Robeson Planetarium and Science Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robeson Planetarium and Science Center clear sky chart from 2005-11-06 to 2026-05-02.

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	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	131906
	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	130611
Transparency	Day	39% 7% 12% 19% 18% 6%	135510
	Night	38% 6% 11% 18% 20% 7%	135077
Seeing	Day	15% 10% 24% 25% 18% 8%	17584
	Night	15% 9% 26% 32% 17% 2	27749

By Month

Percentage Cloud Cover SE (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% 5% 2 5% 3 3 3 3 4 6% 53%	5258
	11th to 20th	Day	13% 4 2 5% 3 3 3 2 3 5% 58%	5280
	21st to end	Day	16% 8% 3 7% 4 4 4 3 4 5% 40%	5780
February	1st to 10th	Day	16% 7% 2 6% 4 4 4 3 4 6% 42%	1890
	11th to 20th	Day	21% 6% 3 6% 3 3 4 3 4 5% 43%	1900
	21st to end	Day	17% 8% 2 6% 4 4 3 3 4 6% 42%	1903
March	1st to 10th	Day	19% 7% 3 7% 4 4 4 3 4 6% 39%	5045
	11th to 20th	Day	10% 5% 2 5% 3 4 3 3 5% 7% 54%	5090
	21st to end	Day	13% 5% 2 6% 4 4 4 3 5% 5% 49%	5586
April	1st to 10th	Day	10% 4 2 4 4 3 4 4 6% 8% 51%	2416
	11th to 20th	Day	10% 4 2 5% 3 4 4 4 6% 7% 52%	2494
	21st to end	Day	10% 5% 2 5% 4 4 4 3 6% 7% 50%	2520
May	1st to 10th	Day	9% 6% 3 8% 5% 5% 6% 5% 7% 11% 36%	5738
	11th to 20th	Day	17% 7% 3 7% 5% 5% 5% 5% 7% 9% 31%	5861
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 4 7% 8% 43%	6433
June	1st to 10th	Day	11% 7% 3 6% 6% 5% 6% 5% 7% 10% 37%	2600
	11th to 20th	Day	9% 4 2 6% 6% 5% 7% 5% 8% 9% 41%	2600
	21st to end	Day	7% 5% 2 7% 6% 5% 7% 6% 8% 12% 35%	2600
July	1st to 10th	Day	9% 6% 3 9% 7% 7% 7% 5% 9% 11% 28%	5900
	11th to 20th	Day	7% 6% 3 8% 6% 6% 7% 6% 9% 13% 28%	5900
	21st to end	Day	8% 7% 3 8% 6% 6% 7% 6% 8% 12% 27%	6424
August	1st to 10th	Day	21% 10% 3 9% 7% 7% 6% 5% 7% 8% 18%	4234
	11th to 20th	Day	11% 7% 3 8% 5% 5% 6% 5% 7% 11% 32%	4014
	21st to end	Day	7% 4 2 6% 5% 5% 5% 4 7% 10% 45%	4312
September	1st to 10th	Day	9% 5% 2 7% 5% 6% 6% 4 6% 8% 42%	2400
	11th to 20th	Day	12% 7% 3 6% 4 5% 5% 4 6% 7% 41%	2230
	21st to end	Day	16% 7% 3 6% 5% 5% 4 3 5% 8% 38%	2170
October	1st to 10th	Day	13% 7% 3 6% 3 4 3 3 5% 7% 46%	2000
	11th to 20th	Day	11% 5% 2 4 3 3 3 2 5% 6% 56%	2000
	21st to end	Day	10% 6% 2 4 3 3 3 3 4 6% 57%	2200
November	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 5% 5% 55%	2057
	11th to 20th	Day	14% 6% 2 4 3 2 3 2 4 7% 52%	2100
	21st to end	Day	12% 6% 2 6% 3 3 3 3 4 6% 51%	1923
December	1st to 10th	Day	12% 5% 2 6% 4 4 4 3 4 5% 51%	3020
	11th to 20th	Day	15% 7% 2 6% 4 3 3 2 4 6% 47%	3463
	21st to end	Day	15% 7% 3 6% 4 3 4 3 5% 6% 45%	4565
January	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 6% 55%	7635
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 4 6% 53%	7680
	21st to end	Night	16% 9% 3 6% 4 3 3 2 4 5% 43%	8401
February	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 5% 45%	2730
	11th to 20th	Night	18% 7% 2 7% 4 4 3 3 5% 6% 42%	2600
	21st to end	Night	16% 5% 3 6% 4 4 4 3 5% 5% 45%	1903
March	1st to 10th	Night	19% 8% 3 7% 4 4 4 3 4 6% 40%	5028
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 8% 51%	5090
	21st to end	Night	12% 4 2 5% 4 4 4 3 6% 6% 50%	5588
April	1st to 10th	Night	12% 5% 2 4 3 3 4 4 5% 7% 51%	2202
	11th to 20th	Night	9% 4 2 5% 4 4 4 3 5% 6% 53%	2075
	21st to end	Night	9% 4 2 6% 4 4 4 3 6% 8% 49%	2100
May	1st to 10th	Night	8% 6% 3 6% 5% 4 5% 4 7% 11% 41%	4209
	11th to 20th	Night	16% 7% 3 7% 5% 4 5% 3 6% 9% 35%	4032
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 7% 9% 41%	4421
June	1st to 10th	Night	10% 7% 2 8% 5% 5% 4 6% 7% 12% 35%	1800
	11th to 20th	Night	10% 5% 3 5% 5% 6% 6% 4 6% 9% 40%	1800
	21st to end	Night	7% 6% 2 6% 6% 6% 6% 6% 8% 12% 37%	1800
July	1st to 10th	Night	11% 7% 3 9% 6% 6% 7% 5% 8% 10% 27%	4058
	11th to 20th	Night	10% 7% 3 8% 6% 6% 6% 5% 9% 14% 26%	4057
	21st to end	Night	12% 9% 3 10% 7% 6% 7% 5% 8% 9% 25%	4427
August	1st to 10th	Night	21% 9% 3 9% 5% 5% 5% 4 6% 9% 25%	2915
	11th to 20th	Night	9% 7% 3 8% 6% 5% 5% 5% 7% 10% 34%	3001
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 8% 10% 46%	3586
September	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	2000
	11th to 20th	Night	13% 6% 2 7% 5% 5% 5% 4 5% 6% 41%	2165
	21st to end	Night	17% 7% 3 7% 4 4 4 3 5% 6% 39%	2229
October	1st to 10th	Night	14% 6% 3 5% 3 3 3 2 5% 7% 49%	2400
	11th to 20th	Night	12% 5% 1 4 3 3 3 2 4 5% 57%	2400
	21st to end	Night	11% 4 2 5% 3 3 3 3 4 5% 57%	2640
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 55%	2461
	11th to 20th	Night	14% 7% 2 4 3 2 3 3 5% 6% 51%	2520
	21st to end	Night	12% 5% 1 5% 3 4 4 3 5% 7% 50%	2693
December	1st to 10th	Night	13% 7% 2 4 3 3 3 3 4 6% 52%	4380
	11th to 20th	Night	15% 7% 3 7% 4 4 4 3 4 5% 43%	4952
	21st to end	Night	14% 6% 3 6% 4 4 4 3 5% 6% 47%	6633

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	33% 3 10% 22% 25% 7%	5259
	11th to 20th	Day	32% 3 4 15% 32% 14%	5280
	21st to end	Day	46% 3 5% 15% 19% 11%	5780
February	1st to 10th	Day	43% 4 10% 19% 18% 6%	1890
	11th to 20th	Day	44% 4 6% 17% 23% 7%	1909
	21st to end	Day	44% 4 8% 17% 18% 8%	1903
March	1st to 10th	Day	47% 4 7% 13% 20% 9%	5045
	11th to 20th	Day	31% 4 8% 15% 28% 14%	5090
	21st to end	Day	38% 4 8% 21% 20% 9%	5586
April	1st to 10th	Day	30% 6% 11% 23% 25% 6%	2416
	11th to 20th	Day	31% 6% 9% 23% 22% 8%	2494
	21st to end	Day	33% 7% 11% 23% 22% 4	2520
May	1st to 10th	Day	40% 9% 16% 24% 9% 1	5771
	11th to 20th	Day	47% 9% 12% 20% 11% 1	5865
	21st to end	Day	36% 8% 13% 20% 20% 3	6447
June	1st to 10th	Day	40% 9% 15% 22% 13% 1	2600
	11th to 20th	Day	36% 10% 18% 21% 12% 3	2600
	21st to end	Day	37% 12% 17% 20% 12% 2	2600
July	1st to 10th	Day	46% 10% 19% 18% 5% 1	5835
	11th to 20th	Day	42% 15% 28% 11% 3 1	5831
	21st to end	Day	44% 13% 16% 18% 8% 1	6240
August	1st to 10th	Day	61% 9% 15% 10% 5%	4221
	11th to 20th	Day	43% 11% 13% 21% 11%	4053
	21st to end	Day	34% 7% 15% 30% 13% 1	4312
September	1st to 10th	Day	38% 9% 14% 19% 15% 5%	2400
	11th to 20th	Day	42% 7% 11% 16% 19% 5%	2230
	21st to end	Day	44% 6% 10% 19% 16% 4	2170
October	1st to 10th	Day	36% 4 7% 20% 26% 6%	3260
	11th to 20th	Day	21% 2 6% 18% 27% 27%	3240
	21st to end	Day	26% 3 5% 21% 27% 17%	3538
November	1st to 10th	Day	32% 5% 7% 18% 28% 10%	2057
	11th to 20th	Day	33% 5% 7% 19% 27% 9%	2100
	21st to end	Day	34% 4 8% 21% 24% 9%	1923
December	1st to 10th	Day	37% 4 7% 16% 24% 12%	3020
	11th to 20th	Day	39% 4 12% 19% 20% 6%	3460
	21st to end	Day	40% 4 11% 21% 22% 2	4565
January	1st to 10th	Night	31% 4 9% 21% 29% 6%	7636
	11th to 20th	Night	33% 4 6% 13% 33% 10%	7680
	21st to end	Night	44% 3 4 15% 23% 10%	8401
February	1st to 10th	Night	40% 4 8% 18% 22% 7%	2730
	11th to 20th	Night	44% 4 8% 15% 21% 7%	2602
	21st to end	Night	39% 5% 8% 16% 22% 10%	1903
March	1st to 10th	Night	46% 5% 7% 11% 25% 6%	5028
	11th to 20th	Night	32% 4 9% 12% 26% 17%	5090
	21st to end	Night	34% 5% 9% 22% 22% 8%	5588
April	1st to 10th	Night	33% 5% 12% 19% 22% 9%	2202
	11th to 20th	Night	30% 6% 11% 23% 21% 10%	2075
	21st to end	Night	32% 7% 12% 24% 21% 5%	2100
May	1st to 10th	Night	36% 9% 18% 22% 13% 2	4238
	11th to 20th	Night	45% 8% 16% 19% 11%	4033
	21st to end	Night	36% 8% 15% 22% 16% 2	4429
June	1st to 10th	Night	39% 10% 16% 23% 10% 1	1800
	11th to 20th	Night	39% 9% 16% 23% 11% 1	1800
	21st to end	Night	38% 11% 18% 22% 10% 2	1800
July	1st to 10th	Night	49% 12% 21% 14% 4 1	4015
	11th to 20th	Night	45% 14% 28% 8% 3	4006
	21st to end	Night	52% 10% 14% 18% 6%	4297
August	1st to 10th	Night	55% 10% 20% 12% 3	2904
	11th to 20th	Night	42% 11% 20% 20% 6% 1	3028
	21st to end	Night	32% 8% 13% 33% 13% 1	3586
September	1st to 10th	Night	36% 11% 15% 19% 15% 5%	2000
	11th to 20th	Night	42% 8% 12% 17% 17% 4	2165
	21st to end	Night	46% 8% 11% 18% 14% 4	2229
October	1st to 10th	Night	37% 4 8% 21% 24% 6%	3920
	11th to 20th	Night	22% 3 5% 15% 26% 29%	3899
	21st to end	Night	26% 4 6% 22% 25% 17%	4252
November	1st to 10th	Night	33% 5% 7% 17% 26% 12%	2461
	11th to 20th	Night	35% 4 8% 14% 27% 11%	2520
	21st to end	Night	34% 5% 8% 20% 25% 8%	2693
December	1st to 10th	Night	34% 4 7% 14% 30% 11%	4380
	11th to 20th	Night	43% 4 11% 15% 18% 8%	4954
	21st to end	Night	39% 4 9% 22% 23% 3	6633

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	19% 24% 38% 17% 2	330
	11th to 20th	Day	19% 22% 38% 16% 5%	330
	21st to end	Day	21% 26% 36% 13% 4	363
February	1st to 10th	Day	19% 21% 37% 19% 4	330
	11th to 20th	Day	35% 17% 35% 10% 3	355
	21st to end	Day	22% 19% 35% 19% 5%	446
March	1st to 10th	Day	18% 18% 32% 23% 8% 1	540
	11th to 20th	Day	18% 21% 33% 20% 7% 1	540
	21st to end	Day	18% 17% 35% 23% 7% 1	594
April	1st to 10th	Day	16% 17% 31% 23% 11% 2	540
	11th to 20th	Day	10% 15% 31% 25% 14% 5%	532
	21st to end	Day	12% 11% 28% 25% 19% 4	540
May	1st to 10th	Day	9% 16% 31% 25% 14% 5%	507
	11th to 20th	Day	13% 7% 20% 30% 21% 8%	527
	21st to end	Day	14% 6% 20% 25% 22% 13%	573
June	1st to 10th	Day	13% 3 19% 32% 24% 9%	530
	11th to 20th	Day	10% 4 15% 30% 24% 16%	530
	21st to end	Day	8% 2 14% 29% 31% 17%	530
July	1st to 10th	Day	10% 2 11% 23% 36% 18%	525
	11th to 20th	Day	10% 2 8% 23% 39% 17%	524
	21st to end	Day	5% 3 11% 28% 38% 15%	576
August	1st to 10th	Day	16% 4 12% 25% 26% 17%	526
	11th to 20th	Day	13% 2 10% 25% 27% 23%	519
	21st to end	Day	12% 2 13% 27% 29% 18%	583
September	1st to 10th	Day	10% 2 15% 29% 25% 18%	530
	11th to 20th	Day	15% 4 16% 27% 27% 12%	530
	21st to end	Day	19% 3 20% 31% 18% 8%	530
October	1st to 10th	Day	14% 9% 20% 28% 18% 10%	530
	11th to 20th	Day	13% 9% 23% 32% 18% 5%	530
	21st to end	Day	12% 10% 28% 26% 19% 5%	583
November	1st to 10th	Day	15% 9% 27% 30% 15% 3	535
	11th to 20th	Day	17% 13% 35% 25% 8% 2	540
	21st to end	Day	13% 17% 30% 25% 13% 2	363
December	1st to 10th	Day	22% 15% 40% 15% 7%	330
	11th to 20th	Day	19% 16% 35% 22% 7% 2	330
	21st to end	Day	20% 17% 38% 16% 7% 2	363
January	1st to 10th	Night	17% 16% 34% 26% 7%	840
	11th to 20th	Night	16% 14% 32% 32% 6%	840
	21st to end	Night	19% 14% 36% 29% 3	924
February	1st to 10th	Night	20% 13% 35% 28% 4	840
	11th to 20th	Night	22% 17% 36% 23% 2	823
	21st to end	Night	18% 15% 37% 27% 3	692
March	1st to 10th	Night	17% 12% 35% 30% 5%	840
	11th to 20th	Night	16% 13% 39% 25% 7% 1	840
	21st to end	Night	15% 15% 36% 27% 7%	924
April	1st to 10th	Night	14% 16% 33% 29% 7%	840
	11th to 20th	Night	11% 12% 34% 32% 10%	831
	21st to end	Night	11% 9% 35% 37% 8% 1	840
May	1st to 10th	Night	9% 9% 34% 36% 13%	681
	11th to 20th	Night	13% 5% 29% 38% 15% 1	591
	21st to end	Night	10% 4 16% 40% 27% 3	650
June	1st to 10th	Night	11% 3 18% 46% 20% 2	600
	11th to 20th	Night	11% 3 17% 35% 29% 6%	600
	21st to end	Night	9% 2 17% 38% 31% 4	600
July	1st to 10th	Night	10% 1 11% 38% 36% 4	585
	11th to 20th	Night	9% 1 9% 36% 39% 6%	582
	21st to end	Night	7% 1 10% 42% 35% 5%	657
August	1st to 10th	Night	15% 1 10% 33% 37% 4	597
	11th to 20th	Night	12% 2 11% 33% 35% 6%	668
	21st to end	Night	11% 3 12% 34% 34% 6%	880
September	1st to 10th	Night	10% 2 15% 35% 34% 4	800
	11th to 20th	Night	15% 2 14% 35% 29% 5%	800
	21st to end	Night	20% 5% 17% 34% 22% 3	800
October	1st to 10th	Night	17% 4 18% 30% 26% 4	800
	11th to 20th	Night	13% 6% 26% 32% 20% 2	800
	21st to end	Night	13% 7% 25% 33% 20% 3	880
November	1st to 10th	Night	14% 8% 24% 35% 16% 3	820
	11th to 20th	Night	18% 9% 30% 30% 13% 1	840
	21st to end	Night	14% 10% 30% 30% 15% 1	840
December	1st to 10th	Night	19% 13% 28% 32% 8%	840
	11th to 20th	Night	18% 10% 27% 33% 11%	840
	21st to end	Night	19% 13% 27% 32% 8%	924

Page generated at 2026-04-29 02:21:45. Version ac07

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