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Planetarium of the Detroit Science Center

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Detroit
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Detroit clear sky chart from 2003-08-01 to 2005-11-07.

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	20% 6% 6% 5% 6% 5% 7% 29%	8730
	Night	21% 6% 5% 5% 6% 5% 7% 30%	8444
Transparency	Day	21% 20% 39% 17%	4118
	Night	19% 18% 43% 16%	3961
Seeing	Day	9% 23% 27% 26% 12%	566
	Night	13% 28% 34% 20%	2470

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	30% 10% 10% 6% 7% 17%	514
	Night	33% 7% 8% 5% 6% 5% 16%	839
February	Day	25% 11% 12% 9% 7% 6% 14%	543
	Night	24% 11% 7% 7% 7% 5% 20%	711
March	Day	32% 9% 9% 6% 5% 5% 16%	668
	Night	25% 6% 7% 8% 6% 6% 5% 6% 7% 17%	696
April	Day	22% 6% 6% 5% 6% 8% 31%	748
	Night	22% 6% 7% 35%	574
May	Day	17% 7% 5% 9% 6% 5% 8% 26%	802
	Night	16% 5% 6% 5% 5% 7% 7% 9% 31%	551
June	Day	13% 5% 7% 6% 11% 33%	871
	Night	10% 5% 5% 7% 48%	443
July	Day	15% 5% 9% 5% 6% 10% 29%	844
	Night	14% 5% 5% 6% 7% 11% 34%	518
August	Day	12% 6% 5% 6% 6% 5% 7% 37%	1208
	Night	9% 7% 7% 8% 9% 40%	834
September	Day	11% 5% 5% 5% 7% 50%	978
	Night	12% 7% 53%	964
October	Day	20% 6% 5% 6% 5% 6% 8% 29%	616
	Night	17% 7% 6% 6% 5% 7% 5% 6% 31%	746
November	Day	32% 7% 5% 5% 5% 23%	461
	Night	33% 5% 6% 5% 5% 7% 20%	706
December	Day	33% 8% 7% 5% 5% 7% 18%	477
	Night	28% 11% 6% 6% 6% 6% 19%	862

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	46% 22% 28%	135
	Night	30% 15% 44% 9%	223
February	Day	44% 22% 23% 8%	135
	Night	24% 28% 37% 9%	226
March	Day	32% 30% 28% 8%	173
	Night	28% 27% 38% 5%	220
April	Day	22% 16% 39% 18%	335
	Night	19% 11% 45% 18% 5%	284
May	Day	23% 22% 44% 10%	368
	Night	15% 18% 52% 12%	245
June	Day	18% 16% 41% 22%	480
	Night	20% 12% 51% 13%	270
July	Day	16% 17% 44% 16% 5%	412
	Night	17% 12% 43% 21%	254
August	Day	19% 22% 39% 18%	642
	Night	17% 22% 43% 15%	516
September	Day	11% 15% 41% 30%	666
	Night	10% 16% 37% 31%	663
October	Day	21% 17% 42% 18%	444
	Night	19% 16% 46% 16%	501
November	Day	27% 26% 41%	194
	Night	24% 25% 43% 6%	292
December	Day	28% 30% 26% 14%	134
	Night	29% 19% 38% 12%	267

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	20% 46% 25% 6%	195
February	Night	17% 32% 33% 14%	183
March	Day	20% 26% 38% 14%	34
	Night	21% 38% 35%	201
April	Day	15% 30% 30% 19%	46
	Night	15% 37% 33% 13%	153
May	Day	10% 23% 28% 28% 8%	56
	Night	10% 26% 42% 18%	164
June	Day	10% 26% 28% 23% 9%	101
	Night	20% 45% 26%	126
July	Day	5% 18% 37% 24% 13%	93
	Night	5% 17% 43% 29%	167
August	Day	6% 18% 19% 32% 22%	88
	Night	12% 39% 34% 9%	262
September	Day	21% 19% 36% 19%	84
	Night	6% 12% 36% 37% 7%	315
October	Day	14% 31% 26% 20% 7%	64
	Night	13% 26% 30% 27%	321
November	Night	21% 46% 21% 8%	183
December	Night	27% 38% 26% 8%	200

Page generated at 2008-08-20 18:20:58. Version ab11