Designated Supernova 2014J, the dying star has peaked at about magnitude 10.6 (as of January 31) — bright enough to be visible in 6-inch telescopes under dark skies. As the chart below shows, M82 is located in the constellation Ursa Major.
It appears that the star exploded on January 14 or 15 — but some 12 million years ago. Yes, you read that correctly. The first images of M82 that show the star were taken on January 15, 2014, but since the galaxy is some 12 million light years away, light from the supernova took 12 million years to reach Earth.
Supernovas come in several different flavours. Early studies of SN2014J’s light curve and spectrum indicate it is a Type 1a — a kind of supernova possible in a binary star system, where two stars are gravitationally bound to each other and one star in the pair is a white dwarf. The dwarf star dramatically flares to prominence when it robs a little extra matter from its neighbour. After its brief burst of glory, the star slowly fades back to obscurity.
Supernovas bright enough to be seen in backyard telescopes don’t happen very often, though they’re not exactly uncommon either. What makes SN2014J notable is that it is situated in a relatively nearby galaxy. The closest, recent supernova was SN1987A, which occurred in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. And there hasn’t been a supernova observed within our own galaxy since Kepler’s Star, which was first noted by German astronomer Johannes Kepler, in October, 1604.