How Far Can You See?

Have you ever wondered just how far into space you can see on a clear night with your unaided eye?  The answer will likely surprise you.  The range of distances is truly amazing! But before turning to the night sky, we need to give a nod to the most important star in the heavens—our Daytime Star, the Sun!  (We orbit it at an average distance of 93,000,000 miles.)

The closest and brightest of all the objects in the night sky is, of course, our lovely Moon.  It orbits us at an average distance of 239,000 miles. Next come the five bright naked-eye planets.  Their distances vary greatly depending not only on their actual distances from the Sun but where they are in their orbits around it.  When we see them at their closest in the evening sky, they range from about 60,000,000 miles from Mercury to nearly 800,000,000 for Saturn from us.

As we turn from the Solar System to stellar and galactic and intergalactic space, note that the objects mentioned can all be found plotted on the Star and Planet Locator set for about 9 p.m. local time in January.   We begin with the stars themselves.  In what follows, keep in mind that a lightyear equals nearly 6,000,000,000,000 (trillion) miles!  The nearest star visible to the unaided eye is Sirius in Canis Major at 8.6 lightyears distant.  The farthest easily visible star in the winter sky is the blue supergiant sun Rigel in Orion at nearly 900 lightyears.  (The record-holder for most distant naked-eye star is Deneb in the summer constellation Cygnus at 2,600 lightyears!)

Going deeper into space is the glittering star cluster, the Pleiades.  You’ll find it above and to the west (right) of Orion in Taurus looking like a tiny dipper in the sky.  It is some 440 lightyears from us.  Looking at Orion itself, note the three obvious stars in a line that form its belt (which also just happens to point to the Pleiades).  Below the belt is the Orion Nebula, the brightest of these star-forming gas clouds to us at over 1300 lightyears.  It’s just visible to the unaided eye as a dim fuzzy-looking star.  Try using what’s called “averted vision” which means looking to one side of a faint object to increase it visibility (typically by a factor of two).  These wonders all lie within our own Milky Way galaxy (which, when you look at its soft glow, you’re seeing the combined light of hundreds of thousands of stars many thousands of lightyears away).

We now jump into really deep space to the realm of the other galaxies themselves.  Without question the most easily visible of them all is the famed Andromeda Galaxy in the constellation of Andromeda. It lies at a whopping 2,500,000 lightyears or nearly 15,000,000,000,000,000,000 miles!  Here again, use averted vision to get a good view.  Also important is that it be a dark clear moonless night away from bright lights.


— James Mullaney

Former assistant editor at Sky & Telescope magazine & author of 10 books on stargazing. His

latest, Celebrating the Universe!, is available from