Morning Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morning Star Observatory clear sky chart from 2005-11-06 to 2024-05-10.

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	17% 12% 5% 8% 6% 3 4 4 5% 7% 29%	83601
	Night	17% 13% 5% 8% 6% 3 4 4 4 6% 30%	85838
Transparency	Day	54% 6% 11% 18% 9% 1	83316
	Night	54% 6% 11% 18% 9% 1	85642
Seeing	Day	27% 17% 24% 18% 10% 4	14051
	Night	25% 15% 22% 25% 11% 1	23791

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% 22% 10% 14% 5% 3 3 3 3 4 17%	2713
	11th to 20th	Day	11% 20% 11% 16% 11% 4 3 3 3 3 15%	2840
	21st to end	Day	23% 17% 11% 11% 10% 3 3 3 3 3 13%	3124
February	1st to 10th	Day	17% 17% 8% 11% 9% 5% 4 3 3 4 20%	1710
	11th to 20th	Day	16% 14% 8% 13% 6% 3 4 5% 4 6% 20%	1663
	21st to end	Day	19% 16% 7% 10% 6% 3 4 3 4 5% 23%	1565
March	1st to 10th	Day	18% 13% 8% 7% 5% 3 4 4 4 6% 29%	3435
	11th to 20th	Day	14% 14% 6% 11% 7% 4 4 3 4 5% 29%	3480
	21st to end	Day	18% 12% 4 7% 5% 3 4 4 4 6% 33%	3815
April	1st to 10th	Day	15% 15% 5% 7% 6% 2 5% 4 5% 7% 29%	2232
	11th to 20th	Day	17% 13% 4 6% 5% 3 4 4 5% 6% 33%	2254
	21st to end	Day	22% 10% 3 6% 5% 3 5% 5% 5% 6% 31%	2430
May	1st to 10th	Day	20% 10% 3 7% 6% 4 5% 5% 5% 6% 28%	2457
	11th to 20th	Day	24% 7% 3 6% 6% 3 5% 4 5% 7% 29%	2322
	21st to end	Day	15% 6% 2 5% 6% 4 5% 6% 6% 9% 36%	2725
June	1st to 10th	Day	18% 6% 3 6% 6% 3 6% 5% 5% 8% 33%	2520
	11th to 20th	Day	17% 6% 3 6% 5% 4 6% 6% 7% 9% 32%	2520
	21st to end	Day	17% 5% 3 6% 6% 4 5% 6% 6% 10% 34%	2520
July	1st to 10th	Day	13% 5% 3 6% 6% 4 5% 6% 6% 7% 38%	2520
	11th to 20th	Day	14% 5% 3 5% 5% 3 6% 6% 7% 9% 36%	2353
	21st to end	Day	15% 7% 4 6% 6% 4 6% 6% 6% 8% 33%	2547
August	1st to 10th	Day	13% 6% 2 6% 6% 4 6% 7% 8% 10% 31%	2327
	11th to 20th	Day	15% 6% 3 6% 7% 4 6% 5% 6% 9% 33%	2303
	21st to end	Day	15% 6% 2 5% 6% 4 5% 6% 7% 9% 35%	2408
September	1st to 10th	Day	17% 6% 2 5% 6% 3 5% 4 4 8% 40%	2160
	11th to 20th	Day	14% 5% 2 6% 6% 3 4 5% 5% 7% 43%	2053
	21st to end	Day	21% 9% 4 6% 5% 3 4 4 4 6% 35%	1940
October	1st to 10th	Day	18% 7% 2 5% 5% 3 4 4 6% 8% 37%	1800
	11th to 20th	Day	21% 9% 4 6% 5% 4 3 5% 4 5% 34%	1800
	21st to end	Day	24% 14% 3 5% 4 3 4 4 3 6% 31%	1980
November	1st to 10th	Day	13% 12% 4 5% 5% 3 4 4 4 7% 40%	1843
	11th to 20th	Day	16% 15% 5% 7% 6% 3 4 4 6% 6% 29%	1520
	21st to end	Day	19% 17% 9% 8% 5% 3 4 3 4 5% 23%	1520
December	1st to 10th	Day	19% 19% 11% 12% 5% 3 4 4 4 4 17%	1520
	11th to 20th	Day	18% 19% 8% 10% 5% 2 3 3 4 6% 20%	1910
	21st to end	Day	22% 23% 9% 9% 6% 2 3 3 4 4 15%	2772
January	1st to 10th	Night	14% 23% 10% 13% 7% 3 3 4 3 4 17%	4228
	11th to 20th	Night	15% 19% 10% 16% 7% 4 5% 3 4 3 15%	4120
	21st to end	Night	25% 17% 10% 10% 10% 3 3 2 2 3 15%	4532
February	1st to 10th	Night	17% 15% 7% 11% 7% 3 4 4 4 5% 23%	2470
	11th to 20th	Night	17% 15% 6% 12% 7% 4 4 4 4 4 22%	2403
	21st to end	Night	18% 15% 6% 12% 6% 2 4 4 4 5% 24%	1884
March	1st to 10th	Night	21% 13% 4 6% 6% 2 3 4 4 6% 30%	3418
	11th to 20th	Night	14% 14% 10% 8% 6% 2 4 3 4 5% 30%	3480
	21st to end	Night	17% 11% 4 8% 5% 3 4 3 4 5% 37%	3817
April	1st to 10th	Night	17% 15% 5% 6% 5% 3 4 4 4 6% 31%	1948
	11th to 20th	Night	18% 10% 3 5% 5% 3 4 5% 4 7% 36%	1875
	21st to end	Night	17% 9% 3 7% 6% 3 5% 4 5% 6% 35%	1766
May	1st to 10th	Night	21% 9% 2 6% 5% 4 4 5% 5% 6% 32%	1707
	11th to 20th	Night	19% 8% 4 6% 6% 3 4 4 6% 7% 34%	1567
	21st to end	Night	10% 6% 3 5% 4 3 4 6% 6% 11% 42%	1550
June	1st to 10th	Night	13% 6% 2 5% 5% 4 5% 5% 6% 7% 43%	1440
	11th to 20th	Night	13% 6% 3 6% 5% 3 6% 5% 5% 10% 36%	1440
	21st to end	Night	14% 6% 2 4 5% 4 4 4 6% 11% 41%	1440
July	1st to 10th	Night	11% 5% 3 6% 5% 3 5% 5% 6% 8% 43%	1440
	11th to 20th	Night	10% 3 3 6% 4 3 4 4 6% 10% 46%	1602
	21st to end	Night	11% 6% 3 5% 6% 3 5% 7% 7% 9% 39%	1771
August	1st to 10th	Night	10% 5% 2 4 5% 3 6% 5% 6% 9% 43%	1611
	11th to 20th	Night	11% 7% 3 5% 5% 3 5% 4 5% 7% 44%	1598
	21st to end	Night	13% 5% 2 4 5% 3 5% 5% 6% 9% 44%	1930
September	1st to 10th	Night	15% 5% 2 5% 4 3 4 5% 5% 7% 46%	1800
	11th to 20th	Night	12% 5% 2 4 4 3 4 3 5% 8% 51%	1903
	21st to end	Night	17% 7% 3 5% 5% 4 4 5% 5% 7% 40%	2020
October	1st to 10th	Night	18% 7% 2 5% 4 3 4 4 5% 7% 42%	2160
	11th to 20th	Night	20% 8% 2 5% 5% 4 5% 4 5% 6% 37%	2160
	21st to end	Night	26% 11% 2 5% 4 2 3 4 5% 6% 32%	2376
November	1st to 10th	Night	12% 11% 5% 5% 5% 3 3 4 4 6% 42%	2233
	11th to 20th	Night	18% 15% 5% 5% 6% 3 4 4 5% 5% 30%	2660
	21st to end	Night	18% 16% 6% 7% 5% 3 4 4 4 4 28%	2660
December	1st to 10th	Night	21% 19% 9% 12% 4 2 4 3 3 5% 16%	2660
	11th to 20th	Night	19% 17% 9% 11% 6% 3 4 4 4 4 21%	3285
	21st to end	Night	21% 22% 8% 10% 7% 3 4 4 4 5% 14%	4884

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	72% 6% 8% 11% 3 1	2714
	11th to 20th	Day	76% 3 7% 10% 3 1	2840
	21st to end	Day	78% 5% 6% 9% 2	3124
February	1st to 10th	Day	69% 4 8% 12% 6% 1	1710
	11th to 20th	Day	65% 6% 9% 13% 6%	1672
	21st to end	Day	64% 5% 10% 13% 7% 2	1565
March	1st to 10th	Day	55% 6% 11% 21% 6%	3435
	11th to 20th	Day	55% 7% 12% 20% 6% 1	3480
	21st to end	Day	51% 6% 12% 20% 10% 1	3815
April	1st to 10th	Day	54% 6% 11% 17% 10% 2	2232
	11th to 20th	Day	51% 5% 11% 16% 15% 2	2254
	21st to end	Day	53% 5% 11% 20% 9% 1	2430
May	1st to 10th	Day	55% 7% 11% 17% 9% 2	2457
	11th to 20th	Day	54% 7% 11% 15% 11% 2	2326
	21st to end	Day	44% 8% 18% 20% 8% 2	2725
June	1st to 10th	Day	48% 8% 11% 22% 10% 1	2520
	11th to 20th	Day	47% 8% 14% 19% 10% 1	2520
	21st to end	Day	45% 8% 12% 25% 11%	2520
July	1st to 10th	Day	44% 9% 12% 20% 12% 3	2450
	11th to 20th	Day	41% 8% 14% 21% 14% 1	2283
	21st to end	Day	46% 7% 11% 22% 12% 1	2405
August	1st to 10th	Day	44% 9% 16% 23% 7%	2314
	11th to 20th	Day	46% 8% 14% 22% 10% 1	2303
	21st to end	Day	42% 8% 12% 22% 12% 3	2408
September	1st to 10th	Day	43% 6% 12% 21% 15% 3	2160
	11th to 20th	Day	39% 6% 12% 27% 15% 1	2053
	21st to end	Day	49% 4 13% 20% 12% 1	1940
October	1st to 10th	Day	44% 7% 12% 21% 14% 1	1800
	11th to 20th	Day	51% 7% 11% 21% 10%	1800
	21st to end	Day	55% 4 10% 18% 11% 1	1980
November	1st to 10th	Day	45% 5% 13% 17% 17% 3	1843
	11th to 20th	Day	55% 6% 10% 16% 10% 2	1520
	21st to end	Day	64% 4 11% 14% 7%	1520
December	1st to 10th	Day	72% 4 9% 10% 4	1520
	11th to 20th	Day	66% 5% 9% 16% 3	1906
	21st to end	Day	73% 5% 8% 11% 2	2772
January	1st to 10th	Night	71% 5% 7% 12% 4 1	4228
	11th to 20th	Night	73% 5% 10% 10% 2	4120
	21st to end	Night	76% 4 5% 12% 3 1	4532
February	1st to 10th	Night	64% 5% 9% 16% 6%	2470
	11th to 20th	Night	66% 5% 9% 14% 7%	2405
	21st to end	Night	63% 5% 9% 14% 8% 1	1884
March	1st to 10th	Night	55% 5% 12% 21% 6%	3418
	11th to 20th	Night	51% 10% 13% 20% 5% 1	3480
	21st to end	Night	48% 6% 11% 22% 13% 1	3817
April	1st to 10th	Night	54% 5% 10% 18% 12% 1	1948
	11th to 20th	Night	47% 6% 13% 17% 15% 2	1875
	21st to end	Night	48% 7% 10% 23% 10% 3	1766
May	1st to 10th	Night	51% 7% 11% 18% 11% 3	1707
	11th to 20th	Night	50% 8% 10% 17% 13% 2	1568
	21st to end	Night	35% 9% 18% 25% 11% 1	1551
June	1st to 10th	Night	40% 8% 11% 27% 13% 1	1440
	11th to 20th	Night	43% 9% 13% 24% 10% 2	1440
	21st to end	Night	38% 8% 14% 25% 14% 1	1440
July	1st to 10th	Night	38% 10% 13% 22% 13% 4	1400
	11th to 20th	Night	32% 8% 15% 26% 18% 1	1549
	21st to end	Night	38% 9% 15% 22% 13% 2	1672
August	1st to 10th	Night	36% 9% 16% 26% 12%	1600
	11th to 20th	Night	38% 8% 15% 24% 14% 1	1598
	21st to end	Night	36% 7% 14% 26% 13% 3	1930
September	1st to 10th	Night	37% 8% 11% 25% 16% 3	1800
	11th to 20th	Night	31% 7% 14% 27% 20% 1	1903
	21st to end	Night	44% 6% 12% 21% 16% 1	2020
October	1st to 10th	Night	41% 7% 13% 23% 13% 2	2160
	11th to 20th	Night	47% 6% 11% 25% 11% 1	2160
	21st to end	Night	53% 5% 10% 21% 10% 2	2376
November	1st to 10th	Night	43% 5% 11% 20% 17% 4	2233
	11th to 20th	Night	56% 5% 9% 17% 11% 3	2660
	21st to end	Night	60% 5% 10% 18% 7% 1	2660
December	1st to 10th	Night	71% 4 9% 10% 4 1	2660
	11th to 20th	Night	68% 5% 8% 15% 4	3288
	21st to end	Night	73% 6% 9% 10% 2	4884

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	39% 28% 18% 9% 5% 1	236
	11th to 20th	Day	43% 29% 21% 4 2 1	270
	21st to end	Day	35% 29% 28% 6% 2	297
February	1st to 10th	Day	34% 28% 30% 7% 1	270
	11th to 20th	Day	46% 28% 20% 6%	270
	21st to end	Day	41% 27% 24% 7% 1	306
March	1st to 10th	Day	35% 25% 24% 13% 2	460
	11th to 20th	Day	35% 24% 25% 12% 4 1	460
	21st to end	Day	35% 23% 25% 13% 3 1	506
April	1st to 10th	Day	30% 25% 24% 15% 4 1	460
	11th to 20th	Day	26% 24% 26% 13% 8% 3	452
	21st to end	Day	31% 20% 25% 18% 5% 1	460
May	1st to 10th	Day	31% 20% 23% 16% 7% 3	459
	11th to 20th	Day	26% 17% 30% 16% 7% 3	447
	21st to end	Day	18% 14% 24% 23% 14% 7%	485
June	1st to 10th	Day	20% 14% 26% 25% 12% 3	450
	11th to 20th	Day	23% 14% 23% 21% 14% 4	450
	21st to end	Day	19% 12% 28% 26% 12% 3	450
July	1st to 10th	Day	17% 7% 22% 24% 18% 12%	445
	11th to 20th	Day	13% 10% 27% 27% 16% 7%	444
	21st to end	Day	16% 9% 24% 28% 18% 5%	488
August	1st to 10th	Day	15% 8% 22% 26% 20% 7%	446
	11th to 20th	Day	20% 7% 22% 23% 18% 10%	439
	21st to end	Day	16% 8% 23% 26% 18% 10%	495
September	1st to 10th	Day	21% 8% 17% 24% 20% 10%	450
	11th to 20th	Day	16% 3 21% 28% 23% 9%	450
	21st to end	Day	26% 14% 22% 17% 15% 5%	450
October	1st to 10th	Day	22% 12% 23% 24% 16% 4	450
	11th to 20th	Day	28% 16% 27% 20% 9% 1	450
	21st to end	Day	36% 16% 25% 16% 6%	495
November	1st to 10th	Day	23% 19% 23% 23% 10% 2	443
	11th to 20th	Day	34% 24% 25% 12% 4 1	180
	21st to end	Day	32% 26% 29% 12% 1	180
December	1st to 10th	Day	38% 29% 21% 7% 3 1	180
	11th to 20th	Day	44% 19% 27% 8% 2	180
	21st to end	Day	39% 26% 24% 8% 3	198
January	1st to 10th	Night	32% 27% 24% 13% 4	760
	11th to 20th	Night	34% 24% 25% 14% 3	760
	21st to end	Night	31% 26% 27% 15% 1	836
February	1st to 10th	Night	32% 21% 27% 17% 2	760
	11th to 20th	Night	34% 29% 25% 11% 1	743
	21st to end	Night	35% 20% 26% 16% 2	628
March	1st to 10th	Night	29% 21% 27% 21% 2	760
	11th to 20th	Night	31% 23% 20% 19% 5% 1	760
	21st to end	Night	29% 21% 27% 18% 5% 1	836
April	1st to 10th	Night	28% 18% 28% 20% 5%	760
	11th to 20th	Night	25% 16% 26% 24% 9% 1	751
	21st to end	Night	22% 14% 27% 30% 6% 1	626
May	1st to 10th	Night	27% 10% 22% 30% 9% 1	569
	11th to 20th	Night	23% 11% 24% 32% 10%	506
	21st to end	Night	12% 7% 22% 31% 25% 3	389
June	1st to 10th	Night	15% 5% 21% 38% 20% 1	360
	11th to 20th	Night	15% 9% 19% 35% 20% 2	360
	21st to end	Night	15% 5% 23% 39% 18% 1	360
July	1st to 10th	Night	12% 3 18% 40% 24% 3	350
	11th to 20th	Night	11% 7% 15% 37% 26% 4	505
	21st to end	Night	14% 5% 15% 41% 24% 2	591
August	1st to 10th	Night	12% 4 12% 41% 29% 3	537
	11th to 20th	Night	14% 5% 11% 37% 29% 4	534
	21st to end	Night	15% 3 15% 36% 27% 4	742
September	1st to 10th	Night	16% 5% 15% 34% 26% 4	720
	11th to 20th	Night	14% 4 17% 33% 28% 4	720
	21st to end	Night	21% 9% 19% 28% 20% 3	720
October	1st to 10th	Night	21% 8% 20% 30% 19% 2	720
	11th to 20th	Night	25% 14% 25% 27% 8% 1	720
	21st to end	Night	32% 13% 24% 25% 5%	792
November	1st to 10th	Night	20% 12% 24% 33% 10% 1	740
	11th to 20th	Night	31% 18% 23% 21% 6% 1	760
	21st to end	Night	30% 20% 26% 19% 5% 1	760
December	1st to 10th	Night	38% 22% 20% 16% 3	760
	11th to 20th	Night	34% 23% 24% 18% 2	760
	21st to end	Night	32% 22% 26% 18% 1	836

Page generated at 2024-05-07 07:25:01. Version ac07

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