Astronight Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astronight Observatory clear sky chart from 2005-11-06 to 2024-03-23.

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
27%
23180
18%
80740
8%
23084
39%
23084
18%
52193

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
15%
754
22%
4333
5%
737
34%
737
12%
2337
January11th to 20thNight
14%
759
21%
4345
3%
740
28%
740
8%
2582
January21st to endNight
16%
831
12%
4864
6%
814
34%
814
8%
3423
February1st to 10thNight
18%
760
17%
2416
5%
760
33%
760
17%
1618
February11th to 20thNight
15%
743
21%
2220
5%
740
33%
740
18%
1450
February21st to endNight
19%
628
23%
1884
7%
628
39%
628
18%
1238
March1st to 10thNight
19%
760
20%
2280
7%
760
36%
760
17%
1530
March11th to 20thNight
16%
760
18%
2176
4%
760
30%
760
17%
1519
March21st to endNight
19%
801
21%
2083
5%
801
31%
801
20%
1446
April1st to 10thNight
21%
720
18%
1800
4%
720
29%
720
20%
1279
April11th to 20thNight
21%
693
17%
1757
4%
693
29%
693
22%
1222
April21st to endNight
19%
540
18%
1620
5%
540
29%
540
18%
1095
May1st to 10thNight
21%
540
13%
1620
6%
540
27%
540
15%
1166
May11th to 20thNight
22%
503
15%
1565
6%
503
31%
503
17%
1057
May21st to endNight
32%
389
13%
1551
11%
388
40%
388
16%
997
June1st to 10thNight
32%
360
13%
1440
9%
360
46%
360
17%
945
June11th to 20thNight
33%
360
12%
1440
12%
360
42%
360
17%
936
June21st to endNight
37%
360
12%
1440
10%
360
46%
360
21%
901
July1st to 10thNight
45%
350
13%
1400
13%
350
53%
350
20%
865
July11th to 20thNight
48%
348
12%
1392
13%
348
52%
348
19%
850
July21st to endNight
47%
394
19%
1486
17%
372
55%
372
24%
872
August1st to 10thNight
48%
484
17%
1548
11%
482
53%
482
28%
959
August11th to 20thNight
45%
548
17%
1612
11%
548
48%
548
23%
1092
August21st to endNight
49%
792
20%
1980
9%
792
52%
792
34%
1288
September1st to 10thNight
41%
720
20%
1804
8%
720
48%
720
34%
1180
September11th to 20thNight
43%
720
24%
1980
13%
720
50%
720
34%
1202
September21st to endNight
39%
720
24%
1980
14%
720
48%
720
29%
1274
October1st to 10thNight
33%
720
17%
1980
9%
720
40%
720
22%
1350
October11th to 20thNight
32%
720
21%
2203
9%
720
45%
720
25%
1377
October21st to endNight
23%
792
15%
2574
6%
792
36%
792
17%
1743
November1st to 10thNight
32%
740
22%
2407
12%
740
46%
740
24%
1473
November11th to 20thNight
24%
760
23%
2470
9%
760
41%
760
21%
1532
November21st to endNight
21%
760
21%
2470
6%
760
39%
760
19%
1548
December1st to 10thNight
18%
760
18%
2631
5%
760
34%
760
15%
1750
December11th to 20thNight
21%
760
17%
3192
4%
759
36%
759
13%
1986
December21st to endNight
17%
831
14%
4797
4%
817
35%
817
9%
3111

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
17%6%35%5%35%45%7%40%
78573
Night
18%7%35%5%3445%6%41%
81306
TransparencyDay
43%7%12%22%14%2
78278
Night
44%6%12%21%15%2
81135
SeeingDay
23%17%32%19%7%2
14144
Night
21%14%33%24%7%1
23197

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
15%6%35%5%3435%6%44%
2517
11th to 20thDay
17%7%36%5%35%445%41%
2520
21st to endDay
21%10%35%5%35%445%35%
2772
February1st to 10thDay
19%7%34435%6%6%6%36%
1760
11th to 20thDay
13%9%26%5%25%5%5%7%40%
1848
21st to endDay
18%9%36%5%35%45%5%37%
1570
March1st to 10thDay
17%8%35%5%45%46%7%37%
1897
11th to 20thDay
16%7%36%5%35%45%6%39%
2001
21st to endDay
19%8%36%5%24346%40%
2316
April1st to 10thDay
19%8%36%5%34447%37%
2160
11th to 20thDay
17%6%25%445%45%7%39%
2152
21st to endDay
22%6%36%5%35%45%6%34%
2340
May1st to 10thDay
24%8%35%5%34346%33%
2340
11th to 20thDay
18%5%26%5%3445%6%41%
2344
21st to endDay
14%5%25%43445%8%44%
2725
June1st to 10thDay
20%5%35%6%36%5%6%8%34%
2520
11th to 20thDay
17%5%25%5%35%5%6%8%39%
2520
21st to endDay
18%5%35%5%36%5%6%8%35%
2520
July1st to 10thDay
15%5%25%5%345%7%8%41%
2520
11th to 20thDay
13%425%5%36%5%6%10%40%
2520
21st to endDay
12%5%25%6%35%6%6%9%41%
2744
August1st to 10thDay
10%5%26%6%46%6%7%10%38%
2361
11th to 20thDay
13%6%35%5%46%6%6%8%40%
2285
21st to endDay
13%424435%5%6%8%46%
2376
September1st to 10thDay
14%5%335%25%5%6%6%46%
2156
11th to 20thDay
16%5%24323336%51%
1980
21st to endDay
17%6%3443435%6%46%
1980
October1st to 10thDay
23%5%35%43345%6%39%
1980
11th to 20thDay
15%5%245%2445%7%46%
1754
21st to endDay
22%6%35%43435%5%40%
1782
November1st to 10thDay
16%6%35%5%33345%49%
1671
11th to 20thDay
20%6%2432335%5%47%
1710
21st to endDay
19%6%35%434446%43%
1710
December1st to 10thDay
18%8%36%6%3445%6%39%
1544
11th to 20thDay
23%6%34324435%44%
1906
21st to endDay
23%10%26%5%34446%33%
2772
January1st to 10thNight
18%8%24333446%46%
4429
11th to 20thNight
15%8%47%7%44445%40%
4440
21st to endNight
21%13%46%5%34445%31%
4884
February1st to 10thNight
16%9%25%6%35%5%5%6%38%
2416
11th to 20thNight
15%8%45%5%34447%40%
2218
21st to endNight
19%8%25%5%33446%41%
1884
March1st to 10thNight
17%8%36%434446%40%
2270
11th to 20thNight
16%7%46%5%36%5%45%39%
2176
21st to endNight
19%9%25%5%3444442%
2083
April1st to 10thNight
19%7%35%6%3445%6%37%
1800
11th to 20thNight
21%6%245%2445%5%41%
1757
21st to endNight
21%7%25%6%3435%5%38%
1620
May1st to 10thNight
22%8%35%6%35%5%5%6%32%
1620
11th to 20thNight
19%5%25%4345%6%7%37%
1564
21st to endNight
18%6%35%445%45%7%39%
1550
June1st to 10thNight
19%8%25%6%34446%38%
1440
11th to 20thNight
20%6%345%345%5%7%38%
1440
21st to endNight
15%4345%35%5%6%10%39%
1440
July1st to 10thNight
16%5%35%5%35%5%6%8%40%
1440
11th to 20thNight
12%6%36%6%35%5%6%9%38%
1440
21st to endNight
13%6%25%435%7%5%8%43%
1574
August1st to 10thNight
9%5%25%5%35%5%6%9%45%
1558
11th to 20thNight
12%436%6%46%7%7%8%38%
1612
21st to endNight
14%4245%3445%8%48%
1980
September1st to 10thNight
14%5%245%2345%6%48%
1804
11th to 20thNight
14%6%14432446%53%
1980
21st to endNight
17%5%3442445%6%46%
1980
October1st to 10thNight
21%6%25%5%24445%42%
1980
11th to 20thNight
17%4244245%5%7%45%
2203
21st to endNight
22%7%26%5%3445%6%38%
2574
November1st to 10thNight
15%5%25%4335%46%48%
2407
11th to 20thNight
19%6%25%424345%46%
2470
21st to endNight
16%7%245%24347%44%
2470
December1st to 10thNight
19%8%36%5%34446%38%
2631
11th to 20thNight
20%6%344345%46%41%
3288
21st to endNight
21%9%36%5%34346%35%
4884

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
40%5%12%32%10%1
2518
11th to 20thDay
44%7%10%25%12%1
2520
21st to endDay
51%6%10%22%9%2
2772
February1st to 10thDay
46%7%12%19%13%3
1760
11th to 20thDay
43%7%12%20%15%3
1857
21st to endDay
49%5%11%19%13%3
1570
March1st to 10thDay
46%5%13%20%12%4
1900
11th to 20thDay
43%6%12%19%16%4
2001
21st to endDay
46%5%9%18%16%7%
2316
April1st to 10thDay
47%5%10%18%17%4
2160
11th to 20thDay
44%7%11%19%17%3
2152
21st to endDay
49%6%8%17%16%4
2340
May1st to 10thDay
53%49%19%13%2
2340
11th to 20thDay
43%7%10%19%17%3
2348
21st to endDay
39%8%14%23%14%3
2725
June1st to 10thDay
48%8%13%20%11%
2520
11th to 20thDay
43%8%13%18%16%2
2520
21st to endDay
45%9%12%22%11%1
2520
July1st to 10thDay
39%9%12%23%15%2
2450
11th to 20thDay
38%9%14%26%12%1
2445
21st to endDay
38%9%14%22%14%3
2591
August1st to 10thDay
40%10%14%23%12%1
2347
11th to 20thDay
40%9%14%23%12%1
2285
21st to endDay
34%8%12%25%18%2
2376
September1st to 10thDay
37%6%12%24%19%1
2156
11th to 20thDay
36%5%9%25%23%2
1980
21st to endDay
38%6%9%23%22%2
1980
October1st to 10thDay
46%6%10%21%14%4
1980
11th to 20thDay
36%7%13%29%14%2
1754
21st to endDay
47%5%11%21%13%3
1782
November1st to 10thDay
38%5%12%26%16%2
1671
11th to 20thDay
41%5%9%23%20%3
1710
21st to endDay
42%5%15%22%13%2
1710
December1st to 10thDay
47%5%14%16%16%1
1544
11th to 20thDay
43%414%18%16%5%
1906
21st to endDay
52%6%12%19%10%1
2772
January1st to 10thNight
40%5%14%27%12%3
4429
11th to 20thNight
45%5%13%20%12%3
4440
21st to endNight
55%6%10%17%10%2
4884
February1st to 10thNight
46%6%13%20%13%2
2416
11th to 20thNight
44%5%12%21%16%4
2220
21st to endNight
44%5%9%23%15%4
1884
March1st to 10thNight
45%5%9%22%14%4
2280
11th to 20thNight
47%6%11%16%16%4
2177
21st to endNight
45%5%8%16%20%6%
2083
April1st to 10thNight
46%6%12%18%16%3
1800
11th to 20thNight
44%5%10%19%18%3
1757
21st to endNight
47%5%13%16%14%4
1620
May1st to 10thNight
52%6%10%17%12%3
1620
11th to 20thNight
44%9%12%16%16%3
1565
21st to endNight
45%8%13%22%12%1
1551
June1st to 10thNight
48%6%12%22%11%
1440
11th to 20thNight
45%8%13%18%15%2
1440
21st to endNight
39%10%16%21%14%1
1440
July1st to 10thNight
41%8%13%22%15%1
1400
11th to 20thNight
40%9%16%25%10%
1392
21st to endNight
37%8%15%28%12%2
1486
August1st to 10thNight
34%9%15%24%15%1
1548
11th to 20thNight
41%10%16%20%12%1
1612
21st to endNight
34%7%12%26%19%1
1980
September1st to 10thNight
36%6%13%25%19%1
1804
11th to 20thNight
33%6%11%22%26%2
1980
21st to endNight
37%7%10%25%20%2
1980
October1st to 10thNight
45%6%12%22%12%3
1980
11th to 20thNight
37%7%14%27%13%1
2203
21st to endNight
48%5%12%20%13%1
2574
November1st to 10thNight
38%6%12%22%20%3
2407
11th to 20thNight
41%411%23%18%3
2470
21st to endNight
41%5%14%24%14%2
2470
December1st to 10thNight
48%5%12%21%13%1
2631
11th to 20thNight
43%6%15%17%18%1
3288
21st to endNight
50%6%9%24%10%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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
26%25%31%15%3
180
11th to 20thDay
34%21%32%11%21
180
21st to endDay
24%26%35%11%4
198
February1st to 10thDay
32%19%34%14%1
362
11th to 20thDay
28%29%31%11%2
456
21st to endDay
28%20%35%13%3
382
March1st to 10thDay
29%20%36%12%3
460
11th to 20thDay
28%24%32%11%31
460
21st to endDay
30%22%30%11%6%2
470
April1st to 10thDay
29%26%25%13%6%1
420
11th to 20thDay
28%25%29%11%6%
412
21st to endDay
29%19%33%14%31
420
May1st to 10thDay
33%21%29%11%42
423
11th to 20thDay
23%17%40%16%41
447
21st to endDay
19%14%38%22%7%1
485
June1st to 10thDay
21%14%38%17%8%2
450
11th to 20thDay
16%19%37%21%5%2
450
21st to endDay
19%14%36%21%9%2
450
July1st to 10thDay
18%10%28%30%11%3
445
11th to 20thDay
15%7%33%29%13%2
444
21st to endDay
12%9%38%31%10%1
488
August1st to 10thDay
11%10%34%30%13%2
446
11th to 20thDay
17%9%28%29%13%4
439
21st to endDay
13%10%34%26%14%4
495
September1st to 10thDay
19%10%28%22%16%5%
450
11th to 20thDay
20%15%27%18%12%7%
450
21st to endDay
19%13%32%21%9%5%
450
October1st to 10thDay
29%12%24%21%10%4
450
11th to 20thDay
20%18%28%23%10%2
399
21st to endDay
29%14%30%18%7%1
396
November1st to 10thDay
21%15%33%20%10%2
365
11th to 20thDay
31%19%27%16%6%1
370
21st to endDay
28%18%31%16%6%1
370
December1st to 10thDay
23%26%32%15%3
204
11th to 20thDay
32%25%32%9%2
180
21st to endDay
23%29%29%14%42
198
January1st to 10thNight
21%20%39%18%3
760
11th to 20thNight
27%19%34%18%2
760
21st to endNight
21%20%36%20%3
836
February1st to 10thNight
23%17%38%21%2
760
11th to 20thNight
21%21%39%17%2
743
21st to endNight
25%19%32%20%3
628
March1st to 10thNight
26%18%35%19%3
760
11th to 20thNight
22%21%37%16%4
760
21st to endNight
26%19%32%19%4
801
April1st to 10thNight
24%19%33%20%4
720
11th to 20thNight
25%19%33%18%6%
693
21st to endNight
24%15%37%21%21
540
May1st to 10thNight
27%14%34%20%4
540
11th to 20thNight
22%15%36%22%5%
503
21st to endNight
18%11%34%30%7%
389
June1st to 10thNight
21%7%34%29%8%1
360
11th to 20thNight
19%10%33%31%7%1
360
21st to endNight
18%436%34%8%
360
July1st to 10thNight
16%5%29%41%9%1
350
11th to 20thNight
14%426%42%13%1
348
21st to endNight
13%429%43%10%
394
August1st to 10thNight
10%5%30%42%13%1
484
11th to 20thNight
13%6%29%38%14%1
548
21st to endNight
15%5%24%38%15%2
792
September1st to 10thNight
16%433%32%14%
720
11th to 20thNight
17%8%28%27%18%2
720
21st to endNight
19%7%28%29%14%2
720
October1st to 10thNight
25%10%26%25%12%2
720
11th to 20thNight
20%12%31%25%11%1
720
21st to endNight
27%13%32%23%5%
792
November1st to 10thNight
18%13%32%27%8%1
740
11th to 20thNight
23%18%32%20%6%1
760
21st to endNight
23%19%33%20%41
760
December1st to 10thNight
25%17%36%18%4
760
11th to 20thNight
24%17%32%23%31
760
21st to endNight
25%17%35%19%3
836
Page generated at 2024-03-19 23:31:07. Version ac07

Copyright © 2024 Attilla Danko.


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