To get distances, we use a variety of techniques. The most basic one is geometric parallax. By photographing the same star 6 months apart, the shift of the star relative to more distant background stars amounts to 1 second of arc at 1 parsec ( 3.24 light years), 1/2 arcsecond at 2 parsecs, 1/10 arcsecond at 10 parsecs etc. The Hipparcos astrometric satellite has determined the distance to tens of thousands of stars in this way. Read an ESA Press Release about the mission accomplishments. For example, the distances to the Nearest 10 stars can be found in their Table of 150 closest stars which I reprint below:
Name Parallax Alpha Centauri C 772.33 Alpha2 Centauri C 742.12 Alpha1 Centauri C 742.12 Barnard's Star 549.01 Alpha Canis Majoris (Sirius) 379.12 Epsilon Eridani 310.75 61 Cygni A 287.13 Alpha Canis Minoris 285.93 61 Cygni B 285.42 Epsilon Indi 275.76 Tau Ceti 274.17 Note: the Parallax is measured in 1/arcseconds. To calculate the distance in parsecs you have to
Stellar diameters can be resolved using a technique called stellar interferometry. The Navy Prototype Optical Interferometer has been operating for over a decade at Mount Wilson Observatory, and routinely measures the angular diameters of bright stars to fractions of a milli arcsecond accuracy. The table below shows only a few stars that have had their diameters measured. Once their distances are accurately known...from the Hipparcos Survey...their linear diameters in millions of kilometers can easily be found.
HR 617 6.99 +/- 0.04
HR 168 5.69 +/- 0.05
HR 1017 3.13 +/- 0.01
HR 1373 2.21 +/- 0.08
Copyright 1997 Dr. Sten Odenwald
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