One of the most fascinating aspects of the science of astronomy is the concept of distance. Everything in the night sky is so incredibly remote! Even the closest star to our solar system, the Alpha Centauri triple-star system, is 25 trillion miles away. The thousands of other stars that we see every clear night with the naked eye, as well as the millions of stars visible through telescopes and binoculars, are farther still!
Scattered among those distant suns are fascinating sights called deep-sky objects, a general catch-all phrase that includes a wide variety of celestial denizens. These include huge clouds of gas and dust called nebulas, which can be divided further into emission nebulas, reflection nebulas, and planetary nebulas. The first two are associated with stellar birth, while the latter are expanding shells expelled from dying stars. Star clusters form a second grouping of deep-sky objects. Open star clusters are made up of anywhere from a dozen to several hundred young, chiefly blue-white stars. Most of these stellar swarms lie within the spiral arms of our own galaxy, the Milky Way. Globular star clusters, made up of some of the oldest stars known, surround the hub of our pinwheel-shaped Milky Way. Each contains between 100,000 and a million constituents. Finally, beyond our Milky Way, are myriad island universes called galaxies. Some are spiral shaped like our own, while others are elliptical or irregular in appearance.
Messier and NGC: A Lifetime of Treasures
Deep-sky objects are usually designated by catalog numbers, such as M42 or NGC 869. The Messier catalog, is the most famous listing of deep-sky objects. Created by Charles Messier, an 18th-century comet hunter, this catalog consists of 109 of the finest objects the sky has to offer. Finding all of the "M" objects is a great introduction into deep-sky observing, since most are bright enough to be seen even through modest equipment. The New General Catalogue of Nebulae and Clusters, or NGC, was compiled in the 1880's by John Dreyer and based on observations by the father-son team of William and John Herschel. More than 7,800 objects are listed in the NGC, certainly more than enough to occupy the owners of even the largest backyard telescopes for a lifetime.
Spotting deep-sky objects through binoculars and backyard telescopes is one of the most exhilarating, challenging, and thought-provoking aspects of the hobby of astronomy. To help set you off on the right foot, here is our top ten list of splendors. Few celestial sights rival these exciting objects. All are visible through modest amateur telescopes, and most can even be seen with binoculars.
Beyond the brighter, showpiece members of the Messier and NGC lists are thousands of other deep-sky objects. Most will test your skills as an observer, but that is the thrill of the challenge.
Tips for Deep-Sky Observing
You don't necessarily need to be a veteran amateur astronomer to enjoy deep-sky observing. Here are a few tips from the experts to give you a head start.
Above all, sit down, relax, and enjoy the view. Dress warmly enough to be comfortable, but not so that you overheat.
As you peer through your eyepiece, remember this: you are seeing an object so distant that its light left there hundreds, thousands, even millions of years ago, and is only arriving here now. You are seeing this cosmic denizen as it was way back then; you're truly looking back in time. Even more amazing, you are not just looking at a photograph ? you are seeing it yourself, with your own telescope! That?s what makes deep-sky observing so exciting!