Bojarzin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bojarzin Observatory clear sky chart from 2005-11-06 to 2026-08-15.

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% 8% 3 7% 5% 4 5% 4 6% 8% 39%	144051
	Night	13% 9% 3 7% 4 4 4 3 5% 7% 41%	138149
Transparency	Day	43% 4 11% 25% 15% 2	147600
	Night	43% 3 11% 24% 16% 2	142680
Seeing	Day	16% 10% 27% 26% 16% 5%	18164
	Night	17% 9% 30% 30% 13% 1	27910

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	12% 10% 5% 14% 6% 5% 4 3 4 7% 29%	4691
	11th to 20th	Day	8% 9% 5% 11% 7% 8% 8% 4 6% 5% 29%	4788
	21st to end	Day	15% 16% 6% 10% 5% 4 3 3 4 5% 29%	5812
February	1st to 10th	Day	14% 13% 5% 9% 6% 5% 3 4 5% 7% 29%	1890
	11th to 20th	Day	13% 12% 3 8% 6% 6% 5% 3 5% 7% 32%	2042
	21st to end	Day	14% 12% 4 9% 5% 3 3 3 4 5% 35%	1730
March	1st to 10th	Day	17% 13% 3 6% 3 3 3 2 3 4 43%	4580
	11th to 20th	Day	7% 9% 3 6% 3 3 4 4 6% 9% 46%	5014
	21st to end	Day	15% 10% 3 9% 5% 4 5% 4 6% 7% 31%	5975
April	1st to 10th	Day	14% 9% 3 7% 5% 4 4 4 6% 7% 36%	2520
	11th to 20th	Day	14% 10% 3 7% 5% 4 4 3 5% 6% 39%	2494
	21st to end	Day	18% 7% 2 7% 5% 5% 5% 3 6% 6% 36%	2520
May	1st to 10th	Day	16% 8% 3 8% 5% 4 4 4 6% 9% 33%	7470
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 3 5% 7% 40%	8137
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 5% 7% 8% 33%	9047
June	1st to 10th	Day	8% 5% 2 6% 4 4 5% 5% 6% 9% 47%	2940
	11th to 20th	Day	8% 5% 2 5% 4 5% 4 5% 5% 8% 48%	2940
	21st to end	Day	7% 6% 3 6% 6% 6% 5% 4 7% 9% 42%	2940
July	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 7% 11% 44%	8280
	11th to 20th	Day	7% 6% 3 7% 5% 5% 5% 4 7% 10% 43%	8280
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 11% 37%	8931
August	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 7% 10% 48%	4334
	11th to 20th	Day	9% 5% 2 7% 4 5% 5% 4 6% 9% 43%	3897
	21st to end	Day	4 4 2 6% 4 5% 5% 5% 7% 10% 48%	4312
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 4 7% 50%	2400
	11th to 20th	Day	9% 5% 2 6% 3 4 5% 3 5% 7% 52%	2343
	21st to end	Day	8% 6% 3 5% 4 3 4 3 6% 8% 50%	2200
October	1st to 10th	Day	11% 5% 2 4 4 4 4 3 5% 7% 53%	2043
	11th to 20th	Day	14% 7% 3 6% 4 4 3 3 5% 6% 46%	2000
	21st to end	Day	17% 9% 3 7% 4 4 4 2 4 6% 41%	2105
November	1st to 10th	Day	10% 7% 2 6% 3 4 4 3 5% 6% 50%	1852
	11th to 20th	Day	15% 10% 3 7% 3 3 3 4 5% 6% 42%	1890
	21st to end	Day	17% 11% 4 7% 4 5% 3 3 4 5% 37%	1806
December	1st to 10th	Day	8% 9% 4 7% 4 4 4 3 4 6% 48%	2690
	11th to 20th	Day	14% 12% 6% 9% 5% 4 4 3 6% 7% 29%	3088
	21st to end	Day	26% 18% 6% 12% 4 3 4 3 3 4 17%	4070
January	1st to 10th	Night	12% 12% 6% 11% 4 4 4 3 4 5% 35%	8232
	11th to 20th	Night	10% 12% 5% 11% 6% 5% 6% 4 4 5% 32%	8186
	21st to end	Night	15% 13% 5% 10% 4 4 4 3 4 6% 32%	8402
February	1st to 10th	Night	16% 11% 5% 8% 5% 4 4 3 5% 6% 33%	2730
	11th to 20th	Night	14% 10% 4 9% 6% 3 4 3 5% 5% 38%	2463
	21st to end	Night	16% 9% 3 8% 5% 3 4 3 5% 6% 39%	2076
March	1st to 10th	Night	19% 12% 3 6% 3 3 3 2 4 5% 40%	5493
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 50%	5195
	21st to end	Night	17% 10% 4 8% 5% 5% 5% 3 5% 6% 32%	5195
April	1st to 10th	Night	12% 8% 3 7% 5% 5% 4 4 4 7% 42%	2100
	11th to 20th	Night	14% 7% 2 5% 4 4 3 3 5% 8% 44%	2075
	21st to end	Night	18% 8% 3 7% 5% 3 3 4 5% 5% 39%	2100
May	1st to 10th	Night	17% 9% 3 7% 4 5% 5% 4 6% 7% 34%	5380
	11th to 20th	Night	12% 6% 2 5% 4 5% 5% 4 6% 9% 42%	4748
	21st to end	Night	13% 7% 3 7% 5% 4 4 4 7% 9% 36%	5139
June	1st to 10th	Night	8% 6% 2 4 3 3 4 4 6% 10% 50%	1680
	11th to 20th	Night	8% 6% 2 5% 3 5% 4 3 6% 9% 49%	1680
	21st to end	Night	7% 5% 2 6% 5% 4 4 4 8% 9% 48%	1680
July	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 6% 9% 46%	4708
	11th to 20th	Night	6% 4 2 5% 4 5% 5% 4 7% 9% 48%	4707
	21st to end	Night	7% 5% 2 7% 4 5% 6% 5% 7% 10% 42%	5171
August	1st to 10th	Night	6% 4 2 5% 3 3 4 4 7% 10% 53%	3043
	11th to 20th	Night	7% 5% 2 5% 4 5% 5% 4 6% 8% 52%	3240
	21st to end	Night	4 3 1 4 4 4 4 4 7% 10% 54%	3586
September	1st to 10th	Night	10% 4 2 5% 3 4 3 3 5% 7% 54%	2000
	11th to 20th	Night	6% 6% 2 6% 3 3 3 4 5% 8% 55%	2035
	21st to end	Night	9% 5% 2 5% 3 4 4 4 5% 7% 52%	2200
October	1st to 10th	Night	10% 4 1 5% 4 4 3 3 5% 6% 56%	2354
	11th to 20th	Night	14% 6% 2 4 3 3 2 3 5% 7% 51%	2400
	21st to end	Night	17% 9% 3 6% 3 3 4 2 5% 5% 43%	2734
November	1st to 10th	Night	10% 6% 3 6% 4 3 4 3 4 6% 53%	2666
	11th to 20th	Night	12% 8% 3 6% 4 4 3 2 4 6% 48%	2730
	21st to end	Night	17% 10% 3 6% 4 4 3 3 4 5% 40%	2812
December	1st to 10th	Night	12% 9% 3 7% 5% 4 4 3 4 5% 45%	4720
	11th to 20th	Night	16% 9% 4 9% 4 4 5% 4 5% 6% 35%	5339
	21st to end	Night	25% 18% 6% 10% 5% 4 4 3 4 4 18%	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	56% 3 11% 20% 9% 1	4692
	11th to 20th	Day	57% 3 10% 17% 11% 2	4788
	21st to end	Day	60% 2 8% 20% 8% 2	5812
February	1st to 10th	Day	55% 4 12% 20% 8% 1	1890
	11th to 20th	Day	52% 5% 10% 21% 11% 2	2052
	21st to end	Day	52% 4 9% 22% 12% 2	1730
March	1st to 10th	Day	47% 3 6% 22% 19% 3	4580
	11th to 20th	Day	35% 4 10% 31% 19% 1	5014
	21st to end	Day	52% 5% 14% 22% 6% 1	5977
April	1st to 10th	Day	45% 5% 13% 23% 14%	2520
	11th to 20th	Day	45% 4 10% 24% 13% 2	2494
	21st to end	Day	47% 5% 12% 22% 12% 1	2520
May	1st to 10th	Day	48% 5% 12% 23% 12% 1	7506
	11th to 20th	Day	44% 3 10% 24% 16% 2	8141
	21st to end	Day	48% 4 10% 22% 16% 1	9061
June	1st to 10th	Day	32% 7% 14% 28% 16% 3	2940
	11th to 20th	Day	33% 6% 11% 25% 23% 2	2940
	21st to end	Day	37% 7% 14% 22% 17% 3	2940
July	1st to 10th	Day	36% 3 14% 29% 17% 1	8211
	11th to 20th	Day	38% 4 14% 26% 18% 1	8205
	21st to end	Day	42% 2 18% 28% 9% 1	8736
August	1st to 10th	Day	30% 4 17% 36% 12% 1	4320
	11th to 20th	Day	38% 4 13% 30% 14% 1	3933
	21st to end	Day	30% 4 15% 31% 16% 4	4311
September	1st to 10th	Day	34% 5% 9% 28% 20% 6%	2400
	11th to 20th	Day	32% 3 9% 26% 25% 5%	2343
	21st to end	Day	33% 4 8% 29% 24% 2	2200
October	1st to 10th	Day	23% 3 7% 19% 45% 4	3329
	11th to 20th	Day	27% 2 8% 23% 35% 5%	3240
	21st to end	Day	40% 3 6% 27% 23% 2	3382
November	1st to 10th	Day	35% 4 12% 26% 19% 4	1852
	11th to 20th	Day	42% 3 10% 25% 16% 3	1890
	21st to end	Day	50% 4 10% 24% 11%	1806
December	1st to 10th	Day	39% 3 16% 31% 11%	2690
	11th to 20th	Day	54% 4 10% 23% 8% 2	3085
	21st to end	Day	71% 4 10% 11% 4	4070
January	1st to 10th	Night	52% 3 14% 24% 7%	8233
	11th to 20th	Night	56% 2 7% 18% 15% 2	8186
	21st to end	Night	56% 2 10% 21% 10% 2	8402
February	1st to 10th	Night	53% 3 11% 20% 11% 2	2730
	11th to 20th	Night	48% 3 10% 22% 15% 2	2464
	21st to end	Night	47% 4 10% 23% 14% 3	2076
March	1st to 10th	Night	49% 3 7% 23% 17% 2	5493
	11th to 20th	Night	36% 3 8% 29% 19% 4	5195
	21st to end	Night	52% 4 9% 25% 8% 1	5195
April	1st to 10th	Night	42% 3 11% 26% 15% 3	2100
	11th to 20th	Night	39% 3 11% 26% 18% 3	2075
	21st to end	Night	47% 4 9% 22% 15% 3	2100
May	1st to 10th	Night	49% 4 10% 24% 11% 2	5408
	11th to 20th	Night	39% 4 12% 25% 17% 3	4749
	21st to end	Night	45% 4 11% 21% 18% 2	5149
June	1st to 10th	Night	30% 5% 14% 29% 18% 4	1680
	11th to 20th	Night	31% 6% 10% 25% 24% 5%	1680
	21st to end	Night	32% 5% 15% 24% 19% 5%	1680
July	1st to 10th	Night	36% 2 12% 29% 19% 1	4670
	11th to 20th	Night	32% 4 14% 29% 20% 1	4662
	21st to end	Night	37% 3 19% 27% 12% 1	5056
August	1st to 10th	Night	26% 4 16% 35% 18% 1	3033
	11th to 20th	Night	32% 3 14% 32% 18% 1	3270
	21st to end	Night	25% 4 16% 34% 16% 4	3586
September	1st to 10th	Night	29% 4 9% 27% 23% 8%	2000
	11th to 20th	Night	28% 4 9% 26% 28% 5%	2035
	21st to end	Night	31% 5% 8% 25% 26% 5%	2200
October	1st to 10th	Night	22% 2 5% 21% 45% 4	3848
	11th to 20th	Night	24% 2 9% 23% 37% 5%	3899
	21st to end	Night	35% 2 9% 24% 25% 5%	4407
November	1st to 10th	Night	34% 4 10% 26% 21% 5%	2666
	11th to 20th	Night	38% 3 9% 28% 20% 2	2730
	21st to end	Night	47% 4 9% 24% 15% 1	2812
December	1st to 10th	Night	43% 2 11% 30% 13% 1	4720
	11th to 20th	Night	50% 3 11% 24% 11%	5341
	21st to end	Night	70% 4 9% 12% 5%	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	23% 19% 32% 18% 7%	330
	11th to 20th	Day	24% 19% 40% 16% 1	330
	21st to end	Day	21% 16% 38% 21% 4	363
February	1st to 10th	Day	22% 18% 39% 16% 5%	330
	11th to 20th	Day	25% 18% 36% 17% 4	330
	21st to end	Day	25% 16% 45% 13% 1	273
March	1st to 10th	Day	23% 17% 42% 16% 2	330
	11th to 20th	Day	28% 18% 33% 15% 5%	330
	21st to end	Day	28% 15% 35% 18% 4	535
April	1st to 10th	Day	22% 15% 34% 23% 5%	540
	11th to 20th	Day	21% 19% 29% 21% 9% 2	532
	21st to end	Day	22% 13% 35% 21% 8% 1	540
May	1st to 10th	Day	19% 13% 34% 24% 8% 2	543
	11th to 20th	Day	18% 12% 26% 28% 13% 3	740
	21st to end	Day	14% 7% 31% 28% 13% 7%	844
June	1st to 10th	Day	10% 5% 24% 31% 24% 6%	780
	11th to 20th	Day	11% 5% 23% 35% 21% 6%	780
	21st to end	Day	9% 5% 26% 35% 20% 4	780
July	1st to 10th	Day	10% 3 13% 32% 28% 14%	771
	11th to 20th	Day	8% 4 18% 35% 26% 11%	768
	21st to end	Day	10% 3 17% 33% 29% 8%	849
August	1st to 10th	Day	9% 3 15% 38% 27% 9%	759
	11th to 20th	Day	7% 4 18% 29% 29% 13%	535
	21st to end	Day	7% 2 16% 30% 35% 10%	583
September	1st to 10th	Day	11% 5% 17% 30% 28% 9%	530
	11th to 20th	Day	9% 3 11% 30% 32% 14%	530
	21st to end	Day	11% 10% 21% 24% 24% 11%	530
October	1st to 10th	Day	13% 7% 25% 31% 20% 4	373
	11th to 20th	Day	17% 17% 30% 24% 11% 2	330
	21st to end	Day	29% 15% 31% 20% 5%	363
November	1st to 10th	Day	13% 16% 35% 23% 10% 4	330
	11th to 20th	Day	22% 17% 34% 19% 7% 2	330
	21st to end	Day	26% 12% 35% 22% 6%	330
December	1st to 10th	Day	14% 19% 40% 19% 5% 3	330
	11th to 20th	Day	21% 18% 38% 20% 3 1	330
	21st to end	Day	30% 18% 35% 15% 2	363
January	1st to 10th	Night	19% 14% 39% 24% 4	1050
	11th to 20th	Night	20% 16% 39% 21% 4	1050
	21st to end	Night	20% 15% 37% 26% 2	1155
February	1st to 10th	Night	23% 13% 36% 25% 3	1050
	11th to 20th	Night	21% 15% 36% 26% 2	828
	21st to end	Night	22% 15% 36% 24% 2	692
March	1st to 10th	Night	24% 14% 35% 24% 3	840
	11th to 20th	Night	20% 13% 34% 28% 6%	683
	21st to end	Night	26% 10% 33% 25% 6%	693
April	1st to 10th	Night	20% 15% 35% 26% 5%	630
	11th to 20th	Night	17% 12% 35% 27% 8%	623
	21st to end	Night	23% 9% 35% 25% 7% 1	630
May	1st to 10th	Night	18% 6% 37% 31% 8% 1	630
	11th to 20th	Night	16% 5% 29% 36% 12% 1	621
	21st to end	Night	13% 4 26% 35% 19% 2	683
June	1st to 10th	Night	10% 3 21% 47% 19%	630
	11th to 20th	Night	10% 3 21% 45% 18% 2	630
	21st to end	Night	10% 3 24% 41% 20% 1	630
July	1st to 10th	Night	11% 2 9% 36% 37% 5%	615
	11th to 20th	Night	6% 2 17% 40% 33% 3	612
	21st to end	Night	6% 2 13% 46% 31% 2	690
August	1st to 10th	Night	9% 2 12% 43% 30% 4	627
	11th to 20th	Night	8% 1 12% 42% 33% 5%	606
	21st to end	Night	5% 1 13% 38% 39% 3	660
September	1st to 10th	Night	11% 2 17% 37% 29% 4	600
	11th to 20th	Night	8% 2 15% 37% 33% 5%	635
	21st to end	Night	11% 7% 21% 32% 25% 4	800
October	1st to 10th	Night	11% 4 27% 32% 24% 2	800
	11th to 20th	Night	17% 12% 29% 30% 12% 1	800
	21st to end	Night	22% 11% 35% 25% 7%	880
November	1st to 10th	Night	13% 10% 40% 27% 9%	820
	11th to 20th	Night	18% 14% 37% 25% 6% 1	840
	21st to end	Night	23% 13% 34% 25% 5%	922
December	1st to 10th	Night	21% 12% 37% 24% 5% 1	1050
	11th to 20th	Night	23% 10% 33% 27% 6%	1050
	21st to end	Night	27% 16% 32% 23% 3	1155

Page generated at 2026-08-12 02:37:16. Version ac07

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