Astronomy Picture of the Day

Explanation: From a garden on planet Earth, 38 hours of exposurewith a camera and small telescope producedthis cosmic photoof the M81 galaxy group.In fact, the group's dominant galaxy M81 is near thecenter of the frame sporting grand spiral arms anda bright yellow core.Also known as Bode's galaxy, M81 itself spans some 100,000light-years.Near the top is cigar-shaped irregular galaxy M82. The pair have been locked in gravitational combat for a billion years.Gravityfrom each galaxy has profoundly affected the other duringa series of cosmic close encounters. Their last go-round lasted about 100 million years andlikely raised density waves rippling around M81, resulting in massivestar forming regions arrayed alongM81's spiral arms. M82 was left with violent star forming regions too, and colliding gas clouds so energetic that the galaxyglows in X-rays. In the next few billion years, theircontinuing gravitational encounters will result in a merger, and asingle galaxy will remain.Another group member, NGC 3077 is below and left of thelarge spiral M81.Far far away, about 12 million light-years distantthe M81 group galaxies are seentoward the northern constellation Ursa Major (the Great Bear).But in the closer foregroundthe wide-field image is filled with integrated flux nebulaewhose faint, dusty interstellar cloudsreflect starlight above the plane of our own Milky Way galaxy.