Astronomy Basics

Have you ever looked at the night sky and wondered about your place in the universe? This section will help you get oriented in the cosmic "big picture." Find out where we are and where we're headed. Learn about Earth and our solar system, plus some of the secrets astronomers have uncovered about the stars, galaxies and universe.

 
Naming the Stars

The word astronomy comes from two Greek words: "astron," which means "star," and "nemein," which means, "to name."

Our Place in Space

We live on a tiny blue planet, one of nine worlds that orbit an average-size star called the Sun. Our Sun and its family of planets exist within a vast group of stars called a galaxy.

Our galaxy is called the Milky Way, and it contains nearly 200 billion stars-that's about the same number as there are grains of sand on a beach.

That might sound like a lot, but it's only the beginning. The Milky Way is one of about 50 galaxies that form a loose cluster called the Local Group. Some of our neighbours in the Local Group are the Large and Small Magellanic Clouds, the Andromeda galaxy and the Triangulum galaxy. 

  
The Local Group belongs to a cluster of more than 2 500 galaxies, known as the Virgo Cluster. Altogether, these galaxies and galaxy groups form the Local Supercluster. And things still get bigger

The Big Picture

As far as astronomers can tell, the universe contains about 100 billion galaxies. These galaxies are grouped into clusters, which in turn are grouped into even bigger groups called superclusters.

Superclusters are arranged in long filaments that reach through space. These filaments are like tendrils of light that embrace large bubbles of empty space called galactic voids. It's as if the universe were a vast, frothy sea, with galaxies forming the surface of the bubbles.


Smaller than a pinprick

At the other end of the scale, everything in the universe - people, planets, stars and galaxies - is made of atoms.

Atoms are unimaginably small-about 10,000 billion could fit in the dot at the end of this sentence.

An atom is a tiny nucleus surrounded by clouds of negatively charged electrons. The nucleus, in turn, consists of even smaller protons and neutrons. Neutrons, like their name implies, are electrically neutral, while protons carry a positive charge. Finally, the smallest particles that we've found are quarks, which are what protons and neutrons are made of.

The speed of light

Light moves through space at about 300 000 km per second.

If you flew to the Sun in a Boeing 747, it would take you 20 years to get there, but light travels the same distance in only eight minutes.

Light-years

Cosmic distances are so vast that astronomers measure them in light-years. A light-year is the distance a beam of light travels in a year-about 10 trillion kilometres. The closest star to us (apart from the Sun) is Proxima Centauri, which is 4.2 light-years away. Its light takes 4.2 years to reach the Earth.