Exploring the Eagle Nebula

Pale but enticing, the Eagle is a telescopic treat when scrutinized from a dark observing site.

Dickinson-Eagle Nebula

Like most nebulous objects in the deep-sky treasury, the Eagle Nebula appears much more prominent in astrophotos than it does to an observer at the eyepiece. Courtesy Terence Dickinson

The Eagle Nebula, Messier 16, is an emission nebula enveloping a cluster of relatively young stars that formed inside the cloud. Ultraviolet radiation streaming from the heftiest and hottest cluster members has caused the vast cauldron of hydrogen to glow. Spectacular portraits of the Eagle by the Hubble Space Telescope indicate that the cluster is still growing. The most famous image, taken in 1995, revealed three massive columns of gas and dust near the centre of the nebula that are incubating suns both nascent and newborn. Hubble scientists dubbed the towering trio the Pillars of Creation.

M16 is 6,500 light-years away and resides in Serpens, where that constellation borders with Scutum and Sagittarius. A broad portion of the Milky Way splashes across this region, so star-hopping can be a challenge. For M16, I begin by sighting third-magnitude lambda (λ) Sagittarii, the top star in the Sagittarius Teapot. From there, I hike northward almost 11 degrees to fifth-magnitude gamma (γ) Scuti, then veer west-northwest for 2½ degrees into Serpens, where my finderscope encounters the sixth-magnitude target. Or, if I’m feeling bold, I simply follow the Milky Way “steam” issuing from the Teapot’s spout. About 15 degrees above the spout, my finder sweeps up the Swan Nebula (M17) and, above it, in the same finder field, the slightly dimmer Eagle Nebula.

Wide chart - M16

The area indicated by the box in the chart above, corresponds to the region shown in the close-up star map below. (Click on either chart to see a larger version.)

LeDrew M16-chart

Cartography by Glenn LeDrew

The brightest portion of M16 is a ¼-degree-wide “wing” of nebulosity spreading northeast-southwest. A short “tail” dotted with stars fans northwestward from the wing, and a minute “head” protrudes southeastward. Experienced observers say they’ve traced this evocative shape (except, perhaps, for the head) in scopes as small as 100mm aperture. However, under a wilderness sky of excellent transparency two summers ago, I examined M16 with my 10-inch Dobsonian. The view at 58× was beguiling but ambiguous: a scatter of stars tangled in a formless gauze suspended in a rich Milky Way star field. Adding a doubly ionized oxygen filter blunted the starlight but greatly enhanced the nebula and revealed a recognizable form—though it wasn’t the elegant Eagle. To my conservative eye, M16 morphed into a mushroom, complete with broad cap and stubby stem. Sorry.

During a high-elevation star party last summer, I camped beside colleague John Karlsson and his finely crafted 15-inch Dobsonian. The very first night was clear, calm and coal-black. Threading a UHC filter onto a wide-angle ocular generating 91×, John invited me to ogle the Eagle. I confess the bird effect still didn’t grab me, whereas the mushroom shape seemed obvious. John’s drawing of M16, above left, supports my “fuzzy mushroom” impression. That night, both of us noted a dusky feature in the form of a lopsided letter V, or check mark, next to a pair of ninth-magnitude stars near the centre of the mushroom cap. Photos of M16 clarify that the west side of the V (the long part of the check mark) corresponds to the central column in the Pillars of Creation. John’s sketch shows this dark digit just left of the above-mentioned star pair.

Karlsson-M16 sketch

John Karlsson’s eyepiece sketch of M16 gives a realistic indication of the nebula’s “mushroom-like” appearance.

The cluster embedded in M16 is attractive in its own right. My 10-inch at 58× (unfiltered) shows the mushroom “fenced” by an irregular circlet of stars broken on the west side. A wedgelike concentration of stars, eighth magnitude and fainter, extends northwestward along the mushroom’s stem. The starry wedge is dominated by a north-south pair of 8.2- and 8.8-magnitude stars 27 arc seconds apart. Each primary sun sports a faint companion eastward. Marking the tip of the wedge is another wide double yielding 9.5- and 11.0-magnitude components 15 arc seconds apart. Between the binaries is an eye-catching cres­cent — concave northward, stretched east-west — comprising five main stars rang­ing in magnitude from 10.2 (eastern side) to 11.1 (western side). Doubling the power shows a dim dot attending each of the two bright eastern stars. Nice!

Patience is the key to ferreting out the fine points in the Eagle’s starry litter. To appreciate the subtle complexity of the nebula itself, you’ll need that perfect country night, filter-equipped optics — and perhaps an eye for mushrooms.

SkyNews contributing editor Ken Hewitt-White conducts his eagle-spotting, day and night, from the mountains of southern British Columbia.

Categories: Clusters, Nebulas, and Galaxies
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