NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/astro/13402

Internet Message Format | 1992-12-24 | 1.6 KB

From: [e-mail] (Andy Goris)
Date: Wed, 23 Dec 1992 17:37:41 GMT
Subject: Solstice Question (simple)
Message-ID: <[e-mail]>
Organization: Hewlett-Packard, Fort Collins, CO, USA
Path: sparky!uunet!cs.utexas.edu!sdd.hp.com!hpscit.sc.hp.com!hplextra!hpfcso!goris
Newsgroups: sci.astro
Lines: 33


I have a simple question for some astronomy guru out there:

   As everyone knows, winter solstice is the day with the shortest time
   between sun-rise and sun-set.  However, it is neither the day
   of latest sun-rise nor earlist sun-set.  Why is this?  I'm having
   trouble picturing in my mind what happens  as the earth rotates
   around the sun, and how the tilt of the earth could cause this.
   One of my coworkers believes the shift is caused by the fact the
   earth is not in perfectly circular orbit around the sun.  I can't
   see how our elliptical orbit could cause this effect.

   I believe the answer to this question would also explain that
   photograph of the sun moving in a figure-8 pattern you see in S&T every
   so often.  It's a time exposure where, for one year, the shutter is
   openened at the same time every day. I understand how the earths tilt
   causes the up-down movement in the figure-8, but what causes the
   left-right movement, and why does it have a period of twice/year?


   Here's some other related questions:

   1. If you live on the equator, is the length of the day always ~12 hours?

   2. If you live on the equator, do you really get effectively two
      summers (when the sun is highest in the sky), that occur on the
      two equinoxes?

   Thanks,

   Andy Goris                [e-mail]