Re: I can't recall if I ever posted this here
- From: "David M. Palmer" <dmpalmer@xxxxxxxxx>
- Date: Sat, 02 May 2009 14:16:06 -0600
In article <gsvp45$a37$1@xxxxxxxxxxxxxxxxx>, Joe Bernstein
<joe@xxxxxxxxxxx> wrote:
That said, Venus is by far the brightest object in the sky after
the sun and moon. I believe it's brighter than all starlight put
together, though I can't be sure, because estimates for the total
brightness of starlight vary by several orders of magnitude. (I wish
I were making this up. It wouldn't be terribly hard to use modern
star maps to come up with an ideal number for starlight depending on
location and date/time, but all kinds of meteorological and positional
issues interfere, and apparently astronomers don't think it's worth
bothering.)
As you know, Bob, Venus at its brightest is about magnitude -5. The
magnitude system is a factor of 100 dimmer for each 5 magnitudes, so
Venus is about 100 times as bright as a single 0th magnitude star.
From this table, which is reliable at least to 10th magnitude butextrapolated beyond that:
http://www.stargazing.net/David/constel/howmanystars.html
you get the number of stars per magnitude range. If you integrate them
all up, the visible stars (up to magnitude 6.5) total about 100 mag
zeros. To get to 200 times mag 0 (because you can see only half the
sphere of the sky) you go to magnitude 9.5
So Venus at its brightest is brighter than all visible stars in the
sky, but not all stars in the sky. Natural airglow is also important.
--
David M. Palmer dmpalmer@xxxxxxxxx (formerly @clark.net, @ematic.com)
.
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