Which unit is not commonly used in Astronomy?

In the field of astronomy, the measurement of distances is crucial, and various units are utilized to describe these vast expanses. Kilometers, light years, and astronomical units are all commonly employed for measuring distances between celestial objects.

Kilometers are used for relatively shorter distances, such as the distance from Earth to the Moon or within our solar system. Light years represent the distance that light travels in one year, a necessary measure when discussing distances to stars and galaxies. Astronomical units provide a useful measure for distances within our solar system, with one astronomical unit being the average distance from the Earth to the Sun.

In contrast, pounds are a unit of weight that have little relevance to astronomy. While weight can be discussed in terms of force, the vast majority of astronomical measurements focus on distance, mass, and energy rather than weight. Therefore, pounds are not a common unit in astronomical contexts, making it the choice that does not belong among the other distance measurements.