Sirius Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sirius Observatory clear sky chart from 2005-11-05 to 2017-12-04.

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
37%
15827
16%
47798
10%
15788
43%
15788
21%
32760

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
17%
898
11%
2506
3%
895
23%
895
12%
1977
January16th to endNight
20%
835
10%
2563
3%
835
28%
835
12%
1990
February1st to 15thNight
16%
701
11%
2283
2%
701
26%
701
11%
1730
February16th to endNight
24%
631
15%
1893
6%
631
32%
631
14%
1404
March1st to 15thNight
24%
720
15%
2063
8%
720
30%
720
17%
1490
March16th to endNight
34%
768
18%
2112
10%
768
40%
768
22%
1471
April1st to 15thNight
28%
608
15%
1812
8%
608
35%
608
21%
1252
April16th to endNight
38%
540
20%
1620
9%
540
48%
540
26%
1041
May1st to 15thNight
41%
540
14%
1620
8%
540
47%
540
23%
1110
May16th to endNight
50%
552
16%
1675
12%
552
56%
552
30%
1027
June1st to 15thNight
54%
360
17%
1272
17%
360
61%
360
29%
747
June16th to endNight
56%
366
18%
1266
18%
366
63%
366
31%
728
July1st to 15thNight
65%
510
16%
1360
14%
510
67%
510
41%
804
July16th to endNight
68%
564
17%
1516
13%
531
70%
531
38%
884
August1st to 15thNight
67%
539
19%
1609
15%
536
70%
536
36%
940
August16th to endNight
62%
573
24%
1719
17%
573
67%
573
36%
1003
September1st to 15thNight
58%
681
23%
1929
17%
681
62%
681
33%
1175
September16th to endNight
61%
717
24%
1980
18%
717
64%
717
35%
1213
October1st to 15thNight
44%
720
19%
2088
14%
720
50%
720
27%
1354
October16th to endNight
25%
768
16%
2388
9%
768
35%
768
16%
1705
November1st to 15thNight
36%
760
20%
2471
15%
760
43%
760
21%
1630
November16th to endNight
26%
780
14%
2659
9%
780
33%
780
15%
1854
December1st to 15thNight
15%
736
8%
2574
2%
736
23%
736
10%
1937
December16th to endNight
14%
960
8%
2820
2%
960
20%
960
10%
2294

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
13%8%37%6%35%5%5%7%33%
48674
Night
14%8%36%5%3445%6%36%
47978
Cloud CoverDay
14%8%37%6%35%45%7%33%
48684
Night
15%8%36%5%3445%6%36%
47982
TransparencyDay
49%5%12%20%10%1
48372
Night
47%5%11%22%11%1
47798
SeeingDay
16%7%26%24%16%8%
6064
Night
18%8%28%30%12%1
15834

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
16%13%6%11%8%35%446%19%
1432
16th to endDay
15%16%8%10%9%4445%5%15%
1659
February1st to 15thDay
14%14%6%10%9%45%5%5%5%19%
1578
16th to endDay
12%13%6%10%7%45%45%6%23%
1580
March1st to 15thDay
16%11%6%8%7%24446%28%
1885
16th to endDay
16%10%5%8%6%44345%28%
2112
April1st to 15thDay
18%10%46%5%2445%7%30%
2145
16th to endDay
16%8%36%5%3445%6%36%
2340
May1st to 15thDay
18%8%26%5%345%47%34%
2331
16th to endDay
14%5%25%5%35%5%5%7%38%
2437
June1st to 15thDay
10%5%35%5%25%5%6%9%39%
2685
16th to endDay
9%425%6%46%6%7%10%36%
2690
July1st to 15thDay
6%425%5%45%6%6%9%43%
2520
16th to endDay
8%425%6%46%6%7%10%38%
2545
August1st to 15thDay
9%426%6%45%6%7%9%37%
2340
16th to endDay
11%6%25%5%35%5%6%8%38%
2483
September1st to 15thDay
11%5%25%5%35%6%5%9%38%
2016
16th to endDay
11%6%25%43447%9%39%
1980
October1st to 15thDay
14%7%35%5%35%446%38%
1872
16th to endDay
20%9%37%6%33436%31%
1833
November1st to 15thDay
14%8%36%6%34447%35%
1717
16th to endDay
15%11%48%6%35%5%46%27%
1628
December1st to 15thDay
15%13%6%11%7%345%45%22%
1465
16th to endDay
20%16%6%9%7%24345%18%
1401
January1st to 15thNight
22%11%5%7%6%34446%24%
2506
16th to endNight
13%13%7%9%7%35%5%46%24%
2563
February1st to 15thNight
13%14%5%9%5%35%445%27%
2281
16th to endNight
15%10%49%7%4435%5%28%
1893
March1st to 15thNight
17%10%47%5%34346%32%
2051
16th to endNight
16%7%35%5%25%45%5%36%
2112
April1st to 15thNight
19%7%36%42445%6%34%
1812
16th to endNight
14%6%25%42445%8%40%
1620
May1st to 15thNight
16%6%25%5%45%45%7%36%
1620
16th to endNight
11%42442445%7%46%
1673
June1st to 15thNight
7%5%25%425%5%6%10%44%
1272
16th to endNight
9%5%244245%7%7%46%
1266
July1st to 15thNight
7%42243445%8%53%
1440
16th to endNight
5%223425%5%6%9%51%
1621
August1st to 15thNight
6%3244346%7%8%48%
1620
16th to endNight
9%424423446%52%
1719
September1st to 15thNight
11%42443345%6%49%
1929
16th to endNight
10%4244246%5%7%47%
1980
October1st to 15thNight
15%5%25%42446%6%41%
2088
16th to endNight
20%8%35%6%2445%6%31%
2388
November1st to 15thNight
15%7%25%425%46%6%38%
2471
16th to endNight
18%10%36%5%35%45%7%29%
2659
December1st to 15thNight
19%12%5%8%6%34446%24%
2574
16th to endNight
21%14%6%9%6%34345%20%
2820

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
16%14%6%11%8%35%35%5%19%
1432
16th to endDay
15%15%8%9%9%4445%5%16%
1659
February1st to 15thDay
14%14%5%11%7%45%46%6%18%
1578
16th to endDay
13%13%6%10%7%36%45%6%23%
1580
March1st to 15thDay
17%12%5%8%6%34446%28%
1896
16th to endDay
16%10%5%8%7%34446%28%
2111
April1st to 15thDay
19%9%46%42445%7%30%
2145
16th to endDay
16%8%35%5%2345%7%36%
2340
May1st to 15thDay
19%6%26%435%346%34%
2331
16th to endDay
14%5%26%5%35%45%8%38%
2437
June1st to 15thDay
10%5%25%5%35%5%6%9%39%
2685
16th to endDay
9%425%6%45%6%7%9%37%
2690
July1st to 15thDay
7%425%5%35%5%7%9%43%
2520
16th to endDay
8%425%6%36%6%7%10%38%
2545
August1st to 15thDay
9%425%6%45%6%7%7%38%
2340
16th to endDay
12%5%25%5%35%5%6%8%39%
2483
September1st to 15thDay
11%5%25%5%35%5%6%9%38%
2016
16th to endDay
12%6%25%435%47%8%40%
1980
October1st to 15thDay
14%7%25%5%25%446%38%
1872
16th to endDay
20%9%26%6%33435%32%
1833
November1st to 15thDay
15%8%26%6%3445%7%34%
1717
16th to endDay
16%11%48%6%35%45%6%27%
1628
December1st to 15thDay
16%12%7%10%6%345%35%22%
1465
16th to endDay
21%16%6%9%6%24346%18%
1401
January1st to 15thNight
22%12%5%7%6%34345%24%
2506
16th to endNight
14%13%7%8%7%35%445%24%
2563
February1st to 15thNight
13%14%5%9%6%35%445%26%
2274
16th to endNight
15%11%5%8%6%44345%28%
1893
March1st to 15thNight
18%9%46%5%33346%32%
2063
16th to endNight
16%7%35%5%25%45%6%36%
2112
April1st to 15thNight
19%7%36%42445%7%34%
1812
16th to endNight
15%6%2442445%8%40%
1620
May1st to 15thNight
16%5%25%5%35%5%5%7%36%
1619
16th to endNight
12%5%24424447%46%
1673
June1st to 15thNight
8%425%3245%6%10%44%
1272
16th to endNight
9%5%2443446%9%46%
1266
July1st to 15thNight
7%413325%45%8%53%
1440
16th to endNight
5%2244345%6%9%51%
1621
August1st to 15thNight
6%3144346%7%9%48%
1620
16th to endNight
9%4235%24446%53%
1719
September1st to 15thNight
11%424424446%49%
1929
16th to endNight
10%4244245%47%48%
1980
October1st to 15thNight
16%5%2442445%7%41%
2088
16th to endNight
21%8%35%5%25%45%6%31%
2388
November1st to 15thNight
15%8%24425%5%6%6%38%
2471
16th to endNight
18%10%35%5%3435%7%29%
2659
December1st to 15thNight
20%12%5%8%5%34445%24%
2574
16th to endNight
22%14%6%9%6%34345%20%
2820

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
66%5%10%12%5%
1433
16th to endDay
70%5%8%11%4
1659
February1st to 15thDay
65%5%8%15%5%
1580
16th to endDay
60%5%9%16%7%1
1580
March1st to 15thDay
57%6%11%16%7%
1896
16th to endDay
56%410%19%8%1
2112
April1st to 15thDay
53%410%20%10%
2145
16th to endDay
47%5%13%17%14%2
2340
May1st to 15thDay
50%410%21%10%2
2331
16th to endDay
42%5%12%23%13%1
2441
June1st to 15thDay
39%6%13%24%14%1
2685
16th to endDay
40%6%14%22%14%1
2690
July1st to 15thDay
34%6%11%27%18%1
2371
16th to endDay
37%8%14%21%14%2
2387
August1st to 15thDay
39%8%12%24%12%1
2327
16th to endDay
40%6%11%26%13%1
2483
September1st to 15thDay
40%6%14%25%12%
2016
16th to endDay
39%5%13%29%11%
1980
October1st to 15thDay
44%411%22%13%1
1872
16th to endDay
55%314%18%7%
1833
November1st to 15thDay
48%6%10%23%9%1
1717
16th to endDay
56%5%12%17%6%1
1628
December1st to 15thDay
63%412%14%4
1465
16th to endDay
68%311%11%3
1401
January1st to 15thNight
62%5%9%15%7%
2506
16th to endNight
61%412%15%4
2563
February1st to 15thNight
59%5%9%16%7%
2283
16th to endNight
58%39%20%7%
1893
March1st to 15thNight
53%410%20%9%1
2063
16th to endNight
47%5%11%23%10%1
2112
April1st to 15thNight
49%411%20%13%
1812
16th to endNight
40%5%11%20%18%3
1620
May1st to 15thNight
46%5%10%21%12%3
1620
16th to endNight
37%5%12%24%16%4
1675
June1st to 15thNight
33%7%12%28%16%1
1272
16th to endNight
34%5%14%24%19%1
1266
July1st to 15thNight
29%5%9%32%21%2
1360
16th to endNight
27%8%16%25%19%3
1516
August1st to 15thNight
29%7%15%31%13%2
1609
16th to endNight
32%411%31%17%2
1719
September1st to 15thNight
35%411%30%16%1
1929
16th to endNight
34%5%11%32%15%
1980
October1st to 15thNight
41%411%23%17%1
2088
16th to endNight
52%411%21%7%
2388
November1st to 15thNight
44%6%11%24%11%1
2471
16th to endNight
53%415%19%6%
2659
December1st to 15thNight
60%413%14%6%
2574
16th to endNight
66%411%12%5%
2820

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
23%16%35%21%21
90
16th to endDay
31%14%36%13%4
96
February1st to 15thDay
18%18%47%13%1
90
16th to endDay
18%18%43%13%6%
81
March1st to 15thDay
27%13%28%23%5%
186
16th to endDay
25%5%30%25%10%2
288
April1st to 15thDay
21%12%30%22%10%3
270
16th to endDay
21%9%29%17%14%8%
270
May1st to 15thDay
23%5%27%22%15%4
288
16th to endDay
16%6%27%22%18%8%
331
June1st to 15thDay
12%6%30%30%16%4
480
16th to endDay
10%5%32%28%16%7%
495
July1st to 15thDay
8%323%33%19%10%
475
16th to endDay
7%5%21%31%21%11%
405
August1st to 15thDay
8%214%29%25%19%
313
16th to endDay
13%314%22%25%19%
332
September1st to 15thDay
11%318%20%26%20%
315
16th to endDay
15%414%21%28%14%
314
October1st to 15thDay
18%5%25%25%18%6%
315
16th to endDay
25%11%33%22%6%1
249
November1st to 15thDay
17%13%33%20%14%1
135
16th to endDay
23%16%39%14%5%
106
December1st to 15thDay
22%25%29%14%5%1
67
16th to endDay
28%17%43%9%
73
January1st to 15thNight
26%13%34%19%41
900
16th to endNight
21%10%35%27%4
835
February1st to 15thNight
20%14%39%21%3
704
16th to endNight
21%12%30%29%5%
631
March1st to 15thNight
22%10%34%26%5%
720
16th to endNight
20%8%30%30%9%1
768
April1st to 15thNight
23%10%31%28%5%
608
16th to endNight
18%5%31%32%10%1
540
May1st to 15thNight
17%5%27%35%11%1
540
16th to endNight
13%323%38%18%2
554
June1st to 15thNight
9%327%45%14%
360
16th to endNight
10%123%45%17%
366
July1st to 15thNight
9%16%41%27%4
510
16th to endNight
5%216%48%24%3
564
August1st to 15thNight
6%114%41%31%3
539
16th to endNight
10%216%35%31%4
573
September1st to 15thNight
13%317%33%27%5%
681
16th to endNight
12%217%35%25%6%
717
October1st to 15thNight
18%5%24%32%16%3
720
16th to endNight
24%12%30%26%5%
768
November1st to 15thNight
19%9%29%25%14%1
760
16th to endNight
23%12%31%23%8%
780
December1st to 15thNight
26%11%36%19%5%
736
16th to endNight
28%10%35%22%3
960
Page generated at 2017-12-05 10:18:57. Version ac04

Copyright 2017 A. Danko


Sirius Observatory Clear Sky Chart |Charts Home