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 2024-12-09.

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	13% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	101379
	Night	12% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	98331
Transparency	Day	41% 8% 12% 22% 14% 2	105027
	Night	39% 9% 13% 23% 14% 2	102823
Seeing	Day	21% 15% 26% 21% 13% 4	14995
	Night	18% 13% 26% 30% 12% 1	24710

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% 9% 5% 9% 6% 5% 5% 3 4 5% 35%	2807
	11th to 20th	Day	10% 15% 5% 11% 10% 4 5% 3 4 4 30%	2840
	21st to end	Day	13% 12% 5% 9% 6% 5% 4 4 5% 6% 32%	3124
February	1st to 10th	Day	13% 12% 4 8% 6% 5% 5% 4 4 6% 34%	1710
	11th to 20th	Day	14% 9% 4 9% 6% 5% 4 3 6% 6% 34%	1663
	21st to end	Day	14% 11% 4 8% 6% 3 4 3 6% 5% 37%	1603
March	1st to 10th	Day	17% 12% 4 7% 5% 4 4 3 4 7% 33%	3435
	11th to 20th	Day	11% 8% 3 6% 4 4 3 4 5% 7% 46%	3480
	21st to end	Day	17% 11% 3 7% 5% 5% 4 4 4 5% 36%	3815
April	1st to 10th	Day	10% 11% 3 9% 6% 5% 5% 4 5% 7% 36%	2237
	11th to 20th	Day	13% 7% 3 7% 4 4 4 4 5% 7% 42%	2254
	21st to end	Day	17% 9% 3 7% 5% 4 4 3 7% 6% 36%	2365
May	1st to 10th	Day	20% 9% 3 8% 5% 5% 5% 4 6% 7% 28%	4082
	11th to 20th	Day	21% 8% 3 7% 5% 5% 5% 3 6% 7% 30%	4081
	21st to end	Day	9% 6% 2 6% 6% 6% 6% 5% 7% 9% 38%	4783
June	1st to 10th	Day	12% 6% 2 6% 5% 4 6% 4 7% 9% 39%	2660
	11th to 20th	Day	11% 5% 2 7% 6% 5% 6% 5% 7% 10% 35%	2660
	21st to end	Day	9% 5% 2 6% 6% 6% 6% 4 7% 10% 39%	2660
July	1st to 10th	Day	5% 5% 2 7% 5% 5% 6% 5% 8% 10% 42%	4328
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 5% 8% 11% 38%	4120
	21st to end	Day	11% 8% 3 8% 6% 6% 5% 4 6% 8% 34%	4466
August	1st to 10th	Day	14% 5% 3 8% 6% 7% 6% 6% 8% 8% 31%	4104
	11th to 20th	Day	8% 5% 2 8% 5% 6% 6% 6% 8% 9% 38%	4022
	21st to end	Day	7% 5% 2 6% 4 4 6% 5% 7% 8% 46%	4180
September	1st to 10th	Day	13% 5% 2 6% 5% 5% 5% 4 6% 6% 43%	2280
	11th to 20th	Day	12% 7% 2 5% 4 4 5% 4 6% 8% 43%	2185
	21st to end	Day	19% 9% 3 7% 4 4 4 4 6% 6% 35%	2034
October	1st to 10th	Day	17% 6% 2 5% 3 4 4 3 5% 6% 45%	1900
	11th to 20th	Day	15% 8% 2 6% 4 4 3 3 5% 6% 43%	1900
	21st to end	Day	13% 8% 2 6% 3 3 4 3 5% 6% 45%	2090
November	1st to 10th	Day	9% 6% 3 6% 4 4 4 3 5% 5% 51%	1957
	11th to 20th	Day	13% 8% 3 6% 5% 4 5% 4 6% 7% 40%	1688
	21st to end	Day	14% 9% 3 7% 5% 5% 4 4 4 8% 39%	1600
December	1st to 10th	Day	14% 12% 3 8% 6% 5% 5% 3 5% 6% 33%	1584
	11th to 20th	Day	14% 11% 4 8% 4 4 4 3 4 6% 37%	1910
	21st to end	Day	15% 7% 3 9% 5% 6% 5% 5% 7% 8% 29%	2772
January	1st to 10th	Night	9% 12% 5% 12% 7% 6% 5% 4 6% 6% 30%	4135
	11th to 20th	Night	13% 10% 4 10% 5% 4 4 3 5% 5% 38%	4120
	21st to end	Night	15% 11% 4 8% 6% 5% 4 4 5% 5% 33%	4532
February	1st to 10th	Night	11% 9% 3 9% 6% 6% 5% 4 6% 6% 36%	2470
	11th to 20th	Night	15% 10% 4 9% 5% 5% 6% 4 4 6% 33%	2403
	21st to end	Night	13% 12% 4 8% 6% 5% 4 4 4 5% 33%	1846
March	1st to 10th	Night	18% 8% 3 9% 5% 4 4 3 4 6% 35%	3418
	11th to 20th	Night	9% 9% 4 8% 6% 4 4 3 4 6% 42%	3480
	21st to end	Night	12% 7% 3 8% 5% 4 4 3 4 5% 45%	3817
April	1st to 10th	Night	12% 10% 3 8% 6% 5% 5% 4 5% 7% 36%	1941
	11th to 20th	Night	13% 8% 2 6% 5% 5% 5% 4 6% 8% 40%	1875
	21st to end	Night	15% 7% 3 6% 4 4 5% 3 5% 7% 40%	1830
May	1st to 10th	Night	20% 9% 3 7% 5% 6% 5% 3 6% 7% 29%	2813
	11th to 20th	Night	20% 10% 3 7% 5% 4 5% 3 4 6% 33%	2812
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 7% 10% 41%	2767
June	1st to 10th	Night	10% 5% 2 4 5% 6% 3 4 6% 9% 45%	1520
	11th to 20th	Night	9% 6% 2 7% 4 5% 5% 5% 6% 10% 41%	1520
	21st to end	Night	8% 5% 1 6% 4 5% 5% 5% 8% 10% 42%	1520
July	1st to 10th	Night	6% 5% 2 6% 6% 5% 6% 5% 7% 10% 43%	2613
	11th to 20th	Night	6% 6% 3 8% 5% 6% 6% 5% 8% 9% 41%	2840
	21st to end	Night	8% 7% 3 7% 5% 5% 6% 5% 7% 9% 37%	3087
August	1st to 10th	Night	12% 5% 2 8% 5% 5% 6% 5% 7% 9% 36%	2825
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 4 7% 10% 42%	2785
	21st to end	Night	8% 6% 2 6% 4 3 4 4 6% 9% 47%	3465
September	1st to 10th	Night	12% 6% 2 5% 3 4 4 4 6% 7% 46%	1900
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 5% 8% 50%	1991
	21st to end	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	2144
October	1st to 10th	Night	17% 6% 2 6% 3 4 4 3 4 6% 45%	2280
	11th to 20th	Night	12% 7% 2 6% 3 4 4 4 5% 6% 49%	2280
	21st to end	Night	14% 7% 2 6% 5% 4 4 3 4 6% 46%	2508
November	1st to 10th	Night	9% 9% 3 6% 4 4 4 3 5% 6% 48%	2341
	11th to 20th	Night	12% 8% 3 7% 4 4 4 4 6% 7% 41%	2705
	21st to end	Night	12% 8% 3 7% 6% 5% 5% 4 6% 7% 38%	2800
December	1st to 10th	Night	13% 9% 5% 10% 6% 4 5% 3 5% 6% 33%	2779
	11th to 20th	Night	15% 7% 3 8% 6% 5% 5% 4 5% 6% 36%	3285
	21st to end	Night	13% 9% 3 8% 6% 6% 6% 5% 6% 8% 29%	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	47% 5% 10% 24% 12% 2	2808
	11th to 20th	Day	52% 6% 11% 16% 12% 2	2840
	21st to end	Day	49% 9% 9% 19% 12% 1	3124
February	1st to 10th	Day	49% 6% 11% 20% 12% 2	1710
	11th to 20th	Day	49% 4 12% 20% 13% 2	1672
	21st to end	Day	47% 6% 12% 19% 13% 3	1603
March	1st to 10th	Day	49% 6% 12% 20% 12% 1	3435
	11th to 20th	Day	33% 6% 10% 29% 20% 2	3480
	21st to end	Day	47% 7% 12% 19% 13% 2	3815
April	1st to 10th	Day	45% 7% 12% 17% 15% 4	2237
	11th to 20th	Day	39% 6% 11% 21% 18% 5%	2254
	21st to end	Day	46% 6% 11% 21% 13% 3	2365
May	1st to 10th	Day	51% 9% 10% 20% 9% 1	4120
	11th to 20th	Day	49% 9% 11% 22% 7% 1	4085
	21st to end	Day	35% 12% 16% 21% 14% 2	4797
June	1st to 10th	Day	38% 10% 14% 23% 15% 1	2660
	11th to 20th	Day	39% 11% 15% 21% 13% 1	2660
	21st to end	Day	37% 9% 15% 24% 13% 2	2660
July	1st to 10th	Day	34% 12% 16% 25% 10% 4	4261
	11th to 20th	Day	35% 10% 16% 28% 9% 1	4051
	21st to end	Day	45% 8% 10% 22% 14% 1	4324
August	1st to 10th	Day	45% 11% 16% 21% 7%	4091
	11th to 20th	Day	37% 9% 14% 27% 12%	4061
	21st to end	Day	33% 10% 15% 26% 15% 1	4180
September	1st to 10th	Day	39% 8% 12% 17% 21% 3	2280
	11th to 20th	Day	37% 6% 10% 25% 18% 3	2185
	21st to end	Day	46% 7% 11% 19% 15% 1	2034
October	1st to 10th	Day	30% 6% 10% 23% 26% 5%	3160
	11th to 20th	Day	30% 7% 11% 24% 17% 12%	3140
	21st to end	Day	27% 4 10% 30% 24% 6%	3428
November	1st to 10th	Day	33% 5% 12% 24% 21% 4	1957
	11th to 20th	Day	40% 6% 12% 18% 20% 4	1688
	21st to end	Day	42% 6% 12% 24% 15% 1	1600
December	1st to 10th	Day	49% 8% 11% 21% 10% 1	1584
	11th to 20th	Day	42% 8% 13% 25% 9% 3	1906
	21st to end	Day	45% 11% 15% 19% 9% 1	2772
January	1st to 10th	Night	41% 12% 12% 21% 11% 2	4135
	11th to 20th	Night	44% 8% 12% 22% 12% 3	4120
	21st to end	Night	48% 7% 12% 23% 9% 1	4532
February	1st to 10th	Night	45% 6% 13% 23% 12% 1	2470
	11th to 20th	Night	49% 5% 11% 20% 13% 2	2405
	21st to end	Night	48% 9% 10% 19% 11% 4	1846
March	1st to 10th	Night	48% 6% 12% 24% 9% 2	3418
	11th to 20th	Night	33% 11% 13% 27% 15% 1	3480
	21st to end	Night	38% 7% 11% 24% 18% 3	3817
April	1st to 10th	Night	44% 8% 11% 19% 15% 3	1941
	11th to 20th	Night	39% 7% 13% 21% 15% 5%	1875
	21st to end	Night	41% 7% 11% 24% 13% 3	1830
May	1st to 10th	Night	50% 11% 10% 17% 9% 2	2840
	11th to 20th	Night	48% 10% 11% 22% 8% 1	2813
	21st to end	Night	32% 14% 17% 25% 9% 4	2774
June	1st to 10th	Night	33% 10% 13% 28% 15% 1	1520
	11th to 20th	Night	36% 12% 15% 24% 13% 1	1520
	21st to end	Night	32% 10% 17% 24% 16% 2	1520
July	1st to 10th	Night	33% 11% 22% 18% 12% 4	2571
	11th to 20th	Night	35% 11% 18% 24% 10% 1	2786
	21st to end	Night	38% 11% 15% 22% 13%	2988
August	1st to 10th	Night	41% 11% 18% 22% 7%	2814
	11th to 20th	Night	36% 9% 16% 23% 16%	2812
	21st to end	Night	32% 9% 16% 30% 12% 1	3465
September	1st to 10th	Night	35% 9% 15% 19% 18% 4	1900
	11th to 20th	Night	32% 7% 12% 28% 19% 2	1991
	21st to end	Night	42% 7% 11% 22% 16% 1	2144
October	1st to 10th	Night	35% 6% 12% 24% 22% 2	3800
	11th to 20th	Night	27% 6% 12% 22% 25% 8%	3779
	21st to end	Night	25% 5% 11% 30% 23% 5%	4120
November	1st to 10th	Night	35% 6% 12% 22% 20% 5%	2341
	11th to 20th	Night	39% 6% 10% 24% 17% 4	2705
	21st to end	Night	42% 8% 12% 21% 15% 2	2800
December	1st to 10th	Night	49% 7% 11% 22% 9% 2	2779
	11th to 20th	Night	43% 7% 12% 22% 14% 1	3288
	21st to end	Night	45% 12% 18% 16% 9%	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	32% 29% 23% 12% 3 1	263
	11th to 20th	Day	33% 23% 29% 11% 3	270
	21st to end	Day	32% 24% 31% 11% 2	297
February	1st to 10th	Day	32% 27% 27% 12% 1	270
	11th to 20th	Day	45% 21% 28% 5%	270
	21st to end	Day	36% 22% 25% 15% 1	342
March	1st to 10th	Day	30% 23% 24% 20% 3	460
	11th to 20th	Day	30% 25% 23% 15% 5% 1	460
	21st to end	Day	28% 22% 29% 15% 5% 1	506
April	1st to 10th	Day	24% 25% 27% 17% 7% 1	460
	11th to 20th	Day	21% 21% 27% 18% 10% 3	452
	21st to end	Day	30% 16% 27% 17% 8% 1	460
May	1st to 10th	Day	24% 21% 26% 16% 10% 4	463
	11th to 20th	Day	22% 15% 31% 18% 11% 3	487
	21st to end	Day	17% 10% 26% 24% 17% 6%	529
June	1st to 10th	Day	16% 12% 27% 25% 14% 5%	490
	11th to 20th	Day	15% 10% 28% 24% 16% 6%	490
	21st to end	Day	10% 13% 31% 27% 15% 3	490
July	1st to 10th	Day	11% 6% 24% 27% 23% 9%	485
	11th to 20th	Day	7% 4 28% 28% 24% 9%	484
	21st to end	Day	14% 6% 21% 29% 23% 7%	532
August	1st to 10th	Day	12% 8% 21% 26% 24% 8%	486
	11th to 20th	Day	11% 6% 25% 26% 21% 11%	479
	21st to end	Day	10% 5% 21% 30% 22% 12%	539
September	1st to 10th	Day	16% 9% 21% 23% 22% 9%	490
	11th to 20th	Day	14% 5% 23% 26% 24% 9%	490
	21st to end	Day	26% 10% 26% 21% 14% 3	490
October	1st to 10th	Day	20% 8% 23% 26% 19% 3	490
	11th to 20th	Day	20% 18% 22% 25% 13% 2	490
	21st to end	Day	18% 19% 30% 22% 9% 3	539
November	1st to 10th	Day	18% 16% 29% 24% 11% 2	495
	11th to 20th	Day	25% 19% 28% 21% 7% 1	273
	21st to end	Day	30% 18% 31% 18% 4 1	200
December	1st to 10th	Day	28% 23% 33% 11% 4 2	196
	11th to 20th	Day	27% 23% 25% 19% 6%	180
	21st to end	Day	24% 21% 28% 22% 5% 1	198
January	1st to 10th	Night	22% 22% 34% 19% 3	760
	11th to 20th	Night	24% 19% 29% 25% 3	760
	21st to end	Night	22% 22% 34% 21% 1	836
February	1st to 10th	Night	19% 20% 31% 28% 2	760
	11th to 20th	Night	27% 26% 28% 17% 1	743
	21st to end	Night	27% 19% 36% 17% 2	628
March	1st to 10th	Night	22% 19% 32% 24% 3	760
	11th to 20th	Night	27% 20% 26% 21% 5% 1	760
	21st to end	Night	22% 20% 32% 21% 5% 1	836
April	1st to 10th	Night	21% 22% 30% 22% 5%	760
	11th to 20th	Night	19% 16% 29% 27% 9%	751
	21st to end	Night	22% 13% 28% 30% 7%	690
May	1st to 10th	Night	21% 10% 25% 29% 14% 1	570
	11th to 20th	Night	17% 8% 27% 35% 13% 1	561
	21st to end	Night	10% 4 26% 37% 21% 2	434
June	1st to 10th	Night	10% 4 25% 38% 20% 2	380
	11th to 20th	Night	11% 4 19% 46% 18% 2	380
	21st to end	Night	8% 3 22% 48% 18% 1	380
July	1st to 10th	Night	9% 3 16% 41% 25% 5%	422
	11th to 20th	Night	6% 2 13% 41% 35% 3	552
	21st to end	Night	8% 2 17% 39% 30% 4	624
August	1st to 10th	Night	8% 3 11% 46% 30% 2	567
	11th to 20th	Night	10% 3 14% 40% 29% 3	564
	21st to end	Night	10% 4 15% 40% 28% 4	825
September	1st to 10th	Night	14% 4 17% 35% 25% 4	760
	11th to 20th	Night	12% 6% 16% 31% 32% 4	760
	21st to end	Night	20% 6% 24% 29% 19% 1	760
October	1st to 10th	Night	19% 9% 19% 29% 22% 3	760
	11th to 20th	Night	16% 15% 23% 31% 13% 1	760
	21st to end	Night	18% 13% 27% 31% 10% 1	836
November	1st to 10th	Night	14% 13% 28% 33% 11% 1	780
	11th to 20th	Night	21% 15% 28% 28% 8% 1	800
	21st to end	Night	21% 18% 27% 28% 6%	800
December	1st to 10th	Night	23% 18% 30% 23% 6%	795
	11th to 20th	Night	20% 15% 33% 30% 3	760
	21st to end	Night	18% 18% 30% 32% 2	836

Page generated at 2024-12-06 03:54:51. Version ac07

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