Mt. Cuba Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt. Cuba Astronomical Observatory clear sky chart from 2005-11-05 to 2009-10-21.

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	14% 5% 5% 5% 5% 7% 38%	15872
	Night	16% 5% 5% 5% 7% 39%	15563
Cloud Cover	Day	14% 5% 5% 5% 5% 7% 39%	15882
	Night	16% 5% 5% 5% 7% 39%	15581
Transparency	Day	8% 15% 24% 17%	12691
	Night	8% 16% 24% 18%	12360
Seeing	Day	6% 24% 29% 19% 5%	1011
	Night	9% 33% 31% 11%	4665

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% 6% 6% 5% 6% 5% 5% 39%	1040
	Night	18% 5% 5% 5% 7% 37%	1659
February	Day	13% 6% 5% 5% 44%	1040
	Night	13% 6% 5% 5% 5% 6% 42%	1367
March	Day	14% 5% 7% 6% 7% 39%	1332
	Night	16% 6% 5% 5% 6% 6% 38%	1347
April	Day	17% 5% 6% 6% 39%	1418
	Night	19% 5% 5% 5% 5% 6% 37%	1186
May	Day	14% 7% 5% 6% 8% 38%	1675
	Night	15% 5% 5% 6% 6% 7% 38%	1038
June	Day	15% 5% 6% 7% 7% 9% 32%	1663
	Night	16% 6% 5% 5% 9% 38%	956
July	Day	8% 6% 8% 6% 6% 10% 35%	1698
	Night	10% 5% 7% 7% 8% 10% 34%	991
August	Day	11% 6% 5% 6% 7% 9% 39%	1524
	Night	13% 5% 7% 42%	1190
September	Day	17% 5% 7% 41%	1374
	Night	17% 7% 47%	1229
October	Day	15% 5% 6% 47%	1107
	Night	17% 5% 7% 45%	1345
November	Day	21% 6% 5% 6% 36%	1009
	Night	19% 7% 5% 5% 7% 7% 30%	1524
December	Day	15% 5% 7% 5% 5% 5% 5% 7% 36%	992
	Night	18% 6% 5% 5% 8% 36%	1731

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% 7% 5% 5% 6% 5% 6% 39%	1038
	Night	19% 5% 5% 7% 38%	1660
February	Day	14% 6% 5% 5% 44%	1038
	Night	13% 6% 5% 5% 6% 43%	1358
March	Day	14% 5% 5% 5% 5% 5% 7% 39%	1353
	Night	15% 6% 5% 6% 7% 37%	1370
April	Day	17% 5% 6% 5% 7% 39%	1417
	Night	20% 5% 5% 5% 6% 37%	1186
May	Day	14% 5% 7% 5% 6% 7% 38%	1669
	Night	15% 5% 6% 5% 5% 5% 8% 38%	1032
June	Day	15% 5% 7% 6% 7% 9% 32%	1672
	Night	15% 7% 5% 5% 8% 38%	958
July	Day	8% 6% 7% 6% 6% 10% 35%	1698
	Night	10% 5% 7% 6% 8% 10% 35%	992
August	Day	11% 6% 5% 5% 5% 7% 8% 39%	1518
	Night	13% 5% 5% 5% 5% 5% 8% 42%	1192
September	Day	17% 5% 5% 6% 41%	1373
	Night	16% 7% 47%	1230
October	Day	14% 5% 5% 6% 47%	1107
	Night	18% 5% 7% 45%	1345
November	Day	22% 6% 6% 37%	1007
	Night	20% 7% 5% 6% 7% 31%	1523
December	Day	15% 6% 6% 6% 7% 36%	992
	Night	18% 5% 5% 5% 8% 37%	1735

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	7% 17% 29% 14%	782
	Night	8% 16% 32% 16%	1221
February	Day	7% 19% 30% 11%	855
	Night	6% 17% 31% 16%	1100
March	Day	7% 16% 25% 18%	1059
	Night	9% 17% 22% 16%	1052
April	Day	7% 13% 14% 25% 7%	1106
	Night	5% 13% 19% 22% 6%	916
May	Day	11% 14% 23% 18%	1384
	Night	10% 14% 19% 19%	835
June	Day	15% 20% 27% 9%	1280
	Night	11% 21% 27% 12%	730
July	Day	9% 13% 27% 15%	1119
	Night	13% 19% 19% 17%	649
August	Day	9% 14% 22% 17%	1361
	Night	7% 14% 21% 22%	1050
September	Day	6% 13% 20% 25%	1186
	Night	5% 9% 23% 27%	1084
October	Day	6% 12% 25% 22%	993
	Night	5% 12% 25% 23%	1198
November	Day	5% 18% 29% 10%	784
	Night	9% 18% 23% 12%	1136
December	Day	10% 20% 24% 13%	782
	Night	8% 21% 25% 13%	1389

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	14% 47% 23%	443
February	Day	14% 51% 20% 5%	54
	Night	19% 42% 25%	408
March	Day	13% 34% 29% 9%	114
	Night	15% 43% 22%	470
April	Day	11% 34% 22% 10%	112
	Night	11% 35% 30% 8%	437
May	Day	5% 23% 31% 21% 5%	117
	Night	6% 34% 36% 11%	290
June	Day	20% 31% 26%	102
	Night	26% 46% 14%	215
July	Day	15% 34% 33% 7%	104
	Night	21% 46% 21%	230
August	Day	10% 23% 31% 16%	118
	Night	12% 41% 25%	424
September	Day	13% 33% 22% 9%	110
	Night	16% 38% 25%	441
October	Day	23% 31% 18%	103
	Night	6% 29% 32% 13%	424
November	Day	5% 35% 28% 7%	77
	Night	9% 38% 28% 9%	417
December	Night	13% 43% 24%	466

Page generated at 2009-10-21 19:32:04. Version ab11