As earth travels in its different constellations are visible at different times of the year.
a.
atmosphere
c.
galaxy
b.
orbit
d.
star cluster

orbit

Explanation:

Our sky is divided into 88 areas known as constellations. These constellations are identified by the brightest stars of these areas forming a recognizable pattern. As the Earth travels in its orbit around the Sun, different constellations are visible at different times of the year. This is because different part of the sky is visible as earth goes around the Sun.

Thus, As Earth travels in its orbit different constellations are visible at different times of the year.

the entire statement is true and correct.  

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