AST 341 Lecture Notes - Lecture 1: Mks System Of Units, Solar Luminosity, Solar Radius

• School: Stony Brook University
• Department: Astronomy
• Course: AST 341
• Professor: Rosalba Perna

Document Summary

There are two systems of units that are in general use within the sciences, mks and. The mks system uses meters, kilograms and seconds, and tends to be favored by physi- cists. For unknown reasons, however, the cgs system (centimeters, grams, seconds) is heavily favored by astronomers and astrophysicists. Therefore this is the system that we will use in this course. Based on this system, other units are built, that are of convenient use especially in situations where one would otherwise have to use big numbers. The astronomical unit is de ned as the mean distance between the earth and the sun: In order to introduce this, let"s review the angle units. A circle has 360 degrees or 2 radians: 60 arcminute = 4. 85 10 6 radians radians = 0. 01765 radians degrees = 2. 9 10 4 radians. A parsec (pc) is de ned as the distance at which a ruler of length 1 au subtends an angle of 1 arcsecond.