Principles of astronomy

Astronomy is the science that studies the celestial bodies: the planets, the stars, and everything else that is outside the Earth's atmosphere. Astronomers study the apparent motions of these objects in order to learn about their real movements, and study the type of light that is emitted by them in order to learn about their composition and internal behaviour.

Until very recently, astronomy has been based entirely on observations made of these celestial bodies with optical telescopes or with the naked eye. Mostly in the last century, astronomers began to use telescopes that measure light at different wavelengths. Observing different types of light, such as infrared or x-ray, provides us with a lot of new information.

Observing the Sky without Telescopes

Without the telescope, we would know little about the stars and planets. The unaided eye can detect the motion of the sun, the moon, and the planets. We can describe the arrangement of the stars. But without the telescope, we can learn little else.

Astronomers long ago noticed that the arrangement of most of the stars does not change from night to night. A few objects, however, appear to move through the constellations. Known as planets, or "wanderers," they included the sun and moon, which also move through the fixed stars.

In order to understand the motions of the planets and the stars, astronomers need to observe them very closely, and track their apparent movements from night to night. Doing this with the naked eye is difficult, as only a certain level of precision can be reached. Using a telescope allows astronomers to make much more accurate measurements of the motions of the celestial bodies.