A protostar is an accumulation of gases in outer space that will become a star.

An alpha particle is really a high-energy electron ejected from the nucleus.

Water containing large amounts of Mg2+ and Ca2+ ions is said to be hard because it is hard to make soap lather in the water.

The water that evaporates from lakes and streams is fresh, whereas water evaporating from the oceans is salty.

Hot, molten rock, welling up from the earth’s interior, spreads the ocean floor, causing the continents to drift apart.

During which phase of the moon would we most likely see a solar eclipse?

A person traveling westward across the International Date Line gains a day.

Water solutions of ionic substances that conduct electricity are called

The temperature of the atmosphere decreases steadily with increasing altitude.

The spreading of the sea floor along the Mid-Atlantic ridge is supported by