Deerfield Academy Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerfield Academy Planetarium clear sky chart from 2005-11-06 to 2024-11-25.

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% 5% 4 5% 4 6% 7% 37%	101469
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	97999
Transparency	Day	45% 5% 12% 22% 14% 2	104994
	Night	45% 5% 12% 22% 14% 2	102563
Seeing	Day	23% 15% 29% 20% 10% 3	14988
	Night	21% 12% 30% 28% 8% 1	23981

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	13% 7% 3 7% 4 5% 4 3 6% 6% 41%	2517
	11th to 20th	Day	16% 9% 5% 11% 5% 4 4 3 5% 5% 33%	2520
	21st to end	Day	19% 12% 5% 8% 6% 4 4 3 4 6% 30%	2772
February	1st to 10th	Day	15% 9% 3 6% 6% 6% 6% 5% 6% 7% 32%	1752
	11th to 20th	Day	13% 8% 3 8% 6% 4 4 5% 5% 5% 38%	1848
	21st to end	Day	19% 10% 3 8% 5% 5% 5% 2 5% 5% 35%	1570
March	1st to 10th	Day	23% 13% 4 7% 5% 3 3 2 4 5% 31%	3116
	11th to 20th	Day	12% 7% 2 8% 5% 5% 5% 4 6% 7% 38%	3243
	21st to end	Day	20% 8% 3 7% 4 4 4 3 5% 6% 37%	4166
April	1st to 10th	Day	19% 8% 3 7% 5% 4 3 3 5% 6% 37%	2280
	11th to 20th	Day	16% 7% 2 6% 5% 4 6% 3 6% 6% 38%	2254
	21st to end	Day	19% 7% 3 7% 5% 5% 4 5% 6% 6% 35%	2422
May	1st to 10th	Day	24% 9% 3 7% 5% 4 5% 4 5% 6% 29%	4106
	11th to 20th	Day	22% 8% 3 7% 4 4 4 3 5% 6% 35%	4324
	21st to end	Day	13% 5% 2 5% 4 4 4 4 7% 9% 43%	4837
June	1st to 10th	Day	16% 6% 2 6% 5% 5% 5% 5% 7% 9% 35%	2660
	11th to 20th	Day	16% 6% 2 5% 5% 5% 5% 5% 6% 8% 38%	2660
	21st to end	Day	15% 7% 3 6% 5% 5% 5% 4 6% 8% 35%	2660
July	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 8% 9% 37%	4440
	11th to 20th	Day	12% 5% 2 6% 5% 5% 5% 4 8% 11% 38%	4440
	21st to end	Day	16% 7% 3 7% 4 4 4 4 6% 8% 36%	4814
August	1st to 10th	Day	15% 6% 2 7% 5% 6% 5% 4 6% 9% 34%	4297
	11th to 20th	Day	12% 6% 3 7% 5% 5% 5% 5% 6% 8% 37%	3837
	21st to end	Day	9% 5% 2 5% 5% 5% 6% 5% 7% 10% 43%	4180
September	1st to 10th	Day	13% 5% 2 5% 5% 4 4 4 6% 7% 44%	2280
	11th to 20th	Day	14% 5% 2 4 3 3 4 3 5% 7% 50%	2142
	21st to end	Day	17% 5% 2 5% 3 3 4 4 6% 8% 42%	2090
October	1st to 10th	Day	21% 6% 2 6% 4 4 5% 3 5% 5% 39%	2066
	11th to 20th	Day	13% 6% 2 5% 4 5% 4 4 5% 7% 44%	1853
	21st to end	Day	21% 7% 2 6% 4 4 4 3 5% 6% 37%	1881
November	1st to 10th	Day	12% 7% 2 5% 4 4 3 3 4 6% 49%	1761
	11th to 20th	Day	17% 7% 3 4 4 4 4 3 5% 7% 44%	1800
	21st to end	Day	18% 8% 2 5% 4 3 4 4 4 6% 40%	1683
December	1st to 10th	Day	19% 9% 3 7% 5% 6% 4 3 5% 6% 33%	1520
	11th to 20th	Day	22% 7% 2 6% 4 3 4 3 5% 5% 40%	1906
	21st to end	Day	20% 11% 4 8% 5% 4 5% 3 4 7% 30%	2772
January	1st to 10th	Night	16% 7% 2 6% 4 3 4 3 5% 6% 43%	4429
	11th to 20th	Night	14% 10% 4 11% 6% 5% 4 3 5% 5% 32%	4440
	21st to end	Night	20% 13% 4 8% 5% 4 4 4 5% 5% 29%	4884
February	1st to 10th	Night	14% 10% 3 6% 6% 5% 5% 4 5% 6% 37%	2421
	11th to 20th	Night	11% 9% 3 8% 5% 4 5% 4 6% 7% 39%	2218
	21st to end	Night	17% 9% 3 7% 5% 4 4 3 4 6% 38%	1884
March	1st to 10th	Night	26% 10% 2 6% 5% 4 4 3 5% 6% 30%	3724
	11th to 20th	Night	12% 8% 3 7% 5% 4 5% 4 7% 7% 39%	3698
	21st to end	Night	20% 9% 3 7% 4 4 4 4 6% 5% 36%	3466
April	1st to 10th	Night	18% 9% 2 6% 5% 4 4 3 5% 6% 38%	1900
	11th to 20th	Night	19% 7% 2 5% 4 5% 4 4 4 6% 39%	1875
	21st to end	Night	21% 7% 2 6% 3 4 3 3 5% 6% 40%	1758
May	1st to 10th	Night	24% 9% 3 6% 4 5% 4 4 5% 6% 29%	2834
	11th to 20th	Night	18% 9% 4 9% 6% 5% 5% 3 6% 6% 27%	2598
	21st to end	Night	16% 5% 2 6% 3 5% 4 3 6% 9% 42%	2738
June	1st to 10th	Night	17% 8% 2 7% 4 4 4 3 5% 6% 40%	1520
	11th to 20th	Night	18% 6% 2 4 5% 3 4 4 6% 7% 40%	1520
	21st to end	Night	15% 6% 2 5% 4 4 3 4 7% 7% 42%	1520
July	1st to 10th	Night	11% 5% 2 5% 5% 5% 6% 4 7% 8% 41%	2520
	11th to 20th	Night	13% 6% 3 6% 4 4 4 4 6% 9% 41%	2520
	21st to end	Night	16% 7% 3 6% 4 5% 4 3 5% 7% 42%	2739
August	1st to 10th	Night	21% 6% 2 7% 4 5% 4 4 5% 6% 34%	2601
	11th to 20th	Night	13% 7% 3 8% 5% 5% 4 3 6% 7% 39%	2973
	21st to end	Night	9% 4 1 4 3 4 4 3 5% 8% 54%	3476
September	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 5% 6% 47%	1900
	11th to 20th	Night	13% 5% 1 5% 3 3 3 3 4 6% 53%	2038
	21st to end	Night	16% 6% 2 6% 4 4 3 3 5% 7% 44%	2090
October	1st to 10th	Night	21% 6% 2 5% 5% 3 3 3 5% 6% 41%	2113
	11th to 20th	Night	15% 5% 2 5% 3 3 4 4 6% 6% 45%	2326
	21st to end	Night	23% 8% 1 6% 4 4 3 3 4 5% 39%	2717
November	1st to 10th	Night	14% 7% 2 5% 4 3 3 3 5% 5% 49%	2537
	11th to 20th	Night	18% 7% 2 5% 4 3 4 3 4 5% 44%	2600
	21st to end	Night	15% 8% 2 5% 5% 4 4 4 6% 5% 42%	2590
December	1st to 10th	Night	18% 9% 3 6% 5% 4 4 3 6% 6% 35%	2660
	11th to 20th	Night	20% 8% 2 7% 4 3 4 3 6% 6% 38%	3288
	21st to end	Night	22% 11% 4 8% 5% 4 4 3 4 5% 30%	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% 4 13% 30% 9% 1	2518
	11th to 20th	Day	52% 5% 11% 22% 9% 1	2520
	21st to end	Day	57% 5% 10% 19% 9% 1	2772
February	1st to 10th	Day	49% 6% 13% 18% 12% 1	1752
	11th to 20th	Day	47% 5% 10% 21% 14% 3	1857
	21st to end	Day	52% 5% 9% 19% 13% 2	1570
March	1st to 10th	Day	58% 3 12% 14% 11% 2	3119
	11th to 20th	Day	42% 7% 15% 22% 11% 2	3243
	21st to end	Day	49% 3 6% 18% 19% 5%	4166
April	1st to 10th	Day	49% 4 10% 21% 13% 3	2280
	11th to 20th	Day	45% 6% 11% 19% 17% 2	2254
	21st to end	Day	48% 6% 9% 19% 15% 3	2422
May	1st to 10th	Day	54% 7% 11% 15% 11% 1	4120
	11th to 20th	Day	50% 6% 14% 18% 10% 1	4328
	21st to end	Day	35% 8% 12% 26% 18% 2	4837
June	1st to 10th	Day	44% 8% 14% 22% 11% 1	2660
	11th to 20th	Day	43% 7% 14% 20% 14% 2	2660
	21st to end	Day	45% 7% 13% 21% 13% 1	2660
July	1st to 10th	Day	43% 5% 12% 23% 15% 1	4370
	11th to 20th	Day	41% 5% 17% 24% 12% 1	4365
	21st to end	Day	47% 5% 13% 20% 15% 1	4661
August	1st to 10th	Day	48% 5% 15% 21% 10% 1	4283
	11th to 20th	Day	45% 4 14% 27% 8% 1	3876
	21st to end	Day	36% 4 14% 29% 15% 2	4180
September	1st to 10th	Day	38% 6% 13% 25% 17% 1	2280
	11th to 20th	Day	36% 5% 9% 26% 22% 2	2142
	21st to end	Day	42% 5% 10% 23% 18% 3	2090
October	1st to 10th	Day	46% 2 7% 23% 20% 2	3430
	11th to 20th	Day	36% 3 9% 28% 22% 2	3056
	21st to end	Day	36% 3 12% 30% 15% 3	3081
November	1st to 10th	Day	38% 4 15% 25% 16% 2	1761
	11th to 20th	Day	41% 5% 11% 21% 20% 3	1800
	21st to end	Day	45% 5% 15% 23% 10% 1	1683
December	1st to 10th	Day	52% 5% 15% 15% 11% 2	1520
	11th to 20th	Day	48% 4 13% 20% 14% 1	1906
	21st to end	Day	56% 5% 11% 18% 10%	2772
January	1st to 10th	Night	41% 5% 14% 25% 11% 2	4429
	11th to 20th	Night	51% 5% 13% 19% 10% 2	4440
	21st to end	Night	57% 5% 10% 17% 9% 2	4884
February	1st to 10th	Night	47% 6% 13% 21% 10% 2	2421
	11th to 20th	Night	44% 6% 12% 20% 15% 3	2220
	21st to end	Night	48% 4 10% 22% 11% 4	1884
March	1st to 10th	Night	54% 6% 9% 19% 10% 2	3734
	11th to 20th	Night	43% 7% 14% 22% 12% 2	3699
	21st to end	Night	49% 4 7% 14% 21% 6%	3466
April	1st to 10th	Night	48% 4 9% 20% 16% 2	1900
	11th to 20th	Night	46% 6% 9% 20% 18% 1	1875
	21st to end	Night	46% 5% 10% 20% 14% 5%	1758
May	1st to 10th	Night	54% 7% 11% 16% 10% 1	2840
	11th to 20th	Night	54% 8% 12% 15% 9% 2	2599
	21st to end	Night	39% 8% 14% 22% 16% 1	2739
June	1st to 10th	Night	45% 6% 11% 25% 11% 1	1520
	11th to 20th	Night	43% 6% 15% 23% 12% 1	1520
	21st to end	Night	41% 6% 14% 24% 14% 1	1520
July	1st to 10th	Night	42% 5% 15% 21% 16% 1	2480
	11th to 20th	Night	43% 6% 12% 26% 14%	2472
	21st to end	Night	44% 4 12% 22% 17% 1	2651
August	1st to 10th	Night	51% 6% 12% 21% 10% 1	2591
	11th to 20th	Night	45% 5% 15% 25% 10%	3000
	21st to end	Night	30% 4 15% 34% 17% 1	3476
September	1st to 10th	Night	38% 6% 11% 26% 18% 1	1900
	11th to 20th	Night	33% 5% 11% 26% 23% 2	2038
	21st to end	Night	41% 5% 9% 25% 17% 2	2090
October	1st to 10th	Night	42% 3 13% 24% 16% 2	3529
	11th to 20th	Night	32% 4 10% 26% 26% 3	3862
	21st to end	Night	37% 3 13% 33% 14% 1	4467
November	1st to 10th	Night	38% 6% 10% 25% 18% 3	2537
	11th to 20th	Night	43% 5% 10% 21% 17% 3	2600
	21st to end	Night	43% 5% 15% 24% 12% 1	2590
December	1st to 10th	Night	49% 6% 14% 20% 11% 1	2660
	11th to 20th	Night	48% 4 15% 17% 14% 2	3288
	21st to end	Night	57% 4 10% 22% 8% 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	24% 26% 26% 20% 4	180
	11th to 20th	Day	30% 24% 30% 10% 4 1	180
	21st to end	Day	22% 24% 32% 17% 4 1	198
February	1st to 10th	Day	31% 26% 31% 10% 2	314
	11th to 20th	Day	30% 23% 31% 14% 2	456
	21st to end	Day	31% 16% 32% 18% 3	382
March	1st to 10th	Day	29% 19% 33% 16% 2	460
	11th to 20th	Day	31% 21% 29% 14% 5%	460
	21st to end	Day	30% 23% 29% 11% 5% 3	506
April	1st to 10th	Day	32% 21% 26% 13% 7% 1	460
	11th to 20th	Day	29% 21% 28% 15% 6% 2	452
	21st to end	Day	29% 18% 30% 15% 6% 2	460
May	1st to 10th	Day	31% 19% 28% 15% 5% 2	463
	11th to 20th	Day	22% 16% 36% 18% 6% 1	487
	21st to end	Day	18% 13% 31% 24% 12% 3	529
June	1st to 10th	Day	17% 14% 33% 22% 11% 3	490
	11th to 20th	Day	16% 14% 33% 24% 10% 2	490
	21st to end	Day	18% 15% 33% 19% 11% 4	490
July	1st to 10th	Day	17% 7% 31% 26% 15% 3	485
	11th to 20th	Day	14% 8% 28% 30% 17% 3	484
	21st to end	Day	16% 7% 32% 28% 14% 3	532
August	1st to 10th	Day	11% 7% 27% 32% 18% 5%	486
	11th to 20th	Day	14% 8% 30% 25% 17% 6%	479
	21st to end	Day	12% 10% 27% 29% 15% 7%	539
September	1st to 10th	Day	19% 7% 25% 23% 18% 7%	490
	11th to 20th	Day	17% 9% 26% 20% 17% 11%	490
	21st to end	Day	20% 10% 28% 24% 12% 7%	490
October	1st to 10th	Day	27% 10% 24% 19% 14% 5%	490
	11th to 20th	Day	19% 15% 29% 23% 11% 3	465
	21st to end	Day	29% 14% 23% 24% 8% 1	429
November	1st to 10th	Day	22% 13% 30% 24% 9% 3	395
	11th to 20th	Day	28% 18% 29% 19% 6% 1	400
	21st to end	Day	30% 17% 27% 21% 5% 1	319
December	1st to 10th	Day	23% 24% 29% 18% 5%	180
	11th to 20th	Day	34% 20% 34% 11% 2	180
	21st to end	Day	28% 17% 34% 16% 5% 1	198
January	1st to 10th	Night	21% 15% 35% 26% 3	760
	11th to 20th	Night	27% 15% 31% 24% 3	760
	21st to end	Night	20% 16% 36% 25% 4	836
February	1st to 10th	Night	22% 15% 37% 24% 2	760
	11th to 20th	Night	21% 19% 38% 20% 2	743
	21st to end	Night	25% 17% 32% 23% 3	628
March	1st to 10th	Night	24% 16% 36% 22% 3	760
	11th to 20th	Night	22% 19% 35% 20% 4	760
	21st to end	Night	23% 17% 32% 21% 6%	836
April	1st to 10th	Night	24% 16% 32% 24% 4	760
	11th to 20th	Night	23% 17% 31% 23% 6%	751
	21st to end	Night	27% 15% 31% 22% 5%	618
May	1st to 10th	Night	28% 14% 30% 24% 5%	570
	11th to 20th	Night	18% 13% 35% 27% 6%	438
	21st to end	Night	19% 7% 29% 34% 11%	411
June	1st to 10th	Night	18% 5% 29% 37% 11%	380
	11th to 20th	Night	19% 7% 29% 35% 9% 1	380
	21st to end	Night	17% 7% 26% 40% 11%	380
July	1st to 10th	Night	14% 5% 25% 42% 14% 1	370
	11th to 20th	Night	16% 2 21% 41% 18% 1	368
	21st to end	Night	11% 4 22% 48% 15%	416
August	1st to 10th	Night	15% 2 22% 46% 15% 1	434
	11th to 20th	Night	15% 4 21% 40% 18% 3	675
	21st to end	Night	16% 4 20% 36% 22% 2	836
September	1st to 10th	Night	16% 4 26% 34% 18% 2	760
	11th to 20th	Night	16% 6% 21% 32% 22% 4	760
	21st to end	Night	19% 5% 25% 35% 14% 2	760
October	1st to 10th	Night	23% 9% 21% 30% 14% 3	760
	11th to 20th	Night	19% 10% 28% 30% 12%	760
	21st to end	Night	27% 10% 30% 26% 7%	836
November	1st to 10th	Night	18% 13% 31% 29% 9% 1	780
	11th to 20th	Night	22% 12% 32% 26% 7% 1	800
	21st to end	Night	22% 12% 31% 28% 6%	779
December	1st to 10th	Night	25% 13% 35% 21% 5%	760
	11th to 20th	Night	25% 14% 33% 26% 3	760
	21st to end	Night	27% 14% 33% 23% 3	836

Page generated at 2024-11-22 08:02:27. Version ac07

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