Boyertown Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boyertown Planetarium clear sky chart from 2005-11-06 to 2024-11-04.

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% 2 6% 4 4 4 4 6% 7% 39%	101332
	Night	17% 7% 2 6% 4 4 4 3 5% 7% 41%	97670
Transparency	Day	42% 6% 11% 23% 15% 2	104892
	Night	41% 6% 11% 24% 16% 2	102198
Seeing	Day	23% 15% 28% 21% 11% 4	14948
	Night	20% 13% 28% 27% 11% 1	24221

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% 9% 2 6% 4 4 4 3 4 5% 44%	2517
	11th to 20th	Day	14% 10% 4 10% 6% 4 4 4 4 6% 34%	2598
	21st to end	Day	20% 10% 3 7% 5% 4 4 3 4 6% 34%	3124
February	1st to 10th	Day	16% 8% 3 7% 5% 4 4 3 6% 7% 38%	1710
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 4 5% 8% 38%	1778
	21st to end	Day	19% 11% 3 6% 4 4 3 3 4 5% 37%	1570
March	1st to 10th	Day	26% 7% 2 5% 4 4 4 2 4 6% 36%	3163
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 6% 45%	3480
	21st to end	Day	22% 7% 2 5% 3 3 3 2 3 6% 43%	4024
April	1st to 10th	Day	17% 7% 2 7% 5% 4 4 3 5% 7% 39%	2280
	11th to 20th	Day	16% 7% 2 6% 4 3 4 3 6% 7% 42%	2254
	21st to end	Day	17% 5% 2 7% 4 4 4 5% 6% 7% 40%	2280
May	1st to 10th	Day	28% 7% 3 6% 4 4 4 4 5% 6% 29%	4094
	11th to 20th	Day	25% 8% 3 8% 6% 4 4 3 4 6% 28%	4398
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 9% 44%	4837
June	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 8% 10% 39%	2660
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 38%	2660
	21st to end	Day	12% 5% 2 6% 4 5% 5% 5% 6% 10% 41%	2660
July	1st to 10th	Day	8% 4 2 6% 5% 6% 6% 6% 8% 11% 38%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	4440
	21st to end	Day	12% 8% 3 8% 5% 5% 5% 5% 6% 8% 34%	4704
August	1st to 10th	Day	19% 5% 3 6% 5% 4 5% 4 6% 8% 34%	4104
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 4 6% 9% 42%	3769
	21st to end	Day	12% 5% 2 5% 4 3 4 3 6% 9% 48%	4180
September	1st to 10th	Day	15% 7% 2 5% 3 4 4 3 5% 6% 45%	2280
	11th to 20th	Day	13% 5% 2 4 3 3 4 3 5% 7% 51%	2266
	21st to end	Day	20% 6% 3 5% 5% 4 4 3 5% 6% 38%	2065
October	1st to 10th	Day	18% 6% 2 5% 4 3 3 4 5% 7% 42%	1900
	11th to 20th	Day	16% 5% 2 5% 4 4 4 3 4 6% 47%	1900
	21st to end	Day	19% 6% 2 5% 3 3 3 3 4 5% 44%	2037
November	1st to 10th	Day	14% 7% 2 4 3 2 4 3 4 6% 52%	1698
	11th to 20th	Day	17% 5% 2 5% 3 4 4 3 5% 6% 46%	1710
	21st to end	Day	15% 7% 2 5% 4 4 3 4 6% 8% 43%	1554
December	1st to 10th	Day	19% 9% 2 6% 4 4 4 3 6% 7% 36%	1520
	11th to 20th	Day	20% 7% 2 5% 3 4 3 3 5% 6% 40%	1906
	21st to end	Day	17% 8% 3 7% 5% 6% 4 4 6% 7% 33%	2772
January	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 5% 6% 44%	4429
	11th to 20th	Night	18% 8% 2 6% 4 4 4 2 5% 6% 41%	4344
	21st to end	Night	24% 9% 2 6% 4 3 3 3 4 5% 36%	4532
February	1st to 10th	Night	17% 9% 2 6% 4 4 4 3 5% 6% 40%	2470
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 4 5% 40%	2286
	21st to end	Night	19% 8% 2 5% 4 3 4 4 5% 6% 41%	1884
March	1st to 10th	Night	22% 9% 3 6% 4 4 3 3 4 4 37%	3674
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 6% 5% 49%	3479
	21st to end	Night	17% 9% 3 6% 3 3 2 2 4 5% 45%	3608
April	1st to 10th	Night	17% 7% 2 6% 5% 4 4 4 6% 7% 39%	1900
	11th to 20th	Night	14% 7% 3 7% 4 4 4 4 5% 8% 41%	1875
	21st to end	Night	20% 5% 2 5% 3 2 3 3 6% 7% 44%	1900
May	1st to 10th	Night	25% 9% 2 6% 4 4 4 3 5% 7% 30%	2875
	11th to 20th	Night	24% 9% 3 7% 5% 4 4 4 5% 6% 28%	2495
	21st to end	Night	13% 6% 2 6% 5% 4 4 4 6% 10% 41%	2738
June	1st to 10th	Night	15% 6% 2 5% 4 4 4 4 5% 8% 42%	1520
	11th to 20th	Night	12% 6% 2 6% 4 5% 4 5% 7% 9% 41%	1520
	21st to end	Night	12% 4 2 5% 5% 5% 4 4 7% 9% 43%	1520
July	1st to 10th	Night	8% 5% 3 6% 6% 5% 7% 5% 7% 9% 38%	2520
	11th to 20th	Night	10% 6% 3 8% 4 5% 5% 5% 7% 11% 36%	2520
	21st to end	Night	15% 7% 2 6% 5% 4 4 4 7% 8% 37%	2832
August	1st to 10th	Night	20% 6% 3 5% 4 4 5% 4 6% 9% 33%	2825
	11th to 20th	Night	15% 7% 3 6% 5% 4 4 3 5% 7% 41%	3025
	21st to end	Night	12% 4 2 5% 4 4 4 4 5% 8% 48%	3476
September	1st to 10th	Night	15% 6% 2 5% 5% 3 3 3 4 7% 47%	1900
	11th to 20th	Night	13% 5% 2 5% 2 4 3 2 5% 7% 52%	1914
	21st to end	Night	19% 6% 2 5% 4 4 4 4 5% 6% 41%	2112
October	1st to 10th	Night	19% 8% 2 5% 3 4 4 3 4 5% 44%	2280
	11th to 20th	Night	16% 5% 1 5% 3 4 3 3 4 7% 50%	2280
	21st to end	Night	18% 7% 1 4 3 3 3 3 4 6% 48%	2560
November	1st to 10th	Night	12% 5% 2 4 3 3 4 4 5% 5% 52%	2453
	11th to 20th	Night	16% 8% 2 5% 4 3 3 3 4 5% 47%	2470
	21st to end	Night	14% 5% 2 5% 5% 4 3 3 6% 8% 44%	2622
December	1st to 10th	Night	20% 7% 3 6% 4 3 5% 4 5% 6% 38%	2660
	11th to 20th	Night	18% 6% 2 6% 4 4 4 4 5% 6% 40%	3288
	21st to end	Night	19% 8% 3 7% 4 4 4 4 4 6% 37%	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% 3 13% 26% 12% 3	2518
	11th to 20th	Day	50% 6% 10% 19% 13% 2	2598
	21st to end	Day	51% 6% 11% 21% 9% 1	3124
February	1st to 10th	Day	45% 6% 13% 22% 12% 2	1710
	11th to 20th	Day	46% 4 9% 24% 14% 2	1787
	21st to end	Day	49% 4 9% 22% 12% 4	1570
March	1st to 10th	Day	50% 4 8% 26% 9% 2	3166
	11th to 20th	Day	36% 7% 10% 29% 16% 3	3480
	21st to end	Day	45% 4 9% 19% 21% 3	4024
April	1st to 10th	Day	43% 6% 9% 23% 15% 5%	2280
	11th to 20th	Day	41% 5% 11% 22% 17% 4	2254
	21st to end	Day	41% 6% 10% 21% 17% 4	2280
May	1st to 10th	Day	54% 6% 9% 19% 10% 2	4106
	11th to 20th	Day	56% 7% 10% 18% 8% 1	4402
	21st to end	Day	35% 8% 12% 27% 17% 2	4837
June	1st to 10th	Day	39% 8% 12% 24% 15% 1	2660
	11th to 20th	Day	41% 8% 14% 25% 10% 3	2660
	21st to end	Day	37% 8% 13% 26% 15% 1	2660
July	1st to 10th	Day	38% 9% 14% 23% 13% 2	4370
	11th to 20th	Day	37% 8% 16% 24% 14% 1	4365
	21st to end	Day	47% 7% 9% 19% 17% 2	4554
August	1st to 10th	Day	47% 7% 13% 23% 10%	4091
	11th to 20th	Day	38% 6% 11% 30% 14% 1	3806
	21st to end	Day	34% 6% 11% 29% 20% 2	4180
September	1st to 10th	Day	40% 6% 11% 20% 20% 3	2280
	11th to 20th	Day	32% 5% 10% 25% 24% 4	2266
	21st to end	Day	47% 5% 8% 18% 20% 2	2065
October	1st to 10th	Day	38% 4 8% 19% 26% 5%	3160
	11th to 20th	Day	26% 4 12% 27% 25% 6%	3140
	21st to end	Day	26% 3 13% 25% 29% 4	3339
November	1st to 10th	Day	34% 4 13% 25% 20% 4	1698
	11th to 20th	Day	38% 6% 9% 25% 20% 2	1710
	21st to end	Day	38% 6% 13% 30% 11% 2	1554
December	1st to 10th	Day	47% 6% 15% 19% 12% 1	1520
	11th to 20th	Day	44% 4 16% 24% 10% 1	1906
	21st to end	Day	48% 7% 12% 21% 10% 1	2772
January	1st to 10th	Night	41% 5% 10% 28% 12% 3	4429
	11th to 20th	Night	45% 4 12% 25% 12% 2	4344
	21st to end	Night	51% 4 8% 26% 10% 2	4532
February	1st to 10th	Night	45% 5% 12% 26% 11% 2	2470
	11th to 20th	Night	46% 4 9% 20% 18% 3	2288
	21st to end	Night	44% 5% 8% 23% 17% 4	1884
March	1st to 10th	Night	50% 4 8% 23% 12% 2	3684
	11th to 20th	Night	35% 7% 11% 29% 17% 2	3480
	21st to end	Night	43% 4 7% 19% 23% 5%	3608
April	1st to 10th	Night	43% 5% 10% 21% 16% 4	1900
	11th to 20th	Night	42% 5% 10% 21% 20% 3	1875
	21st to end	Night	40% 5% 10% 23% 17% 5%	1900
May	1st to 10th	Night	53% 7% 9% 19% 10% 2	2882
	11th to 20th	Night	54% 8% 12% 14% 10% 2	2496
	21st to end	Night	37% 9% 13% 22% 15% 3	2739
June	1st to 10th	Night	39% 6% 11% 22% 19% 2	1520
	11th to 20th	Night	37% 9% 14% 25% 14% 1	1520
	21st to end	Night	35% 8% 13% 28% 13% 2	1520
July	1st to 10th	Night	40% 9% 16% 17% 14% 3	2480
	11th to 20th	Night	40% 8% 16% 23% 12% 2	2472
	21st to end	Night	44% 8% 12% 19% 17% 1	2741
August	1st to 10th	Night	46% 8% 18% 18% 9% 1	2814
	11th to 20th	Night	43% 5% 12% 24% 16% 1	3054
	21st to end	Night	33% 6% 10% 29% 20% 1	3476
September	1st to 10th	Night	39% 6% 9% 21% 22% 3	1900
	11th to 20th	Night	31% 6% 10% 23% 27% 4	1914
	21st to end	Night	43% 6% 7% 21% 21% 2	2112
October	1st to 10th	Night	43% 4 9% 21% 21% 2	3800
	11th to 20th	Night	26% 4 9% 29% 28% 4	3779
	21st to end	Night	27% 3 11% 32% 24% 3	4208
November	1st to 10th	Night	32% 6% 11% 26% 19% 5%	2453
	11th to 20th	Night	40% 4 9% 23% 19% 4	2470
	21st to end	Night	38% 4 13% 28% 15% 2	2622
December	1st to 10th	Night	47% 6% 12% 21% 14% 1	2660
	11th to 20th	Night	43% 5% 12% 22% 15% 3	3288
	21st to end	Night	47% 6% 13% 23% 10% 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	33% 22% 26% 14% 4 1	180
	11th to 20th	Day	38% 26% 26% 8% 1	204
	21st to end	Day	29% 29% 26% 12% 3 1	297
February	1st to 10th	Day	30% 25% 32% 9% 3 1	270
	11th to 20th	Day	32% 25% 32% 10% 1	386
	21st to end	Day	37% 18% 27% 14% 3	382
March	1st to 10th	Day	33% 17% 29% 17% 5%	460
	11th to 20th	Day	30% 25% 28% 12% 3 1	460
	21st to end	Day	31% 23% 30% 10% 5% 1	506
April	1st to 10th	Day	27% 23% 30% 14% 5% 1	460
	11th to 20th	Day	24% 24% 27% 15% 6% 3	452
	21st to end	Day	29% 17% 33% 15% 4 2	460
May	1st to 10th	Day	33% 19% 26% 14% 6% 3	463
	11th to 20th	Day	25% 14% 30% 19% 10% 2	487
	21st to end	Day	19% 10% 27% 24% 16% 4	529
June	1st to 10th	Day	17% 13% 31% 23% 13% 4	490
	11th to 20th	Day	16% 11% 29% 25% 15% 4	490
	21st to end	Day	13% 11% 31% 27% 14% 4	490
July	1st to 10th	Day	12% 4 24% 32% 22% 7%	485
	11th to 20th	Day	10% 3 25% 34% 23% 5%	484
	21st to end	Day	13% 6% 30% 29% 19% 4	532
August	1st to 10th	Day	12% 7% 24% 29% 21% 7%	486
	11th to 20th	Day	13% 6% 20% 34% 19% 8%	479
	21st to end	Day	13% 7% 23% 28% 17% 11%	539
September	1st to 10th	Day	19% 9% 21% 26% 16% 9%	490
	11th to 20th	Day	15% 5% 26% 26% 17% 11%	490
	21st to end	Day	24% 13% 23% 23% 12% 4	490
October	1st to 10th	Day	26% 8% 25% 21% 14% 6%	490
	11th to 20th	Day	20% 18% 25% 24% 12% 2	490
	21st to end	Day	22% 16% 33% 16% 11% 3	511
November	1st to 10th	Day	22% 13% 29% 22% 11% 3	374
	11th to 20th	Day	25% 20% 30% 19% 6% 1	370
	21st to end	Day	24% 19% 33% 19% 4 1	214
December	1st to 10th	Day	35% 22% 28% 9% 5% 1	180
	11th to 20th	Day	37% 23% 24% 12% 3	180
	21st to end	Day	31% 19% 31% 13% 6% 1	198
January	1st to 10th	Night	21% 22% 36% 17% 3	760
	11th to 20th	Night	27% 17% 30% 22% 3	760
	21st to end	Night	20% 21% 35% 22% 2	836
February	1st to 10th	Night	23% 18% 35% 23% 1	760
	11th to 20th	Night	27% 24% 34% 14% 1	743
	21st to end	Night	28% 18% 35% 16% 3	628
March	1st to 10th	Night	24% 20% 29% 22% 4	760
	11th to 20th	Night	24% 22% 31% 17% 5%	760
	21st to end	Night	22% 17% 36% 19% 5%	836
April	1st to 10th	Night	23% 21% 34% 18% 4	760
	11th to 20th	Night	19% 15% 37% 23% 7%	751
	21st to end	Night	23% 14% 30% 26% 6%	760
May	1st to 10th	Night	26% 11% 30% 26% 7% 1	599
	11th to 20th	Night	21% 6% 32% 31% 9%	374
	21st to end	Night	16% 8% 22% 39% 13% 1	411
June	1st to 10th	Night	16% 6% 26% 37% 15%	380
	11th to 20th	Night	12% 6% 29% 41% 13% 1	380
	21st to end	Night	12% 3 25% 46% 14%	380
July	1st to 10th	Night	12% 3 19% 44% 20% 2	370
	11th to 20th	Night	8% 3 21% 40% 26% 2	368
	21st to end	Night	12% 3 18% 41% 23% 2	473
August	1st to 10th	Night	12% 3 15% 42% 27% 2	567
	11th to 20th	Night	14% 4 17% 35% 27% 3	702
	21st to end	Night	15% 3 17% 39% 24% 3	836
September	1st to 10th	Night	19% 4 23% 32% 19% 3	760
	11th to 20th	Night	14% 4 18% 36% 23% 4	760
	21st to end	Night	22% 6% 23% 30% 19% 1	760
October	1st to 10th	Night	23% 7% 23% 26% 17% 3	760
	11th to 20th	Night	18% 10% 29% 29% 13%	760
	21st to end	Night	23% 12% 28% 27% 10%	836
November	1st to 10th	Night	16% 11% 32% 27% 13% 1	755
	11th to 20th	Night	22% 16% 27% 27% 7% 1	760
	21st to end	Night	18% 17% 32% 25% 7%	760
December	1st to 10th	Night	27% 16% 31% 20% 5% 1	760
	11th to 20th	Night	21% 17% 35% 21% 6%	760
	21st to end	Night	23% 17% 31% 26% 3	836

Page generated at 2024-11-01 22:47:34. Version ac07

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