Re: [Phys-l] the sun

["Folkerts, Timothy J" <FolkertsT@bartonccc.edu>]

> > Of all the stars in the Milky Way on the main sequence, is the sun's
mass
?> close to the average or the median?
> You can decide for yourself:
>  http://en.wikipedia.org/wiki/Hertzsprung-Russell_diagram

With all due respect, this link is of almost no value in answering the
question! 

First of all, the HR diagram says nothing directly about mass -- only
temperature and luminosity.

Second, the Hipparcus satellite that collected most of the data measures
stars that are both 1) close enough to measure the paralax and 2) bright
enough to measure.

While (1) is not a big problem (if we assume that stars in our
neighborhood are "typical"), (2) is critical.  This HR diagram makes it
look like the sun is near the middle of the main sequence, but that is
because the small red K & M stars are too dim to see very far away, and
hence are not plotted.  An HR diagram of only nearby stars would show
the majority are small dim stars.

A list of the nearest stars from an intro astro book says the
distribution is 
21 M
5 K
3 G  
1 F
1 A
(and 2 white dwarves)

So 2 or 3 out of 33 (less than 10%) are heavier than the sum.  The
median seems to be somewhere in the class M planets (less than 1/2 the
sun's mass).  The mean value would be greater than this, but I am pretty
sure I have heard it is still well less than the sun's mass.


Tim F