Marstown Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marstown Observatory clear sky chart from 2005-11-05 to 2017-05-01.

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%
14805
20%
45690
10%
14765
47%
14765
24%
28966

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 15thNight
19%
718
21%
2440
7%
716
36%
716
18%
1557
January16th to endNight
17%
768
21%
2496
6%
768
37%
768
20%
1579
February1st to 15thNight
20%
703
18%
2287
5%
701
35%
701
19%
1425
February16th to endNight
15%
631
22%
1920
4%
631
36%
631
19%
1243
March1st to 15thNight
24%
720
20%
2013
8%
720
36%
720
23%
1333
March16th to endNight
21%
768
20%
2083
7%
768
33%
768
24%
1403
April1st to 15thNight
24%
718
18%
1796
4%
718
32%
718
27%
1218
April16th to endNight
37%
720
18%
1800
7%
720
43%
720
29%
1208
May1st to 15thNight
37%
491
18%
1487
10%
491
44%
491
21%
1010
May16th to endNight
49%
342
16%
1369
15%
342
55%
342
21%
826
June1st to 15thNight
48%
330
19%
1320
18%
330
57%
330
23%
780
June16th to endNight
62%
330
16%
1320
18%
330
68%
330
25%
765
July1st to 15thNight
56%
310
13%
1240
14%
310
59%
310
17%
795
July16th to endNight
69%
484
15%
1431
12%
451
73%
451
34%
813
August1st to 15thNight
68%
494
19%
1474
16%
491
69%
491
32%
902
August16th to endNight
64%
689
18%
1739
11%
689
65%
689
34%
1132
September1st to 15thNight
58%
660
26%
1650
14%
660
62%
660
35%
1062
September16th to endNight
53%
657
22%
1809
18%
657
57%
657
30%
1190
October1st to 15thNight
43%
660
23%
1980
18%
660
52%
660
26%
1271
October16th to endNight
36%
704
26%
2112
15%
704
52%
704
31%
1232
November1st to 15thNight
36%
700
24%
2238
15%
700
50%
700
27%
1351
November16th to endNight
28%
720
20%
2478
11%
720
41%
720
20%
1506
December1st to 15thNight
24%
720
16%
2520
6%
720
38%
720
17%
1649
December16th to endNight
20%
768
19%
2688
5%
768
37%
768
18%
1716

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
14%5%25%5%3445%7%40%
46061
Night
14%5%2442445%7%42%
45872
Cloud CoverDay
14%5%25%5%3445%7%40%
46071
Night
14%5%25%42445%7%43%
45876
TransparencyDay
41%6%12%21%14%2
45761
Night
39%6%12%22%16%2
45690
SeeingDay
16%9%23%24%17%6%
5108
Night
17%10%30%28%12%1
14809

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 15thDay
15%7%35%5%25%5%5%6%37%
1497
16th to endDay
14%8%35%434347%40%
1728
February1st to 15thDay
13%8%36%4445%6%5%37%
1575
16th to endDay
13%7%36%5%33446%40%
1551
March1st to 15thDay
14%7%35%5%23346%42%
1935
16th to endDay
15%6%37%6%24446%38%
2139
April1st to 15thDay
15%6%25%5%2445%6%41%
2152
16th to endDay
16%6%25%324346%43%
2160
May1st to 15thDay
16%5%36%4345%6%8%35%
2153
16th to endDay
15%5%25%5%3445%8%40%
2394
June1st to 15thDay
13%415%426%5%7%10%38%
2310
16th to endDay
10%5%25%5%35%5%6%8%43%
2310
July1st to 15thDay
8%5%25%6%36%5%7%9%38%
2310
16th to endDay
7%425%6%37%7%7%10%37%
2319
August1st to 15thDay
10%425%6%45%6%6%9%37%
2145
16th to endDay
11%5%245%345%7%8%40%
2100
September1st to 15thDay
14%5%14334448%44%
1980
16th to endDay
15%6%25%43336%8%40%
1818
October1st to 15thDay
18%5%13423447%44%
1650
16th to endDay
14%5%25%5%1345%5%45%
1760
November1st to 15thDay
13%6%3342345%7%45%
1620
16th to endDay
17%5%25%5%24447%40%
1479
December1st to 15thDay
16%5%36%425%5%5%8%36%
1440
16th to endDay
17%6%35%424448%37%
1536
January1st to 15thNight
16%6%36%42345%7%38%
2440
16th to endNight
16%6%245%34446%41%
2496
February1st to 15thNight
14%6%25%42345%7%42%
2285
16th to endNight
14%7%35%434447%40%
1920
March1st to 15thNight
15%6%3442445%7%41%
2001
16th to endNight
15%5%35%434337%41%
2083
April1st to 15thNight
13%5%445%345%5%7%40%
1796
16th to endNight
15%5%343235%6%7%43%
1800
May1st to 15thNight
17%8%35%32445%6%37%
1487
16th to endNight
11%435%5%245%6%7%44%
1367
June1st to 15thNight
11%5%245%245%6%8%43%
1320
16th to endNight
7%5%24426%6%6%8%45%
1320
July1st to 15thNight
8%5%37%446%6%7%8%36%
1320
16th to endNight
6%3145%25%5%7%13%45%
1538
August1st to 15thNight
9%3334246%7%9%45%
1485
16th to endNight
10%5%24434449%45%
1739
September1st to 15thNight
11%5%2332445%7%47%
1650
16th to endNight
13%6%245%24346%45%
1809
October1st to 15thNight
17%6%23424345%44%
1980
16th to endNight
14%413324347%50%
2112
November1st to 15thNight
13%5%25%423335%49%
2238
16th to endNight
15%42442445%7%42%
2478
December1st to 15thNight
16%5%36%425%45%6%36%
2520
16th to endNight
16%6%25%4245%6%6%38%
2688

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 15thDay
15%7%35%5%345%46%39%
1497
16th to endDay
14%9%35%5%24446%41%
1728
February1st to 15thDay
13%7%36%435%5%6%6%37%
1575
16th to endDay
13%7%36%5%23346%41%
1551
March1st to 15thDay
14%6%35%5%34346%42%
1946
16th to endDay
16%6%36%5%34345%39%
2138
April1st to 15thDay
15%5%245%2445%7%41%
2152
16th to endDay
16%6%25%324346%44%
2160
May1st to 15thDay
16%5%36%43446%8%36%
2153
16th to endDay
15%5%25%5%35%46%7%40%
2394
June1st to 15thDay
13%4145%35%6%6%10%38%
2310
16th to endDay
11%4245%35%5%6%8%43%
2310
July1st to 15thDay
8%435%6%36%6%6%9%39%
2310
16th to endDay
7%325%5%36%7%8%9%38%
2319
August1st to 15thDay
11%5%25%5%46%5%7%8%37%
2145
16th to endDay
11%5%245%345%7%8%41%
2100
September1st to 15thDay
15%414434448%45%
1980
16th to endDay
16%5%2442435%8%41%
1818
October1st to 15thDay
19%5%13422446%44%
1650
16th to endDay
14%6%25%41345%5%46%
1760
November1st to 15thDay
13%6%3432335%6%45%
1620
16th to endDay
17%5%3442445%6%41%
1479
December1st to 15thDay
16%5%26%5%345%5%8%37%
1440
16th to endDay
17%6%35%42445%8%37%
1536
January1st to 15thNight
17%5%36%42435%7%39%
2440
16th to endNight
16%6%245%2445%6%41%
2496
February1st to 15thNight
14%6%25%43445%6%43%
2278
16th to endNight
14%7%35%4245%47%40%
1920
March1st to 15thNight
15%6%25%425%446%42%
2013
16th to endNight
15%5%35%434347%41%
2083
April1st to 15thNight
13%5%35%425%46%7%40%
1796
16th to endNight
15%5%25%31346%7%43%
1800
May1st to 15thNight
18%7%35%325%5%46%37%
1486
16th to endNight
11%5%25%43446%6%44%
1367
June1st to 15thNight
12%4145%245%6%8%43%
1320
16th to endNight
8%434336%5%6%9%45%
1320
July1st to 15thNight
8%5%46%5%36%6%6%9%37%
1320
16th to endNight
6%4135%26%5%7%12%45%
1538
August1st to 15thNight
8%423425%6%6%9%45%
1485
16th to endNight
10%5%244245%5%8%46%
1739
September1st to 15thNight
12%42431445%7%48%
1650
16th to endNight
14%6%245%24247%45%
1809
October1st to 15thNight
18%6%13423445%44%
1980
16th to endNight
14%413323447%50%
2112
November1st to 15thNight
13%5%25%423235%50%
2238
16th to endNight
15%42442445%7%42%
2478
December1st to 15thNight
17%5%26%425%45%6%37%
2520
16th to endNight
16%6%245%335%6%6%39%
2688

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 15thDay
45%5%13%21%11%3
1498
16th to endDay
44%413%22%11%3
1728
February1st to 15thDay
45%5%12%23%10%2
1577
16th to endDay
44%315%23%10%2
1551
March1st to 15thDay
43%412%22%15%1
1946
16th to endDay
46%5%10%18%16%2
2139
April1st to 15thDay
41%6%11%20%16%3
2152
16th to endDay
41%5%8%18%20%5%
2160
May1st to 15thDay
44%7%13%20%12%1
2153
16th to endDay
41%7%14%21%13%1
2398
June1st to 15thDay
39%9%14%23%12%
2310
16th to endDay
36%9%14%22%15%1
2310
July1st to 15thDay
39%9%13%20%13%3
2161
16th to endDay
36%10%15%22%13%2
2163
August1st to 15thDay
41%7%14%20%14%1
2132
16th to endDay
38%6%13%24%15%2
2100
September1st to 15thDay
37%6%12%19%21%2
1980
16th to endDay
41%5%9%21%20%2
1818
October1st to 15thDay
39%5%11%24%16%2
1650
16th to endDay
38%411%25%18%
1760
November1st to 15thDay
37%413%21%17%5%
1620
16th to endDay
43%5%10%25%13%1
1479
December1st to 15thDay
44%5%16%21%10%1
1440
16th to endDay
44%6%13%22%12%
1536
January1st to 15thNight
43%411%21%14%3
2440
16th to endNight
42%412%26%13%1
2496
February1st to 15thNight
40%5%14%22%14%2
2287
16th to endNight
42%5%10%24%15%1
1920
March1st to 15thNight
41%5%12%26%12%1
2013
16th to endNight
42%5%11%21%16%2
2083
April1st to 15thNight
41%412%20%17%3
1796
16th to endNight
38%6%10%20%17%6%
1800
May1st to 15thNight
46%6%11%21%13%2
1487
16th to endNight
36%9%15%19%14%3
1369
June1st to 15thNight
36%8%11%26%16%
1320
16th to endNight
34%8%12%24%17%1
1320
July1st to 15thNight
42%10%13%18%11%3
1240
16th to endNight
28%8%20%22%17%2
1431
August1st to 15thNight
31%9%15%24%16%1
1474
16th to endNight
35%6%12%23%18%3
1739
September1st to 15thNight
34%6%12%20%22%3
1650
16th to endNight
39%5%9%19%21%3
1809
October1st to 15thNight
41%410%23%17%2
1980
16th to endNight
32%411%29%19%1
2112
November1st to 15thNight
37%48%23%19%6%
2238
16th to endNight
40%411%23%16%2
2478
December1st to 15thNight
46%5%12%22%11%1
2520
16th to endNight
43%6%15%22%11%1
2688

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 15thDay
22%28%30%15%11
71
16th to endDay
20%26%31%20%1
96
February1st to 15thDay
21%27%38%12%
90
16th to endDay
19%20%43%16%
210
March1st to 15thDay
17%20%30%26%5%
270
16th to endDay
18%14%37%21%42
288
April1st to 15thDay
19%15%30%19%12%2
270
16th to endDay
20%10%27%18%17%5%
270
May1st to 15thDay
27%11%21%20%13%6%
229
16th to endDay
15%419%25%26%8%
267
June1st to 15thDay
16%424%28%21%5%
255
16th to endDay
11%423%33%21%5%
255
July1st to 15thDay
14%319%25%27%9%
245
16th to endDay
8%110%34%34%11%
270
August1st to 15thDay
12%213%30%29%11%
253
16th to endDay
10%8%29%28%22%
268
September1st to 15thDay
12%5%15%20%27%18%
255
16th to endDay
22%315%28%17%13%
254
October1st to 15thDay
18%9%16%28%20%6%
255
16th to endDay
14%12%31%29%11%1
272
November1st to 15thDay
18%8%26%24%19%2
242
16th to endDay
21%15%31%21%10%1
99
December1st to 15thDay
16%30%23%16%8%5%
60
16th to endDay
21%17%35%21%3
64
January1st to 15thNight
21%17%37%21%2
720
16th to endNight
20%17%41%19%1
768
February1st to 15thNight
19%17%38%24%1
704
16th to endNight
20%18%41%17%1
631
March1st to 15thNight
20%15%36%23%4
720
16th to endNight
18%13%42%18%5%
768
April1st to 15thNight
17%16%39%22%4
718
16th to endNight
17%9%30%29%11%1
720
May1st to 15thNight
21%5%31%29%11%
491
16th to endNight
13%422%37%20%1
343
June1st to 15thNight
12%328%34%21%
330
16th to endNight
11%119%46%20%
330
July1st to 15thNight
10%219%41%25%
310
16th to endNight
7%13%44%29%3
484
August1st to 15thNight
10%13%45%27%1
494
16th to endNight
12%212%38%29%3
689
September1st to 15thNight
13%219%32%29%2
660
16th to endNight
15%319%32%26%3
657
October1st to 15thNight
20%7%22%29%17%2
660
16th to endNight
17%9%33%28%10%
704
November1st to 15thNight
15%9%33%29%10%1
700
16th to endNight
18%17%31%24%8%
720
December1st to 15thNight
20%12%36%20%8%
720
16th to endNight
20%13%40%22%1
768
Page generated at 2017-05-02 08:43:31. Version ac04

Copyright 2017 A. Danko


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