A nebula is a cloud of gas and dust in space. Some nebulas are regions where new stars are being formed, while others are the remains of dead or dying stars. Nebulas come in many different shapes and sizes. There are four main types of nebulas.

Interactive exercise. Assistance may be required. Click on the pictures below to learn more about each type of nebula.

Galaxies are large groupings of stars, dust, and gas in space. Galaxies come in a variety of sizes and shapes. The largest galaxies contain more than a trillion stars, while the smaller ones only have a few million. There are hundreds of billions of galaxies in the universe. There are three types of galaxies.

Interactive exercise. Assistance may be required. Click on the pictures below to learn more about each type of galaxy.