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 2018-10-27.

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
37%
16611
20%
51287
11%
16571
47%
16571
24%
32526

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
20%
778
20%
2644
7%
776
37%
776
19%
1665
January16th to endNight
18%
832
22%
2704
7%
832
37%
832
20%
1707
February1st to 15thNight
19%
763
17%
2482
5%
761
34%
761
19%
1569
February16th to endNight
15%
683
22%
2078
4%
683
35%
683
18%
1364
March1st to 15thNight
23%
780
21%
2181
8%
780
36%
780
23%
1432
March16th to endNight
21%
832
21%
2257
7%
832
33%
832
24%
1513
April1st to 15thNight
23%
778
18%
1946
4%
778
31%
778
27%
1317
April16th to endNight
37%
771
18%
1927
6%
771
42%
771
29%
1299
May1st to 15thNight
38%
576
17%
1746
10%
576
44%
576
23%
1167
May16th to endNight
48%
406
16%
1625
13%
406
54%
406
20%
1007
June1st to 15thNight
50%
390
19%
1560
17%
390
58%
390
23%
921
June16th to endNight
60%
390
17%
1560
18%
390
66%
390
25%
899
July1st to 15thNight
59%
370
13%
1480
15%
370
62%
370
18%
930
July16th to endNight
69%
567
16%
1694
14%
534
73%
534
33%
976
August1st to 15thNight
66%
575
17%
1715
14%
572
66%
572
30%
1078
August16th to endNight
65%
815
19%
2057
12%
815
66%
815
35%
1330
September1st to 15thNight
56%
780
24%
1950
13%
780
60%
780
33%
1285
September16th to endNight
54%
777
24%
2137
19%
777
58%
777
30%
1397
October1st to 15thNight
45%
780
21%
2340
17%
780
52%
780
25%
1523
October16th to endNight
36%
816
27%
2447
17%
816
52%
816
32%
1426
November1st to 15thNight
37%
760
23%
2430
15%
760
49%
760
27%
1469
November16th to endNight
29%
780
22%
2685
12%
780
44%
780
21%
1601
December1st to 15thNight
24%
780
16%
2730
6%
780
37%
780
16%
1792
December16th to endNight
20%
832
19%
2912
6%
832
37%
832
18%
1859

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%6%25%5%3445%7%40%
52256
Night
13%5%2442445%7%42%
51469
Cloud CoverDay
14%5%25%5%3445%7%40%
52266
Night
14%5%25%42445%7%42%
51473
TransparencyDay
41%6%12%21%14%2
51956
Night
39%6%12%23%16%2
51287
SeeingDay
17%10%24%24%16%6%
7093
Night
17%9%30%28%12%1
16615

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%34425%5%5%6%38%
1623
16th to endDay
13%9%35%434346%40%
1872
February1st to 15thDay
14%8%36%445%5%5%5%37%
1710
16th to endDay
16%7%36%5%33446%39%
1679
March1st to 15thDay
14%7%25%5%23345%42%
2097
16th to endDay
16%6%37%6%34445%38%
2317
April1st to 15thDay
15%6%25%5%2445%7%40%
2332
16th to endDay
16%6%25%424346%43%
2308
May1st to 15thDay
16%5%26%4345%6%8%36%
2543
16th to endDay
16%5%25%5%3445%8%37%
2842
June1st to 15thDay
13%5%14435%5%6%10%39%
2730
16th to endDay
10%5%25%5%35%5%6%9%42%
2730
July1st to 15thDay
8%425%5%36%5%7%8%40%
2730
16th to endDay
8%425%5%36%7%7%10%37%
2715
August1st to 15thDay
11%5%25%6%45%6%5%9%36%
2487
16th to endDay
10%5%245%446%6%9%40%
2484
September1st to 15thDay
16%5%24334448%41%
2340
16th to endDay
16%5%25%43436%8%39%
2149
October1st to 15thDay
18%5%1442345%6%42%
1950
16th to endDay
13%5%15%5%2345%5%47%
2034
November1st to 15thDay
14%6%3442345%6%44%
1758
16th to endDay
16%5%24414446%43%
1602
December1st to 15thDay
16%5%37%425%5%48%37%
1560
16th to endDay
16%6%36%42445%8%37%
1664
January1st to 15thNight
16%6%36%42335%7%40%
2644
16th to endNight
15%7%24434446%41%
2704
February1st to 15thNight
14%6%35%42345%7%41%
2480
16th to endNight
15%7%35%434447%39%
2078
March1st to 15thNight
15%6%3442445%6%42%
2169
16th to endNight
15%5%35%434347%42%
2257
April1st to 15thNight
13%5%344345%6%8%40%
1946
16th to endNight
15%5%3432346%7%43%
1927
May1st to 15thNight
16%7%343245%5%7%38%
1746
16th to endNight
13%6%35%5%2346%7%41%
1623
June1st to 15thNight
11%4245%245%5%8%44%
1560
16th to endNight
7%5%24435%5%6%9%44%
1560
July1st to 15thNight
7%5%37%446%6%7%9%38%
1560
16th to endNight
7%314435%5%6%12%44%
1801
August1st to 15thNight
10%3335%346%6%8%43%
1726
16th to endNight
9%5%144345%5%10%44%
2057
September1st to 15thNight
13%5%3432445%7%46%
1950
16th to endNight
14%6%245%24346%45%
2137
October1st to 15thNight
17%6%23424446%42%
2340
16th to endNight
14%413323347%50%
2447
November1st to 15thNight
13%5%25%423345%48%
2430
16th to endNight
15%42442445%7%43%
2685
December1st to 15thNight
16%6%36%5%26%5%5%6%36%
2730
16th to endNight
16%6%25%5%245%6%6%38%
2912

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%
1623
16th to endDay
13%9%35%5%24446%41%
1872
February1st to 15thDay
14%8%36%435%5%5%6%36%
1710
16th to endDay
16%7%36%5%23345%40%
1679
March1st to 15thDay
14%6%35%5%34445%42%
2108
16th to endDay
16%6%36%5%34345%39%
2316
April1st to 15thDay
14%6%345%2445%7%40%
2332
16th to endDay
16%6%14424346%44%
2308
May1st to 15thDay
16%5%26%43446%8%37%
2543
16th to endDay
17%5%25%5%35%45%7%37%
2842
June1st to 15thDay
13%4145%35%5%6%10%39%
2730
16th to endDay
11%4245%35%46%9%42%
2730
July1st to 15thDay
8%4245%36%5%6%8%41%
2730
16th to endDay
9%425%5%36%6%8%9%38%
2715
August1st to 15thDay
11%5%26%5%46%5%7%8%36%
2487
16th to endDay
10%5%245%345%7%8%41%
2484
September1st to 15thDay
16%424434448%42%
2340
16th to endDay
16%5%2442445%7%40%
2149
October1st to 15thDay
19%5%1442245%6%42%
1950
16th to endDay
13%5%2442345%5%48%
2034
November1st to 15thDay
14%6%2432345%6%45%
1758
16th to endDay
16%434424446%43%
1602
December1st to 15thDay
16%5%26%5%345%5%7%37%
1560
16th to endDay
16%5%36%43445%8%37%
1664
January1st to 15thNight
16%5%26%42435%7%40%
2644
16th to endNight
16%6%245%2445%5%42%
2704
February1st to 15thNight
14%6%25%42445%6%41%
2473
16th to endNight
15%7%35%4245%47%39%
2078
March1st to 15thNight
15%6%25%425%446%43%
2181
16th to endNight
15%5%35%434347%42%
2257
April1st to 15thNight
13%5%25%425%46%8%40%
1946
16th to endNight
15%5%25%32346%6%43%
1927
May1st to 15thNight
17%7%25%325%5%47%38%
1745
16th to endNight
13%6%25%43346%7%41%
1623
June1st to 15thNight
11%425%5%245%6%8%44%
1560
16th to endNight
8%434336%5%5%10%44%
1560
July1st to 15thNight
8%436%5%46%6%6%9%38%
1560
16th to endNight
7%4135%25%47%12%45%
1801
August1st to 15thNight
9%424435%5%6%9%43%
1726
16th to endNight
10%5%245%245%6%8%45%
2057
September1st to 15thNight
13%5%25%42445%6%46%
1950
16th to endNight
14%5%245%24346%45%
2137
October1st to 15thNight
17%6%13424446%43%
2340
16th to endNight
14%413323347%50%
2447
November1st to 15thNight
13%5%25%423245%49%
2430
16th to endNight
15%42442445%7%44%
2685
December1st to 15thNight
16%6%26%436%45%6%36%
2730
16th to endNight
16%6%25%5%345%6%6%39%
2912

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
44%6%12%20%12%3
1624
16th to endDay
44%413%22%11%3
1872
February1st to 15thDay
46%5%12%23%10%2
1712
16th to endDay
45%314%24%10%1
1679
March1st to 15thDay
43%411%22%16%1
2108
16th to endDay
46%5%9%18%17%2
2317
April1st to 15thDay
42%5%11%20%16%3
2332
16th to endDay
41%5%7%19%20%5%
2308
May1st to 15thDay
43%7%13%20%13%1
2543
16th to endDay
44%7%14%20%12%1
2846
June1st to 15thDay
38%9%14%23%13%
2730
16th to endDay
36%9%14%23%15%1
2730
July1st to 15thDay
37%9%13%20%15%3
2581
16th to endDay
37%9%15%22%12%2
2559
August1st to 15thDay
42%8%14%19%14%1
2474
16th to endDay
37%7%14%23%14%2
2484
September1st to 15thDay
40%6%11%19%19%2
2340
16th to endDay
42%5%9%21%18%2
2149
October1st to 15thDay
41%5%11%23%15%2
1950
16th to endDay
36%410%26%20%1
2034
November1st to 15thDay
38%413%21%16%5%
1758
16th to endDay
41%410%26%14%1
1602
December1st to 15thDay
44%5%15%22%10%1
1560
16th to endDay
43%6%14%22%12%
1664
January1st to 15thNight
42%411%20%15%4
2644
16th to endNight
42%411%26%13%1
2704
February1st to 15thNight
41%5%14%21%13%2
2482
16th to endNight
43%5%9%24%15%2
2078
March1st to 15thNight
40%5%11%26%13%1
2181
16th to endNight
42%5%11%21%16%3
2257
April1st to 15thNight
40%5%13%20%17%2
1946
16th to endNight
39%6%10%19%18%6%
1927
May1st to 15thNight
44%6%11%21%13%3
1746
16th to endNight
40%8%15%18%14%2
1625
June1st to 15thNight
36%8%11%26%16%
1560
16th to endNight
34%8%13%24%17%1
1560
July1st to 15thNight
40%10%14%17%12%3
1480
16th to endNight
30%8%19%22%17%2
1694
August1st to 15thNight
34%9%15%22%16%1
1715
16th to endNight
34%7%13%23%18%3
2057
September1st to 15thNight
37%6%12%20%20%3
1950
16th to endNight
39%5%9%22%20%3
2137
October1st to 15thNight
42%5%11%22%16%2
2340
16th to endNight
33%410%30%19%1
2447
November1st to 15thNight
37%49%24%18%5%
2430
16th to endNight
38%411%24%18%2
2685
December1st to 15thNight
46%5%12%22%10%1
2730
16th to endNight
42%6%15%22%11%1
2912

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
19%28%32%14%2
107
16th to endDay
19%25%34%18%1
144
February1st to 15thDay
23%26%40%8%
135
16th to endDay
25%16%41%14%1
260
March1st to 15thDay
18%22%30%23%4
330
16th to endDay
19%15%35%22%42
352
April1st to 15thDay
20%17%32%17%10%2
330
16th to endDay
19%11%30%17%15%5%
319
May1st to 15thDay
24%13%23%21%11%5%
348
16th to endDay
20%419%25%23%7%
395
June1st to 15thDay
16%5%24%26%20%6%
375
16th to endDay
12%424%33%20%4
375
July1st to 15thDay
12%218%29%24%12%
365
16th to endDay
11%212%31%30%11%
390
August1st to 15thDay
14%114%29%26%13%
358
16th to endDay
9%110%32%27%19%
396
September1st to 15thDay
17%5%16%19%24%16%
375
16th to endDay
21%414%27%20%12%
374
October1st to 15thDay
20%7%16%27%20%7%
375
16th to endDay
13%14%31%25%11%2
382
November1st to 15thDay
18%7%26%27%18%1
290
16th to endDay
15%17%35%20%9%
132
December1st to 15thDay
17%25%25%20%7%3
90
16th to endDay
16%17%43%17%4
96
January1st to 15thNight
20%16%37%21%3
780
16th to endNight
19%16%41%20%1
832
February1st to 15thNight
19%16%39%23%1
764
16th to endNight
21%18%40%17%1
683
March1st to 15thNight
20%15%37%23%3
780
16th to endNight
18%13%42%19%5%
832
April1st to 15thNight
17%15%40%21%3
778
16th to endNight
18%8%31%29%10%1
771
May1st to 15thNight
19%6%30%31%11%
576
16th to endNight
16%421%36%19%
407
June1st to 15thNight
11%227%34%23%
390
16th to endNight
11%120%46%20%
390
July1st to 15thNight
9%218%41%25%2
370
16th to endNight
8%14%43%29%3
567
August1st to 15thNight
12%13%43%28%2
575
16th to endNight
11%212%37%31%3
815
September1st to 15thNight
15%219%31%28%3
780
16th to endNight
15%318%30%26%4
777
October1st to 15thNight
19%6%22%29%17%3
780
16th to endNight
17%9%34%26%11%
816
November1st to 15thNight
16%8%32%30%10%1
760
16th to endNight
17%16%32%25%7%
780
December1st to 15thNight
20%12%37%20%8%
780
16th to endNight
20%13%41%23%1
832
Page generated at 2018-10-28 08:41:08. Version ac04

Copyright 2018 A. Danko


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