calculating distance

[bridgwater]

Hello. It has been a long while since I studied astronomy. I am trying to recall how distances are calculated for newly observed objects. For instance, Hubble recently viewed a new batch of galaxies, and it was stated that some of them are millions of light years away. So how are these distances calculated?

 

[Saiph]

For really distant objects, one can use the Hubble Constant, which is an empircal relationship between distance and velocity (the reason is believed to be the expansion of the universe).<br /><br />Vr= HoD.<br /><br />Vr = Recessional Velocity (determined by redshift) in km/s<br /><br />Ho = hubbles constant, typically ~70 km/s/Mpc (thats Megaparsec for the last unit)<br /><br />D is distance, in Mega parsec.<br /><br />For closer objects (and for use in determining the hubble constant) Supernovae peak brightness (believed to be the same for all type Ia sukpernovae) is observed. Or Cephied Variable stars, which have a period to luminosity relationship.<br /><br />Most methods (as those above) rely on finding the "absolute" or real magnitude of an object, and comparing it to the observed. The difference between these two magnitudes is proportional to the distance (once one takes into account complicating factors).<br /><br />One can also try to find distance based on where they fit into the HR diagram, use physical parralax (like surveyors use, but only for nearby stars) and a dozen other methods. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[mikeemmert]

Thank you for your reply. Missing is the main distance indicator for objects farther than Saturn and nearer than Proxima Centauri.<br /><br />Those objects' distances are usually determined by their orbital periods and the application of Newtons Laws of Gravitation. This requires a pretty precise determination of the object's orbit. <br /><br />This is fairly easy if you can make precovery observations, in other words, old archival photographs of the objects. This is difficult for objects discovered by the new generation of 8 meter telescopes, since older telescopes are not as large and would have missed the object.