From: Amara Graps (amara@amara.com)
Date: Fri May 02 2003 - 06:47:45 MDT
Transits in General
http://sunearth.gsfc.nasa.gov/eclipse/transit/transit.html
Mercury transit
http://sunearth.gsfc.nasa.gov/eclipse/OH/transit03.html
From the above web page:
"2003 May 07: Transit of Mercury
The transit or passage of a planet across the face of the Sun is a
relatively rare occurrence. As seen from Earth, only transits of
Mercury and Venus are possible. On the average, there are 13
transits of Mercury each century. In comparison, transits of Venus
occur in pairs with more than a century separating each pair.
On Wednesday, 2003 May 07, Mercury will transit the Sun for the
first time since 1999. The entire event will be widely visible from
the Europe, Africa and Asia as shown in the map in figure 1. Japan
Australia, and New Zealand will witness the beginning of the transit
but the Sun will set before the event ends. Similarly, observers in
western Africa, eastern North America and eastern South America will
see the end of the event since the transit will already be in
progress at sunrise from those regions.
The principal events occurring during a transit are conveniently
characterized by contacts, analogous to the contacts of an annular
solar eclipse. The transit begins with contact I which is the
instant when the planet's disk is externally tangent with the Sun.
Shortly after contact I, the planet can be seen as a small notch
along the solar limb. The entire disk of the planet is first seen at
contact II when the planet is internally tangent with the Sun.
During the next several hours, the silhouetted planet slowly
traverses the brilliant solar disk. At contact III, the planet
reaches the opposite limb and once again is internally tangent with
the Sun. Finally, the transit ends at contact IV when the planet's
limb is externally tangent to the Sun. Contacts I and II define the
phase called ingress while contacts III and IV are known as egress.
Position angles for Mercury at each contact are measured
counterclockwise from the north point on the Sun's disk. "
-- ******************************************************************** Amara Graps, PhD email: amara@amara.com Computational Physics vita: ftp://ftp.amara.com/pub/resume.txt Multiplex Answers URL: http://www.amara.com/ ******************************************************************** "Oh you damned observers, you always find extra things." -- Fred Hoyle [quoted by Richard Ellis at IAU Symposium 183]
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