13-Our Place in the Universe

Question 1

What is the current age scale for the universe?

Answer 1

13.8 billion years

Question 2

What is a light-year?

Answer 2

The distance light travels through space in a year

Question 3

What is the speed of light?

Answer 3

3 X 10^8 m/s

Question 4

What is the modern way in the universe to measure distances in the solar system?

Answer 4

Radar

Question 5

What does r.a.d.a.r stand for?

Answer 5

Radio detection and ranging

Question 6

How does radar work?

Answer 6

A signal is sent out and reflected from an object in the solar system and then detected on Earth

Question 7

How can you calculate the distance of an object from earth using radar?

Answer 7

The time there and back / 2 times the speed of light

Question 8

Why can’t we use radar for distant objects in the solar system?

Answer 8

The returing signal is far too weak to be detected

Question 9

What is lidar?

Answer 9

Light detection and ranging

Question 10

How do you measure the relative velocity of an asteroid?

Answer 10

Measure the distance using radar, then measure it again after 100s. Calculate the change in distance to find the relative velocity of the asteroid

Question 11

What are the main assumptions with radar?

Answer 11

• Speed of the signal is same both ways

- The moment of delay was half way through the time delay of the pulse as observed on earth

Question 12

Is the speed of light constant?

Answer 12

Yes

Question 13

What method do astronomers use to measure distance to nearby stars?

Answer 13

Parallax

Question 14

How does parallax work?

Answer 14

We measure the parallax angle to a nearby star at 2 six month intervals, and then we use small angle approximations to find the distance to the nearby

Question 15

What do atoms in a distant star absorb and emit?

Answer 15

Light at particular wavelengths

Question 16

What are the spectral lines of a star?

Answer 16

When atoms from a distant star absorb and emit light at particular wavelengths

Question 17

If a star is moving away, what happens to the wavelengths of its spectral lines?

Answer 17

The wavelengths of its sprectral lines increase

Question 18

Why do receding stars show red-shift?

Answer 18

Because their spectral lines are shifted towards the red end of the spectrum

Question 19

What is the doppler shift?

Answer 19

When the wavelengths of a distant stars spectral lines increase(redshift) as it is moving away from us

Question 20

What did the use of the doppler effect lead to?

Answer 20

The discovery that most stars are moving away from us, first hint of the expanding universe

Question 21

What does Hubble’s law state?

Answer 21

The further away a galaxy is, the faster it is receding from us

Question 22

With the red shift interpreted as a recession velocity, what is the equation of recession velocity?

Answer 22

Recession velocity = hubbles constant X distance r

Question 23

What is the Big Bang theory?

Answer 23

That the universe originated in a very hot, very dense state from which it has expanded and cooled

Question 24

What does the larger the value of Hubble’s Constant mean?

Answer 24

The larger the value of Hubble’s constant, the faster that universe must be expanding

Question 25

What does 1 parsec equal?

Answer 25

3.09 X 10^16

Question 26

What does red shift z =?

Answer 26

Change in wavelength / Wavelength

Question 27

What has space expanded by?

Answer 27

A factor of 1 + z

Question 28

When we observe object of a redishift z=10, what does this mean?

Answer 28

We are looking at a time when the universe was a tenth of its present size

Question 29

What does Hubble’s law present evidence of?

Answer 29

That the universe is expanding

Question 30

What is cosmic background radiation?

Answer 30

Microwave radiation that came from the hot beginnings of the universe

Question 31

How does cosmic background radiation provide evidence that the universe began in a hot, dense stae?

Answer 31

The microwaves have a wavelength of 1mm, as they were streched due to the heat

Question 32

What does Einstein’s second postulate state?

Answer 32

That the speed of light c is constant everywhere in the universe

Question 33

What do space-time diagrams represent?

Answer 33

Objects moving through space and time

Question 34

What is the equation of the relativistic factor y?

Answer 34

1 / root (1 -v squared / c squared)

Question 35

What is time dilation a consequence of?

Answer 35

The speed of light being constant for all observers

Question 36

What does the relativistic value mean?

Answer 36

The factor by which time, length and relativistic mass change

Question 37

What does y / t equal?

Answer 37

The wristwatch time