Astronomy Quiz 2

Question 1

Why is Newton’s equation incorrect?

Answer 1

According to Newton’s equation photons have no mass

1. if photons have no mass, then the photons shouldn’t be affected by gravity, but due to gravitational lensing we know photons are affected by gravity
2. it doesn’t consider time

Question 2

Explain Equivalence Principle

Answer 2

• Imagine an astronaut is orbiting a planet
• the astronaut is weightless (not feeling the effects of gravity
• as the astronaut orbits the velocity is perfect due to the curvature of space time
• 0 g’s gravity) = no acceleration
• astronaut is going in a straight line
• no acceleration = constant velocity
• constant velocity thru space and time means you’re going in a straight line
• astronaut -> 0 g’s -> no acceleration -> constant velocity -> straight line

Question 3

Mercury’s precession

Answer 3

• axis is rotated
• elliptical orbit
• sun is not center of it’s orbit
• space time is curved around a massive body
• Einstein: curvature of space time were different further from the sun and closer to the sun
• Mercury speeds up closer to the sun b/c space time curvature is stronger closer to a massive body
• is curvature is more, spacetime is scrunched up a bit
• Mercury overshoots b/c of higher velocity due to curvature

Question 4

How did Einstein use the orbit of Mercury to determine that space time was curved?

Question 5

How did Einstein use a solar eclipse to see spacetime is curved

Question 6

Describe Einsteins idea for a gravitational wave

Answer 6

• space time is curved
• curvature increases around massive body
• the closer you are to the massive body the closer you are to the waves
• if spacetime is curved and if any mass has motion it will generate a distortion of spacetime

Question 7

Escape Velocity

Answer 7

• if an object has more mass it has more escape velocity (Vesc)
• easier to throw rocks off of the Moon b/c it has less mass than the Earth
• speed of light (C) is finite
• if mass is big enough then the Vesc = C and light cannot escape

Question 8

Einstein General Relativity Equation

Question 9

Rs = 3k (Mbh/Mo)

Answer 9

Rs: Radius Schwarzschild
Mbh: mass black hole
Mo: mass sun

Question 10

If you put a blackhole that fit the UT stadium how big would it be?

Answer 10

• Radius of the UT stadium: 100 meters

Question 11

What is the size of the blackhole in the Milkyway?