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 2025-04-11.

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% 4 4 4 4 6% 8% 39%	113477
	Night	13% 9% 3 7% 4 4 4 3 5% 7% 41%	115007
Transparency	Day	42% 5% 11% 24% 16% 2	117071
	Night	43% 4 10% 24% 17% 2	119557
Seeing	Day	16% 10% 27% 26% 16% 5%	16193
	Night	17% 9% 30% 30% 13% 1	26187

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% 10% 6% 15% 7% 5% 4 3 4 6% 25%	3617
	11th to 20th	Day	10% 9% 6% 11% 7% 8% 9% 4 6% 5% 25%	3684
	21st to end	Day	17% 17% 7% 9% 4 3 3 2 3 5% 29%	4488
February	1st to 10th	Day	15% 13% 5% 9% 6% 5% 3 4 5% 7% 29%	1800
	11th to 20th	Day	13% 12% 3 8% 6% 6% 5% 3 5% 7% 32%	1942
	21st to end	Day	15% 12% 4 9% 5% 3 3 3 4 6% 35%	1650
March	1st to 10th	Day	17% 13% 3 6% 3 3 2 2 3 4 43%	4480
	11th to 20th	Day	7% 9% 3 5% 3 3 4 4 6% 9% 47%	4906
	21st to end	Day	16% 11% 3 9% 5% 4 5% 4 6% 7% 30%	5846
April	1st to 10th	Day	13% 9% 4 7% 5% 4 4 4 6% 7% 37%	2400
	11th to 20th	Day	15% 10% 3 7% 4 4 4 3 5% 6% 39%	2254
	21st to end	Day	19% 7% 2 6% 5% 5% 5% 3 5% 6% 36%	2280
May	1st to 10th	Day	13% 9% 3 7% 6% 4 4 5% 7% 10% 31%	4006
	11th to 20th	Day	16% 8% 3 7% 4 4 5% 3 6% 7% 36%	4354
	21st to end	Day	9% 6% 2 6% 4 5% 4 4 6% 8% 45%	4824
June	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 5% 6% 9% 47%	2660
	11th to 20th	Day	8% 5% 2 5% 4 4 4 5% 5% 8% 50%	2660
	21st to end	Day	6% 6% 2 6% 6% 6% 5% 4 7% 9% 42%	2660
July	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 7% 10% 40%	4440
	11th to 20th	Day	5% 5% 2 6% 4 5% 5% 5% 7% 11% 45%	4440
	21st to end	Day	8% 5% 2 7% 5% 5% 6% 5% 8% 11% 38%	4782
August	1st to 10th	Day	6% 4 2 5% 4 4 5% 4 7% 11% 49%	4076
	11th to 20th	Day	9% 6% 2 7% 4 5% 5% 4 6% 9% 42%	3729
	21st to end	Day	5% 4 2 6% 4 5% 5% 5% 7% 10% 48%	4180
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 5% 7% 49%	2280
	11th to 20th	Day	9% 5% 2 6% 3 4 5% 3 5% 7% 51%	2226
	21st to end	Day	8% 6% 3 5% 4 3 4 3 6% 8% 50%	2090
October	1st to 10th	Day	11% 5% 1 4 4 3 4 3 5% 7% 53%	1941
	11th to 20th	Day	15% 7% 3 6% 3 3 3 3 5% 6% 46%	1900
	21st to end	Day	18% 9% 2 7% 4 4 4 2 4 6% 41%	2000
November	1st to 10th	Day	10% 8% 2 6% 4 4 4 3 5% 6% 50%	1762
	11th to 20th	Day	15% 10% 3 8% 3 3 2 4 5% 6% 42%	1800
	21st to end	Day	17% 11% 4 6% 5% 5% 3 3 4 5% 38%	1720
December	1st to 10th	Day	8% 9% 4 7% 4 4 4 3 4 6% 48%	2610
	11th to 20th	Day	14% 12% 6% 9% 5% 4 4 4 6% 7% 29%	3008
	21st to end	Day	26% 18% 6% 12% 4 3 4 2 3 5% 17%	3982
January	1st to 10th	Night	14% 13% 6% 11% 4 4 3 3 4 5% 32%	6348
	11th to 20th	Night	12% 14% 6% 12% 6% 5% 7% 4 4 4 27%	6294
	21st to end	Night	18% 14% 5% 10% 4 3 3 3 3 6% 30%	6490
February	1st to 10th	Night	16% 12% 6% 8% 5% 4 4 3 5% 6% 32%	2600
	11th to 20th	Night	14% 10% 4 9% 5% 3 4 3 4 5% 38%	2343
	21st to end	Night	16% 9% 3 7% 5% 3 4 3 5% 6% 39%	1980
March	1st to 10th	Night	19% 12% 3 6% 3 3 3 2 4 5% 40%	5373
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 51%	5082
	21st to end	Night	18% 10% 4 8% 5% 5% 5% 3 5% 6% 32%	5082
April	1st to 10th	Night	12% 7% 3 6% 5% 4 4 4 4 7% 43%	2000
	11th to 20th	Night	14% 7% 2 5% 4 4 3 3 5% 8% 44%	1881
	21st to end	Night	19% 8% 3 7% 5% 3 3 4 4 5% 39%	1900
May	1st to 10th	Night	16% 8% 3 7% 4 4 5% 4 6% 7% 36%	2886
	11th to 20th	Night	15% 7% 2 5% 4 5% 4 3 6% 8% 40%	2547
	21st to end	Night	9% 6% 2 6% 5% 4 4 4 7% 10% 44%	2743
June	1st to 10th	Night	7% 6% 2 4 3 3 4 4 6% 10% 50%	1520
	11th to 20th	Night	7% 6% 2 5% 3 5% 4 3 6% 9% 50%	1520
	21st to end	Night	6% 5% 2 6% 5% 4 4 4 8% 9% 48%	1520
July	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 6% 9% 42%	2530
	11th to 20th	Night	3 3 1 4 3 3 4 4 7% 9% 57%	2530
	21st to end	Night	7% 4 2 7% 4 4 5% 5% 8% 11% 43%	2776
August	1st to 10th	Night	5% 3 1 5% 3 3 4 4 7% 10% 54%	2861
	11th to 20th	Night	7% 5% 2 5% 4 5% 5% 4 6% 8% 51%	3100
	21st to end	Night	4 3 1 4 4 4 4 4 7% 10% 53%	3476
September	1st to 10th	Night	10% 4 2 5% 3 4 3 3 5% 7% 54%	1900
	11th to 20th	Night	7% 6% 2 6% 4 3 3 3 5% 8% 54%	1933
	21st to end	Night	9% 5% 2 5% 3 4 4 3 5% 7% 52%	2090
October	1st to 10th	Night	10% 4 2 5% 4 4 3 2 5% 6% 56%	2236
	11th to 20th	Night	14% 6% 2 5% 3 3 2 3 5% 6% 51%	2280
	21st to end	Night	17% 9% 3 5% 3 3 4 2 5% 5% 43%	2597
November	1st to 10th	Night	10% 6% 2 6% 4 3 3 3 4 6% 53%	2536
	11th to 20th	Night	12% 8% 3 6% 4 4 3 2 4 6% 48%	2600
	21st to end	Night	16% 10% 3 6% 4 4 3 3 4 6% 40%	2678
December	1st to 10th	Night	12% 9% 3 7% 4 4 3 3 4 5% 46%	4580
	11th to 20th	Night	16% 9% 4 9% 4 4 5% 4 5% 7% 35%	5199
	21st to end	Night	25% 18% 6% 10% 5% 4 4 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 8% 18% 9% 1	3618
	11th to 20th	Day	60% 3 10% 14% 9% 3	3684
	21st to end	Day	61% 3 7% 19% 9% 1	4488
February	1st to 10th	Day	56% 4 11% 20% 8% 1	1800
	11th to 20th	Day	51% 5% 11% 20% 12% 1	1952
	21st to end	Day	51% 4 9% 22% 12% 2	1650
March	1st to 10th	Day	47% 3 6% 22% 19% 3	4480
	11th to 20th	Day	34% 4 10% 31% 20% 1	4906
	21st to end	Day	52% 5% 14% 22% 6% 1	5848
April	1st to 10th	Day	45% 6% 12% 23% 14%	2400
	11th to 20th	Day	45% 5% 10% 25% 14% 3	2254
	21st to end	Day	48% 6% 12% 20% 13% 2	2280
May	1st to 10th	Day	44% 8% 14% 24% 9%	4043
	11th to 20th	Day	46% 6% 11% 28% 9%	4358
	21st to end	Day	34% 7% 10% 23% 24% 2	4837
June	1st to 10th	Day	31% 7% 14% 28% 16% 3	2660
	11th to 20th	Day	32% 6% 11% 25% 23% 2	2660
	21st to end	Day	36% 8% 13% 23% 17% 3	2660
July	1st to 10th	Day	41% 5% 11% 28% 14% 2	4371
	11th to 20th	Day	32% 5% 14% 28% 20% 1	4365
	21st to end	Day	40% 4 18% 24% 13% 1	4632
August	1st to 10th	Day	30% 5% 16% 36% 12% 1	4062
	11th to 20th	Day	38% 4 12% 30% 15% 1	3765
	21st to end	Day	30% 5% 15% 31% 15% 4	4179
September	1st to 10th	Day	34% 5% 9% 27% 19% 6%	2280
	11th to 20th	Day	33% 4 8% 27% 24% 5%	2226
	21st to end	Day	33% 5% 8% 30% 22% 3	2090
October	1st to 10th	Day	22% 3 7% 19% 46% 3	3227
	11th to 20th	Day	27% 2 7% 23% 35% 5%	3140
	21st to end	Day	39% 3 6% 27% 22% 2	3277
November	1st to 10th	Day	35% 5% 12% 25% 19% 4	1762
	11th to 20th	Day	42% 4 10% 25% 16% 4	1800
	21st to end	Day	50% 4 10% 25% 11%	1720
December	1st to 10th	Day	38% 3 16% 31% 11%	2610
	11th to 20th	Day	54% 4 10% 23% 8% 2	3005
	21st to end	Day	71% 4 10% 11% 4	3982
January	1st to 10th	Night	55% 3 11% 23% 7%	6348
	11th to 20th	Night	61% 3 8% 15% 11% 3	6294
	21st to end	Night	58% 2 7% 20% 11% 2	6490
February	1st to 10th	Night	54% 3 11% 19% 11% 2	2600
	11th to 20th	Night	48% 4 10% 21% 15% 2	2344
	21st to end	Night	47% 4 10% 23% 14% 3	1980
March	1st to 10th	Night	49% 3 7% 23% 17% 2	5373
	11th to 20th	Night	35% 3 8% 30% 19% 4	5082
	21st to end	Night	52% 4 9% 25% 8% 1	5082
April	1st to 10th	Night	41% 4 11% 26% 15% 3	2000
	11th to 20th	Night	38% 3 10% 27% 18% 3	1881
	21st to end	Night	48% 4 9% 21% 16% 3	1900
May	1st to 10th	Night	45% 7% 14% 23% 10% 1	2914
	11th to 20th	Night	40% 7% 12% 28% 11% 1	2548
	21st to end	Night	34% 7% 12% 22% 22% 4	2751
June	1st to 10th	Night	29% 5% 14% 29% 18% 4	1520
	11th to 20th	Night	30% 6% 10% 25% 24% 5%	1520
	21st to end	Night	30% 6% 16% 24% 19% 5%	1520
July	1st to 10th	Night	39% 4 11% 29% 14% 2	2490
	11th to 20th	Night	23% 4 13% 36% 23% 2	2482
	21st to end	Night	35% 4 19% 23% 17% 2	2688
August	1st to 10th	Night	25% 4 16% 35% 18% 1	2851
	11th to 20th	Night	32% 4 13% 32% 19% 1	3130
	21st to end	Night	26% 5% 16% 34% 16% 4	3476
September	1st to 10th	Night	30% 5% 9% 26% 22% 8%	1900
	11th to 20th	Night	28% 4 8% 26% 27% 5%	1933
	21st to end	Night	31% 5% 8% 25% 24% 6%	2090
October	1st to 10th	Night	22% 3 5% 22% 45% 4	3730
	11th to 20th	Night	24% 2 8% 23% 38% 5%	3779
	21st to end	Night	34% 2 9% 25% 25% 5%	4270
November	1st to 10th	Night	34% 4 10% 26% 20% 5%	2536
	11th to 20th	Night	38% 3 9% 28% 20% 2	2600
	21st to end	Night	46% 4 9% 24% 16% 1	2678
December	1st to 10th	Night	42% 2 11% 31% 14% 1	4580
	11th to 20th	Night	50% 3 11% 24% 12%	5201
	21st to end	Night	71% 4 9% 12% 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	24% 19% 33% 18% 7%	300
	11th to 20th	Day	26% 17% 39% 16% 1	300
	21st to end	Day	22% 16% 37% 21% 4	330
February	1st to 10th	Day	23% 19% 39% 15% 4	300
	11th to 20th	Day	25% 19% 34% 17% 4	300
	21st to end	Day	26% 16% 43% 13% 1	249
March	1st to 10th	Day	22% 18% 41% 18% 2	300
	11th to 20th	Day	28% 19% 31% 16% 5%	300
	21st to end	Day	30% 15% 33% 18% 5%	494
April	1st to 10th	Day	21% 16% 34% 24% 5%	500
	11th to 20th	Day	20% 17% 30% 22% 9% 2	452
	21st to end	Day	23% 13% 36% 19% 7% 1	460
May	1st to 10th	Day	18% 13% 34% 25% 8% 2	463
	11th to 20th	Day	19% 10% 26% 29% 14% 3	643
	21st to end	Day	13% 7% 31% 27% 14% 7%	734
June	1st to 10th	Day	9% 5% 23% 31% 25% 7%	680
	11th to 20th	Day	10% 4 22% 36% 22% 6%	680
	21st to end	Day	9% 6% 28% 34% 19% 4	680
July	1st to 10th	Day	11% 3 15% 31% 27% 14%	671
	11th to 20th	Day	7% 3 20% 35% 25% 11%	668
	21st to end	Day	10% 2 17% 33% 29% 9%	739
August	1st to 10th	Day	9% 2 16% 37% 28% 9%	661
	11th to 20th	Day	8% 4 18% 30% 27% 13%	479
	21st to end	Day	8% 1 16% 29% 36% 10%	539
September	1st to 10th	Day	11% 6% 17% 30% 26% 10%	490
	11th to 20th	Day	10% 3 12% 30% 31% 13%	490
	21st to end	Day	11% 11% 22% 24% 23% 9%	490
October	1st to 10th	Day	13% 7% 26% 30% 19% 4	341
	11th to 20th	Day	18% 17% 31% 23% 9% 2	300
	21st to end	Day	31% 13% 31% 19% 6%	330
November	1st to 10th	Day	14% 14% 34% 23% 11% 4	300
	11th to 20th	Day	22% 17% 34% 18% 7% 2	300
	21st to end	Day	25% 12% 36% 22% 5%	300
December	1st to 10th	Day	14% 21% 40% 18% 5% 3	300
	11th to 20th	Day	21% 19% 37% 20% 3	300
	21st to end	Day	30% 19% 34% 15% 2	330
January	1st to 10th	Night	19% 14% 39% 24% 5%	1000
	11th to 20th	Night	21% 15% 38% 21% 5%	1000
	21st to end	Night	20% 15% 36% 26% 3	1100
February	1st to 10th	Night	23% 14% 36% 24% 3	1000
	11th to 20th	Night	21% 15% 36% 26% 2	788
	21st to end	Night	23% 15% 36% 24% 2	660
March	1st to 10th	Night	22% 15% 35% 25% 3	800
	11th to 20th	Night	20% 12% 34% 28% 6%	650
	21st to end	Night	27% 10% 32% 25% 6%	660
April	1st to 10th	Night	19% 15% 35% 27% 5%	600
	11th to 20th	Night	17% 12% 35% 27% 9%	565
	21st to end	Night	25% 9% 35% 24% 7% 1	570
May	1st to 10th	Night	18% 6% 36% 31% 8% 1	570
	11th to 20th	Night	17% 5% 27% 37% 12% 1	561
	21st to end	Night	12% 4 27% 35% 20% 3	617
June	1st to 10th	Night	9% 3 20% 48% 19% 1	570
	11th to 20th	Night	9% 3 22% 45% 19% 2	570
	21st to end	Night	9% 3 25% 41% 20% 1	570
July	1st to 10th	Night	12% 2 9% 34% 37% 5%	555
	11th to 20th	Night	5% 1 18% 41% 32% 3	552
	21st to end	Night	6% 2 13% 46% 31% 2	624
August	1st to 10th	Night	9% 2 11% 43% 31% 4	567
	11th to 20th	Night	8% 2 12% 40% 32% 5%	564
	21st to end	Night	5% 1 13% 37% 40% 3	627
September	1st to 10th	Night	11% 2 17% 37% 28% 4	570
	11th to 20th	Night	8% 2 16% 37% 33% 4	603
	21st to end	Night	11% 7% 22% 32% 24% 4	760
October	1st to 10th	Night	11% 4 28% 31% 24% 2	760
	11th to 20th	Night	17% 13% 30% 28% 12% 1	760
	21st to end	Night	22% 11% 34% 25% 7%	836
November	1st to 10th	Night	14% 10% 39% 27% 9%	780
	11th to 20th	Night	18% 14% 36% 25% 7% 1	800
	21st to end	Night	22% 13% 35% 25% 6%	878
December	1st to 10th	Night	21% 12% 37% 23% 5% 1	1000
	11th to 20th	Night	23% 10% 33% 27% 6%	1000
	21st to end	Night	27% 16% 32% 23% 3	1100

Page generated at 2025-04-08 08:17:28. Version ac07

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