Little Eden Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Eden Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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% 7% 2 6% 4 4 4 3 5% 6% 45%	109202
	Night	12% 6% 2 5% 3 3 3 3 5% 6% 51%	109595
Transparency	Day	38% 5% 10% 23% 19% 5%	112850
	Night	33% 5% 9% 23% 22% 7%	114087
Seeing	Day	16% 10% 25% 26% 18% 5%	15661
	Night	16% 9% 24% 30% 18% 2	25642

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	15% 9% 4 6% 3 3 2 2 3 4 49%	4077
	11th to 20th	Day	7% 8% 2 6% 4 4 4 3 3 4 55%	4080
	21st to end	Day	22% 7% 2 4 2 2 2 2 3 5% 49%	4488
February	1st to 10th	Day	21% 9% 3 6% 4 3 3 3 4 4 40%	1800
	11th to 20th	Day	17% 8% 3 8% 4 4 2 2 4 5% 42%	1806
	21st to end	Day	21% 10% 3 7% 4 3 3 3 4 5% 39%	1727
March	1st to 10th	Day	18% 10% 4 7% 4 3 3 2 3 5% 41%	3436
	11th to 20th	Day	13% 8% 3 7% 4 4 4 4 4 6% 42%	3480
	21st to end	Day	17% 9% 3 7% 4 3 4 3 5% 6% 40%	3814
April	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 5% 6% 45%	2203
	11th to 20th	Day	18% 6% 2 6% 4 4 4 2 5% 6% 43%	2254
	21st to end	Day	17% 7% 3 7% 5% 5% 4 3 5% 5% 39%	2280
May	1st to 10th	Day	19% 9% 3 7% 5% 3 4 3 5% 6% 37%	3916
	11th to 20th	Day	13% 5% 2 7% 5% 5% 5% 4 6% 7% 41%	4082
	21st to end	Day	16% 9% 3 8% 6% 5% 5% 4 5% 6% 34%	4477
June	1st to 10th	Day	8% 6% 3 7% 6% 5% 5% 4 7% 8% 42%	2470
	11th to 20th	Day	6% 6% 2 6% 6% 6% 5% 5% 7% 8% 42%	2470
	21st to end	Day	4 4 1 5% 6% 5% 5% 5% 6% 9% 49%	2470
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 10% 41%	4120
	11th to 20th	Day	5% 3 1 4 4 5% 5% 4 5% 8% 55%	4120
	21st to end	Day	10% 8% 3 8% 6% 6% 6% 5% 7% 10% 32%	4465
August	1st to 10th	Day	3 2 1 4 4 4 6% 4 6% 9% 57%	4104
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 7% 9% 45%	3887
	21st to end	Day	4 3 1 5% 4 5% 6% 5% 7% 9% 49%	4180
September	1st to 10th	Day	11% 6% 2 5% 4 4 5% 3 6% 6% 47%	2280
	11th to 20th	Day	13% 4 2 5% 4 5% 5% 4 7% 7% 44%	2147
	21st to end	Day	9% 4 1 5% 5% 4 4 3 5% 6% 54%	2047
October	1st to 10th	Day	8% 4 2 5% 3 4 4 3 4 6% 56%	1900
	11th to 20th	Day	13% 4 2 5% 2 3 3 2 3 4 57%	1900
	21st to end	Day	18% 6% 2 5% 3 3 3 2 4 4 51%	2090
November	1st to 10th	Day	14% 6% 2 5% 3 3 3 2 4 6% 52%	1958
	11th to 20th	Day	10% 6% 2 4 4 3 3 4 4 6% 54%	2000
	21st to end	Day	17% 6% 2 5% 3 3 3 2 4 5% 49%	1855
December	1st to 10th	Day	16% 8% 3 5% 4 3 2 2 4 4 50%	2940
	11th to 20th	Day	17% 10% 4 6% 4 3 3 2 4 4 43%	3391
	21st to end	Day	20% 10% 3 7% 4 3 3 3 4 5% 39%	4488
January	1st to 10th	Night	14% 7% 2 7% 4 3 3 2 3 4 48%	5888
	11th to 20th	Night	11% 6% 2 3 2 2 2 2 3 5% 63%	5900
	21st to end	Night	22% 8% 2 4 2 2 2 2 3 4 47%	6490
February	1st to 10th	Night	18% 9% 3 6% 4 3 3 3 4 5% 43%	2600
	11th to 20th	Night	17% 8% 3 7% 4 3 3 2 4 5% 44%	2488
	21st to end	Night	18% 8% 2 5% 3 3 4 2 5% 6% 45%	1737
March	1st to 10th	Night	20% 10% 2 6% 4 3 3 2 4 6% 40%	3419
	11th to 20th	Night	16% 8% 2 5% 3 3 3 2 4 5% 49%	3480
	21st to end	Night	13% 7% 3 6% 5% 4 4 3 6% 7% 42%	3817
April	1st to 10th	Night	12% 5% 2 4 5% 3 3 3 4 7% 50%	1976
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 5% 5% 49%	1875
	21st to end	Night	13% 6% 2 5% 3 3 4 4 5% 6% 49%	1900
May	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 5% 6% 39%	2979
	11th to 20th	Night	14% 6% 3 6% 4 3 3 3 6% 8% 43%	2823
	21st to end	Night	14% 8% 3 5% 4 3 4 3 6% 8% 42%	3090
June	1st to 10th	Night	6% 3 2 4 4 4 4 3 5% 9% 56%	1710
	11th to 20th	Night	4 5% 1 4 4 3 4 4 5% 8% 58%	1710
	21st to end	Night	4 4 1 3 2 3 3 3 6% 9% 62%	1710
July	1st to 10th	Night	8% 4 1 4 3 4 5% 5% 8% 10% 49%	2850
	11th to 20th	Night	4 3 1 3 2 3 3 3 5% 9% 63%	2850
	21st to end	Night	7% 7% 2 7% 5% 5% 5% 4 7% 9% 42%	3098
August	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 9% 67%	2836
	11th to 20th	Night	4 2 1 4 3 4 3 4 6% 8% 59%	2947
	21st to end	Night	3 3 2 4 3 4 4 4 6% 9% 57%	3476
September	1st to 10th	Night	6% 5% 2 5% 2 3 3 3 5% 6% 58%	1900
	11th to 20th	Night	12% 4 2 5% 3 4 4 3 5% 8% 50%	2028
	21st to end	Night	8% 3 2 5% 3 3 4 3 5% 6% 57%	2114
October	1st to 10th	Night	7% 5% 1 3 2 3 3 3 4 6% 61%	2280
	11th to 20th	Night	11% 4 2 4 3 3 3 2 4 5% 60%	2280
	21st to end	Night	16% 5% 2 4 3 3 3 2 3 5% 55%	2508
November	1st to 10th	Night	13% 5% 2 4 4 3 3 3 3 5% 56%	2340
	11th to 20th	Night	10% 5% 2 4 3 2 3 2 5% 6% 58%	2400
	21st to end	Night	13% 6% 2 6% 3 3 3 3 4 5% 51%	2540
December	1st to 10th	Night	12% 8% 2 6% 3 3 3 3 4 5% 51%	4250
	11th to 20th	Night	16% 9% 3 6% 4 4 4 2 3 4 44%	4816
	21st to end	Night	18% 8% 3 6% 4 3 3 3 4 5% 42%	6490

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	41% 3 8% 26% 20% 3	4078
	11th to 20th	Day	33% 4 8% 21% 26% 6%	4080
	21st to end	Day	39% 3 4 18% 24% 12%	4488
February	1st to 10th	Day	48% 3 9% 18% 18% 4	1800
	11th to 20th	Day	46% 4 6% 21% 19% 5%	1815
	21st to end	Day	50% 3 6% 14% 18% 9%	1727
March	1st to 10th	Day	48% 3 8% 12% 19% 10%	3436
	11th to 20th	Day	44% 5% 9% 20% 17% 6%	3480
	21st to end	Day	45% 5% 9% 21% 19% 1	3814
April	1st to 10th	Day	41% 4 9% 21% 19% 6%	2203
	11th to 20th	Day	43% 4 10% 19% 19% 6%	2254
	21st to end	Day	46% 6% 8% 20% 18% 3	2280
May	1st to 10th	Day	49% 4 9% 22% 13% 2	3951
	11th to 20th	Day	39% 9% 11% 25% 16% 1	4086
	21st to end	Day	51% 6% 11% 18% 11% 3	4489
June	1st to 10th	Day	37% 8% 13% 25% 14% 2	2470
	11th to 20th	Day	36% 8% 12% 26% 17% 2	2470
	21st to end	Day	30% 7% 13% 30% 17% 2	2470
July	1st to 10th	Day	34% 8% 22% 24% 11% 1	4056
	11th to 20th	Day	25% 6% 10% 34% 22% 2	4051
	21st to end	Day	44% 9% 15% 22% 9% 1	4325
August	1st to 10th	Day	22% 8% 13% 26% 27% 5%	4090
	11th to 20th	Day	34% 8% 15% 33% 10% 1	3926
	21st to end	Day	28% 7% 14% 32% 16% 2	4179
September	1st to 10th	Day	36% 7% 11% 21% 17% 9%	2280
	11th to 20th	Day	35% 7% 12% 22% 18% 6%	2147
	21st to end	Day	30% 6% 9% 21% 25% 9%	2047
October	1st to 10th	Day	17% 3 6% 12% 33% 29%	3160
	11th to 20th	Day	20% 2 4 18% 37% 19%	3140
	21st to end	Day	31% 4 7% 27% 24% 7%	3428
November	1st to 10th	Day	35% 3 7% 24% 23% 7%	1958
	11th to 20th	Day	31% 5% 7% 20% 27% 10%	2000
	21st to end	Day	40% 3 5% 18% 27% 7%	1855
December	1st to 10th	Day	39% 3 7% 29% 18% 4	2940
	11th to 20th	Day	46% 2 5% 18% 24% 5%	3389
	21st to end	Day	48% 4 6% 21% 17% 4	4488
January	1st to 10th	Night	39% 4 6% 25% 22% 3	5888
	11th to 20th	Night	27% 3 7% 20% 32% 11%	5900
	21st to end	Night	42% 3 6% 16% 25% 8%	6490
February	1st to 10th	Night	45% 3 8% 19% 18% 6%	2600
	11th to 20th	Night	44% 4 6% 20% 19% 6%	2489
	21st to end	Night	41% 3 8% 17% 21% 10%	1737
March	1st to 10th	Night	46% 5% 7% 13% 18% 11%	3419
	11th to 20th	Night	39% 4 8% 24% 18% 8%	3480
	21st to end	Night	40% 5% 10% 23% 19% 2	3817
April	1st to 10th	Night	34% 5% 10% 21% 19% 11%	1976
	11th to 20th	Night	36% 5% 8% 21% 20% 10%	1875
	21st to end	Night	35% 5% 11% 23% 22% 3	1900
May	1st to 10th	Night	46% 6% 10% 22% 12% 4	3009
	11th to 20th	Night	37% 7% 14% 25% 15% 1	2824
	21st to end	Night	40% 7% 15% 23% 13% 3	3099
June	1st to 10th	Night	25% 8% 14% 32% 18% 3	1710
	11th to 20th	Night	24% 5% 13% 33% 22% 3	1710
	21st to end	Night	19% 5% 14% 31% 26% 4	1710
July	1st to 10th	Night	26% 9% 21% 27% 15% 2	2805
	11th to 20th	Night	17% 6% 12% 40% 23% 2	2796
	21st to end	Night	37% 9% 15% 26% 14%	2999
August	1st to 10th	Night	14% 5% 16% 30% 29% 6%	2826
	11th to 20th	Night	21% 6% 20% 34% 17% 1	2974
	21st to end	Night	22% 6% 16% 29% 25% 2	3476
September	1st to 10th	Night	26% 7% 10% 25% 22% 10%	1900
	11th to 20th	Night	32% 6% 11% 21% 23% 7%	2028
	21st to end	Night	27% 5% 9% 23% 28% 9%	2114
October	1st to 10th	Night	15% 4 6% 14% 28% 33%	3800
	11th to 20th	Night	18% 2 3 17% 37% 23%	3779
	21st to end	Night	27% 4 5% 25% 28% 12%	4120
November	1st to 10th	Night	32% 4 7% 21% 25% 11%	2340
	11th to 20th	Night	29% 3 8% 21% 27% 12%	2400
	21st to end	Night	36% 3 7% 18% 28% 7%	2540
December	1st to 10th	Night	36% 4 7% 29% 19% 4	4250
	11th to 20th	Night	45% 3 5% 18% 19% 9%	4817
	21st to end	Night	43% 4 7% 22% 18% 4	6490

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% 18% 33% 17% 4 1	300
	11th to 20th	Day	24% 24% 37% 13% 2 1	300
	21st to end	Day	25% 24% 34% 12% 4	330
February	1st to 10th	Day	33% 17% 34% 12% 4	300
	11th to 20th	Day	34% 26% 30% 9% 2	300
	21st to end	Day	40% 23% 28% 7% 2	225
March	1st to 10th	Day	26% 23% 30% 18% 3	270
	11th to 20th	Day	31% 17% 39% 10% 2	270
	21st to end	Day	29% 20% 39% 12% 1	297
April	1st to 10th	Day	23% 19% 37% 14% 7% 1	383
	11th to 20th	Day	28% 15% 33% 17% 6% 1	452
	21st to end	Day	23% 16% 33% 20% 6% 2	460
May	1st to 10th	Day	18% 16% 36% 23% 6% 1	549
	11th to 20th	Day	15% 8% 33% 29% 13% 2	675
	21st to end	Day	13% 6% 33% 26% 16% 5%	734
June	1st to 10th	Day	11% 5% 17% 32% 27% 8%	680
	11th to 20th	Day	7% 3 22% 35% 25% 8%	680
	21st to end	Day	4 4 22% 37% 25% 8%	680
July	1st to 10th	Day	8% 2 15% 31% 33% 10%	671
	11th to 20th	Day	6% 1 11% 36% 34% 12%	668
	21st to end	Day	7% 2 9% 36% 32% 14%	739
August	1st to 10th	Day	5% 1 10% 40% 34% 10%	676
	11th to 20th	Day	12% 2 9% 34% 32% 11%	576
	21st to end	Day	8% 1 6% 28% 41% 15%	539
September	1st to 10th	Day	10% 2 9% 32% 37% 10%	490
	11th to 20th	Day	9% 3 15% 30% 35% 8%	357
	21st to end	Day	16% 5% 20% 36% 20% 4	300
October	1st to 10th	Day	4 3 30% 39% 21% 2	300
	11th to 20th	Day	14% 9% 38% 26% 9% 4	300
	21st to end	Day	28% 13% 32% 20% 6% 1	330
November	1st to 10th	Day	22% 15% 30% 22% 11% 1	300
	11th to 20th	Day	17% 15% 35% 26% 5% 2	300
	21st to end	Day	24% 21% 32% 17% 6% 1	300
December	1st to 10th	Day	24% 20% 31% 18% 4 2	300
	11th to 20th	Day	27% 21% 34% 13% 5% 1	300
	21st to end	Day	26% 19% 37% 14% 3	330
January	1st to 10th	Night	21% 14% 32% 28% 5%	1000
	11th to 20th	Night	22% 18% 31% 25% 4	1000
	21st to end	Night	21% 14% 36% 26% 4	1100
February	1st to 10th	Night	26% 16% 30% 24% 5%	1000
	11th to 20th	Night	25% 19% 34% 20% 2	934
	21st to end	Night	27% 15% 36% 19% 4	481
March	1st to 10th	Night	24% 13% 28% 29% 6%	570
	11th to 20th	Night	22% 12% 32% 27% 5% 1	570
	21st to end	Night	18% 14% 33% 29% 6%	627
April	1st to 10th	Night	18% 15% 32% 27% 8%	570
	11th to 20th	Night	17% 15% 33% 25% 11%	563
	21st to end	Night	17% 12% 37% 26% 8% 1	570
May	1st to 10th	Night	14% 7% 32% 36% 10% 1	570
	11th to 20th	Night	15% 5% 27% 33% 17% 2	561
	21st to end	Night	10% 6% 26% 31% 24% 3	617
June	1st to 10th	Night	6% 4 13% 35% 38% 3	570
	11th to 20th	Night	5% 2 14% 44% 34% 2	570
	21st to end	Night	4 3 14% 34% 39% 6%	570
July	1st to 10th	Night	5% 2 8% 34% 44% 7%	555
	11th to 20th	Night	4 1 6% 33% 48% 8%	552
	21st to end	Night	5% 4 37% 43% 11%	624
August	1st to 10th	Night	5% 1 7% 34% 49% 5%	567
	11th to 20th	Night	9% 1 5% 36% 42% 7%	564
	21st to end	Night	7% 2 5% 31% 48% 7%	627
September	1st to 10th	Night	8% 2 8% 32% 45% 5%	570
	11th to 20th	Night	13% 2 9% 32% 40% 4	570
	21st to end	Night	10% 3 14% 33% 35% 5%	594
October	1st to 10th	Night	10% 3 17% 34% 33% 4	760
	11th to 20th	Night	13% 7% 27% 34% 18% 1	760
	21st to end	Night	19% 8% 28% 28% 16% 2	836
November	1st to 10th	Night	14% 9% 27% 35% 13% 1	780
	11th to 20th	Night	15% 10% 30% 33% 12%	800
	21st to end	Night	19% 12% 31% 28% 10%	940
December	1st to 10th	Night	21% 11% 31% 30% 7%	1000
	11th to 20th	Night	23% 12% 30% 30% 6%	1000
	21st to end	Night	24% 14% 27% 29% 6%	1100

Page generated at 2025-02-18 02:26:31. Version ac07

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