Astronomy 1021 Lecture Notes - Lecture 7: Doppler Spectroscopy, Angular Distance, Orbital Period

• School: Western University
• Department: Astronomy
• Course: Astronomy 1021
• Professor: Sarah Gallagher

Document Summary

Direct imagine of planets around other stars is very difficult: very small angular separation, star is a billion times brighter than a planet. Almost all extrasolar planets have been discovered by indirect methods. Stars and planets orbit their center of mass. Jupiter"s gravitational tug makes the sun wobble around the center of mass with a period of 12 years. Wow, that planet must be massive, given that the distance it needs to have a mass so great to cause the center of mass to be outside the star. I also noticed that the star is not moving at a constant speed in its orbit over those 12 years, therefor this planets orbit must have an eccentricity of 0. 05. The suns motion is more complex because more planets cause gravitational tugs. The doppler technique uses spectroscopy to measure changes in the stars velocities: can only detect velocities toward or away from us.