PCS 181 Lecture Notes - Radial Velocity, Parsec, Vir Chakra

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Published on 13 Apr 2013
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PCS 181
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PCS 181
Friday, January-18-13
Radial Velocity Problem
The spectral line is λ = 656.2850nm in the lab (red line)
The same line (in the spectrum of regulus is λ = 656.2927nm)
Questions to ask: is regulus approaching or receding? What is its radial velocity?
The regulus is longer than in the lab and is red shifted (moving away)
P this Ha/α has a longer wave length in the spectrum (red shifted) and is moving away from us
Vr = C*( Δλ/ λlab) = (3*10^8m/s)*(656.2927nm 656.2850nm/656.2858nm)
= 3519.81m/s or 3500m/s or 3.5km/s
Doppler Effect
Using the Doppler Effect how can you tell that the sun rotates? (it rotates every 30 days)
Cover up half of the star + check spectrum-moving up to you
Cover other half of the star + check spectrum moving away
**moving toward and away at the same time = rotating
Unit 2: The Universe
Distance Units in Astronomy
Light year = 1ly: the distance travelled by light in a year
1ly=9.5*10^15m
Parsec = 1pc: 1pc = 3.26ly (1 Mega parsec = 1000000ly)
Astronomical Unit = 1AU: average distance between the sun and the earth
The Hubble Law
A galaxy is a large assemblage of stars which orbit a common centre and is all held together by
gravity
Some contain a few thousand and some contain a few trillion stars
Hubble and Humason determined the distances and radial velocities in faraway galaxies
The further away the galaxy is, the faster it’s travelling
Hubble Law: radial velocity of a galaxy is directly proportional to its distance
Hubble and Humason’s findings
They concluded that all galaxies are moving away from one another (that the universe is
expanding)
PCS 181
Page 2
All faraway galaxies are red shifted and are receding from us
The Andromeda galaxy is blue shifted and will collide with the Milky Way galaxy
Farther galaxies are receding faster

Document Summary

The spectral line is = 656. 2850nm in the lab (red line) The same line (in the spectrum of regulus is = 656. 2927nm) The regulus is longer than in the lab and is red shifted (moving away) P this ha/ has a longer wave length in the spectrum (red shifted) and is moving away from us. Vr = c*( / lab) = (3*10^8m/s)*(656. 2927nm 656. 2850nm/656. 2858nm) Using the doppler effect how can you tell that the sun rotates? (it rotates every 30 days) Cover up half of the star + check spectrum-moving up to you. Cover other half of the star + check spectrum moving away. **moving toward and away at the same time = rotating. Light year = 1ly: the distance travelled by light in a year. Parsec = 1pc: 1pc = 3. 26ly (1 mega parsec = 1000000ly) Astronomical unit = 1au: average distance between the sun and the earth.