I was wondering what effect latitude has on the amount of sunlight a place gets, especially during the Autumn and Winter months. So I went to the Old Farmers Almanac and picked two places with similar longitudes but different latitudes:
Edgeworth, PA - 40:33:15 N, 80:11:31 W
Miami, FL - 25:46:32 N, 80:12:39 W
Then I started punching numbers into the sunrise/sunset calculator. The following rising and setting times are for Eastern Standard Time at sea level. The site gives EDT for August, September and October, but I corrected it for the purposes of this question. I made no adjustment for leap year.
| Edgeworth, PA | Miami, FL |
Date | Sunrise | Sunset | Total | Sunrise | Sunset | Total |
| | | | | | |
Aug 21, 2003 | 5:37AM | 7:11PM | 13:34 | 5:56AM | 6:52PM | 12:56 |
| | | | | | |
Sep 21, 2003 | 6:07AM | 6:20PM | 12:13 | 6:09AM | 6:19PM | 12:10 |
| | | | | | |
Oct 21, 2003 | 6:38AM | 5:33PM | 10:55 | 6:22AM | 5:48PM | 11:26 |
| | | | | | |
Nov 21, 2003 | 7:13AM | 4:59PM | 9:46 | 6:43AM | 5:31PM | 10:48 |
| | | | | | |
Dec 21, 2003 | 7:40AM | 4:57PM | 9:17 | 7:03AM | 5:35PM | 10:32 |
| | | | | | |
Jan 21, 2004 | 7:39AM | 5:25PM | 9:46 | 7:08AM | 5:56PM | 10:48 |
| | | | | | |
Feb 21, 2004 | 7:07AM | 6:03PM | 10:56 | 6:51AM | 6:18PM | 11:17 |
| | | | | | |
Mar 21, 2004 | 6:21AM | 6:35PM | 12:14 | 6:23AM | 6:33PM | 12:10 |
| | | | | | |
The Pennsylvania data is pretty much what I expected. Sunrise gets later and later until the sometime around the Winter Solstice, when it starts getting earlier again. Likewise, sunset gets earlier and earlier until sometime around the Winter Solstice, when it makes a turnaround and starts getting later again.
But Miami is different. Sunrise appears to continue to get later every day until long after the Winter Solstice. According to the Farmer’s Almanac site, the first day in 2004 that the sun will rise earlier than the day before will be between January 8th and January 19th. It’s probably only a matter of seconds, and the site only gives the time in minutes, so you can’t tell from that exactly which day it will be. Is there a name for that event?
The same thing happens with the sunset in Autumn. The sun will first set later than the previous day sometime between November 21st and December 9th, and will continue to set later from that point on. Is there a name for that event?
Another thing I notice when I advance the calculator day-by-day is that, even though the sun starts setting later in Miami on an earlier date, there is still a net loss of daylight until sometime around the Winter Solstice, because until that time, the sunrise is getting later faster than the sunset is. Then it reverses course, and the lateness of the sunset starts to outpace the lateness of the sunrise, until January 8-19, when the sun just gives up and starts rising earlier like it’s supposed to.
So the question (besides whether there’s a name for the time when the tropical sunrise starts getting earlier, or when the tropical sunset starts getting later) is simply this: Do the tropical latitudes get more total daylight hours than the temperate zones? Or does it all balance out somehow? If so, how? Are the longest days not as long in the tropics as they are up here, while the shortest days aren’t quite as short? Is there a good book or website out there which explains the astronomy of tropical sunrises and sunsets?
Thanks.