ASTR 114 Lecture Notes - Lecture 15: Proper Motion, Stellar Kinematics, Minute And Second Of Arc
10 Jan 2020
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Document Summary
Why are stellar distances important: distances are necessary for estimating total energy emitted by an object (luminosity), masses of objects from orbital motions, True motions through space and physical sizes of objects: the problem is distances are very hard to measure. Trigonometric parallax: parallax is the shift in position of a nearby object against a background of more distant objects: apparent positions of nearest. Stars shift by about an arcsecond as earth orbits the sun; parallax angle depends on distance; Parallax is measured by comparing snapshots taken at different times and measuring the shift in angle to star. Parallax equation: d=1/p- assumes earth is a perfect circle; 1pc=3. 26 light years. This method does not work for stars further away than 100pc. Solar neighborhood: 30 closest stars to the sun all lie within 4pc of earth or 13 light years. Always solve for proper motion as hypotenuse of triangle. M= proper motion in arcsecond/year, d=distance in pc.
