April 12
Hanny's Voorwerp
Observed in 2010
This image shows a ghostly green blob of gas that appears to float near a normal-looking spiral galaxy. The bizarre object, dubbed Hanny's Voorwerp, is the visible part of a 300,000-light-year-long streamer of gas stretching around the galaxy, called IC 2497.
Image credit: NASA, ESA, Hubble Space Telescope