Topic 10

Question 1

What is the Astronomical Unit

Answer 1

The astronomical unit is the mean distance between the Earth and the Sun.

1AU = 1.5 x 10^11 m

Question 2

What is the unit of a light year a measure of

Answer 2

Distance

Question 3

What is a light year

Answer 3

The distance through space that a light photon travels in the space of a year

1ly = 9,46 x 10^15 m

Question 4

What can parallax be used for

Answer 4

Parallax can be used to calculate distances in space, using observations and trigonometry

Question 5

What is a parsec

Answer 5

A parsec is an astronomical unit of distance. A star is one parsec (pc) away from the Earth if the parallax angle is 1 arcsecond

Question 6

What is a Hertzsprung-Russell diagram

Answer 6

A Hertzsprung-Russel diagram is a plot of a star’s stellar luminosity against its surface temperature

Question 7

What category of star is represented by the main diagonal on a HR diagram

Answer 7

The main sequence stars

Question 8

What category of stars lie below the main sequence diagonal on a HR diagram

Answer 8

White dwarfs

Question 9

What categories of stars lie above the main sequence diagonal on a HR diagram

Answer 9

Red giants and red supergiants

Question 10

State the equation linking the intensity, luminosity and distance of a star

Answer 10

I = L / (4πd^2)

Question 11

What is the doppler effect

Answer 11

The doppler effect is the apparent change of wavelength as result of relative movement between a receiver and source

Question 12

What happens to the observed wavelength of a wave source moving away from the observer

Answer 12

The observed wavelength will increase

Question 13

What happens to the observed wavelength of a wave source moving towards an observer

Answer 13

The observed wavelength will decrease

Question 14

What happens to the observed frequency of a wave source moving towards an observer

Answer 14

The observed frequency will increase

Question 15

What is red-shift

Answer 15

Red-shift is the apparent shift of the wavelength of light emitted by a star towards the red end of the light spectrum, as a result of it receding

Question 16

What equations are used to calculate red-shift

Answer 16

z = Δλ/λ = Δf/f = v/c

Question 17

Describe how the relative speed value inputted into the equation differs depending on whether the source and receiver are nearing or receding

Answer 17

If the source and receiver are approaching each other, the value should be negative, otherwise the value is positive

Question 18

What is the difference between a positive and negative ‘z’ value

Answer 18

A positive ‘z’ value represents red shift, whereas a negative value represents blue shift

Question 19

What are the two main conclusions that can be drawn from observations of red shift from distant galaxies

Answer 19

1. All galaxies show red shift and so all galaxies are moving away
2. The more distant a galaxy is, the greater its red shift and so the faster it is receding

Question 20

What does the red-shift of distant galaxies provide evidence for

Answer 20

Red-shift of distant galaxies suggests that they are moving away from us. This supports the concept that the universe is expaning, which supports the Big Bang theory

Question 21

What does CMBR stand for

Answer 21

Cosmic Mircowave Background Radiation

Question 22

What is cosmic microwave background radiation

Answer 22

Radiation in the microwave region of the EM spectrum that is present in very small quantities all around us

Question 23

How does the existance of CMBR support the Big Bang theory

Answer 23

In the big bang, lots of high energy radiation was produced. As the universe has expanded over time, the wavelength of this radiation has been ‘stretched’ so that it is now in the microwave region. Other theories of the universe can’t account for the existance of CMBR

Question 24

What is the Big Bang theory

Answer 24

The Big Bang thery is a theory for the formation of the universe. It proposes that the universe began from a very small, hot and dense region, and expanded from this point

Question 25

What two quantities does Hubble’s law relate

Answer 25

The distance of a galaxy to the speed at which it is moving away

Question 26

Express Hubble’s law in words

Answer 26

The speed at which a galaxy is moving away, is directly proportional to the distance it is at

Question 27

State the defining equation for Hubble’s law

Answer 27

v = Hod

Where Ho is Hubble’s constant

Question 28

Describe what was observed when observations of galaxies’ brightnesses were compared to the predictions made by Hubble’s law

Answer 28

• THe actual and predicted brightnesses of distant galaxies don’t always agree with each other
• Distant galaxies aren’t as bright as predicted by Hubble’s law, suggesting that they are more distant that predicted

Question 29

State the conculsion that can be made from Hubble’s law and observations

Answer 29

The rate of expansion of the universe is accelerating, since galaxies are further away than predicted

Question 30

Give one possible explanation for the acceleration of the universe’s expansion

Answer 30

The existence of dark energy. This would explain where the energy required for the expansion rate to cnstantly accelerate comes from

Question 31

Why is the existence of dark energy still only a hypothesis

Answer 31

Dark matter and energy can’t easily be observed