M102 was long thought to be a duplication of M101, because its discoverer, Pierre Méchain, made an error in the position he sent to Messier and later disavowed the discovery. Based on subsequent communications between the two, it now seems likely that the object involved was NGC 5866, a lenticular galaxy in Ursa Major that both Méchain and Messier observed in 1781. M102 is the brightest member of the 45 million light-years distant NGC 5866 group of galaxies, and the dynamics of the group suggest that although NGC 5866 is only about 70 thousand light-years across, it has a trillion solar masses. This mass includes, as in the case of all galaxies of well-determined mass, large amounts of "dark matter"; but its large nucleus, presumably crammed with a multitude of faint stars, undoubtedly contributes to its unusually large ratio of mass to size. Apparent size 6.5 by 3.1 arcmin.

Below, a HST image of M102 (Image Credits: ESA, The Hubble Heritage Team (STScI/AURA), W. Keel (U. Ala.), NASA). The image is rotated 90 degrees relative to the ones above, so North is on the left. Also, to show fine details in the dusty plane of the disk, the image is slightly underexposed in comparison with the images above; as a result, the nucleus looks much smaller than usual.

See NGC 5826 for images

The first IC states "Not found by Bigourdan". Based on a recessional velocity of 6585 km/sec, NGC 5881 is about 300 million light years away. Given that and its apparent size of 0.8 by 0.7 arcmins, it is about 70 thousand light years across. (Note: A Wikisky search for IC 1100 shows the correct object, but a search for NGC 5881 shows PGC 54150, which the NED lists as "often misidentified as NGC 5881".)

Per Dreyer, NGC 5895 is "very faint, small, extended north-south, apparently connected", the last remark referring to a possible connection to NGC 5896. As it happens, there is no connection between the two galaxies, as their distances differ by nearly 700 million light years; they are merely an "optical double". Based on a recessional velocity of 5355 km/sec, NGC 5895 is about 250 million light years away. Given that and its 1.1 by 0.3 arcmin apparent size, it is about 80 thousand light years across.

Per Dreyer, NGC 5896 is "very faint, very small, round, apparently connected", the last remark referring to a possible connection to NGC 5895, which see for images. As it happens, there is no connection between the two galaxies, as their distances differ by nearly 700 million light years; they are merely an "optical double". Based on a recessional velocity of 19670 km/sec, a straightforward calculation indicates that NGC 5896 is about 915 million light years away. However, for such distant objects, the expansion of the Universe during the time it took their light to reach us must be taken into account. Doing that shows that the galaxy was about 850 million light years away at the time the light by which we see it was emitted, 875 million years ago (the difference between the two numbers being due to the expansion of the intervening space during the light-travel time). Given that and its 0.3 by 0.3 arcmin apparent size, NGC 5896 is about 75 thousand light years across.

Apparent size 3.2 by 1.4 arcmin