Krisitan Anderson wrote (August 18, 2000)
"...when I looked at Deneb, Hipparcos gave a distance of 3229 light
years! Every number I've seen growing up has been somewhere in the
neighborhood of 1500-1800 light years. The problem is that even in many
recent books the distance hasn't been changed. I noticed this in Ken
Croswell's book "See the Stars" which was published just this year. I have
been telling people for years 'Deneb is 1500 light years away.' Can anyone
do a double check, we may have a lot of shows to change!"
The Hipparcos catalog gives Deneb's parallax as 1.01 +/- 0.57 milliarcsec.
That translates to a distance of 3230 l.y. (the program stated too many digits of
accuracy!) with a standard error range of 2060 - 7410 l.y. Deneb is so darn
far away that its parallax is small and hard to measure, even for Hipparcos.
So the answer is yes, if someone says Deneb is 1500 l.y. away, they're shy by
about a factor of two.
Because of this very problem, shortly after the Hipparcos catalog came out I
generated several lists of distances (nearest stars, brightest stars, M-objects)
based on the new Hipparcos data. Some of them are quite a departure from
the old values we grew up with. The biggest adjustment for me has been
M-31, which, as a result of Hipparcos' rescaling of the cosmological distance
ladder, is now estimated at 2.9 million l.y., not the old 2.4 that I'd been quoting
for almost twenty years. Mind you, the larger value is somewhat controversial,
but if you're rounding to the nearest million l.y., 3 is closer to the mark than 2.
Chris Anderson
Faulkner Planetarium Production Specialist
Herrett Center for Arts and Science
College of Southern Idaho
