Ngc 4216


Ursa Major

■ *P ♦


- * -

Leo Minor

Coma Bereniees


V ■ • •

67* 72 •


26 20




•6 I)

X " HT

•B •

• •


*o •




v .


•g Virgo m



© Stephen James O'Meara

Tirion: Churl 13 Uranametria: Chart 193

Tirion: Churl 13 Uranametria: Chart 193

© Stephen James O'Meara

Silver Streak Galaxy, Weaver's Shuttle Galaxy NGC 4216

Type: Mixed Spiral Galaxy (SABb) Con: Virgo

Dist: 55 million light-years Disc: William Herschel, 1784

w. herschel: [ObservedApril 17, 1784] Bright, very much extended, very bright in the middle, 9' or 10' in length. (HI-35)

ngc : Very bright, very large, very much extended toward position angle 17°, suddenly brighter in the middle to a nucleus.

ngc 4216 is a picture-perfect galaxy in Virgo. It lies only 11 ° south of M98 and M99 in Coma Berenices and some 2° west of the very heart of the Great Coma-Virgo Cluster of Galaxies. Compared to other bright galaxies in the region, NGC 4216 stands apart, being inclined to our line of sight by just 1°. But that slim viewing angle is sufficient enough to let us glimpse, in stunning clarity, its bright core, nuclear bulge, luminous arms, and spiral dust patterns. It was among the first spiral "nebulae" photographed with the 36-inch Crossley reflector at Lick Observatory at the turn of the century. Lick Observatory's second director James Keeler (1857-1990), had in 1898 focused his attention on the study of Herschel's nebulae. Keeler believed that by comparing photographs of a spiral nebula over time, it might be possible to sense its direction of rotation. Heber Curtis (1872-1942), who joined the staff at Lick Observatory after receiving his Ph.D. in astronomy from the University of Virginia in 1902, carried on Keeler's work in 1914, noting that it was important because "a knowledge of the proper motions or of any rotational movements which these bodies may have would be of great value in investigations as to the size and distance of the nebulae, and therefore as to their place in the structure of the visible universe." By 1943 Edwin Hubble was using a negative image of NGC 4216 to illustrate a discussion

on the opening of spiral arms relative to the sense of rotation.

Today, images of NGC 4216 are often used in textbooks to illustrate the classic components of a typical, middle-aged Sb spiral galaxy. The galaxy displays a small, extremely bright nucleus partially hidden by dark lanes. A fuzzy halo of light, as soft and transparent as angels' breath marks the position of the galaxy's centralbulge. Knotty regular arms swirl away from this core in luminous concentric rings lined with very strong dark lanes. The outer regions of the disk are very dusty. The intensity of the nucleus and the symmetry of the rings gives the galaxy a look of quiet calamity.

A peculiar brightening some 50" north-northeast of the nucleus, at the very lip of the central lens, could indicate the presence of a bar. As early as 1979, John Kormendy

(University of Texas) found that bars in lens systems usually fill the lens in one dimension. If true, the position of NGC 4216's bright spot at the extreme of the lens argues that NGC 4216 is an edge-on bar.

In a 1999 Astronomical Journal paper, O. K. Sil'chenko (Sternberg Astronomical Institute, Moscow) and his colleagues obtained high-resolution spectra of NGC 4216 with the Soviet 6-meter reflector and found a distinct metal-rich nucleus, whose age appears to be different from that of the surrounding bulge. Normally, these two galactic components are of the same age. But NGC 4216's nucleus is about twice as young as its bulge. It is thought that the age of the nucleus is 8 to 12 billion years, while the bulge of the galaxy is older by a factor of 1.5 to 2. The astronomers also found spectral evidence for starburst activity which may form a circumnuclear ring in the plane of the galaxy's disk. If NGC 4216 is like other mixed spiral galaxies (see Hidden Treasure 51), the smallbar in the lens maybe triggering star formation in the nucleus, keeping it "young."

To find this beautiful system, first locate 5th-magnitude 6 Comae Berenices, which is about 62° due east of Beta O) Leonis (Denebola), the Lion's Tail. NGC 4216 lies 1| ° due south of 6 Comae. You could also start with the famous 10th-magnitude galaxy M99, which is only 50' southeast of 6 Comae and 10' southwest of a magnitude

6.5 star (a). A40' hop south-southeast of M99 to bring you to a 7th-magnitude star (b). A little more than 30' to the southwest will bring you to a roughly 9th-magnitude star (c). NGC 4216 lies almost 50' to the west-southwest.

In the 4-inch at 23 x, the galaxy is very bright and beautiful - quite a simple yet stunning sight. And though it is obvious in a small telescope under a dark sky, it is also small. Look for a bright, 5'-long silver streak, oriented north-northeast-south-southwest. With averted vision, the edges sharpen to a knife edge. The northern half of the lens also looks slightly brighter than the southern half. Admiral Smyth called it a "long pale-white nebula." He also called it a "very curious object, in shape resembling a weaver's shuttle." In keeping with the times, I suppose, the Rev. T.W. Webb seconded Smyth's opinion, noting that the object has a "long shuttle-like nucleus." For these reasons, I call the galaxy the Weaver's Shuttle.

NGC 4216 is all the more stunning at higher powers. At 72 x, a bright core -tack sharp and extremely luminous - burns through the soft and smooth spindle, the ends of which gradually taper to a point, or so it seems. And at 101 x, the brilliant nucleus lies at the center of a white egg-shaped core beyond which extends the oblique and dynamic lens. Smyth makes an interesting comment about the visibility of the galaxy's nucleus as the eyes work to absorb its photons: "and the centre exhibits a palpable nucleus, which in my instrument brightens at intervals, as the eye rallies." As Smyth's observing eye weaved back and forth like a shuttle across the length of the galaxy, the nucleus flared to prominence, then dimmed, in accordance to where its light focused on his retina. If you spend some time surveying the galaxy's length at 101 x, see too if the major axis doesn't seem to suddenly and occasionally fluoresce - like a pulsating neon tube light. This may be due to the presence of a dust lane along the major axis, which the eye intermittently sees. Observers have spied this lane clearly in 12-inch and larger telescopes.

By the way, if for any reason you find yourself unimpressed with the appearance of this system, or somehow feel that it's an insignificant wonder, consider that in physical size and mass (linear diameter = 91,000 light-years;total mass of 190 billion Suns), NGC 4216 is comparable to our own Milky Way system. So as you stare at this near-edge-on galaxy, and perhaps shrug your shoulders at its dimness and simplicity, imagine how an alien observer from another galaxy might feel seeing our Milky Way 55 million light-years distant through a small telescope. It is a failing of human nature that we can so easily brush aside anything that does not immediately appeal to our visual senses. Our inability to comprehend fully all that we see is one of our greatest weaknesses.

In fact, NGC 4216 is the brightest of three edge-on systems within a 25' field of view. The other two galaxies lie beyond the "obvious" in our range of vision. Shining at magnitude 13.3, the exactly edge-on galaxy NGC 4222 lies 12' to the northeast, just over the border in Coma Berenices. And 11' to the southwest lies NGC 4206, a magnitude 12.2 galaxy in Virgo with a small and very bright nucleus.

In light of the profound nature of all these dim and distant systems in the Coma-Virgo Cloud of Galaxies, it is almost nonsensical to look out into the vastness of space with our telescopes and not contemplate at least the possibility of life elsewhere in the uni verse. That curiosity is what sets us aside from other forms of life on Earth. It is what makes us distinct beings, though not necessarily unique in a cosmic sense.

In his 1963 book, The View from a Distant Star, Harlow Shapley said we can shun such possibilities because we are "dumb," congenitally dumb. "Our failure to comprehend the universe," he says, "is that we have been and still are bedeviled by a natural and persisting anthropocentrism. Correctives for our vanities are provided by modern science, but we suffer relapses and return to believing that we are somehow important and supremely powerful and understanding. Of course we are not."

In the words of Salvador Dali, "The universe is a slight thing compared with the amplitude of a brow painted by Raphael."

0 0

Post a comment