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Re: Astronomical Unit (AU)



Regarding Leigh's confirmation of my 1 AU distance quote from JPL:

According to the JPL/NASA web site
http://ssd.jpl.nasa.gov/astro_constants.html the numerical value of the
AU is 149597870691 +/- 3 m.

which translates to 499.004783806(10) light seconds. Pretty good.

Remember, though, this nice 499.00 s value (to 5 sig. figs.) is *not* the
light travel time for sunlight to reach the Earth when it is 1 AU from
its orbital focus, because the visual radius of the Sun is about
2.32 light sec, and this gives the light about a 2.32 s head start. The
radius of the Earth is a more negligible 0.02 light sec.

David Bowman
David_Bowman@georgetowncollege.edu