Astraeus Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astraeus Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
46%
15835
21%
48065
16%
15791
52%
15791
26%
30883

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
22%
765
14%
2472
8%
761
30%
761
14%
1816
January16th to endNight
23%
768
17%
2496
10%
768
32%
768
17%
1738
February1st to 15thNight
24%
704
15%
2122
6%
701
33%
701
18%
1504
February16th to endNight
21%
631
15%
1893
8%
631
28%
631
17%
1369
March1st to 15thNight
28%
720
17%
2102
11%
720
34%
720
20%
1464
March16th to endNight
35%
768
16%
2112
10%
768
40%
768
23%
1473
April1st to 15thNight
41%
560
22%
1818
16%
560
51%
560
27%
1103
April16th to endNight
42%
540
21%
1677
14%
540
50%
540
25%
1089
May1st to 15thNight
44%
539
15%
1619
10%
539
49%
539
21%
1131
May16th to endNight
62%
562
20%
1684
16%
561
65%
561
30%
1059
June1st to 15thNight
72%
540
20%
1614
18%
540
74%
540
41%
892
June16th to endNight
74%
540
21%
1440
17%
540
75%
540
42%
853
July1st to 15thNight
65%
510
16%
1396
13%
510
66%
510
31%
919
July16th to endNight
75%
564
22%
1595
19%
531
78%
531
40%
896
August1st to 15thNight
79%
539
24%
1609
22%
536
80%
536
41%
897
August16th to endNight
78%
573
23%
1887
26%
573
79%
573
38%
1006
September1st to 15thNight
66%
655
25%
1915
23%
655
68%
655
33%
1150
September16th to endNight
64%
717
30%
1980
25%
717
66%
717
38%
1181
October1st to 15thNight
58%
720
31%
1995
26%
720
62%
720
38%
1158
October16th to endNight
46%
768
28%
2394
23%
768
55%
768
30%
1441
November1st to 15thNight
48%
760
28%
2471
24%
760
56%
760
31%
1433
November16th to endNight
39%
780
24%
2535
20%
780
47%
780
25%
1591
December1st to 15thNight
32%
780
15%
2535
10%
780
39%
780
18%
1759
December16th to endNight
24%
832
16%
2704
9%
832
34%
832
15%
1961

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
14%6%35%5%35%45%7%38%
49260
Night
14%7%35%42445%7%41%
48256
TransparencyDay
44%411%22%14%2
48954
Night
42%410%22%16%3
48066
SeeingDay
16%419%23%21%13%
5934
Night
17%5%22%31%20%2
15837

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 15thDay
19%10%38%5%34446%29%
1710
16th to endDay
17%10%5%7%5%23346%33%
1728
February1st to 15thDay
16%11%49%5%25%345%31%
1738
16th to endDay
15%11%47%5%35%45%6%29%
1580
March1st to 15thDay
23%8%36%423345%34%
1857
16th to endDay
17%8%36%5%3446%6%32%
2111
April1st to 15thDay
16%5%35%5%25%45%6%39%
2139
16th to endDay
16%6%345%34447%39%
2283
May1st to 15thDay
20%7%35%5%35%5%47%32%
2331
16th to endDay
10%5%27%5%35%6%6%9%37%
2431
June1st to 15thDay
10%425%446%6%6%7%42%
2340
16th to endDay
7%3245%37%6%6%9%42%
2520
July1st to 15thDay
14%6%35%5%35%5%6%10%33%
2475
16th to endDay
8%5%25%5%47%6%8%8%36%
2465
August1st to 15thDay
9%415%6%35%5%7%11%38%
2340
16th to endDay
7%5%25%6%35%6%7%9%39%
2312
September1st to 15thDay
14%5%24435%5%5%7%40%
2031
16th to endDay
13%5%24324446%47%
1980
October1st to 15thDay
11%414434246%51%
1963
16th to endDay
18%6%24322345%47%
1827
November1st to 15thDay
14%6%245%23346%48%
1717
16th to endDay
17%7%24423335%44%
1755
December1st to 15thDay
23%10%36%423345%32%
1755
16th to endDay
19%12%47%5%24436%30%
1872
January1st to 15thNight
17%11%5%8%7%35%43429%
2472
16th to endNight
18%11%46%5%24435%33%
2496
February1st to 15thNight
20%8%47%42445%433%
2113
16th to endNight
17%11%48%5%2444430%
1893
March1st to 15thNight
18%9%36%42444435%
2102
16th to endNight
15%8%36%5%3345%7%35%
2112
April1st to 15thNight
14%5%2442445%8%43%
1818
16th to endNight
13%5%36%5%25%447%41%
1677
May1st to 15thNight
16%6%35%5%35%6%5%6%33%
1619
16th to endNight
7%426%5%36%5%8%10%40%
1682
June1st to 15thNight
5%3234245%5%11%50%
1614
16th to endNight
5%223436%5%8%13%44%
1440
July1st to 15thNight
10%5%25%5%25%46%7%44%
1479
16th to endNight
7%313435%46%11%49%
1703
August1st to 15thNight
5%213425%47%10%51%
1620
16th to endNight
5%313425%5%7%10%50%
1887
September1st to 15thNight
13%41342445%8%46%
1915
16th to endNight
10%5%15%423245%53%
1980
October1st to 15thNight
10%5%13424446%52%
1995
16th to endNight
15%5%24423346%47%
2394
November1st to 15thNight
13%6%24423346%49%
2471
16th to endNight
17%7%24423335%44%
2535
December1st to 15thNight
20%9%46%424446%31%
2535
16th to endNight
21%12%46%5%24345%29%
2704

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
55%38%19%12%1
1711
16th to endDay
52%29%25%8%1
1728
February1st to 15thDay
55%37%23%8%1
1740
16th to endDay
53%312%21%8%
1580
March1st to 15thDay
52%311%19%12%1
1857
16th to endDay
50%412%22%8%
2112
April1st to 15thDay
43%410%24%15%2
2139
16th to endDay
44%49%23%14%4
2283
May1st to 15thDay
50%5%12%19%12%
2331
16th to endDay
41%6%16%21%12%1
2435
June1st to 15thDay
38%6%13%24%15%1
2340
16th to endDay
36%6%13%20%19%3
2520
July1st to 15thDay
45%5%13%17%14%4
2329
16th to endDay
39%6%15%23%12%2
2310
August1st to 15thDay
37%7%12%23%16%1
2327
16th to endDay
37%6%10%24%16%4
2312
September1st to 15thDay
41%5%12%18%17%4
2031
16th to endDay
36%48%23%24%2
1980
October1st to 15thDay
35%27%26%23%3
1963
16th to endDay
39%28%26%19%2
1827
November1st to 15thDay
38%26%26%18%6%
1717
16th to endDay
43%26%25%20%1
1755
December1st to 15thDay
54%210%20%10%1
1755
16th to endDay
55%311%20%7%
1872
January1st to 15thNight
58%37%15%13%1
2472
16th to endNight
53%29%22%9%1
2496
February1st to 15thNight
53%210%22%9%1
2122
16th to endNight
55%311%18%10%
1893
March1st to 15thNight
50%38%21%13%2
2102
16th to endNight
48%413%22%10%1
2112
April1st to 15thNight
38%49%22%20%3
1818
16th to endNight
42%5%9%22%14%6%
1677
May1st to 15thNight
48%5%11%21%9%2
1620
16th to endNight
34%8%14%23%15%3
1684
June1st to 15thNight
27%415%29%18%4
1614
16th to endNight
27%6%19%22%17%5%
1440
July1st to 15thNight
38%5%12%22%16%4
1396
16th to endNight
26%7%17%27%18%2
1595
August1st to 15thNight
26%6%17%26%19%4
1609
16th to endNight
26%6%15%26%21%4
1887
September1st to 15thNight
35%411%20%21%6%
1915
16th to endNight
33%38%23%26%4
1980
October1st to 15thNight
31%38%26%24%5%
1995
16th to endNight
38%27%26%21%3
2394
November1st to 15thNight
36%26%24%23%6%
2471
16th to endNight
42%37%25%19%1
2535
December1st to 15thNight
52%310%20%11%1
2535
16th to endNight
57%39%19%9%1
2704

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
26%10%39%12%8%2
123
16th to endDay
23%15%46%9%4
96
February1st to 15thDay
17%17%44%16%3
90
16th to endDay
27%13%30%23%4
81
March1st to 15thDay
26%7%40%18%6%
147
16th to endDay
19%9%31%25%12%1
288
April1st to 15thDay
19%10%21%29%15%2
270
16th to endDay
20%8%22%25%13%10%
270
May1st to 15thDay
23%6%24%20%15%8%
288
16th to endDay
14%222%25%19%16%
331
June1st to 15thDay
13%110%21%33%19%
315
16th to endDay
9%318%30%26%12%
495
July1st to 15thDay
17%115%25%25%15%
433
16th to endDay
9%6%21%33%28%
326
August1st to 15thDay
15%5%18%30%30%
313
16th to endDay
9%16%26%32%24%
332
September1st to 15thDay
15%110%19%31%21%
315
16th to endDay
12%211%19%33%20%
314
October1st to 15thDay
16%218%26%23%12%
315
16th to endDay
16%5%24%28%21%4
243
November1st to 15thDay
20%6%22%25%17%7%
135
16th to endDay
21%5%24%34%11%2
135
December1st to 15thDay
17%11%31%28%8%1
135
16th to endDay
26%13%43%13%3
144
January1st to 15thNight
22%12%33%25%5%
765
16th to endNight
25%11%35%25%2
768
February1st to 15thNight
26%8%33%29%1
704
16th to endNight
23%9%38%25%2
631
March1st to 15thNight
25%9%32%26%6%
720
16th to endNight
20%8%28%30%10%
768
April1st to 15thNight
16%7%32%32%10%
560
16th to endNight
16%5%29%32%15%2
540
May1st to 15thNight
20%420%35%16%2
540
16th to endNight
8%314%38%27%8%
563
June1st to 15thNight
6%111%42%34%3
540
16th to endNight
4110%45%35%3
540
July1st to 15thNight
12%19%31%39%5%
510
16th to endNight
7%16%30%45%8%
564
August1st to 15thNight
7%5%33%46%6%
539
16th to endNight
6%5%33%49%4
573
September1st to 15thNight
14%28%28%39%6%
655
16th to endNight
11%211%29%37%6%
717
October1st to 15thNight
12%319%30%27%6%
720
16th to endNight
19%424%33%16%1
768
November1st to 15thNight
16%6%23%31%19%2
760
16th to endNight
20%8%26%31%12%
780
December1st to 15thNight
27%8%26%28%8%
780
16th to endNight
28%9%31%25%4
832
Page generated at 2018-01-12 22:01:32. Version ac04

Copyright 2018 A. Danko


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