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 2025-10-04.

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	16% 12% 4 9% 5% 5% 4 4 5% 7% 29%	126308
	Night	16% 13% 5% 10% 5% 4 4 3 4 6% 29%	123052
Transparency	Day	53% 6% 11% 19% 10% 1	129908
	Night	54% 5% 11% 19% 10% 1	127521
Seeing	Day	27% 17% 25% 18% 10% 4	15937
	Night	25% 15% 22% 25% 11% 1	25504

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	14% 20% 9% 24% 6% 3 3 2 3 4 13%	3891
	11th to 20th	Day	11% 19% 10% 21% 11% 7% 3 2 2 2 12%	4060
	21st to end	Day	19% 17% 10% 10% 8% 4 3 2 4 4 19%	4466
February	1st to 10th	Day	17% 18% 7% 12% 9% 5% 3 3 4 4 20%	1800
	11th to 20th	Day	17% 16% 8% 13% 5% 5% 4 3 4 6% 20%	1753
	21st to end	Day	18% 18% 6% 11% 6% 4 3 3 4 5% 23%	1645
March	1st to 10th	Day	15% 15% 8% 8% 4 4 4 3 4 5% 32%	4935
	11th to 20th	Day	13% 13% 5% 10% 5% 4 4 3 5% 7% 32%	4980
	21st to end	Day	15% 12% 4 9% 5% 5% 4 3 5% 6% 32%	5465
April	1st to 10th	Day	16% 17% 3 8% 5% 3 4 4 5% 6% 28%	2350
	11th to 20th	Day	17% 14% 3 7% 4 4 4 3 6% 6% 32%	2374
	21st to end	Day	22% 11% 3 6% 4 4 5% 3 5% 7% 31%	2558
May	1st to 10th	Day	20% 10% 3 9% 6% 5% 6% 4 6% 6% 25%	5862
	11th to 20th	Day	20% 8% 3 8% 5% 5% 6% 4 7% 8% 27%	5924
	21st to end	Day	21% 9% 3 7% 4 5% 5% 4 6% 7% 29%	6934
June	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 4 6% 8% 33%	2800
	11th to 20th	Day	16% 7% 3 7% 5% 6% 6% 5% 7% 9% 31%	2800
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 5% 6% 10% 35%	2800
July	1st to 10th	Day	11% 6% 3 7% 5% 6% 5% 5% 6% 8% 39%	6360
	11th to 20th	Day	12% 8% 3 7% 6% 5% 7% 5% 7% 10% 30%	5913
	21st to end	Day	13% 8% 3 7% 5% 5% 4 4 6% 7% 38%	6424
August	1st to 10th	Day	16% 9% 3 8% 5% 5% 5% 5% 7% 9% 29%	4234
	11th to 20th	Day	14% 6% 3 7% 5% 5% 6% 5% 6% 7% 36%	4174
	21st to end	Day	10% 5% 2 6% 4 5% 6% 5% 7% 10% 40%	4360
September	1st to 10th	Day	16% 6% 2 5% 4 4 4 4 4 7% 43%	2400
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 3 5% 7% 45%	2281
	21st to end	Day	22% 10% 4 7% 4 3 4 3 4 6% 32%	2154
October	1st to 10th	Day	18% 7% 2 5% 4 4 4 3 6% 8% 39%	1930
	11th to 20th	Day	19% 10% 4 6% 5% 4 4 3 5% 5% 35%	1900
	21st to end	Day	22% 14% 3 6% 3 3 4 3 3 6% 33%	2090
November	1st to 10th	Day	13% 13% 3 6% 4 4 4 3 4 7% 40%	1941
	11th to 20th	Day	15% 17% 5% 7% 5% 4 4 3 6% 6% 29%	1600
	21st to end	Day	18% 19% 8% 9% 4 4 4 2 5% 5% 22%	1600
December	1st to 10th	Day	16% 14% 7% 27% 5% 3 3 2 3 4 16%	2600
	11th to 20th	Day	20% 19% 7% 11% 4 3 3 3 4 5% 21%	2990
	21st to end	Day	19% 23% 7% 11% 5% 4 4 3 4 5% 15%	3960
January	1st to 10th	Night	11% 20% 8% 24% 8% 3 3 2 3 3 13%	6050
	11th to 20th	Night	12% 18% 8% 22% 9% 6% 4 2 3 3 13%	5900
	21st to end	Night	18% 16% 8% 12% 9% 5% 4 3 4 3 18%	6490
February	1st to 10th	Night	17% 16% 7% 12% 6% 4 4 3 4 5% 23%	2600
	11th to 20th	Night	17% 16% 6% 13% 6% 5% 4 3 5% 4 21%	2533
	21st to end	Night	17% 17% 6% 13% 6% 4 4 3 4 4 24%	1980
March	1st to 10th	Night	17% 14% 5% 9% 7% 4 3 3 4 5% 30%	4918
	11th to 20th	Night	12% 12% 7% 7% 4 3 3 3 4 6% 39%	4980
	21st to end	Night	15% 12% 5% 10% 5% 5% 4 3 4 5% 33%	5467
April	1st to 10th	Night	17% 17% 4 7% 5% 4 4 3 4 6% 31%	2050
	11th to 20th	Night	18% 11% 2 5% 4 5% 3 4 5% 7% 35%	1975
	21st to end	Night	17% 10% 3 7% 5% 4 5% 3 5% 6% 35%	1859
May	1st to 10th	Night	26% 12% 3 8% 4 4 4 3 5% 6% 24%	4033
	11th to 20th	Night	18% 12% 4 8% 5% 4 3 3 5% 7% 31%	3951
	21st to end	Night	23% 10% 3 7% 4 4 4 4 5% 8% 30%	3920
June	1st to 10th	Night	13% 7% 2 6% 5% 4 5% 4 6% 7% 42%	1600
	11th to 20th	Night	13% 7% 3 7% 4 4 6% 4 7% 10% 36%	1600
	21st to end	Night	13% 7% 2 5% 4 5% 3 4 6% 11% 41%	1600
July	1st to 10th	Night	11% 8% 3 8% 4 5% 5% 4 6% 8% 38%	3598
	11th to 20th	Night	13% 7% 3 8% 5% 5% 6% 4 6% 10% 34%	4025
	21st to end	Night	12% 9% 3 7% 5% 4 4 4 5% 7% 40%	4427
August	1st to 10th	Night	17% 8% 3 6% 4 5% 5% 4 6% 8% 34%	2915
	11th to 20th	Night	16% 7% 2 6% 4 4 4 3 5% 7% 41%	2875
	21st to end	Night	9% 5% 2 5% 4 5% 5% 4 6% 9% 46%	3505
September	1st to 10th	Night	14% 6% 2 5% 3 4 4 4 5% 7% 47%	2000
	11th to 20th	Night	11% 5% 2 5% 3 4 4 3 6% 8% 51%	2115
	21st to end	Night	18% 9% 3 6% 4 4 5% 3 5% 6% 36%	2245
October	1st to 10th	Night	17% 7% 2 6% 3 4 3 3 5% 7% 43%	2317
	11th to 20th	Night	19% 8% 2 5% 4 5% 4 3 5% 6% 38%	2280
	21st to end	Night	25% 11% 2 6% 3 3 4 3 4 6% 33%	2508
November	1st to 10th	Night	12% 11% 4 6% 4 4 3 3 4 5% 43%	2355
	11th to 20th	Night	18% 16% 4 7% 5% 4 4 3 5% 5% 29%	2800
	21st to end	Night	18% 18% 6% 8% 5% 4 4 3 4 4 27%	2800
December	1st to 10th	Night	17% 16% 8% 22% 4 3 3 2 3 4 18%	4580
	11th to 20th	Night	21% 16% 8% 12% 5% 4 3 3 4 4 21%	5205
	21st to end	Night	17% 23% 7% 13% 5% 4 4 3 4 5% 16%	6996

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	76% 4 8% 8% 3	3892
	11th to 20th	Day	81% 3 5% 7% 3 1	4060
	21st to end	Day	70% 4 8% 11% 7%	4466
February	1st to 10th	Day	69% 4 8% 13% 5% 1	1800
	11th to 20th	Day	66% 6% 9% 13% 6%	1762
	21st to end	Day	63% 5% 11% 13% 7% 2	1645
March	1st to 10th	Day	54% 4 10% 21% 8% 2	4935
	11th to 20th	Day	50% 6% 12% 23% 7% 2	4980
	21st to end	Day	52% 5% 10% 20% 11% 1	5465
April	1st to 10th	Day	56% 6% 10% 17% 10% 2	2350
	11th to 20th	Day	51% 5% 11% 17% 14% 2	2374
	21st to end	Day	52% 5% 11% 21% 10% 1	2558
May	1st to 10th	Day	57% 7% 10% 16% 8% 2	5897
	11th to 20th	Day	52% 8% 10% 20% 9% 1	5928
	21st to end	Day	51% 7% 13% 18% 9% 2	6949
June	1st to 10th	Day	47% 8% 11% 22% 11% 1	2800
	11th to 20th	Day	47% 8% 14% 19% 11% 1	2800
	21st to end	Day	44% 8% 12% 24% 12%	2800
July	1st to 10th	Day	42% 7% 11% 26% 13% 2	6290
	11th to 20th	Day	46% 8% 14% 22% 10%	5843
	21st to end	Day	43% 5% 8% 24% 19% 1	6240
August	1st to 10th	Day	50% 7% 15% 20% 7%	4221
	11th to 20th	Day	45% 7% 11% 28% 10%	4213
	21st to end	Day	36% 8% 13% 28% 13% 2	4360
September	1st to 10th	Day	41% 6% 11% 23% 17% 3	2400
	11th to 20th	Day	38% 6% 12% 27% 16% 1	2281
	21st to end	Day	52% 4 12% 19% 12% 1	2154
October	1st to 10th	Day	36% 6% 8% 30% 19% 1	3190
	11th to 20th	Day	45% 6% 11% 20% 11% 7%	3140
	21st to end	Day	38% 3 10% 29% 19% 1	3428
November	1st to 10th	Day	45% 5% 12% 18% 17% 3	1941
	11th to 20th	Day	55% 6% 10% 16% 10% 2	1600
	21st to end	Day	65% 4 11% 14% 7%	1600
December	1st to 10th	Day	75% 4 11% 8% 3	2600
	11th to 20th	Day	66% 5% 11% 14% 4	2986
	21st to end	Day	72% 5% 8% 12% 4	3960
January	1st to 10th	Night	77% 4 6% 10% 4	6050
	11th to 20th	Night	77% 4 7% 9% 2 1	5900
	21st to end	Night	71% 4 7% 12% 5% 1	6490
February	1st to 10th	Night	64% 4 9% 17% 6%	2600
	11th to 20th	Night	66% 5% 8% 14% 6%	2535
	21st to end	Night	64% 5% 8% 14% 8% 1	1980
March	1st to 10th	Night	57% 4 11% 19% 7% 1	4918
	11th to 20th	Night	43% 8% 16% 23% 7% 3	4980
	21st to end	Night	51% 5% 11% 18% 14% 1	5467
April	1st to 10th	Night	55% 5% 10% 17% 12% 1	2050
	11th to 20th	Night	48% 5% 13% 17% 15% 2	1975
	21st to end	Night	48% 6% 10% 23% 10% 3	1859
May	1st to 10th	Night	60% 6% 10% 13% 9% 3	4060
	11th to 20th	Night	51% 7% 10% 23% 7% 1	3952
	21st to end	Night	51% 8% 12% 19% 8% 3	3927
June	1st to 10th	Night	41% 7% 10% 26% 14% 2	1600
	11th to 20th	Night	42% 9% 13% 25% 10% 1	1600
	21st to end	Night	38% 8% 14% 24% 15% 1	1600
July	1st to 10th	Night	43% 7% 11% 23% 13% 2	3560
	11th to 20th	Night	45% 6% 17% 20% 10% 1	3975
	21st to end	Night	41% 7% 10% 20% 21% 1	4297
August	1st to 10th	Night	46% 8% 15% 22% 8%	2904
	11th to 20th	Night	42% 6% 10% 29% 12% 1	2902
	21st to end	Night	33% 7% 15% 31% 12% 2	3505
September	1st to 10th	Night	36% 7% 10% 25% 18% 3	2000
	11th to 20th	Night	30% 7% 14% 28% 20% 1	2115
	21st to end	Night	47% 6% 12% 20% 14% 1	2245
October	1st to 10th	Night	37% 5% 9% 27% 20% 1	3837
	11th to 20th	Night	39% 4 10% 24% 13% 9%	3779
	21st to end	Night	39% 4 10% 26% 20% 1	4120
November	1st to 10th	Night	43% 5% 11% 20% 18% 4	2355
	11th to 20th	Night	57% 5% 8% 16% 11% 3	2800
	21st to end	Night	61% 4 10% 17% 7% 1	2800
December	1st to 10th	Night	71% 3 11% 11% 3	4580
	11th to 20th	Night	68% 3 12% 14% 3	5208
	21st to end	Night	71% 5% 9% 12% 3	6996

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	41% 28% 17% 8% 4 1	263
	11th to 20th	Day	45% 28% 21% 4 2 1	300
	21st to end	Day	36% 29% 27% 5% 2	330
February	1st to 10th	Day	37% 28% 27% 6% 1	300
	11th to 20th	Day	48% 27% 19% 5%	300
	21st to end	Day	41% 27% 25% 6% 1	334
March	1st to 10th	Day	36% 25% 24% 13% 2	500
	11th to 20th	Day	35% 24% 25% 12% 4 1	500
	21st to end	Day	35% 24% 25% 12% 3 1	550
April	1st to 10th	Day	34% 25% 23% 14% 4 1	500
	11th to 20th	Day	29% 23% 26% 13% 7% 3	492
	21st to end	Day	31% 20% 25% 18% 5% 1	500
May	1st to 10th	Day	31% 20% 24% 15% 7% 2	503
	11th to 20th	Day	26% 17% 29% 17% 8% 3	527
	21st to end	Day	22% 14% 24% 23% 12% 6%	573
June	1st to 10th	Day	21% 15% 25% 24% 12% 3	530
	11th to 20th	Day	22% 14% 25% 20% 14% 4	530
	21st to end	Day	18% 12% 28% 26% 12% 3	530
July	1st to 10th	Day	17% 7% 24% 24% 17% 11%	525
	11th to 20th	Day	13% 10% 28% 27% 16% 6%	524
	21st to end	Day	15% 9% 24% 29% 18% 5%	576
August	1st to 10th	Day	15% 10% 25% 26% 19% 6%	526
	11th to 20th	Day	20% 8% 23% 23% 17% 10%	519
	21st to end	Day	14% 9% 24% 26% 18% 9%	583
September	1st to 10th	Day	20% 9% 18% 23% 20% 9%	530
	11th to 20th	Day	14% 3 21% 30% 24% 8%	530
	21st to end	Day	29% 13% 24% 16% 13% 5%	530
October	1st to 10th	Day	21% 12% 23% 25% 15% 4	502
	11th to 20th	Day	27% 16% 27% 20% 9% 1	490
	21st to end	Day	33% 17% 27% 16% 7%	539
November	1st to 10th	Day	23% 19% 25% 22% 9% 2	481
	11th to 20th	Day	34% 24% 27% 11% 4 1	200
	21st to end	Day	35% 25% 29% 11% 1	200
December	1st to 10th	Day	38% 31% 21% 7% 3 1	200
	11th to 20th	Day	44% 19% 28% 8% 2	200
	21st to end	Day	38% 26% 25% 8% 3	220
January	1st to 10th	Night	32% 28% 24% 12% 4	800
	11th to 20th	Night	35% 24% 25% 14% 3	800
	21st to end	Night	32% 27% 26% 14% 1	880
February	1st to 10th	Night	33% 22% 26% 17% 2	800
	11th to 20th	Night	35% 28% 24% 12% 1	783
	21st to end	Night	35% 21% 26% 16% 2	660
March	1st to 10th	Night	30% 22% 26% 20% 2	800
	11th to 20th	Night	31% 23% 22% 19% 5% 1	800
	21st to end	Night	29% 21% 27% 18% 4 1	880
April	1st to 10th	Night	30% 18% 28% 20% 5%	800
	11th to 20th	Night	26% 16% 26% 23% 9% 1	791
	21st to end	Night	23% 14% 27% 30% 6% 1	659
May	1st to 10th	Night	27% 11% 22% 30% 9% 1	600
	11th to 20th	Night	23% 11% 23% 33% 9%	562
	21st to end	Night	14% 9% 21% 31% 23% 3	433
June	1st to 10th	Night	15% 6% 22% 38% 19% 1	400
	11th to 20th	Night	15% 9% 21% 35% 19% 2	400
	21st to end	Night	15% 5% 24% 37% 19% 1	400
July	1st to 10th	Night	13% 3 18% 41% 22% 3	390
	11th to 20th	Night	12% 6% 15% 37% 25% 4	564
	21st to end	Night	14% 5% 13% 43% 23% 2	657
August	1st to 10th	Night	12% 4 13% 42% 27% 2	597
	11th to 20th	Night	14% 5% 12% 38% 27% 4	594
	21st to end	Night	14% 3 16% 37% 26% 4	825
September	1st to 10th	Night	16% 6% 17% 34% 24% 4	800
	11th to 20th	Night	13% 4 16% 35% 29% 4	800
	21st to end	Night	23% 9% 19% 27% 18% 3	800
October	1st to 10th	Night	21% 8% 19% 31% 20% 2	773
	11th to 20th	Night	25% 13% 25% 26% 9% 1	760
	21st to end	Night	31% 14% 24% 26% 5%	836
November	1st to 10th	Night	20% 13% 25% 32% 9% 1	780
	11th to 20th	Night	31% 18% 23% 21% 6% 1	800
	21st to end	Night	31% 20% 25% 18% 5% 1	800
December	1st to 10th	Night	37% 23% 21% 16% 3	800
	11th to 20th	Night	35% 22% 24% 17% 2	800
	21st to end	Night	32% 22% 27% 18% 1	880

Page generated at 2025-10-01 01:39:06. Version ac07

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