Darlington Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Darlington Observatory clear sky chart from 2005-11-06 to 2024-12-24.

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	2 4 1 4 3 4 4 4 6% 8% 59%	105355
	Night	3 5% 2 5% 3 4 4 3 6% 7% 58%	103505
Transparency	Day	20% 8% 13% 24% 24% 11%	105109
	Night	23% 8% 12% 23% 24% 10%	103341
Seeing	Day	6% 13% 27% 31% 19% 5%	15399
	Night	5% 5% 27% 43% 18% 1	25562

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	1 7% 3 7% 2 2 2 2 4 9% 61%	2663
	11th to 20th	Day	1 4 2 3 2 2 3 6% 7% 7% 63%	2860
	21st to end	Day	2 6% 3 6% 4 4 5% 4 6% 7% 54%	3146
February	1st to 10th	Day	1 5% 2 5% 3 4 4 2 5% 8% 61%	1727
	11th to 20th	Day	2 5% 2 5% 3 3 4 3 5% 8% 59%	1849
	21st to end	Day	2 6% 2 4 3 3 3 4 6% 8% 57%	1570
March	1st to 10th	Day	1 4 2 4 2 4 3 3 4 6% 67%	3241
	11th to 20th	Day	3 7% 2 7% 4 4 4 3 6% 8% 51%	3490
	21st to end	Day	2 6% 2 5% 4 4 5% 4 6% 8% 54%	3979
April	1st to 10th	Day	2 3 1 4 3 3 4 4 5% 8% 63%	2280
	11th to 20th	Day	2 4 2 4 3 4 4 4 5% 7% 62%	2251
	21st to end	Day	3 4 2 3 3 3 4 4 6% 8% 61%	2280
May	1st to 10th	Day	3 4 1 3 3 3 3 3 5% 6% 67%	3800
	11th to 20th	Day	3 4 1 5% 4 4 5% 5% 7% 8% 53%	4114
	21st to end	Day	1 2 1 2 2 3 4 3 5% 7% 70%	4825
June	1st to 10th	Day	2 2 1 3 3 4 4 4 6% 9% 62%	2660
	11th to 20th	Day	2 1 1 2 2 3 3 4 6% 6% 71%	2660
	21st to end	Day	4 3 1 3 4 3 4 5% 7% 8% 57%	2660
July	1st to 10th	Day	2 3 1 4 4 4 5% 4 6% 8% 59%	4430
	11th to 20th	Day	1 1 1 3 4 5% 7% 7% 12% 13% 46%	4242
	21st to end	Day	3 2 1 5% 5% 5% 7% 6% 10% 12% 43%	4454
August	1st to 10th	Day	2 3 2 6% 5% 7% 8% 7% 11% 11% 38%	4005
	11th to 20th	Day	2 2 1 3 3 3 5% 5% 8% 11% 58%	3726
	21st to end	Day	3 3 1 5% 4 5% 7% 6% 9% 13% 45%	4180
September	1st to 10th	Day	5% 3 1 3 5% 4 5% 5% 6% 8% 53%	2280
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 8% 60%	2280
	21st to end	Day	3 2 1 3 2 3 3 2 4 7% 69%	2076
October	1st to 10th	Day	3 2 1 2 2 2 2 2 4 6% 74%	3170
	11th to 20th	Day	4 4 1 4 3 3 4 3 5% 7% 62%	3150
	21st to end	Day	2 2 1 3 2 2 2 2 3 5% 76%	3438
November	1st to 10th	Day	2 3 1 2 2 3 2 3 4 6% 72%	1835
	11th to 20th	Day	1 2 1 2 2 2 2 2 4 6% 75%	1800
	21st to end	Day	3 7% 2 4 3 2 3 2 4 5% 65%	1800
December	1st to 10th	Day	3 5% 2 3 2 2 3 2 4 7% 68%	1610
	11th to 20th	Day	2 6% 1 4 3 3 4 4 5% 10% 58%	2006
	21st to end	Day	2 7% 2 4 3 3 3 2 4 7% 62%	2818
January	1st to 10th	Night	2 7% 4 7% 4 3 3 2 5% 6% 56%	4321
	11th to 20th	Night	2 6% 3 8% 3 3 3 3 5% 6% 57%	4110
	21st to end	Night	3 8% 3 6% 3 3 4 3 4 8% 54%	4521
February	1st to 10th	Night	2 6% 3 5% 3 3 3 3 4 7% 62%	2451
	11th to 20th	Night	3 8% 2 5% 3 3 4 3 5% 6% 58%	2218
	21st to end	Night	4 8% 1 4 3 3 2 2 4 7% 61%	1884
March	1st to 10th	Night	2 6% 2 4 3 3 3 3 4 5% 66%	3624
	11th to 20th	Night	6% 8% 3 7% 3 4 4 3 4 7% 51%	3490
	21st to end	Night	5% 10% 2 6% 3 4 3 3 4 6% 54%	3669
April	1st to 10th	Night	3 4 1 5% 3 3 4 3 5% 6% 61%	1900
	11th to 20th	Night	4 6% 2 3 3 4 4 4 6% 7% 58%	1877
	21st to end	Night	4 5% 1 4 3 2 4 4 6% 6% 60%	1900
May	1st to 10th	Night	5% 4 1 3 3 2 3 3 5% 6% 64%	3170
	11th to 20th	Night	5% 5% 2 6% 5% 5% 5% 4 7% 9% 48%	2786
	21st to end	Night	3 2 1 3 2 3 3 2 4 7% 69%	2762
June	1st to 10th	Night	2 2 1 3 4 4 4 4 6% 8% 63%	1520
	11th to 20th	Night	2 2 1 3 3 3 3 3 5% 5% 70%	1520
	21st to end	Night	3 3 1 4 5% 4 4 5% 7% 10% 53%	1520
July	1st to 10th	Night	3 3 2 7% 6% 5% 5% 5% 7% 7% 51%	2540
	11th to 20th	Night	1 2 1 4 4 5% 6% 7% 12% 14% 43%	2723
	21st to end	Night	4 3 2 5% 5% 6% 6% 6% 10% 12% 41%	3109
August	1st to 10th	Night	4 4 2 7% 6% 8% 9% 7% 10% 11% 32%	2933
	11th to 20th	Night	2 3 1 6% 4 5% 6% 5% 10% 14% 43%	3113
	21st to end	Night	3 4 2 8% 7% 7% 8% 7% 10% 12% 32%	3487
September	1st to 10th	Night	6% 3 2 4 4 4 5% 5% 7% 8% 53%	1900
	11th to 20th	Night	5% 2 1 2 3 3 4 4 7% 7% 61%	1900
	21st to end	Night	5% 2 1 4 3 3 3 3 4 5% 66%	2100
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 6% 72%	3800
	11th to 20th	Night	6% 4 1 4 3 3 3 3 5% 6% 64%	3778
	21st to end	Night	3 2 1 3 2 2 2 2 3 5% 75%	4120
November	1st to 10th	Night	3 2 1 2 2 2 2 2 3 6% 75%	2441
	11th to 20th	Night	1 2 1 1 1 2 2 2 4 6% 78%	2600
	21st to end	Night	5% 5% 1 3 2 2 3 3 5% 6% 66%	2600
December	1st to 10th	Night	4 6% 2 3 3 2 2 2 4 6% 66%	2785
	11th to 20th	Night	3 5% 2 5% 3 3 3 3 5% 9% 58%	3411
	21st to end	Night	3 6% 3 6% 4 3 4 3 4 6% 59%	4922

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	23% 5% 11% 35% 24% 2	2664
	11th to 20th	Day	17% 15% 19% 33% 15% 2	2860
	21st to end	Day	28% 8% 12% 27% 21% 3	3146
February	1st to 10th	Day	24% 8% 16% 26% 21% 6%	1727
	11th to 20th	Day	23% 7% 12% 27% 26% 6%	1859
	21st to end	Day	25% 6% 9% 19% 29% 12%	1570
March	1st to 10th	Day	17% 6% 8% 21% 38% 10%	3241
	11th to 20th	Day	26% 9% 12% 29% 20% 4	3490
	21st to end	Day	25% 9% 10% 31% 20% 6%	3979
April	1st to 10th	Day	20% 6% 10% 24% 27% 14%	2280
	11th to 20th	Day	20% 7% 9% 21% 29% 14%	2254
	21st to end	Day	20% 7% 10% 24% 29% 11%	2280
May	1st to 10th	Day	14% 7% 11% 17% 32% 20%	3800
	11th to 20th	Day	23% 9% 13% 23% 23% 10%	4118
	21st to end	Day	11% 5% 8% 15% 32% 28%	4825
June	1st to 10th	Day	16% 6% 13% 22% 23% 19%	2660
	11th to 20th	Day	12% 5% 8% 17% 25% 33%	2660
	21st to end	Day	22% 6% 11% 21% 22% 19%	2660
July	1st to 10th	Day	21% 9% 11% 17% 20% 22%	4361
	11th to 20th	Day	18% 13% 20% 34% 10% 4	4168
	21st to end	Day	25% 13% 20% 29% 10% 3	4314
August	1st to 10th	Day	29% 15% 23% 21% 8% 5%	3991
	11th to 20th	Day	16% 9% 18% 25% 20% 11%	3762
	21st to end	Day	24% 12% 22% 23% 15% 4	4179
September	1st to 10th	Day	25% 9% 13% 22% 21% 11%	2280
	11th to 20th	Day	21% 7% 11% 19% 27% 15%	2280
	21st to end	Day	14% 5% 8% 24% 35% 13%	2076
October	1st to 10th	Day	13% 4 5% 18% 37% 23%	3170
	11th to 20th	Day	19% 7% 10% 21% 32% 12%	3150
	21st to end	Day	11% 4 6% 26% 42% 11%	3438
November	1st to 10th	Day	14% 4 10% 25% 36% 11%	1835
	11th to 20th	Day	12% 4 9% 33% 35% 7%	1800
	21st to end	Day	22% 5% 8% 25% 32% 9%	1800
December	1st to 10th	Day	18% 6% 17% 29% 23% 7%	1610
	11th to 20th	Day	22% 9% 12% 26% 26% 5%	2004
	21st to end	Day	21% 5% 11% 25% 30% 7%	2818
January	1st to 10th	Night	29% 7% 12% 28% 22% 4	4321
	11th to 20th	Night	24% 16% 14% 27% 17% 2	4110
	21st to end	Night	27% 8% 12% 30% 20% 3	4521
February	1st to 10th	Night	24% 8% 14% 26% 22% 7%	2451
	11th to 20th	Night	27% 7% 11% 25% 25% 5%	2218
	21st to end	Night	25% 6% 7% 21% 31% 10%	1884
March	1st to 10th	Night	19% 7% 8% 19% 39% 7%	3624
	11th to 20th	Night	29% 7% 11% 27% 21% 5%	3490
	21st to end	Night	28% 9% 10% 29% 20% 4	3669
April	1st to 10th	Night	21% 5% 11% 25% 26% 12%	1900
	11th to 20th	Night	22% 8% 9% 20% 26% 14%	1877
	21st to end	Night	23% 7% 11% 23% 27% 10%	1900
May	1st to 10th	Night	18% 6% 12% 15% 29% 20%	3170
	11th to 20th	Night	26% 10% 14% 23% 16% 11%	2787
	21st to end	Night	13% 7% 10% 14% 30% 26%	2762
June	1st to 10th	Night	16% 7% 17% 20% 21% 20%	1520
	11th to 20th	Night	15% 5% 7% 14% 24% 34%	1520
	21st to end	Night	23% 8% 12% 19% 21% 18%	1520
July	1st to 10th	Night	27% 10% 12% 15% 12% 24%	2500
	11th to 20th	Night	22% 14% 28% 24% 7% 5%	2674
	21st to end	Night	29% 12% 23% 26% 8% 1	3011
August	1st to 10th	Night	36% 15% 23% 13% 7% 6%	2924
	11th to 20th	Night	25% 12% 21% 17% 15% 10%	3143
	21st to end	Night	35% 14% 20% 17% 11% 3	3487
September	1st to 10th	Night	26% 8% 14% 24% 18% 10%	1900
	11th to 20th	Night	18% 7% 14% 18% 25% 17%	1900
	21st to end	Night	19% 6% 9% 20% 33% 13%	2100
October	1st to 10th	Night	14% 4 7% 18% 38% 18%	3800
	11th to 20th	Night	19% 6% 9% 19% 35% 13%	3778
	21st to end	Night	12% 4 7% 27% 39% 11%	4120
November	1st to 10th	Night	12% 3 9% 27% 39% 11%	2441
	11th to 20th	Night	10% 4 8% 34% 36% 9%	2600
	21st to end	Night	21% 5% 8% 25% 32% 10%	2600
December	1st to 10th	Night	21% 5% 11% 33% 25% 4	2785
	11th to 20th	Night	23% 7% 11% 27% 27% 4	3412
	21st to end	Night	27% 6% 12% 25% 27% 4	4922

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	5% 19% 34% 33% 8% 2	270
	11th to 20th	Day	8% 13% 36% 35% 6% 2	270
	21st to end	Day	4 9% 33% 38% 12% 4	297
February	1st to 10th	Day	4 15% 38% 33% 9% 1	270
	11th to 20th	Day	4 18% 43% 27% 8%	270
	21st to end	Day	11% 25% 33% 28% 3	225
March	1st to 10th	Day	5% 24% 33% 29% 8% 1	329
	11th to 20th	Day	11% 24% 29% 25% 9% 2	460
	21st to end	Day	11% 32% 34% 17% 5%	506
April	1st to 10th	Day	8% 27% 37% 20% 8% 1	460
	11th to 20th	Day	10% 30% 38% 16% 6% 1	452
	21st to end	Day	8% 30% 37% 20% 4	460
May	1st to 10th	Day	8% 25% 43% 19% 5% 1	463
	11th to 20th	Day	7% 16% 28% 31% 15% 3	603
	21st to end	Day	6% 14% 32% 33% 14% 1	734
June	1st to 10th	Day	1 8% 25% 40% 24% 2	680
	11th to 20th	Day	2 9% 29% 35% 21% 3	680
	21st to end	Day	6% 7% 22% 35% 24% 6%	680
July	1st to 10th	Day	5% 2 16% 35% 35% 7%	671
	11th to 20th	Day	2 1 12% 32% 40% 13%	559
	21st to end	Day	5% 1 10% 32% 37% 15%	531
August	1st to 10th	Day	4 5% 12% 36% 30% 13%	487
	11th to 20th	Day	3 4 18% 36% 29% 10%	477
	21st to end	Day	3 2 17% 40% 27% 10%	539
September	1st to 10th	Day	5% 3 18% 31% 31% 11%	490
	11th to 20th	Day	3 4 26% 39% 22% 6%	490
	21st to end	Day	3 6% 26% 30% 26% 9%	310
October	1st to 10th	Day	4 15% 20% 27% 25% 10%	300
	11th to 20th	Day	6% 12% 25% 31% 20% 6%	300
	21st to end	Day	8% 12% 24% 31% 21% 4	330
November	1st to 10th	Day	7% 17% 26% 34% 14% 2	300
	11th to 20th	Day	3 8% 27% 41% 19% 1	300
	21st to end	Day	9% 11% 35% 28% 13% 4	300
December	1st to 10th	Day	8% 13% 32% 29% 16% 2	300
	11th to 20th	Day	4 13% 30% 41% 12% 1	300
	21st to end	Day	12% 16% 33% 30% 7% 1	306
January	1st to 10th	Night	5% 4 33% 42% 14% 1	893
	11th to 20th	Night	7% 4 34% 42% 12% 2	760
	21st to end	Night	6% 4 31% 43% 13% 2	836
February	1st to 10th	Night	6% 7% 38% 41% 9%	760
	11th to 20th	Night	7% 6% 40% 39% 7% 1	744
	21st to end	Night	10% 7% 44% 36% 3	628
March	1st to 10th	Night	6% 10% 38% 37% 8%	760
	11th to 20th	Night	9% 8% 29% 41% 13% 1	760
	21st to end	Night	9% 10% 40% 34% 8%	741
April	1st to 10th	Night	7% 14% 42% 34% 4	570
	11th to 20th	Night	6% 13% 36% 38% 7%	563
	21st to end	Night	5% 11% 41% 37% 6%	570
May	1st to 10th	Night	5% 8% 35% 42% 11%	570
	11th to 20th	Night	7% 6% 26% 45% 16% 1	561
	21st to end	Night	4 7% 30% 45% 13%	617
June	1st to 10th	Night	2 2 22% 54% 20%	570
	11th to 20th	Night	2 4 22% 55% 17% 1	570
	21st to end	Night	3 2 16% 49% 29% 1	570
July	1st to 10th	Night	3 1 9% 48% 36% 2	555
	11th to 20th	Night	2 1 6% 39% 49% 4	552
	21st to end	Night	4 1 5% 31% 52% 7%	624
August	1st to 10th	Night	3 1 6% 32% 51% 6%	567
	11th to 20th	Night	4 2 7% 44% 41% 2	564
	21st to end	Night	3 6% 47% 40% 4	627
September	1st to 10th	Night	5% 1 11% 48% 32% 2	570
	11th to 20th	Night	4 1 10% 54% 28% 2	570
	21st to end	Night	5% 3 19% 51% 21% 1	590
October	1st to 10th	Night	7% 3 22% 47% 20% 2	760
	11th to 20th	Night	5% 3 29% 44% 17% 3	760
	21st to end	Night	6% 4 26% 42% 19% 4	836
November	1st to 10th	Night	4 4 25% 49% 16% 1	881
	11th to 20th	Night	2 5% 31% 46% 14% 2	1000
	21st to end	Night	7% 7% 28% 41% 16% 1	1000
December	1st to 10th	Night	7% 7% 31% 42% 12% 1	1000
	11th to 20th	Night	7% 7% 33% 42% 11%	1000
	21st to end	Night	8% 7% 35% 43% 8% 1	1063

Page generated at 2024-12-21 02:13:52. Version ac07

Copyright © 2024 Attilla Danko.