When scientists write about topics that may be unfamiliar to the reader, they often compare and contrast the new information with something more familiar.

On Earth, we sometimes sleep in sleeping bags—but they are always on the ground.

This photo and caption describe the familiar first.

In space, astronauts sleep in sleeping bags, too. The sleeping bags have to be … attached to the wall so they don’t fly away!

The second photo and caption contrast a familiar use with a less familiar one.

As you read, make connections to other texts you have read about the topic.