Location, Location, Location...

NGC 752

I personally have spent many fruitless minutes (hours?) attempting to spot the inconceivably faint M33 from either Carrs Mill or Alpha Ridge, only to give up in frustration time and again. For every occasion on which I've successfully observed that most frustrating of objects through the eyepiece, there were at least a dozen failed attempts.

There are two reasons behind this sad ratio. The first, as I have already mentioned, is M33's unforgiving low surface magnitude. Although its apparent magnitude is listed as a whopping 5.72, which would normally make something an easy naked eye object, M33 is so close to our Milky Way that it spans an area of the sky more than 2 full moons across, thus diffusing all that brightness to the point of invisibility. (As J.R.R. Tolkien would say, "Like too little butter spread over too much bread.") So even moderate light pollution (such as we have in suburban Maryland) washes it out altogether.

The second reason why M33 is so difficult to locate is the lack of any signposts along the way for diehard starhoppers like myself. There are no recognizable asterisms to leapfrog from, no relatively bright stars from which to anchor one's search. It's just there, somewhere between the three naked eye stars that make up the Triangulum constellation, and the lower leg of Andromeda.

NGC 752

But there is something in M33's vicinity which is not at all difficult to find, and is extremely rewarding to observe - NGC 752, a beautiful open cluster just off to the left of the elusive galaxy. Why does this jewel of the heavens not get more attention? I believe it is a matter of its unfortunate proximity to both M33 and to its other close neighbor, M31 - probably the most observed galaxy in the entire sky. Sometimes location is a Good Thing, such as when your house is close to work, or convenient to grocery stores and coffee shops. But it can also be a curse, as when you're standing in the shadow of something far more famous and sought after. Who has the time (or motivation) to swing your field of view just a skosh to the side to take in yet another anonymous open cluster?

Well, let's do something about that anonymity, because NGC 752 is well deserving of your attention. First of all, it's both huge and bright. Despite its distance of 1,300 light years, it spans a nearly identical stretch of sky as M33 (about two full moons worth), and at magnitude 5.7 it's an easy naked eye object under dark skies. It is in fact often mistaken by binocular observers for M33 - they're that close!

But unlike the Triangulum Galaxy, which looks like a pathetic smudge of haze under even the most favorable of conditions, even a small amount of aperture will resolve NGC 752 into a spectacular splattering of about 60 stars of all conceivable colors and brightnesses.

NGC 752 is a very unusual open cluster. Instead of being the usual tens of millions (or at most a few hundred million) years old, NGC 752 clocks in at no less than 2 billion years old! This means that its various component stars have had time to experience all sorts of developmental changes. The cluster contains blue-white supergiants, red giants, middling stars like our own Sun, red dwarfs, and even a few white dwarfs - those aged stars which have already gone through all the usual stages of a star's life cycle.

But observe it while you can! The gravity of other stars in the Milky Way is gradually disrupting NGC 752 (thus accounting for its current huge size), and in another billion years or so, it will be only a memory.