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Astronomy

Distance

Measuring distances in astronomy is difficult but crucial. We need to know how far away objects are to look at the differences between them. Two objects can look different but be very similar, with one further away than the other. This can make them challenging to study.

An image of the night sky showing the constellation Orion, with the Orion Belt stars circled in blue for emphasis
This work by Mouser is licensed under GNU General Public License v2.0 or later
Orion's belt

Brightness

Light is the main signal we receive from space. Almost everything we know about space has been found by measuring light.

One of the main ways to measure light is to look at the brightness. Measuring the brightness of something in space isn't as easy as you'd think though. 

A dense star cluster filled with thousands of bright stars, some shining with a blueish hue, while others emit a warmer orange glow, set against the blackness of space.
This work by ESA/Hubble & NASA is licensed under Creative Commons Zero v1.0 Universal
The star cluster NGC6496

Angles

Astronomers use angles a lot to work out where things are in the sky. We can measure the size of an object in the sky and mark its position by using angles.

If we know how much of the sky an object covers (as an angle) and how far away it is - we can work out its actual size.

An image of a coastline with a large coin magnified over a distant cathedral, demonstrating perspective or scale
This work by The Schools' Observatory is licensed under All rights reserved
An arcsecond is a very small angle