Physics For Astronomy

Arinto Yudi Ponco Wardoyo

Standard system SI – Standard International◦Agreed in 1960 by International Committee

cgs – Gaussian System US System

Length [ L] Mass [M} Time [T]

Units◦SI : meter◦ cgs : centimeter (cm)◦US Customary : foot (ft)

Defined in terms of a meter – the distance traveled by light in a vacuum during 1/ 299,792, 458 of a second

Gravitation constant G=6,67x10-11 Nm2kg-2

Sun mass = 1,989 x1030 kg Sun radius = 700 000 km Sun constant : Sun energy on the earth = 1380 w/m2

Sun luminosity = Lo= 3,86x1026J/s Fsun bolometrict =6,28x107 Js-1m-2

Stefan Boltzmann constant, σ=5,67x10-8 Js-1m-2K-4

Earth mass = 5,975x1024kg Earth radius = 6378 km Gravity constant g=9,8 m/s2

Moon mass = 7,343x1023kg Moon Radius = 1738 km 1 astronomical unit = 1,496x1011 m 1 parsec = 3,26x106 light year Light velocity C = 3x105 km/s

IMPORTANT TO UNDERSTAND BASIC PHYSICS◦ Kepler’s Laws ◦ Newton’s Laws (inertia, F=ma, equal and opposite reactions)◦ Gravity, Newton’s Universal Law of Gravitation◦ Surface Gravity◦ Circular motion and orbits◦ Centripetal Force◦ How to get masses from orbital speeds◦ Escape Velocity◦ Conservation of energy, kinetic energy, potential energy◦ Conservation of angular momentum

Angular Size

I drop a 10kg mass and a 5kg mass from 4 feet off of ground.When to they hit?

a. same timeb. 10 kg mass hits firstb. 5 kg mass hits first

WHY? Hint: What is difference between mass and weight? Does acceleration due to gravity depend on mass?

Vcirc GM

d

2

3

YR

AUBA P

aMM

How do you calculate the mass of a star if you can measure the orbital velocity of a planet orbiting around it?

What happens if the string breaks? (INERTIA!)

From Newton’s laws of motion and gravity, we can calculate the velocity necessary for an object to have in order to escape from a planet, called the escape velocity

Vesc 2GM

R