STORM2K

Curious if anyone can explain why is it that although the 'shortest' day of the year in terms of the amount of daylight falls on or around December 21, the earliest sunsets of the year take place quite a bit before December 21, and the latest sunrises of the year tend to take place up to a few weeks after December 21?

Take the example from Fort Lauderdale, the sun is actually starting to set later now...the earliest sunsets of the year took place from November 28-December 1. But the sun continues to rise later during and after that time, making the overall day 'shorter'. In fact, the sun rises at its latest from January 8 - 17. That means the sunsets get later almost 50 days before the sunrises start to get earlier.

I am sure it has to do with the physics of astronomy...but it struck me as interesting that generally, the sunsets get later before the sunrises start to get earlier.


Fort Lauderdale, FL
earliest sunset 5:28 P.M. Nov 28 - Dec 1
latest sunrise 7:10 A.M. Jan. 8 - Jan 17
30-Nov 6:51 A.M. 5:28 P.M.
10-Dec 6:58 A.M. 5:30 P.M
21-Dec 7:04 A.M 5:34 P.M.
2-Jan 7:08 A.M. 5:40P.M.
20-Jan 7:09 A.M. 5:54 P.M.

Boston, MA
earliest sunset 4:12 P.M. Dec 02 - Dec 13
latest sunrise 7:14 A.M. Jan 02-06
30-Nov 6:53 A.M. 4:13 P.M
10-Dec 7:03 A.M. 4:12 P.M
21-Dec 7:10 A.M 4:15 P.M.
2-Jan 7:14 A.M. 4:23 P.M.
20-Jan 7:08 A.M. 4:43 P.M.

Chicago, IL
earliest sunset 4:20 P.M. Dec 02 - Dec 14
latest sunrise 7:18 A.M. Dec 28 - Jan 10
30-Nov 6:58 A.M. 4:21 P.M
10-Dec 7:08 A.M. 4:20 P.M
21-Dec 7:15 A.M 4:23 P.M.
2-Jan 7:18 A.M. 4:31 P.M.
20-Jan 7:13 A.M. 4:50 P.M.

Los Angeles, CA
earliest sunset 4:44 P.M. Nov 28 - Dec 10
latest sunrise 7:00 A.M. Jan. 4 - Jan 12
30-Nov 6:41 A.M. 4:44 P.M
10-Dec 6:49 A.M. 4:44 P.M
21-Dec 6:55 A.M 4:48 P.M.
2-Jan 6:59 A.M. 4:56P.M.
20-Jan 6:58 A.M. 5:12 P.M.

sunrise/sunset data found at http://aa.usno.navy.mil/data/docs/RS_OneYear.php

The answer lies in the Analemma which is the figure 8 pattern that the Sun describes in the sky over the year and which reflects the eccentricity of Earth's orbit as well as the orientation of the Line of the Apsides (line connecting perihelion and Aphelion) with respect to the seasons. Currently, the Sun is at perihelion and is moving eastward faster as it travels along the bottom of the 8 in the sky. Thus when it makes the turn both sunsets and sunrises will get later each day until the turn north begins in January. The reverse happens In June when the Sun is at aphelion. This also affects the equation of time as we go from Sun fast to Sun slow

Steve

totally interesting, esp since today i was just discussing this with someone.

Southern Ontario is now through our earliest sunsets of the year, which is around 4:39pm which occurs nov 30 and dec 1. Today the sun set at 4:40pm yay

the mornings will continue to darken more though through early january.
SUN DATA for Southern Ontario (times approx)
Dec 1 Sunrise 7:33am Sunset 4:39pm
Dec 10 Sunrise 7:41am Sunset 4:41pm
Dec 20 Sunrise 7:48am Sunset 4:44pm
Dec 30 Sunrise 7:53am Sunset 4:49pm

so which means between now and the end of the year, we gain 10 minutes of daylight at the end of the day, but lose 20 minutes at the start of the day... giving us a total loss of 10 minutes daylight for the rest of the year.

incidentally..the latest sunrises are around january 1 and 2nd...when the sun doesnt rise til 7:55am.

so the days start to lenghten , albeit slowly, after january 2, minute by minute at the start and end of each day. Slow slow process.

i loved the explanation. thanks.

justin-

thanks for the info....very interesting stuff.

Aslkahuna wrote:The answer lies in the Analemma which is the figure 8 pattern that the Sun describes in the sky over the year and which reflects the eccentricity of Earth's orbit as well as the orientation of the Line of the Apsides (line connecting perihelion and Aphelion) with respect to the seasons. Currently, the Sun is at perihelion and is moving eastward faster as it travels along the bottom of the 8 in the sky. Thus when it makes the turn both sunsets and sunrises will get later each day until the turn north begins in January. The reverse happens In June when the Sun is at aphelion. This also affects the equation of time as we go from Sun fast to Sun slow

Steve