Starlight Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starlight Hills Observatory clear sky chart from 2005-11-06 to 2025-04-26.

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
51%
25952
28%
112009
18%
25647
61%
25647
33%
51879

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
45%
976
35%
6064
16%
956
61%
956
27%
2535
January11th to 20thNight
42%
940
27%
5835
19%
912
57%
912
30%
2153
January21st to endNight
48%
865
31%
5900
23%
836
64%
836
26%
2281
February1st to 10thNight
35%
800
30%
2578
14%
800
53%
800
41%
1310
February11th to 20thNight
37%
782
28%
2338
14%
780
50%
780
38%
1307
February21st to endNight
34%
660
37%
1980
14%
660
57%
660
47%
983
March1st to 10thNight
39%
785
33%
4601
14%
764
53%
764
28%
1885
March11th to 20thNight
45%
789
19%
4464
14%
760
54%
760
23%
2198
March21st to endNight
36%
698
23%
4419
13%
672
58%
672
21%
2060
April1st to 10thNight
36%
600
28%
2000
14%
600
55%
600
40%
983
April11th to 20thNight
39%
593
22%
1977
15%
593
52%
593
33%
1081
April21st to endNight
42%
587
22%
1955
16%
587
54%
587
33%
1082
May1st to 10thNight
44%
568
28%
2856
18%
559
54%
559
23%
1375
May11th to 20thNight
46%
549
13%
2558
10%
541
50%
541
21%
1343
May21st to endNight
46%
607
13%
2738
10%
593
54%
593
28%
1261
June1st to 10thNight
62%
570
22%
1520
18%
570
65%
570
45%
836
June11th to 20thNight
62%
570
25%
1520
17%
570
66%
570
51%
798
June21st to endNight
65%
570
22%
1520
19%
570
67%
570
42%
869
July1st to 10thNight
68%
542
25%
2187
16%
535
71%
535
25%
1177
July11th to 20thNight
76%
539
21%
2182
23%
533
77%
533
31%
1119
July21st to endNight
70%
611
18%
2262
16%
569
72%
569
26%
1176
August1st to 10thNight
70%
556
12%
2719
13%
545
72%
545
17%
1715
August11th to 20thNight
73%
546
16%
2915
25%
543
75%
543
23%
1539
August21st to endNight
74%
607
20%
3221
26%
605
77%
605
25%
1600
September1st to 10thNight
72%
570
29%
1900
31%
570
77%
570
37%
1013
September11th to 20thNight
68%
570
35%
1938
34%
570
75%
570
46%
908
September21st to endNight
64%
570
33%
2090
31%
570
72%
570
43%
974
October1st to 10thNight
56%
689
45%
3283
21%
689
65%
689
40%
1204
October11th to 20thNight
55%
748
28%
3484
19%
740
69%
740
36%
1632
October21st to endNight
52%
871
39%
3893
18%
863
64%
863
42%
1491
November1st to 10thNight
54%
975
36%
2535
18%
975
62%
975
57%
1307
November11th to 20thNight
51%
1000
37%
2600
18%
1000
61%
1000
59%
1307
November21st to endNight
49%
1000
34%
2635
18%
1000
58%
1000
51%
1382
December1st to 10thNight
44%
984
43%
4188
15%
980
57%
980
47%
1489
December11th to 20thNight
43%
986
23%
4678
16%
978
56%
978
38%
1804
December21st to endNight
37%
1079
27%
6476
14%
1059
52%
1059
26%
2702

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
35%25%44446%8%55%
117570
Night
35%25%33435%7%60%
119947
TransparencyDay
23%7%11%23%25%11%
117315
Night
21%7%11%25%25%11%
119792
SeeingDay
7%11%30%29%17%6%
16097
Night
6%6%32%39%15%2
26259

By Month

Percentage Cloud Cover SW (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
15%2423335%10%63%
3638
11th to 20thDay
121445%5%46%8%59%
3796
21st to endDay
1426%43335%6%62%
4510
February1st to 10thDay
16%35%5%3436%7%59%
1820
11th to 20thDay
1325%44446%9%57%
1949
21st to endDay
15%28%43435%6%58%
1650
March1st to 10thDay
1425%32335%7%64%
4500
11th to 20thDay
39%37%44436%8%50%
4899
21st to endDay
25%35%445%46%8%54%
5852
April1st to 10thDay
36%25%3445%6%9%55%
2400
11th to 20thDay
6%7%36%44447%8%49%
2371
21st to endDay
6%8%25%34446%9%49%
2341
May1st to 10thDay
7%9%25%445%46%8%46%
3990
11th to 20thDay
7%7%26%45%5%5%7%9%44%
4281
21st to endDay
4415%445%5%9%9%49%
4825
June1st to 10thDay
5%424445%6%8%9%47%
2660
11th to 20thDay
5%314445%5%8%9%53%
2660
21st to endDay
3325%5%5%6%6%9%9%48%
2660
July1st to 10thDay
4425%345%5%7%9%52%
4430
11th to 20thDay
3416%5%6%6%6%8%10%45%
4430
21st to endDay
5%425%5%5%5%5%7%8%50%
4690
August1st to 10thDay
9%5%27%6%6%6%6%9%9%37%
4014
11th to 20thDay
4425%5%5%7%6%7%9%48%
3726
21st to endDay
5%425%45%6%5%8%9%48%
4180
September1st to 10thDay
5%324345%47%7%56%
2280
11th to 20thDay
6%31433446%7%59%
2242
21st to endDay
5%414233346%65%
2090
October1st to 10thDay
4313122245%74%
3242
11th to 20thDay
45%26%333346%60%
3150
21st to endDay
3313222346%72%
3319
November1st to 10thDay
241332336%7%67%
1763
11th to 20thDay
131332335%7%69%
1800
21st to endDay
1425%33335%7%64%
1762
December1st to 10thDay
1423323346%71%
2620
11th to 20thDay
1313323348%69%
3026
21st to endDay
1425%33445%7%61%
4004
January1st to 10thNight
15%37%43435%8%57%
6327
11th to 20thNight
132444435%7%64%
6227
21st to endNight
1316%433346%65%
6468
February1st to 10thNight
15%26%43335%8%58%
2578
11th to 20thNight
16%37%43446%7%54%
2338
21st to endNight
15%26%32325%466%
1980
March1st to 10thNight
15%15%34435%7%63%
5374
11th to 20thNight
48%25%44335%6%56%
5093
21st to endNight
37%25%33435%7%57%
5105
April1st to 10thNight
35%1433435%8%61%
2000
11th to 20thNight
6%9%25%24345%7%53%
1977
21st to endNight
7%7%35%34435%8%52%
1955
May1st to 10thNight
8%6%2433435%7%55%
2978
11th to 20thNight
7%8%2434446%9%49%
2620
21st to endNight
7%5%1434445%7%56%
2762
June1st to 10thNight
5%42423347%10%57%
1520
11th to 20thNight
431333336%9%63%
1520
21st to endNight
4414435%5%8%8%52%
1520
July1st to 10thNight
5%415%45%5%45%7%55%
2540
11th to 20thNight
3414445%5%9%11%50%
2540
21st to endNight
4414335%47%9%56%
2870
August1st to 10thNight
9%7%25%5%5%7%5%9%10%36%
2925
11th to 20thNight
4416%45%5%5%8%10%48%
3113
21st to endNight
3315%45%6%6%9%11%47%
3487
September1st to 10thNight
4415%446%47%8%53%
1900
11th to 20thNight
6%413233347%63%
1938
21st to endNight
5%414333346%65%
2090
October1st to 10thNight
5%312222235%72%
3723
11th to 20thNight
7%5%1433335%6%60%
3778
21st to endNight
3323222236%71%
4206
November1st to 10thNight
241433325%7%66%
2535
11th to 20thNight
122332335%5%71%
2600
21st to endNight
2425%33235%7%64%
2635
December1st to 10thNight
214322235%75%
4570
11th to 20thNight
132433335%10%65%
5181
21st to endNight
25%25%33435%7%60%
6974

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
18%49%33%26%10%
3639
11th to 20thDay
19%7%11%22%30%11%
3796
21st to endDay
22%5%8%26%28%11%
4510
February1st to 10thDay
24%5%12%26%23%11%
1820
11th to 20thDay
21%7%9%26%28%8%
1959
21st to endDay
24%5%7%21%24%19%
1650
March1st to 10thDay
17%5%8%16%33%21%
4500
11th to 20thDay
27%8%10%22%27%7%
4899
21st to endDay
21%9%12%37%18%3
5852
April1st to 10thDay
23%7%13%24%22%10%
2400
11th to 20thDay
30%6%12%22%18%11%
2374
21st to endDay
30%7%13%25%20%4
2341
May1st to 10thDay
29%8%13%25%14%12%
3990
11th to 20thDay
31%10%15%21%20%3
4285
21st to endDay
21%12%16%22%20%10%
4825
June1st to 10thDay
26%10%16%22%17%10%
2660
11th to 20thDay
21%8%12%17%24%17%
2660
21st to endDay
26%9%12%19%22%11%
2660
July1st to 10thDay
24%9%11%16%27%14%
4361
11th to 20thDay
27%9%13%21%20%10%
4355
21st to endDay
26%8%13%17%19%16%
4542
August1st to 10thDay
37%9%17%22%10%4
4000
11th to 20thDay
26%11%13%18%19%14%
3762
21st to endDay
25%8%14%20%26%6%
4179
September1st to 10thDay
23%7%10%22%24%14%
2280
11th to 20thDay
21%7%9%17%29%17%
2242
21st to endDay
20%5%8%20%33%14%
2090
October1st to 10thDay
14%47%16%38%22%
3242
11th to 20thDay
22%6%8%21%32%11%
3150
21st to endDay
13%36%22%38%18%
3319
November1st to 10thDay
16%49%24%29%18%
1763
11th to 20thDay
15%5%6%30%33%12%
1800
21st to endDay
19%5%7%23%30%16%
1762
December1st to 10thDay
15%5%8%30%33%10%
2620
11th to 20thDay
15%46%31%30%13%
3024
21st to endDay
19%6%10%27%26%12%
4004
January1st to 10thNight
24%5%8%31%25%7%
6327
11th to 20thNight
17%6%10%26%25%15%
6227
21st to endNight
20%6%11%26%27%11%
6468
February1st to 10thNight
24%5%9%28%24%10%
2578
11th to 20thNight
27%6%9%28%21%8%
2338
21st to endNight
20%47%25%27%17%
1980
March1st to 10thNight
19%5%7%16%38%15%
5374
11th to 20thNight
26%7%10%18%28%12%
5093
21st to endNight
23%8%12%32%21%3
5105
April1st to 10thNight
21%6%13%24%25%11%
2000
11th to 20thNight
28%7%12%25%20%8%
1977
21st to endNight
29%7%14%27%18%5%
1955
May1st to 10thNight
27%8%14%26%16%10%
2978
11th to 20thNight
29%11%17%25%10%8%
2621
21st to endNight
23%10%17%23%20%7%
2762
June1st to 10thNight
22%7%22%24%15%10%
1520
11th to 20thNight
17%8%15%23%20%18%
1520
21st to endNight
24%9%12%22%23%11%
1520
July1st to 10thNight
26%9%11%19%28%7%
2500
11th to 20thNight
22%9%17%30%16%6%
2492
21st to endNight
21%10%16%24%14%15%
2780
August1st to 10thNight
38%10%19%19%9%5%
2916
11th to 20thNight
26%11%19%20%19%5%
3143
21st to endNight
23%11%19%26%17%4
3487
September1st to 10thNight
26%7%11%23%22%11%
1900
11th to 20thNight
19%5%10%23%26%16%
1938
21st to endNight
20%6%8%23%32%11%
2090
October1st to 10thNight
14%5%7%21%35%17%
3723
11th to 20thNight
22%5%8%27%27%10%
3778
21st to endNight
16%47%26%32%15%
4206
November1st to 10thNight
16%5%9%25%28%16%
2535
11th to 20thNight
15%48%28%33%12%
2600
21st to endNight
20%49%24%31%13%
2635
December1st to 10thNight
13%48%33%33%10%
4570
11th to 20thNight
16%5%7%28%34%10%
5182
21st to endNight
22%6%11%22%26%12%
6974

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
6%7%34%37%13%4
300
11th to 20thDay
6%11%35%37%9%2
300
21st to endDay
312%35%35%12%3
330
February1st to 10thDay
417%47%25%6%2
300
11th to 20thDay
315%46%26%10%1
300
21st to endDay
218%46%28%6%1
249
March1st to 10thDay
315%39%31%10%3
300
11th to 20thDay
10%18%38%21%10%3
451
21st to endDay
11%21%39%20%6%2
550
April1st to 10thDay
11%18%39%23%7%2
500
11th to 20thDay
12%24%36%20%6%2
492
21st to endDay
15%16%33%26%8%2
481
May1st to 10thDay
14%17%34%25%8%2
575
11th to 20thDay
13%11%28%30%15%4
675
21st to endDay
9%12%30%26%20%4
734
June1st to 10thDay
7%10%22%32%22%7%
680
11th to 20thDay
6%10%27%33%18%5%
680
21st to endDay
48%24%34%23%7%
680
July1st to 10thDay
6%5%18%31%30%10%
671
11th to 20thDay
5%314%34%33%11%
668
21st to endDay
7%414%28%34%14%
676
August1st to 10thDay
10%218%35%27%8%
487
11th to 20thDay
5%6%22%33%22%12%
477
21st to endDay
7%323%37%21%9%
539
September1st to 10thDay
8%425%32%20%11%
490
11th to 20thDay
6%8%29%27%22%8%
452
21st to endDay
10%8%18%26%26%11%
300
October1st to 10thDay
9%12%19%25%24%11%
300
11th to 20thDay
39%33%32%17%6%
300
21st to endDay
6%12%34%28%17%3
330
November1st to 10thDay
7%12%34%27%13%6%
300
11th to 20thDay
37%40%32%15%3
300
21st to endDay
6%12%34%31%12%4
300
December1st to 10thDay
313%39%26%15%4
300
11th to 20thDay
5%8%41%30%15%1
300
21st to endDay
314%44%29%8%2
330
January1st to 10thNight
37%39%36%13%4
1000
11th to 20thNight
37%42%37%9%2
952
21st to endNight
26%38%43%10%1
880
February1st to 10thNight
36%52%33%6%1
800
11th to 20thNight
37%48%33%8%1
784
21st to endNight
38%49%34%4
660
March1st to 10thNight
37%46%35%8%1
800
11th to 20thNight
8%7%35%39%11%1
800
21st to endNight
5%10%43%35%7%
716
April1st to 10thNight
7%11%43%34%5%
600
11th to 20thNight
14%10%34%34%7%1
593
21st to endNight
13%9%33%35%9%1
587
May1st to 10thNight
10%9%31%36%12%1
570
11th to 20thNight
12%7%26%39%14%2
561
21st to endNight
11%6%30%35%16%2
617
June1st to 10thNight
5%6%21%45%21%3
570
11th to 20thNight
4425%51%15%1
570
21st to endNight
5%318%49%23%2
570
July1st to 10thNight
6%313%42%33%3
555
11th to 20thNight
426%46%37%5%
552
21st to endNight
8%28%35%42%4
624
August1st to 10thNight
8%38%40%37%4
567
11th to 20thNight
7%19%49%30%4
564
21st to endNight
4210%45%34%4
627
September1st to 10thNight
6%312%46%28%6%
570
11th to 20thNight
8%315%47%23%4
570
21st to endNight
7%321%44%21%4
570
October1st to 10thNight
10%424%40%18%3
709
11th to 20thNight
5%432%39%17%4
760
21st to endNight
6%5%32%37%17%3
886
November1st to 10thNight
4434%42%15%2
975
11th to 20thNight
36%37%42%10%2
1000
21st to endNight
5%7%35%39%12%2
1000
December1st to 10thNight
26%41%38%11%2
1000
11th to 20thNight
37%40%38%11%1
1000
21st to endNight
5%8%44%34%8%1
1100
Page generated at 2025-04-23 07:25:01. Version ac07

Copyright © 2025 Attilla Danko.


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