Robinson Lunar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robinson Lunar Observatory clear sky chart from 2005-11-06 to 2024-07-16.

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	12% 7% 3 6% 4 4 4 3 5% 7% 45%	89663
	Night	12% 7% 3 6% 4 4 4 3 5% 6% 48%	89854
Transparency	Day	39% 5% 12% 26% 16% 2	89437
	Night	37% 4 11% 26% 18% 3	89685
Seeing	Day	15% 8% 28% 28% 16% 4	15245
	Night	14% 8% 31% 34% 12% 1	25129

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	16% 9% 3 9% 4 4 3 3 5% 6% 37%	2847
	11th to 20th	Day	11% 10% 5% 9% 6% 6% 6% 2 3 4 39%	2850
	21st to end	Day	15% 16% 6% 8% 4 3 3 3 4 5% 34%	3135
February	1st to 10th	Day	15% 10% 4 7% 5% 3 3 2 4 6% 39%	1710
	11th to 20th	Day	12% 11% 3 8% 4 4 3 3 5% 6% 42%	1664
	21st to end	Day	11% 10% 3 6% 4 3 4 4 6% 6% 44%	1622
March	1st to 10th	Day	14% 9% 2 6% 4 2 3 3 4 6% 48%	3436
	11th to 20th	Day	12% 7% 2 4 2 3 3 3 4 6% 52%	3480
	21st to end	Day	16% 12% 4 7% 4 4 4 3 5% 5% 36%	3814
April	1st to 10th	Day	14% 7% 3 6% 5% 3 3 2 5% 6% 46%	2185
	11th to 20th	Day	14% 9% 2 6% 5% 4 4 4 5% 6% 41%	2254
	21st to end	Day	19% 8% 2 6% 4 4 5% 3 5% 6% 37%	2432
May	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 6% 40%	4082
	11th to 20th	Day	17% 7% 3 7% 4 4 4 3 5% 7% 39%	4082
	21st to end	Day	13% 6% 2 6% 4 4 4 3 6% 7% 45%	4535
June	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 48%	2660
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 9% 48%	2660
	21st to end	Day	7% 3 1 5% 4 4 5% 4 6% 8% 52%	2626
July	1st to 10th	Day	9% 5% 2 5% 4 4 4 4 7% 9% 45%	2470
	11th to 20th	Day	4 4 1 4 4 4 5% 5% 8% 8% 52%	2407
	21st to end	Day	8% 5% 2 5% 5% 5% 6% 5% 7% 9% 45%	2546
August	1st to 10th	Day	7% 4 2 6% 4 5% 6% 4 7% 11% 45%	2328
	11th to 20th	Day	9% 5% 2 5% 4 4 3 4 6% 8% 51%	2301
	21st to end	Day	8% 4 2 5% 3 4 5% 3 5% 7% 54%	2441
September	1st to 10th	Day	13% 5% 1 5% 3 3 4 3 5% 7% 52%	2160
	11th to 20th	Day	9% 5% 3 5% 4 4 5% 4 5% 7% 50%	1980
	21st to end	Day	9% 4 2 5% 4 3 3 3 5% 6% 56%	1977
October	1st to 10th	Day	13% 5% 2 5% 3 3 3 3 6% 7% 51%	1800
	11th to 20th	Day	13% 7% 2 4 3 3 2 3 4 4 56%	1800
	21st to end	Day	15% 7% 3 5% 3 3 3 2 5% 5% 48%	1980
November	1st to 10th	Day	10% 5% 2 5% 3 4 3 3 5% 6% 55%	1840
	11th to 20th	Day	13% 6% 2 5% 3 3 3 3 4 6% 51%	1655
	21st to end	Day	15% 9% 3 5% 4 3 2 2 3 6% 49%	1520
December	1st to 10th	Day	9% 8% 2 6% 6% 4 3 2 5% 8% 46%	1520
	11th to 20th	Day	12% 10% 3 8% 4 4 3 3 4 5% 41%	1918
	21st to end	Day	16% 16% 7% 12% 4 4 4 3 3 6% 26%	2946
January	1st to 10th	Night	9% 9% 4 15% 6% 4 4 3 3 5% 40%	4108
	11th to 20th	Night	11% 10% 4 8% 4 7% 5% 4 5% 5% 38%	4120
	21st to end	Night	16% 13% 5% 10% 4 3 3 2 4 5% 35%	4532
February	1st to 10th	Night	11% 11% 3 7% 6% 5% 3 3 4 7% 39%	2470
	11th to 20th	Night	12% 9% 3 7% 4 4 4 3 4 5% 44%	2403
	21st to end	Night	12% 7% 4 6% 5% 3 3 3 4 5% 47%	1847
March	1st to 10th	Night	12% 8% 3 5% 3 3 3 3 3 5% 51%	3419
	11th to 20th	Night	11% 7% 1 4 3 2 3 2 4 7% 55%	3480
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 6% 38%	3817
April	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 5% 6% 50%	1995
	11th to 20th	Night	13% 8% 2 6% 4 3 4 2 4 6% 47%	1875
	21st to end	Night	17% 7% 2 6% 4 3 4 3 4 6% 43%	1743
May	1st to 10th	Night	15% 6% 3 6% 5% 4 4 4 6% 7% 40%	2823
	11th to 20th	Night	16% 6% 2 6% 4 3 3 3 5% 8% 43%	2823
	21st to end	Night	12% 5% 2 5% 3 3 3 4 5% 7% 53%	3027
June	1st to 10th	Night	6% 3 2 3 4 3 4 4 6% 10% 56%	1520
	11th to 20th	Night	5% 2 2 6% 3 4 5% 5% 7% 9% 53%	1520
	21st to end	Night	5% 3 1 4 2 3 4 3 6% 8% 62%	1546
July	1st to 10th	Night	7% 3 1 5% 4 4 4 5% 7% 8% 53%	1710
	11th to 20th	Night	3 2 1 3 3 3 3 4 6% 11% 61%	1674
	21st to end	Night	6% 4 2 4 4 3 5% 4 8% 9% 50%	1772
August	1st to 10th	Night	4 2 1 3 3 4 5% 5% 7% 10% 55%	1611
	11th to 20th	Night	6% 4 2 4 4 3 4 3 5% 9% 58%	1600
	21st to end	Night	6% 4 1 5% 4 3 3 3 5% 7% 60%	1913
September	1st to 10th	Night	10% 5% 2 4 3 3 3 3 4 5% 56%	1800
	11th to 20th	Night	9% 4 1 4 3 4 4 3 5% 7% 55%	1975
	21st to end	Night	6% 4 2 5% 3 4 3 4 4 6% 59%	1980
October	1st to 10th	Night	12% 5% 1 4 3 4 3 3 5% 4 57%	2144
	11th to 20th	Night	14% 4 2 4 2 3 3 2 4 6% 57%	2160
	21st to end	Night	15% 7% 3 5% 3 3 3 3 3 4 52%	2376
November	1st to 10th	Night	9% 4 2 4 3 3 3 3 4 6% 61%	2234
	11th to 20th	Night	11% 6% 2 4 4 3 3 3 5% 6% 55%	2522
	21st to end	Night	14% 8% 2 4 3 2 3 3 4 5% 52%	2660
December	1st to 10th	Night	10% 8% 3 6% 4 4 5% 3 5% 6% 46%	2660
	11th to 20th	Night	12% 9% 3 7% 3 3 3 3 5% 6% 46%	3279
	21st to end	Night	19% 17% 5% 10% 4 4 3 3 3 4 30%	4716

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	48% 5% 10% 24% 11% 1	2848
	11th to 20th	Day	51% 3 13% 21% 11% 1	2850
	21st to end	Day	54% 4 10% 18% 13% 1	3135
February	1st to 10th	Day	48% 4 13% 22% 11% 3	1710
	11th to 20th	Day	44% 3 12% 24% 15% 2	1673
	21st to end	Day	40% 4 11% 25% 16% 4	1622
March	1st to 10th	Day	38% 4 11% 22% 22% 3	3436
	11th to 20th	Day	32% 5% 12% 27% 20% 3	3480
	21st to end	Day	49% 6% 13% 24% 6% 1	3814
April	1st to 10th	Day	40% 3 13% 23% 19% 2	2185
	11th to 20th	Day	43% 4 12% 23% 16% 1	2254
	21st to end	Day	48% 4 11% 25% 11% 1	2432
May	1st to 10th	Day	45% 7% 10% 23% 14% 2	4120
	11th to 20th	Day	43% 7% 13% 23% 15%	4086
	21st to end	Day	38% 6% 11% 31% 13% 2	4548
June	1st to 10th	Day	29% 7% 17% 30% 16% 2	2660
	11th to 20th	Day	30% 7% 15% 30% 17% 2	2660
	21st to end	Day	28% 6% 15% 31% 17% 4	2626
July	1st to 10th	Day	33% 7% 16% 25% 17% 3	2406
	11th to 20th	Day	25% 8% 15% 28% 20% 4	2338
	21st to end	Day	31% 6% 15% 31% 16% 1	2405
August	1st to 10th	Day	32% 7% 18% 28% 13% 2	2314
	11th to 20th	Day	30% 6% 13% 32% 18% 2	2301
	21st to end	Day	28% 6% 12% 27% 20% 7%	2441
September	1st to 10th	Day	33% 4 12% 28% 18% 6%	2160
	11th to 20th	Day	33% 5% 11% 26% 22% 3	1980
	21st to end	Day	29% 4 9% 32% 24% 3	1977
October	1st to 10th	Day	32% 4 12% 29% 20% 2	1800
	11th to 20th	Day	33% 3 6% 29% 24% 5%	1800
	21st to end	Day	39% 3 11% 23% 19% 5%	1980
November	1st to 10th	Day	30% 4 13% 30% 19% 5%	1840
	11th to 20th	Day	35% 3 10% 28% 21% 3	1655
	21st to end	Day	40% 3 9% 27% 21% 1	1520
December	1st to 10th	Day	38% 3 14% 30% 14% 1	1520
	11th to 20th	Day	45% 4 13% 27% 10% 1	1915
	21st to end	Day	62% 4 10% 16% 7% 1	2946
January	1st to 10th	Night	47% 4 14% 21% 12% 1	4108
	11th to 20th	Night	48% 4 12% 22% 13% 1	4120
	21st to end	Night	53% 4 13% 19% 10% 1	4532
February	1st to 10th	Night	46% 4 11% 22% 15% 3	2470
	11th to 20th	Night	42% 3 12% 23% 17% 3	2404
	21st to end	Night	39% 3 9% 22% 20% 6%	1847
March	1st to 10th	Night	36% 4 9% 26% 22% 3	3419
	11th to 20th	Night	29% 4 9% 28% 26% 5%	3480
	21st to end	Night	46% 6% 16% 24% 7% 1	3817
April	1st to 10th	Night	35% 4 11% 25% 22% 4	1995
	11th to 20th	Night	39% 4 8% 28% 18% 3	1875
	21st to end	Night	43% 5% 11% 25% 15% 1	1743
May	1st to 10th	Night	41% 8% 13% 21% 16% 2	2850
	11th to 20th	Night	39% 6% 12% 27% 15% 1	2824
	21st to end	Night	30% 6% 12% 32% 19% 2	3035
June	1st to 10th	Night	23% 7% 17% 33% 16% 4	1520
	11th to 20th	Night	25% 7% 15% 32% 19% 2	1520
	21st to end	Night	19% 5% 14% 37% 21% 4	1546
July	1st to 10th	Night	27% 6% 15% 32% 17% 4	1665
	11th to 20th	Night	17% 5% 15% 36% 23% 4	1620
	21st to end	Night	26% 5% 13% 34% 21% 1	1673
August	1st to 10th	Night	22% 7% 18% 35% 15% 3	1601
	11th to 20th	Night	24% 5% 13% 34% 22% 2	1600
	21st to end	Night	25% 3 11% 30% 24% 8%	1913
September	1st to 10th	Night	30% 5% 8% 29% 19% 8%	1800
	11th to 20th	Night	28% 4 11% 27% 26% 5%	1975
	21st to end	Night	26% 4 7% 28% 30% 4	1980
October	1st to 10th	Night	31% 3 9% 26% 25% 6%	2144
	11th to 20th	Night	31% 2 6% 29% 23% 8%	2160
	21st to end	Night	38% 3 8% 23% 25% 4	2376
November	1st to 10th	Night	26% 4 12% 28% 25% 6%	2234
	11th to 20th	Night	31% 3 10% 28% 24% 4	2522
	21st to end	Night	36% 2 9% 30% 19% 3	2660
December	1st to 10th	Night	39% 4 12% 28% 16% 1	2660
	11th to 20th	Night	39% 3 11% 31% 15% 1	3281
	21st to end	Night	60% 4 7% 19% 9% 2	4716

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	23% 12% 34% 24% 6%	270
	11th to 20th	Day	24% 17% 37% 20% 3	270
	21st to end	Day	18% 11% 42% 26% 3	297
February	1st to 10th	Day	23% 17% 39% 19% 3 1	270
	11th to 20th	Day	19% 17% 43% 14% 7%	270
	21st to end	Day	18% 24% 40% 13% 4	225
March	1st to 10th	Day	18% 15% 44% 19% 3	270
	11th to 20th	Day	27% 12% 36% 19% 4 1	270
	21st to end	Day	31% 18% 31% 15% 4 1	297
April	1st to 10th	Day	24% 13% 36% 19% 7%	365
	11th to 20th	Day	18% 13% 37% 23% 8% 1	452
	21st to end	Day	24% 13% 33% 20% 10%	612
May	1st to 10th	Day	21% 11% 36% 24% 8% 1	653
	11th to 20th	Day	21% 6% 27% 29% 15% 3	675
	21st to end	Day	18% 6% 28% 26% 17% 4	734
June	1st to 10th	Day	7% 3 21% 36% 25% 8%	680
	11th to 20th	Day	8% 3 26% 36% 20% 6%	680
	21st to end	Day	8% 5% 33% 36% 15% 3	680
July	1st to 10th	Day	10% 3 15% 31% 28% 13%	671
	11th to 20th	Day	5% 1 17% 39% 30% 8%	645
	21st to end	Day	9% 1 14% 36% 32% 8%	684
August	1st to 10th	Day	8% 1 16% 39% 31% 5%	626
	11th to 20th	Day	9% 2 13% 37% 30% 8%	615
	21st to end	Day	9% 1 13% 33% 34% 11%	560
September	1st to 10th	Day	15% 2 14% 36% 26% 7%	450
	11th to 20th	Day	7% 1 21% 39% 24% 7%	270
	21st to end	Day	14% 6% 24% 35% 16% 5%	270
October	1st to 10th	Day	17% 6% 26% 26% 19% 6%	270
	11th to 20th	Day	13% 16% 42% 21% 7% 1	270
	21st to end	Day	22% 13% 36% 20% 8% 2	297
November	1st to 10th	Day	16% 8% 39% 27% 7% 4	270
	11th to 20th	Day	16% 16% 33% 24% 8% 2	270
	21st to end	Day	24% 11% 35% 21% 9%	270
December	1st to 10th	Day	9% 13% 42% 27% 7% 3	270
	11th to 20th	Day	21% 11% 36% 23% 8% 1	270
	21st to end	Day	20% 21% 39% 18% 2	297
January	1st to 10th	Night	13% 11% 38% 31% 7%	950
	11th to 20th	Night	16% 12% 37% 27% 6% 1	950
	21st to end	Night	16% 11% 39% 30% 4	1045
February	1st to 10th	Night	19% 11% 40% 27% 3	950
	11th to 20th	Night	16% 12% 39% 28% 4	929
	21st to end	Night	19% 11% 42% 23% 5% 1	591
March	1st to 10th	Night	15% 12% 43% 24% 6%	570
	11th to 20th	Night	21% 8% 34% 30% 6% 1	570
	21st to end	Night	26% 10% 35% 25% 4	627
April	1st to 10th	Night	14% 12% 40% 28% 6%	570
	11th to 20th	Night	19% 10% 35% 30% 5%	563
	21st to end	Night	20% 6% 37% 29% 7% 1	570
May	1st to 10th	Night	17% 6% 34% 35% 8% 1	570
	11th to 20th	Night	18% 3 29% 36% 14% 1	561
	21st to end	Night	11% 5% 27% 37% 17% 2	617
June	1st to 10th	Night	6% 3 21% 44% 24% 1	570
	11th to 20th	Night	6% 3 26% 45% 19% 2	570
	21st to end	Night	6% 3 31% 44% 15% 1	570
July	1st to 10th	Night	8% 13% 44% 31% 3	555
	11th to 20th	Night	3 1 15% 47% 31% 3	540
	21st to end	Night	7% 1 12% 48% 30% 2	591
August	1st to 10th	Night	5% 1 13% 48% 31% 2	537
	11th to 20th	Night	7% 2 12% 45% 31% 2	534
	21st to end	Night	6% 1 12% 43% 34% 3	594
September	1st to 10th	Night	14% 1 16% 42% 23% 4	540
	11th to 20th	Night	10% 1 20% 41% 25% 3	540
	21st to end	Night	9% 4 19% 49% 16% 3	540
October	1st to 10th	Night	13% 4 28% 32% 20% 2	704
	11th to 20th	Night	16% 8% 38% 29% 8%	720
	21st to end	Night	20% 10% 33% 28% 9%	792
November	1st to 10th	Night	11% 8% 35% 33% 12% 1	754
	11th to 20th	Night	14% 12% 36% 29% 8%	950
	21st to end	Night	18% 10% 34% 31% 6%	950
December	1st to 10th	Night	15% 10% 37% 31% 7% 1	950
	11th to 20th	Night	20% 7% 39% 28% 5%	950
	21st to end	Night	20% 14% 35% 26% 4	1045

Page generated at 2024-07-13 09:19:48. Version ac07

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