Messier 91 (M91) & NGC 4571

Also Known as: NGC 4548 (M91), IC 3588 (NGC 4571)

Object Type: Barred Spiral Galaxy

Constellation: Coma Berenices

Distance from Earth: 63 million light years (M91), 58 million light years (NGC 4571)

Apparent Magnitude: 11.0 (M91), 11.8 (NGC 4571)

Coordinates: RA 12H 35M 26.4S DEC 14deg 35min 26.4sec (M91), RA 12H 36M 56.4S DEC 14deg 13min 02 (NGC 4571)sec

Actual Size: 100,000 light years in diameter (M91)

Apparent Dimensions: 5.4 arc-minutes x 4.3 arc-minutes (M91), 3.6 arc-minutes x 3.2 arc-minutes (NGC 4571)

Discovered by: Messier 91 is one of Charles Messier’s original discoveries.
Messier found it on March 18, 1781, along with seven other galaxies in the Virgo Cluster – M84, M85, M86, M87, M88, M89 and M90 – and the globular cluster M92, located in the constellation Hercules.
M91 was the last member of the Virgo Cluster that Messier discovered that night.
He described the object as a “nebula without star, in Virgo, above the preceding No. 90;” adding that “its light is still fainter than that of the above.”
NGC 4571 is a spiral galaxy located in the constellation of Coma Berenices that William Herschel thought was Messier 91 in Charles Messier' catalog of deep-sky objects, before nearly two centuries later that object was determined to be the nearby barred spiral galaxy NGC 4548.

Description: Messier 91 has a very prominent central bar, oriented at an angle of 65/245 degrees. The galaxy is receding from us at 486 km/s.
Messier 91 is classified as an anemic galaxy, which is to say, it is a spiral galaxy with very little gas and a low rate of star formation compared to similar galaxies. M91 is home to about 400 billion stars.
The galaxy’s membership in the Virgo Cluster was confirmed after its distance was measured at 52 million light years by the Hubble Space Telescope H0 Key Project Team in 1997. The team used Cepheid variables to determine the distance to the galaxy and found that it is similar to the distances of other cluster members.
The galaxy’s membership was questioned for a long time, mainly because it is anemic, has relatively low surface brightness, and is moving away from us more slowly than most cluster members.
The average recession velocity of the Virgo Cluster galaxies is 1,100 km/s. The galaxy’s lack of gas is explained by the ram-pressure stripping that it is experiencing as it moves through the heavily populated cluster. The process has left M91 and other cluster members stripped of gas.
Messier 91 was a missing Messier object for a long time as a result of a mistake made by Messier, who had logged the object’s position from Messier 58 instead of Messier 89. The 91st entry in the Messier catalogue was believed to be either a passing comet or a duplicate observation of M58.
Despite being classified as a late-type galaxy, NGC 4571 has features more typical of spiral galaxies of earlier Hubble type such as a high color index, both low star formation rate and H-Alpha brightness, and relatively little neutral hydrogen, suggesting it may have lost most of its gas due to interactions with Virgo's intragalactic medium and/or past interactions with other galaxies of the cluster.
As majestic as spiral galaxies like NGC 4571 are, they are far from the largest structures known to astronomers.
NGC 4571 is part of the Virgo cluster, which contains more than a thousand galaxies. This cluster is in turn part of the larger Virgo supercluster, which also encompasses the Local Group which contains our own galaxy, the Milky Way.

Click Below Image(s) for Full Size:

M91 is the faintest of all Messier objects and one of the most difficult to observe.
Small telescopes at medium power can reveal hints of the bar structure under exceptionally good conditions, but the bar is better seen in photographs than visually.
In 6-inch and 8-inch telescopes, the galaxy appears as a faint patch of light with a brighter center. Larger instruments show the bright bar region and, depending on the conditions, the galaxy’s spiral arms.
The best time of year to observe M91 and other galaxies in the Virgo Cluster is during the spring.

Platesolve

M91 & NGC 4571 Spiral Galaxies

Imaging Details
Click to Return to Home Page