Stars at Night Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stars at Night Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
49%
24015
27%
74263
19%
23958
57%
23958
35%
41569

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
34%
948
30%
2458
11%
946
46%
946
37%
1484
January11th to 20thNight
31%
930
27%
2418
9%
930
42%
930
34%
1487
January21st to endNight
33%
990
31%
2574
11%
990
44%
990
35%
1580
February1st to 10thNight
30%
861
25%
2301
9%
861
40%
861
31%
1443
February11th to 20thNight
24%
704
22%
2098
9%
700
35%
700
27%
1306
February21st to endNight
21%
526
27%
1710
9%
526
36%
526
23%
1027
March1st to 10thNight
32%
540
25%
1980
13%
540
46%
540
24%
1151
March11th to 20thNight
33%
540
24%
1980
14%
540
46%
540
24%
1164
March21st to endNight
35%
594
25%
2178
16%
594
48%
594
27%
1205
April1st to 10thNight
31%
540
25%
1980
13%
540
49%
540
30%
1052
April11th to 20thNight
33%
533
25%
1820
17%
533
47%
533
28%
1053
April21st to endNight
35%
540
27%
1733
16%
540
51%
540
34%
959
May1st to 10thNight
39%
540
26%
1620
18%
540
52%
540
31%
966
May11th to 20thNight
48%
531
21%
1594
18%
531
55%
531
34%
939
May21st to endNight
52%
584
24%
1745
19%
582
62%
582
35%
1021
June1st to 10thNight
69%
540
23%
1620
23%
540
73%
540
43%
874
June11th to 20thNight
70%
540
26%
1620
27%
540
74%
540
50%
808
June21st to endNight
74%
540
27%
1620
29%
540
77%
540
46%
844
July1st to 10thNight
75%
525
21%
1575
24%
525
78%
525
42%
856
July11th to 20thNight
87%
522
31%
1566
37%
522
89%
522
61%
710
July21st to endNight
88%
591
30%
1673
36%
558
89%
558
51%
818
August1st to 10thNight
89%
537
34%
1601
40%
534
90%
534
63%
707
August11th to 20thNight
78%
534
31%
1600
35%
534
79%
534
42%
873
August21st to endNight
83%
594
27%
1995
34%
594
84%
594
42%
1019
September1st to 10thNight
75%
540
24%
1980
29%
540
76%
540
37%
1005
September11th to 20thNight
72%
540
26%
1980
31%
540
74%
540
33%
1045
September21st to endNight
75%
540
35%
1980
36%
540
79%
540
43%
925
October1st to 10thNight
69%
607
36%
2047
32%
607
73%
607
47%
963
October11th to 20thNight
53%
720
34%
2160
19%
720
64%
720
42%
1167
October21st to endNight
45%
792
33%
2376
20%
792
54%
792
37%
1315
November1st to 10thNight
51%
740
32%
2220
20%
740
60%
740
41%
1219
November11th to 20thNight
46%
825
31%
2345
16%
825
57%
825
38%
1328
November21st to endNight
36%
950
29%
2470
13%
950
46%
950
34%
1546
December1st to 10thNight
36%
950
30%
2470
13%
950
48%
950
34%
1537
December11th to 20thNight
34%
948
29%
2865
13%
948
43%
948
28%
1784
December21st to endNight
33%
1039
17%
4311
11%
1026
43%
1026
23%
2389

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
12%5%2443445%7%50%
74974
Night
11%42442345%7%55%
74862
TransparencyDay
33%6%11%22%21%7%
74699
Night
29%5%10%22%23%10%
74657
SeeingDay
12%6%21%28%25%9%
14030
Night
13%7%27%34%18%2
24025

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 10thDay
14%6%24422345%55%
1707
11th to 20thDay
16%6%23433336%52%
1665
21st to endDay
18%5%24322336%52%
1782
February1st to 10thDay
19%7%36%5%23435%44%
1674
11th to 20thDay
19%8%35%423336%44%
1749
21st to endDay
22%5%34222245%48%
1544
March1st to 10thDay
18%6%24423347%45%
1980
11th to 20thDay
19%6%3333445%6%44%
1980
21st to endDay
15%7%35%43435%6%46%
2178
April1st to 10thDay
14%6%2443445%7%46%
1980
11th to 20thDay
15%5%245%2445%8%45%
2088
21st to endDay
13%425%5%35%46%8%45%
2222
May1st to 10thDay
14%5%35%5%35%45%7%46%
2340
11th to 20thDay
11%6%36%6%35%5%6%7%42%
2302
21st to endDay
12%6%25%6%46%5%7%9%38%
2531
June1st to 10thDay
6%3145%36%6%6%9%50%
2340
11th to 20thDay
5%425%5%35%5%6%10%51%
2340
21st to endDay
5%323435%5%6%8%54%
2340
July1st to 10thDay
7%5%35%5%46%6%8%11%40%
2340
11th to 20thDay
3213435%6%7%9%58%
2340
21st to endDay
43245%36%5%7%11%50%
2546
August1st to 10thDay
21124345%6%10%62%
2328
11th to 20thDay
7%324435%5%7%10%50%
2301
21st to endDay
5%3235%45%6%7%9%50%
2357
September1st to 10thDay
8%425%4345%5%9%52%
1980
11th to 20thDay
10%425%5%345%6%7%48%
1980
21st to endDay
8%42332346%7%59%
1980
October1st to 10thDay
7%324323347%61%
1895
11th to 20thDay
14%413323245%59%
1800
21st to endDay
15%5%2332334457%
1980
November1st to 10thDay
12%423323445%56%
1858
11th to 20thDay
9%325%434445%58%
1831
21st to endDay
17%6%24323335%52%
1710
December1st to 10thDay
15%5%145%2445%6%49%
1710
11th to 20thDay
16%7%35%5%3445%5%45%
2161
21st to endDay
17%7%25%323445%47%
3135
January1st to 10thNight
13%5%23323445%56%
2458
11th to 20thNight
15%6%23323347%53%
2418
21st to endNight
14%6%24423335%55%
2574
February1st to 10thNight
16%6%25%323346%51%
2301
11th to 20thNight
17%5%25%423345%48%
2098
21st to endNight
19%5%14423336%49%
1710
March1st to 10thNight
17%5%25%423448%46%
1980
11th to 20thNight
15%5%34424446%49%
1980
21st to endNight
12%425%42435%6%52%
2178
April1st to 10thNight
10%42442445%8%52%
1980
11th to 20thNight
13%5%2443445%6%50%
1820
21st to endNight
11%42442335%8%54%
1733
May1st to 10thNight
11%435%5%2446%9%50%
1620
11th to 20thNight
9%5%2343446%9%50%
1593
21st to endNight
7%4245%245%7%10%50%
1745
June1st to 10thNight
6%31343446%10%57%
1620
11th to 20thNight
4313323449%64%
1620
21st to endNight
321432446%11%58%
1620
July1st to 10thNight
43244345%6%13%51%
1620
11th to 20thNight
321221345%9%69%
1620
21st to endNight
12123345%8%11%60%
1772
August1st to 10thNight
221221245%11%68%
1611
11th to 20thNight
6%4244245%5%8%57%
1600
21st to endNight
3313445%5%6%9%57%
1995
September1st to 10thNight
8%42342346%8%57%
1980
11th to 20thNight
11%315%4245%5%7%54%
1980
21st to endNight
6%31332345%6%64%
1980
October1st to 10thNight
6%31332335%6%65%
2047
11th to 20thNight
13%412323245%61%
2160
21st to endNight
16%5%1331123461%
2376
November1st to 10thNight
11%42432333461%
2220
11th to 20thNight
8%5%24423446%58%
2345
21st to endNight
16%5%24433335%53%
2470
December1st to 10thNight
14%6%23423346%54%
2470
11th to 20thNight
14%5%35%424345%51%
3036
21st to endNight
16%6%24422335%53%
4532

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
33%48%20%29%6%
1708
11th to 20thDay
37%38%22%24%5%
1665
21st to endDay
37%35%18%28%10%
1782
February1st to 10thDay
45%37%18%19%9%
1674
11th to 20thDay
45%36%20%18%8%
1759
21st to endDay
42%35%15%24%11%
1544
March1st to 10thDay
40%5%8%16%20%11%
1980
11th to 20thDay
40%6%9%18%22%5%
1980
21st to endDay
40%5%9%19%20%6%
2178
April1st to 10thDay
37%7%10%20%17%9%
1980
11th to 20thDay
38%7%9%18%21%8%
2088
21st to endDay
36%7%10%21%23%4
2222
May1st to 10thDay
38%6%9%22%18%6%
2340
11th to 20thDay
38%9%13%22%17%2
2306
21st to endDay
40%10%14%20%14%2
2531
June1st to 10thDay
28%9%16%28%16%2
2340
11th to 20thDay
27%8%16%27%18%4
2340
21st to endDay
26%7%14%27%23%3
2340
July1st to 10thDay
33%12%19%24%12%
2276
11th to 20thDay
18%9%16%33%20%3
2271
21st to endDay
23%10%18%34%13%
2405
August1st to 10thDay
16%8%16%37%21%2
2314
11th to 20thDay
27%8%16%27%18%3
2301
21st to endDay
27%9%17%30%15%3
2357
September1st to 10thDay
29%6%12%24%20%9%
1980
11th to 20thDay
34%8%13%18%21%7%
1980
21st to endDay
24%6%11%21%26%11%
1980
October1st to 10thDay
24%6%12%22%22%14%
1895
11th to 20thDay
29%46%17%28%15%
1800
21st to endDay
31%5%7%16%26%15%
1980
November1st to 10thDay
31%5%8%23%24%9%
1858
11th to 20thDay
29%410%19%28%10%
1831
21st to endDay
36%36%21%24%9%
1710
December1st to 10thDay
36%6%9%19%23%7%
1710
11th to 20thDay
40%5%7%15%24%9%
2159
21st to endDay
38%6%6%22%21%7%
3135
January1st to 10thNight
31%5%7%20%26%11%
2458
11th to 20thNight
34%49%19%26%9%
2418
21st to endNight
34%35%15%29%13%
2574
February1st to 10thNight
37%48%18%22%11%
2301
11th to 20thNight
39%47%16%23%10%
2098
21st to endNight
39%48%14%20%15%
1710
March1st to 10thNight
37%5%9%17%19%13%
1980
11th to 20thNight
38%5%9%15%25%8%
1980
21st to endNight
33%5%11%20%24%7%
2178
April1st to 10thNight
29%6%12%21%18%13%
1980
11th to 20thNight
34%6%8%20%18%13%
1820
21st to endNight
30%6%11%22%27%5%
1733
May1st to 10thNight
32%7%10%22%20%8%
1620
11th to 20thNight
31%8%16%24%19%3
1594
21st to endNight
28%9%17%25%19%2
1746
June1st to 10thNight
22%8%16%29%20%4
1620
11th to 20thNight
19%6%14%35%20%7%
1620
21st to endNight
19%8%13%29%26%5%
1620
July1st to 10thNight
23%8%21%32%15%2
1575
11th to 20thNight
11%6%16%36%26%5%
1566
21st to endNight
14%9%18%39%17%2
1673
August1st to 10thNight
11%5%16%36%27%5%
1601
11th to 20thNight
25%6%14%27%21%6%
1600
21st to endNight
21%8%15%31%21%4
1995
September1st to 10thNight
24%7%12%24%23%10%
1980
11th to 20thNight
29%6%12%22%21%10%
1980
21st to endNight
21%6%9%21%28%16%
1980
October1st to 10thNight
20%5%10%26%21%19%
2047
11th to 20thNight
27%37%16%26%21%
2160
21st to endNight
30%35%18%25%19%
2376
November1st to 10thNight
28%47%21%27%13%
2220
11th to 20thNight
28%47%19%28%14%
2345
21st to endNight
35%38%16%27%11%
2470
December1st to 10thNight
34%5%9%20%22%11%
2470
11th to 20thNight
38%46%16%25%12%
3037
21st to endNight
35%46%18%27%10%
4532

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
18%12%38%24%8%
270
11th to 20thDay
17%16%39%20%7%1
255
21st to endDay
23%12%36%22%7%1
264
February1st to 10thDay
21%14%38%20%7%
240
11th to 20thDay
27%13%42%14%4
240
21st to endDay
32%14%37%14%3
198
March1st to 10thDay
24%11%34%28%3
240
11th to 20thDay
21%18%35%21%5%1
240
21st to endDay
19%14%40%22%6%
264
April1st to 10thDay
19%13%35%26%6%1
240
11th to 20thDay
20%11%32%25%11%
366
21st to endDay
16%13%35%25%9%2
482
May1st to 10thDay
14%9%30%35%10%1
603
11th to 20thDay
16%5%26%34%16%4
625
21st to endDay
13%5%24%33%20%4
679
June1st to 10thDay
7%212%37%32%10%
630
11th to 20thDay
6%115%40%29%8%
630
21st to endDay
4213%34%35%13%
630
July1st to 10thDay
6%110%30%38%15%
621
11th to 20thDay
215%30%47%16%
618
21st to endDay
3425%50%18%
684
August1st to 10thDay
2428%50%15%
626
11th to 20thDay
9%15%29%40%15%
615
21st to endDay
6%15%22%38%28%
476
September1st to 10thDay
8%1216%40%33%
270
11th to 20thDay
6%16%24%34%29%
270
21st to endDay
10%47%20%39%20%
270
October1st to 10thDay
3213%31%40%11%
270
11th to 20thDay
12%5%25%32%20%6%
270
21st to endDay
25%10%21%23%18%3
297
November1st to 10thDay
17%6%31%26%16%6%
270
11th to 20thDay
13%9%30%30%16%3
270
21st to endDay
20%10%32%27%10%1
270
December1st to 10thDay
19%8%32%28%11%2
270
11th to 20thDay
19%13%36%26%6%
270
21st to endDay
20%13%36%23%8%1
297
January1st to 10thNight
17%9%36%30%7%
950
11th to 20thNight
18%14%33%28%6%1
930
21st to endNight
17%9%38%30%6%
990
February1st to 10thNight
19%11%37%28%5%
861
11th to 20thNight
21%12%39%25%2
704
21st to endNight
24%14%39%20%3
526
March1st to 10thNight
20%10%35%28%6%
540
11th to 20thNight
17%11%36%31%5%
540
21st to endNight
14%11%37%32%5%
594
April1st to 10thNight
10%10%47%28%5%
540
11th to 20thNight
16%12%36%27%9%
533
21st to endNight
13%7%42%27%10%1
540
May1st to 10thNight
11%8%38%34%9%1
540
11th to 20thNight
11%333%35%18%1
531
21st to endNight
8%429%39%18%3
584
June1st to 10thNight
6%216%42%31%3
540
11th to 20thNight
4219%51%22%2
540
21st to endNight
4114%40%35%7%
540
July1st to 10thNight
4111%40%39%6%
525
11th to 20thNight
35%42%45%5%
522
21st to endNight
2342%46%7%
591
August1st to 10thNight
2343%47%4
537
11th to 20thNight
8%5%36%45%6%
534
21st to endNight
41434%49%8%
594
September1st to 10thNight
10%7%33%44%6%
540
11th to 20thNight
13%15%32%45%3
540
21st to endNight
7%111%36%38%6%
540
October1st to 10thNight
8%117%42%28%3
607
11th to 20thNight
14%425%37%17%2
720
21st to endNight
17%7%28%30%16%1
792
November1st to 10thNight
11%5%29%39%16%1
740
11th to 20thNight
9%11%30%38%11%1
825
21st to endNight
19%9%32%29%10%1
950
December1st to 10thNight
17%10%33%32%7%
950
11th to 20thNight
20%9%33%33%5%
950
21st to endNight
20%10%35%30%6%
1045
Page generated at 2024-01-13 08:37:52. Version ac07

Copyright 2024 Attilla Danko


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