Sirius Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sirius Astronomical Observatory clear sky chart from 2005-11-06 to 2024-05-15.

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	17% 7% 3 6% 4 4 4 4 5% 7% 39%	83403
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 40%	86130
Transparency	Day	45% 4 11% 23% 15% 2	83108
	Night	45% 4 11% 23% 15% 2	85959
Seeing	Day	24% 16% 31% 19% 8% 2	14342
	Night	23% 13% 32% 24% 7% 1	23487

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	15% 7% 3 5% 4 4 4 3 5% 6% 44%	2517
	11th to 20th	Day	18% 7% 3 8% 5% 4 4 4 5% 5% 36%	2520
	21st to end	Day	23% 12% 3 7% 4 3 4 3 5% 5% 32%	2806
February	1st to 10th	Day	18% 8% 2 5% 4 5% 5% 5% 6% 6% 36%	1786
	11th to 20th	Day	15% 7% 3 7% 4 5% 5% 3 5% 7% 40%	1848
	21st to end	Day	21% 9% 3 5% 4 4 4 4 5% 6% 37%	1570
March	1st to 10th	Day	25% 11% 3 7% 4 3 3 2 3 5% 33%	3116
	11th to 20th	Day	11% 7% 2 7% 6% 5% 5% 4 6% 7% 40%	3246
	21st to end	Day	21% 7% 3 6% 4 4 3 4 5% 7% 37%	4163
April	1st to 10th	Day	19% 8% 2 7% 4 4 4 3 5% 8% 36%	2280
	11th to 20th	Day	19% 6% 2 6% 4 4 4 4 5% 6% 41%	2254
	21st to end	Day	21% 6% 2 6% 4 5% 4 3 4 6% 38%	2406
May	1st to 10th	Day	24% 7% 3 6% 4 5% 3 3 6% 7% 31%	2470
	11th to 20th	Day	19% 6% 2 6% 3 3 4 3 5% 8% 39%	2444
	21st to end	Day	15% 6% 3 5% 4 4 4 3 6% 8% 43%	2725
June	1st to 10th	Day	18% 6% 2 6% 4 5% 5% 4 6% 9% 35%	2520
	11th to 20th	Day	15% 7% 3 7% 6% 4 5% 4 6% 8% 36%	2520
	21st to end	Day	13% 8% 3 7% 4 5% 4 4 7% 9% 37%	2520
July	1st to 10th	Day	12% 7% 3 5% 5% 5% 5% 4 6% 7% 39%	2520
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 10% 39%	2520
	21st to end	Day	13% 5% 2 6% 5% 5% 6% 4 7% 10% 37%	2744
August	1st to 10th	Day	11% 7% 2 7% 5% 5% 6% 5% 8% 10% 35%	2408
	11th to 20th	Day	11% 6% 3 7% 5% 4 5% 5% 6% 8% 40%	2170
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 7% 44%	2376
September	1st to 10th	Day	14% 6% 3 5% 5% 4 4 4 5% 6% 44%	2160
	11th to 20th	Day	14% 6% 2 5% 2 3 3 4 5% 6% 50%	2025
	21st to end	Day	18% 6% 2 6% 3 3 4 4 5% 7% 43%	1980
October	1st to 10th	Day	23% 7% 2 6% 3 4 4 3 5% 5% 39%	1970
	11th to 20th	Day	15% 7% 2 5% 3 3 4 3 6% 7% 45%	1767
	21st to end	Day	20% 7% 3 6% 5% 4 3 4 5% 7% 39%	1782
November	1st to 10th	Day	14% 7% 2 6% 4 3 4 3 4 6% 47%	1671
	11th to 20th	Day	20% 6% 2 4 3 3 4 2 5% 6% 45%	1710
	21st to end	Day	17% 7% 2 6% 5% 3 3 3 4 6% 43%	1691
December	1st to 10th	Day	19% 8% 2 7% 5% 3 4 3 5% 6% 37%	1520
	11th to 20th	Day	22% 7% 2 4 2 4 3 3 4 5% 44%	1906
	21st to end	Day	22% 10% 4 8% 4 4 3 3 5% 6% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 4 4 3 5% 7% 44%	4429
	11th to 20th	Night	16% 9% 3 8% 4 4 3 3 4 5% 41%	4440
	21st to end	Night	24% 12% 4 8% 4 3 3 3 4 4 31%	4848
February	1st to 10th	Night	17% 10% 3 6% 5% 3 3 4 5% 6% 39%	2393
	11th to 20th	Night	15% 9% 3 7% 4 4 4 3 5% 6% 39%	2218
	21st to end	Night	19% 9% 2 7% 4 3 3 3 5% 5% 39%	1884
March	1st to 10th	Night	28% 10% 2 6% 4 3 3 3 5% 5% 32%	3724
	11th to 20th	Night	12% 8% 4 7% 4 5% 5% 3 6% 7% 40%	3713
	21st to end	Night	23% 8% 2 6% 3 3 4 3 5% 5% 37%	3466
April	1st to 10th	Night	19% 7% 3 6% 5% 5% 5% 4 6% 5% 35%	1900
	11th to 20th	Night	20% 6% 3 6% 5% 4 3 4 5% 5% 39%	1875
	21st to end	Night	21% 7% 2 7% 3 4 3 3 5% 5% 40%	1772
May	1st to 10th	Night	23% 8% 3 7% 5% 5% 4 3 5% 7% 31%	1710
	11th to 20th	Night	18% 8% 2 7% 4 4 4 3 7% 7% 36%	1553
	21st to end	Night	18% 6% 3 5% 3 4 4 3 6% 8% 40%	1550
June	1st to 10th	Night	18% 7% 2 7% 3 3 4 4 6% 7% 38%	1440
	11th to 20th	Night	17% 7% 3 6% 5% 4 4 4 6% 7% 38%	1440
	21st to end	Night	12% 6% 1 7% 5% 5% 4 4 7% 9% 42%	1440
July	1st to 10th	Night	12% 6% 2 6% 5% 4 4 4 8% 10% 39%	1440
	11th to 20th	Night	13% 5% 3 8% 4 4 6% 5% 6% 9% 38%	1440
	21st to end	Night	11% 6% 3 6% 5% 4 5% 6% 6% 9% 39%	1574
August	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 4 9% 7% 43%	1512
	11th to 20th	Night	11% 7% 3 7% 5% 5% 6% 4 7% 8% 38%	1728
	21st to end	Night	15% 5% 2 5% 3 4 4 4 5% 8% 46%	1980
September	1st to 10th	Night	14% 6% 3 6% 4 3 5% 4 6% 6% 42%	1800
	11th to 20th	Night	14% 6% 2 4 3 3 3 2 4 6% 51%	1934
	21st to end	Night	17% 6% 2 6% 4 3 4 4 4 6% 44%	1980
October	1st to 10th	Night	21% 7% 2 6% 3 4 3 3 5% 5% 40%	1988
	11th to 20th	Night	17% 5% 2 5% 3 4 4 3 5% 6% 45%	2191
	21st to end	Night	23% 8% 2 6% 3 3 4 3 5% 5% 38%	2574
November	1st to 10th	Night	14% 5% 2 5% 4 3 3 4 5% 6% 48%	2407
	11th to 20th	Night	20% 7% 2 5% 3 3 3 3 5% 5% 43%	2470
	21st to end	Night	17% 7% 2 5% 4 3 4 3 5% 6% 44%	2485
December	1st to 10th	Night	21% 7% 3 6% 4 3 4 3 4 6% 38%	2660
	11th to 20th	Night	21% 7% 2 5% 4 4 4 3 4 6% 41%	3288
	21st to end	Night	23% 11% 3 6% 4 4 3 3 4 5% 35%	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	41% 4 9% 33% 11% 2	2518
	11th to 20th	Day	49% 4 10% 26% 10% 1	2520
	21st to end	Day	55% 3 9% 22% 10% 2	2806
February	1st to 10th	Day	47% 4 13% 22% 13% 2	1786
	11th to 20th	Day	44% 4 9% 24% 16% 3	1857
	21st to end	Day	49% 3 10% 22% 13% 3	1570
March	1st to 10th	Day	56% 3 11% 17% 11% 2	3119
	11th to 20th	Day	40% 7% 10% 29% 12% 2	3246
	21st to end	Day	47% 5% 5% 18% 20% 5%	4163
April	1st to 10th	Day	47% 5% 9% 22% 15% 3	2280
	11th to 20th	Day	44% 4 10% 21% 19% 3	2254
	21st to end	Day	47% 4 9% 21% 16% 4	2406
May	1st to 10th	Day	52% 4 9% 20% 13% 2	2470
	11th to 20th	Day	43% 4 10% 22% 17% 3	2448
	21st to end	Day	41% 6% 15% 22% 14% 2	2725
June	1st to 10th	Day	46% 5% 13% 24% 11% 1	2520
	11th to 20th	Day	46% 5% 12% 22% 14% 1	2520
	21st to end	Day	43% 6% 13% 22% 14% 1	2520
July	1st to 10th	Day	42% 6% 11% 21% 17% 2	2450
	11th to 20th	Day	40% 5% 15% 25% 12% 2	2445
	21st to end	Day	41% 6% 13% 21% 16% 3	2591
August	1st to 10th	Day	43% 5% 14% 24% 14% 1	2394
	11th to 20th	Day	41% 5% 15% 24% 14% 1	2170
	21st to end	Day	39% 6% 10% 25% 18% 2	2376
September	1st to 10th	Day	41% 4 11% 22% 19% 2	2160
	11th to 20th	Day	35% 4 10% 24% 24% 3	2025
	21st to end	Day	42% 4 8% 23% 21% 3	1980
October	1st to 10th	Day	47% 5% 8% 22% 14% 4	1970
	11th to 20th	Day	38% 4 12% 29% 16% 2	1767
	21st to end	Day	46% 4 10% 22% 15% 3	1782
November	1st to 10th	Day	41% 3 12% 22% 19% 3	1671
	11th to 20th	Day	41% 3 10% 24% 19% 3	1710
	21st to end	Day	43% 4 12% 26% 12% 3	1691
December	1st to 10th	Day	48% 3 13% 19% 16% 1	1520
	11th to 20th	Day	44% 3 14% 19% 18% 2	1906
	21st to end	Day	54% 3 11% 21% 10% 1	2772
January	1st to 10th	Night	41% 2 11% 32% 11% 3	4429
	11th to 20th	Night	47% 3 11% 24% 12% 3	4440
	21st to end	Night	57% 3 9% 19% 11% 1	4848
February	1st to 10th	Night	46% 4 13% 23% 12% 2	2393
	11th to 20th	Night	45% 4 9% 21% 17% 4	2220
	21st to end	Night	47% 4 8% 23% 14% 4	1884
March	1st to 10th	Night	55% 3 9% 20% 11% 2	3734
	11th to 20th	Night	42% 4 14% 24% 14% 2	3714
	21st to end	Night	49% 3 6% 14% 23% 5%	3466
April	1st to 10th	Night	49% 4 8% 20% 15% 3	1900
	11th to 20th	Night	46% 4 9% 20% 19% 1	1875
	21st to end	Night	46% 4 9% 23% 13% 5%	1772
May	1st to 10th	Night	53% 5% 11% 17% 13% 3	1710
	11th to 20th	Night	47% 5% 10% 20% 15% 3	1554
	21st to end	Night	42% 7% 17% 19% 14% 1	1551
June	1st to 10th	Night	45% 6% 12% 21% 14% 1	1440
	11th to 20th	Night	45% 4 14% 25% 11% 1	1440
	21st to end	Night	38% 7% 15% 26% 14% 1	1440
July	1st to 10th	Night	39% 7% 16% 21% 16% 1	1400
	11th to 20th	Night	42% 5% 16% 27% 8% 1	1392
	21st to end	Night	37% 7% 16% 23% 14% 2	1486
August	1st to 10th	Night	37% 6% 16% 25% 14% 2	1502
	11th to 20th	Night	42% 6% 14% 26% 11% 1	1728
	21st to end	Night	36% 4 13% 27% 18% 1	1980
September	1st to 10th	Night	41% 5% 10% 26% 17% 1	1800
	11th to 20th	Night	35% 3 11% 22% 26% 2	1934
	21st to end	Night	42% 5% 7% 22% 21% 3	1980
October	1st to 10th	Night	46% 4 10% 22% 14% 3	1988
	11th to 20th	Night	39% 4 12% 29% 15% 1	2191
	21st to end	Night	48% 3 12% 22% 14% 1	2574
November	1st to 10th	Night	38% 4 12% 23% 20% 4	2407
	11th to 20th	Night	43% 4 9% 22% 19% 3	2470
	21st to end	Night	41% 3 13% 29% 12% 1	2485
December	1st to 10th	Night	47% 4 12% 22% 14% 1	2660
	11th to 20th	Night	45% 4 13% 18% 18% 2	3288
	21st to end	Night	53% 3 9% 23% 12% 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	29% 23% 29% 16% 3	180
	11th to 20th	Day	31% 27% 27% 11% 4	180
	21st to end	Day	26% 27% 31% 9% 5% 1	209
February	1st to 10th	Day	33% 24% 27% 16% 1	346
	11th to 20th	Day	31% 25% 33% 9% 1	456
	21st to end	Day	32% 20% 32% 12% 4	382
March	1st to 10th	Day	28% 22% 32% 15% 3	460
	11th to 20th	Day	31% 23% 32% 12% 3	460
	21st to end	Day	32% 21% 30% 10% 5% 2	506
April	1st to 10th	Day	32% 23% 27% 12% 4 1	460
	11th to 20th	Day	31% 19% 29% 15% 5%	452
	21st to end	Day	30% 18% 33% 13% 5% 2	460
May	1st to 10th	Day	35% 16% 28% 12% 7% 1	463
	11th to 20th	Day	26% 16% 36% 15% 6% 1	463
	21st to end	Day	22% 14% 30% 23% 9% 2	485
June	1st to 10th	Day	20% 14% 30% 23% 10% 3	450
	11th to 20th	Day	17% 16% 38% 20% 8% 1	450
	21st to end	Day	17% 15% 31% 25% 10% 2	450
July	1st to 10th	Day	19% 7% 28% 29% 13% 3	445
	11th to 20th	Day	16% 5% 30% 33% 13% 3	444
	21st to end	Day	15% 9% 34% 31% 9% 2	488
August	1st to 10th	Day	14% 7% 31% 34% 10% 4	446
	11th to 20th	Day	14% 8% 33% 25% 15% 5%	439
	21st to end	Day	15% 9% 31% 25% 14% 6%	495
September	1st to 10th	Day	20% 11% 24% 24% 16% 4	450
	11th to 20th	Day	17% 11% 29% 24% 9% 10%	450
	21st to end	Day	21% 12% 34% 18% 10% 5%	450
October	1st to 10th	Day	32% 7% 25% 20% 11% 5%	450
	11th to 20th	Day	18% 17% 30% 26% 8% 2	433
	21st to end	Day	29% 13% 31% 19% 7% 2	396
November	1st to 10th	Day	21% 14% 30% 22% 10% 2	365
	11th to 20th	Day	30% 18% 28% 16% 8% 1	370
	21st to end	Day	26% 17% 30% 19% 6% 1	351
December	1st to 10th	Day	23% 25% 31% 16% 5%	180
	11th to 20th	Day	36% 22% 32% 9% 1	180
	21st to end	Day	28% 23% 29% 15% 3 2	198
January	1st to 10th	Night	22% 19% 39% 17% 3	760
	11th to 20th	Night	30% 19% 30% 19% 2	760
	21st to end	Night	23% 21% 34% 19% 3	836
February	1st to 10th	Night	23% 19% 34% 22% 2	760
	11th to 20th	Night	24% 22% 38% 14% 1	743
	21st to end	Night	29% 19% 34% 16% 2	628
March	1st to 10th	Night	26% 19% 34% 17% 3	760
	11th to 20th	Night	23% 20% 37% 17% 3	760
	21st to end	Night	27% 18% 35% 17% 3	836
April	1st to 10th	Night	25% 18% 34% 19% 3	760
	11th to 20th	Night	24% 18% 34% 19% 4	751
	21st to end	Night	25% 17% 34% 19% 4	632
May	1st to 10th	Night	29% 15% 30% 21% 5%	570
	11th to 20th	Night	22% 15% 37% 22% 4	468
	21st to end	Night	22% 7% 31% 32% 7% 1	389
June	1st to 10th	Night	22% 6% 32% 32% 8%	360
	11th to 20th	Night	21% 6% 30% 33% 9%	360
	21st to end	Night	15% 4 36% 37% 8% 1	360
July	1st to 10th	Night	14% 3 28% 39% 15%	350
	11th to 20th	Night	15% 2 25% 42% 15% 1	348
	21st to end	Night	12% 7% 30% 40% 10% 1	394
August	1st to 10th	Night	10% 5% 29% 43% 12% 1	438
	11th to 20th	Night	15% 3 25% 38% 17% 1	664
	21st to end	Night	16% 5% 24% 36% 17% 2	792
September	1st to 10th	Night	18% 5% 30% 35% 12% 1	720
	11th to 20th	Night	18% 7% 25% 32% 17% 2	720
	21st to end	Night	20% 7% 28% 29% 15% 2	720
October	1st to 10th	Night	26% 9% 27% 24% 12% 2	720
	11th to 20th	Night	22% 11% 30% 28% 9%	720
	21st to end	Night	29% 13% 30% 22% 6%	792
November	1st to 10th	Night	19% 11% 33% 26% 9% 1	740
	11th to 20th	Night	25% 14% 33% 21% 6% 1	760
	21st to end	Night	23% 17% 32% 22% 5%	760
December	1st to 10th	Night	28% 14% 33% 19% 5% 1	760
	11th to 20th	Night	25% 19% 31% 23% 2	760
	21st to end	Night	29% 15% 35% 19% 2	836

Page generated at 2024-05-12 00:20:37. Version ac07

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