Why are many of the stars nearest to Earth not visible to the naked eye?

Question

Why are many of the stars nearest to Earth not visible to the naked eye?

Answer 1

not bright

Answer 2

Proxima Centauri was discovered in the 1900s, even though it's our closest star other than the Sun.  That's because it's really faint.  It's a red dwarf - an M Dwarf.  I haven't seen it.  That's partly because i live too far north, but mostly because i haven't brought a big enough scope on my southern migrations.

These M Dwarf stars can be 10,000 times fainter than the Sun.  And some of the Blue Supergiant stars can be 10,000 times brighter than the Sun.  So many of the stars you see in the sky are not very near us.  For example, Deneb is one of these really bright stars, but it's so far away that we do not have good parallax data for it, even though we've looked at it from space telescopes.  It's well over 1000 light years away.

The brightest star in the sky, Sirius is only slightly brighter than the Sun, and is very close by - only 8.6 light years away.  It's the exception, not the rule.

Answer 3

They aren't bright enough for their light to reach Earth.  Another interesting fact is that some of the stars we do see could be burnt out.  It could take their light a million years to reach earth.  By then, they could be dead.  So when we look up, we're looking at the past.

Answer 4

They are not bright enough.

A faint red dwarf like Barnard's Star just doesn't generate enough light to be seen from earth by the naked eye, even though it is "only" a few light years away.