Heaven Sent Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heaven Sent Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	7% 5% 2 7% 6% 7% 7% 6% 8% 11% 33%	100880
	Night	7% 4 2 6% 5% 5% 5% 5% 7% 10% 43%	98862
Transparency	Day	37% 13% 19% 20% 10% 2	104603
	Night	33% 11% 21% 22% 11% 2	103278
Seeing	Day	8% 3 15% 29% 26% 19%	16152
	Night	8% 2 12% 32% 34% 14%	26277

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	10% 7% 3 7% 5% 5% 5% 5% 8% 10% 35%	2836
	11th to 20th	Day	14% 7% 4 10% 6% 5% 6% 5% 7% 8% 28%	2840
	21st to end	Day	7% 7% 3 9% 7% 7% 6% 4 6% 7% 39%	3256
February	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 4 7% 10% 42%	1900
	11th to 20th	Day	7% 4 1 5% 4 4 5% 5% 7% 11% 48%	1959
	21st to end	Day	6% 4 2 5% 5% 5% 4 5% 7% 8% 49%	1727
March	1st to 10th	Day	5% 4 2 6% 6% 6% 8% 7% 9% 11% 36%	3435
	11th to 20th	Day	4 3 1 5% 4 4 5% 4 7% 9% 52%	3480
	21st to end	Day	9% 4 2 6% 4 5% 5% 4 6% 8% 48%	3815
April	1st to 10th	Day	5% 4 2 5% 4 6% 6% 5% 8% 11% 46%	2090
	11th to 20th	Day	5% 4 2 6% 5% 6% 6% 5% 9% 11% 42%	2126
	21st to end	Day	8% 4 1 6% 4 6% 5% 5% 7% 10% 45%	2280
May	1st to 10th	Day	3 2 1 4 3 4 5% 4 6% 10% 57%	3765
	11th to 20th	Day	7% 5% 2 5% 5% 5% 5% 5% 7% 9% 46%	3782
	21st to end	Day	6% 5% 2 7% 6% 7% 8% 6% 7% 9% 35%	4476
June	1st to 10th	Day	13% 9% 4 11% 10% 7% 8% 6% 7% 8% 16%	2470
	11th to 20th	Day	9% 8% 3 11% 9% 10% 9% 7% 8% 9% 18%	2470
	21st to end	Day	8% 7% 3 11% 10% 8% 9% 8% 9% 10% 17%	2470
July	1st to 10th	Day	5% 5% 2 8% 6% 8% 7% 7% 9% 16% 26%	4120
	11th to 20th	Day	4 5% 2 8% 8% 8% 8% 7% 10% 15% 25%	4120
	21st to end	Day	3 3 2 6% 6% 7% 9% 7% 11% 15% 30%	4466
August	1st to 10th	Day	4 5% 2 9% 8% 9% 10% 9% 12% 13% 21%	4017
	11th to 20th	Day	5% 5% 3 9% 7% 8% 8% 8% 11% 14% 22%	3673
	21st to end	Day	6% 4 2 8% 7% 9% 9% 9% 12% 16% 19%	3828
September	1st to 10th	Day	7% 6% 3 10% 8% 9% 9% 8% 10% 11% 19%	2090
	11th to 20th	Day	9% 8% 4 11% 9% 9% 8% 6% 7% 10% 18%	2090
	21st to end	Day	11% 10% 4 11% 8% 7% 8% 6% 7% 9% 21%	2090
October	1st to 10th	Day	9% 7% 3 9% 7% 8% 8% 7% 9% 11% 22%	2019
	11th to 20th	Day	11% 6% 2 9% 7% 6% 8% 7% 8% 10% 26%	1900
	21st to end	Day	10% 6% 3 9% 6% 5% 6% 5% 6% 9% 35%	2090
November	1st to 10th	Day	8% 6% 2 5% 6% 6% 6% 4 7% 9% 41%	1957
	11th to 20th	Day	9% 6% 2 9% 5% 7% 7% 5% 6% 9% 35%	2000
	21st to end	Day	8% 6% 1 6% 5% 6% 6% 5% 5% 9% 41%	2000
December	1st to 10th	Day	7% 5% 2 7% 5% 5% 5% 4 6% 10% 44%	1966
	11th to 20th	Day	8% 5% 3 6% 6% 5% 5% 4 7% 10% 41%	2153
	21st to end	Day	14% 5% 2 8% 6% 6% 5% 4 7% 9% 32%	3124
January	1st to 10th	Night	9% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	4109
	11th to 20th	Night	15% 8% 3 9% 6% 6% 6% 4 7% 7% 29%	4120
	21st to end	Night	8% 6% 3 9% 6% 5% 5% 4 6% 7% 42%	4396
February	1st to 10th	Night	8% 4 2 6% 5% 4 4 4 5% 9% 49%	2280
	11th to 20th	Night	5% 3 1 4 4 3 4 4 5% 8% 58%	2103
	21st to end	Night	5% 2 1 4 3 3 4 3 6% 9% 60%	1727
March	1st to 10th	Night	6% 4 2 7% 5% 5% 6% 5% 8% 9% 43%	3418
	11th to 20th	Night	4 2 1 3 3 3 4 3 6% 10% 60%	3480
	21st to end	Night	7% 3 1 4 3 3 4 4 6% 7% 59%	3817
April	1st to 10th	Night	4 2 1 3 3 3 4 4 6% 10% 60%	2090
	11th to 20th	Night	5% 3 2 3 3 4 4 4 7% 10% 55%	2002
	21st to end	Night	6% 3 1 5% 3 4 5% 4 6% 10% 53%	1900
May	1st to 10th	Night	3 1 1 2 2 3 3 3 6% 9% 67%	3130
	11th to 20th	Night	6% 2 1 5% 4 4 5% 4 6% 9% 55%	3130
	21st to end	Night	5% 4 1 4 4 4 4 5% 7% 10% 53%	3087
June	1st to 10th	Night	13% 7% 3 8% 5% 7% 5% 5% 9% 11% 26%	1710
	11th to 20th	Night	8% 5% 2 6% 5% 7% 7% 6% 8% 12% 34%	1710
	21st to end	Night	5% 5% 1 6% 6% 6% 8% 8% 11% 13% 33%	1710
July	1st to 10th	Night	3 4 2 7% 4 5% 7% 5% 10% 17% 36%	2840
	11th to 20th	Night	3 4 1 5% 4 5% 7% 5% 10% 15% 39%	2840
	21st to end	Night	2 3 2 5% 5% 5% 6% 6% 9% 15% 43%	3087
August	1st to 10th	Night	3 3 2 7% 6% 7% 8% 7% 10% 14% 34%	2879
	11th to 20th	Night	4 4 2 6% 5% 5% 7% 5% 10% 14% 38%	3147
	21st to end	Night	4 4 2 6% 6% 7% 8% 7% 12% 16% 29%	3828
September	1st to 10th	Night	5% 4 2 6% 6% 6% 7% 6% 10% 14% 34%	2090
	11th to 20th	Night	6% 7% 3 8% 7% 8% 7% 6% 9% 12% 29%	2090
	21st to end	Night	7% 7% 3 9% 7% 6% 7% 6% 9% 10% 29%	2090
October	1st to 10th	Night	8% 5% 2 7% 6% 7% 8% 6% 8% 12% 31%	2158
	11th to 20th	Night	8% 5% 2 8% 5% 6% 6% 5% 7% 11% 35%	2280
	21st to end	Night	10% 5% 3 7% 5% 5% 5% 4 7% 9% 41%	2508
November	1st to 10th	Night	8% 4 2 6% 4 4 5% 5% 7% 9% 47%	2341
	11th to 20th	Night	9% 7% 2 7% 5% 5% 5% 5% 7% 8% 40%	2400
	21st to end	Night	8% 5% 1 5% 4 4 4 4 6% 8% 51%	2400
December	1st to 10th	Night	7% 3 2 5% 4 4 5% 5% 7% 9% 49%	2391
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 5% 8% 50%	3042
	21st to end	Night	13% 7% 3 8% 5% 5% 6% 5% 6% 8% 35%	4532

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	39% 9% 13% 22% 12% 4	2837
	11th to 20th	Day	49% 10% 14% 16% 8% 3	2840
	21st to end	Day	42% 8% 9% 19% 17% 6%	3256
February	1st to 10th	Day	34% 8% 11% 26% 18% 3	1900
	11th to 20th	Day	27% 7% 12% 27% 21% 5%	1969
	21st to end	Day	28% 7% 10% 24% 24% 7%	1727
March	1st to 10th	Day	30% 14% 17% 25% 12% 2	3435
	11th to 20th	Day	20% 12% 20% 36% 10% 3	3480
	21st to end	Day	29% 8% 10% 28% 20% 5%	3815
April	1st to 10th	Day	25% 9% 16% 33% 14% 3	2090
	11th to 20th	Day	29% 10% 18% 23% 17% 3	2126
	21st to end	Day	28% 9% 14% 25% 19% 4	2280
May	1st to 10th	Day	17% 10% 13% 35% 23% 3	3800
	11th to 20th	Day	29% 9% 18% 37% 6%	3786
	21st to end	Day	33% 16% 13% 29% 8% 1	4489
June	1st to 10th	Day	57% 15% 15% 10% 2	2470
	11th to 20th	Day	54% 17% 18% 10% 1	2470
	21st to end	Day	52% 18% 22% 8% 1	2470
July	1st to 10th	Day	36% 17% 31% 17%	4055
	11th to 20th	Day	37% 16% 37% 9%	4051
	21st to end	Day	29% 19% 36% 16% 1	4324
August	1st to 10th	Day	43% 18% 28% 10% 2	4004
	11th to 20th	Day	40% 18% 29% 13% 1	3709
	21st to end	Day	43% 18% 32% 7% 1	3828
September	1st to 10th	Day	46% 21% 21% 11% 1	2090
	11th to 20th	Day	54% 19% 17% 9% 1	2090
	21st to end	Day	53% 16% 13% 12% 5%	2090
October	1st to 10th	Day	46% 13% 20% 16% 5% 1	3357
	11th to 20th	Day	49% 13% 16% 14% 7% 1	3140
	21st to end	Day	38% 8% 10% 26% 14% 3	3428
November	1st to 10th	Day	35% 9% 13% 18% 19% 5%	1957
	11th to 20th	Day	42% 10% 9% 19% 16% 4	2000
	21st to end	Day	36% 9% 12% 18% 21% 4	2000
December	1st to 10th	Day	32% 9% 13% 24% 20% 2	1966
	11th to 20th	Day	35% 8% 12% 21% 18% 7%	2150
	21st to end	Day	44% 9% 15% 16% 14% 2	3124
January	1st to 10th	Night	35% 10% 15% 22% 15% 3	4109
	11th to 20th	Night	51% 9% 13% 17% 7% 2	4120
	21st to end	Night	40% 8% 10% 21% 17% 4	4396
February	1st to 10th	Night	30% 7% 13% 27% 19% 3	2280
	11th to 20th	Night	23% 7% 12% 27% 22% 8%	2104
	21st to end	Night	20% 6% 13% 26% 27% 8%	1727
March	1st to 10th	Night	33% 11% 15% 26% 12% 3	3418
	11th to 20th	Night	17% 8% 26% 35% 12% 2	3480
	21st to end	Night	22% 7% 14% 27% 24% 6%	3817
April	1st to 10th	Night	20% 7% 18% 37% 16% 3	2090
	11th to 20th	Night	24% 8% 20% 27% 19% 3	2002
	21st to end	Night	25% 8% 16% 28% 20% 3	1900
May	1st to 10th	Night	12% 8% 18% 43% 15% 3	3160
	11th to 20th	Night	24% 10% 19% 37% 10%	3131
	21st to end	Night	23% 10% 21% 36% 10%	3095
June	1st to 10th	Night	48% 13% 20% 15% 3	1710
	11th to 20th	Night	38% 17% 25% 17% 3	1710
	21st to end	Night	36% 18% 37% 10%	1710
July	1st to 10th	Night	29% 15% 38% 18%	2795
	11th to 20th	Night	29% 16% 43% 12%	2786
	21st to end	Night	26% 17% 39% 16% 1	2988
August	1st to 10th	Night	35% 17% 32% 14% 2	2868
	11th to 20th	Night	31% 15% 37% 15% 1	3177
	21st to end	Night	36% 20% 37% 7%	3828
September	1st to 10th	Night	33% 21% 31% 13% 1	2090
	11th to 20th	Night	44% 19% 25% 10% 1	2090
	21st to end	Night	45% 17% 20% 13% 5%	2090
October	1st to 10th	Night	43% 15% 21% 17% 3 1	3600
	11th to 20th	Night	49% 12% 19% 12% 8% 1	3779
	21st to end	Night	38% 8% 13% 25% 14% 3	4120
November	1st to 10th	Night	32% 9% 15% 24% 16% 5%	2341
	11th to 20th	Night	39% 8% 12% 24% 13% 4	2400
	21st to end	Night	30% 8% 15% 24% 19% 5%	2400
December	1st to 10th	Night	28% 10% 15% 28% 17% 3	2391
	11th to 20th	Night	32% 6% 12% 23% 19% 8%	3044
	21st to end	Night	44% 10% 14% 16% 14% 2	4532

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	9% 5% 33% 39% 13% 1	270
	11th to 20th	Day	14% 8% 31% 36% 10% 1	270
	21st to end	Day	9% 8% 40% 34% 8%	297
February	1st to 10th	Day	7% 7% 34% 39% 13%	270
	11th to 20th	Day	8% 3 25% 40% 21% 3	382
	21st to end	Day	4 5% 20% 42% 26% 2	382
March	1st to 10th	Day	7% 5% 30% 41% 15% 2	460
	11th to 20th	Day	5% 4 30% 36% 21% 4	460
	21st to end	Day	6% 3 25% 39% 22% 6%	506
April	1st to 10th	Day	5% 3 30% 38% 18% 6%	460
	11th to 20th	Day	4 2 29% 37% 18% 10%	452
	21st to end	Day	6% 1 24% 37% 23% 10%	460
May	1st to 10th	Day	4 1 16% 36% 28% 15%	463
	11th to 20th	Day	10% 2 17% 33% 23% 15%	487
	21st to end	Day	9% 3 6% 29% 29% 24%	529
June	1st to 10th	Day	14% 2 6% 27% 31% 20%	490
	11th to 20th	Day	10% 2 4 22% 28% 33%	490
	21st to end	Day	6% 2 1 14% 32% 46%	490
July	1st to 10th	Day	5% 2 1 14% 27% 50%	485
	11th to 20th	Day	5% 2 1 14% 36% 42%	484
	21st to end	Day	5% 1 1 13% 34% 46%	532
August	1st to 10th	Day	6% 1 2 17% 32% 41%	486
	11th to 20th	Day	5% 1 1 16% 33% 44%	479
	21st to end	Day	7% 2 4 21% 32% 34%	539
September	1st to 10th	Day	6% 3 3 16% 31% 42%	490
	11th to 20th	Day	8% 2 2 13% 32% 43%	490
	21st to end	Day	9% 3 4 20% 31% 33%	490
October	1st to 10th	Day	9% 2 7% 33% 33% 15%	490
	11th to 20th	Day	12% 3 9% 31% 31% 15%	490
	21st to end	Day	8% 3 17% 35% 27% 9%	539
November	1st to 10th	Day	8% 4 21% 36% 24% 7%	495
	11th to 20th	Day	12% 1 22% 35% 25% 6%	500
	21st to end	Day	8% 3 19% 39% 26% 4	500
December	1st to 10th	Day	8% 3 19% 38% 27% 4	478
	11th to 20th	Day	10% 3 24% 38% 21% 5%	270
	21st to end	Day	9% 5% 26% 38% 18% 3	297
January	1st to 10th	Night	8% 3 18% 41% 26% 3	760
	11th to 20th	Night	10% 3 22% 43% 21% 1	760
	21st to end	Night	8% 5% 25% 43% 18% 1	836
February	1st to 10th	Night	9% 3 19% 44% 25% 1	760
	11th to 20th	Night	6% 1 23% 44% 23% 2	743
	21st to end	Night	5% 2 18% 47% 27% 1	628
March	1st to 10th	Night	6% 3 24% 44% 21% 2	760
	11th to 20th	Night	5% 2 18% 46% 27% 2	760
	21st to end	Night	6% 2 23% 44% 24% 2	836
April	1st to 10th	Night	5% 1 16% 50% 25% 2	760
	11th to 20th	Night	6% 2 18% 47% 25% 1	751
	21st to end	Night	6% 1 15% 49% 26% 2	760
May	1st to 10th	Night	4 1 12% 45% 35% 4	760
	11th to 20th	Night	11% 1 12% 40% 33% 4	749
	21st to end	Night	8% 1 5% 26% 47% 14%	625
June	1st to 10th	Night	15% 1 2 24% 42% 16%	570
	11th to 20th	Night	10% 1 1 10% 45% 33%	570
	21st to end	Night	4 1 8% 44% 42%	570
July	1st to 10th	Night	4 2 5% 46% 42%	555
	11th to 20th	Night	5% 1 8% 43% 43%	552
	21st to end	Night	4 1 7% 40% 48%	624
August	1st to 10th	Night	6% 1 1 7% 48% 36%	595
	11th to 20th	Night	3 2 1 11% 44% 39%	750
	21st to end	Night	8% 1 3 15% 44% 29%	836
September	1st to 10th	Night	5% 2 3 11% 41% 39%	760
	11th to 20th	Night	8% 2 2 13% 41% 35%	760
	21st to end	Night	10% 2 3 14% 41% 30%	760
October	1st to 10th	Night	12% 1 5% 29% 39% 14%	760
	11th to 20th	Night	9% 1 8% 30% 40% 13%	760
	21st to end	Night	12% 1 13% 36% 31% 8%	836
November	1st to 10th	Night	9% 2 18% 34% 34% 3	780
	11th to 20th	Night	12% 2 14% 32% 35% 5%	800
	21st to end	Night	8% 2 15% 42% 29% 4	800
December	1st to 10th	Night	8% 3 13% 41% 33% 3	795
	11th to 20th	Night	10% 3 14% 38% 30% 5%	760
	21st to end	Night	8% 2 19% 36% 31% 4	836

Page generated at 2024-12-06 03:54:48. Version ac07

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