Starhoo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starhoo Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	18% 8% 2 6% 4 4 4 3 5% 7% 38%	101207
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	97897
Transparency	Day	45% 4 11% 22% 15% 2	104772
	Night	46% 3 11% 22% 15% 2	102421
Seeing	Day	22% 18% 33% 19% 7% 2	15159
	Night	21% 14% 33% 24% 7% 1	24030

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% 10% 2 6% 3 3 3 3 4 6% 45%	2517
	11th to 20th	Day	19% 9% 2 6% 4 4 4 4 5% 4 40%	2520
	21st to end	Day	20% 13% 3 7% 4 4 3 3 4 5% 33%	2772
February	1st to 10th	Day	20% 8% 3 6% 4 4 5% 4 5% 6% 35%	1815
	11th to 20th	Day	15% 8% 2 6% 3 3 4 5% 5% 6% 42%	1848
	21st to end	Day	18% 10% 3 6% 5% 3 3 3 5% 5% 38%	1570
March	1st to 10th	Day	26% 16% 3 6% 4 3 3 2 3 5% 30%	3116
	11th to 20th	Day	12% 6% 3 6% 4 4 5% 3 7% 8% 43%	3370
	21st to end	Day	24% 10% 2 6% 4 3 4 3 4 4 35%	3988
April	1st to 10th	Day	20% 9% 2 5% 4 4 4 3 5% 6% 38%	2280
	11th to 20th	Day	19% 7% 2 6% 5% 4 4 3 5% 7% 39%	2276
	21st to end	Day	20% 7% 2 6% 5% 4 4 3 5% 6% 38%	2470
May	1st to 10th	Day	26% 12% 3 7% 4 3 3 3 5% 6% 28%	4106
	11th to 20th	Day	24% 11% 3 7% 4 4 3 3 4 6% 32%	4081
	21st to end	Day	17% 6% 2 4 4 3 4 3 5% 8% 44%	4804
June	1st to 10th	Day	20% 6% 2 6% 4 4 4 4 6% 8% 35%	2660
	11th to 20th	Day	17% 5% 2 6% 5% 4 5% 4 6% 8% 38%	2660
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 6% 10% 37%	2660
July	1st to 10th	Day	14% 6% 2 7% 5% 4 6% 5% 7% 10% 34%	4440
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 7% 9% 37%	4440
	21st to end	Day	19% 7% 3 7% 5% 5% 5% 4 6% 8% 32%	4785
August	1st to 10th	Day	18% 7% 3 8% 5% 5% 5% 4 6% 9% 31%	4105
	11th to 20th	Day	12% 7% 3 8% 5% 5% 6% 4 6% 8% 37%	4013
	21st to end	Day	8% 4 2 5% 4 5% 6% 5% 7% 9% 46%	4180
September	1st to 10th	Day	15% 6% 2 5% 4 3 4 3 5% 7% 46%	2256
	11th to 20th	Day	15% 6% 2 5% 3 5% 3 3 4 6% 50%	2090
	21st to end	Day	20% 6% 2 6% 4 3 3 3 5% 6% 42%	2090
October	1st to 10th	Day	23% 6% 1 4 4 3 3 3 4 5% 43%	2090
	11th to 20th	Day	16% 5% 1 5% 4 3 3 3 5% 7% 48%	1879
	21st to end	Day	18% 6% 2 5% 3 3 3 3 5% 6% 44%	1881
November	1st to 10th	Day	17% 7% 2 6% 3 3 3 3 4 5% 47%	1734
	11th to 20th	Day	18% 7% 2 4 3 3 3 4 4 5% 46%	1710
	21st to end	Day	17% 7% 3 5% 4 4 4 3 5% 6% 43%	1710
December	1st to 10th	Day	19% 8% 3 5% 4 4 4 3 4 6% 40%	1613
	11th to 20th	Day	20% 7% 2 5% 3 4 3 2 3 6% 44%	1906
	21st to end	Day	22% 10% 3 8% 5% 4 3 3 5% 5% 34%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 6% 48%	4429
	11th to 20th	Night	16% 12% 4 7% 4 4 3 3 4 4 40%	4440
	21st to end	Night	23% 13% 4 8% 5% 4 4 3 4 4 29%	4884
February	1st to 10th	Night	17% 9% 3 6% 4 3 4 4 4 5% 40%	2361
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 5% 5% 39%	2218
	21st to end	Night	19% 8% 2 6% 4 4 4 3 4 5% 41%	1884
March	1st to 10th	Night	31% 11% 2 4 3 4 3 2 4 5% 33%	3724
	11th to 20th	Night	11% 10% 3 7% 5% 4 4 4 6% 6% 41%	3589
	21st to end	Night	25% 9% 3 7% 4 5% 4 4 3 3 33%	3640
April	1st to 10th	Night	19% 9% 3 6% 4 4 4 3 5% 5% 37%	1900
	11th to 20th	Night	20% 8% 2 6% 4 4 4 3 5% 6% 37%	1851
	21st to end	Night	20% 8% 2 6% 4 5% 4 3 5% 5% 39%	1710
May	1st to 10th	Night	24% 11% 4 8% 4 4 4 3 6% 6% 26%	2834
	11th to 20th	Night	24% 11% 3 8% 4 4 5% 4 5% 7% 24%	2813
	21st to end	Night	18% 7% 2 6% 4 4 5% 3 6% 7% 38%	2785
June	1st to 10th	Night	18% 7% 3 6% 5% 4 5% 4 5% 7% 37%	1520
	11th to 20th	Night	17% 8% 2 6% 6% 4 4 3 5% 8% 37%	1520
	21st to end	Night	17% 9% 2 5% 3 4 4 3 6% 9% 38%	1520
July	1st to 10th	Night	17% 7% 3 6% 4 5% 4 5% 6% 10% 33%	2520
	11th to 20th	Night	17% 6% 2 6% 4 4 5% 4 7% 9% 36%	2520
	21st to end	Night	18% 9% 3 7% 5% 5% 5% 4 7% 6% 32%	2739
August	1st to 10th	Night	22% 8% 2 6% 4 5% 5% 5% 6% 8% 29%	2820
	11th to 20th	Night	9% 7% 3 8% 5% 5% 5% 5% 6% 9% 37%	2810
	21st to end	Night	9% 4 1 5% 3 4 4 3 5% 7% 54%	3476
September	1st to 10th	Night	14% 6% 3 6% 4 4 4 4 4 7% 44%	1924
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 3 7% 51%	2090
	21st to end	Night	19% 6% 3 5% 4 3 5% 3 5% 6% 41%	2090
October	1st to 10th	Night	21% 7% 2 6% 4 4 4 2 4 6% 41%	2090
	11th to 20th	Night	16% 5% 2 4 4 4 3 3 6% 6% 47%	2297
	21st to end	Night	19% 8% 3 5% 4 3 5% 3 4 6% 39%	2717
November	1st to 10th	Night	15% 5% 2 6% 3 3 4 3 5% 6% 46%	2505
	11th to 20th	Night	17% 8% 2 5% 3 3 3 3 4 5% 46%	2470
	21st to end	Night	17% 5% 2 5% 4 3 3 4 5% 6% 45%	2470
December	1st to 10th	Night	20% 8% 2 6% 4 4 4 4 4 5% 39%	2565
	11th to 20th	Night	20% 8% 2 5% 3 3 4 4 5% 6% 41%	3288
	21st to end	Night	20% 12% 3 8% 4 3 3 2 4 5% 36%	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	42% 2 8% 30% 16% 2	2518
	11th to 20th	Day	47% 4 9% 24% 12% 3	2520
	21st to end	Day	56% 2 8% 22% 10% 1	2772
February	1st to 10th	Day	50% 3 11% 19% 13% 3	1815
	11th to 20th	Day	43% 4 11% 23% 16% 3	1857
	21st to end	Day	49% 3 9% 21% 15% 3	1570
March	1st to 10th	Day	60% 2 10% 14% 11% 2	3119
	11th to 20th	Day	38% 3 13% 29% 15% 2	3370
	21st to end	Day	54% 2 5% 16% 15% 7%	3988
April	1st to 10th	Day	49% 3 8% 20% 17% 3	2280
	11th to 20th	Day	47% 3 8% 22% 17% 3	2276
	21st to end	Day	47% 4 9% 21% 16% 4	2470
May	1st to 10th	Day	59% 3 12% 15% 9% 1	4120
	11th to 20th	Day	55% 3 14% 16% 10% 2	4085
	21st to end	Day	39% 4 12% 24% 20% 2	4804
June	1st to 10th	Day	47% 5% 12% 24% 12% 1	2660
	11th to 20th	Day	43% 4 14% 23% 14% 2	2660
	21st to end	Day	43% 6% 14% 23% 14% 1	2660
July	1st to 10th	Day	46% 6% 13% 20% 14% 2	4370
	11th to 20th	Day	43% 4 16% 23% 13% 2	4365
	21st to end	Day	49% 4 12% 20% 12% 2	4632
August	1st to 10th	Day	51% 4 15% 21% 8%	4092
	11th to 20th	Day	44% 5% 15% 26% 10% 1	4052
	21st to end	Day	34% 5% 14% 26% 20% 1	4180
September	1st to 10th	Day	38% 5% 9% 25% 21% 1	2256
	11th to 20th	Day	36% 3 9% 25% 23% 3	2090
	21st to end	Day	44% 4 7% 20% 22% 2	2090
October	1st to 10th	Day	40% 4 10% 26% 17% 4	3480
	11th to 20th	Day	32% 2 6% 31% 26% 3	3095
	21st to end	Day	31% 3 13% 30% 20% 3	3081
November	1st to 10th	Day	41% 4 13% 22% 18% 2	1734
	11th to 20th	Day	41% 4 10% 23% 20% 3	1710
	21st to end	Day	43% 5% 11% 26% 13% 2	1710
December	1st to 10th	Day	48% 3 13% 17% 17% 2	1613
	11th to 20th	Day	45% 3 13% 17% 16% 6%	1906
	21st to end	Day	53% 3 10% 23% 10% 1	2772
January	1st to 10th	Night	40% 2 10% 32% 12% 3	4429
	11th to 20th	Night	49% 3 10% 23% 12% 3	4440
	21st to end	Night	60% 2 8% 17% 11% 2	4884
February	1st to 10th	Night	47% 3 12% 21% 13% 2	2361
	11th to 20th	Night	47% 3 8% 21% 17% 4	2220
	21st to end	Night	46% 3 7% 24% 16% 4	1884
March	1st to 10th	Night	56% 2 9% 18% 12% 3	3734
	11th to 20th	Night	44% 3 13% 21% 17% 3	3590
	21st to end	Night	57% 2 5% 13% 17% 6%	3640
April	1st to 10th	Night	49% 3 9% 19% 17% 4	1900
	11th to 20th	Night	48% 3 8% 20% 18% 3	1851
	21st to end	Night	48% 3 8% 20% 16% 4	1710
May	1st to 10th	Night	60% 3 13% 16% 7% 2	2840
	11th to 20th	Night	59% 4 13% 14% 7% 2	2814
	21st to end	Night	46% 4 13% 23% 13% 1	2786
June	1st to 10th	Night	47% 6% 12% 23% 13% 1	1520
	11th to 20th	Night	46% 4 11% 25% 14% 1	1520
	21st to end	Night	43% 5% 14% 24% 13% 1	1520
July	1st to 10th	Night	48% 5% 11% 19% 16%	2480
	11th to 20th	Night	44% 4 16% 24% 11% 1	2472
	21st to end	Night	51% 5% 11% 18% 12% 2	2651
August	1st to 10th	Night	53% 5% 13% 18% 9% 1	2809
	11th to 20th	Night	43% 4 16% 28% 9%	2837
	21st to end	Night	29% 3 15% 29% 23% 1	3476
September	1st to 10th	Night	40% 5% 10% 25% 19% 2	1924
	11th to 20th	Night	36% 3 10% 24% 25% 2	2090
	21st to end	Night	45% 4 7% 22% 19% 2	2090
October	1st to 10th	Night	42% 4 11% 27% 15% 2	3480
	11th to 20th	Night	27% 2 8% 27% 33% 3	3820
	21st to end	Night	34% 3 11% 28% 21% 2	4467
November	1st to 10th	Night	40% 4 12% 24% 17% 3	2505
	11th to 20th	Night	42% 3 10% 22% 19% 4	2470
	21st to end	Night	39% 3 13% 28% 14% 3	2470
December	1st to 10th	Night	48% 3 12% 21% 15% 1	2565
	11th to 20th	Night	45% 4 13% 18% 18% 2	3288
	21st to end	Night	52% 4 8% 25% 11% 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	25% 29% 28% 16% 2	180
	11th to 20th	Day	25% 28% 36% 8% 2 1	180
	21st to end	Day	24% 26% 37% 10% 2 1	198
February	1st to 10th	Day	29% 24% 33% 13% 1	417
	11th to 20th	Day	28% 30% 33% 7% 2	456
	21st to end	Day	26% 28% 31% 12% 3	382
March	1st to 10th	Day	28% 24% 33% 13% 3	460
	11th to 20th	Day	25% 28% 33% 10% 3 1	460
	21st to end	Day	28% 23% 32% 10% 5% 1	506
April	1st to 10th	Day	29% 25% 29% 12% 5% 1	460
	11th to 20th	Day	25% 27% 32% 13% 3	452
	21st to end	Day	27% 20% 33% 15% 3 2	460
May	1st to 10th	Day	31% 24% 30% 11% 3 1	463
	11th to 20th	Day	23% 16% 41% 13% 6% 1	487
	21st to end	Day	19% 14% 36% 23% 7% 1	529
June	1st to 10th	Day	19% 16% 33% 23% 7% 1	490
	11th to 20th	Day	15% 18% 40% 19% 7% 1	490
	21st to end	Day	16% 13% 39% 25% 6% 2	490
July	1st to 10th	Day	15% 9% 31% 31% 11% 2	485
	11th to 20th	Day	14% 8% 33% 31% 12% 2	484
	21st to end	Day	13% 11% 36% 28% 11% 1	532
August	1st to 10th	Day	13% 9% 36% 30% 10% 2	486
	11th to 20th	Day	14% 11% 30% 28% 14% 3	479
	21st to end	Day	14% 9% 32% 27% 13% 6%	539
September	1st to 10th	Day	19% 10% 31% 24% 13% 3	490
	11th to 20th	Day	18% 12% 28% 24% 11% 8%	490
	21st to end	Day	24% 12% 29% 23% 7% 4	490
October	1st to 10th	Day	26% 13% 27% 20% 9% 5%	490
	11th to 20th	Day	18% 17% 34% 19% 10% 2	428
	21st to end	Day	23% 19% 29% 20% 7% 3	429
November	1st to 10th	Day	18% 18% 35% 17% 9% 2	386
	11th to 20th	Day	27% 22% 31% 15% 5% 1	370
	21st to end	Day	22% 23% 30% 16% 9%	370
December	1st to 10th	Day	21% 25% 36% 14% 4	273
	11th to 20th	Day	30% 28% 32% 8% 2	180
	21st to end	Day	26% 25% 35% 9% 4 2	198
January	1st to 10th	Night	22% 20% 37% 18% 3	760
	11th to 20th	Night	28% 21% 34% 14% 3	760
	21st to end	Night	22% 20% 35% 19% 3	836
February	1st to 10th	Night	24% 18% 38% 18% 1	760
	11th to 20th	Night	25% 22% 39% 13% 1	743
	21st to end	Night	25% 21% 33% 17% 3	628
March	1st to 10th	Night	26% 18% 34% 19% 4	760
	11th to 20th	Night	20% 21% 39% 17% 4	760
	21st to end	Night	25% 19% 35% 17% 3	836
April	1st to 10th	Night	24% 18% 35% 19% 4	760
	11th to 20th	Night	23% 19% 36% 19% 3	727
	21st to end	Night	22% 17% 36% 21% 4	570
May	1st to 10th	Night	29% 14% 33% 20% 4	570
	11th to 20th	Night	22% 14% 40% 19% 4	562
	21st to end	Night	22% 7% 33% 32% 6%	445
June	1st to 10th	Night	18% 9% 31% 32% 9% 1	380
	11th to 20th	Night	20% 6% 33% 33% 8%	380
	21st to end	Night	20% 7% 29% 37% 6%	380
July	1st to 10th	Night	16% 4 29% 40% 10% 1	370
	11th to 20th	Night	16% 5% 27% 42% 10%	368
	21st to end	Night	15% 4 27% 43% 10%	416
August	1st to 10th	Night	13% 7% 33% 39% 8%	563
	11th to 20th	Night	14% 6% 27% 41% 12%	577
	21st to end	Night	14% 5% 24% 39% 17% 2	836
September	1st to 10th	Night	15% 6% 31% 34% 13% 1	760
	11th to 20th	Night	16% 7% 25% 30% 18% 3	760
	21st to end	Night	23% 6% 28% 28% 13% 2	760
October	1st to 10th	Night	24% 9% 26% 27% 13% 2	760
	11th to 20th	Night	18% 11% 34% 23% 12% 1	760
	21st to end	Night	24% 13% 35% 19% 8%	836
November	1st to 10th	Night	17% 14% 33% 25% 10% 1	771
	11th to 20th	Night	21% 22% 33% 18% 7% 1	760
	21st to end	Night	20% 21% 34% 21% 4 1	760
December	1st to 10th	Night	25% 18% 34% 18% 4	760
	11th to 20th	Night	24% 20% 33% 20% 3	760
	21st to end	Night	26% 19% 34% 19% 2	836

Page generated at 2024-11-05 08:15:50. Version ac07

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