The Pinwheel Galaxy, also known as Messier 101 (M101) and NGC 5457, is one of the best known spiral galaxies in the night sky.
M101 is a grand design spiral galaxy (a spiral galaxy with prominent and well-defined spiral arms) located in the constellation Ursa Major, the Great Bear.
The galaxy appears face-on when observed from Earth, and is a popular target for both amateur and professional astronomers. To observe the spiral structure in M101, one needs a larger telescope, a low power eyepiece, and little to no light pollution.
In a smaller telescope, only the bright central region is visible.
The spiral arms begin to appear as nebulous patches in 4-inch telescopes, and views in 6-inch and larger telescopes are significantly more impressive. M101 has an apparent visual magnitude of 7.86 and is approximately 20.9 million light years distant from Earth, which means that we are seeing it as it was about 20.9 million years ago.
The Pinwheel Galaxy contains hundreds of billions of stars and is notable for its many large, bright star forming regions. Various images of the galaxy reveal about 3,000 of the H II regions, ionized by bright hot young stars.
The galaxy is believed to have had an encounter with another galaxy in the past. It appears asymmetrical on one side and this is thought to be a result of the collision. The intense star forming activity in this region is another outcome of the interaction between the two galaxies.
FACTS
The Pinwheel Galaxy is about 170,000 light years in diameter, which makes it roughly 70 percent larger than our galaxy, the Milky Way. The galaxy’s disk has 100 billion solar masses, while the bulge has about 3 billion solar masses.
The Pinwheel Galaxy was discovered by the French astronomer Pierre Méchain on March 27, 1781. Méchain notified Charles Messier of his discovery, and Messier included the galaxy in his catalogue as the 101st object.
Méchain originally described the galaxy as a “nebula without a star, very obscure and pretty large, 6’ to 7’ in diameter, between the left hand of Böotes and the tail of the Great Bear. It is difficult to distinguish when one lits the [grating] wires.”
The Anglo-Irish astronomer Lord Rosse was the first to document the galaxy’s spiral structure in more detail. He observed M101 in a 72-inch Newtonian reflector in the second half of the 19th century.
The Pinwheel Galaxy has several prominent companion galaxies: the irregular spiral galaxy NGC 5204, the peculiar dwarf galaxy NGC 5474, the dwarf galaxy NGC 5477, the spiral galaxy NGC 5585 and the irregular galaxy Holmberg IV (UGC 8837).
M101 is the brightest member of the M101 Group, a group of galaxies in Ursa Major that includes the Pinwheel Galaxy’s companions, UGC 9405, and several other galaxies.
The M101 Group is one of the many groups of galaxies located within the Virgo Supercluster (or Local Supercluster), an irregular supercluster that includes the Local Group of galaxies (which includes the Milky Way and Andromeda Galaxy) and the Virgo Cluster, a cluster of galaxies whose centre is located in Virgo constellation.
Pinwheel Galaxy – M101
Type: SAB(rs)cd
Coordinates: 14h03m12.6s (right ascension), +54°20’57’’ (declination)
Distance: 20.9 ± 1.8 million light years
Apparent dimensions: 28’.8 x 26’9
Apparent magnitude: 7.86
Redshift: 0.000804
Helio radial velocity: 241 ± 2 kilometres per second
Other designations: PGC 50063, Arp 26, UGC 8981
0 Comments