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# PCS 181 Class 3.docx

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School
Ryerson University
Department
Physics
Course
PCS 181
Professor
Margaret Buckby
Semester
Winter

Description
PCS 181 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
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