StarHub Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the StarHub Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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	13% 6% 3 6% 5% 3 5% 5% 6% 8% 42%	74586
	Night	13% 6% 2 5% 5% 3 4 4 5% 8% 45%	75157
Transparency	Day	40% 7% 12% 20% 17% 4	74307
	Night	38% 7% 12% 20% 19% 5%	74955
Seeing	Day	16% 9% 23% 25% 19% 9%	14280
	Night	15% 7% 25% 34% 17% 2	24374

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% 7% 1 5% 5% 3 4 4 4 6% 49%	1706
	11th to 20th	Day	16% 5% 3 5% 4 3 4 5% 3 5% 46%	1656
	21st to end	Day	17% 6% 2 5% 4 3 5% 4 4 5% 47%	1782
February	1st to 10th	Day	16% 6% 4 6% 5% 3 4 3 4 5% 43%	1620
	11th to 20th	Day	20% 5% 2 5% 4 2 3 3 4 5% 46%	1674
	21st to end	Day	17% 6% 2 6% 5% 3 4 4 5% 6% 41%	1528
March	1st to 10th	Day	13% 6% 2 5% 4 2 3 4 5% 6% 52%	1980
	11th to 20th	Day	16% 7% 3 6% 4 3 4 4 5% 7% 43%	1980
	21st to end	Day	16% 6% 4 5% 6% 3 4 4 4 6% 42%	2178
April	1st to 10th	Day	11% 4 2 3 4 3 4 4 5% 6% 53%	2152
	11th to 20th	Day	9% 4 2 4 5% 3 4 4 6% 8% 50%	2134
	21st to end	Day	10% 5% 2 5% 5% 3 5% 5% 5% 7% 49%	2160
May	1st to 10th	Day	11% 5% 3 5% 5% 3 5% 6% 7% 9% 42%	2178
	11th to 20th	Day	14% 6% 3 6% 6% 3 6% 5% 6% 7% 38%	2301
	21st to end	Day	10% 6% 2 5% 6% 4 6% 6% 8% 11% 36%	2531
June	1st to 10th	Day	10% 5% 3 7% 7% 4 6% 5% 7% 9% 36%	2502
	11th to 20th	Day	9% 4 3 5% 6% 3 6% 5% 8% 10% 40%	2520
	21st to end	Day	8% 5% 3 5% 7% 4 7% 7% 8% 10% 36%	2397
July	1st to 10th	Day	9% 5% 2 7% 8% 4 7% 7% 9% 12% 33%	2340
	11th to 20th	Day	10% 5% 3 6% 8% 3 7% 7% 8% 9% 33%	2340
	21st to end	Day	7% 5% 3 7% 7% 5% 7% 7% 9% 11% 32%	2547
August	1st to 10th	Day	12% 6% 3 7% 8% 4 6% 6% 8% 11% 29%	2327
	11th to 20th	Day	11% 7% 3 7% 7% 4 6% 7% 7% 10% 31%	2141
	21st to end	Day	12% 6% 2 7% 7% 4 6% 7% 8% 10% 31%	2376
September	1st to 10th	Day	11% 5% 3 6% 7% 4 5% 7% 7% 8% 38%	2160
	11th to 20th	Day	13% 7% 3 6% 6% 4 5% 5% 4 8% 40%	2158
	21st to end	Day	17% 8% 4 8% 5% 3 4 4 5% 6% 35%	1878
October	1st to 10th	Day	16% 5% 3 5% 4 3 4 5% 4 7% 46%	1800
	11th to 20th	Day	13% 6% 2 4 4 1 4 5% 4 5% 52%	1800
	21st to end	Day	12% 4 3 5% 4 3 4 3 4 4 54%	1980
November	1st to 10th	Day	13% 6% 2 5% 4 2 3 3 4 6% 51%	1857
	11th to 20th	Day	16% 5% 2 4 4 2 4 3 4 5% 50%	1824
	21st to end	Day	13% 6% 2 5% 4 2 3 2 6% 6% 52%	1639
December	1st to 10th	Day	16% 6% 3 5% 5% 3 6% 4 5% 6% 40%	1520
	11th to 20th	Day	17% 6% 2 4 3 2 2 3 3 5% 53%	1910
	21st to end	Day	15% 7% 3 6% 5% 3 3 3 5% 7% 43%	3010
January	1st to 10th	Night	14% 7% 4 5% 4 3 4 4 4 6% 46%	2459
	11th to 20th	Night	14% 6% 2 7% 6% 3 5% 4 4 6% 43%	2399
	21st to end	Night	17% 6% 2 4 4 2 3 3 5% 6% 48%	2574
February	1st to 10th	Night	19% 7% 3 5% 4 2 4 4 4 6% 43%	2340
	11th to 20th	Night	19% 8% 2 5% 4 3 3 4 4 5% 43%	2170
	21st to end	Night	17% 5% 3 4 4 4 4 4 5% 6% 45%	1724
March	1st to 10th	Night	13% 4 2 4 5% 3 3 4 4 6% 53%	1980
	11th to 20th	Night	16% 6% 2 5% 5% 3 4 4 6% 8% 39%	1980
	21st to end	Night	14% 6% 3 4 4 3 4 5% 5% 7% 44%	2178
April	1st to 10th	Night	12% 5% 2 5% 5% 3 4 3 6% 7% 48%	1806
	11th to 20th	Night	10% 5% 2 5% 4 3 5% 4 6% 7% 49%	1775
	21st to end	Night	11% 4 1 4 4 2 4 5% 5% 9% 52%	1800
May	1st to 10th	Night	10% 5% 3 6% 5% 3 5% 5% 6% 8% 46%	1796
	11th to 20th	Night	13% 5% 2 6% 6% 3 5% 5% 6% 10% 39%	1592
	21st to end	Night	9% 5% 2 4 5% 3 5% 5% 8% 10% 45%	1744
June	1st to 10th	Night	9% 5% 2 5% 6% 4 5% 6% 7% 10% 40%	1450
	11th to 20th	Night	9% 5% 3 5% 6% 3 6% 5% 7% 12% 38%	1440
	21st to end	Night	8% 5% 3 6% 6% 4 6% 7% 8% 10% 36%	1553
July	1st to 10th	Night	8% 5% 3 6% 6% 4 5% 7% 6% 12% 37%	1620
	11th to 20th	Night	6% 4 2 4 5% 4 5% 7% 8% 13% 40%	1620
	21st to end	Night	7% 5% 3 6% 6% 4 6% 6% 7% 13% 37%	1771
August	1st to 10th	Night	9% 7% 3 6% 6% 3 6% 6% 7% 11% 34%	1611
	11th to 20th	Night	11% 6% 3 7% 7% 4 6% 6% 6% 11% 32%	1740
	21st to end	Night	11% 5% 3 6% 6% 4 5% 5% 8% 11% 37%	1980
September	1st to 10th	Night	11% 5% 2 4 5% 4 5% 5% 6% 10% 43%	1800
	11th to 20th	Night	14% 5% 2 5% 6% 3 5% 5% 6% 8% 42%	1800
	21st to end	Night	18% 7% 3 6% 7% 3 5% 4 5% 7% 35%	2078
October	1st to 10th	Night	14% 6% 2 4 3 2 3 5% 5% 7% 49%	2160
	11th to 20th	Night	14% 4 2 4 4 3 4 3 4 6% 52%	2160
	21st to end	Night	11% 4 2 4 4 2 4 4 4 5% 55%	2376
November	1st to 10th	Night	13% 6% 2 4 4 3 3 3 3 6% 52%	2221
	11th to 20th	Night	14% 7% 2 5% 4 2 3 3 4 5% 50%	2351
	21st to end	Night	13% 4 2 5% 4 2 4 4 4 7% 51%	2536
December	1st to 10th	Night	16% 7% 3 6% 4 3 4 4 5% 7% 42%	2660
	11th to 20th	Night	17% 6% 2 5% 3 2 4 4 3 5% 48%	3285
	21st to end	Night	14% 7% 2 5% 4 2 4 4 5% 6% 47%	4628

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	38% 4 10% 20% 20% 7%	1707
	11th to 20th	Day	41% 5% 8% 17% 23% 5%	1656
	21st to end	Day	40% 4 6% 19% 23% 8%	1782
February	1st to 10th	Day	43% 4 10% 20% 18% 5%	1620
	11th to 20th	Day	42% 3 8% 18% 23% 6%	1683
	21st to end	Day	44% 5% 10% 18% 16% 7%	1528
March	1st to 10th	Day	35% 4 9% 20% 24% 7%	1980
	11th to 20th	Day	42% 6% 8% 19% 19% 6%	1980
	21st to end	Day	44% 6% 9% 18% 19% 5%	2178
April	1st to 10th	Day	32% 5% 8% 23% 24% 8%	2152
	11th to 20th	Day	32% 5% 11% 23% 21% 8%	2134
	21st to end	Day	35% 7% 11% 22% 21% 5%	2160
May	1st to 10th	Day	37% 8% 15% 21% 17% 3	2178
	11th to 20th	Day	44% 8% 13% 21% 13% 2	2305
	21st to end	Day	39% 10% 16% 22% 12% 1	2531
June	1st to 10th	Day	43% 9% 15% 19% 13% 1	2502
	11th to 20th	Day	38% 9% 17% 21% 13% 2	2520
	21st to end	Day	40% 11% 16% 19% 11% 2	2397
July	1st to 10th	Day	40% 12% 17% 18% 11% 2	2275
	11th to 20th	Day	42% 12% 18% 20% 7% 1	2271
	21st to end	Day	41% 11% 19% 22% 6% 1	2405
August	1st to 10th	Day	45% 12% 19% 16% 7%	2314
	11th to 20th	Day	45% 11% 15% 19% 9% 1	2141
	21st to end	Day	45% 10% 16% 18% 9% 2	2376
September	1st to 10th	Day	41% 11% 14% 17% 14% 3	2160
	11th to 20th	Day	44% 5% 12% 17% 19% 4	2158
	21st to end	Day	49% 6% 9% 18% 16% 3	1878
October	1st to 10th	Day	40% 5% 9% 21% 22% 3	1800
	11th to 20th	Day	34% 4 9% 25% 22% 6%	1800
	21st to end	Day	34% 5% 6% 19% 29% 7%	1980
November	1st to 10th	Day	36% 4 7% 19% 27% 8%	1857
	11th to 20th	Day	37% 4 7% 19% 26% 7%	1824
	21st to end	Day	34% 4 7% 25% 24% 6%	1639
December	1st to 10th	Day	44% 5% 11% 21% 14% 5%	1520
	11th to 20th	Day	36% 3 6% 25% 21% 9%	1906
	21st to end	Day	42% 4 9% 21% 22% 2	3010
January	1st to 10th	Night	41% 4 9% 17% 24% 6%	2459
	11th to 20th	Night	43% 6% 8% 19% 18% 6%	2399
	21st to end	Night	39% 3 6% 21% 24% 7%	2574
February	1st to 10th	Night	43% 4 8% 19% 19% 7%	2340
	11th to 20th	Night	43% 4 9% 17% 19% 7%	2172
	21st to end	Night	41% 5% 9% 18% 19% 8%	1724
March	1st to 10th	Night	34% 4 9% 23% 23% 8%	1980
	11th to 20th	Night	41% 7% 11% 17% 18% 5%	1980
	21st to end	Night	39% 7% 11% 21% 18% 5%	2178
April	1st to 10th	Night	35% 6% 11% 17% 24% 7%	1806
	11th to 20th	Night	33% 7% 11% 22% 20% 7%	1775
	21st to end	Night	30% 6% 14% 27% 18% 4	1800
May	1st to 10th	Night	35% 8% 14% 23% 16% 4	1796
	11th to 20th	Night	40% 10% 13% 21% 15% 1	1593
	21st to end	Night	32% 11% 19% 25% 12% 1	1745
June	1st to 10th	Night	36% 11% 18% 22% 11% 2	1450
	11th to 20th	Night	37% 10% 17% 23% 11% 1	1440
	21st to end	Night	39% 11% 17% 21% 11% 1	1553
July	1st to 10th	Night	37% 13% 19% 19% 10% 2	1575
	11th to 20th	Night	32% 13% 24% 23% 7% 1	1566
	21st to end	Night	36% 11% 22% 24% 6% 1	1672
August	1st to 10th	Night	41% 10% 25% 19% 5%	1600
	11th to 20th	Night	44% 11% 19% 17% 8% 1	1740
	21st to end	Night	39% 12% 19% 20% 8% 3	1980
September	1st to 10th	Night	36% 10% 18% 17% 15% 4	1800
	11th to 20th	Night	39% 9% 12% 20% 17% 3	1800
	21st to end	Night	48% 6% 10% 19% 14% 2	2078
October	1st to 10th	Night	35% 7% 9% 21% 25% 4	2160
	11th to 20th	Night	34% 4 10% 21% 24% 7%	2160
	21st to end	Night	31% 5% 8% 22% 26% 8%	2376
November	1st to 10th	Night	36% 4 6% 20% 27% 7%	2221
	11th to 20th	Night	38% 4 8% 15% 26% 9%	2351
	21st to end	Night	34% 4 7% 22% 26% 7%	2536
December	1st to 10th	Night	43% 5% 12% 17% 18% 5%	2660
	11th to 20th	Night	39% 4 8% 19% 24% 7%	3288
	21st to end	Night	38% 4 8% 23% 24% 3	4628

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	19% 24% 40% 11% 6%	270
	11th to 20th	Day	17% 23% 33% 24% 4	252
	21st to end	Day	25% 19% 33% 17% 6%	264
February	1st to 10th	Day	21% 17% 40% 18% 3 1	240
	11th to 20th	Day	30% 14% 34% 18% 4	342
	21st to end	Day	21% 14% 36% 22% 7%	346
March	1st to 10th	Day	17% 15% 34% 24% 8% 1	420
	11th to 20th	Day	22% 18% 35% 17% 7% 1	420
	21st to end	Day	18% 16% 29% 24% 10% 2	462
April	1st to 10th	Day	19% 17% 28% 24% 10% 4	420
	11th to 20th	Day	13% 12% 30% 26% 13% 6%	412
	21st to end	Day	14% 10% 30% 25% 18% 3	420
May	1st to 10th	Day	16% 11% 33% 21% 14% 5%	423
	11th to 20th	Day	16% 6% 18% 31% 21% 8%	447
	21st to end	Day	15% 3 16% 29% 23% 13%	485
June	1st to 10th	Day	13% 1 19% 32% 27% 8%	450
	11th to 20th	Day	12% 4 14% 27% 23% 19%	450
	21st to end	Day	9% 3 15% 30% 27% 17%	450
July	1st to 10th	Day	11% 2 9% 29% 31% 19%	445
	11th to 20th	Day	10% 2 9% 25% 38% 16%	444
	21st to end	Day	6% 2 13% 31% 36% 12%	488
August	1st to 10th	Day	14% 4 12% 24% 28% 19%	446
	11th to 20th	Day	13% 2 13% 21% 30% 21%	439
	21st to end	Day	12% 3 9% 27% 29% 20%	495
September	1st to 10th	Day	12% 3 14% 26% 25% 21%	450
	11th to 20th	Day	17% 4 12% 28% 26% 14%	450
	21st to end	Day	20% 4 21% 23% 23% 10%	450
October	1st to 10th	Day	18% 5% 21% 22% 22% 12%	450
	11th to 20th	Day	13% 8% 22% 31% 19% 6%	450
	21st to end	Day	13% 8% 25% 31% 18% 5%	495
November	1st to 10th	Day	18% 9% 26% 29% 14% 4	455
	11th to 20th	Day	18% 9% 31% 30% 10% 2	424
	21st to end	Day	15% 11% 27% 27% 17% 2	299
December	1st to 10th	Day	21% 11% 39% 19% 10% 1	180
	11th to 20th	Day	17% 16% 33% 21% 11% 3	180
	21st to end	Day	17% 17% 36% 18% 10% 3	267
January	1st to 10th	Night	19% 15% 30% 29% 6%	760
	11th to 20th	Night	17% 13% 31% 32% 7%	739
	21st to end	Night	20% 10% 39% 27% 4	792
February	1st to 10th	Night	21% 12% 32% 29% 6%	720
	11th to 20th	Night	23% 15% 37% 23% 2	703
	21st to end	Night	18% 14% 35% 29% 4	592
March	1st to 10th	Night	15% 11% 38% 30% 6%	720
	11th to 20th	Night	18% 12% 37% 26% 7% 1	720
	21st to end	Night	17% 11% 35% 31% 7%	792
April	1st to 10th	Night	14% 13% 36% 31% 5%	720
	11th to 20th	Night	12% 10% 35% 32% 11%	711
	21st to end	Night	14% 6% 34% 37% 9% 1	720
May	1st to 10th	Night	12% 9% 31% 38% 10%	716
	11th to 20th	Night	15% 4 23% 41% 17%	531
	21st to end	Night	11% 2 13% 40% 32% 3	584
June	1st to 10th	Night	9% 1 21% 48% 20% 1	370
	11th to 20th	Night	9% 3 12% 47% 26% 3	360
	21st to end	Night	8% 2 15% 41% 32% 2	473
July	1st to 10th	Night	9% 2 9% 40% 35% 5%	525
	11th to 20th	Night	7% 2 7% 35% 43% 6%	522
	21st to end	Night	9% 1 11% 45% 32% 2	591
August	1st to 10th	Night	13% 1 7% 37% 38% 4	537
	11th to 20th	Night	13% 2 9% 34% 36% 5%	676
	21st to end	Night	13% 1 9% 31% 38% 7%	792
September	1st to 10th	Night	13% 1 10% 32% 37% 7%	720
	11th to 20th	Night	16% 1 14% 35% 31% 3	720
	21st to end	Night	22% 3 15% 34% 24% 2	720
October	1st to 10th	Night	17% 3 17% 31% 28% 4	720
	11th to 20th	Night	15% 6% 23% 33% 20% 2	720
	21st to end	Night	14% 5% 25% 36% 17% 3	792
November	1st to 10th	Night	16% 5% 23% 36% 17% 3	740
	11th to 20th	Night	19% 8% 26% 33% 13% 2	760
	21st to end	Night	16% 8% 28% 34% 14% 2	760
December	1st to 10th	Night	20% 8% 29% 35% 7%	760
	11th to 20th	Night	18% 8% 29% 35% 9%	760
	21st to end	Night	17% 12% 29% 33% 9%	836

Page generated at 2024-01-12 07:31:50. Version ac07

Copyright 2024 Attilla Danko