Post by glactus on Nov 8, 2008 21:18:26 GMT
Messier 101 The Pinwheel galaxy
The Pinwheel Galaxy - Messier 101- is a face-on spiral about 27 million light-years away in the constellation of Ursa Major. Magnitude is 8.2
To observe the spiral structure in modern instruments requires a fairly large instrument, very dark skies, and a low power eye piece.
On February 28, 2006, NASA and the ESA released a very detailed image of the Pinwheel Galaxy, which was the largest and most detailed image of a galaxy by Hubble Space Telescope at the time. The image was composed from 51 individual exposures, plus some extra ground-based photos.
M101 is a relatively large galaxy compared to the Milky Way. With a diameter of 170,000 light-years it is nearly twice the size of the Milky Way. Less is known about its mass however.
Frequently cited is that it has an equivalent mass of about 16 billion solar masses. That value is almost certainly too low, and probably stems from M101's low surface brightness. New insights in its HII regions and rotational velocities have put the number between 100 billion and 1 trillion suns.
Another remarkable property of this galaxy are its huge and extremely bright HII regions, of which a total of about 3000 can be seen on photographs.
HII regions are places that often contain large numbers of extremely bright and hot young stars giving them their characteristic blue color.
Credits: M101 is a NASA/ Hubble image