Astrophysics

Question 1

What is the equation for red shift?

Answer 1

z = Δ λ / λ

Question 2

What is the equation for change in wavelength due to red shift?

Answer 2

Δ λ = λ_app - λ where λ_app is the apparent wavelength and λ is the actual wavelength.

Question 3

What is Doppler red shift?

Answer 3

Where the wavelength of light is stretched by the object moving away from the observer.

Question 4

What is cosmological red shift?

Answer 4

When the space between the object and the observer is stretched.

Question 5

What does chromatic aberration cause in a telescope?

Answer 5

When white light enters the telescope, the different wavelengths which compose white light each focus on a different point along the optical axis.

Question 6

What is the principal focus?

Answer 6

The point where the rays parallel to the principal axis converge.

Question 7

What is focal length?

Answer 7

The distance from the lens to the principal focus or focal plane.

Question 8

What is a refracting telescope?

Answer 8

One with two converging lenses; an objective lens and an eye lens.

Question 9

Where is the real image in a refracting telescope?

Answer 9

Between the objective lens and the eye lens. At the focal point.

Question 10

What is the equation for angular magnification?

Answer 10

M = θ_i / θ_o where M is angular magnification, θ_i is the angle subtended by the image and θ_o is the angle subtended by the object.

Question 11

What is the resolving power of a telescope?

Answer 11

How much detail you can see.

Question 12

State four problems with refracting telescopes.

Answer 12

Chromatic aberration can be caused by different colours refracting different amounts leading to a blurry image,
Bubbles and impurities in the glass absorb some light which means very faint objects aren’t seen and building large lenses of good enough quality to avoid this is expensive,
Large lenses are very heavy and can only be supported from their edges so their shape can become distorted,
For a large magnification, the objective lens needs to have a very long focal length which means they have to be very long which means they have to be housed in very large and expensive buildings.

Question 13

Give an example of a non-optical telescope.

Answer 13

Radio telescope.

Question 14

What is the role of the eye lens in a refracting telescope?

Answer 14

To act as a magnifying glass on the real image formed by the objective lens to form a magnified virtual image.

Question 15

What is the role of the objective lens in a refracting telescope?

Answer 15

To converge the rays from the object to form a real image.

Question 16

What do we have to assume in order to suggest that the rays from an object are parallel to a refracting telescope?

Answer 16

The object is at infinity.

Question 17

What is absolute magnitude?

Answer 17

The apparent magnitude which an object would be if it were 10 parsecs away from Earth.

Question 18

In the data sheet equations, what is M?

Answer 18

Absolute magnitude.

Question 19

When might you need to use absolute magnitude to measure the distance of a star from Earth?

Answer 19

When the distance is too big to measure using parallax.

Question 20

What is the angle of parallax of a star that is exactly one parsec away from Earth?

Answer 20

1 arcsecond = 1/3600 degrees

Question 21

What is the cosmological principle?

Answer 21

On a large scale the universe is homogenous (every part is the same as every other part) and isotropic (everything looks the same in every direction) so it doesn’t have a centre.

Question 22

Define the terms in Hubble’s law and give the units: v = Hd

Answer 22

v is recessional velocity in kms^-1, H is Hubble’s constant in kms^-1 Mpc^-1 and d is distance in Mpc.

Question 23

How can we work out the age of the universe?

Answer 23

t = 1/H

Question 24

What idea did Hubble have about how the universe began?

Answer 24

The hot big bang theory (HBB): The universe started off very hot and very dense and has been expanding ever since. The universe is accelerating outwards.

Question 25

What property of quasars first lead to their discovery?

Answer 25

They are a strong radio source.

Question 26

What are quasars?

Answer 26

An astronomical object of very high luminosity found in the centres of some galaxies and powered by gas spiralling at high velocity into an extremely large black hole.

Question 27

When is a real image formed?

Answer 27

When the distance between the object and the lens is larger than the focal length.

Question 28

When is a virtual image formed?

Answer 28

When the distance between the object and the lens is less than the focal length.

Question 29

When chromatic aberration occurs, which wavelength of light focuses closes to the lens along the principal axis?

Answer 29

Blue.

Question 30

What is the Hipparcos scale?

Answer 30

A scale of star brightness to the naked eye with 1 being the brightest and 6 being the dimmest.

Question 31

What is the radial velocity method in the detection of stars?

Answer 31

When there is a periodic doppler shift in light received from a star due to the star and another body having a common centre of mass.

Question 32

What is a standard candle?

Answer 32

An astronomical object with a known absolute magnitude and luminosity due to some characteristic quality possessed by the entire class of objects.

Question 33

What is another name for a standard candle?

Answer 33

Type 1a supernova

Question 34

What makes measuring the distance away from extremely distant objects such as quasars so difficult?

Answer 34

The universe is accelerating outwards due to the effect of dark energy and the inverse square law and Hubble’s law aren’t reliable over large distances.