Phil wrote:
What does it mean when you see this line in a header on a message
that you received in your inbox? particularly, the -0500??      Phil
"Tue, 26 Nov 2002 07:42:20 -0500 (EST) "
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I think it usually tells you what time zone the sender is in.
An attempt at a celestial explanation is below.
I have no idea how the internet figures this out.

The earth rotates once, 360 degrees, each day.  That makes the sun, which
doesn't move, appear to rise and set. Because the sun (apparently) takes 24
hours to go around the earth, we divide the earth into 24 "time zones".
Each time zone is 15 degrees of longitude (360/24). The sun progresses 15
degrees westward (one time zone) each hour. The "Zero" point of longitude
was designated at the Royal Observatory in Greenwich, England.  The -0500
number represents the sender's time in relation to Greenwich (GMT, Zulu,
Universal) time, five hours earlier, which would be our "Eastern Standard
Time" zone or Eastern United States (5 x 15 or about 75 degrees West
longitude). Time zone -0800 is the US west coast. That progression
continues to -1200, then the date changes, it becomes +1200, and it then
diminishes to 0000 at Greenwich.

You are therefore able to estimate the sender's approximate longitude, east
or west of London, but he could be anywhere in his time zone, from the
North Pole to the South Pole. Chances are he's in a heavily populated or
technically advanced area so you can make a guess as to his probable location.

Here's an illustration of the time zones. If you view or print it, you will
be able to speculate where the contributors to this group are located.
http://aa.usno.navy.mil/faq/docs/world_tzones.html