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.
- How do we measure distance?
Knowing the distance to objects in space is important. However, measuring it is also very hard—you can't just use a ruler! Astronomers have created a range of ways to measure the distance to objects in space.
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.
(1) Luminosity
This is a more physical measurement. It measures the energy output of the object. This is done by looking at how much light is given out by the object over time.
The units of luminosity are more standard, given in Watts - much like a light bulb! A typical LED light bulb in a house might be 20 Watts - the Sun is 20 million billion billion (2 x 1025) times brighter!
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.
We often use measurements called arcminutes and arcseconds. The way we define each of these measurements is:
- there are 360 degrees in a circle.
- an arcminute is 1/60th of a degree.
- an arcsecond is 1/60th of an arcminute.
So that means there are 1,296,000 arcseconds in a circle (360 degrees × 60 arcminutes × 60 arcseconds).