Speed of star moving away from the Sun???

Question

At an astronomical conference, an astronomer gives a report on a star which has recently begun to interest astronomers because of hints that it might have a planet around it. In his report the astronomer gives the speed with which this star is moving away from the Sun. How did the astronomer measure this speed?

A.by looking at the Doppler shift in the lines of the star's spectrum
B. there is no way to measure the speed with which stars move away or toward us
C.by seeing how the luminosity of the star has been decreasing as it moves farther and farther away
D.by seeing the star become much redder than it used to be
E.by measuring the diameter of the star (which is easy to do) and noticing that it is getting smaller and smaller

Answer 1

A, The Doppler shift is a very sensitive way to measure speed toward or away from us.

Answer 2

Three techniques have been used to detect the existence of exo-solar planets.

The speed of a star can be accurately measured by spectroscopy and through the Dopplar shift.
Quantum physics tells us that certain chemicals emit (and absorb) electromagnetic radiation along very specific frequencies. One of the best for astronomy is the Lyman Hydrogen Alpha line (its wavelength of 121.6 nanometres, corresponding to a frequency of 2.47 × 1015 hertz) starts out as a reddish color.
We can measure the frequencies emitted by a star very accurately. By measuring the difference between the Lyman Hydrogen Alpha line and the star's line, we can determine how quickly a star is moving towards us or away from us. By taking measurements spaced over several years, we can take note of slight changes in that velocity. The exo-solar planets found first had very small orbits, and created a rapid shift in velocity.

But, that's not the only way we've found planets. We can also take very accurate position fixes on a star, and compare them over long periods of time. Yes, stars move relative to the Sun, and this movement has to be taken into account. But, even then, the star with a large planet around it will tend to wobble back and forth somewhat.

The last way we've used to find exo-solar planets is through the dimming of starlight, as a planet passes between the star and us.

Now that we know what we are looking for, we are discovering more exo-solar planets because we are taking more time. Initial planets were found using five years' worth of observations. Now, we've had over twenty years of similar observations, and are finding planets with more typical orbits (like Jupiter's).

The first thing to note about all these techniques is that they are very good at finding very large planets, and almost useless at finding small, Earth-like planets. Smaller planets just don't leave as big a hint of their existence as big, gas giant planets.

Answer 3

A. Doppler Shift

Answer 4

Doppler shift.

Answer 5

A. You'd have to watch the star for a hundred years to notice any change in apparent diameter or brightness.

Answer 6

Gotta love how those Physics teachers make up a long story to go with their question.

Answer 7

A

Answer 8

A.