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New double star and binary star site
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#2
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newbie question
How do you know it is a true double, and not just two stars in our line of
sight but light years apart? Steve |
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newbie question
Steven Gill wrote:
How do you know it is a true double, and not just two stars in our line of sight but light years apart? We can observe their motion around each other. |
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newbie question
"Steven Gill" wrote in message
. uk... How do you know it is a true double, and not just two stars in our line of sight but light years apart? Steve 1. Watch the pair for years or decades and see if there is orbital motion. Works best on very close pairs. 2. Check for common proper motion of wider pairs, since they won't show much orbital motion on timescales of a few centuries. If you can use spectroscopy to check for common radial velocity that can also help, but this is difficult for very faint stars. 3. Use statistical methods to assign a probability of a pair of given magnitude and separation being a physical pair. The famous double-star observer Robert G. Aitken offered the formula log (separation in arcsec) = 2.8 - 0.2 m where m is the magnitude of the double star (I think this is for combined magnitude of two nearly equal components). A wide pair of fourth or fifth magnitude stars might well be physical (e.g., epsilon Lyrae) by this criterion, but the same separation for 11th magnitude stars would not be. -- Mike Dworetsky (Remove pants sp*mbl*ck to reply) |
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newbie question
Question to all re Dark Matter, etc.
Does Einstein maintain (in his 'M'' equation) that there is no such thing as ''empty'' space in the cosmos? Vacuum ?? tks ClaudiaMarie |
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newbie question
Question to all;
In some galaxies are some stars only gas & therefore able to pass through each other ( without collisions or exerting dominate magnetism one over another) ?? tks, ClaudiaMarie |
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