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ActonStarParty
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ActonStarParty clear sky chart from 2005-11-05 to 2017-08-12.

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
27%
14750
18%
46456
8%
14718
39%
14718
21%
30337

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
17%
720
19%
2506
7%
716
33%
716
16%
1622
January16th to endNight
15%
768
20%
2688
4%
768
34%
768
15%
1724
February1st to 15thNight
17%
704
16%
2194
5%
701
31%
701
17%
1476
February16th to endNight
18%
631
23%
1893
7%
631
38%
631
19%
1246
March1st to 15thNight
18%
720
17%
2160
6%
720
32%
720
16%
1493
March16th to endNight
21%
768
22%
2025
7%
768
34%
768
22%
1373
April1st to 15thNight
21%
718
18%
1796
4%
718
29%
718
22%
1266
April16th to endNight
22%
594
18%
1674
5%
594
32%
594
19%
1143
May1st to 15thNight
24%
540
15%
1620
6%
540
32%
540
19%
1121
May16th to endNight
25%
408
11%
1530
7%
407
33%
407
15%
1016
June1st to 15thNight
30%
360
12%
1440
9%
360
41%
360
16%
969
June16th to endNight
37%
360
12%
1440
11%
360
47%
360
21%
888
July1st to 15thNight
46%
340
12%
1360
15%
340
51%
340
22%
823
July16th to endNight
47%
376
15%
1418
15%
354
54%
354
21%
864
August1st to 15thNight
46%
489
17%
1538
11%
487
51%
487
27%
953
August16th to endNight
51%
665
19%
1715
10%
665
55%
665
34%
1110
September1st to 15thNight
40%
660
20%
1705
9%
660
47%
660
33%
1097
September16th to endNight
46%
657
26%
1815
17%
657
54%
657
35%
1100
October1st to 15thNight
33%
660
23%
1841
11%
660
44%
660
25%
1194
October16th to endNight
24%
704
16%
2288
6%
704
38%
704
20%
1495
November1st to 15thNight
30%
700
21%
2277
11%
700
44%
700
22%
1444
November16th to endNight
25%
720
20%
2340
8%
720
40%
720
18%
1510
December1st to 15thNight
21%
720
17%
2505
5%
720
36%
720
17%
1617
December16th to endNight
17%
768
19%
2688
5%
768
34%
768
15%
1793

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
17%5%25%42445%6%39%
47521
Night
17%6%2442445%6%41%
46626
Cloud CoverDay
17%6%25%5%2445%6%39%
47531
Night
16%6%24424446%40%
46631
TransparencyDay
43%6%11%21%14%2
47209
Night
43%5%11%21%15%2
46456
SeeingDay
22%12%31%21%9%2
5737
Night
21%12%33%24%7%
14750

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
16%7%25%425%345%41%
1432
16th to endDay
15%6%2343445%5%43%
1536
February1st to 15thDay
16%7%35%426%5%5%7%34%
1663
16th to endDay
15%8%36%5%24435%40%
1580
March1st to 15thDay
21%7%35%424346%36%
1790
16th to endDay
18%6%36%423345%41%
2196
April1st to 15thDay
18%7%35%5%34436%38%
2152
16th to endDay
18%424425%447%40%
2286
May1st to 15thDay
25%7%345%2435%5%31%
2332
16th to endDay
17%425%43435%7%39%
2593
June1st to 15thDay
25%5%2442446%6%33%
2520
16th to endDay
16%425%5%36%6%6%8%34%
2520
July1st to 15thDay
12%5%25%5%36%6%6%9%37%
2520
16th to endDay
11%425%5%35%6%6%8%39%
2654
August1st to 15thDay
11%415%6%45%5%5%8%39%
2314
16th to endDay
12%425%5%36%5%5%8%42%
2133
September1st to 15thDay
14%5%25%42445%7%45%
1925
16th to endDay
13%5%23313345%51%
1815
October1st to 15thDay
20%5%245%23345%42%
1787
16th to endDay
16%5%25%43335%6%42%
1584
November1st to 15thDay
20%6%2432333444%
1581
16th to endDay
16%5%35%42444443%
1620
December1st to 15thDay
18%6%35%5%24446%39%
1452
16th to endDay
23%7%335%24435%35%
1536
January1st to 15thNight
16%8%25%5%23345%40%
2506
16th to endNight
16%8%35%423345%40%
2688
February1st to 15thNight
15%8%36%5%3445%6%38%
2193
16th to endNight
16%9%33424346%41%
1893
March1st to 15thNight
19%7%245%24445%37%
2147
16th to endNight
15%8%35%42433444%
2025
April1st to 15thNight
16%7%35%5%34347%37%
1796
16th to endNight
21%5%24424345%40%
1674
May1st to 15thNight
21%6%35%433445%37%
1620
16th to endNight
19%5%25%5%235%48%35%
1528
June1st to 15thNight
23%6%3442335%7%34%
1440
16th to endNight
14%5%245%2446%8%40%
1440
July1st to 15thNight
12%425%5%25%5%7%7%41%
1440
16th to endNight
11%5%247%35%45%7%41%
1514
August1st to 15thNight
10%3245%35%5%5%8%45%
1548
16th to endNight
12%42343446%8%44%
1715
September1st to 15thNight
14%425%32345%6%47%
1705
16th to endNight
13%5%13313346%52%
1815
October1st to 15thNight
19%5%1432235%5%45%
1841
16th to endNight
20%6%245%1345%6%39%
2288
November1st to 15thNight
18%6%2442335%5%44%
2277
16th to endNight
19%6%34424346%41%
2340
December1st to 15thNight
19%7%245%24346%39%
2505
16th to endNight
18%9%35%424446%36%
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
16%7%35%425%345%41%
1432
16th to endDay
15%5%245%2445%5%43%
1536
February1st to 15thDay
16%7%35%436%5%5%7%33%
1663
16th to endDay
15%8%26%5%35%335%40%
1580
March1st to 15thDay
22%6%35%42435%5%35%
1800
16th to endDay
18%6%25%424346%40%
2196
April1st to 15thDay
18%7%35%5%24446%38%
2152
16th to endDay
18%4245%3445%6%40%
2286
May1st to 15thDay
24%8%34424346%32%
2332
16th to endDay
17%425%5%3435%7%39%
2593
June1st to 15thDay
25%42442445%7%33%
2520
16th to endDay
15%5%25%5%36%6%6%8%34%
2520
July1st to 15thDay
11%6%35%5%36%6%6%8%37%
2520
16th to endDay
11%5%25%5%36%5%6%8%38%
2654
August1st to 15thDay
11%425%6%45%5%6%8%39%
2314
16th to endDay
11%425%5%36%5%48%42%
2133
September1st to 15thDay
13%5%2442345%7%45%
1925
16th to endDay
13%5%23413345%51%
1815
October1st to 15thDay
20%5%14423345%42%
1787
16th to endDay
16%5%2443345%6%42%
1584
November1st to 15thDay
21%6%2332333444%
1581
16th to endDay
16%6%35%42445%5%43%
1620
December1st to 15thDay
18%6%35%5%23445%40%
1452
16th to endDay
23%7%335%245%35%35%
1536
January1st to 15thNight
16%9%25%5%24345%40%
2506
16th to endNight
16%9%35%423345%41%
2688
February1st to 15thNight
14%8%26%5%34446%37%
2186
16th to endNight
16%10%33423346%41%
1893
March1st to 15thNight
19%7%345%34445%37%
2160
16th to endNight
15%8%35%423335%44%
2024
April1st to 15thNight
17%6%36%6%34346%37%
1796
16th to endNight
21%5%2442434440%
1674
May1st to 15thNight
21%6%25%43445%5%36%
1620
16th to endNight
19%6%246%245%5%8%35%
1528
June1st to 15thNight
22%7%35%423448%34%
1440
16th to endNight
14%5%245%3445%9%39%
1440
July1st to 15thNight
12%5%25%5%345%6%8%41%
1440
16th to endNight
11%5%25%6%25%5%5%8%40%
1514
August1st to 15thNight
9%3245%45%5%5%8%45%
1548
16th to endNight
12%41343446%8%45%
1715
September1st to 15thNight
14%424323447%46%
1705
16th to endNight
13%6%1421335%6%52%
1815
October1st to 15thNight
19%5%23323345%44%
1841
16th to endNight
20%6%2442435%6%40%
2288
November1st to 15thNight
17%6%2442335%5%44%
2277
16th to endNight
19%5%34423346%41%
2340
December1st to 15thNight
18%7%245%33346%39%
2505
16th to endNight
18%9%35%424446%36%
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
44%5%10%23%11%3
1433
16th to endDay
40%5%11%26%13%1
1536
February1st to 15thDay
47%6%12%19%12%1
1666
16th to endDay
46%5%9%20%15%3
1580
March1st to 15thDay
49%410%20%11%3
1800
16th to endDay
44%49%19%15%6%
2196
April1st to 15thDay
47%410%18%15%3
2152
16th to endDay
42%6%8%19%18%3
2286
May1st to 15thDay
53%5%7%17%13%2
2332
16th to endDay
44%6%12%20%13%2
2597
June1st to 15thDay
49%7%12%20%10%1
2520
16th to endDay
43%9%12%18%14%
2520
July1st to 15thDay
41%8%10%21%15%1
2371
16th to endDay
39%8%14%20%13%2
2487
August1st to 15thDay
39%8%15%21%13%1
2300
16th to endDay
38%7%10%25%15%2
2133
September1st to 15thDay
37%6%11%22%20%1
1925
16th to endDay
34%48%23%25%2
1815
October1st to 15thDay
44%49%23%14%3
1787
16th to endDay
41%6%12%23%14%1
1584
November1st to 15thDay
43%312%23%14%1
1581
16th to endDay
42%413%20%16%1
1620
December1st to 15thDay
45%415%16%17%
1452
16th to endDay
50%7%11%19%11%
1536
January1st to 15thNight
46%411%21%13%2
2506
16th to endNight
45%410%20%15%2
2688
February1st to 15thNight
46%5%12%21%12%2
2194
16th to endNight
44%49%22%16%2
1893
March1st to 15thNight
47%5%10%19%13%3
2160
16th to endNight
43%48%17%19%5%
2025
April1st to 15thNight
46%410%18%17%2
1796
16th to endNight
46%5%8%18%16%4
1674
May1st to 15thNight
48%5%10%17%15%3
1620
16th to endNight
47%7%13%18%11%1
1530
June1st to 15thNight
49%6%12%20%10%1
1440
16th to endNight
40%7%12%22%15%1
1440
July1st to 15thNight
37%8%12%25%14%
1360
16th to endNight
39%7%12%27%10%2
1418
August1st to 15thNight
35%9%13%23%16%1
1538
16th to endNight
35%6%13%27%16%
1715
September1st to 15thNight
37%414%23%19%
1705
16th to endNight
33%47%24%28%1
1815
October1st to 15thNight
41%412%22%15%3
1841
16th to endNight
44%5%13%22%13%
2288
November1st to 15thNight
41%5%11%20%17%2
2277
16th to endNight
44%411%21%15%2
2340
December1st to 15thNight
46%414%21%12%
2505
16th to endNight
47%5%11%22%12%
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
23%26%25%23%1
60
16th to endDay
31%20%35%12%
64
February1st to 15thDay
25%18%35%16%3
217
16th to endDay
21%20%34%17%5%
239
March1st to 15thDay
29%18%31%15%3
270
16th to endDay
24%19%34%11%9%1
288
April1st to 15thDay
26%16%33%13%9%1
270
16th to endDay
24%13%33%18%6%2
270
May1st to 15thDay
35%13%26%14%6%2
288
16th to endDay
21%10%37%22%6%1
331
June1st to 15thDay
23%12%33%20%8%1
315
16th to endDay
17%11%40%23%5%2
315
July1st to 15thDay
18%8%32%26%13%1
305
16th to endDay
13%6%30%32%13%3
326
August1st to 15thDay
13%8%27%29%16%3
297
16th to endDay
13%5%26%27%19%7%
268
September1st to 15thDay
20%6%24%27%15%7%
255
16th to endDay
17%6%29%19%12%14%
254
October1st to 15thDay
23%9%23%21%15%5%
254
16th to endDay
20%15%30%24%8%
240
November1st to 15thDay
28%8%28%20%10%2
235
16th to endDay
24%15%30%17%10%2
240
December1st to 15thDay
20%34%27%12%4
72
16th to endDay
26%31%25%17%
64
January1st to 15thNight
22%16%37%19%3
720
16th to endNight
23%17%36%18%2
768
February1st to 15thNight
20%17%39%21%1
704
16th to endNight
23%17%34%20%3
631
March1st to 15thNight
24%18%35%18%3
720
16th to endNight
20%17%36%18%6%
768
April1st to 15thNight
22%16%36%19%4
718
16th to endNight
24%15%34%18%7%
594
May1st to 15thNight
25%12%33%22%5%
540
16th to endNight
21%9%37%26%4
408
June1st to 15thNight
25%435%26%8%
360
16th to endNight
17%338%32%7%
360
July1st to 15thNight
13%428%41%11%
340
16th to endNight
13%329%41%11%
376
August1st to 15thNight
11%429%42%11%
489
16th to endNight
14%226%38%16%2
665
September1st to 15thNight
17%432%29%14%
660
16th to endNight
16%5%26%27%20%3
657
October1st to 15thNight
23%10%27%26%11%1
660
16th to endNight
24%12%34%21%6%
704
November1st to 15thNight
21%12%31%24%10%
700
16th to endNight
22%16%29%21%7%1
720
December1st to 15thNight
25%15%33%21%4
720
16th to endNight
25%16%36%17%2
768
Page generated at 2017-08-13 14:16:35. Version ac04

Copyright 2017 A. Danko


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