Question

How can scientists determine whether a star or asteroid is moving toward earth

Answer 1

Using the Doppler shift effect

If the celestial body is in the blue shift, then its moving towards earth and if it's in the red-shift then it's moving away from earth.

Explanation:

Doppler shift effect is a phenomenon that occurs in waves due to relativity. When an object is relatively moving toward an observer, it tends to  ‘compress’ the waves into a higher frequency/ shorter wavelength.  Visible light will be observed in blue shift because blue light is of higher frequency than red. If the object is relatively moving away from the observer, it tends to ‘stretch’ the waves. Remember ALWAYS this is relative to the observer. hence giving them the perception of viewing the object in longer wavelength. The object is observed in red shift because red light it has a longer wavelength/lower frequency than blue light.

This phenomenon is not limited to light waves, but happens even in mechanical waves like sound. When a wailing  ambulance is approaching you, you hear it in high pitch. However, when it passes you and moves away from you, you hear it in low pitch.

Learn More:

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