Astronomers use to remotely identify the of an object by the unique pattern of lines in its spectrum.

spectroscopy, density

cratering, age

radiometric dating, age

spectroscopy, composition

Spectroscopy helps astronomers to determine the composition, temperature, density, and motion of an object.

Infrared spectroscopy helps to identify the atoms and molecules in the object.

The red shift or blue shift (Doppler Effect) in a spectral line tells how fast the object is receding from Earth or coming toward it.

The Doppler shift enables astronomers to discover extrasolar planets.

As a planet orbits its star, the star is alternately moving away from or toward us.

Astronomers can use the Doppler shifts to calculate the speed of the star and the mass of the planet that is tugging on it.

Explanation:

b - the respond is innate and varies over time.

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