Goethe Link Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Goethe Link Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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% 9% 3 7% 5% 4 4 4 6% 7% 37%	126364
	Night	15% 10% 3 8% 5% 4 4 3 5% 6% 37%	123832
Transparency	Day	44% 6% 11% 23% 14% 2	129960
	Night	45% 5% 10% 22% 15% 2	128309
Seeing	Day	17% 10% 26% 24% 16% 6%	16932
	Night	17% 9% 27% 30% 14% 2	26698

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	14% 15% 8% 12% 6% 4 4 3 4 5% 25%	3617
	11th to 20th	Day	12% 13% 7% 14% 7% 5% 5% 4 4 4 25%	3620
	21st to end	Day	20% 15% 7% 10% 5% 5% 3 3 3 4 25%	4201
February	1st to 10th	Day	18% 13% 6% 9% 5% 4 4 4 4 5% 29%	2000
	11th to 20th	Day	15% 10% 5% 11% 4 5% 4 3 5% 6% 31%	1948
	21st to end	Day	16% 14% 5% 9% 4 3 3 3 4 6% 34%	1650
March	1st to 10th	Day	19% 15% 5% 7% 4 3 3 3 3 4 35%	4480
	11th to 20th	Day	12% 10% 2 6% 4 4 4 4 5% 8% 43%	4787
	21st to end	Day	16% 12% 3 8% 5% 4 5% 4 5% 6% 31%	5737
April	1st to 10th	Day	14% 10% 3 8% 5% 4 4 3 5% 7% 35%	2400
	11th to 20th	Day	16% 10% 2 7% 4 4 4 3 6% 6% 38%	2374
	21st to end	Day	20% 8% 2 8% 5% 4 4 3 5% 7% 35%	2550
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 8% 28%	5862
	11th to 20th	Day	19% 8% 2 7% 5% 4 4 3 5% 6% 36%	5861
	21st to end	Day	12% 6% 3 8% 5% 5% 6% 5% 8% 9% 33%	6588
June	1st to 10th	Day	11% 7% 2 6% 5% 4 4 4 6% 8% 43%	2800
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 4 7% 9% 44%	2800
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 10% 41%	2800
July	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 7% 11% 41%	6360
	11th to 20th	Day	8% 6% 2 7% 5% 5% 6% 5% 8% 11% 37%	6360
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 9% 34%	6744
August	1st to 10th	Day	7% 5% 2 5% 3 4 5% 4 7% 10% 48%	4234
	11th to 20th	Day	8% 5% 2 6% 4 4 6% 4 8% 11% 40%	3945
	21st to end	Day	5% 4 2 5% 4 4 4 3 6% 10% 54%	4312
September	1st to 10th	Day	12% 5% 2 5% 4 4 5% 4 6% 8% 46%	2376
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 6% 8% 49%	2200
	21st to end	Day	13% 5% 2 6% 4 4 4 3 6% 6% 49%	2200
October	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 8% 49%	2200
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 5% 7% 45%	2046
	21st to end	Day	18% 10% 3 8% 4 4 4 3 4 6% 37%	1980
November	1st to 10th	Day	9% 5% 3 6% 4 3 4 3 5% 6% 52%	1780
	11th to 20th	Day	15% 11% 3 7% 4 4 4 3 5% 6% 39%	1800
	21st to end	Day	17% 12% 3 8% 4 4 4 2 4 6% 36%	1800
December	1st to 10th	Day	12% 12% 4 7% 4 3 3 3 4 5% 43%	2930
	11th to 20th	Day	15% 15% 6% 10% 5% 5% 4 4 5% 5% 26%	3040
	21st to end	Day	25% 19% 7% 9% 4 4 3 3 4 5% 16%	3982
January	1st to 10th	Night	16% 15% 7% 13% 6% 5% 3 3 4 6% 22%	6348
	11th to 20th	Night	13% 18% 6% 14% 7% 6% 5% 3 3 4 20%	6360
	21st to end	Night	20% 13% 5% 8% 5% 4 4 3 4 5% 30%	6761
February	1st to 10th	Night	19% 11% 5% 10% 6% 4 4 3 5% 5% 29%	2400
	11th to 20th	Night	15% 12% 4 10% 5% 5% 4 3 5% 6% 32%	2338
	21st to end	Night	18% 13% 4 8% 4 3 4 3 4 5% 33%	1980
March	1st to 10th	Night	19% 15% 3 6% 4 3 3 2 3 5% 37%	5373
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 4 7% 46%	5172
	21st to end	Night	17% 9% 3 7% 5% 4 5% 4 5% 7% 34%	5220
April	1st to 10th	Night	15% 9% 3 6% 4 4 4 4 5% 6% 39%	2000
	11th to 20th	Night	15% 9% 3 7% 4 4 4 3 4 7% 42%	1975
	21st to end	Night	16% 8% 2 7% 4 4 4 4 6% 7% 37%	1849
May	1st to 10th	Night	19% 10% 3 8% 5% 5% 4 4 5% 7% 30%	4033
	11th to 20th	Night	16% 7% 3 7% 4 4 3 4 6% 9% 37%	4032
	21st to end	Night	13% 7% 3 7% 5% 5% 4 4 6% 9% 37%	4256
June	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 5% 8% 49%	1600
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 5% 9% 48%	1600
	21st to end	Night	6% 4 2 6% 4 5% 5% 5% 8% 9% 47%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 9% 48%	3618
	11th to 20th	Night	7% 5% 3 6% 4 5% 5% 4 7% 10% 44%	3617
	21st to end	Night	8% 7% 3 6% 5% 5% 5% 4 7% 10% 40%	4118
August	1st to 10th	Night	9% 4 2 6% 4 4 4 3 4 8% 51%	2915
	11th to 20th	Night	7% 4 1 5% 5% 4 5% 5% 7% 9% 48%	3100
	21st to end	Night	4 3 1 5% 4 4 4 4 5% 8% 57%	3586
September	1st to 10th	Night	10% 6% 2 5% 3 4 4 2 5% 6% 51%	2002
	11th to 20th	Night	7% 5% 1 5% 3 4 4 4 5% 7% 56%	2200
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 6% 49%	2200
October	1st to 10th	Night	9% 3 2 5% 3 4 4 4 5% 6% 56%	2200
	11th to 20th	Night	16% 7% 2 5% 3 3 3 2 5% 5% 49%	2349
	21st to end	Night	18% 8% 3 6% 3 4 4 3 5% 6% 40%	2860
November	1st to 10th	Night	12% 7% 2 6% 4 3 3 4 5% 5% 49%	2563
	11th to 20th	Night	14% 9% 3 7% 4 4 4 3 6% 7% 40%	2600
	21st to end	Night	19% 12% 4 8% 5% 4 4 3 4 5% 34%	2600
December	1st to 10th	Night	15% 10% 4 8% 4 3 3 3 4 6% 40%	4250
	11th to 20th	Night	18% 13% 5% 11% 5% 4 3 3 4 5% 29%	5161
	21st to end	Night	27% 19% 6% 9% 5% 4 3 3 4 4 17%	6996

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	60% 4 7% 21% 7% 1	3618
	11th to 20th	Day	61% 5% 10% 12% 10% 2	3620
	21st to end	Day	63% 4 6% 17% 7% 2	4201
February	1st to 10th	Day	57% 4 10% 18% 10% 1	2000
	11th to 20th	Day	54% 5% 10% 20% 10% 1	1958
	21st to end	Day	53% 4 8% 22% 10% 3	1650
March	1st to 10th	Day	54% 4 5% 19% 15% 3	4480
	11th to 20th	Day	40% 5% 10% 31% 13% 1	4787
	21st to end	Day	52% 6% 12% 19% 9% 2	5739
April	1st to 10th	Day	47% 5% 12% 20% 14% 1	2400
	11th to 20th	Day	45% 6% 10% 24% 12% 3	2374
	21st to end	Day	48% 5% 10% 23% 11% 3	2550
May	1st to 10th	Day	51% 7% 12% 19% 10%	5897
	11th to 20th	Day	47% 7% 10% 24% 10%	5865
	21st to end	Day	43% 9% 13% 20% 14% 1	6602
June	1st to 10th	Day	38% 7% 11% 25% 16% 3	2800
	11th to 20th	Day	36% 7% 11% 23% 20% 3	2800
	21st to end	Day	37% 8% 15% 20% 17% 4	2800
July	1st to 10th	Day	35% 7% 11% 27% 17% 2	6291
	11th to 20th	Day	37% 10% 15% 24% 13% 1	6285
	21st to end	Day	42% 9% 14% 21% 12% 2	6551
August	1st to 10th	Day	28% 9% 15% 32% 15% 1	4221
	11th to 20th	Day	33% 8% 13% 30% 14% 1	3984
	21st to end	Day	26% 7% 15% 31% 18% 4	4311
September	1st to 10th	Day	36% 6% 11% 25% 18% 4	2376
	11th to 20th	Day	32% 5% 11% 27% 23% 3	2200
	21st to end	Day	34% 6% 10% 23% 25% 2	2200
October	1st to 10th	Day	23% 4 8% 30% 33% 2	3590
	11th to 20th	Day	32% 5% 8% 26% 28% 2	3301
	21st to end	Day	40% 3 9% 23% 24% 1	3180
November	1st to 10th	Day	33% 4 12% 29% 18% 4	1780
	11th to 20th	Day	46% 4 9% 22% 15% 5%	1800
	21st to end	Day	51% 3 9% 22% 14% 1	1800
December	1st to 10th	Day	45% 3 10% 28% 14%	2930
	11th to 20th	Day	60% 5% 8% 20% 8% 1	3037
	21st to end	Day	69% 5% 10% 11% 5%	3982
January	1st to 10th	Night	63% 5% 9% 16% 7%	6348
	11th to 20th	Night	68% 4 8% 10% 8% 3	6360
	21st to end	Night	58% 3 8% 20% 9% 1	6761
February	1st to 10th	Night	58% 4 11% 18% 7% 1	2400
	11th to 20th	Night	53% 4 10% 19% 12% 1	2339
	21st to end	Night	55% 3 10% 19% 11% 2	1980
March	1st to 10th	Night	51% 3 6% 25% 11% 4	5373
	11th to 20th	Night	37% 5% 10% 27% 19% 2	5172
	21st to end	Night	49% 6% 9% 28% 8% 1	5220
April	1st to 10th	Night	45% 5% 11% 23% 13% 2	2000
	11th to 20th	Night	44% 5% 9% 21% 17% 5%	1975
	21st to end	Night	44% 6% 10% 23% 14% 3	1849
May	1st to 10th	Night	53% 8% 10% 18% 9% 2	4060
	11th to 20th	Night	44% 6% 12% 26% 12% 1	4033
	21st to end	Night	42% 8% 14% 21% 12% 3	4264
June	1st to 10th	Night	34% 6% 10% 25% 21% 3	1600
	11th to 20th	Night	33% 8% 10% 24% 21% 5%	1600
	21st to end	Night	30% 7% 15% 23% 20% 4	1600
July	1st to 10th	Night	32% 7% 11% 27% 19% 3	3580
	11th to 20th	Night	32% 9% 17% 26% 15% 1	3572
	21st to end	Night	36% 9% 16% 24% 12% 3	3999
August	1st to 10th	Night	30% 7% 14% 34% 13% 1	2904
	11th to 20th	Night	30% 8% 14% 29% 18% 1	3127
	21st to end	Night	24% 6% 13% 31% 22% 4	3586
September	1st to 10th	Night	34% 5% 10% 25% 20% 6%	2002
	11th to 20th	Night	27% 6% 9% 27% 28% 4	2200
	21st to end	Night	36% 5% 10% 22% 24% 4	2200
October	1st to 10th	Night	19% 5% 7% 24% 43% 3	3590
	11th to 20th	Night	27% 3 7% 26% 34% 3	3833
	21st to end	Night	35% 4 8% 23% 25% 5%	4610
November	1st to 10th	Night	36% 4 9% 25% 21% 4	2563
	11th to 20th	Night	43% 4 10% 21% 18% 4	2600
	21st to end	Night	54% 3 9% 22% 12% 1	2600
December	1st to 10th	Night	47% 4 11% 25% 12%	4250
	11th to 20th	Night	57% 4 10% 17% 10% 1	5163
	21st to end	Night	71% 5% 8% 11% 5%	6996

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% 13% 35% 21% 5% 1	300
	11th to 20th	Day	27% 20% 32% 17% 3 1	300
	21st to end	Day	27% 21% 30% 18% 4	330
February	1st to 10th	Day	28% 17% 36% 16% 3	300
	11th to 20th	Day	25% 23% 32% 15% 5%	300
	21st to end	Day	24% 21% 39% 12% 3	249
March	1st to 10th	Day	25% 24% 33% 15% 4	300
	11th to 20th	Day	24% 19% 36% 16% 5%	411
	21st to end	Day	29% 17% 31% 17% 7%	550
April	1st to 10th	Day	20% 16% 31% 22% 8% 1	500
	11th to 20th	Day	22% 18% 25% 22% 11% 2	492
	21st to end	Day	24% 14% 32% 20% 8% 2	500
May	1st to 10th	Day	21% 13% 29% 26% 9% 3	503
	11th to 20th	Day	22% 9% 25% 24% 13% 6%	527
	21st to end	Day	12% 7% 26% 27% 19% 9%	637
June	1st to 10th	Day	12% 6% 26% 32% 18% 6%	730
	11th to 20th	Day	12% 6% 23% 32% 20% 8%	730
	21st to end	Day	12% 6% 26% 28% 20% 8%	730
July	1st to 10th	Day	11% 3 16% 27% 25% 18%	721
	11th to 20th	Day	6% 4 19% 33% 26% 12%	718
	21st to end	Day	10% 2 17% 30% 29% 11%	714
August	1st to 10th	Day	8% 3 13% 26% 32% 17%	526
	11th to 20th	Day	12% 4 17% 26% 29% 12%	519
	21st to end	Day	7% 2 15% 29% 33% 15%	583
September	1st to 10th	Day	9% 4 16% 29% 30% 11%	530
	11th to 20th	Day	9% 2 14% 26% 33% 16%	530
	21st to end	Day	15% 7% 21% 22% 24% 11%	530
October	1st to 10th	Day	11% 5% 24% 32% 22% 7%	530
	11th to 20th	Day	12% 13% 35% 24% 14% 2	443
	21st to end	Day	27% 15% 35% 21% 2	363
November	1st to 10th	Day	12% 16% 34% 25% 11% 3	306
	11th to 20th	Day	22% 18% 31% 18% 10% 1	300
	21st to end	Day	25% 15% 36% 19% 5%	300
December	1st to 10th	Day	16% 25% 35% 18% 4 1	300
	11th to 20th	Day	25% 15% 37% 18% 5% 1	300
	21st to end	Day	30% 18% 31% 17% 4	330
January	1st to 10th	Night	21% 17% 33% 24% 4	1000
	11th to 20th	Night	24% 18% 35% 20% 3	1000
	21st to end	Night	20% 15% 38% 24% 3	1025
February	1st to 10th	Night	24% 14% 36% 24% 2	800
	11th to 20th	Night	22% 17% 36% 23% 3	783
	21st to end	Night	24% 13% 39% 21% 2	660
March	1st to 10th	Night	24% 15% 32% 26% 4	800
	11th to 20th	Night	20% 12% 36% 25% 6% 1	800
	21st to end	Night	25% 10% 33% 27% 5% 1	775
April	1st to 10th	Night	17% 12% 36% 28% 7%	600
	11th to 20th	Night	18% 12% 30% 29% 10% 1	593
	21st to end	Night	19% 8% 39% 24% 9% 1	600
May	1st to 10th	Night	19% 6% 34% 30% 10% 1	600
	11th to 20th	Night	18% 5% 23% 35% 15% 3	591
	21st to end	Night	10% 3 22% 39% 23% 3	650
June	1st to 10th	Night	11% 3 23% 42% 21% 1	600
	11th to 20th	Night	11% 4 18% 46% 21% 1	600
	21st to end	Night	7% 3 21% 40% 28% 2	600
July	1st to 10th	Night	9% 3 10% 37% 34% 7%	585
	11th to 20th	Night	6% 3 15% 37% 35% 4	582
	21st to end	Night	8% 3 10% 43% 33% 4	657
August	1st to 10th	Night	8% 2 10% 39% 38% 4	597
	11th to 20th	Night	7% 2 11% 41% 35% 4	594
	21st to end	Night	7% 2 12% 34% 39% 6%	660
September	1st to 10th	Night	11% 3 13% 37% 31% 4	602
	11th to 20th	Night	8% 2 14% 35% 36% 4	800
	21st to end	Night	14% 7% 17% 34% 26% 3	800
October	1st to 10th	Night	9% 5% 22% 37% 24% 4	800
	11th to 20th	Night	19% 9% 26% 31% 15% 2	800
	21st to end	Night	22% 11% 34% 26% 7%	880
November	1st to 10th	Night	15% 9% 31% 33% 11% 1	789
	11th to 20th	Night	18% 14% 31% 28% 9%	800
	21st to end	Night	25% 13% 25% 29% 7%	800
December	1st to 10th	Night	23% 12% 37% 23% 5%	800
	11th to 20th	Night	24% 11% 33% 25% 6% 1	975
	21st to end	Night	32% 13% 31% 20% 4	1100

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