Starbrite Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starbrite Observatory clear sky chart from 2005-11-05 to 2017-09-20.

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
62%
16284
17%
46972
14%
16244
65%
16244
27%
30811

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
53%
716
16%
2327
13%
716
59%
716
22%
1484
January16th to endNight
51%
768
24%
2477
18%
768
60%
768
30%
1456
February1st to 15thNight
51%
703
26%
2091
20%
699
59%
699
33%
1227
February16th to endNight
55%
631
29%
1735
20%
631
63%
631
37%
1023
March1st to 15thNight
54%
720
26%
1980
15%
720
63%
720
37%
1174
March16th to endNight
56%
768
24%
2112
20%
768
60%
768
37%
1259
April1st to 15thNight
64%
718
23%
1976
18%
718
68%
718
46%
1084
April16th to endNight
60%
720
24%
1800
14%
720
65%
720
38%
1126
May1st to 15thNight
71%
719
23%
1799
16%
719
73%
719
45%
1061
May16th to endNight
68%
617
14%
1739
12%
617
68%
617
25%
1195
June1st to 15thNight
62%
540
8%
1620
6%
540
63%
540
16%
1240
June16th to endNight
77%
540
7%
1620
6%
540
77%
540
22%
1135
July1st to 15thNight
71%
510
6%
1530
6%
510
71%
510
17%
1134
July16th to endNight
81%
564
10%
1595
9%
531
81%
531
28%
1038
August1st to 15thNight
76%
617
7%
1687
7%
614
76%
614
27%
1136
August16th to endNight
71%
764
6%
2009
5%
764
71%
764
20%
1499
September1st to 15thNight
67%
720
4%
1980
4%
720
67%
720
16%
1509
September16th to endNight
61%
677
6%
1870
7%
677
61%
677
14%
1482
October1st to 15thNight
64%
660
14%
1924
15%
660
66%
660
21%
1355
October16th to endNight
52%
704
17%
2112
15%
704
56%
704
20%
1489
November1st to 15thNight
58%
700
24%
2101
20%
700
65%
700
30%
1303
November16th to endNight
52%
720
23%
2160
19%
720
59%
720
25%
1426
December1st to 15thNight
54%
720
20%
2232
19%
720
60%
720
23%
1489
December16th to endNight
63%
768
23%
2496
22%
768
67%
768
28%
1487

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
8%6%37%8%5%7%7%7%9%27%
47851
Night
6%425%5%36%6%7%10%40%
47177
TransparencyDay
48%10%14%14%9%2
47552
Night
36%10%17%20%11%2
46980
SeeingDay
9%316%24%24%21%
6091
Night
8%315%31%28%13%
16292

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
9%6%36%8%47%6%7%9%30%
1611
16th to endDay
9%6%36%6%25%5%6%10%36%
1745
February1st to 15thDay
11%6%35%5%36%45%9%39%
1764
16th to endDay
7%425%5%346%7%9%42%
1738
March1st to 15thDay
6%426%6%46%8%7%10%37%
1980
16th to endDay
7%6%25%7%46%7%7%9%35%
2111
April1st to 15thDay
5%435%5%45%6%8%12%37%
1972
16th to endDay
6%426%7%38%7%8%9%34%
2160
May1st to 15thDay
4325%6%47%7%7%10%41%
2152
16th to endDay
10%6%47%8%6%8%8%8%10%21%
2383
June1st to 15thDay
12%8%411%9%7%8%7%6%7%14%
2340
16th to endDay
8%7%39%10%5%8%8%9%10%16%
2340
July1st to 15thDay
8%7%5%8%9%7%9%8%9%10%16%
2340
16th to endDay
7%6%39%10%6%7%8%9%12%18%
2465
August1st to 15thDay
8%7%48%8%5%8%9%10%10%18%
2247
16th to endDay
9%7%28%9%6%8%10%9%11%16%
2189
September1st to 15thDay
8%7%410%11%7%10%8%9%9%13%
1980
16th to endDay
14%10%311%10%6%8%7%6%5%14%
1859
October1st to 15thDay
9%7%38%9%5%8%7%9%10%19%
1705
16th to endDay
14%6%37%6%46%7%6%8%28%
1760
November1st to 15thDay
8%5%27%6%46%7%6%9%35%
1757
16th to endDay
10%5%26%7%46%7%7%8%33%
1800
December1st to 15thDay
9%7%37%7%46%6%6%7%32%
1725
16th to endDay
7%5%35%6%45%6%7%11%35%
1728
January1st to 15thNight
8%436%5%36%6%7%10%38%
2327
16th to endNight
5%4345%35%5%6%9%46%
2477
February1st to 15thNight
8%42433346%8%48%
2088
16th to endNight
5%214415%6%5%9%51%
1735
March1st to 15thNight
42235%35%6%5%9%50%
1980
16th to endNight
44235%345%6%9%50%
2112
April1st to 15thNight
312322447%9%56%
1976
16th to endNight
6%4244245%7%9%49%
1800
May1st to 15thNight
2213325%48%9%55%
1799
16th to endNight
7%5%35%5%37%6%11%11%32%
1738
June1st to 15thNight
10%6%37%8%48%7%7%11%24%
1620
16th to endNight
5%325%6%37%8%9%16%30%
1620
July1st to 15thNight
5%5%37%7%47%7%8%10%32%
1620
16th to endNight
25%146%45%6%8%13%40%
1703
August1st to 15thNight
5%4146%35%7%9%14%37%
1698
16th to endNight
7%425%6%47%8%9%12%30%
2009
September1st to 15thNight
6%437%8%5%8%8%10%13%23%
1980
16th to endNight
9%6%27%8%6%8%8%8%9%23%
1870
October1st to 15thNight
5%5%27%7%46%8%9%11%31%
1924
16th to endNight
12%7%36%5%36%5%6%9%34%
2112
November1st to 15thNight
5%325%5%36%5%5%9%45%
2101
16th to endNight
8%5%25%6%45%5%6%9%40%
2160
December1st to 15thNight
8%6%35%5%26%6%7%10%38%
2232
16th to endNight
6%4245%35%5%6%10%45%
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
48%7%12%15%11%4
1612
16th to endDay
41%7%11%18%15%5%
1745
February1st to 15thDay
41%5%8%20%17%6%
1766
16th to endDay
35%7%12%23%16%5%
1738
March1st to 15thDay
38%6%14%21%16%2
1980
16th to endDay
41%6%12%19%13%5%
2112
April1st to 15thDay
35%7%16%24%13%2
1972
16th to endDay
39%8%12%18%16%3
2160
May1st to 15thDay
35%6%15%24%12%6%
2152
16th to endDay
52%11%13%16%5%
2387
June1st to 15thDay
64%10%12%9%3
2340
16th to endDay
56%14%18%8%
2340
July1st to 15thDay
56%15%21%7%
2201
16th to endDay
50%15%25%8%
2310
August1st to 15thDay
50%16%20%11%1
2234
16th to endDay
52%17%22%7%
2189
September1st to 15thDay
58%16%17%5%1
1980
16th to endDay
64%12%12%6%3
1859
October1st to 15thDay
54%11%13%13%6%
1705
16th to endDay
50%7%11%14%11%4
1760
November1st to 15thDay
44%7%10%15%17%4
1757
16th to endDay
46%7%8%12%18%6%
1800
December1st to 15thDay
49%6%10%15%15%2
1725
16th to endDay
41%6%11%21%15%3
1728
January1st to 15thNight
40%8%15%21%11%2
2327
16th to endNight
33%6%14%24%15%4
2477
February1st to 15thNight
32%5%10%26%18%6%
2097
16th to endNight
27%8%12%27%17%5%
1735
March1st to 15thNight
28%7%12%26%20%4
1980
16th to endNight
29%7%15%26%17%4
2112
April1st to 15thNight
22%6%19%30%17%2
1976
16th to endNight
29%8%14%24%19%4
1800
May1st to 15thNight
24%8%15%32%15%4
1800
16th to endNight
40%10%18%24%6%
1740
June1st to 15thNight
50%13%20%12%3
1620
16th to endNight
37%17%31%13%1
1620
July1st to 15thNight
44%16%27%11%
1530
16th to endNight
32%14%35%15%2
1595
August1st to 15thNight
32%16%32%17%1
1687
16th to endNight
41%18%27%12%
2009
September1st to 15thNight
44%18%25%9%1
1980
16th to endNight
51%15%18%10%3
1870
October1st to 15thNight
43%11%17%16%9%1
1924
16th to endNight
46%8%10%17%11%3
2112
November1st to 15thNight
35%7%11%19%21%5%
2101
16th to endNight
40%7%10%16%16%7%
2160
December1st to 15thNight
40%10%12%18%16%2
2232
16th to endNight
33%7%11%25%17%3
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
17%12%41%23%5%
90
16th to endDay
17%18%29%28%42
96
February1st to 15thDay
12%7%37%27%13%1
105
16th to endDay
9%6%28%35%19%
239
March1st to 15thDay
7%7%35%30%16%3
270
16th to endDay
9%7%29%26%22%4
288
April1st to 15thDay
48%28%27%23%7%
270
16th to endDay
8%226%27%24%10%
270
May1st to 15thDay
5%219%30%28%14%
288
16th to endDay
6%29%28%30%20%
331
June1st to 15thDay
12%212%19%27%25%
315
16th to endDay
31417%29%42%
315
July1st to 15thDay
6%215%33%41%
305
16th to endDay
4315%25%49%
326
August1st to 15thDay
8%315%28%43%
313
16th to endDay
12%16%18%26%34%
332
September1st to 15thDay
8%5%16%25%43%
315
16th to endDay
16%312%28%37%
270
October1st to 15thDay
9%112%29%31%15%
255
16th to endDay
17%325%22%17%12%
272
November1st to 15thDay
8%319%32%26%9%
265
16th to endDay
10%6%28%31%20%2
270
December1st to 15thDay
20%420%34%15%5%
195
16th to endDay
11%5%18%47%13%3
96
January1st to 15thNight
10%7%21%36%21%2
720
16th to endNight
7%6%27%39%17%1
768
February1st to 15thNight
10%6%26%38%17%
704
16th to endNight
6%5%26%43%16%
631
March1st to 15thNight
5%6%27%38%19%2
720
16th to endNight
5%426%44%17%1
768
April1st to 15thNight
2323%42%25%1
718
16th to endNight
8%322%41%22%1
720
May1st to 15thNight
4215%45%30%2
720
16th to endNight
9%37%35%34%9%
619
June1st to 15thNight
11%26%19%38%21%
540
16th to endNight
4212%44%35%
540
July1st to 15thNight
5%211%42%36%
510
16th to endNight
4210%36%46%
564
August1st to 15thNight
7%210%41%37%
617
16th to endNight
7%1417%36%32%
764
September1st to 15thNight
8%15%15%33%36%
720
16th to endNight
12%1315%37%29%
677
October1st to 15thNight
8%38%33%33%12%
660
16th to endNight
16%316%29%24%9%
704
November1st to 15thNight
7%5%21%34%26%5%
700
16th to endNight
9%6%21%37%20%4
720
December1st to 15thNight
10%6%21%34%26%1
720
16th to endNight
7%5%17%38%26%4
768
Page generated at 2017-09-21 07:18:23. Version ac04

Copyright 2017 A. Danko


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