* Astronomy

Galaxies come in a variety of shapes, but most fit into one of just a few categories - simple spheroids or ellipses, flattened discs, elegant spirals like the Milky Way or irregularly shaped blobs. But Hoag's object is so bizarre that when astronomer Arthur Hoag first spotted it in 1950, he wasn't even sure it was a galaxy.
Instead he thought it might be a ring-shaped puff of gas given off by a dying star: a type of object called a planetary nebula that is commonly found in the Milky Way. But Hoag himself was unsatisfied with that explanation, noting that the ring was not emitting light at the wavelengths characteristic of the hot gas in such clouds.
He further speculated that the ring could be an optical illusion, the result of a phenomenon called gravitational lensing, in which a foreground galaxy's gravity bends the light of a more distant galaxy, giving it a peculiar shape - like looking at it in a funhouse mirror.
But that explanation failed, too. In 1974, observations of the core of Hoag's object showed it weighs far too little to cause the extreme gravitational lensing needed to turn a background galaxy into a ring.
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Google earth file: Hoag's object.kmz (2kb, kmz)

Position (J2000):     R.A. 15 17 14.4  |  Dec. +21° 35' 08''