The Structure of Galaxies

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Galaxies have many shapes, sizes, distances (from us) and spectral signatures, but they can be broadly classified into four types: elliptical, spiral, barred spiral and irregular. Elliptical galaxies are nearly featurless spheroidal masses of stars, and are believed to be some of the oldest galaxies. Spiral and barred spiral galaxies are picturesque spirals that appear to be spinning (which they are, just very slowly). Irregular galaxies are just what the name implies, irregular collections of stars with no discernable shape.

The images below are created with just the luminance channel of the data collected, and presented in black & white. The surrounding Milky Way stars have been removed from the image using software, allowing the beautiful and unique structure of each galaxy to be more fully appreciated.

 
 

M31 Andromeda Galaxy

M101 Pinwheel Galaxy

The Andromeda galaxy is the closest large galaxy to the Milky Way at a distance of 765 pc (2.50 million light years), and is large enough to be seen with the naked eye (at dark sky locations). It is classified as a barred spiral galaxy and has two prominant companion galaxies: M32 (small bright galaxy upper left) and M110 (lower right). It sits at an angle of approximately 13 degrees to us, and has very prominant dust lanes.The Pinwheel galaxy is a face-on spiral lying 6.64 mpc (21.6 million light years) away from us. It has an interesting appearance as, unlike most spiral galaxies, it seems to be unsymmetrical.
 
 

M81 Bode's Galaxy

M51 Whirlpool Galaxy

IC 342 Phantom Galaxy

M81 is a beautiful, classic example of a "grand design" spiral galaxy. Inclined at an oblique angle to our line of sight, the bright nucleus is surrounded by two distinct spiral arms. Just below M81 in this view lies a small, irregular galaxy designated UGC 5336. M81 is estimated to lie 3.68 mpc (2 million light years) from us.Pictured here are two galaxies, the larger, classic spiral galaxy M51 is gravitatially interacting with the much smaller NGC 5195, seen at the tip of the lower spiral arm. The distance to this pair, which sits nearly face-on to our line of sight, is estimated to be 7.22 mpc (23.5 million light years).IC 342 is sometimes called the "Phantom Galaxy" because, sitting near to the galactic plane of the Milky Way, it is partially obscured by dust and many stars in our own galaxy. Sitting nearly face-on to us, its spiral structure is clearly evident despite the obscuring dust. The galaxy is estimated to sit 3.3 mpc (10.7 million light years) from us.
 
 

M106

NGC 891

M74

M106 is a large spiral galaxy sitting at an angle of 25 degrees to our line of sight. The central region clearly shows a spiral structure, but the extended disk seems to show only a hint of its spirals. The galaxy is estimated to lie 7 mpc (23.7 million light years) from our position. Another small spiral galaxy, NGC 4248, can be seen to the lower right of M106.NGC 891 is a spiral galaxy sitting perfectly edge-on to our line of sight. It has a central bulge of stars and a clear, dark dust lane along its disk. It lies 8.4 mpc (27.3 million light years) from us.Another face-on spiral galaxy, M74 has an estimated distance from us of 10 mpc (33 million light years). Despite its rather faint brightness, it displays a magnificent spiral structure.
 
 
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