Heaven Sent Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heaven Sent Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
68%
16353
18%
47165
16%
16313
70%
16313
29%
30245

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
62%
718
17%
2327
16%
716
66%
716
28%
1429
January16th to endNight
60%
768
25%
2443
23%
768
65%
768
32%
1404
February1st to 15thNight
59%
701
26%
2092
22%
699
64%
699
35%
1226
February16th to endNight
67%
631
31%
1735
24%
631
73%
631
45%
965
March1st to 15thNight
63%
720
24%
1980
18%
720
68%
720
40%
1160
March16th to endNight
67%
768
25%
2112
22%
768
70%
768
43%
1200
April1st to 15thNight
77%
718
24%
1976
21%
718
79%
718
48%
1069
April16th to endNight
69%
720
25%
1819
17%
720
72%
720
42%
1084
May1st to 15thNight
78%
719
24%
1799
16%
719
79%
719
51%
1009
May16th to endNight
72%
622
15%
1744
12%
622
72%
622
28%
1167
June1st to 15thNight
63%
540
9%
1620
8%
540
63%
540
15%
1238
June16th to endNight
79%
540
7%
1620
7%
540
79%
540
22%
1148
July1st to 15thNight
78%
510
4%
1530
4%
510
78%
510
21%
1067
July16th to endNight
82%
564
10%
1595
10%
531
83%
531
29%
1022
August1st to 15thNight
78%
617
9%
1687
8%
614
78%
614
26%
1147
August16th to endNight
69%
764
6%
2057
5%
764
69%
764
20%
1505
September1st to 15thNight
70%
720
5%
1980
5%
720
70%
720
17%
1526
September16th to endNight
66%
717
6%
1980
6%
717
66%
717
16%
1539
October1st to 15thNight
69%
684
12%
1975
14%
684
69%
684
21%
1415
October16th to endNight
60%
704
17%
2112
17%
704
62%
704
23%
1444
November1st to 15thNight
64%
700
24%
2101
23%
700
67%
700
30%
1299
November16th to endNight
62%
720
25%
2160
24%
720
66%
720
30%
1360
December1st to 15thNight
62%
720
22%
2225
21%
720
66%
720
27%
1406
December16th to endNight
69%
768
24%
2496
26%
768
72%
768
34%
1416

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 ForecastData
Points
Cloud CoverDay
8%6%37%8%5%7%7%7%9%27%
48009
Night
6%425%5%36%6%7%11%42%
47371
TransparencyDay
46%11%14%15%9%2
47710
Night
34%10%19%21%11%2
47174
SeeingDay
9%111%23%28%26%
6160
Night
7%111%30%32%15%
16361

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
11%6%37%6%45%5%6%11%31%
1611
16th to endDay
9%436%5%36%5%8%10%36%
1779
February1st to 15thDay
9%6%25%5%35%46%8%41%
1760
16th to endDay
6%4245%35%6%7%10%43%
1738
March1st to 15thDay
6%5%25%6%46%6%8%10%37%
1980
16th to endDay
6%5%26%7%46%46%9%39%
2111
April1st to 15thDay
6%315%5%36%6%10%12%37%
1972
16th to endDay
8%426%6%46%6%7%11%36%
2139
May1st to 15thDay
4426%7%46%7%6%9%39%
2152
16th to endDay
10%6%37%8%5%9%9%8%9%21%
2378
June1st to 15thDay
14%8%5%10%10%6%9%7%6%7%12%
2340
16th to endDay
8%7%49%11%7%11%9%8%8%13%
2340
July1st to 15thDay
7%6%49%11%6%10%8%9%10%16%
2340
16th to endDay
6%5%38%10%7%9%9%11%10%18%
2465
August1st to 15thDay
6%7%38%8%6%9%9%9%10%19%
2247
16th to endDay
9%7%39%11%7%8%10%8%10%14%
2140
September1st to 15thDay
10%7%410%10%7%9%9%8%8%13%
1980
16th to endDay
12%10%410%11%6%8%7%6%7%13%
1980
October1st to 15thDay
11%6%39%9%5%8%8%7%10%20%
1781
16th to endDay
14%7%37%9%36%6%5%8%26%
1760
November1st to 15thDay
9%6%36%6%46%5%5%8%37%
1757
16th to endDay
10%5%26%6%47%7%5%9%35%
1800
December1st to 15thDay
9%6%37%5%46%5%6%10%34%
1731
16th to endDay
6%436%7%45%6%8%11%34%
1728
January1st to 15thNight
7%425%435%6%8%12%39%
2327
16th to endNight
6%325%435%5%6%10%47%
2443
February1st to 15thNight
8%3245%3445%9%49%
2090
16th to endNight
424325%45%9%56%
1735
March1st to 15thNight
5%324425%5%6%8%52%
1980
16th to endNight
43234245%6%9%54%
2112
April1st to 15thNight
321232446%10%59%
1976
16th to endNight
5%3133246%6%10%50%
1819
May1st to 15thNight
211232446%11%59%
1799
16th to endNight
7%4246%36%6%8%12%37%
1743
June1st to 15thNight
11%6%37%7%5%6%6%8%11%24%
1620
16th to endNight
4425%6%48%8%10%15%29%
1620
July1st to 15thNight
4425%5%37%7%9%14%34%
1620
16th to endNight
23245%37%6%8%15%40%
1703
August1st to 15thNight
3325%6%35%7%9%15%37%
1698
16th to endNight
6%5%16%8%47%8%8%11%30%
2057
September1st to 15thNight
5%426%8%47%9%9%13%27%
1980
16th to endNight
6%6%37%8%5%6%7%9%11%26%
1980
October1st to 15thNight
6%5%26%7%5%7%8%8%12%31%
1975
16th to endNight
11%6%25%6%45%5%7%9%34%
2112
November1st to 15thNight
7%425%436%5%5%9%44%
2101
16th to endNight
9%5%25%425%5%6%8%44%
2160
December1st to 15thNight
8%425%436%6%6%9%41%
2225
16th to endNight
6%313436%5%6%11%47%
2496

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
44%8%12%18%10%5%
1612
16th to endDay
39%7%13%19%15%5%
1779
February1st to 15thDay
36%7%10%22%18%5%
1762
16th to endDay
32%6%12%28%15%4
1738
March1st to 15thDay
35%9%13%22%17%2
1980
16th to endDay
36%8%12%23%15%5%
2112
April1st to 15thDay
31%9%16%25%15%2
1972
16th to endDay
36%8%14%20%16%3
2139
May1st to 15thDay
36%8%13%22%14%5%
2152
16th to endDay
50%13%15%16%4
2382
June1st to 15thDay
63%13%11%8%2
2340
16th to endDay
59%15%15%7%1
2340
July1st to 15thDay
52%19%19%8%
2201
16th to endDay
47%19%22%9%
2310
August1st to 15thDay
49%16%20%11%1
2234
16th to endDay
54%18%16%9%
2140
September1st to 15thDay
59%18%15%6%
1980
16th to endDay
62%15%11%7%2
1980
October1st to 15thDay
54%11%13%11%7%1
1781
16th to endDay
52%9%9%13%10%4
1760
November1st to 15thDay
43%7%10%16%18%3
1757
16th to endDay
41%9%9%14%19%6%
1800
December1st to 15thDay
43%8%11%17%16%2
1731
16th to endDay
38%8%13%21%14%3
1728
January1st to 15thNight
35%8%19%23%10%3
2327
16th to endNight
31%7%14%26%16%4
2443
February1st to 15thNight
31%6%10%26%18%6%
2099
16th to endNight
24%5%15%27%20%6%
1735
March1st to 15thNight
28%6%15%27%17%4
1980
16th to endNight
25%6%18%26%19%3
2112
April1st to 15thNight
21%6%18%33%16%3
1976
16th to endNight
26%7%17%24%20%3
1819
May1st to 15thNight
20%7%17%33%17%4
1800
16th to endNight
37%10%19%23%8%
1745
June1st to 15thNight
49%14%19%13%3
1620
16th to endNight
37%17%32%11%1
1620
July1st to 15thNight
36%18%34%10%
1530
16th to endNight
28%16%36%15%2
1595
August1st to 15thNight
30%19%29%18%1
1687
16th to endNight
42%15%29%12%
2057
September1st to 15thNight
42%21%24%10%1
1980
16th to endNight
48%17%21%10%3
1980
October1st to 15thNight
42%13%19%15%7%1
1975
16th to endNight
45%6%14%18%11%3
2112
November1st to 15thNight
36%6%13%22%17%3
2101
16th to endNight
36%6%12%20%17%6%
2160
December1st to 15thNight
38%7%15%20%16%2
2225
16th to endNight
30%6%14%27%17%2
2496

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
18%5%31%31%13%
90
16th to endDay
10%12%23%39%10%3
96
February1st to 15thDay
6%6%27%37%17%2
101
16th to endDay
7%24%39%27%
239
March1st to 15thDay
6%126%35%26%3
270
16th to endDay
8%219%35%28%6%
288
April1st to 15thDay
4118%35%26%12%
270
16th to endDay
9%14%33%32%10%
270
May1st to 15thDay
413%26%35%21%
288
16th to endDay
5%5%19%36%31%
331
June1st to 15thDay
15%18%18%25%30%
315
16th to endDay
5%113%26%54%
315
July1st to 15thDay
7%17%29%53%
305
16th to endDay
7%26%27%55%
326
August1st to 15thDay
9%17%28%53%
313
16th to endDay
11%313%27%44%
332
September1st to 15thDay
11%39%22%53%
315
16th to endDay
11%311%25%46%
314
October1st to 15thDay
8%18%26%35%20%
278
16th to endDay
15%218%26%25%11%
272
November1st to 15thDay
12%110%32%33%10%
265
16th to endDay
11%224%32%25%3
270
December1st to 15thDay
17%113%33%27%5%
201
16th to endDay
7%211%39%37%2
96
January1st to 15thNight
9%417%35%29%3
720
16th to endNight
6%322%43%22%1
768
February1st to 15thNight
8%222%39%25%
704
16th to endNight
4219%47%25%
631
March1st to 15thNight
6%121%42%25%2
720
16th to endNight
5%19%44%27%2
768
April1st to 15thNight
314%46%32%2
718
16th to endNight
8%113%45%29%2
720
May1st to 15thNight
310%40%40%4
720
16th to endNight
9%17%24%44%13%
624
June1st to 15thNight
13%1220%36%25%
540
16th to endNight
428%39%44%
540
July1st to 15thNight
6%16%41%44%
510
16th to endNight
316%34%54%
564
August1st to 15thNight
6%17%42%41%
617
16th to endNight
9%310%39%36%
764
September1st to 15thNight
7%311%33%42%
720
16th to endNight
9%414%35%35%
717
October1st to 15thNight
9%7%27%40%14%
684
16th to endNight
14%112%27%29%13%
704
November1st to 15thNight
9%115%37%32%4
700
16th to endNight
9%116%39%28%4
720
December1st to 15thNight
10%214%38%30%2
720
16th to endNight
6%214%37%33%5%
768
Page generated at 2017-10-07 14:07:49. Version ac04

Copyright 2017 A. Danko


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