Martin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Martin Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	14% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	101261
	Night	14% 7% 3 6% 5% 4 5% 4 6% 8% 39%	97835
Transparency	Day	43% 8% 12% 21% 13% 3	104937
	Night	41% 8% 13% 22% 14% 3	102298
Seeing	Day	21% 14% 24% 22% 14% 6%	15254
	Night	18% 13% 22% 29% 16% 2	25326

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	17% 9% 3 6% 4 4 4 4 6% 8% 36%	2836
	11th to 20th	Day	14% 11% 4 9% 7% 5% 5% 4 6% 5% 31%	2840
	21st to end	Day	20% 11% 4 7% 4 4 4 3 5% 5% 33%	3124
February	1st to 10th	Day	13% 9% 3 10% 5% 6% 4 3 5% 6% 35%	1710
	11th to 20th	Day	18% 8% 2 7% 5% 5% 4 3 6% 6% 34%	1741
	21st to end	Day	20% 9% 3 8% 5% 4 4 3 5% 6% 34%	1613
March	1st to 10th	Day	22% 9% 2 6% 4 4 4 4 6% 7% 33%	3435
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 3 4 6% 47%	3480
	21st to end	Day	17% 9% 3 7% 5% 4 4 3 5% 7% 36%	3815
April	1st to 10th	Day	11% 8% 3 7% 4 4 5% 3 5% 8% 42%	2133
	11th to 20th	Day	14% 7% 2 7% 5% 4 4 4 5% 6% 41%	2254
	21st to end	Day	17% 6% 3 7% 5% 4 5% 4 5% 7% 38%	2455
May	1st to 10th	Day	18% 9% 3 8% 6% 5% 6% 5% 7% 6% 27%	4082
	11th to 20th	Day	21% 8% 2 7% 6% 5% 5% 4 7% 9% 27%	4081
	21st to end	Day	10% 5% 2 7% 6% 5% 6% 5% 8% 10% 37%	4476
June	1st to 10th	Day	12% 6% 2 5% 6% 5% 5% 4 7% 10% 37%	2470
	11th to 20th	Day	9% 6% 3 6% 6% 5% 5% 6% 7% 10% 36%	2470
	21st to end	Day	9% 6% 2 7% 5% 6% 6% 5% 8% 11% 36%	2470
July	1st to 10th	Day	7% 4 2 7% 6% 7% 6% 6% 8% 10% 36%	4120
	11th to 20th	Day	9% 5% 2 7% 6% 5% 7% 6% 8% 11% 35%	4120
	21st to end	Day	15% 9% 4 10% 8% 7% 6% 5% 7% 7% 22%	4466
August	1st to 10th	Day	12% 7% 2 8% 6% 7% 6% 6% 8% 11% 27%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 7% 7% 6% 8% 12% 32%	4044
	21st to end	Day	6% 5% 2 6% 5% 4 5% 4 7% 10% 47%	4262
September	1st to 10th	Day	12% 5% 2 7% 5% 4 6% 4 6% 7% 42%	2198
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 4 5% 7% 37%	2090
	21st to end	Day	21% 7% 2 7% 5% 5% 4 4 5% 7% 33%	2090
October	1st to 10th	Day	16% 6% 2 5% 3 3 3 3 5% 6% 48%	1938
	11th to 20th	Day	15% 7% 2 5% 4 3 5% 3 5% 6% 45%	1900
	21st to end	Day	15% 7% 2 6% 4 4 4 3 4 6% 46%	2090
November	1st to 10th	Day	12% 6% 2 6% 3 3 4 2 5% 7% 49%	1947
	11th to 20th	Day	12% 9% 2 4 4 4 4 4 5% 7% 44%	1710
	21st to end	Day	16% 6% 2 6% 4 3 4 3 4 7% 45%	1710
December	1st to 10th	Day	16% 11% 3 8% 5% 4 5% 4 6% 6% 32%	1710
	11th to 20th	Day	17% 9% 3 6% 4 3 3 3 5% 7% 40%	2153
	21st to end	Day	19% 11% 3 7% 4 5% 6% 4 6% 7% 28%	3124
January	1st to 10th	Night	13% 10% 6% 7% 6% 5% 5% 4 7% 8% 29%	4109
	11th to 20th	Night	16% 9% 3 9% 6% 3 3 3 4 5% 39%	4120
	21st to end	Night	23% 11% 2 5% 4 3 4 3 4 6% 35%	4532
February	1st to 10th	Night	14% 9% 3 6% 4 4 5% 4 7% 7% 36%	2470
	11th to 20th	Night	19% 8% 3 6% 5% 6% 5% 4 5% 6% 33%	2323
	21st to end	Night	16% 7% 4 8% 5% 5% 4 4 6% 7% 34%	1839
March	1st to 10th	Night	23% 10% 3 6% 5% 4 5% 3 5% 5% 31%	3418
	11th to 20th	Night	11% 5% 3 6% 4 4 5% 4 6% 7% 44%	3480
	21st to end	Night	16% 6% 2 5% 4 3 4 4 5% 7% 44%	3817
April	1st to 10th	Night	13% 8% 2 6% 5% 4 4 3 6% 8% 39%	2047
	11th to 20th	Night	15% 5% 2 5% 4 4 4 3 5% 7% 45%	1875
	21st to end	Night	15% 7% 2 6% 4 4 4 3 4 7% 44%	1741
May	1st to 10th	Night	19% 8% 3 8% 5% 4 4 4 5% 8% 32%	2813
	11th to 20th	Night	23% 7% 3 7% 4 3 4 4 4 7% 34%	2812
	21st to end	Night	11% 5% 2 6% 5% 4 5% 4 7% 10% 41%	3079
June	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 5% 9% 11% 40%	1710
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 6% 10% 44%	1710
	21st to end	Night	9% 4 2 6% 4 5% 5% 5% 7% 11% 43%	1710
July	1st to 10th	Night	7% 5% 2 6% 5% 5% 6% 6% 7% 11% 40%	2840
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 5% 7% 12% 44%	2840
	21st to end	Night	11% 8% 3 9% 7% 6% 6% 5% 7% 9% 29%	3087
August	1st to 10th	Night	14% 8% 3 9% 5% 5% 5% 4 6% 10% 33%	2825
	11th to 20th	Night	10% 6% 2 6% 5% 5% 7% 5% 7% 10% 38%	2785
	21st to end	Night	7% 3 1 5% 4 4 4 4 6% 9% 52%	3348
September	1st to 10th	Night	11% 6% 2 6% 4 5% 5% 3 6% 7% 45%	1978
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 8% 42%	2090
	21st to end	Night	19% 7% 3 6% 4 4 4 3 4 5% 40%	2090
October	1st to 10th	Night	15% 7% 2 5% 4 3 3 3 6% 5% 47%	2241
	11th to 20th	Night	14% 7% 2 7% 4 4 4 3 5% 6% 47%	2280
	21st to end	Night	13% 5% 2 6% 3 4 4 3 5% 7% 48%	2508
November	1st to 10th	Night	14% 7% 3 4 4 3 4 4 4 6% 48%	2336
	11th to 20th	Night	13% 6% 2 4 4 3 4 3 6% 7% 46%	2468
	21st to end	Night	14% 6% 2 5% 5% 4 4 4 5% 7% 44%	2470
December	1st to 10th	Night	19% 10% 3 7% 4 4 4 3 6% 7% 33%	2470
	11th to 20th	Night	14% 7% 4 8% 5% 4 5% 4 5% 8% 36%	3042
	21st to end	Night	19% 10% 5% 7% 5% 5% 5% 4 5% 7% 28%	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	46% 6% 11% 23% 12% 2	2837
	11th to 20th	Day	51% 6% 10% 17% 14% 2	2840
	21st to end	Day	52% 6% 7% 17% 15% 2	3124
February	1st to 10th	Day	49% 5% 10% 20% 15% 2	1710
	11th to 20th	Day	49% 6% 11% 19% 13% 3	1750
	21st to end	Day	51% 5% 9% 15% 15% 4	1613
March	1st to 10th	Day	49% 6% 10% 21% 11% 4	3435
	11th to 20th	Day	37% 6% 9% 24% 18% 6%	3480
	21st to end	Day	47% 6% 10% 22% 13% 3	3815
April	1st to 10th	Day	39% 7% 11% 22% 16% 4	2133
	11th to 20th	Day	41% 6% 11% 22% 16% 4	2254
	21st to end	Day	45% 7% 11% 22% 12% 3	2455
May	1st to 10th	Day	52% 9% 11% 17% 9% 1	4120
	11th to 20th	Day	52% 8% 12% 21% 7% 1	4085
	21st to end	Day	37% 12% 17% 18% 13% 3	4489
June	1st to 10th	Day	40% 11% 15% 21% 13%	2470
	11th to 20th	Day	39% 12% 15% 18% 14% 2	2470
	21st to end	Day	39% 11% 15% 20% 13% 2	2470
July	1st to 10th	Day	38% 13% 19% 19% 8% 4	4055
	11th to 20th	Day	38% 11% 18% 24% 8% 1	4051
	21st to end	Day	57% 10% 11% 15% 7%	4324
August	1st to 10th	Day	46% 11% 18% 19% 6%	4091
	11th to 20th	Day	39% 12% 15% 23% 10% 1	4083
	21st to end	Day	31% 9% 17% 28% 13% 1	4262
September	1st to 10th	Day	39% 9% 13% 18% 17% 4	2198
	11th to 20th	Day	44% 8% 10% 22% 15% 1	2090
	21st to end	Day	50% 6% 11% 17% 14% 1	2090
October	1st to 10th	Day	29% 7% 9% 20% 27% 8%	3224
	11th to 20th	Day	27% 4 10% 24% 18% 16%	3140
	21st to end	Day	28% 5% 10% 27% 17% 13%	3428
November	1st to 10th	Day	34% 6% 10% 22% 23% 4	1947
	11th to 20th	Day	37% 6% 11% 21% 21% 4	1710
	21st to end	Day	39% 5% 12% 22% 20% 3	1710
December	1st to 10th	Day	50% 8% 11% 16% 13% 3	1710
	11th to 20th	Day	43% 4 11% 19% 20% 3	2150
	21st to end	Day	51% 7% 13% 19% 9% 1	3124
January	1st to 10th	Night	50% 7% 13% 15% 13% 2	4109
	11th to 20th	Night	47% 5% 9% 18% 16% 4	4120
	21st to end	Night	50% 6% 8% 23% 12% 2	4532
February	1st to 10th	Night	44% 7% 15% 19% 14% 1	2470
	11th to 20th	Night	49% 7% 10% 18% 13% 4	2325
	21st to end	Night	48% 7% 11% 20% 10% 4	1839
March	1st to 10th	Night	54% 6% 9% 19% 10% 2	3418
	11th to 20th	Night	37% 6% 10% 26% 18% 4	3480
	21st to end	Night	38% 7% 13% 22% 17% 3	3817
April	1st to 10th	Night	41% 7% 15% 20% 15% 3	2047
	11th to 20th	Night	37% 5% 13% 21% 19% 4	1875
	21st to end	Night	40% 6% 14% 26% 13% 1	1741
May	1st to 10th	Night	49% 10% 13% 19% 9% 1	2840
	11th to 20th	Night	49% 8% 13% 22% 7% 1	2813
	21st to end	Night	34% 12% 20% 23% 8% 3	3087
June	1st to 10th	Night	35% 12% 18% 22% 13% 1	1710
	11th to 20th	Night	34% 10% 18% 25% 12% 1	1710
	21st to end	Night	32% 12% 16% 24% 14% 2	1710
July	1st to 10th	Night	36% 13% 18% 20% 11% 2	2795
	11th to 20th	Night	31% 10% 21% 28% 7% 2	2786
	21st to end	Night	46% 13% 15% 20% 6%	2988
August	1st to 10th	Night	44% 11% 19% 20% 6%	2814
	11th to 20th	Night	37% 10% 17% 26% 10%	2812
	21st to end	Night	28% 8% 16% 34% 13% 1	3348
September	1st to 10th	Night	37% 10% 13% 19% 16% 4	1978
	11th to 20th	Night	40% 7% 13% 22% 17% 1	2090
	21st to end	Night	45% 7% 11% 21% 14% 2	2090
October	1st to 10th	Night	34% 6% 8% 21% 27% 4	3735
	11th to 20th	Night	27% 5% 9% 22% 23% 13%	3779
	21st to end	Night	23% 5% 10% 28% 20% 13%	4120
November	1st to 10th	Night	37% 6% 10% 21% 22% 4	2336
	11th to 20th	Night	36% 6% 10% 22% 21% 5%	2468
	21st to end	Night	38% 5% 10% 25% 17% 4	2470
December	1st to 10th	Night	49% 6% 12% 20% 11% 2	2470
	11th to 20th	Night	46% 6% 10% 20% 16% 2	3044
	21st to end	Night	53% 7% 13% 15% 12% 1	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	36% 29% 20% 11% 4	270
	11th to 20th	Day	40% 21% 29% 10% 1	270
	21st to end	Day	36% 25% 26% 11% 3	297
February	1st to 10th	Day	28% 26% 30% 13% 3	270
	11th to 20th	Day	45% 26% 22% 6% 1	270
	21st to end	Day	37% 25% 27% 9% 2	268
March	1st to 10th	Day	27% 26% 23% 18% 5%	460
	11th to 20th	Day	31% 25% 25% 15% 4 1	460
	21st to end	Day	27% 21% 29% 16% 5% 1	506
April	1st to 10th	Day	25% 26% 23% 17% 9%	460
	11th to 20th	Day	23% 20% 27% 17% 10% 3	452
	21st to end	Day	25% 19% 27% 16% 11% 2	460
May	1st to 10th	Day	21% 19% 30% 17% 8% 5%	463
	11th to 20th	Day	21% 11% 27% 22% 15% 5%	487
	21st to end	Day	15% 9% 24% 26% 18% 9%	529
June	1st to 10th	Day	12% 9% 28% 25% 18% 8%	490
	11th to 20th	Day	10% 10% 24% 27% 20% 9%	490
	21st to end	Day	10% 10% 29% 27% 16% 8%	490
July	1st to 10th	Day	12% 4 18% 30% 24% 12%	485
	11th to 20th	Day	8% 4 18% 33% 24% 13%	484
	21st to end	Day	12% 5% 20% 29% 23% 12%	532
August	1st to 10th	Day	17% 6% 21% 21% 23% 12%	486
	11th to 20th	Day	12% 5% 19% 26% 24% 14%	479
	21st to end	Day	10% 3 15% 30% 22% 20%	539
September	1st to 10th	Day	13% 4 19% 26% 26% 13%	490
	11th to 20th	Day	16% 4 16% 28% 24% 12%	490
	21st to end	Day	24% 11% 21% 26% 15% 3	490
October	1st to 10th	Day	20% 9% 21% 26% 21% 4	490
	11th to 20th	Day	17% 17% 20% 25% 18% 2	490
	21st to end	Day	19% 16% 27% 23% 13% 3	539
November	1st to 10th	Day	19% 15% 25% 26% 13% 2	491
	11th to 20th	Day	28% 20% 22% 22% 7% 1	270
	21st to end	Day	23% 22% 24% 24% 5% 1	270
December	1st to 10th	Day	28% 27% 28% 14% 4	270
	11th to 20th	Day	27% 24% 25% 16% 7%	270
	21st to end	Day	32% 18% 27% 14% 9%	297
January	1st to 10th	Night	26% 25% 27% 19% 3	760
	11th to 20th	Night	27% 22% 28% 21% 3	760
	21st to end	Night	23% 26% 31% 18% 2	836
February	1st to 10th	Night	22% 21% 30% 25% 2	760
	11th to 20th	Night	30% 25% 28% 16% 1	743
	21st to end	Night	25% 22% 33% 19% 1	628
March	1st to 10th	Night	22% 19% 33% 23% 3	760
	11th to 20th	Night	26% 20% 26% 21% 7%	760
	21st to end	Night	21% 16% 34% 24% 6%	836
April	1st to 10th	Night	22% 21% 26% 26% 5%	760
	11th to 20th	Night	19% 17% 27% 26% 11%	751
	21st to end	Night	17% 15% 26% 33% 9%	601
May	1st to 10th	Night	16% 13% 27% 29% 13% 1	570
	11th to 20th	Night	16% 10% 22% 34% 18% 1	561
	21st to end	Night	14% 3 16% 31% 31% 4	617
June	1st to 10th	Night	9% 2 17% 44% 25% 3	570
	11th to 20th	Night	11% 4 16% 34% 32% 4	570
	21st to end	Night	9% 3 15% 40% 29% 4	570
July	1st to 10th	Night	11% 2 8% 38% 34% 6%	555
	11th to 20th	Night	6% 2 9% 34% 44% 5%	552
	21st to end	Night	7% 2 9% 39% 38% 4	624
August	1st to 10th	Night	13% 3 10% 36% 33% 4	567
	11th to 20th	Night	14% 1 10% 32% 38% 5%	564
	21st to end	Night	11% 3 9% 31% 40% 7%	760
September	1st to 10th	Night	12% 4 12% 32% 35% 5%	760
	11th to 20th	Night	16% 4 13% 30% 32% 5%	760
	21st to end	Night	23% 6% 19% 30% 22% 1	760
October	1st to 10th	Night	18% 9% 17% 29% 24% 2	760
	11th to 20th	Night	17% 12% 24% 29% 17% 1	760
	21st to end	Night	18% 11% 22% 34% 13% 1	836
November	1st to 10th	Night	17% 10% 24% 34% 14% 1	779
	11th to 20th	Night	19% 15% 23% 32% 11% 1	760
	21st to end	Night	19% 16% 25% 30% 10% 1	760
December	1st to 10th	Night	26% 20% 27% 22% 5%	760
	11th to 20th	Night	19% 18% 31% 26% 6%	760
	21st to end	Night	26% 17% 27% 27% 3	836

Page generated at 2024-11-07 06:55:47. Version ac07

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