9 beautiful edge-on galaxies, and why they're important

What are edge-on galaxies, and why are they important?

Ask a room full of astronomers how many galaxies there are in the observable Universe, and you’re likely to get a wide range of estimates: from as few as 200 billion (200,000 million) to as many as two trillion (two million million).

Either way, there are a lot… so it’s no surprise that there are a lot of different kinds of galaxy.

There are elliptical, spiral and irregular galaxies – the three main categories – as well as more exotic varieties such as lenticular galaxies, peculiar galaxies, radio galaxies, ring galaxies, shell galaxies and so on.

Edge-on galaxy UGC 11537 HUBBLE SPACE TELESCOPE, 15 November 2021 Image credit: ESA/Hubble & NASA, A. Seth — Edge-on galaxies like UGC 11537 can't be seen in their entirety from Earth. Credit: ESA/Hubble & NASA, A. Seth

Edge-on galaxies explained

Edge-on galaxies, on the other hand, are slightly different. The terms above all describe the morphology (shape) of a galaxy, whereas ‘edge-on’ merely describes the angle at which it is seen from Earth.

Elliptical galaxies generally appear as a round-ish blob, whatever angle you’re looking at them from. Spiral and lenticular galaxies, on the other hand, can be either ‘face-on’ or ‘edge-on’.

Put very simply, if it looks like a whirlpool, it’s a face-on spiral galaxy (for example, the Whirlpool Galaxy, one of the most famous of all).

While if it’s vaguely cigar-shaped, it’s an edge-on spiral (or possibly lenticular) galaxy.

So far, so straightforward – and to make matters even easier, there’s another clue in the name of some of the best-known edge-on galaxies, such as the Cigar Galaxy, the Needle Galaxy and the Hockey Stick Galaxy.

We won’t insult your intelligence by pointing out that cigars, needles and hockey sticks are all long, thin objects – which is exactly how edge-on galaxies appear on the night sky when viewed from Earth.

The difference perspective can make! Galaxy NGC 4302 appears edge-on while galaxy NGC 4298 appears face-on, from our perspective on Earth. Both galaxies are 55 million lightyears away. Credit: ESA/NASA Hubble

The science of edge-on galaxies

As for these galaxies’ scientific significance – that’s nice and easy, too.

Viewing galaxies edge-on, as opposed to face-on, can reveal much more about their three-dimensional structure, and hence give us clues as to the mechanics of their formation.

For instance, were all galaxies neatly arranged at right-angles to the Earth, so we saw them squarely face-on, it may have taken us a longer to work out that spiral galaxies have a central ‘bulge’, a thickening of the galactic disc in its centre.

A good example of this is the UFO Galaxy, an edge-on spiral that bears a remarkable similarity to the classic, cartoon-y idea of a ‘flying saucer’.

But that’s just one well-known example here are some more edge-on galaxies, and we've included the Right Ascension and Declination coordinates to help you find them yourself in the night sky.

For another observing challenge try and spot each of our lesser known galaxies you may not have seen before.