What is Magnitude in Astronomy? Definition, Examples

Magnitude (in astronomy, stargazing, and astrophotography) is simply a measure of the brightness of an astronomical (celestial) object (e.g. a star like Betelgeuse or a galaxy like Andromeda galaxy).

Why it’s so important for an amateur (professional too) astronomer, stargazer and astrophotographer? It’s very simple – the brighter the object, the easier to spot, gaze, and photograph!

Magnitude Types

There are two types of magnitude in astronomy: apparent and absolute. In our hobby, we mostly use the apparent one – the brightness as it appears to our eyes on the night sky, not the absolute “quantity”/”amount” of light that a certain celestial object “produces” objectively.

How is Calculated

There are two facts about the magnitude that may be counterintuitive for a newcomer to the hobby:

1. It is “reversed” – the smaller the number, the brighter the celestial object appears on the night sky.
2. It can be negative.

Look at the table below.

Magnitude Examples on Different Astronomical Objects

Here I curated few interesting astrophotography and stargazing objects in order of their magnitude. Sorted from the brightest to the dimmest (non-visible).

Practical Tips

It’s important to remember that there is one more important factor in stargazing and astrophotography than magnitude itself – the clear, dark sky. It can be hard to spot even bright objects like Pleiades or Orion Nebula on a highly light-polluted night sky in a city. If you live in a town area like me, then get into the car, drive some distance from the center, and enjoy astronomy as it should be – without (or with greatly reduced) artificial light. Use this fantastic map to find dark-sky spots in your area.