The 720 km/sec recessional velocity is too small to give a reliable distance, as peculiar (non-Hubble expansion) velocities can be a substantial portion of the value. Still, the corresponding distance of 32 million light years is in reasonable agreement with redshift-independent distance estimates of 35 to 50 million light years. Given a probable distance of around 40 million light years, its apparent size of 3.5 by 0.8 arcmin implies that it is about 40 thousand light years in diameter.

A young cluster of stars surrounded by clouds of gas and dust out of which it formed, and which it is heating and lighting up. Located in the Carina arm of the our galaxy, the nebula and cluster are about 20 thousand light years away. The more than fifty O and B stars in the cluster have more than 2000 solar masses, and more than 100 times the ionizing power of the Trapezium, which energizes the much closer and therefore more famous Orion Nebula. Normally clusters which contain such hot, massive stars have relatively few lower-mass stars, because they take longer to form; but in this case, a "starburst" of stellar formation has created large numbers of lower mass stars, as well as massive ones. Based on the characteristics of the lower mass stars which have not yet reached the Main Sequence, the cluster's age is estimated at between 300 thousand and a million years, making it one of the youngest as well as the intrinsically brightest in our galaxy. The cluster has an apparent size of 1 arcmin, and is only a little over 5 light years in diameter, but the surrounding nebula is over six times that size.

Apparent size 3.2 by 2.6 arcmin. Used by the de Vaucouleurs Atlas of Galaxy Types as an example of galaxy type E2.

Apparent size 3.4 by 3.0 arcmin. Used by the de Vaucouleurs Atlas of Galaxy Types as an example of galaxy type S0 pec / E(shell). (The galaxy's peculiar appearance makes classification uncertain, varying from SB(r)0° pec (as listed above) to E5 (?) to the de Vaucouleurs double typing.)

Per Dreyer, NGC 3616 (= John Herschel's GC 2366, William Herschel's III 76, 1860 RA 11 10 53, NPD 74 29.6) is "extremely faint, pretty large". The second IC adds "3616 = III 76. Not seen by M. Wolf, 1907".

     M66 is a member of the Leo Triplet of galaxies, which also includes M65 and NGC 3628. Gravitational interaction with the other members of the small group has influenced the structure of its dust-filled arms, and the formation of clusters of bright young stars which light up those arms. It is listed as #16 in Halton Arp's Atlas of Peculiar Galaxies, as an example of a spiral galaxy with detached segments. (The Leo Triplet is also used as an example of a group of galaxies, as Arp 317.) M66 has a recessional velocity of 725 km/sec, which is too small in comparison to peculiar (non-Hubble-expansion) velocities to provide a reliable indication of its distance. Ignoring that caveat yields a distance estimate of 32 million light years, which is in good agreement with redshift-independent distance estimates of 22 to 49 million light years. Given that and apparent size of 9.1 by 4.2 arcmin, about 90 thousand light years across.

NGC 3628 is a member of the Leo Triplet of galaxies, which also includes M65 and M66. The triplet is used as an example of a group of galaxies in Halton Arp's Atlas of Peculiar Galaxies (as Arp 317). NGC 3628 has a recessional velocity of 845 km/sec, which is too small in comparison to peculiar (non-Hubble-expansion) velocities to provide a reliable indication of its distance. Ignoring that caveat yields a distance estimate of 38 million light years, which is in good agreement with redshift-independent distance estimates of 25 to 45 million light years. Given that and its 14.8 by 3.0 arcmin apparent size, about 165 thousand light years across.

Based on recessional velocity of 1155 km/sec, about 50 million light years away, in fair agreement with a redshift-independent distance estimate of 70 million light years. Given those values and an apparent size of 4.5 by 4.5 arcmin, about 80 thousand light years across.