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Astronomy/How to calculate Doppler Shift?

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Expert: - 3/31/2010


Question
Hi:

In hydrogen, the transition from level 2 to level1 has a rest wavelength of 121.6 nm. suppose you see this line at a wavelength of 120.5 nm in star A, at 121.2 nm in star B, at 121.9 nm in star C, and at 122.9 nm in star D. Which stars are moving away? Which stars are coming toward us? Which star is moving faster relative to us? No calculation

How can I find out which one is negative or positive without calculating?

Thanks,

Answer
Hi Anahita,
Like sound, the wavelength of light will lengthen if object is moving away, and shorten
when approaching the observer.  Since the laboratory standard is 121.6, then the longer
wavelength objects, C and D, are receding from the observer, and A and B are approaching.
And obviously, since 122.9 - 121.6 is the greater amount of wavelength difference, that object D
is moving the fastest of the given samples, relative to us.
If I'm interpreting it correctly.  (Not my specific field of astronomy).
Clear Skies,
Tom Whiting
Erie, PA USA

Astronomy

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Tom Whiting

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Astronomy has been my hobby/pasttime for over 50 years.  Currently own 3 telescopes, the largest of which is a 30 inch Newtonian truss Dob that is portable.I taught Astronomy/Meteorology at the University Level for 13 years before retiring in 1995. Being retired and home most of the time, I am able to answer all questions relatively quickly, unless it's a new moon weekend with good observing conditions.  No astrology questions please, or questions about alleged UFO picture identifications.

Experience

Experience: Astronomy has been my hobby and study for over 50 years. We currently now own a 30 inch portable telescope (Updated - Pennsylvania`s largest portable telescope). It can be seen on our website at:http://www.velocity.net/~bwhiting and also attend several regional starparties during the year, and have been on 5 total solar eclipse expeditions.

Organizations: President, Erie County Mobile Observers Group for over 15 years.

Publications: Wrote the "Over Erie Skies" newspaper article in our local newspaper for 11 years (1975-86).

Education: Masters Degree- Taught at the University level for 13 years. Retired 20 years -USAF Pilot - KC-135 with 180 combat missions;  Also Eagle Scout, Philmont staff 2 Yrs, Order of Arrow Lodge Chief, Ham Radio (inactive).

Awards: two discoveries: The mini-coathanger asterism in Ursa Minor (the little dipper) And the mini-ladle- another asterism in the bowl of Ursa Minor. Clients: Currently President of the ECMOG as mentioned above.

Education/Credentials
BS  Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PA Also retired USAF pilot, 20 years.

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