Discovered by Pierre Méchain in 1781.
NGC 3992 (Messier 109, M109) is one of the "Theta"-like barred
spirals, which appears as a "hazy spot" situated just 40' SE of the mag
2.44 star Gamma Ursae Majoris (Phad, or Phecda).
This object was observed by
Pierre
Méchain on March 12, 1781, and by
Charles
Messier on March 24, 1781, together with
M108 when he
measured M97.
Messier
listed the object now called "M109" under number "99" in a
preliminary manuscript version of his catalog without a position, and
Méchain
mentioned it in his letter to Bernoulli of May 6, 1783. But together
with M108, it was not
added to the
"official" Messier catalog until 1953, by
Owen
Gingerich.
William
Herschel has found this galaxy independently on April 12, 1789, and
cataloged it as H IV.61 (incorrectly misclassifying it as a
planetary nebula).
Kenneth Glyn Jones has erroneously misclassified M109 in his General
Description chapter 1 as type Sb, while in the galaxy description, he
correctly gives its class (Hubble type) as SBc.
M109 is about 7-by-4 arc minutes in angular extent, and of apparent
visual magnitude 9.5 or 9.6. Visually, only its bright central region
together with the bar can be seen, and appear pear-shaped in smaller
telescopes, "with a strong suspicion of a granular texture" (Mallas).
According to Brent Tully's Nearby Galaxies Catalog, M109 is
about 55 million light years distant, as it is receding at 1142 km/sec,
and a member of the Ursa Major Cloud, a giant but loose agglomeration of
galaxies. Tully took individual distances from the red shift in a model
taking the Virgo-centric flow into account. The distance of this galaxy,
however, may be a bit smaller, as the average recession in this cloud is
lower, and some part of the surplus may be peculiar velocity.
In a newer article, Brent Tully and his
coworkers (1996) establish the existence of this Ursa Major Cluster,
as they now call it, by identifying 79 member galaxies (among them
M109).
The type I supernova 1956A occurred in this galaxy on March 17, 1956,
and reached 12.8 mag (or up to 12.3, according to some sources) in its
maximum.
