Observatoire Aster
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Aster clear sky chart from 2005-11-05 to 2017-12-20.

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
23%
15036
10%
48039
5%
15004
29%
15004
12%
35867

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
12%
737
7%
2611
2%
733
18%
733
5%
2110
January16th to endNight
16%
768
11%
2688
4%
768
25%
768
9%
2030
February1st to 15thNight
18%
704
8%
2350
3%
701
25%
701
8%
1822
February16th to endNight
15%
631
10%
1922
2%
631
23%
631
9%
1521
March1st to 15thNight
20%
720
13%
2109
7%
720
27%
720
12%
1606
March16th to endNight
23%
768
15%
2096
6%
768
30%
768
16%
1528
April1st to 15thNight
20%
653
14%
1731
4%
653
26%
653
14%
1313
April16th to endNight
25%
540
16%
1620
8%
540
32%
540
16%
1142
May1st to 15thNight
25%
516
10%
1596
7%
516
30%
516
14%
1189
May16th to endNight
25%
375
9%
1325
5%
374
33%
374
10%
993
June1st to 15thNight
35%
360
7%
1260
5%
360
37%
360
15%
888
June16th to endNight
30%
360
6%
1260
4%
360
32%
360
13%
925
July1st to 15thNight
35%
340
8%
1190
5%
340
40%
340
17%
806
July16th to endNight
37%
376
8%
1398
8%
354
43%
354
15%
943
August1st to 15thNight
38%
467
10%
1538
7%
465
43%
465
17%
1085
August16th to endNight
36%
573
14%
1719
7%
573
42%
573
23%
1139
September1st to 15thNight
32%
696
10%
1872
5%
696
36%
696
23%
1306
September16th to endNight
32%
717
18%
1980
9%
717
39%
717
24%
1311
October1st to 15thNight
27%
720
16%
2083
6%
720
36%
720
19%
1445
October16th to endNight
22%
768
9%
2490
4%
768
28%
768
11%
1870
November1st to 15thNight
22%
773
13%
2527
7%
773
30%
773
11%
1888
November16th to endNight
20%
825
10%
2798
5%
825
26%
825
9%
2142
December1st to 15thNight
11%
825
5%
2925
0%
825
15%
825
6%
2432
December16th to endNight
13%
824
7%
2951
2%
824
19%
824
4%
2433

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
18%10%47%6%35%45%6%27%
48816
Night
16%10%47%6%35%5%5%6%27%
48198
TransparencyDay
56%6%12%16%7%
48493
Night
54%8%12%16%7%
48039
SeeingDay
26%16%28%17%8%1
6732
Night
23%17%29%21%7%
15036

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 15thDay
12%13%5%10%9%46%5%7%7%16%
1325
16th to endDay
10%10%5%10%7%5%8%8%6%7%18%
1536
February1st to 15thDay
8%13%5%8%9%7%10%7%5%5%18%
1509
16th to endDay
14%13%6%8%10%5%6%445%18%
1550
March1st to 15thDay
16%13%5%7%7%45%5%5%6%24%
1841
16th to endDay
15%13%5%8%7%35%43428%
2127
April1st to 15thDay
21%12%46%6%3435%5%25%
2217
16th to endDay
22%11%36%423245%32%
2340
May1st to 15thDay
21%10%36%6%3434430%
2366
16th to endDay
24%9%46%5%35%435%27%
2789
June1st to 15thDay
22%8%35%6%35%5%5%6%27%
2700
16th to endDay
24%9%36%6%35%45%7%23%
2700
July1st to 15thDay
17%7%36%6%46%45%9%29%
2700
16th to endDay
16%7%37%6%35%5%6%6%30%
2673
August1st to 15thDay
18%7%37%7%35%6%6%7%27%
2400
16th to endDay
13%7%46%5%35%45%8%36%
2483
September1st to 15thDay
18%7%25%5%23346%39%
2086
16th to endDay
16%7%26%5%24346%41%
1980
October1st to 15thDay
18%12%37%5%33445%31%
1876
16th to endDay
24%13%37%5%25%43424%
1734
November1st to 15thDay
19%12%49%5%34445%26%
1659
16th to endDay
19%14%48%7%35%445%20%
1488
December1st to 15thDay
20%15%5%11%6%6%6%43415%
1365
16th to endDay
19%13%6%9%7%37%5%4417%
1372
January1st to 15thNight
13%13%5%9%8%48%6%6%6%17%
2611
16th to endNight
9%11%5%8%7%47%8%7%8%21%
2688
February1st to 15thNight
7%12%410%9%5%8%7%7%6%20%
2349
16th to endNight
13%15%6%8%7%45%436%23%
1922
March1st to 15thNight
14%11%5%7%5%38%5%45%26%
2096
16th to endNight
11%13%5%7%6%34435%33%
2096
April1st to 15thNight
22%10%46%5%245%5%428%
1731
16th to endNight
23%9%24333435%35%
1620
May1st to 15thNight
22%10%47%42444429%
1596
16th to endNight
21%9%27%5%35%5%5%5%28%
1323
June1st to 15thNight
20%7%45%5%3445%5%31%
1260
16th to endNight
20%6%35%6%45%5%6%7%27%
1260
July1st to 15thNight
17%5%36%425%5%5%7%34%
1260
16th to endNight
15%6%15%5%26%6%6%7%34%
1493
August1st to 15thNight
14%5%37%6%35%6%5%7%33%
1548
16th to endNight
12%5%25%6%35%6%5%10%37%
1719
September1st to 15thNight
17%5%25%43446%6%39%
1872
16th to endNight
17%424323446%44%
1980
October1st to 15thNight
17%6%35%5%24347%38%
2083
16th to endNight
23%9%26%43445%6%28%
2490
November1st to 15thNight
20%9%47%4245%5%6%28%
2527
16th to endNight
16%12%48%6%45%46%6%24%
2798
December1st to 15thNight
19%13%6%10%8%45%5%5%5%16%
2925
16th to endNight
18%13%49%8%46%6%5%6%15%
2951

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
63%8%13%12%2
1326
16th to endDay
60%7%12%11%7%
1536
February1st to 15thDay
63%8%12%9%5%
1512
16th to endDay
65%6%10%12%5%
1550
March1st to 15thDay
59%410%13%9%1
1851
16th to endDay
58%5%7%15%10%1
2127
April1st to 15thDay
58%48%16%8%2
2217
16th to endDay
54%48%17%13%1
2340
May1st to 15thDay
56%5%9%16%11%
2366
16th to endDay
59%6%8%18%7%
2793
June1st to 15thDay
55%8%11%14%8%
2700
16th to endDay
59%7%11%15%6%
2700
July1st to 15thDay
51%7%16%18%6%
2541
16th to endDay
53%8%14%17%6%
2505
August1st to 15thDay
53%10%15%16%4
2386
16th to endDay
44%8%18%22%5%
2483
September1st to 15thDay
45%6%15%23%8%
2086
16th to endDay
44%6%15%22%11%
1980
October1st to 15thDay
54%7%10%19%8%
1876
16th to endDay
63%6%11%14%3
1734
November1st to 15thDay
59%7%11%16%4
1659
16th to endDay
63%7%12%13%2
1488
December1st to 15thDay
72%6%9%8%2
1365
16th to endDay
69%6%9%9%4
1372
January1st to 15thNight
64%8%12%10%3
2611
16th to endNight
55%9%11%16%5%
2688
February1st to 15thNight
58%10%12%12%5%
2350
16th to endNight
61%6%9%14%6%
1922
March1st to 15thNight
56%6%9%16%10%
2109
16th to endNight
52%412%19%9%1
2096
April1st to 15thNight
56%48%13%14%2
1731
16th to endNight
50%5%8%18%15%1
1620
May1st to 15thNight
56%6%9%16%10%
1596
16th to endNight
56%8%9%16%7%
1325
June1st to 15thNight
51%7%11%20%8%1
1260
16th to endNight
53%8%12%15%8%
1260
July1st to 15thNight
44%9%18%20%6%
1190
16th to endNight
45%10%15%19%7%
1398
August1st to 15thNight
47%10%16%21%3
1538
16th to endNight
39%10%21%23%5%
1719
September1st to 15thNight
42%9%16%22%8%1
1872
16th to endNight
38%8%16%25%9%
1980
October1st to 15thNight
45%7%12%25%7%1
2083
16th to endNight
55%7%15%16%4
2490
November1st to 15thNight
54%8%14%14%7%
2527
16th to endNight
59%7%14%14%3
2798
December1st to 15thNight
68%8%11%9%2
2925
16th to endNight
66%9%9%10%3
2951

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
38%18%31%11%
60
16th to endDay
18%21%37%10%7%3
64
February1st to 15thDay
21%14%35%20%8%
170
16th to endDay
26%22%26%16%7%
234
March1st to 15thDay
32%17%27%15%5%
270
16th to endDay
26%21%21%15%11%1
288
April1st to 15thDay
31%19%31%9%6%2
270
16th to endDay
26%21%32%11%5%2
270
May1st to 15thDay
30%16%32%14%4
288
16th to endDay
28%19%26%15%8%
503
June1st to 15thDay
28%15%23%23%8%1
495
16th to endDay
27%14%28%19%9%
495
July1st to 15thDay
23%12%28%24%9%2
475
16th to endDay
19%11%39%21%7%
344
August1st to 15thDay
19%10%30%24%11%2
313
16th to endDay
21%16%26%21%11%2
332
September1st to 15thDay
22%15%28%19%10%2
315
16th to endDay
20%15%32%18%7%5%
314
October1st to 15thDay
25%17%27%16%10%2
289
16th to endDay
38%16%25%11%6%
288
November1st to 15thDay
31%20%23%17%5%2
280
16th to endDay
32%17%26%15%6%1
213
December1st to 15thDay
27%27%28%10%32
90
16th to endDay
41%13%38%5%
72
January1st to 15thNight
23%25%31%15%3
737
16th to endNight
18%22%34%19%4
768
February1st to 15thNight
15%23%32%22%5%
704
16th to endNight
25%19%32%16%4
631
March1st to 15thNight
24%19%31%19%5%
720
16th to endNight
20%21%28%19%8%1
768
April1st to 15thNight
30%19%24%17%7%
653
16th to endNight
30%14%26%19%7%
540
May1st to 15thNight
27%10%30%22%7%1
516
16th to endNight
25%15%27%23%7%
375
June1st to 15thNight
24%8%24%32%10%
360
16th to endNight
25%7%28%29%8%
360
July1st to 15thNight
17%10%30%26%13%1
340
16th to endNight
18%5%31%32%11%
376
August1st to 15thNight
19%5%26%31%16%
467
16th to endNight
13%11%34%26%12%1
573
September1st to 15thNight
20%12%29%25%9%1
696
16th to endNight
19%13%31%24%9%1
717
October1st to 15thNight
21%17%29%21%9%1
720
16th to endNight
29%20%23%19%7%
768
November1st to 15thNight
27%20%24%19%7%
773
16th to endNight
26%21%27%17%6%
825
December1st to 15thNight
29%21%31%13%4
825
16th to endNight
29%20%27%16%5%
824
Page generated at 2017-12-21 07:04:42. Version ac04

Copyright 2017 A. Danko


Observatoire Aster Clear Sky Chart |Charts Home