Explanation: What could cause a nebula to appear square? No one is quite sure. The hot star system known as MWC 922, however, appears to be embedded in a nebula with just such a shape. The above image combines infrared exposures from the Hale Telescope on Mt. Palomar in California, and the Keck-2 Telescope on Mauna Kea in Hawaii. A leading progenitor hypothesis for the square nebula is that the central star or stars somehow expelled cones of gas during a late developmental stage. For MWC 922, these cones happen to incorporate nearly right angles and be visible from the...