Astronomers use Doppler shifts to calculate precisely how fast stars and other astronomical objects move toward or away from Earth. For example the spectral lines emitted by hydrogen gas in distant galaxies which is normally found at a wavelength of 21 centimeters on Earth, might be observed at 21.1 centimeters instead. What would this difference indicate to astronomers?

Doppler shifts in the spectrum indicate about the motion of celestial bodies. Doppler effect is the apparent change in wavelength or frequency when there is relative motion between the source and the observer. Red-shifted light indicates that celestial body is moving away and blue-shifted light indicates that it is moving closer.

When astronomers observe a wavelength of 21 cm to be shifted to 21.1 cm - it means the light is red-shifted because the apparent wavelength is longer. Thus, astronomers can conclude that from the difference in the wavelengths that the galaxy is moving away from the Earth.

adityaso adityaso · Answer 2 · 2020-01-29T08:13:37+01:00

The increase in the apparent wavelength of the hydrogen spectrum shows that the galaxy is moving away from the Earth.

Explanation:

The Doppler is defined as the increase or decrease in the wavelength of the light observed by the observer due to the relative motion between the source and the observer.

If the source and the observer are moving towards each other, there will be a decrease in the wavelength of the light coming from the source. This is termed as the Blue shift in the light whereas if the source and observer are moving away from each other, the apparent wavelength of the light from the source will be increased and it is termed as the Red Shift.

The wavelength for the hydrogen spectrum is found to be [tex]21\text{ cm}[/tex] on the Earth whereas the apparent wavelength for the spectrum observed from distant galaxy is [tex]21.1\text{ cm}[/tex].

Since there is a increase in the apparent wavelength of the spectrum, it is considered that there is red shift in the wavelength of the light.

Thus, The increase in the apparent wavelength of the hydrogen spectrum shows that the galaxy is moving away from the Earth.

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Answer Details:

Grade: High School

Subject: Physics

Chapter: Astronomy

Keywords:

astronomer, Doppler, blue shift, red shifty, source, observer, relative motion, towards, away, galaxies, hydrogen spectrum.