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 2024-01-13.

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% 6% 3 5% 5% 3 4 5% 5% 7% 40%	74793
	Night	18% 7% 3 5% 5% 3 4 4 5% 6% 40%	74929
Transparency	Day	44% 4 11% 23% 15% 2	74498
	Night	44% 4 11% 23% 15% 2	74758
Seeing	Day	24% 16% 31% 20% 8% 2	13893
	Night	23% 13% 32% 25% 7% 1	23016

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% 6% 3 4 5% 3 5% 4 5% 8% 42%	1517
	11th to 20th	Day	19% 7% 3 5% 5% 3 4 6% 7% 7% 35%	1456
	21st to end	Day	15% 8% 1 5% 4 3 4 5% 6% 7% 42%	1604
February	1st to 10th	Day	20% 7% 3 5% 4 4 5% 6% 6% 7% 34%	1692
	11th to 20th	Day	15% 7% 3 6% 6% 3 6% 4 4 7% 40%	1748
	21st to end	Day	21% 9% 3 5% 4 3 4 5% 5% 6% 36%	1480
March	1st to 10th	Day	16% 6% 3 5% 5% 3 4 4 5% 7% 42%	1797
	11th to 20th	Day	17% 6% 2 5% 6% 4 5% 5% 6% 7% 38%	1844
	21st to end	Day	20% 7% 3 5% 6% 3 3 4 4 6% 40%	2373
April	1st to 10th	Day	19% 6% 3 6% 4 3 4 4 5% 8% 37%	2160
	11th to 20th	Day	19% 6% 2 5% 4 2 4 4 5% 6% 43%	2134
	21st to end	Day	21% 5% 2 5% 5% 4 5% 4 4 7% 38%	2279
May	1st to 10th	Day	24% 7% 4 5% 5% 4 4 4 5% 6% 32%	2340
	11th to 20th	Day	19% 5% 2 5% 4 2 4 4 5% 8% 40%	2392
	21st to end	Day	15% 6% 3 4 5% 2 5% 4 5% 8% 43%	2725
June	1st to 10th	Day	18% 6% 3 5% 5% 4 5% 5% 6% 9% 35%	2520
	11th to 20th	Day	15% 6% 4 6% 6% 3 5% 5% 5% 8% 36%	2520
	21st to end	Day	13% 7% 3 6% 5% 3 5% 5% 6% 9% 37%	2520
July	1st to 10th	Day	13% 6% 3 5% 6% 4 6% 5% 6% 8% 40%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 6% 5% 6% 10% 39%	2520
	21st to end	Day	13% 5% 2 5% 6% 4 5% 5% 6% 10% 38%	2744
August	1st to 10th	Day	11% 7% 2 6% 7% 4 5% 6% 8% 10% 35%	2408
	11th to 20th	Day	11% 6% 3 6% 6% 3 5% 5% 6% 8% 40%	2170
	21st to end	Day	12% 5% 2 6% 5% 3 5% 5% 6% 7% 44%	2376
September	1st to 10th	Day	14% 6% 3 4 6% 3 4 5% 5% 6% 44%	2160
	11th to 20th	Day	14% 6% 2 4 3 2 3 5% 4 6% 50%	2025
	21st to end	Day	18% 5% 2 5% 4 2 4 5% 5% 7% 43%	1980
October	1st to 10th	Day	23% 7% 3 5% 4 3 4 4 4 5% 39%	1970
	11th to 20th	Day	15% 6% 2 5% 4 3 4 4 5% 8% 45%	1767
	21st to end	Day	20% 6% 3 5% 5% 3 3 4 5% 7% 39%	1782
November	1st to 10th	Day	14% 6% 2 6% 5% 2 4 4 4 6% 47%	1671
	11th to 20th	Day	21% 5% 2 4 4 2 4 3 5% 6% 45%	1710
	21st to end	Day	17% 7% 2 6% 5% 3 4 4 4 6% 43%	1691
December	1st to 10th	Day	19% 8% 2 5% 6% 2 4 5% 5% 6% 37%	1520
	11th to 20th	Day	23% 6% 2 4 3 2 4 4 4 5% 44%	1906
	21st to end	Day	22% 10% 4 7% 5% 3 4 3 5% 6% 32%	2772
January	1st to 10th	Night	16% 8% 2 5% 5% 3 4 4 5% 7% 43%	2649
	11th to 20th	Night	21% 8% 3 6% 5% 3 3 4 5% 6% 36%	2549
	21st to end	Night	15% 8% 4 6% 4 2 4 4 5% 6% 43%	2750
February	1st to 10th	Night	18% 9% 4 5% 6% 2 4 4 5% 6% 38%	2267
	11th to 20th	Night	16% 8% 3 6% 5% 3 5% 4 5% 7% 38%	2098
	21st to end	Night	19% 8% 2 6% 5% 3 4 4 5% 5% 39%	1776
March	1st to 10th	Night	17% 7% 2 5% 5% 3 4 4 5% 7% 40%	2150
	11th to 20th	Night	17% 6% 4 5% 5% 3 5% 4 5% 7% 38%	2115
	21st to end	Night	19% 7% 3 5% 4 2 4 4 4 6% 41%	1980
April	1st to 10th	Night	19% 6% 3 5% 6% 3 5% 5% 6% 6% 37%	1800
	11th to 20th	Night	19% 6% 3 5% 5% 3 4 4 4 6% 40%	1775
	21st to end	Night	22% 7% 3 7% 4 2 4 4 4 5% 39%	1679
May	1st to 10th	Night	23% 8% 3 5% 6% 4 4 5% 5% 6% 31%	1620
	11th to 20th	Night	18% 7% 2 7% 5% 3 4 4 6% 7% 37%	1516
	21st to end	Night	18% 5% 3 5% 3 3 5% 4 6% 8% 40%	1550
June	1st to 10th	Night	18% 6% 3 6% 4 3 4 6% 5% 8% 38%	1440
	11th to 20th	Night	17% 6% 3 6% 6% 3 5% 4 6% 7% 38%	1440
	21st to end	Night	12% 6% 2 6% 5% 3 4 4 7% 9% 42%	1440
July	1st to 10th	Night	12% 5% 3 6% 5% 3 4 5% 8% 10% 39%	1440
	11th to 20th	Night	13% 5% 3 7% 6% 3 5% 7% 6% 9% 38%	1440
	21st to end	Night	11% 5% 3 5% 6% 3 5% 7% 6% 9% 40%	1574
August	1st to 10th	Night	10% 5% 2 5% 6% 3 5% 5% 8% 8% 43%	1512
	11th to 20th	Night	11% 6% 3 7% 5% 4 5% 6% 6% 8% 38%	1728
	21st to end	Night	15% 4 2 4 4 3 5% 4 5% 8% 46%	1980
September	1st to 10th	Night	14% 5% 3 6% 5% 2 5% 4 6% 7% 43%	1800
	11th to 20th	Night	14% 5% 2 4 4 2 3 3 4 6% 52%	1934
	21st to end	Night	17% 6% 2 5% 4 2 4 4 4 6% 44%	1980
October	1st to 10th	Night	21% 7% 2 5% 4 3 3 3 5% 6% 41%	1988
	11th to 20th	Night	17% 5% 2 5% 4 3 4 4 5% 6% 45%	2191
	21st to end	Night	23% 7% 2 5% 4 2 4 4 5% 5% 38%	2574
November	1st to 10th	Night	15% 5% 3 4 5% 2 3 4 5% 6% 48%	2407
	11th to 20th	Night	20% 6% 3 4 4 2 4 4 5% 5% 44%	2470
	21st to end	Night	17% 7% 2 5% 4 3 4 4 5% 6% 44%	2485
December	1st to 10th	Night	21% 7% 3 6% 4 2 4 4 4 6% 38%	2660
	11th to 20th	Night	21% 6% 2 5% 4 3 4 4 4 6% 41%	3288
	21st to end	Night	23% 10% 3 5% 5% 3 3 3 4 4 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 10% 29% 13% 3	1518
	11th to 20th	Day	47% 5% 14% 20% 12% 2	1456
	21st to end	Day	40% 5% 11% 26% 15% 3	1604
February	1st to 10th	Day	49% 4 13% 21% 13% 2	1692
	11th to 20th	Day	45% 4 10% 23% 15% 3	1757
	21st to end	Day	50% 3 9% 21% 14% 3	1480
March	1st to 10th	Day	44% 3 12% 23% 14% 4	1800
	11th to 20th	Day	46% 4 9% 24% 14% 3	1844
	21st to end	Day	48% 3 7% 19% 18% 5%	2373
April	1st to 10th	Day	46% 5% 9% 22% 15% 4	2160
	11th to 20th	Day	43% 4 9% 22% 19% 3	2134
	21st to end	Day	48% 4 9% 20% 15% 4	2279
May	1st to 10th	Day	52% 4 8% 20% 13% 2	2340
	11th to 20th	Day	43% 5% 10% 22% 17% 3	2396
	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% 3 11% 25% 16% 3	2649
	11th to 20th	Night	51% 4 12% 20% 10% 2	2549
	21st to end	Night	42% 3 11% 23% 19% 3	2750
February	1st to 10th	Night	48% 4 12% 21% 12% 2	2267
	11th to 20th	Night	46% 4 10% 21% 15% 4	2100
	21st to end	Night	47% 4 7% 23% 15% 4	1776
March	1st to 10th	Night	44% 4 11% 23% 15% 3	2160
	11th to 20th	Night	46% 4 9% 22% 15% 3	2116
	21st to end	Night	45% 3 8% 19% 19% 5%	1980
April	1st to 10th	Night	49% 4 8% 21% 15% 3	1800
	11th to 20th	Night	45% 4 9% 21% 19% 1	1775
	21st to end	Night	47% 4 9% 22% 13% 5%	1679
May	1st to 10th	Night	53% 5% 10% 17% 13% 3	1620
	11th to 20th	Night	46% 5% 10% 20% 16% 3	1517
	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	29% 27% 28% 11% 5%	164
	21st to end	Day	24% 30% 32% 10% 4 1	186
February	1st to 10th	Day	35% 23% 25% 15% 1	312
	11th to 20th	Day	31% 25% 34% 8% 1	416
	21st to end	Day	32% 22% 32% 12% 3	346
March	1st to 10th	Day	26% 23% 33% 15% 3	420
	11th to 20th	Day	30% 24% 32% 11% 3	420
	21st to end	Day	32% 21% 30% 11% 5% 2	462
April	1st to 10th	Day	31% 23% 29% 12% 4 1	420
	11th to 20th	Day	29% 19% 30% 16% 5%	412
	21st to end	Day	32% 18% 33% 12% 4 1	420
May	1st to 10th	Day	36% 15% 29% 11% 7% 1	423
	11th to 20th	Day	26% 16% 37% 15% 6% 1	447
	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% 18% 30% 19% 2	729
	21st to end	Night	22% 21% 34% 20% 3	792
February	1st to 10th	Night	24% 19% 33% 21% 2	720
	11th to 20th	Night	25% 21% 38% 15% 1	703
	21st to end	Night	28% 20% 34% 16% 2	592
March	1st to 10th	Night	25% 20% 35% 17% 3	720
	11th to 20th	Night	24% 20% 36% 17% 3	720
	21st to end	Night	26% 18% 35% 18% 4	792
April	1st to 10th	Night	25% 18% 33% 20% 3	720
	11th to 20th	Night	23% 19% 33% 20% 4	711
	21st to end	Night	26% 18% 33% 20% 4 1	599
May	1st to 10th	Night	30% 14% 30% 21% 5%	540
	11th to 20th	Night	22% 15% 37% 21% 5%	455
	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 2024-01-10 01:25:01. Version ac07

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