14 June 2007
NASA recently published an exquisite image of M81, the picturesque spiral galaxy, acquired by the Hubble Space Telescope (HST). The color composite image is the sharpest view ever obtained of M81.
The image was composed from images in the visual and infrared, taken with HST's sophisticated imaging device, the Advanced Camera for Surveys (ACS). The resolution is so fine that individual stars, star clusters and gas clouds of M81 are resolved.
A spiral galaxy is a huge assemblage of stars and nebulae (vast cosmic clouds). The spiral arms of the galaxy emanate from its yellowish core, consisting of billions of old, reddish stars.
M81 is estimated to be approximately 12 million years distant. It is visible in the direction of the stars of Ursa Major, the Great Bear. It is the 81st entry in the Messier catalog of deep sky objects, compiled by the French astronomer Charles Messier (1730-1817).
M81 is the largest member of a group of gravitationally-bound galaxies, including the intriguing starburst galaxy M82. A starburst galaxy is characterized by a peculiarly high rate of star formation, often due to interaction with one or more galaxies.
Further Reading
Hubble Site
http://Hubblesite.org/
Hubble Photographs Grand Design Spiral Galaxy M81
http://hubblesite.org/newscenter/archive/releases/2007/19/
Aymen Mohamed Ibrahem
Senior Astronomy Specialist