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Astronomy 101
If you are new to astronomy, start here. No advanced mathematics—just the foundational ideas behind the study of space.
What is astronomy?
Astronomy is the study of everything beyond Earth: stars, planets, moons, galaxies, and the universe as a whole. It's one of the oldest sciences - people have been looking up and keeping records of the sky for thousands of years. The remarkable thing is that you don't need a billion-dollar telescope to start. You can begin with your eyes, a dark backyard, and curiosity.
Astronomy is a bit different from most sciences because we usually can't touch the things we study or do experiments on them. Instead, astronomers are like detectives: they collect light from distant objects and work out what's happening from clues hidden in that light.
Why do we study space?
To understand where we came from
The atoms in your body were made inside stars. Studying space is partly studying our own origins.
To answer big questions
How did the universe begin? Are we alone? These are some of the biggest questions humans have ever asked.
To protect Earth
Tracking asteroids, understanding the Sun's weather, and learning how planets work all help us look after our own planet.
To invent new things
Technology built for space - from cameras to medical scanners - ends up improving life back on Earth.
The scale of the universe
This is the part that's almost impossible to picture. Distances in space are so huge that kilometres become useless, so astronomers use the light-year - the distance light travels in one year (about 9.5 trillion km). Light is the fastest thing there is, so a light-year is enormous.
| From... | Light travel time to Earth |
|---|---|
| The Moon | about 1.3 seconds |
| The Sun | about 8 minutes |
| The nearest star (Proxima Centauri) | about 4.2 years |
| The centre of our galaxy | about 26,000 years |
| The Andromeda galaxy | about 2.5 million years |
How astronomers measure distance
A common question in astronomy is: how do scientists know how far away a star is? Several methods apply. The simplest is parallax: hold your thumb up and close one eye, then the other—your thumb seems to jump against the background. Astronomers use the same principle with nearby stars as Earth moves around the Sun; the tiny shift reveals the distance. For more distant objects, they use special stars and exploding stars whose true brightness is known, then compare that to how bright the object appears.
Famous discoveries
Mapping the sky
Early astronomers across many cultures tracked the Sun, Moon and planets, and used the stars to navigate and keep calendars.
Galileo's telescope
Galileo pointed a telescope at the sky and found moons orbiting Jupiter - proof that not everything goes around Earth.
The universe is expanding
Edwin Hubble showed there are galaxies far beyond our own, and that the universe is getting bigger.
The first pulsar
Jocelyn Bell Burnell spotted a strange, regular radio pulse - the first known neutron star spinning like a lighthouse.
Picturing a black hole
Astronomers released the first ever image of a black hole's shadow, using telescopes all over the world working together.