Yr 13 - Astrophysics & Cosmology (Cosmology) Flashcards

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1
Q

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

A

Arc seconds

  • 3600 Arc seconds in 1degree
  • 60 Arc minutes in 1 degree
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2
Q

Parsec

A

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

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3
Q

Tan(P) = 1/d

What can we assume and use?

What are the limitations for the small angle approximation?

A

Small angle approximation

P = 1/d

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

Limitations - Distance Must be < 100 Parsecs

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4
Q

What is Stella parallax

  • And what happens to stars that are close?
A

Difference due to change in position of earth

  • Close stars change apparent position as earth orbits whereas further (background) stars don’t.
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5
Q

Parallax angle

A

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

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6
Q

What is the cosmological principle?

A

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

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7
Q

What are absorption Klines?

A

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

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8
Q

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

A

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

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9
Q

Explain the doppler effect in terms of wavelengths

A

Object is moving forward you - Shorter wavelengths - Higher frequency

Object moving away from you - Longer wavelengths - lower frequency

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10
Q

What is red shift?

A

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

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11
Q

What is Blue Shift?

A

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

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12
Q

The equation that is given is

△λ/λ = △f/f = v/c

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

A

△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

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13
Q

Using the equation △λ = λobs - λ

  • When is the object moving away?
  • When is the object moving toward?
A
  • When (+) observer and source moving apart
  • When (-) observer and source moving together
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14
Q

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

A

△λ or △f

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