When measuring radial velocity ($V_r$), what spectral phenomenon indicates a star is moving toward the observer?
Answer
A shift toward the blue end of the spectrum, known as blueshift
The radial velocity component relies fundamentally on the Doppler effect applied to light emitted by the star. If a light source, like a star, is moving directly toward an observer, the wavelengths of the emitted light are compressed due to this relative motion. This compression shifts the observed spectral lines to higher frequencies, corresponding to the blue end of the visible light spectrum, a phenomenon explicitly termed blueshift. Conversely, movement away causes stretching, leading to redshift. Astronomers utilize this precise shift, comparing the observed absorption line positions to their known laboratory wavelengths, to calculate the exact speed of approach.
Related Questions
What mathematical relationship connects the total space velocity (V) using the radial velocity ($V_r$) and tangential velocity ($V_t$)?When measuring radial velocity ($V_r$), what spectral phenomenon indicates a star is moving toward the observer?What essential measurement, expressed in angular units like arcseconds per year ($ ext{arcsec}/ ext{year}$), is required to define tangential velocity ($V_t$)?What is the standard reference frame used when quoting the measured velocity of a star relative to the Milky Way?If a star’s distance ($d$) estimate is incorrect by a factor of two, how does this error propagate into the calculated tangential velocity ($V_t$)?What observation, related to the Doppler effect, signifies that a star has a negative radial velocity ($V_r$)?What astrophysical insights can researchers gain by analyzing the velocity distributions of large groups of stars within the Milky Way?How do the random motion components typically compare between ancient, halo stars and younger stars concentrated in the galactic plane?What inherent advantage in precision does the measurement technique for radial velocity ($V_r$) offer over tangential velocity ($V_t$) determination?What study, foundational to astrophysics, involves determining the speed and direction of stars within the Milky Way?