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Messier 109

Spiral Galaxy M109 (NGC 3992), type SBc, in Ursa Major

Right Ascension 11 : 57.6 (h:m)
Declination +53 : 23 (deg:m)
Distance 55000 (kly)
Visual Brightness 9.8 (mag)
Apparent Dimension 7x4 (arc min)

Probably discovered by Charles Messier in 1781.
Independently rediscovered by William Herschel in 1789.

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).

Charles Messier probably discovered this object in March, April, or May 1781 when checking the position of two "nebulae" reported to him by his colleague, Pierre Méchain, which he (Messier) had included in the description of M97. Méchain had found three objects in this region which he had reported to Messier, and are listed in Messier's manuscript notes under the numbers 97, 98, and 99:

Apparently, before publishing the catalog, Messier had found occasion only to measure one of them, M97, on March 24, 1781. He just mentioned the other two in his description; in his catalog, M98 and M99 are completely different objects. Méchain also mentions his findings in his letter to Bernoulli of May 6, 1783.

Probably shortly after these observations, Messier added a position to the personal copy of his catalog, namely RA=11h 43m, Dec=+54.5 deg (c. 1781.3). This position is strange, as its RA coordinate coincides well with that of NGC 3953 (and with Gamma UMa), while the Dec coordinate coincides with that of NGC 3992. Therefore, it seems probable that Messier had seen both these objects, and if actually so, originally discovered NGC 3992. Anyway, when Owen Gingerich investigated this position in 1953, he identified this object with NGC 3992 and added it to the "official" Messier catalog as M109, together with M108.

It was not until October 2006 that Henk Bril, investigating the maps of Fortin's atlas of 1795 (Fortin 1795), found that Pierre Méchain had not observed this object, but neighboring NGC 3953. We acknowledge this here by assigning that object the designation M109B, and offering the designation "M109A" as an alternative for NGC 3992. We prefer to keep also the name "M109" for NGC 3992, first because this is widely used, and second to acknowledge Messier's probable or possible original discovery of this object.

See the story and discussion of the identification of the two galaxies M109 and M109B.

William Herschel has found this galaxy independently on April 12, 1789, and cataloged it as H IV.61; he 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 (sometimes called the M109 group). Tully took individual distances from the redshift 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 occured in this galaxy on March 17, 1956, and reached 12.8 mag (or up to 12.3, according to some sources) in its maximum.

  • Historical Observations and Descriptions of M109
  • More images of M109
  • Amateur images of M109

  • SIMBAD Data of M109
  • NED data of M109
  • Publications on M109 (NASA ADS)
  • Observing Reports for M109 (IAAC Netastrocatalog)
  • NGC Online data for M109


    Hartmut Frommert
    Christine Kronberg

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    Last Modification: October 14, 2013