1what is the relative size and composition of the universe, a galaxy, and a solar system

2. how can light speed be used to calculate distances between objects in space

3. when is it useful to use astronomical units and light years for measuring distance in space

The solar system is smaller than a galaxy. Galaxies are composed of solar systems. The solar system is composed of planets revolving around a star (such as our sun). To put into perspective, there are about hundreds of billions of stars in our galaxy (the milky way). On the other hand, billions of galaxies make up the universe.

The speed of light is constant which is 299 792 458 m / s. The time is taken for light to reach an object can be used to measure the distance between objects in space. This is done by multiplying the time by the speed of light.

Distance in space is so vast and therefore impractical to use the basic SI units of meters and kilometers we use here on earth. Therefore the use of astronomical units and light years is used. Light years is the distance that light can cover in a year in the vacuum of space, while astronomical units is the distance between solar systems.