 10th	Day	47% 7% 15% 22% 8% 1	1708
	11th to 20th	Day	55% 6% 10% 18% 9% 1	1530
	21st to end	Day	59% 8% 13% 12% 7%	1520
December	1st to 10th	Day	65% 6% 12% 13% 4	1520
	11th to 20th	Day	63% 7% 13% 13% 3	1906
	21st to end	Day	69% 6% 6% 15% 3	2772
January	1st to 10th	Night	62% 7% 15% 12% 4	4429
	11th to 20th	Night	65% 8% 12% 11% 4	4440
	21st to end	Night	67% 6% 10% 11% 5% 1	4651
February	1st to 10th	Night	63% 5% 11% 14% 6%	2470
	11th to 20th	Night	56% 5% 10% 19% 9%	2405
	21st to end	Night	57% 5% 11% 18% 9% 1	1889
March	1st to 10th	Night	53% 6% 9% 23% 9% 1	3652
	11th to 20th	Night	57% 5% 14% 15% 9% 1	3480
	21st to end	Night	44% 6% 7% 23% 18% 2	3642
April	1st to 10th	Night	52% 4 8% 20% 14% 2	1900
	11th to 20th	Night	49% 5% 10% 19% 17% 1	1875
	21st to end	Night	52% 5% 9% 16% 15% 3	1829
May	1st to 10th	Night	53% 5% 11% 18% 10% 3	2524
	11th to 20th	Night	47% 7% 14% 22% 9% 2	2496
	21st to end	Night	38% 7% 14% 21% 18% 2	2739
June	1st to 10th	Night	46% 8% 13% 21% 11% 1	1520
	11th to 20th	Night	37% 7% 14% 22% 18% 2	1520
	21st to end	Night	44% 8% 13% 20% 13% 1	1520
July	1st to 10th	Night	41% 7% 12% 23% 16% 1	2480
	11th to 20th	Night	36% 6% 13% 35% 11%	2472
	21st to end	Night	35% 8% 15% 28% 12% 2	2651
August	1st to 10th	Night	39% 7% 14% 27% 13% 1	2685
	11th to 20th	Night	38% 7% 13% 32% 10% 1	2812
	21st to end	Night	36% 9% 16% 29% 10% 1	3476
September	1st to 10th	Night	37% 5% 13% 30% 13% 1	1900
	11th to 20th	Night	31% 7% 14% 33% 14% 1	1900
	21st to end	Night	41% 6% 12% 29% 12% 1	2160
October	1st to 10th	Night	38% 6% 12% 28% 16% 1	3800
	11th to 20th	Night	42% 6% 15% 27% 10%	3779
	21st to end	Night	48% 6% 14% 23% 8%	4298
November	1st to 10th	Night	47% 7% 14% 22% 10% 1	2470
	11th to 20th	Night	49% 7% 13% 19% 10% 2	2648
	21st to end	Night	59% 7% 12% 16% 6%	2660
December	1st to 10th	Night	64% 7% 12% 14% 4	2660
	11th to 20th	Night	60% 6% 11% 16% 6% 1	3288
	21st to end	Night	69% 6% 10% 12% 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	28% 19% 33% 14% 4 1	180
	11th to 20th	Day	33% 18% 33% 13% 2 1	180
	21st to end	Day	28% 20% 30% 17% 4	263
February	1st to 10th	Day	33% 27% 29% 9% 2	270
	11th to 20th	Day	31% 27% 34% 7%	270
	21st to end	Day	34% 20% 32% 12% 2	376
March	1st to 10th	Day	25% 21% 33% 16% 5%	460
	11th to 20th	Day	28% 20% 32% 15% 4	460
	21st to end	Day	30% 22% 28% 13% 6% 1	506
April	1st to 10th	Day	29% 22% 31% 13% 4	460
	11th to 20th	Day	31% 22% 23% 13% 8% 3	452
	21st to end	Day	26% 23% 30% 13% 5% 2	460
May	1st to 10th	Day	25% 14% 32% 21% 6% 2	463
	11th to 20th	Day	20% 12% 36% 21% 9% 2	487
	21st to end	Day	17% 15% 32% 25% 9% 2	529
June	1st to 10th	Day	23% 11% 35% 21% 7% 2	490
	11th to 20th	Day	15% 15% 35% 21% 11% 3	490
	21st to end	Day	21% 13% 31% 22% 10% 2	490
July	1st to 10th	Day	13% 11% 30% 29% 15% 3	485
	11th to 20th	Day	14% 11% 30% 26% 14% 4	484
	21st to end	Day	13% 8% 36% 30% 10% 4	532
August	1st to 10th	Day	15% 8% 30% 28% 15% 4	486
	11th to 20th	Day	13% 7% 29% 29% 16% 6%	479
	21st to end	Day	15% 9% 32% 26% 12% 6%	539
September	1st to 10th	Day	14% 10% 33% 25% 12% 6%	490
	11th to 20th	Day	11% 9% 24% 25% 18% 12%	490
	21st to end	Day	19% 11% 29% 26% 13% 3	490
October	1st to 10th	Day	27% 15% 26% 17% 11% 4	490
	11th to 20th	Day	26% 21% 30% 15% 7% 1	490
	21st to end	Day	30% 19% 27% 20% 4	483
November	1st to 10th	Day	27% 19% 28% 19% 7% 1	378
	11th to 20th	Day	27% 16% 39% 11% 5% 3	190
	21st to end	Day	27% 22% 32% 13% 5%	180
December	1st to 10th	Day	33% 22% 28% 14% 2 1	180
	11th to 20th	Day	26% 24% 37% 11% 2	180
	21st to end	Day	34% 19% 32% 13% 2	198
January	1st to 10th	Night	31% 17% 29% 19% 4	760
	11th to 20th	Night	30% 18% 29% 18% 5%	760
	21st to end	Night	21% 15% 36% 23% 5%	836
February	1st to 10th	Night	25% 20% 34% 19% 2	760
	11th to 20th	Night	22% 19% 38% 18% 3	743
	21st to end	Night	25% 21% 33% 18% 3	628
March	1st to 10th	Night	24% 16% 37% 20% 3	760
	11th to 20th	Night	28% 17% 30% 20% 4 1	760
	21st to end	Night	23% 15% 34% 20% 7%	836
April	1st to 10th	Night	26% 16% 34% 22% 3	760
	11th to 20th	Night	22% 20% 33% 18% 7% 1	751
	21st to end	Night	27% 12% 29% 22% 9%	689
May	1st to 10th	Night	24% 9% 27% 28% 11% 1	384
	11th to 20th	Night	14% 9% 36% 33% 7%	374
	21st to end	Night	12% 9% 36% 30% 12% 1	411
June	1st to 10th	Night	17% 7% 33% 33% 9% 1	380
	11th to 20th	Night	16% 9% 28% 33% 13% 1	380
	21st to end	Night	19% 4 26% 37% 13%	380
July	1st to 10th	Night	9% 5% 29% 39% 17%	370
	11th to 20th	Night	13% 3 28% 36% 18% 1	368
	21st to end	Night	13% 4 26% 41% 14% 1	416
August	1st to 10th	Night	12% 3 28% 31% 23% 1	489
	11th to 20th	Night	14% 4 24% 33% 23% 3	564
	21st to end	Night	10% 7% 30% 34% 16% 2	836
September	1st to 10th	Night	15% 7% 29% 32% 15% 3	760
	11th to 20th	Night	14% 8% 21% 27% 24% 6%	760
	21st to end	Night	18% 9% 24% 28% 18% 3	760
October	1st to 10th	Night	21% 12% 28% 20% 17% 2	760
	11th to 20th	Night	25% 15% 28% 23% 8% 1	760
	21st to end	Night	27% 15% 29% 24% 5%	836
November	1st to 10th	Night	26% 15% 29% 22% 8%	760
	11th to 20th	Night	24% 18% 31% 18% 8% 1	760
	21st to end	Night	30% 18% 28% 17% 7%	760
December	1st to 10th	Night	30% 20% 28% 18% 4	760
	11th to 20th	Night	28% 19% 33% 16% 3 1	760
	21st to end	Night	33% 18% 30% 17% 2	836

Page generated at 2024-11-03 02:11:09. Version ac07

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