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 2024-01-14.

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% 6% 3 5% 5% 3 5% 5% 5% 7% 39%	74794
	Night	17% 7% 3 5% 5% 3 4 4 5% 6% 40%	74958
Transparency	Day	45% 6% 12% 21% 14% 2	74499
	Night	44% 5% 12% 22% 14% 2	74787
Seeing	Day	23% 15% 29% 20% 10% 3	13807
	Night	21% 12% 30% 28% 8% 1	22917

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% 6% 3 6% 5% 5% 4 5% 7% 7% 38%	1517
	11th to 20th	Day	17% 9% 3 6% 5% 4 4 5% 7% 7% 33%	1464
	21st to end	Day	12% 9% 3 5% 6% 3 5% 5% 5% 8% 39%	1584
February	1st to 10th	Day	16% 9% 4 6% 7% 4 6% 6% 6% 7% 30%	1661
	11th to 20th	Day	13% 7% 4 7% 7% 3 4 6% 5% 6% 38%	1748
	21st to end	Day	19% 9% 4 7% 6% 3 6% 3 4 5% 34%	1480
March	1st to 10th	Day	15% 7% 4 6% 6% 3 4 4 6% 7% 39%	1797
	11th to 20th	Day	17% 7% 3 7% 5% 3 5% 4 5% 6% 38%	1841
	21st to end	Day	18% 8% 3 7% 5% 3 4 4 4 5% 41%	2376
April	1st to 10th	Day	19% 7% 3 6% 6% 3 4 3 5% 7% 38%	2160
	11th to 20th	Day	15% 6% 3 6% 6% 3 5% 4 6% 7% 39%	2134
	21st to end	Day	20% 6% 3 6% 5% 4 5% 5% 6% 6% 34%	2294
May	1st to 10th	Day	23% 8% 3 5% 5% 3 5% 5% 5% 6% 32%	2340
	11th to 20th	Day	18% 5% 3 5% 4 3 4 4 5% 6% 42%	2432
	21st to end	Day	15% 6% 2 5% 4 4 4 5% 5% 9% 42%	2725
June	1st to 10th	Day	17% 5% 3 5% 6% 4 5% 6% 6% 9% 34%	2520
	11th to 20th	Day	17% 5% 3 4 5% 3 5% 6% 6% 8% 38%	2520
	21st to end	Day	15% 6% 3 6% 6% 4 5% 6% 6% 8% 36%	2520
July	1st to 10th	Day	13% 5% 2 5% 6% 3 6% 6% 7% 8% 40%	2520
	11th to 20th	Day	12% 4 2 6% 5% 3 5% 5% 7% 9% 41%	2520
	21st to end	Day	12% 5% 3 5% 5% 3 5% 6% 7% 9% 38%	2744
August	1st to 10th	Day	10% 6% 2 5% 6% 4 6% 6% 7% 9% 39%	2435
	11th to 20th	Day	12% 5% 3 5% 7% 3 5% 7% 6% 9% 39%	2194
	21st to end	Day	12% 5% 2 4 5% 3 5% 6% 7% 8% 43%	2376
September	1st to 10th	Day	13% 5% 2 5% 6% 3 4 5% 6% 8% 43%	2160
	11th to 20th	Day	15% 5% 2 3 4 2 3 4 5% 6% 50%	2030
	21st to end	Day	17% 5% 2 4 4 3 3 5% 5% 7% 44%	1980
October	1st to 10th	Day	23% 6% 2 5% 5% 3 5% 4 4 5% 38%	1958
	11th to 20th	Day	14% 5% 3 4 5% 4 4 5% 5% 8% 43%	1756
	21st to end	Day	23% 7% 2 5% 5% 3 4 4 4 5% 36%	1782
November	1st to 10th	Day	13% 7% 2 5% 4 3 4 4 3 6% 49%	1671
	11th to 20th	Day	18% 7% 3 4 4 3 4 4 4 7% 42%	1710
	21st to end	Day	18% 7% 2 5% 5% 2 5% 4 4 6% 41%	1647
December	1st to 10th	Day	19% 8% 4 6% 6% 4 5% 4 4 6% 33%	1520
	11th to 20th	Day	22% 7% 3 5% 5% 2 4 4 4 5% 40%	1906
	21st to end	Day	20% 10% 4 7% 6% 3 5% 5% 3 7% 30%	2772
January	1st to 10th	Night	15% 8% 3 5% 4 3 5% 4 5% 6% 42%	2649
	11th to 20th	Night	17% 9% 3 7% 6% 4 5% 5% 6% 6% 33%	2569
	21st to end	Night	11% 8% 4 6% 6% 3 5% 6% 6% 8% 39%	2772
February	1st to 10th	Night	15% 10% 4 6% 6% 4 5% 5% 5% 6% 35%	2293
	11th to 20th	Night	12% 8% 3 7% 6% 3 5% 5% 5% 7% 39%	2098
	21st to end	Night	17% 9% 3 7% 5% 4 4 5% 4 6% 37%	1776
March	1st to 10th	Night	14% 8% 3 6% 5% 3 4 4 5% 7% 41%	2150
	11th to 20th	Night	16% 8% 3 5% 5% 3 5% 5% 5% 7% 40%	2114
	21st to end	Night	15% 8% 4 6% 5% 3 4 5% 5% 5% 41%	1980
April	1st to 10th	Night	18% 8% 2 5% 6% 3 5% 4 5% 6% 39%	1800
	11th to 20th	Night	19% 6% 2 4 5% 4 4 5% 4 6% 40%	1775
	21st to end	Night	22% 7% 2 6% 4 2 3 4 4 6% 39%	1666
May	1st to 10th	Night	23% 8% 3 6% 4 2 5% 5% 6% 7% 32%	1620
	11th to 20th	Night	18% 5% 3 5% 5% 3 5% 4 6% 7% 38%	1476
	21st to end	Night	17% 5% 2 6% 4 3 5% 4 5% 8% 41%	1550
June	1st to 10th	Night	18% 6% 3 6% 5% 3 4 4 4 6% 40%	1440
	11th to 20th	Night	18% 5% 3 4 5% 3 4 5% 6% 7% 39%	1440
	21st to end	Night	15% 5% 3 5% 4 3 4 5% 7% 7% 43%	1440
July	1st to 10th	Night	13% 5% 2 5% 5% 3 6% 5% 5% 7% 46%	1440
	11th to 20th	Night	13% 5% 3 4 5% 3 4 5% 7% 10% 40%	1440
	21st to end	Night	11% 4 2 4 4 4 5% 4 6% 9% 48%	1574
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 5% 5% 8% 47%	1485
	11th to 20th	Night	12% 6% 2 6% 7% 3 5% 5% 6% 8% 40%	1703
	21st to end	Night	15% 4 1 4 4 3 4 4 5% 8% 47%	1980
September	1st to 10th	Night	14% 5% 2 4 5% 3 5% 5% 5% 6% 47%	1800
	11th to 20th	Night	14% 5% 1 5% 3 2 3 4 4 6% 53%	1930
	21st to end	Night	16% 6% 2 4 5% 3 3 5% 4 7% 45%	1980
October	1st to 10th	Night	22% 5% 2 4 5% 3 3 3 5% 6% 40%	2001
	11th to 20th	Night	16% 5% 2 5% 4 3 4 5% 6% 6% 44%	2203
	21st to end	Night	24% 7% 2 5% 4 3 4 4 4 5% 38%	2574
November	1st to 10th	Night	14% 7% 2 5% 4 3 3 4 4 5% 48%	2407
	11th to 20th	Night	19% 6% 2 4 5% 3 4 4 4 6% 43%	2470
	21st to end	Night	15% 7% 3 4 5% 3 4 4 6% 6% 43%	2531
December	1st to 10th	Night	19% 8% 3 5% 6% 3 4 4 6% 6% 35%	2660
	11th to 20th	Night	20% 8% 2 5% 5% 2 4 4 5% 6% 38%	3288
	21st to end	Night	22% 10% 4 7% 6% 3 4 4 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	43% 5% 13% 26% 12% 2	1518
	11th to 20th	Day	50% 6% 15% 17% 10% 2	1464
	21st to end	Day	44% 5% 14% 22% 14% 2	1584
February	1st to 10th	Day	51% 6% 14% 16% 12% 1	1661
	11th to 20th	Day	48% 5% 11% 20% 14% 3	1757
	21st to end	Day	53% 5% 9% 18% 14% 2	1480
March	1st to 10th	Day	47% 4 14% 20% 12% 4	1800
	11th to 20th	Day	48% 5% 12% 18% 14% 4	1841
	21st to end	Day	48% 4 8% 17% 17% 6%	2376
April	1st to 10th	Day	48% 4 10% 21% 14% 4	2160
	11th to 20th	Day	43% 6% 11% 20% 18% 3	2134
	21st to end	Day	49% 5% 9% 18% 15% 3	2294
May	1st to 10th	Day	53% 5% 8% 19% 13% 2	2340
	11th to 20th	Day	44% 5% 9% 21% 18% 2	2436
	21st to end	Day	41% 7% 14% 23% 13% 2	2725
June	1st to 10th	Day	45% 8% 15% 22% 11% 1	2520
	11th to 20th	Day	43% 7% 14% 20% 14% 2	2520
	21st to end	Day	45% 8% 12% 22% 12% 1	2520
July	1st to 10th	Day	42% 7% 11% 23% 15% 2	2450
	11th to 20th	Day	39% 7% 15% 27% 12% 1	2445
	21st to end	Day	40% 8% 14% 22% 15% 2	2591
August	1st to 10th	Day	39% 8% 15% 24% 12% 1	2421
	11th to 20th	Day	40% 7% 14% 25% 12% 2	2194
	21st to end	Day	36% 7% 13% 26% 16% 2	2376
September	1st to 10th	Day	39% 6% 14% 24% 16% 1	2160
	11th to 20th	Day	36% 5% 9% 25% 22% 2	2030
	21st to end	Day	40% 5% 10% 24% 18% 3	1980
October	1st to 10th	Day	50% 4 9% 21% 13% 3	1958
	11th to 20th	Day	39% 6% 14% 27% 11% 2	1756
	21st to end	Day	50% 5% 12% 17% 12% 3	1782
November	1st to 10th	Day	38% 4 15% 25% 15% 2	1671
	11th to 20th	Day	42% 5% 11% 22% 18% 2	1710
	21st to end	Day	44% 6% 15% 23% 11% 2	1647
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	43% 5% 14% 21% 15% 2	2649
	11th to 20th	Night	52% 6% 14% 18% 8% 2	2569
	21st to end	Night	44% 5% 12% 21% 16% 3	2772
February	1st to 10th	Night	49% 6% 13% 20% 10% 2	2293
	11th to 20th	Night	45% 6% 12% 20% 14% 3	2100
	21st to end	Night	49% 4 10% 22% 11% 4	1776
March	1st to 10th	Night	44% 4 10% 25% 14% 3	2160
	11th to 20th	Night	45% 5% 13% 21% 14% 3	2115
	21st to end	Night	45% 5% 10% 17% 19% 5%	1980
April	1st to 10th	Night	48% 4 10% 20% 16% 2	1800
	11th to 20th	Night	45% 6% 9% 21% 18% 1	1775
	21st to end	Night	47% 5% 10% 20% 13% 6%	1666
May	1st to 10th	Night	53% 5% 9% 18% 13% 2	1620
	11th to 20th	Night	45% 5% 12% 19% 16% 3	1477
	21st to end	Night	42% 8% 14% 23% 13% 1	1551
June	1st to 10th	Night	46% 6% 11% 25% 11% 1	1440
	11th to 20th	Night	45% 6% 14% 22% 13% 1	1440
	21st to end	Night	39% 7% 15% 25% 14% 1	1440
July	1st to 10th	Night	37% 8% 15% 24% 15% 1	1400
	11th to 20th	Night	39% 8% 14% 29% 10%	1392
	21st to end	Night	33% 7% 17% 27% 14% 2	1486
August	1st to 10th	Night	34% 8% 15% 26% 16% 1	1475
	11th to 20th	Night	41% 7% 15% 25% 12%	1703
	21st to end	Night	36% 7% 11% 27% 18% 1	1980
September	1st to 10th	Night	39% 6% 12% 26% 17% 1	1800
	11th to 20th	Night	33% 5% 11% 25% 23% 2	1930
	21st to end	Night	39% 6% 8% 26% 18% 3	1980
October	1st to 10th	Night	46% 5% 12% 23% 11% 3	2001
	11th to 20th	Night	39% 7% 13% 27% 13% 1	2203
	21st to end	Night	49% 4 13% 20% 12% 1	2574
November	1st to 10th	Night	38% 6% 11% 23% 18% 3	2407
	11th to 20th	Night	44% 5% 11% 22% 16% 3	2470
	21st to end	Night	42% 5% 15% 24% 12% 1	2531
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% 11% 5% 1	166
	21st to end	Day	21% 26% 34% 15% 4 1	176
February	1st to 10th	Day	34% 25% 30% 10% 1	283
	11th to 20th	Day	29% 23% 31% 14% 2	416
	21st to end	Day	32% 17% 31% 18% 2	346
March	1st to 10th	Day	27% 19% 34% 16% 3	420
	11th to 20th	Day	31% 21% 29% 14% 4	420
	21st to end	Day	29% 22% 29% 11% 5% 3	462
April	1st to 10th	Day	32% 20% 26% 13% 7% 1	420
	11th to 20th	Day	27% 21% 28% 16% 6% 2	412
	21st to end	Day	31% 17% 29% 16% 6% 2	420
May	1st to 10th	Day	32% 20% 26% 14% 5% 2	423
	11th to 20th	Day	22% 17% 36% 18% 6% 1	447
	21st to end	Day	18% 13% 31% 22% 13% 3	485
June	1st to 10th	Day	18% 14% 33% 21% 11% 3	450
	11th to 20th	Day	17% 15% 33% 22% 10% 3	450
	21st to end	Day	18% 14% 32% 20% 12% 4	450
July	1st to 10th	Day	18% 6% 30% 27% 16% 3	445
	11th to 20th	Day	14% 8% 27% 30% 18% 3	444
	21st to end	Day	14% 7% 33% 29% 15% 3	488
August	1st to 10th	Day	10% 8% 27% 32% 18% 5%	446
	11th to 20th	Day	14% 8% 29% 26% 17% 6%	439
	21st to end	Day	12% 11% 27% 28% 15% 7%	495
September	1st to 10th	Day	20% 7% 24% 24% 18% 7%	450
	11th to 20th	Day	18% 9% 28% 19% 16% 10%	450
	21st to end	Day	20% 11% 27% 23% 12% 7%	450
October	1st to 10th	Day	28% 10% 24% 18% 14% 5%	450
	11th to 20th	Day	18% 15% 30% 23% 11% 3	428
	21st to end	Day	30% 14% 22% 23% 9% 1	396
November	1st to 10th	Day	22% 12% 28% 26% 9% 3	365
	11th to 20th	Day	29% 17% 27% 19% 6% 1	370
	21st to end	Day	29% 15% 28% 22% 5% 1	307
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	735
	21st to end	Night	19% 16% 36% 25% 4	792
February	1st to 10th	Night	23% 15% 37% 23% 2	720
	11th to 20th	Night	21% 19% 38% 21% 2	703
	21st to end	Night	24% 18% 32% 23% 3	592
March	1st to 10th	Night	23% 16% 37% 22% 2	720
	11th to 20th	Night	23% 19% 34% 20% 4	720
	21st to end	Night	23% 16% 32% 22% 7%	792
April	1st to 10th	Night	24% 17% 31% 24% 4	720
	11th to 20th	Night	23% 16% 31% 23% 7%	711
	21st to end	Night	27% 15% 30% 22% 5%	586
May	1st to 10th	Night	28% 13% 30% 24% 5%	540
	11th to 20th	Night	19% 13% 35% 27% 6%	415
	21st to end	Night	19% 7% 28% 34% 12% 1	389
June	1st to 10th	Night	19% 5% 27% 38% 11%	360
	11th to 20th	Night	20% 7% 29% 35% 9% 1	360
	21st to end	Night	15% 6% 26% 42% 11%	360
July	1st to 10th	Night	14% 5% 25% 42% 15% 1	350
	11th to 20th	Night	16% 2 21% 42% 18% 1	348
	21st to end	Night	9% 5% 22% 49% 15%	394
August	1st to 10th	Night	13% 2 22% 47% 16% 1	411
	11th to 20th	Night	14% 4 21% 41% 18% 3	639
	21st to end	Night	17% 5% 20% 36% 21% 2	792
September	1st to 10th	Night	17% 4 26% 34% 18% 1	720
	11th to 20th	Night	17% 6% 22% 32% 21% 4	720
	21st to end	Night	18% 5% 26% 35% 15% 2	720
October	1st to 10th	Night	24% 9% 21% 30% 13% 3	720
	11th to 20th	Night	20% 10% 28% 30% 11%	720
	21st to end	Night	28% 10% 30% 25% 7%	792
November	1st to 10th	Night	18% 13% 29% 29% 9% 1	740
	11th to 20th	Night	23% 12% 31% 26% 6% 1	760
	21st to end	Night	21% 12% 31% 29% 6%	760
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 2024-01-11 04:22:44. Version ac07

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