Lecture 3 - Nature of Light

Question 1

Earth is the ____ planet from the sun

Answer 1

Earth is the 3rd planet from the sun

Question 2

describe the galaxy of Earth

Answer 2

Earth is in the spiral arm of the Milky Way, which is in the Local Group, which is in the Local Supercluster

Question 3

what is the shape of the Milky Way

Answer 3

disk

Question 4

approx how many stars are in the milky way?

Answer 4

> 100 billion

Question 5

where is our solar system in the milky way disk?

Answer 5

a bit over halfway from the center

Question 6

describe the composition of the galaxy

Answer 6

5% stars and planets
the rest is gas and 90% dark matter

Question 7

1. what is dark matter
2. what does dark matter look like, why?

Answer 7

1. particles that don’t produce light and don’t interact with anything else
2. looks like a spherical ball –> not disk shaped bc it doesn’t interact with anything and is collapsed with gravity

Question 8

where is most of the mass of a galaxy located?

Answer 8

outside the visible disk in a galactic halo

Question 9

what is a star? what is a binary star?

Answer 9

star = large, glowing ball of gas that generates heat and light thru nuclear fusion

binary star = 2 stars that orbit each other

Question 10

what is a black hole? where is it located?

Answer 10

black hole = star that has collapsed on itself and gotten so small that a huge gravitational force pulls into it, so any light that enters is turned around –> irreversible
**its curvature changed with gravity

located at the center of every large galaxy

Question 11

1. what is a planet?
2. how do planets shine? how do planets glow?
3. what types of material can planets be made of?

Answer 11

1. large object orbiting a star
2. shines by reflected light, glows in radio waves
3. can be rocky, icy, or gaseous

Question 12

what makes mars red?

Answer 12

depends on whether you are looking at reflective light from inside or outside the atmosphere

Question 13

what is a moon/satellite?

Answer 13

object that orbits a planet

Question 14

what is a moonmoon? are there any known moonmoons?

Answer 14

moon that orbits another moon

no known moonmoons

Question 15

what is an asteroid?

Answer 15

small, ROCKY object that orbits a star

Question 16

what is a comet?

Answer 16

small, ICY object that orbits a star

Question 17

what is a nebula? when do they light up?

Answer 17

interstellar cloud of gas and/or dust btwn stars

light up when ionized

Question 18

what is a galaxy?

Answer 18

island of stars in space held together by gravity and orbiting a common center

Question 19

when we look at space, what are we also looking at?

Answer 19

looking at space = looking back in time

further away we look in distance = further away we look back in time

Question 20

what does it mean when we see the Andromeda Galaxy 2.5 million ly away?

Answer 20

we are looking at the galaxy as it looked 2.5 million years ago and in 2.5 million years we can see what it looks like right now

can never see the galaxy go thru its evolution, just see what it was before