Gov Aker Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gov Aker Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
73%
15452
35%
46956
29%
15411
80%
15411
53%
22340

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
70%
717
33%
2327
33%
716
76%
716
49%
1102
January16th to endNight
67%
768
36%
2496
34%
768
76%
768
45%
1234
February1st to 15thNight
70%
699
35%
2270
33%
696
80%
696
55%
1027
February16th to endNight
62%
632
42%
1787
31%
632
73%
632
58%
848
March1st to 15thNight
63%
720
41%
1980
29%
720
73%
720
61%
947
March16th to endNight
67%
768
40%
2112
25%
768
79%
768
66%
968
April1st to 15thNight
64%
632
36%
1891
24%
632
77%
632
61%
824
April16th to endNight
64%
540
45%
1800
34%
540
80%
540
70%
660
May1st to 15thNight
69%
539
37%
1671
29%
539
78%
539
67%
682
May16th to endNight
75%
562
39%
1684
33%
561
81%
561
70%
692
June1st to 15thNight
81%
540
34%
1620
28%
540
84%
540
69%
678
June16th to endNight
84%
540
27%
1620
22%
540
86%
540
57%
750
July1st to 15thNight
76%
510
19%
1530
15%
510
77%
510
33%
916
July16th to endNight
81%
564
16%
1593
15%
531
81%
531
30%
988
August1st to 15thNight
83%
539
22%
1611
20%
536
83%
536
34%
946
August16th to endNight
84%
573
27%
1896
29%
573
84%
573
36%
1041
September1st to 15thNight
76%
645
27%
1905
26%
645
77%
645
34%
1138
September16th to endNight
82%
692
41%
1914
31%
692
86%
692
63%
896
October1st to 15thNight
81%
660
39%
1960
32%
660
85%
660
62%
882
October16th to endNight
83%
704
42%
2112
35%
704
89%
704
69%
886
November1st to 15thNight
78%
700
42%
2100
35%
700
84%
700
69%
878
November16th to endNight
73%
720
40%
2241
34%
720
80%
720
54%
1047
December1st to 15thNight
72%
720
38%
2340
37%
720
77%
720
52%
1070
December16th to endNight
66%
768
34%
2496
32%
768
73%
768
44%
1240

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
2112213446%67%
47964
Night
2112223346%68%
47157
TransparencyDay
17%47%15%29%26%
47659
Night
17%47%14%27%28%
46963
SeeingDay
37%18%34%28%8%
5322
Night
3216%43%31%3
15462

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
1213324346%66%
1611
16th to endDay
4213323335%66%
1728
February1st to 15thDay
2213313336%68%
1585
16th to endDay
211232345%5%66%
1686
March1st to 15thDay
21221335%6%69%
1980
16th to endDay
111112335%77%
2112
April1st to 15thDay
111113335%74%
2055
16th to endDay
111112483%
2160
May1st to 15thDay
1111335%5%76%
2277
16th to endDay
11111223479%
2429
June1st to 15thDay
1212345%77%
2340
16th to endDay
112312446%69%
2340
July1st to 15thDay
3213435%6%7%10%51%
2340
16th to endDay
3324436%7%9%12%40%
2467
August1st to 15thDay
4224435%7%9%9%45%
2340
16th to endDay
5%213325%5%6%10%51%
2306
September1st to 15thDay
5%2144345%6%7%52%
2052
16th to endDay
211212235%74%
1904
October1st to 15thDay
112212445%73%
1669
16th to endDay
1111123479%
1760
November1st to 15thDay
111111235%78%
1759
16th to endDay
22223236%73%
1716
December1st to 15thDay
322214337%68%
1620
16th to endDay
331222345%7%63%
1728
January1st to 15thNight
3212323337%67%
2327
16th to endNight
4312323346%64%
2496
February1st to 15thNight
121122345%5%70%
2264
16th to endNight
21232335%6%68%
1787
March1st to 15thNight
2111212345%71%
1980
16th to endNight
111112235%76%
2112
April1st to 15thNight
111212345%73%
1891
16th to endNight
11113384%
1800
May1st to 15thNight
111112225%79%
1671
16th to endNight
3111125%81%
1684
June1st to 15thNight
111112225%79%
1620
16th to endNight
11121435%6%70%
1620
July1st to 15thNight
2215%437%6%8%11%46%
1620
16th to endNight
3114436%8%11%14%38%
1701
August1st to 15thNight
2213437%6%7%11%49%
1620
16th to endNight
3213425%5%8%10%51%
1896
September1st to 15thNight
5%4244345%6%9%49%
1905
16th to endNight
22221223475%
1914
October1st to 15thNight
111122224474%
1960
16th to endNight
11111222381%
2112
November1st to 15thNight
111111335%78%
2100
16th to endNight
32222224471%
2241
December1st to 15thNight
322222347%68%
2340
16th to endNight
32133245%46%62%
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
19%47%17%33%16%
1612
16th to endDay
21%4418%31%19%
1728
February1st to 15thDay
18%26%16%29%25%
1585
16th to endDay
19%45%15%34%20%
1686
March1st to 15thDay
16%2411%37%26%
1980
16th to endDay
11%1412%43%24%
2112
April1st to 15thDay
12%2410%39%29%
2055
16th to endDay
8%1310%31%44%
2160
May1st to 15thDay
8%26%10%31%39%
2277
16th to endDay
9%349%29%43%
2432
June1st to 15thDay
9%24425%53%
2340
16th to endDay
15%25%9%18%47%
2340
July1st to 15thDay
23%8%16%17%15%17%
2201
16th to endDay
29%14%21%21%11%1
2312
August1st to 15thDay
29%10%14%17%18%9%
2325
16th to endDay
25%8%15%18%19%12%
2306
September1st to 15thDay
27%7%9%18%22%13%
2052
16th to endDay
13%25%15%36%26%
1904
October1st to 15thDay
14%45%14%30%30%
1669
16th to endDay
8%25%15%35%30%
1760
November1st to 15thDay
11%2316%39%26%
1759
16th to endDay
15%35%14%35%25%
1716
December1st to 15thDay
18%36%25%29%16%
1620
16th to endDay
20%5%8%23%32%8%
1728
January1st to 15thNight
20%35%17%31%21%
2327
16th to endNight
23%3417%31%19%
2496
February1st to 15thNight
15%45%17%29%27%
2275
16th to endNight
15%36%16%33%23%
1787
March1st to 15thNight
15%25%13%29%33%
1980
16th to endNight
11%2411%37%31%
2112
April1st to 15thNight
13%15%11%37%30%
1891
16th to endNight
8%129%29%49%
1800
May1st to 15thNight
10%25%8%29%45%
1672
16th to endNight
8%2410%24%48%
1685
June1st to 15thNight
10%14321%57%
1620
16th to endNight
14%5%7%7%15%49%
1620
July1st to 15thNight
29%10%13%17%12%15%
1530
16th to endNight
27%14%27%20%7%2
1593
August1st to 15thNight
27%10%16%18%15%10%
1611
16th to endNight
24%10%17%17%18%12%
1896
September1st to 15thNight
30%8%10%19%16%14%
1905
16th to endNight
14%2412%34%31%
1914
October1st to 15thNight
13%26%17%25%33%
1960
16th to endNight
9%2414%28%39%
2112
November1st to 15thNight
10%25%14%37%29%
2100
16th to endNight
18%25%13%27%32%
2241
December1st to 15thNight
18%35%21%33%17%
2340
16th to endNight
22%410%21%31%9%
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
8%8%17%44%18%1
90
16th to endDay
2325%33%26%10%
96
February1st to 15thDay
5%5%15%33%37%5%
100
16th to endDay
16%35%30%15%1
238
March1st to 15thDay
315%24%29%20%7%
270
16th to endDay
115%27%30%19%5%
288
April1st to 15thDay
116%25%35%17%4
269
16th to endDay
120%27%30%16%2
270
May1st to 15thDay
14%29%33%19%2
288
16th to endDay
18%23%42%22%1
330
June1st to 15thDay
219%38%30%6%
315
16th to endDay
413%33%38%10%
315
July1st to 15thDay
312%38%35%9%
305
16th to endDay
36%33%33%20%
327
August1st to 15thDay
415%29%44%14%
315
16th to endDay
4430%42%18%
332
September1st to 15thDay
5%12%36%38%6%
315
16th to endDay
5%118%33%33%7%
288
October1st to 15thDay
2215%35%23%19%
109
16th to endDay
4110%25%40%18%
96
November1st to 15thDay
3327%33%23%8%
90
16th to endDay
212%28%33%22%1
90
December1st to 15thDay
1211%41%42%2
90
16th to endDay
9%9%23%42%14%
96
January1st to 15thNight
4218%51%20%2
720
16th to endNight
5%319%47%22%1
768
February1st to 15thNight
2121%45%25%2
704
16th to endNight
3228%48%16%
632
March1st to 15thNight
3327%41%22%2
720
16th to endNight
1324%40%27%1
768
April1st to 15thNight
25%25%46%19%
632
16th to endNight
5%27%47%16%2
540
May1st to 15thNight
1225%47%20%2
540
16th to endNight
3117%49%27%
563
June1st to 15thNight
114%52%29%
540
16th to endNight
19%48%38%1
540
July1st to 15thNight
38%40%44%3
510
16th to endNight
21432%49%9%
564
August1st to 15thNight
31424%54%12%
539
16th to endNight
3327%53%10%
573
September1st to 15thNight
6%18%29%48%5%
645
16th to endNight
39%40%41%4
692
October1st to 15thNight
212%45%35%2
660
16th to endNight
111%44%35%5%
704
November1st to 15thNight
116%43%33%5%
700
16th to endNight
5%116%45%27%3
720
December1st to 15thNight
5%117%46%26%2
720
16th to endNight
4321%48%19%2
768
Page generated at 2017-09-25 06:02:29. Version ac04

Copyright 2017 A. Danko


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