Knox College Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Knox College Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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
36%
24760
18%
80426
11%
24659
44%
24659
22%
53107

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
20%
938
12%
4382
5%
926
31%
926
12%
3016
January11th to 20thNight
20%
949
13%
4330
5%
930
28%
930
10%
3224
January21st to endNight
20%
1040
9%
4497
4%
1023
27%
1023
10%
3495
February1st to 10thNight
22%
950
15%
2470
3%
950
30%
950
19%
1813
February11th to 20thNight
26%
811
19%
2289
7%
810
34%
810
22%
1543
February21st to endNight
19%
611
21%
1831
5%
611
32%
611
20%
1232
March1st to 10thNight
24%
720
17%
2160
7%
720
32%
720
20%
1461
March11th to 20thNight
30%
553
19%
1993
12%
553
41%
553
20%
1276
March21st to endNight
23%
594
13%
2055
7%
594
32%
594
13%
1495
April1st to 10thNight
27%
540
18%
1800
12%
540
38%
540
22%
1143
April11th to 20thNight
32%
533
20%
1775
15%
533
42%
533
21%
1140
April21st to endNight
32%
540
17%
1800
9%
540
42%
540
20%
1184
May1st to 10thNight
31%
540
15%
1606
8%
540
38%
540
23%
1089
May11th to 20thNight
39%
531
20%
1417
11%
531
46%
531
28%
958
May21st to endNight
46%
584
17%
1551
10%
582
51%
582
30%
1030
June1st to 10thNight
57%
540
18%
1440
11%
540
61%
540
39%
870
June11th to 20thNight
52%
540
22%
1440
12%
540
57%
540
37%
873
June21st to endNight
52%
540
19%
1440
11%
540
56%
540
34%
902
July1st to 10thNight
71%
525
19%
1400
15%
525
71%
525
39%
849
July11th to 20thNight
66%
522
25%
1392
16%
522
71%
522
48%
774
July21st to endNight
71%
591
26%
1495
20%
558
74%
558
43%
864
August1st to 10thNight
69%
537
22%
1601
22%
534
71%
534
39%
886
August11th to 20thNight
69%
534
24%
1726
27%
534
72%
534
36%
959
August21st to endNight
69%
594
25%
1980
25%
594
74%
594
40%
1033
September1st to 10thNight
60%
540
26%
1800
26%
540
64%
540
36%
973
September11th to 20thNight
61%
544
33%
1804
31%
544
66%
544
36%
967
September21st to endNight
52%
720
26%
1988
17%
720
59%
720
37%
1173
October1st to 10thNight
47%
720
24%
2160
18%
720
53%
720
35%
1255
October11th to 20thNight
35%
720
24%
2160
14%
720
45%
720
28%
1304
October21st to endNight
28%
792
19%
2452
10%
792
38%
792
21%
1611
November1st to 10thNight
33%
740
27%
2406
17%
740
46%
740
31%
1357
November11th to 20thNight
26%
760
23%
2470
11%
760
42%
760
23%
1537
November21st to endNight
26%
929
19%
2639
9%
929
35%
929
23%
1793
December1st to 10thNight
23%
950
15%
2660
5%
950
31%
950
21%
1861
December11th to 20thNight
25%
950
16%
3163
7%
948
32%
948
17%
2176
December21st to endNight
18%
1038
8%
4854
4%
1026
27%
1026
7%
3991

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%47%6%35%5%5%7%37%
78427
Night
13%9%47%5%3445%6%39%
80917
TransparencyDay
46%5%12%23%13%2
78128
Night
46%411%23%14%2
80736
SeeingDay
16%10%28%26%15%5%
14735
Night
17%10%30%30%12%1
24787

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
11%11%7%14%8%45%446%26%
2527
11th to 20thDay
12%11%5%11%10%5%8%6%6%6%21%
2544
21st to endDay
16%18%9%12%8%34345%18%
3135
February1st to 10thDay
15%11%6%9%7%45%446%29%
1710
11th to 20thDay
15%8%47%7%4445%6%35%
1779
21st to endDay
14%13%5%9%6%3335%6%32%
1520
March1st to 10thDay
16%11%6%7%5%34446%34%
1803
11th to 20thDay
13%10%46%8%345%5%8%33%
1980
21st to endDay
20%12%5%8%6%445%5%6%26%
2300
April1st to 10thDay
15%10%47%44445%7%36%
2160
11th to 20thDay
15%9%46%6%34447%37%
2134
21st to endDay
20%8%37%7%34446%35%
2160
May1st to 10thDay
18%7%37%6%35%5%7%8%32%
2352
11th to 20thDay
19%8%36%5%3446%8%35%
2479
21st to endDay
14%6%36%7%45%6%6%10%33%
2725
June1st to 10thDay
9%5%25%435%5%6%9%46%
2520
11th to 20thDay
8%5%27%6%345%5%8%47%
2520
21st to endDay
10%6%36%5%45%5%7%9%40%
2520
July1st to 10thDay
7%425%5%35%5%7%11%46%
2520
11th to 20thDay
8%5%245%35%5%7%11%46%
2520
21st to endDay
6%4246%36%6%7%11%45%
2732
August1st to 10thDay
7%5%35%5%45%7%9%10%40%
2328
11th to 20thDay
8%6%25%6%35%5%6%8%47%
2172
21st to endDay
7%425%5%35%5%5%8%50%
2376
September1st to 10thDay
12%426%4345%6%7%48%
2160
11th to 20thDay
11%42333445%7%53%
2138
21st to endDay
8%5%25%5%346%6%8%48%
1967
October1st to 10thDay
13%6%26%43435%6%48%
1800
11th to 20thDay
16%9%35%434345%43%
1800
21st to endDay
19%8%36%3345%46%39%
1904
November1st to 10thDay
11%7%35%5%3445%7%47%
1672
11th to 20thDay
17%8%36%6%2445%7%37%
1710
21st to endDay
16%10%47%5%34345%38%
1539
December1st to 10thDay
13%13%49%6%35%45%5%33%
1520
11th to 20thDay
14%11%47%6%445%6%6%33%
1918
21st to endDay
22%19%9%11%7%3334416%
2783
January1st to 10thNight
13%11%6%11%6%44445%31%
4428
11th to 20thNight
12%16%7%11%6%45%48%423%
4410
21st to endNight
19%15%6%12%6%24445%23%
4532
February1st to 10thNight
16%10%47%6%35%446%33%
2470
11th to 20thNight
13%10%45%6%35%46%6%39%
2288
21st to endNight
16%10%47%5%34346%39%
1831
March1st to 10thNight
14%10%46%5%345%45%39%
2160
11th to 20thNight
14%9%5%6%44445%7%38%
1993
21st to endNight
20%11%5%8%6%44446%29%
2055
April1st to 10thNight
13%8%37%5%445%5%8%39%
1800
11th to 20thNight
16%9%36%434445%43%
1775
21st to endNight
17%7%27%6%3445%7%38%
1800
May1st to 10thNight
15%6%47%6%45%5%5%8%36%
1606
11th to 20thNight
18%6%36%43436%7%40%
1416
21st to endNight
11%5%35%7%45%5%6%8%41%
1551
June1st to 10thNight
8%5%245%35%46%9%50%
1440
11th to 20thNight
8%5%35%5%345%6%9%48%
1440
21st to endNight
10%425%5%35%5%6%8%48%
1440
July1st to 10thNight
8%323445%5%7%10%50%
1440
11th to 20thNight
5%3133245%5%10%58%
1440
21st to endNight
5%324437%5%7%9%51%
1583
August1st to 10thNight
44245%35%46%10%53%
1611
11th to 20thNight
6%425%5%345%5%7%54%
1726
21st to endNight
7%31342445%8%58%
1980
September1st to 10thNight
12%423433346%56%
1800
11th to 20thNight
10%5%243335%5%7%53%
1804
21st to endNight
8%4245%35%5%5%7%51%
1988
October1st to 10thNight
9%6%25%43445%5%53%
2160
11th to 20thNight
14%6%25%5%24346%48%
2160
21st to endNight
18%8%25%5%3445%6%40%
2452
November1st to 10thNight
11%6%25%323347%53%
2406
11th to 20thNight
13%8%36%5%2445%7%42%
2470
21st to endNight
16%10%36%5%34446%39%
2639
December1st to 10thNight
14%11%38%5%45%45%6%35%
2660
11th to 20thNight
14%11%5%8%6%34446%36%
3279
21st to endNight
22%16%7%10%7%4444418%
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
60%310%19%6%
2528
11th to 20thDay
64%310%15%8%
2544
21st to endDay
71%29%12%6%
3135
February1st to 10thDay
58%214%18%7%2
1710
11th to 20thDay
50%5%11%22%11%1
1788
21st to endDay
54%410%22%9%1
1520
March1st to 10thDay
51%412%22%9%1
1803
11th to 20thDay
50%414%23%10%1
1980
21st to endDay
59%411%19%6%1
2300
April1st to 10thDay
49%412%23%12%
2160
11th to 20thDay
48%49%24%13%2
2134
21st to endDay
52%5%9%21%13%2
2160
May1st to 10thDay
49%6%13%22%10%1
2352
11th to 20thDay
48%5%11%23%13%
2483
21st to endDay
46%7%14%17%14%2
2725
June1st to 10thDay
34%6%15%27%16%2
2520
11th to 20thDay
35%6%11%24%22%3
2520
21st to endDay
38%7%15%23%15%2
2520
July1st to 10thDay
32%6%14%29%15%4
2451
11th to 20thDay
32%6%16%29%14%3
2445
21st to endDay
33%6%16%28%16%1
2580
August1st to 10thDay
35%7%16%29%11%1
2314
11th to 20thDay
34%7%12%29%17%1
2172
21st to endDay
31%6%12%28%19%4
2376
September1st to 10thDay
35%5%12%25%18%5%
2160
11th to 20thDay
30%410%28%23%4
2138
21st to endDay
33%5%10%28%21%2
1967
October1st to 10thDay
38%310%28%20%2
1800
11th to 20thDay
44%38%26%17%2
1800
21st to endDay
46%412%23%12%3
1904
November1st to 10thDay
37%316%25%16%4
1672
11th to 20thDay
47%412%23%12%1
1710
21st to endDay
50%313%23%10%1
1539
December1st to 10thDay
53%413%21%9%1
1520
11th to 20thDay
52%311%25%7%3
1915
21st to endDay
73%37%11%5%
2783
January1st to 10thNight
55%312%21%9%
4428
11th to 20thNight
62%310%14%10%1
4410
21st to endNight
65%39%16%6%1
4532
February1st to 10thNight
53%410%20%12%1
2470
11th to 20thNight
46%412%24%12%2
2289
21st to endNight
48%38%24%14%3
1831
March1st to 10thNight
48%411%24%12%1
2160
11th to 20thNight
46%412%23%12%3
1993
21st to endNight
58%410%19%8%1
2055
April1st to 10thNight
44%411%26%14%2
1800
11th to 20thNight
45%38%23%17%4
1775
21st to endNight
46%5%11%20%14%4
1800
May1st to 10thNight
47%5%13%23%12%1
1606
11th to 20thNight
43%5%12%23%16%1
1417
21st to endNight
40%5%14%21%17%3
1552
June1st to 10thNight
31%5%14%26%20%4
1440
11th to 20thNight
32%6%12%24%22%5%
1440
21st to endNight
34%7%15%20%21%3
1440
July1st to 10thNight
30%7%14%29%17%4
1400
11th to 20thNight
23%5%15%32%22%2
1392
21st to endNight
27%6%13%31%20%4
1495
August1st to 10thNight
26%7%18%32%14%2
1601
11th to 20thNight
29%6%12%30%20%2
1726
21st to endNight
25%6%12%29%21%6%
1980
September1st to 10thNight
30%410%27%23%5%
1800
11th to 20thNight
30%411%29%21%5%
1804
21st to endNight
32%410%27%24%3
1988
October1st to 10thNight
33%410%24%24%4
2160
11th to 20thNight
37%49%26%21%3
2160
21st to endNight
46%410%22%17%2
2452
November1st to 10thNight
33%412%27%20%4
2406
11th to 20thNight
42%411%25%16%2
2470
21st to endNight
47%310%25%13%1
2639
December1st to 10thNight
49%413%23%10%1
2660
11th to 20thNight
50%412%25%9%1
3281
21st to endNight
71%37%13%5%
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
21%18%30%23%7%
270
11th to 20thDay
27%19%35%15%3
270
21st to endDay
20%20%35%20%6%
297
February1st to 10thDay
23%17%41%15%5%
270
11th to 20thDay
24%17%34%20%41
270
21st to endDay
23%14%48%14%1
210
March1st to 10thDay
21%21%36%18%31
240
11th to 20thDay
25%15%36%16%7%
240
21st to endDay
31%14%33%15%5%1
386
April1st to 10thDay
22%14%33%25%5%1
420
11th to 20thDay
19%15%33%19%12%2
412
21st to endDay
24%15%30%20%9%2
420
May1st to 10thDay
20%11%33%25%8%3
485
11th to 20thDay
21%11%29%25%12%2
625
21st to endDay
15%7%29%28%14%8%
679
June1st to 10thDay
8%7%25%33%21%7%
630
11th to 20thDay
9%428%33%22%4
630
21st to endDay
11%8%30%29%17%5%
630
July1st to 10thDay
10%415%31%25%15%
621
11th to 20thDay
11%322%33%22%9%
618
21st to endDay
7%220%37%27%5%
684
August1st to 10thDay
6%320%34%28%8%
626
11th to 20thDay
9%5%17%29%26%13%
486
21st to endDay
6%218%33%29%12%
495
September1st to 10thDay
14%6%16%30%27%6%
450
11th to 20thDay
9%219%31%28%11%
450
21st to endDay
9%9%27%23%25%7%
437
October1st to 10thDay
17%5%31%29%14%3
270
11th to 20thDay
19%23%31%18%8%1
270
21st to endDay
31%15%29%19%5%1
297
November1st to 10thDay
10%13%41%23%9%4
270
11th to 20thDay
23%16%31%21%7%1
270
21st to endDay
27%10%35%23%4
270
December1st to 10thDay
13%17%42%20%5%3
270
11th to 20thDay
19%14%38%22%7%
270
21st to endDay
24%22%37%15%2
297
January1st to 10thNight
16%15%40%21%7%
950
11th to 20thNight
19%15%39%21%5%
950
21st to endNight
19%13%37%27%4
1045
February1st to 10thNight
23%12%37%23%5%
950
11th to 20thNight
19%16%34%27%4
813
21st to endNight
22%15%41%18%4
611
March1st to 10thNight
21%13%38%23%5%
720
11th to 20thNight
19%11%35%28%7%
553
21st to endNight
26%14%30%24%5%
594
April1st to 10thNight
17%15%37%25%5%
540
11th to 20thNight
23%11%31%27%8%
533
21st to endNight
20%11%31%33%5%
540
May1st to 10thNight
16%9%36%31%7%1
540
11th to 20thNight
20%6%28%34%12%
531
21st to endNight
13%5%28%35%19%1
584
June1st to 10thNight
11%423%45%17%1
540
11th to 20thNight
11%426%39%19%1
540
21st to endNight
11%428%38%19%1
540
July1st to 10thNight
8%211%42%31%5%
525
11th to 20thNight
6%219%44%26%2
522
21st to endNight
7%115%46%30%1
591
August1st to 10thNight
6%213%45%30%4
537
11th to 20thNight
6%213%44%30%5%
534
21st to endNight
9%114%40%34%2
594
September1st to 10thNight
13%5%16%37%24%4
540
11th to 20thNight
11%319%35%27%5%
544
21st to endNight
11%6%24%32%24%3
720
October1st to 10thNight
12%6%30%31%19%2
720
11th to 20thNight
17%12%31%28%12%
720
21st to endNight
23%11%34%24%7%
792
November1st to 10thNight
16%9%39%27%8%1
740
11th to 20thNight
18%15%36%25%7%
760
21st to endNight
22%12%35%24%6%
929
December1st to 10thNight
20%14%37%24%5%
950
11th to 20thNight
23%12%33%26%6%
950
21st to endNight
26%17%32%23%3
1045
Page generated at 2024-02-22 05:05:42. Version ac07

Copyright 2024 Attilla Danko


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