Doppler Shift Spectrometer

Measure radial velocity from line shifts (Lecture 10)

Station Card (PDF)
Mission
If Δλ is negative, is the object approaching or receding?
Rest vs observed spectrum
vr
0
km/s
λ0
656.281
nm
λobs
656.281
nm
Δλ
0.000
nm
v from Δλ/λ0
0
km/s
Motion mode radial
Only radial (line-of-sight) motion shifts wavelengths.
Radial velocity 0 km/s
approaching receding
Line selection Hα
Rest spectrum is gray; observed spectrum is blue.
Instrument resolution (broadening) 0.20 nm
narrow wide
Check your sign —
Approaching or receding
Convention: Δλ = λobs − λ0. Δλ > 0 is redshift (receding).

Predict → Play → Explain

Predict the sign first, then use the slider. Use the readouts to justify your choice.