Bucknell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bucknell Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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% 3 6% 6% 4 5% 5% 5% 7% 36%	78408
	Night	17% 7% 3 6% 5% 3 5% 5% 5% 7% 37%	80879
Transparency	Day	47% 6% 11% 21% 12% 2	78121
	Night	46% 6% 12% 22% 13% 2	80701
Seeing	Day	21% 13% 25% 23% 13% 5%	13803
	Night	20% 9% 28% 30% 11% 1	23324

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% 11% 4 7% 6% 3 5% 4 4 5% 36%	2517
	11th to 20th	Day	14% 12% 7% 12% 8% 5% 5% 5% 4 5% 23%	2709
	21st to end	Day	20% 13% 5% 9% 7% 4 4 4 5% 6% 23%	3124
February	1st to 10th	Day	16% 10% 4 8% 6% 5% 5% 6% 5% 6% 28%	1710
	11th to 20th	Day	13% 9% 3 8% 7% 4 4 5% 6% 8% 32%	1695
	21st to end	Day	19% 8% 5% 9% 6% 3 5% 5% 4 5% 32%	1520
March	1st to 10th	Day	14% 9% 4 5% 5% 3 5% 5% 5% 6% 39%	1895
	11th to 20th	Day	17% 8% 3 7% 7% 4 4 5% 5% 7% 33%	1980
	21st to end	Day	19% 9% 4 6% 6% 3 3 4 5% 6% 35%	2235
April	1st to 10th	Day	16% 7% 3 7% 7% 3 5% 4 5% 7% 36%	2160
	11th to 20th	Day	18% 7% 3 5% 5% 3 5% 5% 5% 6% 38%	2134
	21st to end	Day	18% 6% 2 6% 6% 3 5% 5% 6% 7% 37%	2164
May	1st to 10th	Day	20% 6% 3 6% 6% 3 5% 5% 5% 7% 35%	2376
	11th to 20th	Day	19% 6% 3 6% 7% 4 5% 5% 5% 7% 33%	2478
	21st to end	Day	16% 5% 2 5% 5% 4 5% 5% 6% 8% 40%	2725
June	1st to 10th	Day	13% 5% 4 6% 7% 4 6% 5% 6% 8% 37%	2520
	11th to 20th	Day	14% 6% 3 5% 6% 4 6% 5% 5% 9% 38%	2520
	21st to end	Day	11% 4 2 5% 5% 4 5% 6% 6% 10% 41%	2520
July	1st to 10th	Day	9% 5% 2 5% 6% 4 7% 6% 7% 10% 38%	2520
	11th to 20th	Day	7% 6% 2 6% 6% 4 6% 5% 7% 10% 41%	2520
	21st to end	Day	11% 6% 3 6% 6% 4 6% 6% 7% 8% 37%	2616
August	1st to 10th	Day	11% 5% 2 6% 7% 4 6% 6% 8% 10% 37%	2327
	11th to 20th	Day	14% 6% 3 6% 6% 3 5% 5% 7% 8% 35%	2236
	21st to end	Day	15% 5% 2 5% 5% 4 5% 5% 7% 8% 38%	2376
September	1st to 10th	Day	18% 5% 2 4 5% 3 4 5% 4 6% 43%	2160
	11th to 20th	Day	14% 4 2 4 4 3 3 4 5% 6% 50%	2160
	21st to end	Day	20% 6% 2 5% 4 3 3 4 5% 7% 40%	1902
October	1st to 10th	Day	19% 6% 2 5% 5% 3 4 4 5% 6% 40%	1800
	11th to 20th	Day	19% 5% 3 6% 5% 3 5% 4 6% 8% 37%	1800
	21st to end	Day	19% 7% 3 5% 5% 4 6% 5% 5% 6% 35%	1980
November	1st to 10th	Day	13% 6% 3 6% 5% 3 4 3 5% 7% 45%	1681
	11th to 20th	Day	18% 7% 2 6% 5% 4 4 5% 5% 7% 38%	1630
	21st to end	Day	18% 6% 3 6% 5% 4 4 5% 7% 6% 36%	1520
December	1st to 10th	Day	19% 9% 5% 8% 7% 5% 6% 4 5% 6% 27%	1520
	11th to 20th	Day	22% 7% 3 5% 5% 4 5% 5% 5% 7% 33%	1906
	21st to end	Day	22% 12% 4 8% 8% 4 6% 5% 5% 5% 22%	2772
January	1st to 10th	Night	16% 9% 3 7% 6% 3 6% 5% 5% 6% 33%	4429
	11th to 20th	Night	16% 10% 6% 9% 7% 4 4 4 4 5% 30%	4248
	21st to end	Night	24% 9% 4 10% 6% 3 4 5% 4 5% 27%	4532
February	1st to 10th	Night	16% 9% 4 8% 6% 3 4 4 4 6% 34%	2470
	11th to 20th	Night	15% 8% 4 6% 6% 4 6% 5% 5% 7% 34%	2370
	21st to end	Night	18% 9% 3 6% 6% 3 5% 4 5% 5% 35%	1831
March	1st to 10th	Night	15% 7% 2 5% 6% 3 5% 5% 6% 7% 40%	2048
	11th to 20th	Night	17% 9% 4 4 4 3 4 4 4 7% 40%	1979
	21st to end	Night	17% 7% 3 6% 6% 4 5% 5% 4 7% 36%	2120
April	1st to 10th	Night	19% 8% 3 7% 6% 3 4 5% 5% 7% 34%	1800
	11th to 20th	Night	16% 5% 3 5% 6% 3 4 5% 6% 8% 39%	1775
	21st to end	Night	19% 5% 2 5% 5% 3 5% 4 5% 7% 41%	1800
May	1st to 10th	Night	20% 7% 3 6% 4 4 4 3 4 7% 38%	1591
	11th to 20th	Night	17% 5% 2 6% 5% 4 4 5% 6% 6% 40%	1415
	21st to end	Night	12% 6% 3 6% 5% 2 5% 5% 5% 9% 41%	1550
June	1st to 10th	Night	15% 5% 3 5% 5% 3 4 4 5% 8% 43%	1440
	11th to 20th	Night	13% 5% 2 5% 5% 3 5% 5% 7% 8% 41%	1440
	21st to end	Night	11% 4 1 5% 5% 3 5% 5% 7% 9% 44%	1440
July	1st to 10th	Night	11% 5% 2 5% 5% 3 5% 6% 5% 8% 43%	1440
	11th to 20th	Night	8% 5% 2 5% 5% 3 6% 7% 7% 9% 43%	1440
	21st to end	Night	11% 4 2 4 4 4 5% 5% 7% 8% 44%	1699
August	1st to 10th	Night	10% 6% 2 5% 5% 4 5% 6% 7% 9% 43%	1611
	11th to 20th	Night	12% 7% 3 7% 6% 4 5% 4 5% 8% 39%	1647
	21st to end	Night	13% 5% 2 5% 5% 3 4 5% 6% 8% 43%	1980
September	1st to 10th	Night	16% 5% 2 5% 5% 3 4 4 5% 6% 45%	1800
	11th to 20th	Night	13% 5% 2 4 4 2 3 3 5% 8% 51%	1800
	21st to end	Night	17% 6% 3 4 4 2 4 4 5% 7% 44%	2053
October	1st to 10th	Night	20% 7% 2 4 5% 2 3 5% 5% 6% 42%	2160
	11th to 20th	Night	18% 6% 3 4 5% 3 3 4 5% 7% 43%	2160
	21st to end	Night	21% 7% 2 5% 5% 3 4 4 5% 6% 38%	2376
November	1st to 10th	Night	12% 6% 2 5% 5% 2 3 5% 5% 6% 49%	2397
	11th to 20th	Night	18% 8% 2 5% 5% 3 4 4 5% 6% 40%	2546
	21st to end	Night	16% 7% 3 6% 5% 4 5% 5% 6% 7% 37%	2660
December	1st to 10th	Night	19% 10% 4 7% 5% 3 5% 5% 6% 7% 30%	2660
	11th to 20th	Night	20% 8% 3 6% 5% 3 5% 4 4 7% 33%	3288
	21st to end	Night	22% 10% 4 7% 6% 3 5% 4 5% 6% 27%	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	50% 4 13% 22% 8% 2	2518
	11th to 20th	Day	64% 5% 9% 14% 7% 1	2709
	21st to end	Day	61% 6% 11% 16% 5% 1	3124
February	1st to 10th	Day	55% 6% 11% 17% 10% 1	1710
	11th to 20th	Day	51% 5% 10% 23% 9% 1	1704
	21st to end	Day	55% 4 10% 21% 8% 3	1520
March	1st to 10th	Day	46% 4 12% 24% 11% 2	1898
	11th to 20th	Day	50% 5% 9% 20% 12% 3	1980
	21st to end	Day	52% 3 8% 19% 16% 3	2235
April	1st to 10th	Day	49% 4 10% 20% 13% 4	2160
	11th to 20th	Day	46% 5% 10% 20% 15% 3	2134
	21st to end	Day	46% 6% 9% 21% 14% 4	2164
May	1st to 10th	Day	49% 6% 8% 20% 14% 3	2376
	11th to 20th	Day	51% 5% 9% 19% 13% 3	2482
	21st to end	Day	42% 7% 13% 23% 12% 2	2725
June	1st to 10th	Day	44% 6% 12% 22% 14% 2	2520
	11th to 20th	Day	44% 6% 13% 21% 13% 2	2520
	21st to end	Day	37% 7% 14% 27% 14% 1	2520
July	1st to 10th	Day	40% 9% 12% 23% 14% 2	2450
	11th to 20th	Day	36% 8% 13% 26% 15% 2	2445
	21st to end	Day	41% 9% 11% 20% 17% 1	2470
August	1st to 10th	Day	41% 8% 15% 23% 14%	2314
	11th to 20th	Day	43% 9% 13% 21% 13% 1	2236
	21st to end	Day	41% 8% 10% 22% 16% 3	2376
September	1st to 10th	Day	42% 6% 11% 23% 16% 3	2160
	11th to 20th	Day	35% 5% 10% 25% 22% 3	2160
	21st to end	Day	45% 5% 10% 19% 19% 2	1902
October	1st to 10th	Day	44% 6% 11% 23% 14% 1	1800
	11th to 20th	Day	44% 6% 10% 25% 14%	1800
	21st to end	Day	49% 5% 11% 22% 11% 1	1980
November	1st to 10th	Day	39% 4 12% 25% 16% 3	1681
	11th to 20th	Day	46% 5% 11% 23% 13% 2	1630
	21st to end	Day	46% 5% 12% 27% 9% 1	1520
December	1st to 10th	Day	59% 5% 13% 16% 7% 1	1520
	11th to 20th	Day	51% 4 18% 20% 6%	1906
	21st to end	Day	63% 5% 13% 14% 5%	2772
January	1st to 10th	Night	49% 6% 15% 21% 8% 2	4429
	11th to 20th	Night	56% 5% 12% 17% 8% 1	4248
	21st to end	Night	58% 5% 10% 18% 7% 1	4532
February	1st to 10th	Night	50% 5% 12% 22% 8% 1	2470
	11th to 20th	Night	50% 5% 10% 21% 12% 2	2372
	21st to end	Night	52% 4 9% 19% 13% 2	1831
March	1st to 10th	Night	44% 4 11% 25% 13% 3	2058
	11th to 20th	Night	46% 4 11% 22% 15% 2	1980
	21st to end	Night	49% 5% 9% 18% 16% 3	2120
April	1st to 10th	Night	51% 4 9% 21% 14% 2	1800
	11th to 20th	Night	42% 6% 9% 22% 18% 3	1775
	21st to end	Night	43% 6% 10% 22% 16% 4	1800
May	1st to 10th	Night	48% 5% 9% 22% 12% 3	1591
	11th to 20th	Night	44% 6% 11% 19% 17% 3	1416
	21st to end	Night	40% 9% 15% 19% 14% 3	1551
June	1st to 10th	Night	40% 7% 11% 24% 17% 2	1440
	11th to 20th	Night	40% 7% 14% 22% 15% 2	1440
	21st to end	Night	35% 8% 13% 29% 14% 1	1440
July	1st to 10th	Night	39% 8% 13% 22% 14% 4	1400
	11th to 20th	Night	34% 10% 13% 24% 17% 2	1392
	21st to end	Night	35% 9% 16% 22% 17% 2	1605
August	1st to 10th	Night	36% 9% 14% 24% 16% 1	1600
	11th to 20th	Night	42% 8% 13% 19% 17% 1	1647
	21st to end	Night	37% 8% 12% 22% 18% 2	1980
September	1st to 10th	Night	39% 6% 11% 24% 17% 3	1800
	11th to 20th	Night	32% 5% 9% 29% 21% 3	1800
	21st to end	Night	40% 5% 9% 23% 21% 1	2053
October	1st to 10th	Night	44% 4 13% 23% 15% 1	2160
	11th to 20th	Night	40% 5% 13% 26% 14% 2	2160
	21st to end	Night	47% 5% 10% 24% 13% 1	2376
November	1st to 10th	Night	37% 5% 13% 25% 18% 3	2397
	11th to 20th	Night	46% 4 10% 25% 14% 3	2546
	21st to end	Night	46% 5% 14% 24% 9% 1	2660
December	1st to 10th	Night	54% 6% 13% 19% 8%	2660
	11th to 20th	Night	51% 5% 12% 21% 9% 1	3288
	21st to end	Night	57% 5% 14% 18% 5%	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% 22% 28% 18% 4 2	180
	11th to 20th	Day	27% 23% 30% 18% 2	233
	21st to end	Day	22% 23% 32% 15% 7% 1	297
February	1st to 10th	Day	26% 21% 34% 14% 4	270
	11th to 20th	Day	26% 24% 36% 13% 1	302
	21st to end	Day	29% 18% 31% 20% 3	362
March	1st to 10th	Day	25% 22% 27% 22% 4	420
	11th to 20th	Day	27% 20% 30% 18% 4 2	420
	21st to end	Day	28% 23% 23% 18% 5% 3	462
April	1st to 10th	Day	25% 20% 28% 20% 7% 1	420
	11th to 20th	Day	22% 21% 25% 17% 9% 6%	412
	21st to end	Day	26% 15% 30% 18% 8% 2	420
May	1st to 10th	Day	28% 15% 26% 18% 10% 4	423
	11th to 20th	Day	19% 16% 28% 23% 11% 3	447
	21st to end	Day	20% 7% 24% 23% 18% 9%	485
June	1st to 10th	Day	16% 11% 26% 26% 17% 4	450
	11th to 20th	Day	17% 12% 25% 26% 16% 4	450
	21st to end	Day	13% 8% 28% 30% 17% 4	450
July	1st to 10th	Day	12% 4 22% 31% 22% 9%	445
	11th to 20th	Day	7% 4 21% 36% 26% 7%	444
	21st to end	Day	13% 6% 24% 31% 22% 5%	488
August	1st to 10th	Day	13% 4 22% 28% 25% 10%	446
	11th to 20th	Day	15% 4 18% 29% 20% 13%	439
	21st to end	Day	14% 6% 20% 28% 19% 12%	495
September	1st to 10th	Day	19% 7% 20% 22% 20% 12%	450
	11th to 20th	Day	15% 6% 18% 27% 23% 12%	450
	21st to end	Day	22% 11% 18% 25% 16% 7%	450
October	1st to 10th	Day	24% 8% 21% 22% 16% 9%	450
	11th to 20th	Day	19% 15% 25% 26% 13% 1	450
	21st to end	Day	24% 13% 30% 22% 10%	495
November	1st to 10th	Day	21% 11% 26% 25% 15% 2	370
	11th to 20th	Day	24% 16% 27% 22% 10% 1	290
	21st to end	Day	22% 21% 31% 19% 6% 1	180
December	1st to 10th	Day	31% 19% 28% 16% 5% 2	180
	11th to 20th	Day	28% 17% 34% 16% 3 1	180
	21st to end	Day	28% 21% 28% 18% 6%	198
January	1st to 10th	Night	20% 16% 39% 22% 3	760
	11th to 20th	Night	24% 13% 32% 27% 3	760
	21st to end	Night	19% 13% 39% 27% 2	836
February	1st to 10th	Night	23% 12% 33% 30% 2	760
	11th to 20th	Night	22% 16% 43% 18% 2	743
	21st to end	Night	24% 14% 39% 20% 3	611
March	1st to 10th	Night	22% 15% 33% 26% 4	720
	11th to 20th	Night	26% 13% 32% 25% 4	720
	21st to end	Night	22% 11% 38% 22% 6% 1	792
April	1st to 10th	Night	24% 15% 31% 24% 5%	720
	11th to 20th	Night	20% 11% 34% 26% 8% 1	711
	21st to end	Night	21% 11% 29% 32% 6%	720
May	1st to 10th	Night	23% 8% 26% 30% 12% 1	511
	11th to 20th	Night	18% 5% 32% 37% 8% 1	354
	21st to end	Night	16% 6% 20% 38% 19% 1	389
June	1st to 10th	Night	15% 6% 22% 38% 19%	360
	11th to 20th	Night	14% 5% 25% 41% 15%	360
	21st to end	Night	11% 2 21% 51% 15%	360
July	1st to 10th	Night	13% 2 21% 38% 23% 3	350
	11th to 20th	Night	10% 2 14% 46% 25% 2	348
	21st to end	Night	12% 4 17% 42% 24% 2	519
August	1st to 10th	Night	13% 2 11% 43% 29% 2	537
	11th to 20th	Night	15% 3 11% 36% 33% 2	583
	21st to end	Night	15% 4 14% 35% 29% 3	792
September	1st to 10th	Night	18% 3 19% 33% 24% 2	720
	11th to 20th	Night	16% 4 16% 31% 29% 4	720
	21st to end	Night	19% 5% 21% 33% 20% 2	720
October	1st to 10th	Night	23% 5% 21% 28% 20% 3	720
	11th to 20th	Night	20% 7% 27% 35% 11% 1	720
	21st to end	Night	25% 9% 29% 30% 7%	792
November	1st to 10th	Night	16% 9% 30% 33% 12% 1	740
	11th to 20th	Night	23% 11% 29% 28% 8% 1	760
	21st to end	Night	20% 11% 32% 31% 6%	760
December	1st to 10th	Night	26% 13% 32% 24% 6%	760
	11th to 20th	Night	23% 11% 33% 29% 5%	760
	21st to end	Night	24% 13% 32% 29% 3	836

Page generated at 2024-02-22 06:05:48. Version ac07

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