Question 1

What makes a galaxy bright in this sense?

Accepted Answer

Nearness, mostly. All the galaxies at the top of this list are close by; a far more luminous one a hundred times further away drops out of sight entirely, because apparent brightness falls with the square of distance.

Question 2

Why is a galaxy's magnitude awkward?

Accepted Answer

Because it is spread out. A magnitude is the total light added up over the whole object, so a large faint galaxy and a small sharp one can share a figure while looking nothing alike through an eyepiece — surface brightness, not magnitude, decides what you can actually see.

Question 3

Does brightest mean the most luminous?

Accepted Answer

No. This ranks apparent magnitude — how bright the object looks from here — which mixes how much light it gives off with how far away it is. A modest star nearby outshines a monster across the galaxy, and the ranking says nothing about which is the greater object.

Question 4

Why do smaller numbers come first?

Accepted Answer

Because the magnitude scale runs backwards. It was built from the naked-eye classes of antiquity, where first magnitude was the brightest, and it kept that direction when it was made numerical — so the top of this list holds the lowest numbers, and the very brightest are negative.

Question 5

Why are some galaxies missing?

Accepted Answer

Because no magnitude is recorded for them here. Brightness is also not a single number for everything: a magnitude measured through one filter is not comparable with one measured through another, and every figure on this site says which band it belongs to.

Question 6

Which galaxies can be seen with the naked eye?

Accepted Answer

Andromeda and the Triangulum Galaxy from a dark northern site, and the two Magellanic Clouds from the south. Everything else needs at least binoculars, and most of this list needs a telescope.

Question 7

Why does a bright galaxy look like a grey smudge?

Accepted Answer

Because its light is spread over a large area and the eye has almost no colour response at low light levels. Photographs accumulate light over minutes or hours, which is a thing the eye cannot do at all.

Question 8

Are the brightest galaxies the biggest?

Accepted Answer

No. The ranking is dominated by distance, so it mixes small nearby dwarfs with large spirals a few million light years off. Ranking by luminosity or by mass gives a completely different list.

The brightest galaxies

COMMON QUESTIONS