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fun with science
This grew out of a conversation in ![[livejournal.com profile]](https://www.dreamwidth.org/img/external/lj-userinfo.gif)
eub's journal. I started to comment there, but it got long and off of his original topic, so here I am.
I had always assumed that the main factor in determining local sunrise/sunset time was your east-west placement within the time zone. (Yes, very far north things would get wonky around solstices, but somehow I thought not so much otherwise.) That is, New York City and Pittsburgh are both in the same time zone, but the sun sets in New York about half an hour before it sets here. By definition, you can have variation of up to an hour within a single time zone.
But it turns out that the north-south position is much more important. Using my longitude (80W) and this tool, I played around with different lattitudes. Here are sunset times for today (all lats N, all times EDT):
0: 19:08
10: 18:59
20: 18:50
30: 18:40
40: 18:28 (so far we're pretty regular, but watch this:)
50: 18:11
60: 17:46
70: 16:54 (10 degrees, almost an hour! let's take smaller steps)
(IIRC, the arctic circle is around 70N, which presumably accounts for that jump. But we still get sunrise/sunset up there this time of year.)
75: 15:56 (5 degrees, another hour)
76: 15:37
77: 15:12
78: 14:36 (!)
78:15: 14:23
78:30: 14:08
78:45: 13:46
78:55: 13:18 (last point for a reading)
78:56: none
At good old 78:55, the time from sunrise to sunset is a mere 39 minutes.
But it's not dark for 23+ hours. What about twilight? Around here, it's order of 30-40 minutes at each end. Here is the complete picture of the day at our point within the arctic circle:
Begin civil twilight 09:08
Sunrise 12:49
Sun transit 13:04
Sunset 13:18
End civil twilight 16:58
So while sunrise to sunset is only 39 minutes, the period of "light" (for some value of light) is closer to 8 hours. This makes sense.
Contrariwise, at the equator, twilight is 21 minutes on each end of a ~12.5-hour day:
Begin civil twilight 06:40
Sunrise 07:01
Sun transit 13:04
Sunset 19:08
End civil twilight 19:29
So, a roughly 6-hour difference in sunset (and sunrise) times, but only about a 4.5-hour difference in the actual length of the perceptible "day".
Interesting, in a goofy, useless, just-plain-odd way. :-)
One thing is clear from this data, though: it must suck to be Jewish that far north, even setting aside being so far north that you never get sunrise/sunset in December/June. Imagine starting Shabbat at 1 in the afternoon! Especially as it won't actually get dark for 4 more hours!
eub's journal. I started to comment there, but it got long and off of his original topic, so here I am.I had always assumed that the main factor in determining local sunrise/sunset time was your east-west placement within the time zone. (Yes, very far north things would get wonky around solstices, but somehow I thought not so much otherwise.) That is, New York City and Pittsburgh are both in the same time zone, but the sun sets in New York about half an hour before it sets here. By definition, you can have variation of up to an hour within a single time zone.
But it turns out that the north-south position is much more important. Using my longitude (80W) and this tool, I played around with different lattitudes. Here are sunset times for today (all lats N, all times EDT):
0: 19:08
10: 18:59
20: 18:50
30: 18:40
40: 18:28 (so far we're pretty regular, but watch this:)
50: 18:11
60: 17:46
70: 16:54 (10 degrees, almost an hour! let's take smaller steps)
(IIRC, the arctic circle is around 70N, which presumably accounts for that jump. But we still get sunrise/sunset up there this time of year.)
75: 15:56 (5 degrees, another hour)
76: 15:37
77: 15:12
78: 14:36 (!)
78:15: 14:23
78:30: 14:08
78:45: 13:46
78:55: 13:18 (last point for a reading)
78:56: none
At good old 78:55, the time from sunrise to sunset is a mere 39 minutes.
But it's not dark for 23+ hours. What about twilight? Around here, it's order of 30-40 minutes at each end. Here is the complete picture of the day at our point within the arctic circle:
Begin civil twilight 09:08
Sunrise 12:49
Sun transit 13:04
Sunset 13:18
End civil twilight 16:58
So while sunrise to sunset is only 39 minutes, the period of "light" (for some value of light) is closer to 8 hours. This makes sense.
Contrariwise, at the equator, twilight is 21 minutes on each end of a ~12.5-hour day:
Begin civil twilight 06:40
Sunrise 07:01
Sun transit 13:04
Sunset 19:08
End civil twilight 19:29
So, a roughly 6-hour difference in sunset (and sunrise) times, but only about a 4.5-hour difference in the actual length of the perceptible "day".
Interesting, in a goofy, useless, just-plain-odd way. :-)
One thing is clear from this data, though: it must suck to be Jewish that far north, even setting aside being so far north that you never get sunrise/sunset in December/June. Imagine starting Shabbat at 1 in the afternoon! Especially as it won't actually get dark for 4 more hours!
Ramadan