Answer:
<u>Geocentric Model</u>: - this model is Earth Centered
-Retrograde motion is explained by epicycles
<u>Heliocentric Model</u>: - This model is Sun Centered
-Retrograde motion is explained by the orbital speeds of planets
<u>Both models</u>:- Epicycles and deferents help explain planetary motion
-Planets move in circular orbits and with uniform motion
-The brightness of a planet increases when the planet is closest to Earth
Explanation:
Retrograde motion is an apparent change in the movement of the planet through the sky. Ptolemy's model of the solar systems was geocentric, where the Sun, Moon, planets and start all orbit the Earth in perfectly circular orbits. However this perfectly circular orbits around the Earth did not explain the occasional retrograde motion of the planets. In the Copernicus' heliocentric model, retrograde motion of planets is naturally explained. The explanation for retrograde motion in a heliocentric model is that retrograde occurs roughly when a faster moving planet catches up to and passes a slower moving planet.
The explanation for the differences in wavelength observed from earth and a distant star with a shift towards the red end of the spectrum is the Redshift- Doppler effect.
<h3>What is the Doppler effect?</h3>
The Doppler effect is the difference that occur between the frequency of a wave in relation to observer from the wave source.
The wavelength changes with change in the frequency.
<h3>How does the Doppler effect explain the redshift?</h3>
As an object moves away from Earth, the waves moves to the red end of the electromagnetic spectrum and becomes elongated. This results to the increase in wavelength.
Therefore, the explanation for the differences in wavelength observed from earth and a distant star with a shift towards the red end of the spectrum is the redshift-Doppler effect.
Read more on Doppler effect here:
brainly.com/question/4052291
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