Hahnenberg Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hahnenberg Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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% 11% 5% 11% 6% 5% 4 3 5% 6% 32%	130136
	Night	14% 13% 5% 13% 7% 5% 4 3 4 5% 26%	130931
Transparency	Day	52% 5% 11% 21% 10% 1	133629
	Night	60% 5% 10% 16% 8% 1	135525
Seeing	Day	17% 10% 26% 27% 16% 4	17415
	Night	20% 10% 26% 29% 13% 2	27449

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	12% 21% 12% 30% 9% 5% 2 1 2 2 4	4691
	11th to 20th	Day	10% 18% 9% 29% 14% 10% 3 2 2 1 2	4679
	21st to end	Day	10% 16% 8% 18% 12% 10% 8% 3 3 3 11%	5156
February	1st to 10th	Day	9% 19% 7% 18% 16% 7% 4 2 3 4 12%	1785
	11th to 20th	Day	12% 14% 7% 18% 12% 7% 5% 3 3 4 14%	1998
	21st to end	Day	12% 18% 6% 13% 9% 6% 5% 4 6% 5% 18%	1650
March	1st to 10th	Day	12% 11% 3 12% 8% 4 4 3 5% 6% 32%	4478
	11th to 20th	Day	10% 10% 5% 13% 6% 5% 5% 4 6% 7% 28%	4830
	21st to end	Day	21% 11% 7% 16% 5% 4 3 3 4 4 22%	5711
April	1st to 10th	Day	17% 14% 4 9% 5% 4 4 3 5% 6% 30%	2400
	11th to 20th	Day	18% 12% 4 6% 4 4 4 3 5% 6% 35%	2466
	21st to end	Day	15% 9% 3 9% 4 5% 4 4 6% 6% 35%	2600
May	1st to 10th	Day	12% 8% 3 6% 4 4 3 3 5% 7% 44%	5888
	11th to 20th	Day	10% 9% 3 7% 5% 4 4 3 4 6% 45%	6129
	21st to end	Day	12% 8% 2 7% 4 4 4 3 5% 7% 45%	6949
June	1st to 10th	Day	12% 5% 2 6% 5% 4 3 4 6% 7% 45%	2806
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 4 6% 9% 43%	2990
	21st to end	Day	12% 7% 2 6% 4 3 4 4 6% 7% 45%	2800
July	1st to 10th	Day	15% 6% 2 5% 3 3 4 3 6% 9% 45%	6359
	11th to 20th	Day	9% 5% 2 4 3 3 4 4 6% 8% 54%	6360
	21st to end	Day	7% 5% 2 5% 4 3 4 4 6% 10% 50%	6926
August	1st to 10th	Day	7% 5% 2 7% 4 5% 5% 5% 7% 10% 44%	4410
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 6% 49%	4174
	21st to end	Day	11% 6% 3 7% 4 4 4 3 5% 6% 46%	4454
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 8% 43%	2385
	11th to 20th	Day	12% 4 3 6% 3 4 4 4 6% 8% 46%	2200
	21st to end	Day	16% 7% 2 7% 4 4 5% 4 7% 7% 38%	2200
October	1st to 10th	Day	17% 8% 3 8% 5% 4 3 3 4 7% 37%	2200
	11th to 20th	Day	22% 15% 4 10% 5% 6% 5% 3 5% 5% 21%	1885
	21st to end	Day	23% 14% 5% 12% 5% 5% 5% 4 4 5% 19%	1980
November	1st to 10th	Day	17% 18% 4 8% 6% 4 4 2 5% 6% 26%	1852
	11th to 20th	Day	14% 22% 6% 15% 6% 5% 5% 3 5% 5% 15%	1890
	21st to end	Day	17% 24% 9% 14% 6% 4 4 3 3 4 13%	1767
December	1st to 10th	Day	12% 30% 12% 19% 7% 5% 4 2 2 2 5%	2350
	11th to 20th	Day	12% 25% 11% 21% 9% 6% 4 2 3 3 5%	2691
	21st to end	Day	20% 22% 9% 16% 9% 5% 4 2 3 4 7%	4047
January	1st to 10th	Night	12% 21% 8% 30% 10% 5% 2 2 2 2 6%	8233
	11th to 20th	Night	9% 18% 9% 24% 17% 8% 4 2 2 2 5%	8236
	21st to end	Night	8% 15% 8% 18% 14% 10% 8% 3 4 3 9%	9058
February	1st to 10th	Night	11% 18% 6% 18% 14% 8% 4 3 3 3 13%	2834
	11th to 20th	Night	12% 14% 6% 18% 10% 6% 4 3 4 4 17%	2399
	21st to end	Night	15% 16% 5% 14% 7% 5% 4 4 4 7% 21%	1980
March	1st to 10th	Night	15% 10% 3 10% 6% 4 3 3 4 6% 34%	5362
	11th to 20th	Night	10% 12% 4 9% 5% 4 6% 4 5% 8% 32%	5128
	21st to end	Night	19% 12% 5% 12% 6% 4 4 3 4 6% 27%	5251
April	1st to 10th	Night	18% 13% 3 9% 5% 4 4 4 5% 6% 30%	2000
	11th to 20th	Night	20% 9% 3 8% 4 4 3 3 5% 5% 35%	1882
	21st to end	Night	16% 10% 3 7% 4 5% 5% 4 5% 5% 37%	1800
May	1st to 10th	Night	13% 8% 3 6% 4 4 5% 3 5% 7% 42%	4053
	11th to 20th	Night	12% 9% 3 8% 5% 4 4 4 6% 6% 40%	3774
	21st to end	Night	17% 8% 2 6% 4 3 3 3 5% 6% 43%	3949
June	1st to 10th	Night	13% 6% 2 6% 5% 5% 4 3 5% 6% 44%	1580
	11th to 20th	Night	13% 6% 3 6% 4 5% 5% 4 6% 9% 41%	1400
	21st to end	Night	12% 7% 2 7% 5% 4 4 3 5% 7% 44%	1594
July	1st to 10th	Night	11% 6% 3 7% 3 4 4 4 6% 8% 43%	3620
	11th to 20th	Night	8% 5% 2 6% 3 3 4 3 6% 7% 53%	3620
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 8% 51%	3948
August	1st to 10th	Night	10% 6% 3 7% 6% 5% 4 3 5% 7% 43%	2742
	11th to 20th	Night	13% 5% 1 5% 3 4 4 3 4 8% 48%	2875
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 7% 48%	3442
September	1st to 10th	Night	10% 7% 3 5% 4 4 4 3 5% 7% 48%	2000
	11th to 20th	Night	13% 5% 2 5% 4 4 4 3 6% 7% 47%	2195
	21st to end	Night	17% 6% 3 8% 5% 4 4 4 5% 7% 38%	2200
October	1st to 10th	Night	17% 8% 3 8% 4 4 3 3 5% 6% 38%	2200
	11th to 20th	Night	22% 12% 4 9% 4 4 4 4 5% 6% 25%	2513
	21st to end	Night	23% 13% 4 11% 6% 5% 4 3 4 5% 23%	2860
November	1st to 10th	Night	16% 16% 4 10% 5% 5% 5% 2 4 6% 27%	2666
	11th to 20th	Night	15% 21% 6% 13% 6% 5% 4 3 4 4 18%	2730
	21st to end	Night	16% 24% 7% 15% 5% 5% 4 3 4 4 13%	2843
December	1st to 10th	Night	12% 23% 12% 19% 8% 5% 4 3 3 3 8%	5060
	11th to 20th	Night	12% 23% 9% 20% 11% 5% 4 2 3 3 8%	5736
	21st to end	Night	22% 20% 8% 15% 6% 4 4 2 3 4 10%	7168

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	89% 3 5% 2	4692
	11th to 20th	Day	91% 3 4 2	4710
	21st to end	Day	80% 4 8% 7% 1	5156
February	1st to 10th	Day	79% 4 6% 10% 1	1785
	11th to 20th	Day	73% 6% 8% 9% 3	2008
	21st to end	Day	67% 7% 8% 14% 4 1	1650
March	1st to 10th	Day	53% 4 16% 16% 10% 1	4480
	11th to 20th	Day	54% 5% 14% 18% 7% 1	4830
	21st to end	Day	65% 5% 9% 15% 6%	5711
April	1st to 10th	Day	56% 4 10% 20% 10%	2400
	11th to 20th	Day	49% 5% 10% 21% 13% 2	2466
	21st to end	Day	47% 6% 12% 17% 15% 3	2600
May	1st to 10th	Day	40% 5% 10% 24% 19% 2	5897
	11th to 20th	Day	40% 6% 8% 26% 18% 1	6133
	21st to end	Day	39% 5% 11% 24% 19% 3	6949
June	1st to 10th	Day	37% 6% 12% 27% 16% 2	2806
	11th to 20th	Day	37% 7% 13% 24% 17% 2	2990
	21st to end	Day	37% 7% 15% 26% 14% 1	2800
July	1st to 10th	Day	36% 5% 14% 30% 14% 1	6291
	11th to 20th	Day	28% 5% 15% 38% 13% 1	6285
	21st to end	Day	30% 6% 13% 34% 17% 1	6728
August	1st to 10th	Day	34% 6% 16% 30% 13% 1	4395
	11th to 20th	Day	36% 5% 13% 32% 13% 1	4213
	21st to end	Day	38% 6% 14% 30% 11% 1	4453
September	1st to 10th	Day	39% 6% 14% 26% 14% 1	2385
	11th to 20th	Day	35% 8% 15% 30% 12% 1	2200
	21st to end	Day	44% 6% 14% 25% 10%	2200
October	1st to 10th	Day	35% 4 9% 33% 18% 1	3590
	11th to 20th	Day	57% 4 9% 20% 10%	3049
	21st to end	Day	63% 5% 13% 16% 3	3180
November	1st to 10th	Day	60% 5% 10% 17% 7%	1852
	11th to 20th	Day	71% 6% 10% 10% 4	1890
	21st to end	Day	77% 4 10% 7% 2	1767
December	1st to 10th	Day	88% 3 4 4	2350
	11th to 20th	Day	87% 5% 5% 3 1	2691
	21st to end	Day	82% 5% 7% 5% 2	4047
January	1st to 10th	Night	87% 4 6% 3	8233
	11th to 20th	Night	89% 3 5% 2 1	8280
	21st to end	Night	81% 4 7% 7% 1	9058
February	1st to 10th	Night	78% 4 7% 8% 3	2834
	11th to 20th	Night	71% 5% 8% 13% 3	2400
	21st to end	Night	65% 6% 11% 15% 3	1980
March	1st to 10th	Night	52% 4 17% 19% 8%	5373
	11th to 20th	Night	49% 6% 18% 19% 7% 1	5129
	21st to end	Night	59% 4 12% 16% 8%	5251
April	1st to 10th	Night	55% 6% 9% 18% 11% 1	2000
	11th to 20th	Night	51% 5% 8% 20% 13% 3	1882
	21st to end	Night	49% 5% 9% 20% 14% 3	1800
May	1st to 10th	Night	42% 5% 10% 21% 18% 3	4060
	11th to 20th	Night	44% 6% 7% 26% 16% 1	3775
	21st to end	Night	42% 6% 11% 22% 13% 6%	3950
June	1st to 10th	Night	40% 6% 10% 29% 14% 1	1580
	11th to 20th	Night	39% 7% 13% 23% 16% 3	1400
	21st to end	Night	40% 5% 12% 26% 15% 2	1594
July	1st to 10th	Night	37% 5% 14% 26% 15% 3	3580
	11th to 20th	Night	30% 5% 12% 31% 20% 1	3572
	21st to end	Night	31% 5% 15% 29% 18% 1	3832
August	1st to 10th	Night	41% 6% 14% 26% 13% 1	2733
	11th to 20th	Night	35% 6% 15% 29% 15% 1	2902
	21st to end	Night	37% 5% 14% 25% 18% 1	3442
September	1st to 10th	Night	36% 7% 14% 24% 19% 1	2000
	11th to 20th	Night	37% 7% 14% 28% 13%	2195
	21st to end	Night	45% 8% 14% 23% 10% 1	2200
October	1st to 10th	Night	41% 4 10% 32% 12% 1	3590
	11th to 20th	Night	51% 5% 11% 22% 11%	4088
	21st to end	Night	57% 5% 12% 21% 6%	4610
November	1st to 10th	Night	60% 6% 10% 17% 7% 1	2666
	11th to 20th	Night	71% 5% 9% 9% 5% 1	2730
	21st to end	Night	76% 6% 9% 7% 1	2843
December	1st to 10th	Night	82% 5% 6% 6% 1	5060
	11th to 20th	Night	83% 4 7% 5% 1	5735
	21st to end	Night	78% 6% 8% 5% 2	7168

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	18% 16% 35% 23% 6% 2	330
	11th to 20th	Day	22% 13% 38% 21% 5% 1	330
	21st to end	Day	19% 15% 35% 25% 5% 1	363
February	1st to 10th	Day	19% 19% 37% 18% 6% 1	330
	11th to 20th	Day	16% 19% 38% 20% 6%	315
	21st to end	Day	17% 25% 39% 17% 2	249
March	1st to 10th	Day	19% 17% 39% 20% 4	300
	11th to 20th	Day	19% 15% 30% 24% 10% 2	428
	21st to end	Day	26% 12% 29% 23% 10% 1	550
April	1st to 10th	Day	23% 13% 30% 26% 8% 1	500
	11th to 20th	Day	25% 13% 28% 20% 11% 3	492
	21st to end	Day	18% 10% 30% 27% 13% 3	500
May	1st to 10th	Day	17% 9% 31% 27% 13% 3	503
	11th to 20th	Day	15% 5% 28% 33% 15% 4	639
	21st to end	Day	14% 6% 23% 29% 22% 5%	789
June	1st to 10th	Day	13% 6% 25% 33% 19% 4	730
	11th to 20th	Day	15% 4 25% 33% 19% 4	730
	21st to end	Day	16% 5% 21% 34% 20% 4	730
July	1st to 10th	Day	10% 2 17% 36% 27% 7%	721
	11th to 20th	Day	9% 4 21% 34% 24% 8%	718
	21st to end	Day	8% 3 20% 36% 28% 5%	794
August	1st to 10th	Day	8% 3 17% 33% 29% 10%	638
	11th to 20th	Day	13% 3 16% 30% 27% 10%	519
	21st to end	Day	15% 4 19% 29% 25% 8%	583
September	1st to 10th	Day	16% 8% 21% 24% 22% 9%	530
	11th to 20th	Day	10% 5% 21% 25% 27% 12%	530
	21st to end	Day	18% 8% 16% 29% 22% 7%	530
October	1st to 10th	Day	20% 11% 24% 25% 16% 4	530
	11th to 20th	Day	26% 13% 29% 26% 6% 1	390
	21st to end	Day	28% 14% 26% 22% 8% 1	363
November	1st to 10th	Day	28% 15% 29% 17% 10% 1	330
	11th to 20th	Day	19% 20% 38% 17% 5%	330
	21st to end	Day	28% 21% 32% 16% 2	303
December	1st to 10th	Day	32% 17% 30% 14% 6%	220
	11th to 20th	Day	24% 25% 32% 16% 3	220
	21st to end	Day	29% 18% 35% 14% 3 1	358
January	1st to 10th	Night	20% 15% 36% 22% 6% 1	1050
	11th to 20th	Night	24% 16% 31% 22% 7% 1	1050
	21st to end	Night	19% 13% 35% 25% 8% 1	1155
February	1st to 10th	Night	17% 15% 34% 25% 8% 1	955
	11th to 20th	Night	20% 14% 34% 25% 8%	804
	21st to end	Night	22% 15% 30% 28% 5%	660
March	1st to 10th	Night	17% 11% 30% 30% 11% 1	800
	11th to 20th	Night	16% 11% 35% 29% 8% 1	800
	21st to end	Night	21% 9% 26% 33% 10% 1	793
April	1st to 10th	Night	23% 10% 29% 31% 7% 1	600
	11th to 20th	Night	23% 10% 24% 31% 11% 1	593
	21st to end	Night	19% 7% 27% 35% 12% 1	600
May	1st to 10th	Night	17% 5% 26% 36% 16% 1	600
	11th to 20th	Night	18% 3 21% 38% 18% 2	591
	21st to end	Night	14% 4 22% 34% 24% 2	650
June	1st to 10th	Night	17% 3 21% 38% 20% 1	580
	11th to 20th	Night	13% 5% 19% 40% 22% 2	400
	21st to end	Night	14% 3 19% 38% 25% 2	594
July	1st to 10th	Night	10% 2 12% 43% 28% 4	585
	11th to 20th	Night	11% 1 17% 38% 28% 5%	582
	21st to end	Night	9% 2 17% 38% 30% 3	657
August	1st to 10th	Night	11% 1 15% 41% 28% 4	597
	11th to 20th	Night	11% 4 15% 32% 32% 6%	594
	21st to end	Night	15% 3 15% 37% 28% 2	660
September	1st to 10th	Night	14% 4 20% 31% 27% 4	600
	11th to 20th	Night	16% 4 17% 31% 27% 6%	795
	21st to end	Night	19% 7% 19% 30% 20% 5%	800
October	1st to 10th	Night	22% 9% 21% 30% 17% 2	800
	11th to 20th	Night	29% 11% 25% 26% 8% 1	800
	21st to end	Night	31% 11% 27% 23% 8% 1	880
November	1st to 10th	Night	26% 14% 25% 28% 6% 1	820
	11th to 20th	Night	28% 17% 30% 20% 5%	840
	21st to end	Night	28% 16% 30% 21% 4	909
December	1st to 10th	Night	26% 20% 31% 19% 4	1050
	11th to 20th	Night	25% 17% 35% 18% 5% 1	1050
	21st to end	Night	30% 13% 34% 20% 3	1155

Page generated at 2026-02-13 01:42:11. Version ac07

Copyright © 2026 Attilla Danko.