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When the wavelength decreases, that's known as a "blue shift", becausethe color of any visible light shifts toward the blue end of the spectrum.That phenomenon is associated with a light source that's moving TOWARDthe observer.
wavelength shift
Both the absorption and the luminosity of a blackbody in equilibrium increase in magnitude with increasing temperature, and the spectral distribution of the luminosity increases in frequency (decreases in wavelength).
You think probable to the wavelength.
Green.
A spectral line that appears at a wavelength of 321 nm in the laboratory appears at a wavelength of 328 nm in the spectrum of a distant object. We say that the object's spectrum is red shifted.
A spectral line
Barium has an atomic spectra of lines, not only one line (with one wavelength); I reccomend to consult a catalog of spectral lines. See the link below.
It would change by shifting to the wavelength blue.
Use the Rydberg formula. A useful article about this is on Wikipedia. It is called "Hydrogen spectral series".
The spectral lines move towards one direction, or towards the other direction, depending on the relative speed.
Increasing wavelength is an indication of a Doppler shift caused by an object moving away from the viewer. Longer wavelengths (of the visible spectrum) are redder, shorter wavelengths are bluer. Objects moving away from you have a red shift, objects moving toward you have a blue shift.