ASTROTX Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ASTROTX Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
46%
24069
28%
74412
18%
24011
56%
24011
36%
41032

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
31%
2458
12%
946
47%
946
39%
1448
January11th to 20thNight
32%
950
29%
2470
9%
950
44%
950
34%
1484
January21st to endNight
33%
1025
31%
2665
11%
1025
44%
1025
33%
1647
February1st to 10thNight
30%
824
26%
2264
9%
824
41%
824
30%
1402
February11th to 20thNight
25%
704
23%
2098
9%
700
36%
700
28%
1274
February21st to endNight
21%
554
28%
1738
8%
554
37%
554
25%
1037
March1st to 10thNight
29%
540
25%
1980
12%
540
44%
540
25%
1157
March11th to 20thNight
30%
540
24%
1980
14%
540
43%
540
24%
1140
March21st to endNight
29%
594
26%
2178
13%
594
47%
594
28%
1189
April1st to 10thNight
30%
540
28%
1980
14%
540
51%
540
30%
1032
April11th to 20thNight
30%
533
25%
1847
15%
533
45%
533
27%
1032
April21st to endNight
34%
540
29%
1690
16%
540
52%
540
34%
944
May1st to 10thNight
35%
540
27%
1620
17%
540
50%
540
32%
960
May11th to 20thNight
40%
531
21%
1594
16%
531
49%
531
33%
946
May21st to endNight
46%
584
23%
1745
17%
582
58%
582
36%
1004
June1st to 10thNight
67%
540
23%
1620
24%
540
73%
540
44%
840
June11th to 20thNight
61%
540
27%
1620
25%
540
70%
540
52%
791
June21st to endNight
68%
540
26%
1620
27%
540
73%
540
47%
838
July1st to 10thNight
71%
525
23%
1575
24%
525
76%
525
42%
848
July11th to 20thNight
82%
522
32%
1566
37%
522
87%
522
64%
693
July21st to endNight
84%
591
31%
1673
35%
558
87%
558
54%
816
August1st to 10thNight
87%
537
36%
1601
41%
534
89%
534
67%
672
August11th to 20thNight
76%
534
33%
1600
36%
534
79%
534
45%
842
August21st to endNight
81%
594
28%
2023
33%
594
83%
594
45%
989
September1st to 10thNight
72%
540
25%
1980
30%
540
74%
540
38%
990
September11th to 20thNight
70%
540
26%
1980
29%
540
72%
540
33%
1051
September21st to endNight
71%
540
36%
1980
36%
540
77%
540
46%
897
October1st to 10thNight
62%
580
35%
2020
30%
580
70%
580
46%
942
October11th to 20thNight
50%
720
35%
2160
18%
720
62%
720
42%
1150
October21st to endNight
44%
792
33%
2376
20%
792
53%
792
37%
1318
November1st to 10thNight
47%
740
32%
2220
18%
740
58%
740
40%
1214
November11th to 20thNight
43%
859
31%
2379
15%
859
55%
859
41%
1331
November21st to endNight
34%
950
30%
2470
12%
950
46%
950
34%
1520
December1st to 10thNight
34%
950
32%
2470
12%
950
47%
950
36%
1491
December11th to 20thNight
32%
949
30%
2860
12%
948
42%
948
28%
1745
December21st to endNight
32%
1039
18%
4312
11%
1026
43%
1026
24%
2358

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%51%
75062
Night
11%424323447%56%
75015
TransparencyDay
33%5%10%23%21%7%
74787
Night
29%410%22%24%11%
74810
SeeingDay
13%8%24%28%21%6%
14050
Night
13%8%29%34%15%1
24078

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
13%5%24422346%55%
1707
11th to 20thDay
14%6%24423335%54%
1710
21st to endDay
17%5%24313336%51%
1836
February1st to 10thDay
18%7%36%42343446%
1712
11th to 20thDay
19%7%34432345%46%
1749
21st to endDay
23%6%2331324451%
1516
March1st to 10thDay
19%5%2442445%6%45%
1980
11th to 20thDay
18%6%24433446%46%
1980
21st to endDay
14%6%35%424346%48%
2178
April1st to 10thDay
13%5%25%5%3446%7%47%
1980
11th to 20thDay
15%6%25%5%345%5%7%45%
2060
21st to endDay
13%5%2443445%6%48%
2266
May1st to 10thDay
14%6%26%43445%7%46%
2340
11th to 20thDay
12%5%36%5%35%5%5%7%43%
2302
21st to endDay
12%5%36%6%45%6%7%8%37%
2531
June1st to 10thDay
6%3145%36%5%7%9%52%
2340
11th to 20thDay
6%3245%45%45%9%53%
2340
21st to endDay
6%4245%3446%9%54%
2340
July1st to 10thDay
7%425%5%45%6%8%10%43%
2340
11th to 20thDay
3212435%5%6%9%60%
2340
21st to endDay
33245%35%6%7%11%52%
2546
August1st to 10thDay
31134235%6%10%63%
2328
11th to 20thDay
7%4145%346%7%10%50%
2301
21st to endDay
5%3145%35%6%7%10%52%
2328
September1st to 10thDay
8%42432445%7%56%
1980
11th to 20thDay
10%5%25%435%5%5%7%49%
1980
21st to endDay
8%413433447%59%
1980
October1st to 10thDay
6%31343445%6%61%
1922
11th to 20thDay
14%413223345%60%
1800
21st to endDay
15%42432332458%
1980
November1st to 10thDay
13%5%23313346%57%
1858
11th to 20thDay
7%424433446%58%
1796
21st to endDay
16%5%34422345%52%
1710
December1st to 10thDay
16%5%2443345%6%50%
1710
11th to 20thDay
17%6%25%5%3344447%
2161
21st to endDay
18%7%24323345%49%
3135
January1st to 10thNight
12%5%24323345%57%
2458
11th to 20thNight
15%5%23423345%55%
2470
21st to endNight
15%5%34322335%54%
2665
February1st to 10thNight
17%424333435%52%
2264
11th to 20thNight
17%6%34423335%50%
2098
21st to endNight
20%5%34322245%50%
1738
March1st to 10thNight
17%425%42346%8%45%
1980
11th to 20thNight
16%6%24323447%49%
1980
21st to endNight
12%425%324446%54%
2178
April1st to 10thNight
10%42342346%9%53%
1980
11th to 20thNight
15%5%24423446%51%
1847
21st to endNight
12%5%24323347%55%
1690
May1st to 10thNight
10%5%3442446%8%50%
1620
11th to 20thNight
11%4244245%6%8%49%
1593
21st to endNight
9%4234345%7%11%49%
1745
June1st to 10thNight
431442446%10%59%
1620
11th to 20thNight
421242345%10%63%
1620
21st to endNight
32134345%7%10%58%
1620
July1st to 10thNight
4324435%46%11%53%
1620
11th to 20thNight
311221335%8%72%
1620
21st to endNight
12133245%6%13%59%
1772
August1st to 10thNight
211121235%10%72%
1611
11th to 20thNight
5%4143245%5%8%60%
1600
21st to endNight
42233245%7%9%57%
2023
September1st to 10thNight
8%42432445%9%56%
1980
11th to 20thNight
12%325%32345%7%54%
1980
21st to endNight
6%313213448%64%
1980
October1st to 10thNight
6%31332345%7%63%
2020
11th to 20thNight
13%423313235%63%
2160
21st to endNight
16%5%2322222461%
2376
November1st to 10thNight
10%5%2432333462%
2220
11th to 20thNight
7%5%2442335%6%59%
2379
21st to endNight
16%5%34423345%53%
2470
December1st to 10thNight
14%5%24313346%54%
2470
11th to 20thNight
13%6%35%5%24336%51%
3036
21st to endNight
17%5%24322235%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
32%38%20%30%7%
1708
11th to 20thDay
35%37%23%26%6%
1710
21st to endDay
36%35%18%28%10%
1836
February1st to 10thDay
43%46%18%21%9%
1712
11th to 20thDay
43%38%18%20%8%
1759
21st to endDay
39%35%16%23%14%
1516
March1st to 10thDay
40%46%17%21%11%
1980
11th to 20thDay
41%48%18%23%6%
1980
21st to endDay
38%410%19%21%8%
2178
April1st to 10thDay
37%411%21%17%10%
1980
11th to 20thDay
39%5%9%18%21%8%
2060
21st to endDay
36%6%9%21%24%5%
2266
May1st to 10thDay
38%5%9%23%18%7%
2340
11th to 20thDay
40%6%12%22%17%2
2306
21st to endDay
42%8%13%21%14%2
2531
June1st to 10thDay
26%10%16%29%16%3
2340
11th to 20thDay
28%6%13%30%18%5%
2340
21st to endDay
26%6%12%29%23%4
2340
July1st to 10thDay
33%8%18%27%14%1
2276
11th to 20thDay
18%8%14%36%20%4
2271
21st to endDay
22%8%19%36%14%1
2405
August1st to 10thDay
16%6%16%36%24%3
2314
11th to 20thDay
28%8%15%28%19%3
2301
21st to endDay
25%8%15%31%17%4
2328
September1st to 10thDay
27%6%11%25%22%9%
1980
11th to 20thDay
35%6%11%19%21%7%
1980
21st to endDay
25%5%8%23%27%12%
1980
October1st to 10thDay
23%5%11%25%20%16%
1922
11th to 20thDay
28%47%18%27%17%
1800
21st to endDay
32%36%17%26%16%
1980
November1st to 10thDay
31%39%23%25%9%
1858
11th to 20thDay
28%49%20%29%10%
1796
21st to endDay
36%36%21%24%10%
1710
December1st to 10thDay
36%48%21%24%7%
1710
11th to 20thDay
41%46%15%26%8%
2159
21st to endDay
38%35%23%22%8%
3135
January1st to 10thNight
30%37%20%28%12%
2458
11th to 20thNight
32%37%20%27%10%
2470
21st to endNight
35%35%16%28%13%
2665
February1st to 10thNight
37%47%18%22%13%
2264
11th to 20thNight
38%38%16%24%10%
2098
21st to endNight
38%37%14%20%16%
1738
March1st to 10thNight
38%48%16%20%13%
1980
11th to 20thNight
37%5%10%14%26%9%
1980
21st to endNight
33%411%20%24%7%
2178
April1st to 10thNight
28%5%11%24%19%13%
1980
11th to 20thNight
34%49%20%18%14%
1847
21st to endNight
30%5%9%23%28%5%
1690
May1st to 10thNight
32%7%10%23%20%8%
1620
11th to 20thNight
32%7%16%25%18%3
1594
21st to endNight
29%7%18%26%18%3
1746
June1st to 10thNight
21%7%16%31%20%5%
1620
11th to 20thNight
18%5%13%36%20%7%
1620
21st to endNight
20%7%13%29%26%5%
1620
July1st to 10thNight
24%7%17%34%16%3
1575
11th to 20thNight
11%5%14%37%27%6%
1566
21st to endNight
15%8%18%38%19%2
1673
August1st to 10thNight
9%414%38%30%5%
1601
11th to 20thNight
22%6%14%29%22%6%
1600
21st to endNight
21%6%15%32%22%4
2023
September1st to 10thNight
26%5%12%23%24%10%
1980
11th to 20thNight
30%5%12%21%21%11%
1980
21st to endNight
21%49%22%29%16%
1980
October1st to 10thNight
20%410%26%20%19%
2020
11th to 20thNight
26%37%16%25%22%
2160
21st to endNight
30%35%17%26%20%
2376
November1st to 10thNight
27%46%21%27%14%
2220
11th to 20thNight
27%37%19%28%15%
2379
21st to endNight
35%37%16%27%11%
2470
December1st to 10thNight
33%48%21%23%11%
2470
11th to 20thNight
37%36%16%26%12%
3037
21st to endNight
35%36%18%26%12%
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
19%14%39%22%5%
270
11th to 20thDay
20%20%37%17%41
270
21st to endDay
21%17%39%17%6%
282
February1st to 10thDay
24%18%35%21%2
240
11th to 20thDay
26%22%40%10%3
240
21st to endDay
34%21%35%7%3
198
March1st to 10thDay
26%18%38%16%2
240
11th to 20thDay
29%15%37%15%3
240
21st to endDay
19%20%43%14%4
264
April1st to 10thDay
18%18%39%20%4
240
11th to 20thDay
21%15%34%22%7%
338
21st to endDay
18%17%36%22%6%1
526
May1st to 10thDay
16%13%37%28%5%1
603
11th to 20thDay
16%5%34%30%13%2
625
21st to endDay
14%5%30%34%14%3
679
June1st to 10thDay
6%317%39%27%7%
630
11th to 20thDay
8%220%40%24%7%
630
21st to endDay
5%316%37%29%10%
630
July1st to 10thDay
6%311%32%37%11%
621
11th to 20thDay
217%36%43%12%
618
21st to endDay
315%32%46%13%
684
August1st to 10thDay
318%34%44%10%
626
11th to 20thDay
8%15%38%38%9%
615
21st to endDay
6%15%28%44%16%
447
September1st to 10thDay
6%17%24%43%20%
270
11th to 20thDay
2210%30%41%15%
270
21st to endDay
10%210%32%30%15%
270
October1st to 10thDay
4324%31%32%6%
270
11th to 20thDay
14%8%29%31%16%3
270
21st to endDay
27%10%22%25%15%1
297
November1st to 10thDay
19%9%36%24%9%3
270
11th to 20thDay
13%12%32%30%10%3
270
21st to endDay
20%16%36%23%6%
270
December1st to 10thDay
22%12%34%22%7%3
270
11th to 20thDay
23%13%39%20%5%
270
21st to endDay
20%15%41%18%6%
297
January1st to 10thNight
15%10%36%31%7%
950
11th to 20thNight
20%13%32%30%5%
950
21st to endNight
17%12%34%31%5%
1025
February1st to 10thNight
20%13%36%27%4
824
11th to 20thNight
21%14%37%25%3
704
21st to endNight
24%16%38%19%3
554
March1st to 10thNight
19%12%36%26%6%
540
11th to 20thNight
19%11%37%28%5%
540
21st to endNight
14%13%42%26%4
594
April1st to 10thNight
11%14%42%28%4
540
11th to 20thNight
18%12%38%25%7%
533
21st to endNight
14%11%40%26%9%1
540
May1st to 10thNight
10%9%41%32%6%1
540
11th to 20thNight
11%5%38%30%14%1
531
21st to endNight
9%5%33%37%14%2
584
June1st to 10thNight
6%218%47%24%3
540
11th to 20thNight
4228%50%15%1
540
21st to endNight
3121%45%26%4
540
July1st to 10thNight
4116%42%33%5%
525
11th to 20thNight
3111%48%35%2
522
21st to endNight
117%51%36%4
591
August1st to 10thNight
216%52%35%4
537
11th to 20thNight
7%19%44%34%6%
534
21st to endNight
416%42%41%6%
594
September1st to 10thNight
8%211%39%36%5%
540
11th to 20thNight
13%17%41%35%3
540
21st to endNight
8%116%39%30%6%
540
October1st to 10thNight
7%224%37%26%4
580
11th to 20thNight
15%5%27%36%16%1
720
21st to endNight
19%8%27%31%14%1
792
November1st to 10thNight
11%5%33%34%16%1
740
11th to 20thNight
10%10%34%34%12%1
859
21st to endNight
19%11%33%27%9%1
950
December1st to 10thNight
17%9%36%30%7%
950
11th to 20thNight
20%10%33%31%6%
950
21st to endNight
19%11%35%29%6%
1045
Page generated at 2024-01-24 08:37:29. Version ac07

Copyright 2024 Attilla Danko


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