Sun, Moon and Stars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sun, Moon and Stars 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 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
38%
22597
9%
74791
7%
22541
41%
22541
14%
56307

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 10thNight
17%
850
7%
2836
5%
846
20%
846
6%
2422
January11th to 20thNight
25%
805
5%
2715
4%
805
27%
805
6%
2295
January21st to endNight
25%
822
7%
2797
5%
822
29%
822
8%
2296
February1st to 10thNight
24%
720
8%
2340
4%
720
29%
720
9%
1926
February11th to 20thNight
31%
700
9%
2274
6%
700
35%
700
11%
1795
February21st to endNight
27%
592
10%
1924
7%
592
32%
592
11%
1488
March1st to 10thNight
29%
720
8%
2082
5%
720
31%
720
13%
1665
March11th to 20thNight
29%
720
9%
1980
6%
720
31%
720
12%
1618
March21st to endNight
29%
792
7%
2142
3%
792
31%
792
11%
1801
April1st to 10thNight
36%
720
7%
1800
3%
720
37%
720
15%
1442
April11th to 20thNight
35%
584
11%
1652
7%
584
38%
584
15%
1261
April21st to endNight
40%
509
10%
1589
6%
509
43%
509
15%
1177
May1st to 10thNight
50%
360
12%
1440
17%
360
53%
360
18%
925
May11th to 20thNight
55%
354
11%
1416
17%
354
56%
354
16%
945
May21st to endNight
50%
388
7%
1444
9%
388
52%
388
16%
997
June1st to 10thNight
48%
360
3%
1260
3%
360
48%
360
16%
897
June11th to 20thNight
52%
360
3%
1260
1%
360
52%
360
15%
909
June21st to endNight
61%
360
6%
1260
2%
360
62%
360
21%
805
July1st to 10thNight
67%
350
7%
1225
5%
350
67%
350
28%
726
July11th to 20thNight
73%
348
13%
1218
16%
348
74%
348
34%
646
July21st to endNight
80%
394
16%
1391
25%
372
82%
372
42%
643
August1st to 10thNight
75%
399
16%
1465
21%
397
77%
397
35%
724
August11th to 20thNight
80%
534
20%
1602
19%
534
82%
534
42%
857
August21st to endNight
64%
624
19%
1812
16%
624
65%
624
30%
1135
September1st to 10thNight
68%
720
20%
1800
12%
720
69%
720
39%
1114
September11th to 20thNight
54%
720
18%
1831
11%
720
55%
720
26%
1293
September21st to endNight
49%
720
15%
2043
12%
720
51%
720
23%
1424
October1st to 10thNight
48%
720
10%
2160
10%
720
50%
720
23%
1463
October11th to 20thNight
40%
720
10%
2160
10%
720
43%
720
16%
1613
October21st to endNight
30%
792
11%
2533
8%
792
35%
792
13%
1920
November1st to 10thNight
22%
740
6%
2590
4%
740
25%
740
8%
2143
November11th to 20thNight
24%
760
7%
2660
5%
760
28%
760
9%
2139
November21st to endNight
22%
760
7%
2660
3%
760
27%
760
8%
2150
December1st to 10thNight
29%
798
8%
2739
5%
798
33%
798
10%
2196
December11th to 20thNight
16%
850
3%
3516
2%
849
18%
849
5%
3088
December21st to endNight
14%
932
5%
5175
3%
905
21%
905
4%
4369

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
22%8%36%5%3445%7%33%
74719
Night
27%9%36%5%34446%30%
74998
TransparencyDay
51%11%15%16%7%1
74405
Night
56%9%13%15%7%1
74830
SeeingDay
25%8%21%26%17%3
14339
Night
32%6%16%24%18%3
22605

By Month

Percentage Cloud Cover NW (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 10thDay
46%9%36%6%1444313%
1329
11th to 20thDay
32%11%5%8%6%35%446%17%
1267
21st to endDay
34%12%36%6%36%445%16%
1553
February1st to 10thDay
33%10%46%5%35%5%5%417%
1620
11th to 20thDay
29%9%36%5%45%5%5%7%23%
1575
21st to endDay
23%10%39%6%46%46%5%24%
1332
March1st to 10thDay
29%10%47%6%45%45%6%20%
1873
11th to 20thDay
31%11%48%6%34445%21%
1980
21st to endDay
27%11%47%6%35%345%25%
2213
April1st to 10thDay
26%10%37%6%35%5%6%6%22%
2160
11th to 20thDay
23%8%47%6%45%5%6%6%27%
2255
21st to endDay
22%9%46%4445%5%6%30%
2371
May1st to 10thDay
15%6%46%6%45%5%5%8%36%
2520
11th to 20thDay
16%7%35%6%35%6%7%9%33%
2477
21st to endDay
16%8%46%6%35%5%5%8%33%
2829
June1st to 10thDay
20%7%36%6%35%5%5%9%31%
2700
11th to 20thDay
17%7%36%7%46%6%7%8%29%
2700
21st to endDay
14%5%25%5%35%5%6%8%42%
2700
July1st to 10thDay
9%5%25%5%35%5%5%6%50%
2700
11th to 20thDay
9%42343445%8%54%
2700
21st to endDay
7%323323346%63%
2842
August1st to 10thDay
9%42442335%8%55%
2464
11th to 20thDay
7%5%25%33345%7%56%
2298
21st to endDay
10%5%35%5%345%6%8%47%
2543
September1st to 10thDay
12%6%35%43445%8%47%
2160
11th to 20thDay
18%6%36%5%3445%6%42%
2127
21st to endDay
23%5%2443446%8%36%
1916
October1st to 10thDay
25%7%24425%45%7%34%
1800
11th to 20thDay
32%7%35%5%35%448%24%
1800
21st to endDay
33%8%25%445%35%7%25%
1820
November1st to 10thDay
39%9%36%5%34436%18%
1488
11th to 20thDay
36%10%35%423445%23%
1520
21st to endDay
38%9%35%5%3445%421%
1520
December1st to 10thDay
29%14%45%6%445%45%21%
1440
11th to 20thDay
39%13%37%6%3433415%
1685
21st to endDay
41%14%48%5%3422413%
2442
January1st to 10thNight
42%10%37%5%3433416%
2836
11th to 20thNight
37%11%46%43445%5%17%
2715
21st to endNight
32%12%37%434446%20%
2797
February1st to 10thNight
33%11%37%6%35%45%5%20%
2340
11th to 20thNight
26%11%37%5%345%45%27%
2272
21st to endNight
27%11%46%5%3445%6%25%
1924
March1st to 10thNight
30%10%47%5%44445%23%
2082
11th to 20thNight
31%10%37%5%34346%22%
1979
21st to endNight
29%11%47%6%35%5%46%20%
2142
April1st to 10thNight
25%11%36%6%46%5%5%6%24%
1800
11th to 20thNight
21%10%38%7%445%5%7%28%
1652
21st to endNight
22%9%46%5%45%5%47%30%
1589
May1st to 10thNight
16%5%36%6%445%5%7%40%
1440
11th to 20thNight
16%7%35%5%46%5%7%9%33%
1416
21st to endNight
14%9%47%5%35%5%5%8%35%
1444
June1st to 10thNight
21%7%48%6%35%435%34%
1260
11th to 20thNight
16%8%46%6%45%46%9%31%
1260
21st to endNight
11%5%36%6%35%5%5%8%43%
1260
July1st to 10thNight
10%435%5%2435%6%53%
1260
11th to 20thNight
7%4245%3445%8%57%
1260
21st to endNight
6%223434346%64%
1473
August1st to 10thNight
6%413334336%62%
1473
11th to 20thNight
6%2142245%5%8%61%
1602
21st to endNight
10%4246%345%6%8%47%
1812
September1st to 10thNight
9%423434446%56%
1800
11th to 20thNight
20%5%35%43445%6%43%
1831
21st to endNight
21%7%25%5%34346%41%
2043
October1st to 10thNight
20%6%26%43436%6%41%
2160
11th to 20thNight
29%8%25%434346%31%
2160
21st to endNight
34%8%25%5%24445%29%
2533
November1st to 10thNight
37%10%36%5%34345%19%
2590
11th to 20thNight
34%9%36%5%3345%424%
2660
21st to endNight
37%9%36%5%34445%22%
2660
December1st to 10thNight
31%10%46%5%45%435%23%
2739
11th to 20thNight
42%14%37%5%2334413%
3520
21st to endNight
43%14%47%42333415%
5214

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 10thDay
74%7%7%6%41
1329
11th to 20thDay
70%8%11%6%31
1267
21st to endDay
71%9%9%9%1
1553
February1st to 10thDay
68%9%9%7%32
1620
11th to 20thDay
59%11%12%13%4
1584
21st to endDay
60%12%12%10%41
1332
March1st to 10thDay
63%10%14%8%4
1873
11th to 20thDay
67%7%10%11%41
1980
21st to endDay
62%10%13%12%2
2213
April1st to 10thDay
59%13%14%10%4
2160
11th to 20thDay
55%10%13%13%8%
2255
21st to endDay
55%10%13%14%7%1
2371
May1st to 10thDay
45%12%18%17%7%1
2520
11th to 20thDay
46%13%16%19%5%1
2480
21st to endDay
47%13%16%19%4
2830
June1st to 10thDay
50%11%19%13%42
2700
11th to 20thDay
49%15%19%12%5%
2700
21st to endDay
40%12%20%18%9%2
2700
July1st to 10thDay
34%12%18%23%11%3
2626
11th to 20thDay
28%12%20%30%9%1
2619
21st to endDay
20%10%21%31%14%3
2684
August1st to 10thDay
28%13%18%28%11%2
2447
11th to 20thDay
27%10%21%25%14%3
2298
21st to endDay
33%12%21%26%6%1
2543
September1st to 10thDay
35%11%18%23%11%3
2160
11th to 20thDay
43%10%14%18%13%2
2127
21st to endDay
46%11%17%16%9%1
1916
October1st to 10thDay
48%11%17%16%8%
1800
11th to 20thDay
59%11%14%12%3
1800
21st to endDay
59%9%14%12%6%1
1820
November1st to 10thDay
68%8%11%8%5%1
1488
11th to 20thDay
65%10%10%9%42
1520
21st to endDay
67%7%9%11%6%
1520
December1st to 10thDay
64%8%10%11%6%1
1440
11th to 20thDay
73%8%11%5%21
1688
21st to endDay
76%9%7%6%21
2442
January1st to 10thNight
72%7%7%9%31
2836
11th to 20thNight
69%10%10%7%41
2715
21st to endNight
66%9%9%13%31
2797
February1st to 10thNight
66%8%10%10%5%2
2340
11th to 20thNight
59%10%12%12%7%
2274
21st to endNight
59%8%12%14%6%1
1924
March1st to 10thNight
60%9%15%12%4
2082
11th to 20thNight
63%8%10%13%5%1
1980
21st to endNight
65%9%11%12%3
2142
April1st to 10thNight
58%10%14%16%3
1800
11th to 20thNight
55%8%12%15%8%1
1652
21st to endNight
53%9%14%14%9%
1589
May1st to 10thNight
43%9%18%22%8%1
1440
11th to 20thNight
44%12%19%19%6%1
1416
21st to endNight
47%11%17%20%5%
1444
June1st to 10thNight
52%7%16%18%43
1260
11th to 20thNight
49%12%18%17%5%
1260
21st to endNight
38%11%19%19%9%3
1260
July1st to 10thNight
34%8%15%26%13%3
1225
11th to 20thNight
26%9%23%28%12%2
1218
21st to endNight
19%7%17%32%20%4
1391
August1st to 10thNight
24%8%19%28%18%3
1465
11th to 20thNight
20%10%24%25%15%5%
1602
21st to endNight
33%10%18%29%9%
1812
September1st to 10thNight
28%9%17%29%13%3
1800
11th to 20thNight
42%9%12%16%16%4
1831
21st to endNight
45%9%16%20%9%2
2043
October1st to 10thNight
44%8%17%19%12%
2160
11th to 20thNight
54%8%15%17%6%
2160
21st to endNight
58%7%12%16%7%
2533
November1st to 10thNight
68%8%11%9%41
2590
11th to 20thNight
63%9%11%10%5%2
2660
21st to endNight
65%8%9%10%7%1
2660
December1st to 10thNight
64%8%11%12%5%1
2739
11th to 20thNight
75%8%8%6%3
3516
21st to endNight
73%6%8%8%3
5214

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 10thDay
42%9%21%15%8%5%
180
11th to 20thDay
43%16%16%14%11%1
162
21st to endDay
46%8%21%15%9%1
217
February1st to 10thDay
41%9%26%16%7%1
340
11th to 20thDay
38%9%24%19%9%1
335
21st to endDay
28%14%29%18%10%1
280
March1st to 10thDay
34%11%25%19%9%1
416
11th to 20thDay
33%13%20%21%13%1
420
21st to endDay
34%10%26%20%9%1
462
April1st to 10thDay
35%12%23%18%10%1
420
11th to 20thDay
30%10%24%20%15%
412
21st to endDay
26%11%26%23%13%1
420
May1st to 10thDay
19%8%23%32%18%
423
11th to 20thDay
19%420%31%22%4
448
21st to endDay
17%6%24%31%18%3
591
June1st to 10thDay
24%7%22%27%19%1
630
11th to 20thDay
18%8%25%30%17%2
630
21st to endDay
16%421%34%22%3
630
July1st to 10thDay
16%417%33%27%4
621
11th to 20thDay
9%5%19%39%25%3
618
21st to endDay
7%314%34%35%7%
588
August1st to 10thDay
11%416%28%33%9%
447
11th to 20thDay
9%314%35%32%7%
437
21st to endDay
15%418%37%22%2
495
September1st to 10thDay
18%6%25%32%17%2
450
11th to 20thDay
26%7%18%26%18%5%
450
21st to endDay
26%7%23%24%16%4
450
October1st to 10thDay
31%6%19%22%18%4
450
11th to 20thDay
38%7%17%19%15%5%
450
21st to endDay
38%14%18%20%7%4
369
November1st to 10thDay
40%12%23%17%8%
180
11th to 20thDay
42%10%12%19%12%6%
180
21st to endDay
48%9%18%11%8%6%
180
December1st to 10thDay
43%7%23%12%9%5%
180
11th to 20thDay
44%9%19%21%7%1
180
21st to endDay
43%9%30%14%4
198
January1st to 10thNight
49%9%18%14%9%1
850
11th to 20thNight
44%7%16%20%12%
805
21st to endNight
41%7%20%22%10%
822
February1st to 10thNight
40%7%23%21%9%
720
11th to 20thNight
35%7%21%27%9%1
704
21st to endNight
35%11%19%22%11%2
592
March1st to 10thNight
35%9%20%21%12%2
720
11th to 20thNight
42%7%16%23%11%1
720
21st to endNight
37%8%18%21%14%2
792
April1st to 10thNight
33%7%16%26%13%5%
720
11th to 20thNight
27%9%20%27%15%2
584
21st to endNight
29%5%20%29%15%2
509
May1st to 10thNight
18%418%32%23%4
360
11th to 20thNight
21%5%9%29%31%6%
354
21st to endNight
20%414%30%27%5%
389
June1st to 10thNight
25%5%10%31%24%4
360
11th to 20thNight
24%411%32%23%6%
360
21st to endNight
15%39%35%32%6%
360
July1st to 10thNight
13%110%23%43%10%
350
11th to 20thNight
9%38%31%39%10%
348
21st to endNight
7%2426%48%13%
394
August1st to 10thNight
11%25%22%44%16%
399
11th to 20thNight
8%15%27%49%10%
534
21st to endNight
15%410%29%37%5%
624
September1st to 10thNight
13%211%35%31%8%
720
11th to 20thNight
23%5%12%21%29%10%
720
21st to endNight
29%414%27%24%3
720
October1st to 10thNight
25%5%15%29%23%3
720
11th to 20thNight
36%5%13%26%17%2
720
21st to endNight
40%8%18%24%8%2
792
November1st to 10thNight
44%8%19%24%5%
740
11th to 20thNight
41%8%21%20%9%1
760
21st to endNight
44%6%21%21%7%1
760
December1st to 10thNight
37%8%18%26%10%1
798
11th to 20thNight
49%8%20%19%4
850
21st to endNight
46%12%22%16%4
935
Page generated at 2024-01-08 19:31:27. Version ac07

Copyright 2024 Attilla Danko


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