Located in the constellation Ursa Major, M81 is an exemplary spiral galaxy. Its two main arms, tracing an S shape in the sky, are so perfectly formed that astronomers have called M81 a “grand-design spiral galaxy.” The arms can be resolved into star clusters and bright nebulae, and, if one looks closely, it is even possible to make out individual giant stars and bright H II regions.
    M81’s central region—one of the most dense nuclear regions known—is dominated by old stars that emit a soft, amorphous glow. 
    The galaxy is not perfectly symmetrical: one of its arms appears slightly distorted, a disruption that probably results from gravitational interaction with the neighboring galaxy M82.