The North America Nebula (NGC 7000) is a large expanse of glowing hydrogen gas mixed with opaque clouds of cosmic dust just 3° east of Deneb [Alpha (α) Cygni] and 1° to the west of 4th-magnitude Xi (ξ) Cygni.  Famous as one of the most luminous blue supergiants visible in the night sky, Deneb marks the tail of Cygnus the Swan, or if you prefer, the top of the Northern Cross asterism.

The North America Nebula epitomizes how observational astronomy has evolved over the years.  When he discovered it on October 24, 1786, Sir William Herschel (1738-1822) described the view through his 18.7-inch reflecting telescope as "very large diffused nebulosity, brighter in the middle."  Honestly, I am surprised he could see it at all because of his instrument's very narrow field of view.  That's one of the biggest challenges to seeing the North America Nebula through a telescope -- it spans an area nearly 2° in diameter.  From the sounds of Herschel's notes, the thought of trying to spot it in anything less never crossed his mind.

Five score and four years later, the German astronomer Max Wolf became the first to photograph the full span of NGC 7000.  Upon seeing his results, he christened it the North America Nebula for its eerie resemblance to that continent.  Since then, images of this vast emission nebula have appeared in nearly every introductory astronomy textbook and coffee-table astrophoto album alike.

Before the 1970s, conventional wisdom had it that, although this huge celestial continent was prominent in photographs, it was nearly invisible to the human eye because it was too large and too red.  Part of that mindset has to be attributed to the observing guides that were in print at the time.  Nearly all concentrated solely on telescopic observing.  They were so fixated on what could be seen through conventional long focal length instruments using the comparatively narrow field eyepieces of the day that they ignored other options.   And since NGC 7000 could not squeeze into a single field of view, it was nearly impossible to isolate its clouds from their surroundings.

One of the first authors to mention the North America Nebula, though not by name, was the Reverend Thomas W. Webb.  In volume 2 of his classic compendium Celestial Objects for Common Telescopes (), Webb described the nebula as having a "sharply defined south [edge], and containing a dark opening like a cross; visible as a glow in a field glass, but brightest part scarcely visible in 17¼-in reflector."

Still, most considered seeing the North America Nebula by eye to be futile.  The winds of change began to blow, however, with the landmark work Burnham's Celestial Handbook, published originally in 1966.  Author Robert Burnham, Jr., advised "Binoculars show an irregular glow more than 1½° in diameter with the North American shape becoming unmistakable on a clear night.  Perhaps the best view of the unusual outline is obtained with a 3 or 4-inch rich-field telescope and wide-angle eyepiece."

Another pioneer who urged amateurs to look for the North America Nebula was Walter Scott Houston (1912-1993).  Throughout his nearly half century of penning the Deep-Sky Wonders column in Sky & Telescope magazine, Houston often mused about seeing this difficult object.  His evolving views captured the changing attitudes over its visibility.  For instance, in his September 1948 column, he wrote, "the North America nebula near Deneb cannot be observed readily without photography."  But then, fast forward several decades to find Scotty advising "if observing conditions are very good, and you know what size and shape to expect, the North America Nebula can be made out easily with the naked eye."

Part of that change in attitude was undoubtedly due to the advent of narrowband nebula filters in the 1970s.  As previously discussed, these filters block light at all but a few select visible wavelengths.  Narrowband filters pass only the hydrogen alpha (656nm), hydrogen beta (486nm), and oxygen III (496nm and 501nm) regions, where emission nebulae are strongest.  The net result is increased contrast between the object under observation and the filter darkened background. As a result, the North America Nebula is now a regular target at summertime star parties.

That still doesn't address the size issue, however.  For that, we turn back to Burnham and Houston, who advise using binoculars or small, rich-field telescopes.  Let's take it one step further.  Can we spot the North America Nebula without any optical aid at all, save for perhaps a narrowband filter?

To try this yourself, first, can you see the Cygnus Milky Way clearly?  A reasonably dark suburban sky should be sufficient, but be sure to look when Cygnus is nearest the zenith in order to isolate it from any errant clouds or light pollution.  Zero in on the area between Deneb and Xi (ξ) Cygni, which lies at the edge of the Northern Coalsack, a large expanse of dark nebulosity at the northern terminus of the Milky Way's Great Rift.  The Great Rift slices the galactic plane in half lengthwise, extending southward from Cygnus through Vulpecula, Sagitta, and Aquila on its way toward Sagittarius.  The brightest part of the North America Nebula, marking "Mexico" and "Florida," juts into the Northern Coalsack in much the same way as their earthly counterparts mark the Gulf of Mexico's shoreline.  The nebula's hook-shaped glow appears slightly brighter than the Milky Way immediately surrounding it, but be forewarned that, by eye alone, it is deceptively small.  If you cannot see it by eye alone, try using a narrowband filter.  It might be best to try the filter test with a friend who owns the same filter as you, since viewing through a pair of filters is preferred.  Otherwise, you will lose the two-eyed advantage by squinting through only one eye.

Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's test.  Contact me through my web site or post to this month's discussion forum.

Until next month, remember that half of the fun is the thrill of the chase.  Game on!