Starsearch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starsearch Observatory clear sky chart from 2005-11-05 to 2008-11-20.

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	10% 8% 5% 6% 45%	12236
	Night	11% 8% 5% 5% 43%	12051
Transparency	Day	7% 15% 21% 21% 11%	9020
	Night	8% 17% 23% 18% 9%	8753
Seeing	Day	20% 32% 26% 12%	758
	Night	8% 21% 38% 20%	3714

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	13% 20% 9% 7% 5% 5% 21%	790
	Night	15% 15% 7% 8% 6% 26%	1247
February	Day	14% 20% 8% 10% 5% 6% 20%	759
	Night	11% 13% 10% 7% 5% 5% 6% 5% 29%	1020
March	Day	10% 16% 11% 7% 5% 6% 6% 25%	1005
	Night	11% 11% 6% 6% 6% 5% 7% 34%	1035
April	Day	11% 12% 6% 5% 6% 6% 35%	1114
	Night	10% 7% 5% 6% 6% 5% 6% 39%	861
May	Day	10% 5% 5% 6% 9% 45%	1225
	Night	9% 5% 6% 53%	821
June	Day	6% 6% 60%	1332
	Night	5% 7% 5% 58%	647
July	Day	5% 5% 65%	1272
	Night	5% 6% 66%	768
August	Day	5% 69%	1201
	Night	5% 69%	836
September	Day	6% 5% 63%	1000
	Night	7% 64%	975
October	Day	13% 5% 7% 45%	922
	Night	12% 5% 6% 52%	1111
November	Day	22% 9% 6% 5% 38%	899
	Night	14% 8% 5% 5% 5% 5% 5% 5% 37%	1401
December	Day	21% 12% 8% 7% 5% 5% 5% 24%	717
	Night	23% 14% 6% 6% 5% 24%	1329

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	12% 28% 15%	461
	Night	14% 25% 23%	752
February	Day	17% 23% 16%	421
	Night	13% 27% 23%	627
March	Day	15% 25% 25%	592
	Night	14% 22% 32% 8%	645
April	Day	8% 21% 30% 15%	737
	Night	9% 24% 30% 18%	572
May	Day	6% 16% 30% 23%	989
	Night	6% 14% 32% 27%	670
June	Day	5% 10% 22% 34% 17%	1103
	Night	8% 12% 17% 27% 23%	537
July	Day	6% 11% 28% 42%	809
	Night	7% 10% 29% 43%	508
August	Day	6% 13% 36% 28%	1142
	Night	14% 30% 34%	788
September	Day	9% 24% 31% 11%	901
	Night	5% 9% 24% 28% 17%	888
October	Day	7% 17% 29% 16%	790
	Night	5% 16% 31% 20%	969
November	Day	8% 23% 21% 16%	626
	Night	11% 18% 22% 20%	985
December	Day	13% 28% 13%	449
	Night	10% 24% 16% 5%	812

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	12% 30% 34% 11%	340
February	Day	35% 35% 7%	28
	Night	15% 30% 37% 10%	303
March	Day	39% 34% 13%	88
	Night	12% 25% 40% 14%	347
April	Day	36% 34% 15%	82
	Night	13% 26% 38% 16%	281
May	Day	15% 48% 16% 10%	106
	Night	8% 17% 39% 23%	274
June	Day	12% 23% 33% 22%	173
	Night	17% 37% 30% 7%	183
July	Day	8% 29% 42% 16%	91
	Night	39% 44% 9%	202
August	Day	13% 43% 35% 5%	88
	Night	14% 51% 28%	264
September	Day	21% 22% 26% 18%	87
	Night	5% 11% 34% 31% 12%	329
October	Day	20% 20% 26% 13%	15
	Night	6% 17% 37% 24%	355
November	Night	7% 23% 37% 15% 5%	428
December	Night	12% 25% 34% 12%	408

Page generated at 2008-11-20 22:15:53. Version ab11