1. 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.
2. Knowing the time it takes for light to travel between objects can help us determine distances in space.We can determine the distance to the sun using the time light takes to get to Earth. Just multiply the speed of light by the amount of time it takes light to get to Earth. That's 500 seconds. 186,282 miles per second x 500 seconds = 93,141,000 milesThe sun is about 93 million miles away from Earth. It will take our fastest space shuttle moving at a constant maximum speed about 108 days to travel this same distance.
3. Writing out the large numbers that result from using miles or kilometers for space distances can take more time. It is similar to when we use feet to measure things around the house and miles to measure larger distances outside. Scientists use the unit of measurement that is most convenient to what they are measuring.
Hope this helps!