A Shooting Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the A Shooting Star Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
51%
15560
32%
46838
21%
15519
63%
15519
40%
23800

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
48%
720
29%
2327
22%
716
61%
716
37%
1182
January16th to endNight
44%
768
33%
2496
24%
768
58%
768
33%
1334
February1st to 15thNight
47%
700
31%
2223
23%
700
61%
700
40%
1116
February16th to endNight
35%
632
35%
1895
21%
632
53%
632
33%
988
March1st to 15thNight
43%
720
35%
1980
19%
720
59%
720
39%
1047
March16th to endNight
42%
768
34%
2112
16%
768
58%
768
40%
1097
April1st to 15thNight
33%
687
28%
1946
10%
687
48%
687
32%
1015
April16th to endNight
39%
540
40%
1667
18%
540
61%
540
42%
747
May1st to 15thNight
40%
540
34%
1619
17%
539
54%
539
44%
754
May16th to endNight
40%
561
33%
1684
17%
561
53%
561
42%
784
June1st to 15thNight
46%
540
31%
1620
19%
540
56%
540
52%
721
June16th to endNight
63%
540
33%
1620
26%
540
70%
540
60%
697
July1st to 15thNight
65%
510
20%
1530
14%
510
69%
510
40%
835
July16th to endNight
65%
564
16%
1593
12%
531
67%
531
28%
1010
August1st to 15thNight
73%
539
25%
1611
21%
536
74%
536
38%
897
August16th to endNight
74%
603
33%
1812
28%
603
78%
603
43%
953
September1st to 15thNight
71%
700
27%
1925
19%
700
76%
700
42%
1085
September16th to endNight
68%
656
42%
1815
26%
656
78%
656
60%
825
October1st to 15thNight
55%
660
36%
1903
20%
660
68%
660
48%
923
October16th to endNight
59%
704
40%
2112
27%
704
72%
704
50%
993
November1st to 15thNight
54%
700
35%
2172
25%
700
66%
700
43%
1063
November16th to endNight
52%
720
37%
2340
27%
720
66%
720
43%
1090
December1st to 15thNight
49%
720
32%
2340
21%
720
64%
720
37%
1196
December16th to endNight
41%
768
29%
2496
21%
768
52%
768
27%
1448

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
342442445%6%55%
47788
Night
131332445%6%62%
47034
TransparencyDay
28%46%18%26%15%
47483
Night
22%47%20%29%16%
46840
SeeingDay
12%20%28%24%11%2
5377
Night
6%14%21%27%22%7%
15566

By Month

Percentage Cloud Cover SW (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
15%2342335%7%60%
1611
16th to endDay
35%244235%45%56%
1728
February1st to 15thDay
17%245%2345%8%55%
1637
16th to endDay
15%2443445%9%54%
1579
March1st to 15thDay
14233235%5%8%59%
1980
16th to endDay
243332335%7%59%
2112
April1st to 15thDay
1414424447%59%
2000
16th to endDay
1424413436%62%
2291
May1st to 15thDay
3414423446%59%
2331
16th to endDay
3324324445%61%
2429
June1st to 15thDay
211221424473%
2340
16th to endDay
221232333470%
2340
July1st to 15thDay
6%5%27%6%46%7%7%6%38%
2340
16th to endDay
10%7%37%9%5%7%7%8%8%23%
2467
August1st to 15thDay
10%7%36%8%5%6%6%5%5%34%
2340
16th to endDay
6%6%26%8%46%5%5%7%39%
2388
September1st to 15thDay
6%5%25%6%47%5%6%6%42%
1922
16th to endDay
2214323345%66%
1815
October1st to 15thDay
332331332466%
1726
16th to endDay
3312312246%67%
1760
November1st to 15thDay
212223345%70%
1684
16th to endDay
241232224470%
1620
December1st to 15thDay
24143245%5%6%58%
1620
16th to endDay
2425%6%26%6%6%7%48%
1728
January1st to 15thNight
13244245%45%60%
2327
16th to endNight
25%235%245%5%6%56%
2496
February1st to 15thNight
5%133235%5%7%61%
2212
16th to endNight
1313425%5%5%8%60%
1895
March1st to 15thNight
1212425%45%7%61%
1980
16th to endNight
131231445%6%64%
2112
April1st to 15thNight
1323324445%63%
1946
16th to endNight
12213336%71%
1667
May1st to 15thNight
1212322346%68%
1619
16th to endNight
2212313235%71%
1684
June1st to 15thNight
1112313235%73%
1620
16th to endNight
11122223477%
1620
July1st to 15thNight
33234245%7%8%52%
1620
16th to endNight
4435%6%37%7%10%11%35%
1701
August1st to 15thNight
32135%35%5%6%9%52%
1620
16th to endNight
32144245%7%9%54%
1812
September1st to 15thNight
33234345%6%6%55%
1925
16th to endNight
111212335%77%
1815
October1st to 15thNight
1112223446%69%
1903
16th to endNight
2313212345%70%
2112
November1st to 15thNight
1213325%45%5%64%
2172
16th to endNight
121333334468%
2340
December1st to 15thNight
14223245%5%8%58%
2340
16th to endNight
25%25%6%35%5%6%7%50%
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
24%35%23%32%9%
1612
16th to endDay
29%37%19%30%10%
1728
February1st to 15thDay
28%37%26%19%15%
1637
16th to endDay
27%38%23%28%8%
1579
March1st to 15thDay
23%36%23%32%11%
1980
16th to endDay
24%36%26%27%10%
2112
April1st to 15thDay
25%36%22%31%12%
2000
16th to endDay
24%2420%33%13%
2291
May1st to 15thDay
25%3419%34%12%
2331
16th to endDay
25%4416%35%13%
2432
June1st to 15thDay
15%2211%31%36%
2340
16th to endDay
18%317%28%40%
2340
July1st to 15thDay
41%8%9%10%11%19%
2201
16th to endDay
52%10%12%11%9%2
2312
August1st to 15thDay
48%6%9%11%15%9%
2325
16th to endDay
42%7%8%16%18%6%
2388
September1st to 15thDay
39%6%8%13%16%14%
1922
16th to endDay
20%4416%33%20%
1815
October1st to 15thDay
24%2318%30%20%
1726
16th to endDay
18%2418%39%17%
1760
November1st to 15thDay
17%26%26%30%16%
1684
16th to endDay
19%3419%35%18%
1620
December1st to 15thDay
26%410%26%23%7%
1620
16th to endDay
36%38%22%21%7%
1728
January1st to 15thNight
25%37%21%31%11%
2327
16th to endNight
29%36%18%30%11%
2496
February1st to 15thNight
22%47%23%24%17%
2223
16th to endNight
24%46%21%30%11%
1895
March1st to 15thNight
21%45%24%33%10%
1980
16th to endNight
20%47%26%30%11%
2112
April1st to 15thNight
22%35%21%34%12%
1946
16th to endNight
15%2323%37%16%
1667
May1st to 15thNight
17%35%25%32%16%
1620
16th to endNight
17%2419%41%14%
1685
June1st to 15thNight
14%2210%31%38%
1620
16th to endNight
12%126%26%49%
1620
July1st to 15thNight
26%6%14%14%15%22%
1530
16th to endNight
36%8%19%17%13%4
1593
August1st to 15thNight
26%8%13%17%23%11%
1611
16th to endNight
23%5%12%25%23%9%
1812
September1st to 15thNight
26%5%11%19%22%16%
1925
16th to endNight
11%2319%34%28%
1815
October1st to 15thNight
17%35%21%30%22%
1903
16th to endNight
17%2416%38%20%
2112
November1st to 15thNight
20%35%23%28%18%
2172
16th to endNight
19%2419%33%20%
2340
December1st to 15thNight
25%38%25%25%12%
2340
16th to endNight
34%48%21%22%7%
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
20%24%31%16%5%2
90
16th to endDay
15%21%33%14%12%2
96
February1st to 15thDay
10%26%25%21%13%2
152
16th to endDay
21%34%25%13%4
238
March1st to 15thDay
14%25%31%19%6%2
270
16th to endDay
15%29%32%16%5%1
288
April1st to 15thDay
17%31%30%10%7%2
269
16th to endDay
19%32%31%11%4
270
May1st to 15thDay
12%31%34%14%5%
288
16th to endDay
12%26%30%22%6%
330
June1st to 15thDay
6%26%33%22%8%3
315
16th to endDay
5%8%37%31%13%2
315
July1st to 15thDay
8%9%31%34%12%3
305
16th to endDay
15%5%16%34%22%4
327
August1st to 15thDay
13%5%21%35%17%6%
315
16th to endDay
11%419%37%21%5%
332
September1st to 15thDay
10%11%27%31%13%4
294
16th to endDay
9%16%25%29%14%4
255
October1st to 15thDay
10%30%26%16%12%3
166
16th to endDay
12%17%26%29%11%3
96
November1st to 15thDay
7%16%23%30%12%10%
90
16th to endDay
12%32%23%21%11%
90
December1st to 15thDay
8%22%34%18%15%
90
16th to endDay
19%17%25%27%9%1
96
January1st to 15thNight
9%11%25%27%15%10%
720
16th to endNight
9%15%23%26%18%6%
768
February1st to 15thNight
5%15%26%28%18%5%
704
16th to endNight
8%24%29%21%12%3
632
March1st to 15thNight
7%21%23%24%17%5%
720
16th to endNight
6%21%26%27%14%3
768
April1st to 15thNight
8%30%23%22%12%2
687
16th to endNight
425%28%24%12%4
540
May1st to 15thNight
422%30%28%12%2
540
16th to endNight
5%22%25%24%19%3
563
June1st to 15thNight
214%32%31%15%3
540
16th to endNight
27%22%38%25%3
540
July1st to 15thNight
5%215%34%34%7%
510
16th to endNight
6%110%29%40%9%
564
August1st to 15thNight
5%29%27%45%10%
539
16th to endNight
428%30%37%16%
603
September1st to 15thNight
5%49%26%42%11%
700
16th to endNight
410%13%24%33%13%
656
October1st to 15thNight
5%14%23%29%20%7%
660
16th to endNight
5%12%18%27%23%13%
704
November1st to 15thNight
314%22%27%23%8%
700
16th to endNight
6%15%23%27%18%9%
720
December1st to 15thNight
8%14%24%26%22%4
720
16th to endNight
11%16%25%25%16%5%
768
Page generated at 2017-09-11 16:35:21. Version ac04

Copyright 2017 A. Danko


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