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 2026-04-02.

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 7% 5% 5% 5% 4 6% 8% 37%	131305
	Night	11% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	130497
Transparency	Day	40% 8% 12% 22% 14% 3	134909
	Night	39% 9% 13% 22% 14% 2	134964
Seeing	Day	22% 16% 26% 21% 12% 4	16660
	Night	19% 13% 26% 29% 12% 1	26461

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	11% 9% 5% 10% 5% 5% 5% 3 4 6% 37%	5216
	11th to 20th	Day	8% 12% 4 10% 7% 4 4 3 4 5% 39%	5280
	21st to end	Day	11% 7% 3 7% 7% 6% 6% 5% 6% 6% 37%	5780
February	1st to 10th	Day	12% 11% 4 7% 6% 5% 5% 4 4 5% 36%	1890
	11th to 20th	Day	15% 9% 4 10% 6% 5% 4 3 5% 6% 34%	1843
	21st to end	Day	13% 10% 4 8% 5% 3 5% 3 6% 5% 38%	1767
March	1st to 10th	Day	14% 9% 3 8% 5% 4 4 3 4 6% 39%	5045
	11th to 20th	Day	10% 7% 3 7% 4 4 3 3 5% 7% 46%	5090
	21st to end	Day	13% 9% 3 8% 6% 5% 5% 4 5% 6% 36%	5586
April	1st to 10th	Day	11% 11% 3 9% 6% 5% 5% 4 5% 6% 35%	2366
	11th to 20th	Day	13% 8% 3 7% 4 4 4 4 5% 7% 41%	2374
	21st to end	Day	16% 8% 3 7% 5% 4 4 4 6% 7% 37%	2490
May	1st to 10th	Day	16% 8% 3 8% 6% 5% 6% 5% 7% 8% 29%	5862
	11th to 20th	Day	19% 8% 3 7% 5% 5% 5% 4 7% 8% 28%	5861
	21st to end	Day	14% 6% 2 7% 6% 6% 6% 5% 7% 8% 32%	6880
June	1st to 10th	Day	12% 6% 2 6% 5% 4 6% 4 7% 9% 39%	2800
	11th to 20th	Day	11% 5% 2 7% 6% 5% 6% 5% 7% 10% 35%	2800
	21st to end	Day	8% 5% 2 6% 6% 6% 6% 4 7% 10% 40%	2800
July	1st to 10th	Day	5% 5% 2 7% 5% 5% 5% 5% 8% 10% 43%	6206
	11th to 20th	Day	7% 6% 3 8% 6% 6% 7% 6% 9% 11% 31%	5900
	21st to end	Day	9% 6% 3 7% 5% 6% 6% 5% 7% 10% 36%	6424
August	1st to 10th	Day	14% 5% 3 7% 6% 6% 6% 6% 7% 8% 31%	4234
	11th to 20th	Day	8% 5% 2 8% 5% 6% 6% 6% 8% 9% 37%	4151
	21st to end	Day	7% 5% 2 6% 4 4 5% 5% 7% 8% 46%	4312
September	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 6% 7% 44%	2400
	11th to 20th	Day	11% 7% 2 5% 4 4 5% 4 6% 8% 44%	2300
	21st to end	Day	19% 9% 3 7% 4 4 5% 4 6% 6% 34%	2141
October	1st to 10th	Day	16% 6% 2 5% 3 4 4 3 5% 7% 45%	2000
	11th to 20th	Day	15% 8% 2 6% 4 4 3 3 5% 6% 44%	2000
	21st to end	Day	13% 8% 3 7% 4 3 4 4 5% 6% 44%	2200
November	1st to 10th	Day	9% 6% 2 5% 4 4 4 3 6% 5% 51%	2057
	11th to 20th	Day	12% 8% 3 6% 5% 3 5% 3 6% 7% 41%	1772
	21st to end	Day	14% 9% 3 7% 5% 5% 4 4 4 8% 39%	1680
December	1st to 10th	Day	10% 8% 2 7% 5% 5% 5% 3 5% 5% 44%	2680
	11th to 20th	Day	16% 11% 4 8% 4 4 4 3 4 6% 35%	3070
	21st to end	Day	14% 8% 3 10% 5% 5% 5% 5% 7% 9% 29%	4048
January	1st to 10th	Night	8% 10% 4 14% 7% 6% 5% 4 6% 6% 30%	7661
	11th to 20th	Night	9% 8% 3 10% 6% 4 5% 3 5% 5% 40%	7680
	21st to end	Night	11% 7% 2 7% 6% 5% 5% 4 5% 5% 42%	8401
February	1st to 10th	Night	11% 9% 3 9% 6% 6% 5% 4 6% 6% 36%	2730
	11th to 20th	Night	15% 10% 4 9% 5% 5% 6% 4 4 5% 33%	2663
	21st to end	Night	12% 12% 4 8% 6% 6% 4 4 5% 5% 34%	2034
March	1st to 10th	Night	14% 7% 3 8% 5% 4 4 3 4 6% 44%	5028
	11th to 20th	Night	8% 7% 3 7% 5% 4 4 3 5% 8% 45%	5090
	21st to end	Night	9% 7% 3 9% 6% 5% 4 4 5% 6% 42%	5588
April	1st to 10th	Night	12% 10% 3 8% 6% 5% 5% 4 5% 7% 35%	2055
	11th to 20th	Night	13% 8% 2 6% 5% 5% 5% 4 6% 8% 39%	1975
	21st to end	Night	15% 7% 3 6% 4 4 5% 3 5% 7% 40%	1926
May	1st to 10th	Night	17% 9% 3 7% 5% 6% 5% 4 6% 8% 29%	4033
	11th to 20th	Night	21% 10% 3 7% 5% 4 5% 4 5% 7% 29%	4032
	21st to end	Night	14% 8% 3 9% 5% 5% 5% 4 6% 8% 32%	3969
June	1st to 10th	Night	10% 5% 2 5% 5% 6% 4 4 6% 8% 45%	1600
	11th to 20th	Night	10% 6% 2 7% 5% 6% 5% 4 5% 10% 41%	1600
	21st to end	Night	8% 5% 2 6% 4 5% 5% 5% 8% 10% 42%	1600
July	1st to 10th	Night	5% 5% 2 7% 6% 5% 5% 5% 6% 11% 42%	3733
	11th to 20th	Night	6% 6% 3 10% 6% 7% 7% 6% 8% 9% 32%	4057
	21st to end	Night	6% 6% 3 7% 5% 5% 7% 5% 8% 11% 37%	4427
August	1st to 10th	Night	12% 5% 2 8% 5% 5% 6% 5% 7% 9% 36%	2915
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 4 7% 10% 42%	2875
	21st to end	Night	8% 6% 2 6% 4 3 4 4 6% 9% 47%	3575
September	1st to 10th	Night	12% 5% 2 5% 3 4 4 4 6% 6% 48%	2000
	11th to 20th	Night	10% 6% 2 6% 3 3 3 3 5% 8% 50%	2096
	21st to end	Night	17% 8% 2 6% 4 4 4 3 6% 6% 39%	2257
October	1st to 10th	Night	16% 6% 2 6% 3 4 4 3 4 6% 47%	2400
	11th to 20th	Night	12% 7% 2 6% 3 4 4 4 5% 6% 49%	2400
	21st to end	Night	13% 7% 3 6% 5% 5% 4 3 4 6% 45%	2640
November	1st to 10th	Night	9% 8% 3 7% 4 4 4 3 5% 6% 48%	2461
	11th to 20th	Night	12% 8% 3 7% 4 4 4 4 6% 7% 41%	2841
	21st to end	Night	11% 8% 3 8% 6% 5% 4 4 6% 7% 38%	2940
December	1st to 10th	Night	8% 7% 4 9% 5% 5% 5% 3 5% 8% 40%	4720
	11th to 20th	Night	15% 8% 4 9% 6% 4 5% 4 5% 7% 34%	5345
	21st to end	Night	12% 8% 4 9% 7% 6% 7% 5% 7% 7% 28%	7150

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	45% 5% 10% 22% 15% 3	5217
	11th to 20th	Day	43% 6% 10% 18% 18% 6%	5280
	21st to end	Day	42% 8% 11% 25% 12% 3	5780
February	1st to 10th	Day	47% 6% 11% 21% 13% 2	1890
	11th to 20th	Day	49% 4 11% 20% 13% 2	1852
	21st to end	Day	46% 6% 12% 20% 13% 3	1767
March	1st to 10th	Day	43% 6% 11% 21% 14% 6%	5045
	11th to 20th	Day	34% 6% 11% 27% 17% 5%	5090
	21st to end	Day	46% 7% 11% 17% 16% 4	5586
April	1st to 10th	Day	46% 7% 11% 17% 15% 4	2366
	11th to 20th	Day	40% 6% 11% 21% 18% 5%	2374
	21st to end	Day	45% 6% 11% 22% 13% 3	2490
May	1st to 10th	Day	47% 10% 12% 19% 8% 2	5897
	11th to 20th	Day	50% 10% 11% 22% 7% 1	5865
	21st to end	Day	42% 11% 14% 20% 12% 2	6895
June	1st to 10th	Day	38% 10% 14% 23% 16% 1	2800
	11th to 20th	Day	40% 11% 15% 21% 13% 1	2800
	21st to end	Day	37% 9% 15% 24% 13% 2	2800
July	1st to 10th	Day	33% 12% 14% 25% 13% 3	6139
	11th to 20th	Day	39% 14% 17% 23% 7% 1	5831
	21st to end	Day	39% 9% 12% 23% 16% 1	6240
August	1st to 10th	Day	45% 11% 16% 21% 7%	4221
	11th to 20th	Day	37% 9% 14% 27% 12%	4190
	21st to end	Day	32% 10% 15% 26% 15% 1	4312
September	1st to 10th	Day	38% 8% 12% 18% 21% 3	2400
	11th to 20th	Day	37% 6% 10% 26% 18% 3	2300
	21st to end	Day	47% 7% 11% 19% 15% 1	2141
October	1st to 10th	Day	29% 6% 10% 24% 27% 5%	3260
	11th to 20th	Day	30% 7% 10% 24% 17% 12%	3240
	21st to end	Day	27% 4 10% 29% 24% 6%	3538
November	1st to 10th	Day	33% 6% 12% 24% 22% 4	2057
	11th to 20th	Day	40% 6% 12% 19% 20% 4	1772
	21st to end	Day	42% 6% 12% 24% 14% 1	1680
December	1st to 10th	Day	38% 8% 13% 24% 14% 3	2680
	11th to 20th	Day	46% 8% 14% 21% 10% 2	3066
	21st to end	Day	45% 11% 15% 17% 11%	4048
January	1st to 10th	Night	42% 12% 11% 21% 13% 1	7662
	11th to 20th	Night	38% 8% 11% 20% 17% 5%	7680
	21st to end	Night	38% 8% 12% 26% 14% 1	8401
February	1st to 10th	Night	45% 7% 13% 22% 13% 1	2730
	11th to 20th	Night	49% 5% 11% 20% 12% 2	2665
	21st to end	Night	46% 8% 11% 19% 12% 4	2034
March	1st to 10th	Night	39% 6% 11% 25% 13% 6%	5028
	11th to 20th	Night	31% 9% 12% 28% 15% 4	5090
	21st to end	Night	38% 7% 13% 22% 16% 3	5588
April	1st to 10th	Night	45% 8% 12% 18% 14% 3	2055
	11th to 20th	Night	40% 7% 13% 21% 15% 5%	1975
	21st to end	Night	41% 7% 11% 25% 14% 3	1926
May	1st to 10th	Night	49% 11% 13% 15% 9% 2	4060
	11th to 20th	Night	49% 10% 12% 22% 7%	4033
	21st to end	Night	43% 13% 15% 21% 6% 3	3976
June	1st to 10th	Night	34% 10% 12% 27% 15% 1	1600
	11th to 20th	Night	37% 11% 15% 23% 13% 1	1600
	21st to end	Night	32% 10% 17% 23% 16% 1	1600
July	1st to 10th	Night	35% 12% 20% 20% 11% 3	3693
	11th to 20th	Night	43% 14% 17% 18% 7% 1	4006
	21st to end	Night	35% 12% 16% 24% 14%	4297
August	1st to 10th	Night	41% 11% 18% 22% 7%	2904
	11th to 20th	Night	35% 9% 16% 24% 15%	2902
	21st to end	Night	32% 9% 16% 30% 12% 1	3575
September	1st to 10th	Night	34% 8% 15% 20% 19% 4	2000
	11th to 20th	Night	32% 7% 12% 28% 19% 2	2096
	21st to end	Night	44% 7% 12% 21% 16% 1	2257
October	1st to 10th	Night	34% 5% 12% 24% 22% 2	3920
	11th to 20th	Night	27% 6% 12% 22% 25% 8%	3899
	21st to end	Night	25% 6% 11% 29% 23% 5%	4252
November	1st to 10th	Night	35% 6% 12% 22% 20% 4	2461
	11th to 20th	Night	39% 6% 10% 24% 17% 4	2841
	21st to end	Night	42% 8% 12% 21% 14% 2	2940
December	1st to 10th	Night	37% 7% 15% 27% 12% 1	4720
	11th to 20th	Night	45% 7% 14% 18% 14% 2	5348
	21st to end	Night	46% 12% 16% 16% 10%	7150

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	37% 28% 21% 11% 3 1	322
	11th to 20th	Day	39% 23% 27% 9% 2	330
	21st to end	Day	33% 26% 29% 9% 2	363
February	1st to 10th	Day	35% 27% 24% 12% 1	330
	11th to 20th	Day	49% 19% 27% 5%	330
	21st to end	Day	35% 23% 26% 15% 1	402
March	1st to 10th	Day	31% 22% 24% 20% 2	540
	11th to 20th	Day	31% 24% 24% 15% 5% 1	540
	21st to end	Day	28% 24% 30% 14% 4 1	594
April	1st to 10th	Day	26% 26% 26% 16% 6% 1	504
	11th to 20th	Day	23% 21% 27% 17% 9% 3	492
	21st to end	Day	29% 17% 28% 18% 8% 1	500
May	1st to 10th	Day	24% 22% 26% 16% 9% 3	503
	11th to 20th	Day	23% 16% 30% 18% 11% 2	527
	21st to end	Day	18% 12% 25% 23% 16% 6%	573
June	1st to 10th	Day	16% 13% 27% 25% 15% 5%	530
	11th to 20th	Day	16% 11% 28% 24% 16% 6%	530
	21st to end	Day	9% 12% 30% 28% 17% 4	530
July	1st to 10th	Day	11% 6% 24% 28% 24% 8%	525
	11th to 20th	Day	7% 4 28% 28% 23% 10%	524
	21st to end	Day	13% 6% 22% 28% 24% 7%	576
August	1st to 10th	Day	13% 9% 21% 26% 24% 8%	526
	11th to 20th	Day	11% 6% 24% 27% 21% 10%	519
	21st to end	Day	10% 6% 21% 29% 22% 12%	583
September	1st to 10th	Day	15% 9% 21% 24% 21% 9%	530
	11th to 20th	Day	14% 5% 22% 26% 24% 9%	530
	21st to end	Day	26% 11% 25% 21% 13% 3	530
October	1st to 10th	Day	19% 8% 23% 27% 19% 5%	530
	11th to 20th	Day	21% 18% 22% 24% 12% 2	530
	21st to end	Day	21% 18% 30% 21% 8% 2	583
November	1st to 10th	Day	19% 18% 28% 23% 10% 2	535
	11th to 20th	Day	26% 20% 27% 20% 6% 1	297
	21st to end	Day	32% 17% 30% 18% 3	220
December	1st to 10th	Day	28% 22% 35% 10% 3 1	220
	11th to 20th	Day	27% 24% 26% 17% 6%	220
	21st to end	Day	27% 23% 26% 19% 4	242
January	1st to 10th	Night	24% 23% 32% 19% 3	840
	11th to 20th	Night	27% 19% 28% 23% 3	840
	21st to end	Night	23% 21% 35% 19% 1	924
February	1st to 10th	Night	20% 20% 31% 26% 2	840
	11th to 20th	Night	30% 25% 29% 16% 1	823
	21st to end	Night	27% 19% 36% 16% 2	692
March	1st to 10th	Night	23% 20% 32% 23% 3	840
	11th to 20th	Night	27% 20% 27% 21% 4 1	840
	21st to end	Night	23% 20% 33% 19% 4 1	924
April	1st to 10th	Night	22% 22% 29% 22% 5%	805
	11th to 20th	Night	20% 17% 28% 26% 8%	791
	21st to end	Night	22% 13% 29% 30% 7%	726
May	1st to 10th	Night	21% 10% 26% 29% 13% 1	600
	11th to 20th	Night	18% 9% 27% 34% 12% 1	591
	21st to end	Night	11% 5% 26% 35% 20% 2	457
June	1st to 10th	Night	11% 5% 26% 38% 20% 2	400
	11th to 20th	Night	12% 5% 19% 46% 17% 2	400
	21st to end	Night	8% 3 22% 47% 19% 2	400
July	1st to 10th	Night	9% 3 17% 41% 25% 5%	445
	11th to 20th	Night	6% 2 13% 41% 34% 4	582
	21st to end	Night	8% 2 17% 39% 30% 4	657
August	1st to 10th	Night	8% 3 11% 46% 29% 2	597
	11th to 20th	Night	10% 3 15% 40% 29% 3	594
	21st to end	Night	10% 4 16% 40% 27% 3	869
September	1st to 10th	Night	13% 4 18% 36% 25% 4	800
	11th to 20th	Night	12% 6% 15% 31% 32% 4	800
	21st to end	Night	20% 7% 25% 30% 18% 1	800
October	1st to 10th	Night	18% 9% 19% 29% 22% 3	800
	11th to 20th	Night	17% 15% 24% 31% 12% 1	800
	21st to end	Night	18% 13% 27% 31% 10% 1	880
November	1st to 10th	Night	16% 12% 27% 33% 11% 1	820
	11th to 20th	Night	22% 16% 27% 26% 7% 1	840
	21st to end	Night	22% 18% 27% 27% 6%	840
December	1st to 10th	Night	23% 18% 31% 23% 5%	840
	11th to 20th	Night	22% 15% 31% 29% 3	840
	21st to end	Night	20% 18% 29% 31% 2	924

Page generated at 2026-03-30 02:18:40. Version ac07

Copyright © 2026 Attilla Danko.