I think this riddle describes
Less is more and more is less, But let's go down the wondrous list -
Less meaning less star magnitude - the lower it is, the brighter they appear.
Ignoring the one, so high and near, And yet the lowest of all, I fear.
The Sun, our nearest star, is the lowest magnitude at -27 and we will ignore it below, especially as the Sun isn't visible in the night sky.
The dog's on top, then find your way, The nearest, and a giant far away.
The dog's on top: The brightest star in the Earth's night sky is the dog star aka Sirius with a magnitude of -1.5
Find your way: The next brightest star visible from Earth is Canopus, with a magnitude of -0.7
Canopus was a navigator in Greek mythology.
The nearest: Then the next brightest is Alpha Centauri (star system) which is the nearest star after the Sun with a magnitude of -0.3
A giant far away: Then Arcturus a red giant is −0.05
These are all above what's naught, And yet in truth they are below.
Star magnitudes - These are the only stars which have magnitudes below zero. The next in the magnitude list is Vega which is positive at +0.4
So many more, some more, some less: Shining beacons of hope, God bless.
Now you've read this tale bizarre, Don't you wonder what they are?
Twinkle, twinkle, little star, How I wonder what you are!
"Shining beacons of hope" - Babylon 5