ActonStarParty
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ActonStarParty clear sky chart from 2005-11-06 to 2024-01-16.

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	17% 6% 3 5% 5% 3 5% 4 5% 7% 40%	74831
	Night	17% 7% 3 5% 5% 3 4 4 5% 6% 41%	74954
Transparency	Day	43% 6% 11% 21% 15% 3	74536
	Night	43% 6% 12% 22% 16% 2	74783
Seeing	Day	23% 16% 32% 19% 8% 2	13915
	Night	22% 13% 33% 25% 7% 1	22942

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	14% 8% 3 6% 5% 3 5% 3 4 6% 43%	1517
	11th to 20th	Day	19% 8% 3 5% 4 3 5% 5% 5% 6% 38%	1480
	21st to end	Day	13% 7% 3 4 5% 3 5% 5% 5% 5% 44%	1584
February	1st to 10th	Day	20% 8% 3 6% 5% 3 5% 5% 5% 7% 34%	1672
	11th to 20th	Day	13% 8% 3 6% 6% 3 6% 5% 5% 7% 39%	1748
	21st to end	Day	19% 9% 3 6% 5% 3 5% 3 4 5% 37%	1480
March	1st to 10th	Day	18% 7% 3 5% 4 3 5% 4 5% 7% 38%	1797
	11th to 20th	Day	18% 6% 3 6% 5% 3 4 4 6% 6% 38%	1890
	21st to end	Day	19% 8% 3 7% 5% 3 3 3 4 5% 40%	2304
April	1st to 10th	Day	19% 9% 3 5% 5% 3 4 4 4 7% 38%	2160
	11th to 20th	Day	18% 6% 2 5% 4 3 5% 5% 5% 7% 39%	2142
	21st to end	Day	22% 6% 3 6% 6% 3 5% 4 4 6% 35%	2340
May	1st to 10th	Day	25% 8% 3 4 5% 3 5% 4 5% 7% 32%	2340
	11th to 20th	Day	18% 5% 3 5% 6% 3 4 3 5% 7% 40%	2349
	21st to end	Day	14% 5% 2 5% 4 3 5% 4 5% 7% 44%	2725
June	1st to 10th	Day	19% 5% 2 6% 5% 3 4 5% 7% 7% 35%	2520
	11th to 20th	Day	17% 5% 2 5% 6% 3 5% 5% 6% 8% 37%	2520
	21st to end	Day	18% 5% 3 5% 6% 3 5% 5% 6% 9% 35%	2520
July	1st to 10th	Day	14% 5% 3 5% 5% 3 6% 5% 5% 8% 41%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 6% 6% 5% 9% 40%	2520
	21st to end	Day	11% 5% 3 5% 5% 3 5% 5% 7% 9% 41%	2744
August	1st to 10th	Day	9% 6% 2 6% 6% 4 6% 5% 6% 10% 39%	2366
	11th to 20th	Day	13% 5% 2 6% 5% 3 6% 6% 6% 8% 40%	2271
	21st to end	Day	12% 4 2 5% 5% 4 5% 5% 5% 7% 46%	2376
September	1st to 10th	Day	14% 6% 2 4 4 3 5% 4 6% 7% 45%	2160
	11th to 20th	Day	15% 6% 2 4 3 2 3 4 4 6% 51%	1980
	21st to end	Day	17% 5% 3 5% 5% 2 4 3 5% 6% 46%	1980
October	1st to 10th	Day	23% 5% 2 4 5% 2 4 3 5% 5% 40%	1980
	11th to 20th	Day	15% 6% 2 4 5% 3 3 4 5% 7% 46%	1756
	21st to end	Day	22% 6% 2 5% 5% 3 4 4 4 6% 40%	1782
November	1st to 10th	Day	16% 6% 2 5% 5% 3 3 2 4 5% 49%	1671
	11th to 20th	Day	19% 6% 2 4 3 2 4 4 4 5% 47%	1710
	21st to end	Day	19% 6% 3 5% 4 2 4 5% 5% 5% 43%	1710
December	1st to 10th	Day	18% 8% 3 6% 5% 2 5% 4 5% 6% 39%	1539
	11th to 20th	Day	23% 5% 3 3 5% 2 3 4 4 4 45%	1906
	21st to end	Day	23% 10% 3 5% 5% 3 4 4 4 6% 34%	2772
January	1st to 10th	Night	17% 8% 2 4 5% 3 4 4 4 5% 44%	2649
	11th to 20th	Night	18% 9% 4 6% 5% 3 4 5% 5% 6% 36%	2591
	21st to end	Night	13% 9% 4 6% 5% 3 4 5% 5% 6% 41%	2772
February	1st to 10th	Night	18% 9% 3 6% 6% 3 4 4 5% 6% 38%	2283
	11th to 20th	Night	16% 8% 4 5% 5% 3 4 4 5% 6% 40%	2098
	21st to end	Night	18% 9% 3 5% 5% 2 4 3 4 6% 40%	1776
March	1st to 10th	Night	16% 7% 3 5% 5% 3 4 4 5% 6% 41%	2150
	11th to 20th	Night	16% 8% 4 6% 6% 3 6% 4 4 5% 38%	2069
	21st to end	Night	17% 10% 3 5% 4 3 4 4 4 5% 41%	2050
April	1st to 10th	Night	18% 7% 3 6% 6% 3 4 3 5% 7% 37%	1800
	11th to 20th	Night	19% 6% 3 5% 5% 3 4 4 4 7% 40%	1767
	21st to end	Night	21% 7% 3 5% 5% 2 4 4 4 6% 39%	1620
May	1st to 10th	Night	24% 7% 3 5% 6% 3 4 5% 5% 6% 33%	1620
	11th to 20th	Night	19% 6% 3 5% 5% 3 4 6% 6% 7% 38%	1558
	21st to end	Night	17% 5% 3 6% 5% 3 4 5% 4 8% 39%	1550
June	1st to 10th	Night	19% 7% 3 6% 4 3 3 4 6% 7% 37%	1440
	11th to 20th	Night	19% 7% 3 5% 5% 2 4 5% 5% 8% 37%	1440
	21st to end	Night	14% 5% 2 5% 5% 2 4 5% 7% 10% 40%	1440
July	1st to 10th	Night	14% 4 3 5% 6% 2 5% 5% 7% 8% 41%	1440
	11th to 20th	Night	12% 7% 3 5% 6% 3 5% 5% 7% 10% 38%	1440
	21st to end	Night	12% 5% 3 3 6% 2 6% 5% 6% 8% 45%	1574
August	1st to 10th	Night	9% 5% 2 4 5% 3 5% 6% 6% 9% 46%	1553
	11th to 20th	Night	11% 5% 2 5% 7% 4 6% 6% 7% 8% 38%	1626
	21st to end	Night	15% 4 2 4 4 3 3 4 6% 8% 48%	1980
September	1st to 10th	Night	13% 6% 3 5% 4 3 4 4 5% 7% 48%	1800
	11th to 20th	Night	15% 5% 2 4 4 2 3 4 4 6% 52%	1978
	21st to end	Night	17% 6% 2 4 4 2 3 5% 5% 6% 46%	1980
October	1st to 10th	Night	22% 6% 2 5% 4 3 3 3 5% 5% 42%	1980
	11th to 20th	Night	17% 5% 1 4 5% 2 4 5% 5% 7% 45%	2201
	21st to end	Night	23% 7% 3 4 5% 2 4 4 5% 5% 38%	2574
November	1st to 10th	Night	16% 5% 2 4 4 3 4 4 5% 5% 48%	2407
	11th to 20th	Night	20% 6% 2 4 4 2 3 3 4 5% 47%	2470
	21st to end	Night	16% 7% 3 4 4 2 4 4 5% 7% 45%	2470
December	1st to 10th	Night	19% 9% 3 5% 5% 3 4 3 4 6% 39%	2636
	11th to 20th	Night	20% 6% 3 5% 4 3 4 4 4 6% 42%	3288
	21st to end	Night	21% 10% 3 6% 5% 3 4 4 4 6% 35%	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	44% 4 9% 26% 14% 3	1518
	11th to 20th	Day	45% 8% 13% 19% 13% 3	1480
	21st to end	Day	40% 5% 12% 24% 16% 3	1584
February	1st to 10th	Day	49% 6% 12% 18% 12% 3	1672
	11th to 20th	Day	44% 7% 11% 20% 14% 3	1757
	21st to end	Day	50% 5% 8% 19% 15% 3	1480
March	1st to 10th	Day	45% 5% 12% 21% 12% 5%	1800
	11th to 20th	Day	45% 5% 11% 19% 16% 4	1890
	21st to end	Day	47% 4 8% 17% 16% 7%	2304
April	1st to 10th	Day	48% 4 9% 18% 17% 4	2160
	11th to 20th	Day	43% 6% 11% 19% 18% 3	2142
	21st to end	Day	49% 6% 7% 17% 17% 4	2340
May	1st to 10th	Day	53% 5% 8% 19% 13% 2	2340
	11th to 20th	Day	44% 6% 10% 18% 18% 3	2353
	21st to end	Day	40% 7% 13% 23% 14% 2	2725
June	1st to 10th	Day	46% 8% 13% 22% 11% 1	2520
	11th to 20th	Day	43% 8% 12% 19% 16% 2	2520
	21st to end	Day	45% 9% 12% 21% 12% 1	2520
July	1st to 10th	Day	40% 8% 10% 23% 16% 2	2450
	11th to 20th	Day	39% 8% 13% 26% 13% 1	2445
	21st to end	Day	37% 8% 15% 22% 14% 3	2591
August	1st to 10th	Day	39% 9% 15% 23% 14% 1	2352
	11th to 20th	Day	41% 9% 13% 24% 13% 1	2271
	21st to end	Day	36% 7% 11% 24% 19% 3	2376
September	1st to 10th	Day	37% 7% 12% 24% 18% 2	2160
	11th to 20th	Day	36% 4 9% 25% 23% 3	1980
	21st to end	Day	39% 5% 10% 21% 23% 2	1980
October	1st to 10th	Day	47% 5% 9% 21% 14% 4	1980
	11th to 20th	Day	36% 6% 12% 30% 15% 2	1756
	21st to end	Day	46% 6% 12% 20% 14% 3	1782
November	1st to 10th	Day	39% 4 12% 25% 17% 2	1671
	11th to 20th	Day	41% 4 10% 22% 21% 3	1710
	21st to end	Day	43% 5% 15% 23% 13% 2	1710
December	1st to 10th	Day	47% 5% 14% 16% 17% 1	1539
	11th to 20th	Day	43% 4 14% 18% 18% 4	1906
	21st to end	Day	52% 6% 11% 20% 11% 1	2772
January	1st to 10th	Night	43% 5% 11% 23% 16% 3	2649
	11th to 20th	Night	49% 6% 14% 20% 9% 3	2591
	21st to end	Night	44% 5% 11% 20% 18% 3	2772
February	1st to 10th	Night	47% 5% 13% 19% 13% 2	2283
	11th to 20th	Night	46% 5% 10% 20% 15% 4	2100
	21st to end	Night	45% 4 8% 23% 16% 3	1776
March	1st to 10th	Night	44% 5% 9% 23% 15% 4	2160
	11th to 20th	Night	47% 6% 10% 16% 17% 4	2070
	21st to end	Night	46% 4 9% 17% 19% 5%	2050
April	1st to 10th	Night	47% 4 11% 18% 16% 3	1800
	11th to 20th	Night	45% 4 9% 21% 19% 3	1767
	21st to end	Night	47% 5% 10% 18% 15% 4	1620
May	1st to 10th	Night	52% 6% 9% 17% 13% 3	1620
	11th to 20th	Night	44% 7% 12% 17% 16% 3	1559
	21st to end	Night	45% 6% 14% 21% 13% 1	1551
June	1st to 10th	Night	47% 6% 12% 23% 11% 1	1440
	11th to 20th	Night	46% 7% 12% 19% 15% 2	1440
	21st to end	Night	37% 10% 15% 22% 14% 1	1440
July	1st to 10th	Night	39% 9% 13% 23% 16% 1	1400
	11th to 20th	Night	40% 8% 16% 26% 10% 1	1392
	21st to end	Night	36% 8% 13% 29% 12% 2	1486
August	1st to 10th	Night	33% 10% 14% 24% 16% 2	1543
	11th to 20th	Night	41% 8% 17% 21% 13%	1626
	21st to end	Night	35% 6% 11% 26% 20% 1	1980
September	1st to 10th	Night	37% 5% 13% 25% 19% 1	1800
	11th to 20th	Night	34% 5% 10% 22% 27% 2	1978
	21st to end	Night	38% 6% 9% 24% 21% 3	1980
October	1st to 10th	Night	45% 5% 12% 22% 12% 4	1980
	11th to 20th	Night	37% 6% 14% 27% 15% 1	2201
	21st to end	Night	48% 5% 12% 20% 14% 1	2574
November	1st to 10th	Night	38% 6% 11% 21% 20% 3	2407
	11th to 20th	Night	41% 4 11% 22% 19% 3	2470
	21st to end	Night	40% 6% 13% 25% 14% 2	2470
December	1st to 10th	Night	48% 4 13% 22% 13% 1	2636
	11th to 20th	Night	43% 5% 15% 17% 18% 2	3288
	21st to end	Night	51% 4 9% 25% 11% 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	28% 23% 29% 15% 4	180
	11th to 20th	Day	32% 21% 34% 9% 4	170
	21st to end	Day	26% 25% 34% 11% 4	176
February	1st to 10th	Day	34% 19% 33% 12% 2	330
	11th to 20th	Day	27% 26% 33% 12% 2	416
	21st to end	Day	30% 19% 34% 14% 3	346
March	1st to 10th	Day	29% 19% 36% 14% 2	420
	11th to 20th	Day	29% 22% 33% 13% 3 1	420
	21st to end	Day	29% 19% 33% 11% 6% 2	462
April	1st to 10th	Day	30% 24% 25% 14% 6% 1	420
	11th to 20th	Day	28% 23% 31% 10% 7% 1	412
	21st to end	Day	30% 19% 31% 15% 3 2	420
May	1st to 10th	Day	34% 18% 30% 13% 4 2	423
	11th to 20th	Day	24% 15% 41% 14% 5% 1	447
	21st to end	Day	19% 13% 36% 21% 9% 2	485
June	1st to 10th	Day	17% 15% 39% 18% 9% 2	450
	11th to 20th	Day	17% 15% 40% 21% 7% 1	450
	21st to end	Day	17% 13% 37% 21% 9% 2	450
July	1st to 10th	Day	18% 9% 29% 27% 14% 2	445
	11th to 20th	Day	14% 7% 34% 31% 12% 3	444
	21st to end	Day	13% 8% 34% 33% 10% 1	488
August	1st to 10th	Day	12% 9% 30% 33% 13% 3	446
	11th to 20th	Day	16% 8% 32% 28% 13% 3	439
	21st to end	Day	13% 8% 34% 26% 14% 5%	495
September	1st to 10th	Day	20% 9% 26% 24% 16% 5%	450
	11th to 20th	Day	20% 11% 31% 18% 12% 8%	450
	21st to end	Day	19% 13% 31% 22% 10% 5%	450
October	1st to 10th	Day	28% 12% 26% 20% 10% 4	450
	11th to 20th	Day	19% 17% 29% 24% 10% 2	403
	21st to end	Day	28% 14% 30% 19% 9% 1	396
November	1st to 10th	Day	22% 14% 33% 19% 9% 2	365
	11th to 20th	Day	30% 19% 27% 19% 5% 1	370
	21st to end	Day	28% 17% 31% 17% 6% 1	370
December	1st to 10th	Day	20% 29% 31% 17% 4	199
	11th to 20th	Day	31% 27% 31% 9% 2	180
	21st to end	Day	24% 26% 30% 15% 4 2	198
January	1st to 10th	Night	22% 17% 39% 19% 3	760
	11th to 20th	Night	28% 17% 34% 19% 2	741
	21st to end	Night	20% 19% 38% 21% 3	792
February	1st to 10th	Night	25% 17% 38% 19% 2	720
	11th to 20th	Night	24% 17% 40% 19% 1	703
	21st to end	Night	26% 19% 33% 19% 3 1	592
March	1st to 10th	Night	24% 17% 36% 19% 3	720
	11th to 20th	Night	22% 19% 39% 16% 4	720
	21st to end	Night	25% 17% 34% 19% 5%	792
April	1st to 10th	Night	24% 19% 33% 20% 4	720
	11th to 20th	Night	24% 17% 33% 19% 6%	703
	21st to end	Night	24% 18% 36% 20% 3	540
May	1st to 10th	Night	29% 12% 32% 22% 4	540
	11th to 20th	Night	21% 16% 38% 20% 5%	497
	21st to end	Night	19% 9% 33% 32% 6% 1	389
June	1st to 10th	Night	23% 5% 37% 27% 9% 1	360
	11th to 20th	Night	19% 9% 34% 29% 8% 1	360
	21st to end	Night	16% 4 40% 33% 8%	360
July	1st to 10th	Night	16% 4 28% 41% 11% 1	350
	11th to 20th	Night	14% 5% 26% 44% 11% 1	348
	21st to end	Night	12% 5% 30% 44% 9% 1	394
August	1st to 10th	Night	11% 5% 29% 42% 13% 1	479
	11th to 20th	Night	12% 5% 30% 39% 13% 1	562
	21st to end	Night	15% 5% 24% 39% 15% 2	792
September	1st to 10th	Night	16% 5% 31% 33% 14% 1	720
	11th to 20th	Night	17% 7% 27% 29% 17% 2	720
	21st to end	Night	20% 7% 28% 30% 13% 2	720
October	1st to 10th	Night	24% 10% 26% 26% 12% 2	720
	11th to 20th	Night	20% 12% 32% 24% 11% 1	720
	21st to end	Night	27% 13% 32% 22% 5% 1	792
November	1st to 10th	Night	19% 14% 30% 28% 9% 1	740
	11th to 20th	Night	24% 16% 34% 20% 7% 1	760
	21st to end	Night	23% 18% 33% 20% 5% 1	760
December	1st to 10th	Night	27% 17% 34% 18% 4	760
	11th to 20th	Night	25% 16% 33% 23% 3	760
	21st to end	Night	26% 16% 36% 20% 3	836

Page generated at 2024-01-13 01:38:12. Version ac07

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