Essay Topics: Virtual Particles, String Theory.
*Know the Hydrogen spectrum for Test # 1.
The Doppler Effect in Astronomy:
Star = Light Waves… take spectrum.
If the entire pattern of spectral lines is:
Shifted to the blue end of the spectrum (blue – shifted) =
Shorter distance between wave crests =
Object is moving toward you.
If the pattern is:
Shifted to the red end of the spectrum (red – shifted) =
Greater distance between wave crests =
Object is moving away from you.
Direction of Motion:
Take the Spectrum of a stationary (= NOT Moving) Source (e.g., hydrogen) in the
Take the Spectrum of a moving object (e.g., a Star).
Compare the two spectra’s.
Hydrogen Spectrum in Lab compared to Stellar Spectrum.
Two Blues, One Green, One Red = Know this Laboratory Spectrum.
Purple, Second Blue Line
Two Blues = Hydrogen Delta, Second Blue Line = 434 nm = Hydrogen Gamma, One
Green = Hydrogen Beta, One Red = Hydrogen Alpha.
*Test Question: Is the star moving toward you or away from you.
Doppler Effect to Determine Velocity:
Let C = Speed of Light = 3 x 10 m/s.
Triangle Delta = Wave length difference between lab and stellar (STAR) Spectra.
Delta = Wave length on lab Spectrum.
V =rRadial Velocity of Star.
V =rC Triangle Delta
Velocity of Star,
V =r(3 x 10 m/s) = (434.1 – 434) nm
V = r.91 x 10 m/s = Divide by 1000 to get in 1000’s. To get meters divide by 1000.
V = r9.1 Km/s
Radial Velocity Problem: = *TEST Question for Sure! = Different Numbers!
A Spectral line of hydrogen has a wavelength of 656.2850 nm in the lab. This same line
appears at 656.2927 nm in the Spectrum of Regulus. Is Regulus approaching or receding?
What is its radial velocity?
The same line has a longer wavelength in the Spectrum of Regulus, so it is red – shifted =
Moving away from us.
V = r Triangle Delta = (3 x 10 m/s) (656.2927 – 656.2850) nm =
Deltalab 656.2850 nm
V r ~ 3500 m/s =3.5 Km/s
*NOTE: Divide m/s by 1000 to get form in km/s.
Using the Doppler Effect discussed here, how can you tell that our sun rotates?
Distance Units in Astronomy:
Light - year = ly: Distance that light travels in one year.
1 light-year = 9.5 x 10 m
Parsec = pc: 1 pc (units in millions) = 3.26 light-year.
Astronomical Unit = AU = Average distance between the Earth and Sun.
*NOTE: Takes 8 mins for sun light to