New Moon Telescopes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New Moon Telescopes Observatory clear sky chart from 2005-11-06 to 2026-08-30.

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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	143404
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	138793
Transparency	Day	38% 7% 12% 21% 17% 4	147005
	Night	38% 6% 11% 22% 19% 5%	143262
Seeing	Day	18% 12% 27% 24% 14% 4	17557
	Night	17% 11% 29% 30% 13% 1	27214

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 5% 52%	5217
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 4 4 56%	5280
	21st to end	Day	14% 7% 3 7% 5% 4 4 3 4 5% 45%	5780
February	1st to 10th	Day	12% 7% 2 6% 4 4 6% 4 6% 7% 41%	1890
	11th to 20th	Day	22% 6% 2 5% 4 3 3 3 5% 5% 42%	1924
	21st to end	Day	18% 6% 3 7% 4 4 5% 4 5% 7% 38%	1740
March	1st to 10th	Day	17% 8% 3 7% 4 4 4 3 5% 6% 39%	5045
	11th to 20th	Day	10% 6% 2 5% 3 3 4 3 5% 6% 52%	5090
	21st to end	Day	15% 5% 2 6% 4 4 4 3 5% 7% 44%	5623
April	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 6% 8% 50%	2520
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 7% 49%	2494
	21st to end	Day	15% 6% 2 6% 3 3 5% 3 5% 7% 44%	2520
May	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 7% 9% 38%	7334
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 5% 8% 41%	7626
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 8% 40%	9005
June	1st to 10th	Day	10% 5% 2 5% 5% 4 5% 5% 7% 10% 44%	2940
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 5% 7% 10% 42%	2940
	21st to end	Day	8% 4 2 5% 5% 4 6% 5% 8% 11% 41%	2940
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 12% 38%	8067
	11th to 20th	Day	11% 7% 2 7% 6% 6% 6% 6% 8% 12% 28%	7680
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 8% 10% 34%	8340
August	1st to 10th	Day	16% 7% 3 7% 6% 5% 6% 5% 7% 11% 28%	4364
	11th to 20th	Day	10% 6% 2 8% 5% 6% 6% 5% 8% 9% 36%	4072
	21st to end	Day	8% 4 2 5% 4 4 4 4 7% 10% 48%	4420
September	1st to 10th	Day	14% 5% 2 5% 4 5% 4 4 6% 8% 44%	2400
	11th to 20th	Day	13% 6% 3 7% 5% 5% 4 4 5% 7% 42%	2400
	21st to end	Day	19% 8% 3 7% 5% 4 4 3 5% 6% 36%	2091
October	1st to 10th	Day	16% 6% 2 6% 4 4 3 3 4 6% 47%	2000
	11th to 20th	Day	16% 5% 2 4 4 3 3 2 3 6% 53%	2000
	21st to end	Day	13% 5% 2 5% 3 3 3 3 4 6% 54%	2200
November	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 4 6% 54%	2052
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 4 6% 51%	1890
	21st to end	Day	14% 4 2 5% 4 3 3 3 5% 6% 52%	1722
December	1st to 10th	Day	11% 5% 2 6% 4 4 3 2 5% 6% 52%	2680
	11th to 20th	Day	17% 7% 2 6% 3 3 3 2 4 5% 47%	3070
	21st to end	Day	13% 6% 2 5% 4 4 3 4 6% 7% 47%	4048
January	1st to 10th	Night	12% 6% 2 5% 3 3 4 3 4 6% 51%	7658
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 4 55%	7680
	21st to end	Night	17% 6% 2 6% 3 3 3 3 4 6% 49%	8401
February	1st to 10th	Night	16% 7% 2 6% 4 2 4 3 6% 6% 44%	2730
	11th to 20th	Night	20% 8% 2 6% 4 4 3 3 4 6% 41%	2580
	21st to end	Night	16% 8% 2 6% 3 3 3 3 5% 6% 46%	2061
March	1st to 10th	Night	18% 6% 2 5% 4 3 3 3 5% 6% 45%	5028
	11th to 20th	Night	13% 4 2 5% 3 3 3 3 5% 6% 51%	5090
	21st to end	Night	13% 5% 2 6% 4 4 4 3 5% 7% 48%	5550
April	1st to 10th	Night	13% 6% 2 6% 4 5% 4 3 5% 6% 45%	2100
	11th to 20th	Night	12% 5% 2 5% 3 3 3 4 5% 7% 50%	2075
	21st to end	Night	13% 5% 2 5% 4 4 5% 2 5% 7% 47%	2100
May	1st to 10th	Night	12% 7% 3 7% 5% 5% 5% 4 6% 9% 37%	5562
	11th to 20th	Night	17% 7% 3 6% 4 3 4 3 5% 7% 41%	5234
	21st to end	Night	21% 8% 2 6% 4 4 4 3 5% 8% 35%	5131
June	1st to 10th	Night	11% 5% 2 5% 5% 5% 5% 6% 7% 9% 41%	1680
	11th to 20th	Night	9% 6% 3 6% 5% 4 6% 4 7% 10% 40%	1680
	21st to end	Night	7% 5% 2 5% 6% 4 6% 4 6% 11% 42%	1680
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 5% 8% 9% 38%	4872
	11th to 20th	Night	13% 7% 3 8% 6% 5% 6% 6% 8% 10% 28%	5277
	21st to end	Night	13% 7% 3 9% 7% 6% 6% 4 7% 8% 30%	5736
August	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 4 7% 10% 29%	3005
	11th to 20th	Night	10% 6% 3 7% 5% 4 5% 4 7% 9% 40%	3161
	21st to end	Night	9% 4 2 5% 4 4 5% 4 7% 9% 46%	3677
September	1st to 10th	Night	12% 5% 3 7% 5% 4 4 4 5% 8% 45%	2000
	11th to 20th	Night	14% 5% 2 6% 4 5% 5% 3 6% 7% 44%	2000
	21st to end	Night	23% 7% 3 7% 4 4 4 3 5% 6% 34%	2303
October	1st to 10th	Night	16% 5% 2 6% 4 4 4 3 4 6% 48%	2400
	11th to 20th	Night	15% 6% 2 6% 3 3 3 2 4 5% 50%	2400
	21st to end	Night	15% 4 2 5% 3 3 3 3 3 7% 52%	2640
November	1st to 10th	Night	12% 6% 2 6% 4 3 3 2 4 5% 52%	2462
	11th to 20th	Night	15% 6% 2 4 3 3 4 3 4 6% 49%	2730
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 6% 51%	2895
December	1st to 10th	Night	10% 5% 2 4 4 4 4 3 4 5% 54%	4720
	11th to 20th	Night	18% 7% 3 7% 5% 4 3 3 4 6% 40%	5345
	21st to end	Night	13% 7% 2 6% 4 3 4 3 5% 6% 47%	7150

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	34% 3 10% 23% 21% 8%	5218
	11th to 20th	Day	31% 4 5% 17% 29% 14%	5280
	21st to end	Day	42% 3 7% 26% 17% 5%	5780
February	1st to 10th	Day	40% 5% 12% 24% 16% 4	1890
	11th to 20th	Day	43% 5% 7% 20% 20% 5%	1933
	21st to end	Day	46% 5% 11% 16% 17% 5%	1740
March	1st to 10th	Day	45% 4 8% 17% 18% 8%	5045
	11th to 20th	Day	31% 6% 9% 22% 22% 10%	5090
	21st to end	Day	39% 6% 11% 19% 18% 6%	5623
April	1st to 10th	Day	32% 6% 12% 22% 20% 7%	2520
	11th to 20th	Day	34% 5% 11% 24% 20% 6%	2494
	21st to end	Day	39% 6% 13% 22% 15% 5%	2520
May	1st to 10th	Day	40% 9% 14% 20% 16% 1	7366
	11th to 20th	Day	40% 7% 14% 23% 16% 1	7630
	21st to end	Day	41% 7% 13% 19% 16% 3	9020
June	1st to 10th	Day	33% 9% 15% 26% 15% 1	2940
	11th to 20th	Day	34% 10% 16% 23% 16% 1	2940
	21st to end	Day	33% 11% 17% 24% 14% 2	2940
July	1st to 10th	Day	35% 11% 19% 22% 10% 3	8000
	11th to 20th	Day	45% 11% 20% 16% 6% 1	7611
	21st to end	Day	41% 10% 13% 18% 17%	8156
August	1st to 10th	Day	49% 8% 18% 19% 5%	4351
	11th to 20th	Day	40% 10% 15% 23% 11%	4111
	21st to end	Day	29% 7% 15% 28% 18% 1	4420
September	1st to 10th	Day	37% 9% 14% 17% 20% 4	2400
	11th to 20th	Day	40% 6% 11% 21% 18% 3	2400
	21st to end	Day	48% 7% 10% 19% 14% 3	2091
October	1st to 10th	Day	36% 4 8% 19% 27% 6%	3260
	11th to 20th	Day	24% 3 5% 21% 33% 13%	3240
	21st to end	Day	21% 3 8% 27% 26% 14%	3538
November	1st to 10th	Day	32% 5% 9% 25% 25% 4	2052
	11th to 20th	Day	35% 5% 9% 22% 22% 7%	1890
	21st to end	Day	34% 4 9% 25% 24% 5%	1722
December	1st to 10th	Day	34% 4 8% 27% 20% 7%	2680
	11th to 20th	Day	41% 3 12% 23% 17% 5%	3066
	21st to end	Day	36% 6% 13% 27% 17% 2	4048
January	1st to 10th	Night	35% 4 11% 21% 21% 9%	7659
	11th to 20th	Night	34% 3 5% 19% 30% 9%	7680
	21st to end	Night	38% 3 6% 27% 20% 6%	8401
February	1st to 10th	Night	40% 4 12% 22% 18% 4	2730
	11th to 20th	Night	45% 4 8% 19% 18% 6%	2582
	21st to end	Night	39% 5% 8% 21% 18% 8%	2061
March	1st to 10th	Night	39% 5% 8% 18% 21% 8%	5028
	11th to 20th	Night	33% 5% 7% 18% 25% 11%	5090
	21st to end	Night	37% 5% 9% 23% 20% 6%	5550
April	1st to 10th	Night	38% 6% 11% 18% 22% 6%	2100
	11th to 20th	Night	32% 6% 11% 23% 21% 7%	2075
	21st to end	Night	36% 7% 13% 24% 17% 4	2100
May	1st to 10th	Night	42% 8% 15% 23% 11% 1	5592
	11th to 20th	Night	42% 7% 12% 24% 14% 1	5235
	21st to end	Night	46% 8% 11% 19% 14% 2	5138
June	1st to 10th	Night	35% 10% 16% 22% 15% 2	1680
	11th to 20th	Night	38% 10% 16% 21% 14% 1	1680
	21st to end	Night	34% 10% 13% 22% 18% 3	1680
July	1st to 10th	Night	40% 11% 15% 22% 11% 2	4831
	11th to 20th	Night	48% 13% 18% 15% 6% 1	5226
	21st to end	Night	50% 8% 12% 17% 13%	5606
August	1st to 10th	Night	49% 9% 19% 19% 5%	2994
	11th to 20th	Night	38% 9% 19% 22% 12%	3188
	21st to end	Night	32% 8% 13% 27% 20% 2	3677
September	1st to 10th	Night	37% 9% 14% 19% 17% 5%	2000
	11th to 20th	Night	38% 8% 10% 21% 21% 2	2000
	21st to end	Night	49% 7% 10% 17% 14% 3	2303
October	1st to 10th	Night	40% 4 11% 17% 24% 4	3920
	11th to 20th	Night	26% 3 7% 20% 30% 14%	3899
	21st to end	Night	22% 3 5% 31% 25% 14%	4252
November	1st to 10th	Night	35% 4 10% 22% 24% 5%	2462
	11th to 20th	Night	36% 5% 9% 18% 22% 10%	2730
	21st to end	Night	34% 5% 9% 23% 24% 6%	2895
December	1st to 10th	Night	32% 4 7% 27% 24% 6%	4720
	11th to 20th	Night	46% 4 10% 18% 16% 6%	5348
	21st to end	Night	37% 5% 12% 28% 17% 2	7150

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	26% 27% 29% 13% 4	322
	11th to 20th	Day	28% 32% 29% 10% 2	330
	21st to end	Day	24% 24% 39% 11% 1	363
February	1st to 10th	Day	20% 27% 39% 11% 2	330
	11th to 20th	Day	36% 25% 29% 10% 1	411
	21st to end	Day	28% 19% 32% 18% 3	446
March	1st to 10th	Day	24% 20% 32% 19% 5%	540
	11th to 20th	Day	23% 22% 35% 15% 4 1	540
	21st to end	Day	21% 20% 40% 15% 5% 1	594
April	1st to 10th	Day	22% 19% 33% 19% 7% 1	540
	11th to 20th	Day	17% 15% 34% 22% 9% 2	532
	21st to end	Day	19% 13% 34% 25% 8% 2	540
May	1st to 10th	Day	17% 17% 35% 21% 8% 2	543
	11th to 20th	Day	20% 10% 29% 28% 11% 3	567
	21st to end	Day	21% 6% 25% 26% 16% 5%	617
June	1st to 10th	Day	12% 5% 30% 29% 21% 4	570
	11th to 20th	Day	10% 7% 24% 34% 19% 6%	570
	21st to end	Day	9% 5% 25% 34% 22% 5%	570
July	1st to 10th	Day	9% 3 17% 33% 28% 9%	565
	11th to 20th	Day	8% 3 15% 34% 30% 11%	564
	21st to end	Day	10% 3 20% 34% 24% 9%	620
August	1st to 10th	Day	15% 4 18% 30% 27% 7%	566
	11th to 20th	Day	12% 4 16% 32% 28% 8%	559
	21st to end	Day	8% 2 21% 32% 24% 13%	619
September	1st to 10th	Day	15% 3 19% 27% 21% 15%	530
	11th to 20th	Day	16% 5% 17% 29% 21% 12%	530
	21st to end	Day	26% 9% 26% 23% 13% 3	530
October	1st to 10th	Day	19% 6% 20% 26% 19% 9%	530
	11th to 20th	Day	18% 13% 23% 27% 16% 2	530
	21st to end	Day	16% 12% 33% 25% 10% 4	583
November	1st to 10th	Day	16% 12% 33% 23% 14% 3	532
	11th to 20th	Day	20% 15% 31% 22% 10% 1	430
	21st to end	Day	20% 19% 28% 22% 9% 2	262
December	1st to 10th	Day	21% 20% 37% 15% 5%	220
	11th to 20th	Day	22% 14% 38% 20% 6%	220
	21st to end	Day	23% 17% 32% 20% 7% 1	242
January	1st to 10th	Night	20% 19% 38% 21% 3	840
	11th to 20th	Night	19% 20% 32% 25% 4	840
	21st to end	Night	20% 17% 38% 23% 1	924
February	1st to 10th	Night	20% 14% 39% 25% 3	840
	11th to 20th	Night	26% 19% 36% 18% 1	823
	21st to end	Night	21% 17% 38% 21% 3	692
March	1st to 10th	Night	19% 17% 36% 25% 3	840
	11th to 20th	Night	21% 18% 34% 22% 5%	840
	21st to end	Night	18% 16% 43% 20% 4	924
April	1st to 10th	Night	17% 18% 38% 22% 4	840
	11th to 20th	Night	13% 15% 39% 25% 8%	831
	21st to end	Night	15% 11% 36% 31% 7%	840
May	1st to 10th	Night	17% 10% 35% 29% 8%	750
	11th to 20th	Night	16% 7% 30% 37% 10% 1	621
	21st to end	Night	18% 4 20% 38% 19% 1	466
June	1st to 10th	Night	10% 4 21% 45% 20%	420
	11th to 20th	Night	9% 5% 20% 46% 18% 3	420
	21st to end	Night	8% 2 21% 47% 21% 1	420
July	1st to 10th	Night	12% 1 16% 41% 27% 2	471
	11th to 20th	Night	6% 1 13% 40% 36% 3	612
	21st to end	Night	8% 2 17% 43% 24% 5%	690
August	1st to 10th	Night	13% 2 15% 41% 26% 3	627
	11th to 20th	Night	12% 3 14% 41% 26% 4	742
	21st to end	Night	12% 3 14% 35% 31% 5%	917
September	1st to 10th	Night	13% 3 13% 39% 26% 5%	800
	11th to 20th	Night	16% 3 17% 32% 30% 4	800
	21st to end	Night	26% 5% 20% 31% 16% 1	800
October	1st to 10th	Night	17% 6% 21% 29% 23% 5%	800
	11th to 20th	Night	19% 8% 26% 30% 16% 1	800
	21st to end	Night	17% 9% 28% 29% 14% 2	880
November	1st to 10th	Night	15% 10% 30% 29% 14% 2	820
	11th to 20th	Night	18% 13% 31% 29% 9%	840
	21st to end	Night	14% 14% 30% 30% 10% 1	840
December	1st to 10th	Night	22% 13% 35% 23% 7%	840
	11th to 20th	Night	18% 12% 36% 28% 6%	840
	21st to end	Night	19% 16% 29% 32% 4	924

Page generated at 2026-08-27 04:07:13. Version ac07

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