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RE: starship-design: Stars_within_16_light_years_of_the_Sun


I already wrote Zenon back regarding this. I'm not qualified to argue this point, I simply copied it off of the web. I wrote the author and asked HIM to check his data.

There has recently been a new more accurate study completed called HIPPARCOS which has provided much more accurate data on several MILLION stars, by far the largest sky survey ever. Along with charting positions and movements more accurately, it also increased both the size and age of the universe. Perhaps his data is from this survey. I don't know.

I agree with Zenon as well. I always THOUGHT that they were approximately the same distance away. I think half a parsec is a little farther than I had in mind. Incidentally, the HIPPARCOS data is available for download along with database access software for PC/Windows, Macintosh and UNIX. Of course the data is over a hundred megabytes....

Lee Parker

Long experience has taught me not to believe in the limitations indicated by purely theoretical considerations. These - as we well know - are based on insufficient knowledge of all the relevant factors." 

Guglielmo Marconi

-----Original Message-----
From:	Steve VanDevender [SMTP:stevev@darkwing.uoregon.edu]
Sent:	Monday, June 23, 1997 1:23 PM
To:	starship-design@lists.uoregon.edu
Subject:	RE: starship-design: Stars_within_16_light_years_of_the_Sun

Zenon Kulpa writes:
 > Sorry, but this MUST be in error.
 > Your data gives B farther away than A by 0.5 ps, that is 1.6 ly,
 > and at the same distance as to Barnard.
 > And both these are certainly not true.

I'll have to agree with Zenon on this one.  Alpha Centauri is a trinary
system, with Proxima being distant from A/B; the apparent distance to
A and B should be nearly identical.

 > I am also including some data from some other sources for comparison below.
 > Note also differences concerning spectral types and magnitudes
 > between the sources.

Lee's chart is also mislabeled; substitute "absolute" for "visual" in
the heading.

The difference in spectral class is likely a difference in opinion.
Spectral class is judged primarily by the appearance and relative
strength of sets of spectral lines corresponding to different elements
and compounds in their various ionization states; these can provide a
good estimate of the surface temperature of the star, as well as the
abundance of the elements involved.  Several components of spectral
class are rather subjective and may be interpreted differently by
different astronomers, resulting in the different subclass numbers.  The
'V' following the spectral type in Lee's chart is the luminosity class
(most main sequence stars are class V; the classes are roman numerals).

 > NAME                 DISTANCE         SPECTRAL     APPARENT     VISUAL	
 >                      (ps/ly)          TYPE         MAGNITUDE    MAGNITUDE
 > L. Parker source:
 > -----------------
 > Proxima Centauri       1.3            M6 V         11.05        15.49	
 > Alpha Centauri A       1.33           G2 V         -0.01         4.37	
 > Alpha Centauri B       1.83           K1 V          1.33         5.71	
 > Barnard's Star         1.83           M4 V          9.54        13.22	
 > http://www.essex1.com/people/speer/stars.html:
 > ----------------------------------------------
 > Proxima Centauri      (1.29)/4.2      M5e          11.3
 > Alpha Centauri A      (1.32)/4.3      G0             .33
 > Alpha Centauri B      (1.32)/4.3      K5            1.70
 > Barnard's Star        (1.83)/5.96     M5            9.5
 > http://monet.physik.unibas.ch/~schatzer/Alpha-Centauri.html:
 > ------------------------------------------------------------
 > Proxima Centauri      (1.29)/4.22     M5e 
 > Alpha Centauri A      (1.33)/4.35     G2 
 > Alpha Centauri B      (1.33)/4.35     K1 
 > Separation A/B (current): 23 AU = 0.00001 ps
 > The units:
 > ----------
 > AU =   149 598 770 km
 > ly =  9.4543*10^12 km =  63197.7 AU = 0.3066 ps
 > ps = 30.8361*10^12 km = 206125.7 AU = 3.2616 ly 
 > -- Zenon