In this topic you will learn about the tools astronomers use to study the universe.

The branch of science that deals with "what's up there" is astronomy. Astronomy is the study of the universe. The universe is everything that exists—Earth and all the things in space. The contents of space include the planets, stars, and galaxies.

An astronomer is someone who observes the universe and tries to explain what is observed. The universe is a huge place and has many different parts. Different astronomers study different parts of the universe.

One method to observe the universe is to use the eyes. This is good for such things as observing night and day, the position of the Sun and the Moon in the sky, and the location of the planets and stars.

Another method of observing objects such as the Moon is to send a robot or a human there. Both robots and humans have traveled to the Moon. Only robots have been on or near the other planets.

A third method of observing the universe is to use a telescope. A telescope is a device that collects light and makes distant objects appear closer and larger. Most of our knowledge of the stars and the planets comes through using telescopes.

We have learned much about the universe from the study of light. Light is also called electromagnetic radiation, or electromagnetic waves, because light is related to electricity and magnetism. It will help you understand light if you think of light as a wave. One property of waves is called refraction. Refraction means the bending of waves as they go from one substance to another. Another property of light is reflection. Reflection is the bouncing of waves off a surface. A wave carries energy from one place to another. As a wave travels, the distance from one peak to the next is called wavelength. The number of waves that pass through a point in a second is called the wave's frequency.

Light not only means light we can see. It also means radio waves, infrared waves, X rays, and gamma rays. These waves vary in wavelength. Waves of light arranged in order, by wavelength, are referred to as the electromagnetic spectrum.