Bigger isn’t always better but in this case…
120 feet (37 meters) long, 3 feet (1 meter) tall at its sides and 6 feet (2 meters) tall in the middle…
The large image was made from stitching together 800,000 individual pictures taken by Spitzer, for a total of 2.5 billion infrared pixels.
via SPACE.com — World’s Largest Milky Way Image Unveiled.
2013 update: i am removing the link to
http://www.space.com/scienceastronomy/091202-largest-milky-way-image.html
because that site got hacked and is on google’s malware warning list I want to thank Wordfence for finding this issue.