Galactic Stone Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Galactic Stone 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
58%
24412
20%
74545
16%
24357
63%
24357
28%
46912

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
41%
759
22%
2459
15%
757
52%
757
27%
1493
January11th to 20thNight
50%
736
25%
2391
19%
736
58%
736
30%
1386
January21st to endNight
38%
792
22%
2426
15%
792
47%
792
26%
1541
February1st to 10thNight
44%
720
22%
2160
16%
720
50%
720
30%
1327
February11th to 20thNight
48%
700
23%
2099
15%
700
57%
700
35%
1205
February21st to endNight
47%
592
27%
1731
17%
592
55%
592
32%
1052
March1st to 10thNight
46%
720
30%
1980
18%
720
56%
720
43%
1107
March11th to 20thNight
51%
720
28%
1980
17%
720
59%
720
38%
1160
March21st to endNight
50%
792
29%
2178
19%
792
57%
792
41%
1241
April1st to 10thNight
51%
720
23%
1980
16%
720
56%
720
41%
1127
April11th to 20thNight
48%
711
20%
1953
13%
711
54%
711
35%
1173
April21st to endNight
58%
695
29%
1807
19%
695
64%
695
45%
1039
May1st to 10thNight
74%
540
30%
1620
25%
540
76%
540
52%
790
May11th to 20thNight
68%
531
16%
1592
11%
531
72%
531
33%
1001
May21st to endNight
75%
582
23%
1744
20%
582
76%
582
37%
1027
June1st to 10thNight
68%
540
14%
1620
13%
540
69%
540
24%
1123
June11th to 20thNight
78%
540
12%
1620
11%
540
78%
540
28%
1066
June21st to endNight
75%
540
9%
1620
9%
540
75%
540
22%
1157
July1st to 10thNight
74%
525
5%
1575
5%
525
74%
525
20%
1174
July11th to 20thNight
77%
522
4%
1566
4%
522
77%
522
20%
1190
July21st to endNight
74%
591
8%
1672
7%
558
76%
558
20%
1207
August1st to 10thNight
79%
537
5%
1600
5%
534
79%
534
23%
1146
August11th to 20thNight
76%
534
6%
1776
7%
534
76%
534
20%
1249
August21st to endNight
64%
769
8%
2155
9%
769
65%
769
17%
1620
September1st to 10thNight
66%
720
7%
1980
6%
720
66%
720
19%
1478
September11th to 20thNight
61%
720
8%
1980
9%
720
62%
720
19%
1481
September21st to endNight
62%
720
18%
1980
16%
720
64%
720
23%
1397
October1st to 10thNight
57%
720
21%
1980
18%
720
60%
720
28%
1316
October11th to 20thNight
64%
720
28%
2119
27%
720
68%
720
36%
1227
October21st to endNight
58%
792
27%
2376
24%
792
64%
792
34%
1389
November1st to 10thNight
55%
740
26%
2221
21%
740
63%
740
37%
1259
November11th to 20thNight
53%
760
28%
2280
23%
760
62%
760
32%
1365
November21st to endNight
49%
760
26%
2437
21%
760
57%
760
30%
1439
December1st to 10thNight
52%
760
27%
2470
21%
760
62%
760
33%
1415
December11th to 20thNight
50%
759
24%
2943
20%
758
57%
758
24%
1698
December21st to endNight
48%
833
15%
4475
21%
817
56%
817
15%
2847

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%5%36%7%46%6%7%9%38%
74854
Night
8%5%35%5%35%5%7%9%44%
74909
TransparencyDay
39%10%15%17%14%5%
74577
Night
35%10%17%19%15%5%
74705
SeeingDay
8%6%19%26%24%18%
14317
Night
9%421%33%25%8%
24422

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 10thDay
10%5%45%4345%7%11%43%
1706
11th to 20thDay
8%5%245%35%46%12%47%
1647
21st to endDay
11%6%35%5%35%46%7%46%
1926
February1st to 10thDay
13%5%25%6%345%6%8%44%
1800
11th to 20thDay
7%425%435%45%5%56%
1748
21st to endDay
8%5%26%5%25%5%6%8%49%
1524
March1st to 10thDay
4314435%5%6%9%57%
1980
11th to 20thDay
7%4246%35%5%5%8%53%
1980
21st to endDay
7%425%5%35%45%8%53%
2178
April1st to 10thDay
7%3235%45%6%6%9%49%
1980
11th to 20thDay
7%5%25%8%46%6%7%8%42%
1956
21st to endDay
4215%5%36%6%6%9%52%
2161
May1st to 10thDay
5%2145%3446%8%58%
2340
11th to 20thDay
8%5%36%6%5%6%6%7%9%40%
2301
21st to endDay
6%426%7%5%7%7%7%9%37%
2531
June1st to 10thDay
12%6%47%8%5%9%7%7%11%23%
2340
11th to 20thDay
5%6%37%8%6%9%9%9%12%26%
2340
21st to endDay
7%6%47%9%5%8%8%9%11%26%
2340
July1st to 10thDay
8%6%38%9%6%9%9%10%10%22%
2340
11th to 20thDay
6%7%49%8%6%11%8%9%11%21%
2340
21st to endDay
6%6%39%10%6%9%9%9%11%22%
2547
August1st to 10thDay
7%6%28%9%7%8%10%9%10%23%
2322
11th to 20thDay
6%7%38%10%8%10%9%9%10%21%
2125
21st to endDay
9%7%39%10%6%9%8%8%9%23%
2180
September1st to 10thDay
7%6%39%10%7%8%8%9%12%22%
1980
11th to 20thDay
10%7%38%9%5%7%8%7%11%25%
1980
21st to endDay
8%6%38%8%5%7%7%8%9%30%
1980
October1st to 10thDay
8%6%37%7%5%6%6%6%9%36%
1980
11th to 20thDay
6%425%6%36%6%6%8%49%
1839
21st to endDay
6%425%6%346%7%9%48%
1980
November1st to 10thDay
8%426%4345%6%8%49%
1857
11th to 20thDay
9%6%25%6%35%5%5%8%47%
1900
21st to endDay
8%5%25%6%45%6%6%9%44%
1739
December1st to 10thDay
6%5%35%5%46%6%6%10%46%
1710
11th to 20thDay
11%5%26%5%35%46%8%45%
2153
21st to endDay
13%8%38%7%45%6%6%7%35%
3124
January1st to 10thNight
9%6%46%5%35%5%6%9%44%
2459
11th to 20thNight
9%5%35%6%35%45%9%47%
2391
21st to endNight
13%6%35%6%35%5%5%7%43%
2426
February1st to 10thNight
11%6%35%5%345%5%8%46%
2160
11th to 20thNight
8%5%245%3346%8%51%
2098
21st to endNight
7%6%36%5%3445%7%48%
1731
March1st to 10thNight
5%42443336%8%58%
1980
11th to 20thNight
7%425%435%46%10%51%
1980
21st to endNight
5%4344345%48%56%
2178
April1st to 10thNight
6%3244345%5%10%53%
1980
11th to 20thNight
6%5%35%5%346%7%9%48%
1953
21st to endNight
6%324435%45%7%58%
1807
May1st to 10thNight
33133235%5%9%62%
1620
11th to 20thNight
5%4346%45%7%6%10%46%
1592
21st to endNight
5%3245%346%7%10%51%
1744
June1st to 10thNight
10%7%26%5%47%6%7%11%36%
1620
11th to 20thNight
5%425%5%36%7%8%15%38%
1620
21st to endNight
6%5%36%6%5%7%7%8%14%33%
1620
July1st to 10thNight
7%5%26%6%5%6%8%10%14%31%
1620
11th to 20thNight
5%6%26%7%5%7%9%11%13%30%
1620
21st to endNight
45%37%8%5%8%7%11%12%31%
1771
August1st to 10thNight
4426%6%5%8%8%10%14%34%
1611
11th to 20thNight
46%36%6%47%8%10%14%31%
1776
21st to endNight
8%7%48%7%46%7%9%11%29%
2155
September1st to 10thNight
5%5%37%9%5%8%9%8%12%29%
1980
11th to 20thNight
8%8%48%8%37%6%7%11%30%
1980
21st to endNight
7%8%37%7%46%6%7%10%34%
1980
October1st to 10thNight
8%7%26%6%35%6%7%9%41%
1980
11th to 20thNight
6%5%246%3445%8%52%
2119
21st to endNight
7%5%36%5%3345%9%50%
2376
November1st to 10thNight
7%424435%45%8%54%
2221
11th to 20thNight
9%6%25%5%4445%6%51%
2280
21st to endNight
7%6%36%6%345%6%9%46%
2437
December1st to 10thNight
8%4245%35%5%6%8%49%
2470
11th to 20thNight
12%7%25%43345%7%47%
3042
21st to endNight
15%8%37%6%45%5%7%7%35%
4532

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
34%7%11%22%18%8%
1707
11th to 20thDay
31%5%10%24%21%9%
1647
21st to endDay
38%5%8%17%24%9%
1926
February1st to 10thDay
37%6%10%19%18%11%
1800
11th to 20thDay
29%410%19%26%11%
1758
21st to endDay
32%6%11%18%23%10%
1524
March1st to 10thDay
23%6%13%24%24%11%
1980
11th to 20thDay
30%5%12%25%18%10%
1980
21st to endDay
29%5%10%25%22%8%
2178
April1st to 10thDay
29%8%15%22%18%8%
1980
11th to 20thDay
36%8%11%17%21%7%
1956
21st to endDay
27%7%12%23%25%7%
2161
May1st to 10thDay
22%7%12%25%24%10%
2340
11th to 20thDay
38%9%15%19%16%3
2305
21st to endDay
40%10%13%19%16%3
2531
June1st to 10thDay
50%12%18%15%4
2340
11th to 20thDay
44%15%21%16%4
2340
21st to endDay
46%16%22%13%31
2340
July1st to 10thDay
51%18%23%7%1
2275
11th to 20thDay
52%17%23%8%
2271
21st to endDay
48%18%23%11%1
2405
August1st to 10thDay
48%16%26%9%
2309
11th to 20thDay
52%17%22%9%1
2125
21st to endDay
52%16%19%11%1
2180
September1st to 10thDay
49%17%20%12%2
1980
11th to 20thDay
49%15%19%13%4
1980
21st to endDay
44%12%15%18%9%3
1980
October1st to 10thDay
42%10%12%16%11%9%
1980
11th to 20thDay
32%8%10%21%23%6%
1839
21st to endDay
29%7%13%18%21%12%
1980
November1st to 10thDay
32%6%12%21%19%12%
1857
11th to 20thDay
36%7%9%19%21%9%
1900
21st to endDay
35%6%10%21%20%7%
1739
December1st to 10thDay
32%7%13%26%15%6%
1710
11th to 20thDay
36%6%11%17%18%12%
2150
21st to endDay
46%7%11%17%14%5%
3124
January1st to 10thNight
37%6%11%19%18%8%
2459
11th to 20thNight
34%5%11%22%20%7%
2391
21st to endNight
41%5%10%17%19%8%
2426
February1st to 10thNight
35%7%12%17%19%10%
2160
11th to 20thNight
30%6%11%19%24%10%
2099
21st to endNight
34%6%12%19%22%7%
1731
March1st to 10thNight
25%6%12%27%23%8%
1980
11th to 20thNight
29%6%14%28%15%8%
1980
21st to endNight
26%6%12%28%21%7%
2178
April1st to 10thNight
26%7%20%24%17%7%
1980
11th to 20thNight
30%8%14%23%20%5%
1953
21st to endNight
25%6%13%25%24%7%
1807
May1st to 10thNight
18%5%15%30%23%9%
1620
11th to 20thNight
31%11%21%19%17%1
1593
21st to endNight
26%10%19%23%19%2
1745
June1st to 10thNight
41%12%20%21%6%
1620
11th to 20thNight
33%14%29%21%4
1620
21st to endNight
39%17%24%15%5%
1620
July1st to 10thNight
40%20%30%9%2
1575
11th to 20thNight
40%20%30%8%1
1566
21st to endNight
39%19%30%12%
1672
August1st to 10thNight
35%20%34%10%1
1600
11th to 20thNight
38%18%31%13%
1776
21st to endNight
45%17%23%13%3
2155
September1st to 10thNight
41%20%25%12%3
1980
11th to 20thNight
45%15%21%15%31
1980
21st to endNight
42%12%17%18%9%3
1980
October1st to 10thNight
35%12%14%18%13%7%
1980
11th to 20thNight
29%8%13%23%23%5%
2119
21st to endNight
31%7%12%18%22%10%
2376
November1st to 10thNight
27%8%13%20%20%11%
2221
11th to 20thNight
34%6%11%20%21%8%
2280
21st to endNight
35%5%11%23%18%8%
2437
December1st to 10thNight
32%6%13%28%16%5%
2470
11th to 20thNight
36%6%10%19%18%11%
3044
21st to endNight
45%8%13%16%14%4
4532

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
11%11%44%25%8%
270
11th to 20thDay
8%14%33%33%11%2
249
21st to endDay
17%17%42%18%6%
264
February1st to 10thDay
13%11%33%28%13%1
240
11th to 20thDay
9%10%35%29%13%4
240
21st to endDay
7%13%29%35%14%2
242
March1st to 10thDay
5%10%40%33%11%1
420
11th to 20thDay
11%9%28%31%20%2
420
21st to endDay
7%7%31%33%21%2
462
April1st to 10thDay
9%11%29%28%19%3
420
11th to 20thDay
8%10%26%32%19%4
412
21st to endDay
5%5%25%31%27%7%
420
May1st to 10thDay
5%420%35%24%11%
423
11th to 20thDay
9%217%28%29%16%
447
21st to endDay
7%210%22%33%26%
485
June1st to 10thDay
13%49%22%26%26%
450
11th to 20thDay
6%28%25%28%31%
450
21st to endDay
416%18%29%42%
450
July1st to 10thDay
5%2311%28%50%
445
11th to 20thDay
5%413%31%47%
444
21st to endDay
9%15%17%28%40%
488
August1st to 10thDay
7%1414%32%43%
446
11th to 20thDay
8%15%12%28%46%
439
21st to endDay
9%26%18%30%35%
495
September1st to 10thDay
6%28%15%32%37%
450
11th to 20thDay
10%27%24%31%26%
450
21st to endDay
9%27%25%33%24%
450
October1st to 10thDay
10%317%36%27%8%
450
11th to 20thDay
5%416%35%31%8%
450
21st to endDay
7%5%19%40%25%5%
495
November1st to 10thDay
10%5%22%33%25%5%
455
11th to 20thDay
13%6%24%37%16%4
460
21st to endDay
7%10%31%31%18%2
299
December1st to 10thDay
6%11%35%27%16%5%
270
11th to 20thDay
11%13%33%27%14%2
270
21st to endDay
7%12%29%36%13%2
297
January1st to 10thNight
11%8%34%35%11%1
760
11th to 20thNight
10%8%27%41%13%1
736
21st to endNight
15%8%33%35%9%
792
February1st to 10thNight
16%5%30%34%14%
720
11th to 20thNight
10%7%30%39%13%1
703
21st to endNight
10%5%28%47%10%
592
March1st to 10thNight
6%6%38%42%9%1
720
11th to 20thNight
8%7%30%40%15%1
720
21st to endNight
6%7%31%41%15%
792
April1st to 10thNight
6%6%30%42%15%
720
11th to 20thNight
8%7%32%39%14%1
711
21st to endNight
8%426%43%19%1
695
May1st to 10thNight
5%214%47%29%3
540
11th to 20thNight
7%216%39%33%4
531
21st to endNight
5%212%36%39%6%
584
June1st to 10thNight
11%210%26%41%10%
540
11th to 20thNight
6%15%22%43%24%
540
21st to endNight
6%1318%44%28%
540
July1st to 10thNight
7%138%45%35%
525
11th to 20thNight
5%1211%44%38%
522
21st to endNight
41312%48%33%
591
August1st to 10thNight
4311%48%33%
537
11th to 20thNight
5%1310%40%40%
534
21st to endNight
11%27%23%36%21%
769
September1st to 10thNight
8%17%22%44%19%
720
11th to 20thNight
12%36%28%38%13%
720
21st to endNight
11%211%30%36%11%
720
October1st to 10thNight
10%222%40%22%4
720
11th to 20thNight
6%418%39%31%2
720
21st to endNight
9%422%42%23%2
792
November1st to 10thNight
9%228%38%20%3
740
11th to 20thNight
11%424%41%19%1
760
21st to endNight
9%5%29%42%14%1
760
December1st to 10thNight
9%429%37%21%1
760
11th to 20thNight
10%6%27%39%17%1
760
21st to endNight
9%8%28%37%17%1
836
Page generated at 2024-01-11 13:32:03. Version ac07

Copyright 2024 Attilla Danko


Galactic Stone Observatory Clear Sky Chart |Charts Home