Northern stargazers in spring look out of the plane of the Milky Way in the night sky before midnight, so there are few bright stars and star clusters visible, and even fewer bright nebula. But there is a little gem under the bowl of the Big Dipper, the famous Owl Nebula, also known as M97. A young planetary nebula, M97 is a speeding cloud of glowing gas ejected by a small dying star. In a small telescope under dark sky, the nebula resembles the eyes of wise old barn owl gazing out of the interstellar darkness.
The Owl Nebula’s name was inspired by a sketch made by the 19th-century Irish astronomer Lord Rosse, who observed the nebula with his homemade 72-inch reflector telescope. Rosse’s sketch reveals, as do modern images, two large central markings that resemble the eyes of an owl.
While Messier and his contemporaries could see M97 with tiny 2 to 4-inch instruments, modern stargazers, who are scourged by light pollution, rank the object as one of the most challenging of all sights on the Messier list. That’s because the 9th-magnitude nebula is spread over a patch of sky about five times the size of Jupiter’s disk. Light pollution renders the object very difficult to see in urban skies. In suburban skies or darker, the object is much easier. Once you locate the nebula, experiment with your eyepieces to get the best view. Your best bet is magnification of 100-120x, and you’ll need a 6-inch or larger scope to see the “eyes”. A UHC or OIII filter help bring out the elusive detail in this object.
Look for the Owl Nebula just below the bowl of the Dipper, about 2.3° east-southeast of Mirak, or β Ursa Majoris. At 14th-magnitude, the nebula’s central star can be glimpsed in a 10-inch or large scope. The star lies exactly between the two “eyes”. About 1/3 the distance between the Owl Nebula and Mirak lies another Messier object, the mottled cigar-shaped galaxy M108. The 10th-magnitude galaxy reveals some texture and shape in a 4-inch or larger scope, and lies within the same low-power field of view as M97.
M97 lies about 1600 light years from Earth. The central star began ejecting the nebula about 6,000 years ago, and it will remain as a lone white dwarf star, a glowing ember about the size of the Earth, that will slowly cool over the next many billions of years.