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 2024-12-24.

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	12% 7% 3 6% 4 4 4 3 5% 7% 46%	101406
	Night	11% 7% 2 6% 4 4 4 3 5% 6% 48%	98791
Transparency	Day	37% 5% 12% 26% 17% 3	105057
	Night	35% 4 11% 27% 19% 3	103280
Seeing	Day	15% 8% 28% 28% 16% 4	15822
	Night	14% 8% 31% 34% 12% 1	25740

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	11% 6% 2 6% 4 5% 5% 4 7% 9% 41%	4120
	11th to 20th	Day	5% 4 1 4 3 3 4 4 8% 9% 53%	4120
	21st to end	Day	6% 4 1 5% 4 5% 6% 5% 7% 10% 47%	4465
August	1st to 10th	Day	5% 4 2 5% 4 4 5% 3 6% 10% 53%	4104
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 8% 47%	4041
	21st to end	Day	6% 3 2 5% 3 4 4 3 5% 8% 56%	4287
September	1st to 10th	Day	12% 4 1 5% 3 3 4 2 5% 7% 53%	2280
	11th to 20th	Day	9% 5% 3 6% 4 4 5% 4 5% 7% 49%	2090
	21st to end	Day	9% 4 2 5% 4 3 3 3 5% 6% 55%	2086
October	1st to 10th	Day	12% 5% 1 5% 3 3 3 3 6% 6% 54%	1900
	11th to 20th	Day	12% 6% 2 4 3 3 2 3 4 4 57%	1900
	21st to end	Day	15% 7% 3 5% 3 3 3 2 5% 5% 49%	2090
November	1st to 10th	Day	10% 6% 2 5% 3 4 3 3 5% 6% 54%	1939
	11th to 20th	Day	14% 6% 2 4 3 3 3 4 4 6% 51%	1742
	21st to end	Day	15% 9% 3 5% 3 3 2 2 3 6% 49%	1600
December	1st to 10th	Day	9% 8% 2 6% 6% 4 3 2 5% 8% 47%	1600
	11th to 20th	Day	12% 10% 3 8% 4 5% 3 3 4 5% 42%	1998
	21st to end	Day	16% 16% 7% 12% 4 4 4 3 3 6% 26%	2970
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	11% 6% 2 6% 4 4 4 3 5% 6% 49%	2850
	11th to 20th	Night	3 2 1 3 3 3 4 4 6% 10% 61%	2850
	21st to end	Night	6% 4 1 4 4 4 5% 4 9% 11% 49%	3098
August	1st to 10th	Night	3 1 1 3 3 4 4 5% 7% 10% 60%	2836
	11th to 20th	Night	11% 6% 2 5% 4 3 4 3 4 8% 51%	2798
	21st to end	Night	4 3 2 5% 4 3 4 3 6% 7% 59%	3370
September	1st to 10th	Night	10% 5% 2 4 3 3 3 3 3 5% 57%	1900
	11th to 20th	Night	8% 4 1 4 3 4 4 3 5% 7% 55%	2085
	21st to end	Night	6% 4 2 4 3 4 3 4 4 6% 59%	2090
October	1st to 10th	Night	11% 4 1 4 2 3 3 3 5% 4 59%	2264
	11th to 20th	Night	14% 4 2 4 2 3 3 2 4 6% 58%	2280
	21st to end	Night	14% 7% 3 5% 3 3 3 3 3 4 52%	2508
November	1st to 10th	Night	10% 5% 2 4 3 3 3 3 4 6% 61%	2355
	11th to 20th	Night	11% 6% 2 4 4 3 3 3 5% 5% 55%	2655
	21st to end	Night	14% 8% 2 4 3 2 3 3 4 5% 52%	2800
December	1st to 10th	Night	10% 8% 3 6% 4 4 5% 3 5% 5% 47%	2800
	11th to 20th	Night	12% 8% 3 7% 3 3 3 3 5% 6% 46%	3419
	21st to end	Night	19% 17% 5% 9% 4 4 3 3 3 4 30%	4765

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	39% 6% 14% 22% 17% 3	4056
	11th to 20th	Day	25% 6% 12% 36% 19% 2	4051
	21st to end	Day	27% 8% 16% 33% 14% 2	4325
August	1st to 10th	Day	28% 5% 13% 29% 22% 3	4090
	11th to 20th	Day	35% 5% 17% 25% 17% 1	4080
	21st to end	Day	26% 5% 16% 33% 15% 6%	4286
September	1st to 10th	Day	31% 4 11% 28% 20% 6%	2280
	11th to 20th	Day	33% 5% 10% 27% 22% 3	2090
	21st to end	Day	30% 4 9% 31% 24% 3	2086
October	1st to 10th	Day	19% 3 7% 23% 42% 7%	3160
	11th to 20th	Day	20% 2 4 28% 37% 10%	3140
	21st to end	Day	32% 3 11% 26% 25% 3	3428
November	1st to 10th	Day	31% 4 12% 29% 19% 5%	1939
	11th to 20th	Day	35% 3 9% 28% 21% 4	1742
	21st to end	Day	40% 3 9% 28% 20% 1	1600
December	1st to 10th	Day	37% 3 14% 31% 14% 1	1600
	11th to 20th	Day	45% 4 13% 28% 10% 1	1995
	21st to end	Day	61% 4 10% 16% 7% 1	2970
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	36% 4 11% 25% 20% 4	2805
	11th to 20th	Night	18% 4 14% 37% 23% 3	2796
	21st to end	Night	25% 6% 19% 32% 16% 1	2999
August	1st to 10th	Night	18% 6% 19% 28% 24% 5%	2826
	11th to 20th	Night	33% 4 13% 29% 20% 2	2825
	21st to end	Night	25% 4 12% 38% 17% 5%	3370
September	1st to 10th	Night	30% 5% 8% 28% 21% 9%	1900
	11th to 20th	Night	28% 4 10% 27% 26% 4	2085
	21st to end	Night	27% 4 7% 28% 30% 4	2090
October	1st to 10th	Night	19% 2 6% 19% 47% 7%	3784
	11th to 20th	Night	21% 2 5% 28% 31% 13%	3779
	21st to end	Night	34% 3 6% 30% 25% 2	4120
November	1st to 10th	Night	27% 3 12% 28% 24% 6%	2355
	11th to 20th	Night	31% 3 9% 27% 24% 5%	2655
	21st to end	Night	35% 2 10% 31% 19% 3	2800
December	1st to 10th	Night	38% 4 12% 29% 16% 1	2800
	11th to 20th	Night	39% 3 11% 30% 15% 1	3421
	21st to end	Night	59% 4 7% 20% 9% 2	4765

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 18% 38% 29% 8%	668
	21st to end	Day	9% 1 15% 35% 31% 9%	739
August	1st to 10th	Day	7% 1 17% 39% 30% 5%	676
	11th to 20th	Day	10% 3 16% 36% 28% 7%	665
	21st to end	Day	9% 1 14% 32% 34% 10%	607
September	1st to 10th	Day	14% 2 14% 36% 27% 7%	490
	11th to 20th	Day	7% 2 21% 40% 24% 6%	300
	21st to end	Day	14% 6% 24% 35% 15% 5%	300
October	1st to 10th	Day	15% 6% 27% 27% 19% 7%	300
	11th to 20th	Day	12% 15% 40% 24% 8% 1	300
	21st to end	Day	20% 15% 36% 20% 8% 2	330
November	1st to 10th	Day	16% 11% 37% 26% 6% 4	300
	11th to 20th	Day	18% 17% 32% 23% 8% 2	300
	21st to end	Day	24% 12% 35% 21% 8%	300
December	1st to 10th	Day	8% 14% 43% 25% 7% 3	300
	11th to 20th	Day	21% 14% 35% 22% 7% 1	300
	21st to end	Day	20% 20% 39% 18% 3	306
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 14% 48% 30% 3	552
	21st to end	Night	7% 1 12% 47% 30% 3	624
August	1st to 10th	Night	5% 1 13% 48% 31% 2	567
	11th to 20th	Night	8% 2 13% 45% 30% 2	564
	21st to end	Night	6% 1 13% 45% 33% 3	627
September	1st to 10th	Night	13% 1 16% 42% 24% 4	570
	11th to 20th	Night	10% 1 20% 41% 25% 3	570
	21st to end	Night	9% 4 19% 49% 16% 2	570
October	1st to 10th	Night	13% 4 28% 32% 22% 1	744
	11th to 20th	Night	16% 7% 39% 30% 8%	760
	21st to end	Night	19% 10% 33% 28% 9%	836
November	1st to 10th	Night	12% 9% 34% 33% 11% 1	795
	11th to 20th	Night	15% 13% 36% 29% 8%	1000
	21st to end	Night	18% 10% 35% 31% 6%	1000
December	1st to 10th	Night	15% 11% 36% 32% 6% 1	1000
	11th to 20th	Night	20% 8% 39% 28% 5%	1000
	21st to end	Night	20% 14% 35% 27% 5%	1063

Page generated at 2024-12-21 03:13:46. Version ac07

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