Robeson Planetarium and Science Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robeson Planetarium and Science Center clear sky chart from 2005-11-06 to 2024-01-17.

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
45%
24600
21%
74391
13%
24551
53%
24551
26%
46974

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
30%
757
23%
2459
11%
757
46%
757
24%
1495
January11th to 20thNight
35%
748
23%
2430
13%
748
49%
748
22%
1536
January21st to endNight
29%
792
26%
2574
13%
792
46%
792
25%
1558
February1st to 10thNight
30%
720
20%
2340
11%
720
43%
720
24%
1468
February11th to 20thNight
21%
701
20%
2219
9%
699
35%
699
21%
1415
February21st to endNight
26%
592
27%
1628
13%
592
40%
592
26%
1059
March1st to 10thNight
32%
720
26%
1980
14%
720
44%
720
31%
1225
March11th to 20thNight
29%
720
19%
1980
10%
720
38%
720
24%
1324
March21st to endNight
32%
792
22%
2178
10%
792
43%
792
28%
1393
April1st to 10thNight
34%
720
24%
1888
10%
720
45%
720
32%
1168
April11th to 20thNight
39%
711
24%
1775
9%
711
47%
711
35%
1120
April21st to endNight
41%
720
24%
1800
10%
720
47%
720
37%
1129
May1st to 10thNight
43%
609
18%
1689
8%
609
48%
609
32%
1037
May11th to 20thNight
48%
531
17%
1592
9%
531
54%
531
27%
1044
May21st to endNight
66%
582
17%
1744
14%
582
68%
582
28%
1113
June1st to 10thNight
57%
540
15%
1620
13%
540
59%
540
24%
1083
June11th to 20thNight
59%
540
14%
1620
10%
540
62%
540
25%
1077
June21st to endNight
61%
540
14%
1620
11%
540
64%
540
24%
1092
July1st to 10thNight
68%
525
12%
1575
11%
525
68%
525
22%
1101
July11th to 20thNight
70%
522
11%
1566
10%
522
71%
522
26%
1038
July21st to endNight
68%
591
13%
1672
11%
558
69%
558
26%
1113
August1st to 10thNight
63%
537
10%
1600
9%
534
63%
534
22%
1104
August11th to 20thNight
61%
600
13%
1664
9%
600
62%
600
21%
1189
August21st to endNight
62%
792
15%
1980
11%
792
63%
792
25%
1432
September1st to 10thNight
65%
720
21%
1800
16%
720
66%
720
31%
1220
September11th to 20thNight
58%
720
20%
1948
17%
720
60%
720
27%
1317
September21st to endNight
51%
720
17%
2005
14%
720
55%
720
23%
1397
October1st to 10thNight
54%
720
24%
2160
22%
720
59%
720
31%
1314
October11th to 20thNight
50%
720
30%
2160
25%
720
60%
720
34%
1242
October21st to endNight
49%
792
31%
2376
22%
792
62%
792
35%
1343
November1st to 10thNight
48%
740
27%
2221
21%
740
58%
740
33%
1289
November11th to 20thNight
39%
760
27%
2280
17%
760
52%
760
30%
1377
November21st to endNight
43%
760
27%
2436
18%
760
55%
760
30%
1411
December1st to 10thNight
35%
760
23%
2470
13%
760
48%
760
21%
1601
December11th to 20thNight
41%
759
26%
2943
20%
758
52%
758
23%
1718
December21st to endNight
35%
827
17%
4399
14%
817
46%
817
15%
2432

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
12%6%35%5%35%5%6%8%43%
75006
Night
13%5%25%5%3445%7%45%
74832
TransparencyDay
39%8%12%19%18%5%
74728
Night
38%7%12%19%19%6%
74629
SeeingDay
15%10%23%24%19%9%
14453
Night
15%8%25%32%18%2
24617

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
15%6%26%5%2335%6%46%
1706
11th to 20thDay
16%5%26%42445%7%44%
1674
21st to endDay
15%7%25%5%34346%47%
1782
February1st to 10thDay
17%6%35%5%25%446%42%
1620
11th to 20thDay
20%5%34424346%45%
1621
21st to endDay
18%7%35%5%34446%42%
1628
March1st to 10thDay
13%5%2432345%6%52%
1980
11th to 20thDay
16%6%36%5%3445%7%42%
1980
21st to endDay
15%6%36%5%3446%7%41%
2178
April1st to 10thDay
10%3234245%6%7%53%
2070
11th to 20thDay
11%5%244345%5%7%50%
2134
21st to endDay
10%425%43445%8%50%
2160
May1st to 10thDay
8%5%25%5%36%5%5%9%46%
2286
11th to 20thDay
10%6%37%6%5%5%5%6%7%40%
2301
21st to endDay
10%6%36%6%5%6%6%8%9%36%
2531
June1st to 10thDay
11%7%35%6%46%6%7%9%37%
2340
11th to 20thDay
9%435%6%47%6%8%9%40%
2340
21st to endDay
8%5%26%6%47%8%8%12%34%
2340
July1st to 10thDay
8%5%35%7%47%6%9%12%34%
2340
11th to 20thDay
9%5%36%7%47%7%8%11%32%
2340
21st to endDay
6%5%37%7%47%9%8%13%32%
2547
August1st to 10thDay
10%7%36%8%5%7%7%7%10%30%
2327
11th to 20thDay
12%7%37%6%5%7%7%8%10%28%
2218
21st to endDay
12%6%37%6%5%6%6%7%9%33%
2376
September1st to 10thDay
9%5%26%6%46%6%7%8%41%
2160
11th to 20thDay
12%7%35%5%45%5%5%7%43%
2008
21st to endDay
15%7%35%6%345%5%8%38%
1954
October1st to 10thDay
14%6%35%434447%47%
1800
11th to 20thDay
11%5%24423346%55%
1800
21st to endDay
10%6%24422446%57%
1980
November1st to 10thDay
12%5%24334445%55%
1857
11th to 20thDay
14%6%15%32335%6%52%
1900
21st to endDay
12%6%35%433446%51%
1741
December1st to 10thDay
17%7%26%5%45%45%6%40%
1710
11th to 20thDay
16%5%24322345%54%
2153
21st to endDay
16%7%36%5%24446%43%
3124
January1st to 10thNight
16%6%25%434446%47%
2459
11th to 20thNight
13%6%35%6%345%5%7%43%
2430
21st to endNight
16%7%245%2445%5%47%
2574
February1st to 10thNight
18%6%3442445%6%44%
2340
11th to 20thNight
19%6%25%433446%44%
2219
21st to endNight
16%436%435%5%5%6%44%
1628
March1st to 10thNight
15%425%433447%50%
1980
11th to 20thNight
14%6%36%435%5%5%8%40%
1980
21st to endNight
13%6%24435%48%7%44%
2178
April1st to 10thNight
12%4244345%5%7%51%
1888
11th to 20thNight
10%435%5%3445%6%51%
1775
21st to endNight
9%425%5%2446%9%50%
1800
May1st to 10thNight
8%425%5%346%6%8%48%
1689
11th to 20thNight
11%6%26%5%45%5%7%8%41%
1592
21st to endNight
9%5%25%5%36%5%7%10%42%
1744
June1st to 10thNight
10%6%37%5%45%6%7%12%35%
1620
11th to 20thNight
11%4445%47%5%7%9%40%
1620
21st to endNight
8%5%25%6%46%7%7%12%35%
1620
July1st to 10thNight
7%5%37%6%46%7%8%11%36%
1620
11th to 20thNight
7%337%6%47%6%8%11%38%
1620
21st to endNight
6%5%35%7%46%7%8%12%36%
1771
August1st to 10thNight
8%6%36%7%46%6%8%11%35%
1611
11th to 20thNight
10%6%36%7%5%6%7%7%11%32%
1664
21st to endNight
11%6%26%6%46%5%8%11%35%
1980
September1st to 10thNight
9%425%6%45%5%8%10%42%
1800
11th to 20thNight
12%6%26%6%45%5%5%6%43%
1948
21st to endNight
17%7%36%5%35%45%6%40%
2005
October1st to 10thNight
14%6%35%423347%49%
2160
11th to 20thNight
12%5%24434346%55%
2160
21st to endNight
10%424433445%56%
2376
November1st to 10thNight
12%6%34423345%56%
2221
11th to 20thNight
15%6%24414447%49%
2280
21st to endNight
14%42442445%7%50%
2436
December1st to 10thNight
17%8%25%42445%7%41%
2470
11th to 20thNight
17%6%25%42433451%
3042
21st to endNight
17%5%35%5%3435%6%45%
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
39%5%10%19%21%6%
1707
11th to 20thDay
41%5%8%19%21%6%
1674
21st to endDay
39%47%18%25%7%
1782
February1st to 10thDay
43%410%19%17%6%
1620
11th to 20thDay
42%46%18%23%7%
1630
21st to endDay
45%5%9%17%17%7%
1628
March1st to 10thDay
34%5%8%20%26%7%
1980
11th to 20thDay
42%6%10%18%17%7%
1980
21st to endDay
42%7%10%16%20%4
2178
April1st to 10thDay
30%6%10%22%26%7%
2070
11th to 20thDay
33%6%10%21%21%9%
2134
21st to endDay
33%7%11%23%22%5%
2160
May1st to 10thDay
34%8%14%23%18%3
2286
11th to 20thDay
43%8%11%22%15%2
2305
21st to endDay
42%10%15%18%15%1
2531
June1st to 10thDay
41%9%14%22%13%1
2340
11th to 20thDay
36%11%18%21%11%3
2340
21st to endDay
39%13%16%18%13%2
2340
July1st to 10thDay
40%12%20%16%10%3
2275
11th to 20thDay
40%14%18%19%7%2
2271
21st to endDay
36%14%19%21%7%1
2405
August1st to 10thDay
46%12%17%16%9%1
2314
11th to 20thDay
47%14%15%15%10%
2218
21st to endDay
46%10%17%17%8%2
2376
September1st to 10thDay
39%10%15%17%15%5%
2160
11th to 20thDay
41%8%11%14%21%5%
2008
21st to endDay
44%6%10%18%17%4
1954
October1st to 10thDay
38%5%9%20%25%3
1800
11th to 20thDay
32%410%24%24%7%
1800
21st to endDay
30%47%20%28%11%
1980
November1st to 10thDay
32%5%7%18%29%10%
1857
11th to 20thDay
34%5%7%18%27%9%
1900
21st to endDay
35%48%21%23%9%
1741
December1st to 10thDay
46%6%10%18%16%5%
1710
11th to 20thDay
34%36%22%25%9%
2150
21st to endDay
42%5%9%20%23%3
3124
January1st to 10thNight
39%5%9%18%23%7%
2459
11th to 20thNight
41%6%10%16%21%7%
2430
21st to endNight
39%45%19%25%8%
2574
February1st to 10thNight
41%48%17%21%7%
2340
11th to 20thNight
43%48%16%22%7%
2221
21st to endNight
40%5%10%16%19%10%
1628
March1st to 10thNight
36%48%19%23%11%
1980
11th to 20thNight
42%6%11%15%19%6%
1980
21st to endNight
36%8%12%21%18%5%
2178
April1st to 10thNight
33%6%11%18%25%9%
1888
11th to 20thNight
33%6%11%21%20%10%
1775
21st to endNight
31%7%12%23%22%5%
1800
May1st to 10thNight
31%9%15%21%20%4
1689
11th to 20thNight
39%9%14%21%16%1
1593
21st to endNight
35%10%17%23%12%2
1745
June1st to 10thNight
40%11%16%23%10%1
1620
11th to 20thNight
39%10%16%23%10%1
1620
21st to endNight
40%11%18%19%10%2
1620
July1st to 10thNight
40%14%18%18%8%2
1575
11th to 20thNight
35%14%26%17%7%1
1566
21st to endNight
36%13%22%19%9%1
1672
August1st to 10thNight
40%13%23%19%5%1
1600
11th to 20thNight
43%12%19%17%7%1
1664
21st to endNight
42%13%16%20%8%2
1980
September1st to 10thNight
35%11%16%17%15%5%
1800
11th to 20thNight
41%9%12%17%18%4
1948
21st to endNight
45%8%10%18%14%4
2005
October1st to 10thNight
36%5%9%20%25%5%
2160
11th to 20thNight
32%5%9%21%24%9%
2160
21st to endNight
30%5%8%19%26%12%
2376
November1st to 10thNight
32%5%7%17%27%13%
2221
11th to 20thNight
36%49%13%26%12%
2280
21st to endNight
34%5%8%20%25%8%
2436
December1st to 10thNight
43%6%10%15%20%6%
2470
11th to 20thNight
39%46%19%25%8%
3044
21st to endNight
40%47%20%26%3
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
20%24%37%17%3
270
11th to 20thDay
17%23%36%19%5%
258
21st to endDay
20%26%35%15%4
264
February1st to 10thDay
21%23%36%17%3
240
11th to 20thDay
33%17%34%12%3
261
21st to endDay
21%21%34%20%41
346
March1st to 10thDay
17%19%33%23%7%1
420
11th to 20thDay
20%22%31%20%7%1
420
21st to endDay
19%17%33%22%7%1
462
April1st to 10thDay
17%18%31%22%10%2
420
11th to 20thDay
11%17%29%22%14%6%
412
21st to endDay
13%13%28%24%18%5%
420
May1st to 10thDay
9%16%30%25%16%4
423
11th to 20thDay
12%6%19%29%24%10%
447
21st to endDay
15%417%27%24%15%
485
June1st to 10thDay
14%317%32%26%10%
450
11th to 20thDay
12%5%15%26%24%19%
450
21st to endDay
9%215%29%28%16%
450
July1st to 10thDay
9%211%22%36%19%
445
11th to 20thDay
9%210%25%38%16%
444
21st to endDay
5%311%30%38%14%
488
August1st to 10thDay
13%411%24%29%19%
446
11th to 20thDay
13%28%24%28%24%
439
21st to endDay
13%112%24%29%20%
495
September1st to 10thDay
10%213%27%27%21%
450
11th to 20thDay
15%315%27%28%12%
450
21st to endDay
18%320%30%19%10%
450
October1st to 10thDay
16%9%20%26%17%11%
450
11th to 20thDay
13%9%22%31%20%6%
450
21st to endDay
11%9%27%28%19%5%
495
November1st to 10thDay
16%9%27%28%16%4
455
11th to 20thDay
17%12%35%26%7%3
460
21st to endDay
13%15%29%26%15%2
301
December1st to 10thDay
22%14%40%16%8%
270
11th to 20thDay
20%17%33%20%8%1
270
21st to endDay
21%17%36%15%9%2
297
January1st to 10thNight
18%15%32%27%8%
760
11th to 20thNight
17%13%30%33%7%
748
21st to endNight
19%13%35%30%3
792
February1st to 10thNight
21%12%33%28%5%
720
11th to 20thNight
22%16%37%23%2
703
21st to endNight
18%13%38%27%3
592
March1st to 10thNight
17%11%37%30%5%1
720
11th to 20thNight
17%12%37%26%8%1
720
21st to endNight
16%13%34%29%8%
792
April1st to 10thNight
14%16%33%29%8%
720
11th to 20thNight
12%12%33%31%11%
711
21st to endNight
12%8%34%37%8%1
720
May1st to 10thNight
8%9%33%36%13%
609
11th to 20thNight
13%428%38%16%1
531
21st to endNight
10%314%41%29%4
584
June1st to 10thNight
11%316%46%21%3
540
11th to 20thNight
12%316%35%28%6%
540
21st to endNight
9%118%37%30%4
540
July1st to 10thNight
10%111%38%37%4
525
11th to 20thNight
8%110%35%40%5%
522
21st to endNight
6%111%43%36%4
591
August1st to 10thNight
12%110%33%39%5%
537
11th to 20thNight
13%211%33%36%6%
600
21st to endNight
12%212%32%36%6%
792
September1st to 10thNight
10%212%35%36%5%
720
11th to 20thNight
15%214%34%31%5%
720
21st to endNight
20%5%16%34%23%3
720
October1st to 10thNight
17%418%29%27%4
720
11th to 20thNight
13%6%26%31%22%2
720
21st to endNight
12%7%27%33%19%3
792
November1st to 10thNight
14%8%24%34%18%3
740
11th to 20thNight
19%9%29%30%13%1
760
21st to endNight
15%9%29%29%17%1
760
December1st to 10thNight
19%13%28%32%8%1
760
11th to 20thNight
19%9%28%33%11%1
760
21st to endNight
21%12%26%31%9%
836
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