M40 is an optical double star (a chance alignment of two independent stars at different distances from earth) in the constellation Ursa Major and in the center of the photo below. Ursa Major is known as the Big Dipper and is circumpolar for northern observers (it never sets). Many apparent single stars are actually double stars, held together by mutual gravity and called binary systems. Roughly half the sky’s stars are binary.

M40

The Big Dipper has a famous optical double star that ancient Arabic texts refer to as a visual test. At the bend in the Dipper’s handle is bright Mizar, with dimmer Alcor close-by to its east-northeast. It is a visual test to see them both with your naked eye. Like M40, Mizar and Alcor are not an actual binary system. Ironically, Alcor is a binary star.

At magnitude 8.4, M40 is not visible to the naked eye. See below for location of this photo of M40. The bright star with spikes is Ursa Major 70, magnitude 5.5.

Some versions of the Messier catalog omit M40 as an “obscure” object, despite its reality in the sky. Messier might have cataloged M40 simply because he had the coordinates. It does not look much like a comet.

North (always toward Polaris) is up in the photo. The picture was taken with a fully modified Canon Rebel camera (this is my one shot color camera) on a TEC 140 telescope in the Alpenglow-Torrey House Observatory in the dark sky community of Torrey, Utah (Bortle 2-3). The ten best of 14 45-second sub-frames were used and stacked in Deep Sky Stacker = 7.5 minute photo. Unguided, binned 2X2 (to make smaller files for transfer), no calibration frames. Processed in Photoshop (CS5).

Location in the night sky of the photo:

Source: Astrometry.net