Yr 13 - Astrophysics & Cosmology (Cosmology)

Question 1

What is the unit for angles in astronomy? And how many In 1 degrees?

Answer 1

Arc seconds

• 3600 Arc seconds in 1degree
• 60 Arc minutes in 1 degree

Question 2

Parsec

Answer 2

Distance from SOL to astronomical object which has angle of 1 arc second between SOL and Earth (Parallax angle)

Question 3

Tan(P) = 1/d

What can we assume and use?

What are the limitations for the small angle approximation?

Answer 3

Small angle approximation

P = 1/d

P (Parallax angle)
1 = Astronomical unit
d (distance in Parsecs)

Limitations - Distance Must be < 100 Parsecs

Question 4

What is Stella parallax

• And what happens to stars that are close?

Answer 4

Difference due to change in position of earth

• Close stars change apparent position as earth orbits whereas further (background) stars don’t.

Question 5

Parallax angle

Answer 5

Angle of apparent shift when a close star is observed from 2 different positions against background stars.

Question 6

What is the cosmological principle?

Answer 6

Universe is Isotropic & Homogenous & laws of physics apply everywhere (on a large scale)

Question 7

What are absorption Klines?

Answer 7

Lines missing on absorption spectra due to certain elements in stars atmosphere absorbing certain wavelengths of em radiation.

Question 8

Label each end of the colour spectra in terms of wavelength length and frequency

Answer 8

R - Long λ - Low F
O
Y
G
B
I
V - Short λ - High F

Question 9

Explain the doppler effect in terms of wavelengths

Answer 9

Object is moving forward you - Shorter wavelengths - Higher frequency

Object moving away from you - Longer wavelengths - lower frequency

Question 10

What is red shift?

Answer 10

When the wavelength is shifted towards the red section of the spectrum
- Longer wavelengths
- Occurs when object moving away (recessional velocity)

Question 11

What is Blue Shift?

Answer 11

When the wavelength is shifted towards the blue section of the spectrum
- Shorter wavelengths
- Occurs when the object is moving towards

Question 12

The equation that is given is

△λ/λ = △f/f = v/c

What is the other equation using the observed wavelength and true wavelength

Answer 12

△λ = λobs - λ
△f = fobs - f

λ/fobs = λ/f when there is relative motion (Observed wavelength) From earth!

λ/f = λ/f with no relative motion (Source wavelength) As perceived from source!

λ/f is λ or f not λ divide f

Question 13

Using the equation △λ = λobs - λ

• When is the object moving away?
• When is the object moving toward?

Answer 13

• When (+) observer and source moving apart
• When (-) observer and source moving together

Question 14

What is meant by ‘doppler shifted wavelength’ or ‘doppler shifter frequency’?

Answer 14

△λ or △f