Lance Green, age 10, of , Kansas, for his question:

How big is our Universe?

Our Universe is also called the Galaxy, the Milky Way and. a spiral nebula. It is a vast pinwheel, made from billions of sparkling stars. The size of our huge home in the heavens cannot be measured in miles, or even in millions of miles. The unit used to measure it is the light year which is the distance light travels in one year. As light travels at about 186,000 miles a second a light year is equal to about six million million miles.

From side to side the great wheel of our Galaxy is about 100,000 light years. The wheel is thicker in the center and thinner towards the edges. The thickness at the hub is about 10,000 light years. Our sun and its planets are but a tiny speck in this huge universe. Our big home in the heavens is but one of many millions of galaxies, separated from each other by vast oceans of space.