Changstars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Changstars Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
30%
23077
12%
74600
5%
23035
37%
23035
11%
57303

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 10thNight
17%
760
13%
2649
3%
757
29%
757
9%
2001
January11th to 20thNight
17%
735
10%
2569
4%
735
25%
735
6%
2061
January21st to endNight
19%
792
14%
2732
4%
792
32%
792
10%
2008
February1st to 10thNight
17%
720
10%
2254
2%
720
26%
720
9%
1754
February11th to 20thNight
14%
703
12%
2100
2%
700
26%
700
10%
1654
February21st to endNight
16%
592
16%
1776
6%
592
28%
592
9%
1373
March1st to 10thNight
20%
720
14%
2160
4%
720
32%
720
13%
1612
March11th to 20thNight
23%
720
11%
2113
4%
720
31%
720
11%
1680
March21st to endNight
21%
792
15%
1980
4%
792
30%
792
15%
1565
April1st to 10thNight
24%
720
13%
1800
4%
720
29%
720
13%
1441
April11th to 20thNight
29%
711
13%
1775
4%
711
33%
711
14%
1428
April21st to endNight
25%
612
13%
1692
4%
612
30%
612
12%
1348
May1st to 10thNight
29%
540
10%
1620
5%
540
33%
540
10%
1314
May11th to 20thNight
23%
473
13%
1535
5%
473
32%
473
10%
1197
May21st to endNight
41%
388
10%
1551
9%
388
45%
388
10%
1181
June1st to 10thNight
39%
360
9%
1440
9%
360
46%
360
10%
1109
June11th to 20thNight
44%
360
9%
1440
11%
360
49%
360
11%
1090
June21st to endNight
50%
360
8%
1440
10%
360
54%
360
11%
1088
July1st to 10thNight
51%
350
8%
1400
10%
350
53%
350
10%
1091
July11th to 20thNight
57%
348
8%
1392
10%
348
59%
348
12%
1040
July21st to endNight
51%
394
11%
1486
11%
372
55%
372
11%
1109
August1st to 10thNight
53%
452
10%
1516
8%
450
56%
450
13%
1157
August11th to 20thNight
54%
683
10%
1747
5%
683
56%
683
15%
1393
August21st to endNight
52%
792
10%
1980
5%
792
54%
792
15%
1587
September1st to 10thNight
44%
720
13%
1800
5%
720
48%
720
16%
1426
September11th to 20thNight
45%
720
18%
1934
10%
720
50%
720
19%
1432
September21st to endNight
40%
720
14%
1980
7%
720
45%
720
15%
1552
October1st to 10thNight
34%
720
12%
1984
7%
720
39%
720
13%
1560
October11th to 20thNight
33%
720
13%
2182
6%
720
42%
720
13%
1674
October21st to endNight
22%
792
10%
2574
4%
792
30%
792
10%
2031
November1st to 10thNight
32%
740
13%
2407
7%
740
40%
740
13%
1789
November11th to 20thNight
23%
760
16%
2470
8%
760
34%
760
11%
1881
November21st to endNight
23%
760
13%
2470
5%
760
34%
760
11%
1866
December1st to 10thNight
22%
760
11%
2655
3%
760
32%
760
8%
2058
December11th to 20thNight
20%
760
13%
3190
2%
759
30%
759
8%
2305
December21st to endNight
15%
828
8%
4807
3%
817
26%
817
5%
3448

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
17%6%35%43445%7%41%
74800
Night
18%7%35%43445%7%41%
74946
TransparencyDay
26%38%9%15%10%1
74505
Night
28%38%8%14%10%1
74775
SeeingDay
20%14%32%22%9%2
13936
Night
21%13%30%25%9%1
23086

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 10thDay
16%6%2443446%7%45%
1517
11th to 20thDay
19%8%35%434448%38%
1464
21st to endDay
15%7%35%424448%43%
1620
February1st to 10thDay
19%7%35%5%36%45%7%37%
1704
11th to 20thDay
16%6%25%5%345%47%43%
1748
21st to endDay
22%9%345%3445%6%36%
1480
March1st to 10thDay
16%7%345%34348%42%
1797
11th to 20thDay
16%6%36%5%35%5%5%8%39%
1842
21st to endDay
20%7%36%5%34445%40%
2376
April1st to 10thDay
19%6%3443445%7%41%
2160
11th to 20thDay
20%6%35%42345%6%43%
2134
21st to endDay
21%6%3444435%6%40%
2268
May1st to 10thDay
24%7%35%434447%36%
2340
11th to 20thDay
20%5%24435%45%7%40%
2375
21st to endDay
16%6%35%42445%8%43%
2725
June1st to 10thDay
19%6%245%345%7%9%35%
2520
11th to 20thDay
18%6%25%5%35%5%5%9%39%
2520
21st to endDay
13%5%26%5%35%6%5%8%42%
2520
July1st to 10thDay
13%6%25%435%5%6%10%42%
2520
11th to 20thDay
13%5%35%5%35%5%7%9%42%
2520
21st to endDay
13%5%35%435%6%7%8%41%
2744
August1st to 10thDay
11%5%25%5%35%5%6%10%41%
2395
11th to 20thDay
13%5%25%4345%7%9%42%
2151
21st to endDay
12%6%35%5%345%7%9%42%
2376
September1st to 10thDay
13%6%35%5%3445%8%44%
2160
11th to 20thDay
13%5%2342345%7%52%
2025
21st to endDay
20%6%2443445%7%42%
1980
October1st to 10thDay
23%6%34423445%42%
1972
11th to 20thDay
15%6%2433435%8%47%
1776
21st to endDay
19%7%2443445%6%41%
1782
November1st to 10thDay
15%6%25%5%34445%49%
1671
11th to 20thDay
19%5%13424346%47%
1710
21st to endDay
17%6%34424448%45%
1710
December1st to 10thDay
20%6%25%6%35%45%6%38%
1520
11th to 20thDay
23%6%24423336%45%
1906
21st to endDay
21%11%36%5%33346%34%
2772
January1st to 10thNight
16%7%25%43345%7%45%
2649
11th to 20thNight
22%8%35%434445%39%
2569
21st to endNight
15%8%35%42345%6%45%
2732
February1st to 10thNight
18%8%46%5%34446%40%
2254
11th to 20thNight
18%7%26%43345%7%41%
2098
21st to endNight
22%6%35%43444441%
1776
March1st to 10thNight
18%6%2442435%7%44%
2150
11th to 20thNight
17%8%35%4345%5%7%40%
2112
21st to endNight
19%8%245%35%445%42%
1980
April1st to 10thNight
20%8%36%5%2445%6%38%
1800
11th to 20thNight
20%5%35%5%3445%6%42%
1775
21st to endNight
22%6%35%43445%440%
1692
May1st to 10thNight
23%7%36%5%45%5%5%7%32%
1620
11th to 20thNight
22%7%35%434448%37%
1534
21st to endNight
19%8%245%2435%9%38%
1550
June1st to 10thNight
19%6%35%5%3445%6%39%
1440
11th to 20thNight
18%6%3443446%9%39%
1440
21st to endNight
15%5%344345%5%9%42%
1440
July1st to 10thNight
13%6%36%5%35%6%6%9%38%
1440
11th to 20thNight
14%6%245%35%5%6%11%38%
1440
21st to endNight
13%5%36%5%36%47%9%40%
1574
August1st to 10thNight
9%426%5%45%7%8%9%41%
1526
11th to 20thNight
11%7%36%6%5%6%6%7%8%36%
1747
21st to endNight
13%6%25%5%3445%8%45%
1980
September1st to 10thNight
15%6%25%5%45%5%6%7%41%
1800
11th to 20thNight
14%5%24423346%53%
1934
21st to endNight
19%5%26%5%35%446%42%
1980
October1st to 10thNight
21%7%25%5%33335%41%
1984
11th to 20thNight
15%7%25%424446%47%
2182
21st to endNight
22%7%25%42345%6%40%
2574
November1st to 10thNight
13%5%25%434446%48%
2407
11th to 20thNight
20%6%34323445%47%
2470
21st to endNight
16%5%25%424447%46%
2470
December1st to 10thNight
21%7%24425%446%39%
2655
11th to 20thNight
21%7%24434446%42%
3288
21st to endNight
22%10%35%433345%37%
4884

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 10thDay
24%40%9%19%7%
1518
11th to 20thDay
31%42%10%11%7%
1464
21st to endDay
24%38%8%20%8%2
1620
February1st to 10thDay
29%37%9%14%11%1
1704
11th to 20thDay
25%39%9%17%8%2
1757
21st to endDay
31%36%7%13%11%2
1480
March1st to 10thDay
25%37%11%16%9%2
1800
11th to 20thDay
28%38%9%15%10%1
1842
21st to endDay
28%38%6%12%13%3
2376
April1st to 10thDay
25%38%9%14%11%3
2160
11th to 20thDay
28%37%8%14%10%2
2134
21st to endDay
26%38%8%14%10%3
2268
May1st to 10thDay
29%39%7%14%10%1
2340
11th to 20thDay
27%39%8%13%11%2
2379
21st to endDay
23%41%11%14%9%2
2725
June1st to 10thDay
27%40%11%16%6%1
2520
11th to 20thDay
26%40%11%16%7%1
2520
21st to endDay
26%40%11%16%7%1
2520
July1st to 10thDay
24%42%10%15%9%1
2450
11th to 20thDay
24%40%9%17%8%1
2445
21st to endDay
23%41%9%14%11%1
2591
August1st to 10thDay
24%40%12%15%8%
2381
11th to 20thDay
25%39%10%15%10%1
2151
21st to endDay
27%39%8%14%12%1
2376
September1st to 10thDay
24%39%9%14%13%2
2160
11th to 20thDay
20%38%9%17%15%2
2025
21st to endDay
28%38%6%13%12%2
1980
October1st to 10thDay
27%37%7%16%13%1
1972
11th to 20thDay
24%37%10%19%9%1
1776
21st to endDay
28%38%8%16%9%1
1782
November1st to 10thDay
23%41%9%14%13%2
1671
11th to 20thDay
24%40%9%15%10%1
1710
21st to endDay
27%39%9%16%7%1
1710
December1st to 10thDay
28%42%9%13%7%1
1520
11th to 20thDay
30%32%11%12%13%1
1906
21st to endDay
39%28%9%17%7%
2772
January1st to 10thNight
25%41%9%16%8%1
2649
11th to 20thNight
31%42%7%13%6%1
2569
21st to endNight
24%38%8%18%11%1
2732
February1st to 10thNight
31%37%9%14%8%1
2254
11th to 20thNight
29%38%9%14%8%2
2100
21st to endNight
31%36%6%16%9%2
1776
March1st to 10thNight
25%37%10%16%11%2
2160
11th to 20thNight
30%39%9%13%8%2
2113
21st to endNight
28%37%6%13%13%3
1980
April1st to 10thNight
29%38%7%13%10%2
1800
11th to 20thNight
31%36%6%13%12%1
1775
21st to endNight
31%37%6%13%9%4
1692
May1st to 10thNight
33%39%6%10%10%2
1620
11th to 20thNight
29%39%7%12%11%3
1535
21st to endNight
28%40%10%11%10%1
1551
June1st to 10thNight
30%39%10%12%9%1
1440
11th to 20thNight
28%39%11%16%6%
1440
21st to endNight
27%40%11%14%8%
1440
July1st to 10thNight
29%41%9%13%7%1
1400
11th to 20thNight
25%40%11%16%6%1
1392
21st to endNight
25%41%10%14%8%2
1486
August1st to 10thNight
24%42%11%15%8%
1516
11th to 20thNight
29%38%9%15%8%1
1747
21st to endNight
27%40%8%14%10%1
1980
September1st to 10thNight
27%38%8%14%12%2
1800
11th to 20thNight
22%37%8%17%15%1
1934
21st to endNight
27%38%6%13%14%2
1980
October1st to 10thNight
30%37%6%15%11%1
1984
11th to 20thNight
28%37%9%16%9%
2182
21st to endNight
31%38%8%13%9%1
2574
November1st to 10thNight
21%42%9%13%12%3
2407
11th to 20thNight
26%39%7%16%10%1
2470
21st to endNight
24%40%9%18%8%1
2470
December1st to 10thNight
28%41%9%12%9%1
2655
11th to 20thNight
29%34%10%13%13%1
3288
21st to endNight
38%27%9%17%8%
4884

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 10thDay
22%26%33%16%4
180
11th to 20thDay
21%34%29%13%21
166
21st to endDay
21%23%39%11%42
192
February1st to 10thDay
27%21%36%15%1
324
11th to 20thDay
23%25%38%13%1
416
21st to endDay
29%24%32%12%4
346
March1st to 10thDay
19%26%35%17%3
420
11th to 20thDay
21%20%40%14%31
420
21st to endDay
27%20%35%14%41
462
April1st to 10thDay
24%24%32%14%6%
420
11th to 20thDay
23%18%33%17%7%1
412
21st to endDay
27%15%35%16%5%2
420
May1st to 10thDay
31%16%31%14%5%2
423
11th to 20thDay
21%14%39%19%7%1
447
21st to endDay
22%7%26%27%15%2
485
June1st to 10thDay
19%9%33%23%14%2
450
11th to 20thDay
19%11%31%27%10%2
450
21st to endDay
15%8%30%30%14%2
450
July1st to 10thDay
17%5%26%30%18%4
445
11th to 20thDay
14%426%35%16%5%
444
21st to endDay
12%7%32%36%10%2
488
August1st to 10thDay
13%6%26%36%15%4
446
11th to 20thDay
15%5%26%32%17%5%
439
21st to endDay
11%7%32%30%14%7%
495
September1st to 10thDay
18%9%27%25%17%5%
450
11th to 20thDay
14%8%34%24%13%7%
450
21st to endDay
21%10%33%23%10%2
450
October1st to 10thDay
29%9%25%19%14%3
450
11th to 20thDay
16%17%32%25%9%1
437
21st to endDay
25%15%34%18%7%1
396
November1st to 10thDay
16%13%35%24%10%3
365
11th to 20thDay
23%21%31%19%6%
370
21st to endDay
18%21%31%23%7%
370
December1st to 10thDay
22%23%32%17%6%1
180
11th to 20thDay
25%27%34%12%2
180
21st to endDay
25%21%31%14%7%2
198
January1st to 10thNight
20%22%36%17%4
760
11th to 20thNight
28%19%32%19%2
735
21st to endNight
19%24%33%20%31
792
February1st to 10thNight
21%19%37%21%2
720
11th to 20thNight
23%20%39%16%2
703
21st to endNight
25%21%34%17%3
592
March1st to 10thNight
23%17%36%21%4
720
11th to 20thNight
22%13%38%21%5%1
720
21st to endNight
22%16%37%20%5%
792
April1st to 10thNight
25%15%33%22%5%
720
11th to 20thNight
22%12%33%28%5%
711
21st to endNight
23%12%34%24%7%1
612
May1st to 10thNight
26%11%29%24%10%1
540
11th to 20thNight
24%8%37%23%8%
473
21st to endNight
23%5%22%33%15%2
389
June1st to 10thNight
24%5%23%33%14%1
360
11th to 20thNight
22%321%39%14%1
360
21st to endNight
17%323%43%14%1
360
July1st to 10thNight
15%5%19%40%20%1
350
11th to 20thNight
13%5%15%47%18%2
348
21st to endNight
16%422%42%15%1
394
August1st to 10thNight
9%324%44%18%1
452
11th to 20thNight
15%318%42%20%2
683
21st to endNight
15%419%37%20%5%
792
September1st to 10thNight
16%5%27%33%16%3
720
11th to 20thNight
18%426%29%18%5%
720
21st to endNight
22%7%24%27%16%3
720
October1st to 10thNight
24%9%27%24%12%3
720
11th to 20thNight
19%13%31%26%10%1
720
21st to endNight
27%11%36%18%7%1
792
November1st to 10thNight
17%13%34%23%12%2
740
11th to 20thNight
21%19%32%21%6%1
760
21st to endNight
18%21%33%21%5%1
760
December1st to 10thNight
26%18%29%21%5%1
760
11th to 20thNight
24%21%30%21%4
760
21st to endNight
26%16%39%18%2
836
Page generated at 2024-01-11 04:22:38. Version ac07

Copyright 2024 Attilla Danko


Changstars Observatory Clear Sky Chart |Charts Home