Starhoo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starhoo Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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	18% 7% 3 5% 5% 3 4 4 5% 7% 41%	74821
	Night	18% 7% 3 5% 5% 3 4 4 5% 6% 40%	74893
Transparency	Day	44% 4 11% 23% 16% 3	74527
	Night	45% 4 11% 22% 15% 2	74721
Seeing	Day	22% 18% 33% 19% 7% 2	14027
	Night	22% 14% 33% 24% 7% 1	23021

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% 9% 3 6% 4 3 3 4 4 6% 43%	1517
	11th to 20th	Day	20% 9% 2 5% 4 2 4 4 5% 5% 39%	1454
	21st to end	Day	14% 7% 4 5% 4 4 3 4 5% 7% 43%	1584
February	1st to 10th	Day	21% 8% 3 5% 4 4 4 5% 5% 7% 36%	1720
	11th to 20th	Day	15% 8% 2 5% 4 2 4 5% 5% 6% 42%	1748
	21st to end	Day	19% 10% 4 5% 5% 3 3 4 5% 5% 38%	1480
March	1st to 10th	Day	17% 8% 3 5% 4 3 4 4 4 7% 40%	1797
	11th to 20th	Day	17% 7% 3 6% 5% 2 5% 4 6% 7% 39%	1912
	21st to end	Day	18% 10% 3 5% 4 2 3 4 4 5% 41%	2268
April	1st to 10th	Day	20% 8% 2 5% 4 3 4 4 4 6% 39%	2160
	11th to 20th	Day	18% 6% 2 5% 6% 3 4 5% 5% 7% 40%	2154
	21st to end	Day	21% 6% 3 6% 6% 3 4 4 4 6% 38%	2340
May	1st to 10th	Day	26% 9% 3 5% 5% 2 3 4 5% 6% 33%	2340
	11th to 20th	Day	20% 7% 2 4 5% 3 4 4 4 6% 41%	2301
	21st to end	Day	16% 6% 2 4 5% 2 4 4 5% 8% 44%	2706
June	1st to 10th	Day	21% 6% 2 6% 4 3 4 5% 6% 8% 34%	2520
	11th to 20th	Day	18% 5% 2 6% 5% 3 5% 5% 5% 8% 37%	2520
	21st to end	Day	15% 6% 2 4 5% 3 5% 5% 6% 10% 38%	2520
July	1st to 10th	Day	13% 6% 2 6% 5% 3 5% 5% 6% 9% 40%	2520
	11th to 20th	Day	14% 6% 3 5% 5% 3 6% 5% 6% 9% 38%	2520
	21st to end	Day	12% 4 3 6% 4 3 6% 5% 7% 9% 40%	2728
August	1st to 10th	Day	12% 5% 2 5% 6% 4 5% 6% 7% 9% 39%	2327
	11th to 20th	Day	13% 6% 2 6% 5% 3 6% 5% 6% 8% 39%	2286
	21st to end	Day	14% 5% 2 4 5% 3 5% 5% 6% 7% 43%	2376
September	1st to 10th	Day	15% 6% 3 4 5% 2 4 4 5% 7% 46%	2138
	11th to 20th	Day	15% 6% 2 4 3 3 3 3 4 6% 51%	1980
	21st to end	Day	20% 5% 2 4 4 3 3 4 4 6% 44%	1980
October	1st to 10th	Day	24% 6% 2 3 5% 2 3 4 4 5% 43%	1980
	11th to 20th	Day	17% 5% 2 4 5% 2 3 3 5% 7% 47%	1781
	21st to end	Day	19% 6% 2 5% 4 2 4 4 5% 6% 42%	1782
November	1st to 10th	Day	18% 6% 2 5% 4 2 4 4 4 5% 47%	1671
	11th to 20th	Day	18% 6% 2 4 3 2 3 4 5% 6% 46%	1710
	21st to end	Day	17% 6% 3 4 4 3 4 4 5% 7% 43%	1710
December	1st to 10th	Day	20% 7% 3 5% 5% 3 4 3 4 6% 40%	1613
	11th to 20th	Day	20% 7% 2 4 4 3 3 3 3 6% 45%	1906
	21st to end	Day	22% 10% 3 7% 6% 2 4 4 4 5% 34%	2772
January	1st to 10th	Night	17% 8% 2 5% 4 3 4 3 4 6% 45%	2649
	11th to 20th	Night	20% 11% 3 5% 5% 3 3 4 5% 6% 35%	2546
	21st to end	Night	15% 9% 4 5% 4 2 4 4 5% 6% 42%	2772
February	1st to 10th	Night	18% 9% 3 5% 5% 2 4 5% 4 5% 40%	2236
	11th to 20th	Night	19% 8% 4 5% 5% 3 4 4 5% 5% 38%	2098
	21st to end	Night	18% 7% 3 5% 5% 3 4 4 4 5% 41%	1776
March	1st to 10th	Night	17% 8% 3 4 4 3 4 4 5% 7% 42%	2150
	11th to 20th	Night	16% 8% 4 6% 5% 2 5% 4 5% 7% 39%	2047
	21st to end	Night	18% 9% 3 6% 5% 3 3 3 3 5% 41%	2084
April	1st to 10th	Night	18% 8% 4 6% 5% 3 4 4 5% 5% 38%	1800
	11th to 20th	Night	20% 7% 3 5% 5% 3 5% 4 5% 7% 38%	1753
	21st to end	Night	21% 7% 3 5% 5% 3 5% 4 4 6% 38%	1620
May	1st to 10th	Night	23% 10% 3 6% 5% 2 4 4 5% 6% 31%	1620
	11th to 20th	Night	19% 6% 3 7% 5% 2 5% 5% 5% 8% 35%	1593
	21st to end	Night	19% 7% 3 5% 5% 3 5% 4 5% 7% 37%	1583
June	1st to 10th	Night	19% 6% 3 5% 6% 3 6% 4 5% 7% 37%	1440
	11th to 20th	Night	18% 7% 3 5% 6% 3 5% 5% 4 8% 36%	1440
	21st to end	Night	17% 8% 2 4 3 3 4 4 5% 9% 40%	1440
July	1st to 10th	Night	14% 6% 3 6% 5% 2 5% 6% 5% 8% 39%	1440
	11th to 20th	Night	15% 6% 3 5% 5% 4 5% 5% 7% 9% 36%	1440
	21st to end	Night	13% 6% 3 5% 6% 3 6% 6% 7% 7% 39%	1574
August	1st to 10th	Night	9% 7% 3 4 5% 3 5% 6% 7% 9% 42%	1607
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 6% 6% 10% 38%	1610
	21st to end	Night	13% 4 2 6% 3 3 5% 4 6% 7% 46%	1980
September	1st to 10th	Night	14% 6% 3 5% 5% 4 4 5% 5% 6% 43%	1822
	11th to 20th	Night	15% 5% 2 4 4 2 3 4 3 7% 51%	1980
	21st to end	Night	18% 6% 3 4 5% 2 5% 4 5% 6% 43%	1980
October	1st to 10th	Night	22% 7% 2 5% 4 3 4 3 4 5% 41%	1980
	11th to 20th	Night	16% 5% 2 4 5% 3 3 4 6% 6% 46%	2175
	21st to end	Night	20% 9% 3 4 5% 2 5% 4 4 6% 38%	2574
November	1st to 10th	Night	16% 5% 2 5% 4 3 4 4 5% 6% 46%	2407
	11th to 20th	Night	18% 7% 2 4 4 2 4 4 4 5% 46%	2470
	21st to end	Night	17% 5% 2 4 4 2 4 4 5% 7% 46%	2470
December	1st to 10th	Night	20% 8% 2 5% 5% 3 4 4 3 5% 40%	2565
	11th to 20th	Night	20% 7% 2 4 4 3 4 4 5% 6% 41%	3288
	21st to end	Night	20% 11% 4 7% 4 2 3 3 4 5% 36%	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	43% 2 8% 27% 16% 4	1518
	11th to 20th	Day	47% 6% 12% 20% 12% 3	1454
	21st to end	Day	42% 3 10% 27% 16% 3	1584
February	1st to 10th	Day	49% 3 12% 19% 13% 3	1720
	11th to 20th	Day	43% 4 12% 22% 16% 3	1757
	21st to end	Day	49% 3 9% 21% 15% 3	1480
March	1st to 10th	Day	45% 3 12% 22% 14% 4	1800
	11th to 20th	Day	44% 3 9% 24% 16% 4	1912
	21st to end	Day	48% 4 8% 18% 17% 6%	2268
April	1st to 10th	Day	47% 3 8% 20% 18% 4	2160
	11th to 20th	Day	46% 3 8% 22% 17% 3	2154
	21st to end	Day	48% 4 9% 21% 15% 4	2340
May	1st to 10th	Day	52% 3 8% 21% 13% 2	2340
	11th to 20th	Day	45% 4 10% 19% 18% 3	2305
	21st to end	Day	40% 5% 16% 23% 14% 2	2706
June	1st to 10th	Day	48% 5% 12% 23% 11% 1	2520
	11th to 20th	Day	45% 4 12% 23% 14% 2	2520
	21st to end	Day	42% 6% 14% 23% 13% 1	2520
July	1st to 10th	Day	41% 5% 11% 25% 15% 3	2450
	11th to 20th	Day	42% 4 13% 26% 13% 2	2445
	21st to end	Day	39% 6% 13% 25% 14% 3	2575
August	1st to 10th	Day	40% 6% 15% 25% 14% 1	2314
	11th to 20th	Day	42% 6% 13% 25% 14% 1	2286
	21st to end	Day	39% 5% 11% 22% 20% 2	2376
September	1st to 10th	Day	39% 5% 10% 25% 20% 1	2138
	11th to 20th	Day	36% 4 10% 24% 23% 3	1980
	21st to end	Day	42% 4 8% 21% 23% 2	1980
October	1st to 10th	Day	45% 4 9% 23% 16% 3	1980
	11th to 20th	Day	38% 3 9% 32% 17% 1	1781
	21st to end	Day	43% 4 12% 20% 16% 4	1782
November	1st to 10th	Day	42% 4 12% 22% 18% 3	1671
	11th to 20th	Day	41% 4 10% 23% 20% 3	1710
	21st to end	Day	43% 5% 11% 26% 13% 2	1710
December	1st to 10th	Day	48% 3 13% 17% 17% 2	1613
	11th to 20th	Day	45% 3 13% 17% 16% 6%	1906
	21st to end	Day	53% 3 10% 23% 10% 1	2772
January	1st to 10th	Night	43% 2 11% 24% 16% 3	2649
	11th to 20th	Night	52% 4 12% 20% 10% 3	2546
	21st to end	Night	45% 3 9% 21% 19% 3	2772
February	1st to 10th	Night	48% 3 12% 22% 13% 2	2236
	11th to 20th	Night	48% 4 8% 21% 15% 4	2100
	21st to end	Night	46% 4 7% 24% 16% 3	1776
March	1st to 10th	Night	44% 3 9% 22% 16% 5%	2160
	11th to 20th	Night	47% 3 10% 19% 17% 4	2048
	21st to end	Night	48% 3 7% 18% 18% 6%	2084
April	1st to 10th	Night	49% 3 9% 18% 17% 4	1800
	11th to 20th	Night	47% 3 8% 21% 18% 3	1753
	21st to end	Night	49% 3 9% 20% 14% 4	1620
May	1st to 10th	Night	56% 4 9% 17% 12% 3	1620
	11th to 20th	Night	48% 5% 11% 20% 12% 4	1594
	21st to end	Night	49% 5% 14% 19% 12% 1	1584
June	1st to 10th	Night	48% 6% 12% 21% 13% 1	1440
	11th to 20th	Night	47% 4 11% 24% 14% 1	1440
	21st to end	Night	42% 5% 15% 24% 14% 1	1440
July	1st to 10th	Night	43% 6% 13% 24% 15% 1	1400
	11th to 20th	Night	43% 5% 13% 28% 10% 1	1392
	21st to end	Night	42% 5% 12% 27% 11% 3	1486
August	1st to 10th	Night	38% 5% 16% 26% 14% 2	1596
	11th to 20th	Night	41% 5% 17% 24% 12% 1	1610
	21st to end	Night	37% 4 11% 27% 20% 2	1980
September	1st to 10th	Night	41% 5% 10% 24% 18% 2	1822
	11th to 20th	Night	37% 3 10% 24% 25% 2	1980
	21st to end	Night	43% 5% 7% 23% 20% 3	1980
October	1st to 10th	Night	47% 4 9% 21% 15% 3	1980
	11th to 20th	Night	39% 3 12% 30% 15% 1	2175
	21st to end	Night	49% 4 11% 20% 14% 2	2574
November	1st to 10th	Night	41% 4 12% 23% 18% 3	2407
	11th to 20th	Night	42% 3 10% 22% 19% 4	2470
	21st to end	Night	39% 3 13% 28% 14% 3	2470
December	1st to 10th	Night	48% 3 12% 21% 15% 1	2565
	11th to 20th	Night	45% 4 13% 18% 18% 2	3288
	21st to end	Night	52% 4 8% 25% 11% 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% 29% 28% 16% 2	180
	11th to 20th	Day	23% 30% 35% 9% 2 1	164
	21st to end	Day	23% 28% 37% 9% 2 1	176
February	1st to 10th	Day	31% 23% 32% 12% 2	382
	11th to 20th	Day	27% 30% 34% 7% 2	416
	21st to end	Day	26% 29% 32% 11% 2	346
March	1st to 10th	Day	26% 24% 35% 12% 3	420
	11th to 20th	Day	24% 28% 34% 10% 4 1	420
	21st to end	Day	26% 23% 34% 11% 5% 2	462
April	1st to 10th	Day	29% 25% 28% 12% 5% 1	420
	11th to 20th	Day	24% 27% 32% 14% 3	412
	21st to end	Day	28% 19% 33% 15% 3 2	420
May	1st to 10th	Day	31% 24% 29% 12% 3 1	423
	11th to 20th	Day	22% 17% 42% 13% 6% 1	447
	21st to end	Day	19% 13% 35% 24% 8% 1	485
June	1st to 10th	Day	20% 16% 32% 23% 8% 1	450
	11th to 20th	Day	16% 18% 40% 19% 6% 2	450
	21st to end	Day	16% 13% 37% 26% 6% 2	450
July	1st to 10th	Day	15% 9% 31% 32% 11% 2	445
	11th to 20th	Day	14% 8% 31% 32% 13% 2	444
	21st to end	Day	12% 12% 35% 30% 11% 1	488
August	1st to 10th	Day	13% 9% 35% 31% 11% 2	446
	11th to 20th	Day	14% 11% 31% 28% 13% 3	439
	21st to end	Day	15% 9% 32% 26% 12% 5%	495
September	1st to 10th	Day	19% 9% 31% 24% 14% 3	450
	11th to 20th	Day	18% 13% 30% 24% 10% 6%	450
	21st to end	Day	24% 12% 29% 23% 7% 5%	450
October	1st to 10th	Day	27% 13% 26% 20% 8% 5%	450
	11th to 20th	Day	19% 16% 34% 20% 11% 1	395
	21st to end	Day	25% 19% 29% 19% 6% 3	396
November	1st to 10th	Day	19% 18% 34% 18% 9% 2	365
	11th to 20th	Day	27% 22% 31% 15% 5% 1	370
	21st to end	Day	22% 23% 30% 16% 9%	370
December	1st to 10th	Day	21% 25% 36% 14% 4	273
	11th to 20th	Day	30% 28% 32% 8% 2	180
	21st to end	Day	26% 25% 35% 9% 4 2	198
January	1st to 10th	Night	22% 20% 37% 18% 3	760
	11th to 20th	Night	28% 20% 34% 14% 3	728
	21st to end	Night	22% 20% 35% 19% 3	792
February	1st to 10th	Night	26% 18% 38% 18% 1	720
	11th to 20th	Night	26% 21% 39% 13% 1	703
	21st to end	Night	24% 22% 34% 17% 2	592
March	1st to 10th	Night	24% 19% 35% 19% 3	720
	11th to 20th	Night	21% 20% 39% 17% 4	720
	21st to end	Night	24% 19% 35% 18% 3	792
April	1st to 10th	Night	24% 18% 35% 19% 4	720
	11th to 20th	Night	23% 18% 36% 20% 3	689
	21st to end	Night	24% 16% 36% 20% 4	540
May	1st to 10th	Night	29% 14% 33% 19% 4	540
	11th to 20th	Night	22% 14% 40% 19% 4	532
	21st to end	Night	23% 7% 32% 31% 6%	422
June	1st to 10th	Night	19% 8% 30% 33% 9% 1	360
	11th to 20th	Night	21% 6% 33% 32% 8%	360
	21st to end	Night	20% 6% 29% 38% 7%	360
July	1st to 10th	Night	15% 4 30% 40% 10% 1	350
	11th to 20th	Night	16% 5% 26% 43% 10%	348
	21st to end	Night	14% 4 28% 44% 10%	394
August	1st to 10th	Night	11% 6% 34% 40% 9%	533
	11th to 20th	Night	15% 6% 27% 41% 11%	546
	21st to end	Night	14% 5% 24% 39% 16% 2	792
September	1st to 10th	Night	15% 5% 31% 35% 13% 1	720
	11th to 20th	Night	17% 8% 26% 30% 17% 3	720
	21st to end	Night	22% 6% 28% 29% 13% 2	720
October	1st to 10th	Night	25% 9% 27% 26% 12% 2	720
	11th to 20th	Night	18% 11% 34% 24% 12% 1	720
	21st to end	Night	25% 13% 35% 19% 7% 1	792
November	1st to 10th	Night	18% 14% 32% 25% 10% 1	740
	11th to 20th	Night	21% 22% 33% 18% 7% 1	760
	21st to end	Night	20% 21% 34% 21% 4 1	760
December	1st to 10th	Night	25% 18% 34% 18% 4	760
	11th to 20th	Night	24% 20% 33% 20% 3	760
	21st to end	Night	26% 19% 34% 19% 2	836

Page generated at 2024-01-09 16:24:21. Version ac07

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