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|blueshift ||doppler effect ||proper motion
|radial velocity ||redshift ||spectroscopy
- redshift: > 0. Object moving
away from you.
- blueshift: < 0. Object moving
- Radial velocity = (/
rest) × c,
where is the doppler shift,
rest is the wavelength
you would see if the star was at rest. The rest wavelength is also the
wavelength of light emitted by the star. Larger doppler shift means greater
- Tangential velocity = k × (the star's distance) ×
(d/dt), where k
is a conversion factor and
(d/dt) is the angular velocity
or proper motion of the star.
- Total velocity =
Sqrt[(radial velocity)2 + (tangential velocity)2]
- How is spectroscopy used to find the composition of stars?
- How do scientists know that the laws of physics are the same everywhere in the
Galaxy and have been the same for billions of years?
- How does the amount of doppler shift in the
spectral lines depend on the relative speed? How does the direction of shift of
the spectral lines depend on the direction of motion?
- Given three stars moving with the same total speed of 40 kilometers/second but in
different directions: (A) moving away at an angle=45° from our line of
sight, (B) moving directly away from us, (C) moving perpendicular to our line
of sight, put the stars in order of increasing amount of shift you see in their
spectral lines (the smallest shift first).
- The H-alpha spectral line is at 656.3 nanometers. Star (A) has that line at
656.8 nanometers, star (B) has that line at 656.0 nanometers, star (C) has that line at
656.3 nanometers. Which star is moving the fastest (along the line of sight) and what is the
three stars' directions of motion?
- What must you first know about a star before you can convert its
angular velocity to a tangential velocity in kilometers/second?
- Two stars have proper motions of 0.5 arc seconds/year. Star (A) is 20 parsecs
away and star (B) is 30 parsecs away. Which one is moving faster in space?
- Two stars orbit about a common point in a plane that is oriented
our line of sight. What will you see happening to the spectral lines of each
star? If there is a change, will both stars' spectra be changing in the same
direction at the same time?
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last updated: 23 May 2001
Is this page a copy of Strobel's
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