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 2024-02-20.

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% 8% 4 6% 5% 3 5% 5% 5% 7% 38%	78401
	Night	14% 9% 4 6% 5% 3 4 4 5% 7% 40%	80837
Transparency	Day	44% 6% 12% 23% 14% 2	78104
	Night	44% 5% 10% 23% 15% 3	80656
Seeing	Day	16% 10% 26% 26% 16% 5%	14643
	Night	17% 9% 29% 30% 13% 1	24667

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% 12% 7% 13% 8% 4 5% 4 4 6% 26%	2527
	11th to 20th	Day	14% 9% 6% 9% 10% 5% 10% 6% 7% 5% 20%	2566
	21st to end	Day	19% 19% 9% 8% 4 2 3 3 3 6% 22%	3135
February	1st to 10th	Day	15% 12% 6% 8% 6% 4 4 4 4 6% 30%	1710
	11th to 20th	Day	13% 11% 4 7% 6% 4 6% 5% 5% 8% 33%	1832
	21st to end	Day	16% 12% 6% 8% 6% 3 4 4 4 5% 31%	1480
March	1st to 10th	Day	15% 10% 5% 7% 6% 3 4 4 4 5% 36%	1800
	11th to 20th	Day	14% 11% 5% 7% 5% 3 4 4 5% 7% 34%	1948
	21st to end	Day	20% 12% 4 8% 7% 3 4 4 5% 7% 26%	2325
April	1st to 10th	Day	13% 7% 4 7% 5% 3 5% 5% 6% 8% 38%	2160
	11th to 20th	Day	15% 9% 3 6% 5% 3 4 4 5% 6% 39%	2134
	21st to end	Day	19% 7% 2 5% 7% 4 5% 4 5% 6% 36%	2160
May	1st to 10th	Day	15% 8% 3 6% 6% 3 5% 5% 6% 8% 34%	2291
	11th to 20th	Day	17% 7% 3 6% 5% 3 5% 4 6% 7% 37%	2448
	21st to end	Day	11% 7% 3 6% 6% 4 6% 6% 7% 9% 36%	2725
June	1st to 10th	Day	7% 5% 2 5% 5% 3 5% 6% 6% 9% 48%	2520
	11th to 20th	Day	8% 5% 2 5% 5% 4 4 6% 5% 8% 49%	2520
	21st to end	Day	7% 5% 3 6% 7% 5% 5% 5% 7% 9% 42%	2520
July	1st to 10th	Day	8% 4 2 4 4 3 6% 6% 8% 10% 45%	2520
	11th to 20th	Day	5% 4 2 4 5% 3 6% 6% 8% 11% 46%	2520
	21st to end	Day	8% 3 2 5% 5% 3 5% 5% 7% 10% 46%	2725
August	1st to 10th	Day	8% 5% 2 5% 6% 4 6% 6% 7% 11% 42%	2314
	11th to 20th	Day	7% 5% 3 6% 5% 3 6% 5% 6% 10% 45%	2125
	21st to end	Day	7% 4 2 5% 5% 4 4 6% 7% 9% 48%	2376
September	1st to 10th	Day	12% 5% 2 5% 4 3 4 4 5% 8% 47%	2160
	11th to 20th	Day	9% 5% 3 6% 4 3 5% 3 5% 7% 51%	2109
	21st to end	Day	7% 5% 3 4 5% 2 4 5% 5% 8% 52%	1980
October	1st to 10th	Day	12% 5% 1 4 4 3 4 4 5% 7% 51%	1839
	11th to 20th	Day	16% 7% 3 6% 4 2 3 4 5% 6% 44%	1800
	21st to end	Day	18% 9% 3 6% 4 3 4 3 4 6% 40%	1895
November	1st to 10th	Day	10% 6% 2 4 4 2 5% 4 4 7% 51%	1672
	11th to 20th	Day	15% 9% 3 6% 4 2 2 5% 4 7% 42%	1710
	21st to end	Day	17% 9% 5% 6% 5% 3 4 4 4 5% 38%	1634
December	1st to 10th	Day	13% 10% 6% 7% 6% 3 5% 5% 5% 6% 33%	1520
	11th to 20th	Day	14% 10% 4 7% 6% 2 4 5% 6% 8% 32%	1918
	21st to end	Day	21% 16% 7% 12% 6% 3 4 4 4 5% 19%	2783
January	1st to 10th	Night	14% 12% 6% 9% 6% 3 5% 4 4 5% 32%	4428
	11th to 20th	Night	14% 16% 6% 8% 6% 4 8% 5% 4 4 24%	4402
	21st to end	Night	23% 16% 7% 10% 5% 2 3 3 3 6% 22%	4532
February	1st to 10th	Night	16% 11% 6% 7% 6% 3 5% 4 5% 6% 33%	2470
	11th to 20th	Night	13% 8% 5% 8% 7% 2 4 4 5% 5% 39%	2218
	21st to end	Night	18% 9% 3 7% 6% 2 4 4 5% 6% 36%	1776
March	1st to 10th	Night	16% 10% 3 6% 5% 3 3 4 4 6% 39%	2160
	11th to 20th	Night	16% 8% 3 6% 5% 2 4 4 6% 6% 40%	2026
	21st to end	Night	22% 11% 3 6% 5% 3 4 4 5% 7% 30%	2030
April	1st to 10th	Night	12% 7% 3 6% 6% 4 4 5% 4 8% 44%	1800
	11th to 20th	Night	14% 7% 3 5% 4 3 3 4 5% 8% 44%	1775
	21st to end	Night	20% 8% 3 6% 6% 2 4 4 4 5% 39%	1800
May	1st to 10th	Night	15% 6% 2 5% 4 3 6% 5% 7% 8% 39%	1666
	11th to 20th	Night	15% 7% 2 4 5% 3 4 4 5% 8% 42%	1444
	21st to end	Night	10% 6% 3 6% 6% 3 5% 6% 7% 9% 39%	1551
June	1st to 10th	Night	7% 6% 2 4 4 2 3 5% 6% 10% 51%	1440
	11th to 20th	Night	8% 5% 2 4 4 3 5% 4 6% 9% 50%	1440
	21st to end	Night	6% 4 2 5% 5% 3 5% 4 8% 9% 49%	1440
July	1st to 10th	Night	8% 4 1 4 5% 3 5% 5% 5% 10% 49%	1440
	11th to 20th	Night	5% 3 2 3 4 2 5% 4 6% 9% 56%	1440
	21st to end	Night	5% 3 2 5% 4 3 6% 5% 7% 9% 52%	1588
August	1st to 10th	Night	7% 3 2 4 4 2 4 5% 7% 10% 51%	1623
	11th to 20th	Night	7% 4 2 4 4 4 5% 5% 5% 8% 52%	1776
	21st to end	Night	5% 3 1 4 5% 3 5% 5% 7% 8% 55%	1980
September	1st to 10th	Night	11% 4 2 4 4 2 4 3 5% 8% 53%	1800
	11th to 20th	Night	7% 6% 2 5% 4 2 3 4 5% 7% 55%	1831
	21st to end	Night	8% 5% 2 4 4 3 4 4 5% 7% 54%	1980
October	1st to 10th	Night	10% 4 2 5% 4 3 4 3 5% 6% 54%	2118
	11th to 20th	Night	15% 6% 2 4 4 2 3 4 5% 7% 49%	2160
	21st to end	Night	18% 8% 3 5% 4 2 4 3 5% 5% 43%	2460
November	1st to 10th	Night	10% 5% 2 5% 4 2 3 4 4 6% 54%	2406
	11th to 20th	Night	12% 7% 3 5% 4 3 4 3 4 6% 49%	2470
	21st to end	Night	17% 9% 3 5% 4 3 4 4 4 6% 41%	2544
December	1st to 10th	Night	16% 11% 4 6% 6% 3 5% 4 4 7% 33%	2660
	11th to 20th	Night	16% 8% 4 8% 5% 3 4 4 4 6% 39%	3279
	21st to end	Night	22% 18% 6% 10% 6% 4 4 4 4 4 18%	4884

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	59% 5% 8% 19% 8%	2528
	11th to 20th	Day	64% 5% 12% 14% 5%	2566
	21st to end	Day	65% 4 9% 15% 7%	3135
February	1st to 10th	Day	56% 4 11% 19% 9% 1	1710
	11th to 20th	Day	50% 5% 11% 21% 11% 1	1842
	21st to end	Day	55% 4 9% 20% 10% 2	1480
March	1st to 10th	Day	50% 5% 10% 23% 11% 1	1800
	11th to 20th	Day	50% 4 13% 21% 10% 1	1948
	21st to end	Day	58% 6% 10% 18% 7% 1	2325
April	1st to 10th	Day	43% 6% 13% 24% 14% 1	2160
	11th to 20th	Day	46% 4 10% 24% 13% 2	2134
	21st to end	Day	48% 6% 12% 20% 13% 2	2160
May	1st to 10th	Day	46% 7% 15% 22% 9% 1	2291
	11th to 20th	Day	45% 6% 13% 23% 12% 1	2452
	21st to end	Day	42% 8% 13% 21% 15% 2	2725
June	1st to 10th	Day	31% 7% 14% 28% 16% 3	2520
	11th to 20th	Day	32% 7% 12% 24% 23% 3	2520
	21st to end	Day	36% 8% 13% 23% 17% 4	2520
July	1st to 10th	Day	32% 8% 14% 29% 14% 4	2451
	11th to 20th	Day	29% 8% 15% 29% 16% 2	2445
	21st to end	Day	31% 6% 14% 30% 17% 2	2574
August	1st to 10th	Day	33% 8% 16% 30% 12% 2	2300
	11th to 20th	Day	33% 7% 13% 30% 16% 1	2125
	21st to end	Day	29% 7% 14% 26% 19% 6%	2376
September	1st to 10th	Day	36% 5% 9% 28% 16% 6%	2160
	11th to 20th	Day	33% 4 8% 27% 23% 5%	2109
	21st to end	Day	30% 5% 9% 30% 23% 3	1980
October	1st to 10th	Day	32% 5% 11% 26% 23% 3	1839
	11th to 20th	Day	41% 4 8% 24% 21% 3	1800
	21st to end	Day	45% 5% 9% 24% 15% 2	1895
November	1st to 10th	Day	34% 5% 13% 26% 19% 4	1672
	11th to 20th	Day	42% 4 10% 25% 16% 3	1710
	21st to end	Day	49% 4 10% 25% 11%	1634
December	1st to 10th	Day	51% 5% 13% 20% 10%	1520
	11th to 20th	Day	49% 6% 9% 26% 7% 2	1915
	21st to end	Day	67% 6% 9% 13% 6%	2783
January	1st to 10th	Night	54% 4 11% 21% 9%	4428
	11th to 20th	Night	64% 4 8% 17% 7%	4402
	21st to end	Night	65% 3 8% 17% 6% 1	4532
February	1st to 10th	Night	54% 3 10% 19% 11% 2	2470
	11th to 20th	Night	47% 4 10% 22% 15% 2	2219
	21st to end	Night	49% 4 10% 22% 11% 3	1776
March	1st to 10th	Night	48% 4 8% 24% 15% 1	2160
	11th to 20th	Night	45% 4 13% 21% 14% 3	2026
	21st to end	Night	55% 5% 10% 21% 8% 1	2030
April	1st to 10th	Night	40% 4 11% 27% 15% 3	1800
	11th to 20th	Night	39% 3 11% 26% 18% 3	1775
	21st to end	Night	48% 4 9% 20% 16% 3	1800
May	1st to 10th	Night	42% 6% 12% 25% 14% 1	1666
	11th to 20th	Night	41% 6% 12% 22% 18% 1	1445
	21st to end	Night	40% 7% 14% 19% 16% 4	1552
June	1st to 10th	Night	29% 5% 15% 29% 19% 4	1440
	11th to 20th	Night	29% 7% 10% 25% 24% 5%	1440
	21st to end	Night	30% 6% 16% 24% 19% 5%	1440
July	1st to 10th	Night	31% 6% 14% 29% 16% 4	1400
	11th to 20th	Night	22% 6% 15% 33% 20% 3	1392
	21st to end	Night	27% 7% 15% 29% 19% 3	1500
August	1st to 10th	Night	26% 8% 17% 32% 17% 2	1613
	11th to 20th	Night	29% 6% 11% 29% 22% 2	1776
	21st to end	Night	25% 7% 15% 27% 20% 7%	1980
September	1st to 10th	Night	31% 5% 10% 27% 20% 8%	1800
	11th to 20th	Night	28% 5% 8% 27% 27% 5%	1831
	21st to end	Night	29% 5% 9% 25% 26% 6%	1980
October	1st to 10th	Night	32% 5% 9% 24% 26% 5%	2118
	11th to 20th	Night	35% 4 8% 27% 22% 4	2160
	21st to end	Night	44% 4 9% 22% 19% 3	2460
November	1st to 10th	Night	32% 4 11% 26% 21% 6%	2406
	11th to 20th	Night	37% 3 9% 28% 20% 2	2470
	21st to end	Night	45% 4 10% 25% 16% 1	2544
December	1st to 10th	Night	51% 4 12% 21% 11% 1	2660
	11th to 20th	Night	47% 4 11% 26% 12% 1	3281
	21st to end	Night	69% 5% 6% 12% 6% 1	4884

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% 17% 7%	270
	11th to 20th	Day	29% 17% 37% 17% 1	270
	21st to end	Day	22% 17% 35% 22% 5%	297
February	1st to 10th	Day	24% 20% 37% 16% 4	270
	11th to 20th	Day	26% 18% 31% 20% 4 1	267
	21st to end	Day	30% 14% 43% 12% 1	198
March	1st to 10th	Day	23% 17% 40% 18% 2	240
	11th to 20th	Day	30% 17% 32% 16% 5%	240
	21st to end	Day	32% 14% 30% 19% 6%	411
April	1st to 10th	Day	18% 15% 34% 27% 6%	420
	11th to 20th	Day	20% 17% 30% 22% 10% 2	412
	21st to end	Day	23% 13% 35% 20% 8% 1	420
May	1st to 10th	Day	19% 13% 33% 24% 9% 2	423
	11th to 20th	Day	20% 10% 25% 28% 14% 3	594
	21st to end	Day	13% 6% 30% 27% 15% 8%	679
June	1st to 10th	Day	9% 4 22% 32% 26% 7%	630
	11th to 20th	Day	11% 5% 22% 35% 22% 6%	630
	21st to end	Day	9% 6% 26% 34% 20% 4	630
July	1st to 10th	Day	10% 2 14% 30% 28% 15%	621
	11th to 20th	Day	7% 4 20% 34% 24% 11%	618
	21st to end	Day	10% 2 18% 33% 29% 9%	684
August	1st to 10th	Day	9% 2 15% 37% 28% 9%	612
	11th to 20th	Day	8% 3 17% 29% 28% 14%	439
	21st to end	Day	7% 1 17% 29% 35% 10%	495
September	1st to 10th	Day	12% 6% 17% 31% 24% 9%	450
	11th to 20th	Day	10% 4 12% 30% 31% 12%	450
	21st to end	Day	8% 11% 23% 25% 24% 10%	450
October	1st to 10th	Day	14% 8% 26% 32% 17% 3	309
	11th to 20th	Day	20% 19% 32% 22% 7% 1	270
	21st to end	Day	34% 11% 31% 19% 5%	297
November	1st to 10th	Day	11% 14% 36% 21% 12% 5%	270
	11th to 20th	Day	22% 17% 32% 20% 7% 2	270
	21st to end	Day	24% 11% 37% 22% 5%	270
December	1st to 10th	Day	15% 20% 39% 17% 6% 3	270
	11th to 20th	Day	20% 17% 39% 20% 3	270
	21st to end	Day	28% 21% 35% 14% 2	297
January	1st to 10th	Night	19% 15% 39% 23% 5%	950
	11th to 20th	Night	21% 15% 37% 21% 5%	950
	21st to end	Night	21% 15% 35% 27% 3	1045
February	1st to 10th	Night	23% 13% 35% 25% 3	950
	11th to 20th	Night	20% 14% 37% 26% 3	747
	21st to end	Night	25% 15% 34% 23% 3	592
March	1st to 10th	Night	22% 14% 35% 24% 4	720
	11th to 20th	Night	21% 11% 33% 29% 7%	586
	21st to end	Night	28% 9% 31% 25% 6%	594
April	1st to 10th	Night	18% 14% 35% 27% 5%	540
	11th to 20th	Night	17% 11% 35% 27% 10%	533
	21st to end	Night	25% 9% 34% 24% 7% 1	540
May	1st to 10th	Night	18% 6% 36% 31% 8% 1	540
	11th to 20th	Night	18% 5% 27% 36% 13% 2	531
	21st to end	Night	12% 4 26% 35% 21% 3	584
June	1st to 10th	Night	9% 3 19% 49% 20% 1	540
	11th to 20th	Night	9% 3 21% 45% 20% 2	540
	21st to end	Night	9% 3 25% 41% 21% 1	540
July	1st to 10th	Night	12% 2 9% 33% 39% 6%	525
	11th to 20th	Night	5% 1 18% 41% 32% 3	522
	21st to end	Night	6% 2 14% 46% 31% 2	591
August	1st to 10th	Night	9% 2 11% 43% 31% 4	537
	11th to 20th	Night	9% 2 12% 39% 34% 6%	534
	21st to end	Night	5% 1 14% 37% 39% 3	594
September	1st to 10th	Night	12% 1 18% 37% 27% 4	540
	11th to 20th	Night	8% 2 17% 37% 32% 4	571
	21st to end	Night	10% 7% 22% 32% 25% 4	720
October	1st to 10th	Night	12% 4 29% 31% 23% 2	720
	11th to 20th	Night	17% 12% 31% 28% 11%	720
	21st to end	Night	23% 12% 34% 24% 7%	792
November	1st to 10th	Night	12% 11% 40% 27% 10%	740
	11th to 20th	Night	18% 14% 35% 25% 7% 1	760
	21st to end	Night	22% 12% 35% 25% 6%	834
December	1st to 10th	Night	22% 12% 36% 23% 6% 1	950
	11th to 20th	Night	23% 10% 33% 27% 7%	950
	21st to end	Night	26% 17% 32% 23% 3	1045

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