Question

State three properties of any visible object in the universe that one can determine by spectroscopy

Answer 1

Answer:

1. Temperature.

2. Velocity.

3. Chemical composition.

Explanation:

1. Temperature.

The effective temperature can be known by means of the Wien's displacement law

$T = \frac{2.898x10^{-3} m. K}{\lambda max}$ (1)

Therefore,  ($\lambda_{max}$) is the maximum peak of emission in the continuum of the spectrum of the object (see the image below) and T is the temperature.

         

2. Velocity.

Spectral lines will be shifted to the blue part of the spectrum if the source of the observed light is moving toward the observer, or to the red part of the spectrum when is moving away from the observer (that is known as the Doppler effect).

Then, by using that shift in the spectral lines the velocity of the source can be determined.

$v = c\frac{\Delta \lambda}{\lambda_{0}}$  (2)

Where $\Delta \lambda$ is the wavelength shift, $\lambda_{0}$ is the wavelength at rest, v is the velocity of the source and c is the speed of light.  

3. Chemical composition.

The absorption lines and emission lines give information of the chemical composition of the source, since those lines are produced when a photon coming from the source is absorbed by an electron (of an atom in the same source) and goes to a higher state, then when the electron comes back to a lower state it will emit a photon with the same energy of the difference between the two states. If the photon does not follow the same direction of the incident photon an absorption line will be created in the spectrum of the source.