Stardom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stardom Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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% 7% 2 6% 4 4 5% 4 6% 7% 40%	101254
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	97689
Transparency	Day	43% 6% 11% 23% 15% 2	101010
	Night	42% 5% 11% 23% 16% 3	97553
Seeing	Day	22% 15% 29% 21% 10% 3	15026
	Night	19% 13% 31% 27% 9% 1	24245

By Month

Percentage Cloud Cover NE (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	15% 9% 2 5% 3 3 3 3 5% 6% 47%	2517
	11th to 20th	Day	15% 9% 3 8% 5% 4 4 3 5% 6% 38%	2534
	21st to end	Day	23% 8% 3 7% 5% 4 3 3 4 5% 35%	3124
February	1st to 10th	Day	16% 8% 2 7% 5% 5% 4 3 5% 5% 40%	1710
	11th to 20th	Day	17% 7% 2 6% 4 4 4 3 5% 6% 42%	1834
	21st to end	Day	18% 8% 3 7% 5% 4 3 3 5% 5% 39%	1570
March	1st to 10th	Day	26% 7% 2 5% 3 4 3 2 4 5% 38%	3116
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 4 6% 7% 48%	3434
	21st to end	Day	22% 6% 2 5% 3 3 4 2 4 5% 43%	4086
April	1st to 10th	Day	16% 8% 3 5% 5% 4 5% 3 6% 6% 40%	2280
	11th to 20th	Day	14% 7% 2 5% 4 4 4 4 5% 7% 43%	2254
	21st to end	Day	16% 6% 2 5% 4 4 4 5% 6% 7% 40%	2280
May	1st to 10th	Day	26% 9% 3 6% 4 4 4 3 5% 7% 28%	4033
	11th to 20th	Day	24% 8% 3 7% 5% 5% 4 3 5% 6% 30%	4394
	21st to end	Day	12% 6% 2 5% 4 4 5% 4 5% 9% 44%	4837
June	1st to 10th	Day	13% 5% 2 5% 6% 5% 5% 4 7% 9% 39%	2660
	11th to 20th	Day	11% 7% 2 6% 6% 5% 5% 4 7% 8% 39%	2660
	21st to end	Day	10% 5% 2 7% 4 5% 6% 4 6% 9% 41%	2660
July	1st to 10th	Day	8% 5% 3 7% 6% 6% 8% 6% 9% 10% 34%	4440
	11th to 20th	Day	11% 6% 2 6% 4 5% 6% 5% 8% 10% 37%	4440
	21st to end	Day	11% 9% 3 8% 6% 5% 7% 4 7% 8% 32%	4793
August	1st to 10th	Day	18% 6% 3 7% 5% 5% 5% 5% 7% 7% 31%	4052
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 5% 7% 9% 39%	3730
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 44%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 3 5% 7% 44%	2280
	11th to 20th	Day	12% 6% 1 5% 4 3 4 4 5% 7% 50%	2228
	21st to end	Day	18% 7% 3 7% 4 3 4 4 5% 6% 39%	2090
October	1st to 10th	Day	18% 6% 2 6% 3 4 4 3 5% 6% 45%	1938
	11th to 20th	Day	15% 5% 2 5% 3 3 3 3 4 6% 51%	1900
	21st to end	Day	17% 5% 3 6% 3 2 4 2 5% 6% 47%	1996
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 2 5% 6% 52%	1671
	11th to 20th	Day	16% 6% 2 6% 3 3 4 3 5% 5% 47%	1710
	21st to end	Day	15% 5% 2 5% 5% 4 4 2 5% 7% 47%	1625
December	1st to 10th	Day	18% 8% 2 6% 4 3 3 3 6% 7% 39%	1520
	11th to 20th	Day	19% 8% 3 4 3 3 4 3 4 6% 44%	1906
	21st to end	Day	16% 7% 2 6% 4 4 6% 5% 6% 7% 37%	2772
January	1st to 10th	Night	17% 6% 2 5% 4 3 4 3 5% 6% 45%	4429
	11th to 20th	Night	18% 9% 3 7% 3 3 3 3 4 5% 44%	4408
	21st to end	Night	23% 8% 3 6% 4 4 4 2 4 5% 36%	4532
February	1st to 10th	Night	16% 8% 2 6% 3 4 4 3 5% 6% 42%	2470
	11th to 20th	Night	18% 8% 2 6% 4 3 3 3 5% 6% 41%	2230
	21st to end	Night	18% 8% 2 6% 3 3 3 4 5% 5% 42%	1884
March	1st to 10th	Night	23% 11% 2 5% 3 3 4 2 4 5% 37%	3724
	11th to 20th	Night	11% 6% 3 5% 4 4 4 3 4 7% 49%	3523
	21st to end	Night	18% 9% 3 6% 4 3 3 3 3 4 44%	3545
April	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 5% 6% 41%	1900
	11th to 20th	Night	15% 6% 3 6% 4 4 4 3 4 7% 43%	1875
	21st to end	Night	18% 6% 2 5% 3 4 4 3 5% 6% 44%	1900
May	1st to 10th	Night	22% 9% 4 8% 3 4 3 4 5% 8% 30%	2904
	11th to 20th	Night	24% 9% 3 7% 5% 4 4 3 4 6% 31%	2527
	21st to end	Night	14% 7% 2 5% 4 4 4 3 6% 10% 41%	2738
June	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 6% 8% 43%	1520
	11th to 20th	Night	10% 7% 2 6% 6% 5% 4 4 6% 6% 44%	1520
	21st to end	Night	8% 5% 2 4 5% 6% 5% 5% 8% 10% 41%	1520
July	1st to 10th	Night	8% 5% 3 7% 5% 6% 6% 5% 9% 10% 36%	2520
	11th to 20th	Night	11% 6% 2 6% 3 5% 5% 6% 7% 11% 38%	2520
	21st to end	Night	15% 7% 3 7% 4 5% 5% 4 6% 7% 35%	2756
August	1st to 10th	Night	22% 6% 2 7% 4 5% 5% 4 7% 8% 32%	2844
	11th to 20th	Night	12% 6% 2 7% 4 5% 4 3 6% 8% 42%	3097
	21st to end	Night	9% 6% 2 5% 4 3 4 4 6% 7% 50%	3476
September	1st to 10th	Night	14% 6% 2 5% 5% 5% 4 4 4 6% 45%	1900
	11th to 20th	Night	10% 6% 2 4 3 3 4 3 5% 8% 52%	1952
	21st to end	Night	18% 7% 2 6% 4 3 3 3 5% 7% 40%	2090
October	1st to 10th	Night	18% 6% 2 5% 4 4 3 3 5% 6% 44%	2237
	11th to 20th	Night	14% 5% 2 4 4 3 3 3 4 6% 52%	2280
	21st to end	Night	17% 6% 2 5% 4 3 3 3 4 5% 48%	2599
November	1st to 10th	Night	12% 5% 2 5% 4 4 3 3 5% 6% 52%	2414
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 4 5% 48%	2470
	21st to end	Night	13% 5% 2 5% 4 4 4 4 6% 7% 46%	2553
December	1st to 10th	Night	20% 6% 3 6% 3 3 4 4 5% 6% 40%	2660
	11th to 20th	Night	17% 6% 3 6% 4 4 4 3 5% 7% 41%	3288
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	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	40% 3 11% 26% 15% 4	2518
	11th to 20th	Day	48% 4 9% 22% 14% 3	2534
	21st to end	Day	52% 4 10% 22% 10% 2	3124
February	1st to 10th	Day	45% 4 11% 26% 12% 2	1710
	11th to 20th	Day	44% 4 9% 25% 16% 2	1843
	21st to end	Day	48% 4 9% 22% 14% 5%	1570
March	1st to 10th	Day	50% 3 7% 28% 9% 2	3119
	11th to 20th	Day	33% 4 9% 32% 18% 3	3434
	21st to end	Day	44% 4 7% 19% 21% 4	4086
April	1st to 10th	Day	43% 6% 9% 22% 15% 5%	2280
	11th to 20th	Day	40% 5% 12% 23% 17% 4	2254
	21st to end	Day	42% 5% 9% 20% 19% 4	2280
May	1st to 10th	Day	55% 6% 10% 17% 10% 2	4047
	11th to 20th	Day	54% 6% 11% 20% 8% 1	4398
	21st to end	Day	35% 8% 11% 27% 17% 2	4837
June	1st to 10th	Day	40% 8% 11% 24% 16% 2	2660
	11th to 20th	Day	40% 8% 12% 25% 13% 3	2660
	21st to end	Day	38% 7% 12% 23% 17% 2	2660
July	1st to 10th	Day	42% 9% 15% 18% 13% 2	4370
	11th to 20th	Day	41% 7% 16% 21% 14% 1	4365
	21st to end	Day	48% 7% 10% 18% 15% 1	4640
August	1st to 10th	Day	50% 6% 13% 21% 10% 1	4039
	11th to 20th	Day	40% 7% 12% 25% 14% 1	3766
	21st to end	Day	35% 6% 11% 27% 19% 2	4180
September	1st to 10th	Day	40% 6% 10% 19% 22% 3	2280
	11th to 20th	Day	34% 5% 9% 23% 25% 4	2228
	21st to end	Day	47% 5% 7% 19% 21% 2	2090
October	1st to 10th	Day	42% 4 10% 22% 20% 2	1938
	11th to 20th	Day	35% 4 10% 24% 24% 3	1900
	21st to end	Day	39% 4 8% 25% 21% 3	1996
November	1st to 10th	Day	35% 3 11% 27% 21% 3	1671
	11th to 20th	Day	40% 4 8% 24% 22% 3	1710
	21st to end	Day	39% 4 11% 31% 13% 2	1625
December	1st to 10th	Day	45% 3 14% 23% 14% 1	1520
	11th to 20th	Day	44% 3 11% 28% 12% 2	1906
	21st to end	Day	45% 6% 12% 22% 13% 1	2772
January	1st to 10th	Night	40% 4 9% 30% 14% 4	4429
	11th to 20th	Night	44% 3 10% 26% 14% 3	4408
	21st to end	Night	51% 3 7% 24% 13% 2	4532
February	1st to 10th	Night	44% 3 13% 24% 13% 2	2470
	11th to 20th	Night	44% 5% 8% 20% 19% 5%	2232
	21st to end	Night	43% 4 7% 23% 17% 5%	1884
March	1st to 10th	Night	50% 4 7% 24% 13% 2	3734
	11th to 20th	Night	36% 5% 11% 28% 16% 3	3524
	21st to end	Night	45% 4 6% 17% 23% 5%	3545
April	1st to 10th	Night	43% 5% 9% 19% 19% 5%	1900
	11th to 20th	Night	42% 4 9% 21% 19% 4	1875
	21st to end	Night	40% 6% 9% 20% 20% 5%	1900
May	1st to 10th	Night	52% 6% 10% 19% 11% 1	2910
	11th to 20th	Night	54% 6% 13% 15% 10% 2	2528
	21st to end	Night	38% 7% 14% 22% 17% 2	2739
June	1st to 10th	Night	39% 7% 11% 22% 19% 2	1520
	11th to 20th	Night	39% 8% 12% 27% 13% 2	1520
	21st to end	Night	35% 8% 15% 24% 16% 2	1520
July	1st to 10th	Night	42% 9% 19% 18% 11% 2	2480
	11th to 20th	Night	38% 7% 18% 25% 10% 1	2472
	21st to end	Night	46% 6% 14% 19% 14% 1	2668
August	1st to 10th	Night	49% 6% 18% 17% 9% 1	2833
	11th to 20th	Night	40% 5% 12% 29% 13% 1	3127
	21st to end	Night	32% 5% 11% 28% 22% 2	3476
September	1st to 10th	Night	38% 7% 11% 20% 21% 3	1900
	11th to 20th	Night	31% 4 11% 24% 26% 4	1952
	21st to end	Night	43% 6% 8% 22% 20% 2	2090
October	1st to 10th	Night	41% 6% 10% 23% 18% 3	2237
	11th to 20th	Night	34% 4 11% 28% 20% 3	2280
	21st to end	Night	39% 4 8% 26% 20% 3	2599
November	1st to 10th	Night	34% 4 11% 25% 21% 5%	2414
	11th to 20th	Night	40% 4 8% 23% 20% 5%	2470
	21st to end	Night	37% 5% 12% 27% 17% 2	2553
December	1st to 10th	Night	45% 4 12% 23% 14% 2	2660
	11th to 20th	Night	42% 4 12% 20% 18% 4	3288
	21st to end	Night	45% 6% 12% 25% 12% 1	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	26% 26% 28% 15% 3 1	180
	11th to 20th	Day	37% 27% 22% 13% 1	186
	21st to end	Day	31% 25% 26% 14% 3 1	297
February	1st to 10th	Day	29% 30% 27% 11% 3	270
	11th to 20th	Day	32% 25% 33% 9% 2	442
	21st to end	Day	32% 23% 31% 12% 2	382
March	1st to 10th	Day	29% 22% 29% 16% 3	460
	11th to 20th	Day	28% 23% 32% 12% 3 2	460
	21st to end	Day	28% 24% 30% 14% 4 1	506
April	1st to 10th	Day	28% 25% 29% 12% 4 1	460
	11th to 20th	Day	23% 21% 34% 15% 6% 2	452
	21st to end	Day	29% 18% 32% 15% 4 2	460
May	1st to 10th	Day	31% 19% 26% 15% 7% 2	463
	11th to 20th	Day	23% 15% 34% 20% 7% 2	487
	21st to end	Day	19% 11% 24% 29% 14% 4	529
June	1st to 10th	Day	16% 13% 32% 25% 12% 3	490
	11th to 20th	Day	15% 13% 30% 27% 11% 3	490
	21st to end	Day	12% 10% 32% 30% 12% 3	490
July	1st to 10th	Day	12% 6% 28% 29% 20% 6%	485
	11th to 20th	Day	8% 5% 29% 33% 21% 5%	484
	21st to end	Day	13% 7% 30% 30% 14% 5%	532
August	1st to 10th	Day	13% 6% 28% 31% 15% 7%	486
	11th to 20th	Day	13% 4 25% 32% 20% 5%	479
	21st to end	Day	13% 6% 29% 27% 17% 9%	539
September	1st to 10th	Day	16% 10% 26% 25% 16% 8%	490
	11th to 20th	Day	14% 8% 26% 30% 14% 9%	490
	21st to end	Day	27% 12% 24% 21% 11% 4	490
October	1st to 10th	Day	25% 10% 27% 20% 13% 6%	490
	11th to 20th	Day	20% 16% 28% 21% 11% 3	490
	21st to end	Day	19% 17% 34% 18% 11% 2	489
November	1st to 10th	Day	19% 13% 35% 19% 14% 1	365
	11th to 20th	Day	25% 20% 30% 18% 7%	370
	21st to end	Day	21% 19% 32% 20% 7% 1	285
December	1st to 10th	Day	26% 32% 28% 8% 7%	180
	11th to 20th	Day	37% 16% 32% 12% 2 1	180
	21st to end	Day	32% 18% 29% 16% 5% 1	198
January	1st to 10th	Night	21% 22% 34% 20% 3	760
	11th to 20th	Night	26% 18% 30% 22% 4	760
	21st to end	Night	19% 21% 37% 22% 2	836
February	1st to 10th	Night	21% 19% 36% 22% 2	760
	11th to 20th	Night	25% 26% 34% 14% 1	743
	21st to end	Night	26% 21% 32% 19% 2	628
March	1st to 10th	Night	24% 20% 32% 19% 4	760
	11th to 20th	Night	23% 23% 32% 17% 6%	760
	21st to end	Night	22% 17% 38% 18% 5%	836
April	1st to 10th	Night	22% 22% 35% 16% 5%	760
	11th to 20th	Night	20% 15% 38% 22% 5%	751
	21st to end	Night	21% 14% 35% 24% 5%	760
May	1st to 10th	Night	21% 14% 36% 23% 6%	614
	11th to 20th	Night	18% 14% 38% 26% 5%	393
	21st to end	Night	17% 7% 24% 40% 10% 2	411
June	1st to 10th	Night	17% 6% 31% 36% 10%	380
	11th to 20th	Night	12% 5% 29% 41% 12%	380
	21st to end	Night	10% 4 30% 45% 10% 1	380
July	1st to 10th	Night	10% 2 27% 43% 16% 2	370
	11th to 20th	Night	7% 3 23% 48% 17% 2	368
	21st to end	Night	11% 5% 27% 40% 16%	421
August	1st to 10th	Night	12% 3 19% 43% 21% 2	573
	11th to 20th	Night	13% 4 20% 40% 20% 3	750
	21st to end	Night	14% 3 20% 39% 22% 3	836
September	1st to 10th	Night	16% 5% 27% 34% 16% 2	760
	11th to 20th	Night	14% 4 23% 33% 23% 4	760
	21st to end	Night	23% 6% 25% 28% 17% 1	760
October	1st to 10th	Night	22% 7% 27% 27% 16% 3	760
	11th to 20th	Night	17% 11% 28% 30% 13% 1	760
	21st to end	Night	21% 12% 35% 23% 9%	836
November	1st to 10th	Night	16% 11% 35% 27% 11% 1	743
	11th to 20th	Night	20% 16% 28% 26% 9%	760
	21st to end	Night	18% 15% 36% 22% 7% 1	760
December	1st to 10th	Night	26% 17% 32% 19% 6% 1	760
	11th to 20th	Night	21% 18% 34% 22% 5%	760
	21st to end	Night	22% 17% 34% 25% 2	836

Page generated at 2024-10-29 11:20:45. Version ac07

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