A gravitationally interacting pair with NGC 5218, referred to as Keenan's System, or Arp 104. A Seyfert galaxy (type Sy1). Based on a recessional velocity of 2940 km/sec, NGC 5216 is about 135 million light years away, in fair agreement with redshift-independent distance estimates of 155 to 185 million light years. Whatever the actual distance, the galaxy is obviously at essentially the same distance as its companion, NGC 5218, so I have adopted a common distance of 160 million light years for comparison purposes. Given that and its apparent size of 1.3 by 1.1 arcmin, NGC 5216 is about 60 thousand light years across. The overall extent of Keenan's system, including the trails of gas extending between and beyond the pair, is estimated at about 250 thousand light years. (This pair was featured as the Astronomy Picture of the Day for July 2, 2010. Unfortunately, the accompanying description of the system contained a factor of ten error in distances and dimensions. This appears to be the result of an all-too-common propagation of incorrect data across the Internet; but LEDA and NED make it clear that the system is much more distant than usually stated, and even the NOAO site, although giving incorrect dimensions for the system, correctly states that it is well over 100 million light years away. The APoD caption also incorrectly states that Keenan discovered the system. William Herschel was the first to record the nebulae; Keenan discovered the bridge of stellar material connecting the pair.)

Based on a recessional velocity of 3080 km/sec, PGC 47854 is about 145 million light years away, in reasonable agreement with redshift-independent distance estimates of 145 to 150 million light years. Given that and its apparent size of 1.35 by 0.45 arcmins, it is about 55 thousand light years across. (Unlike many NGC"A" or "B" galaxies, which are close companions of the original NGC object, NGC 5216A has no obvious connection to NGC 5216, being separated from it by a full degree. However, if it happens to be at the same distance, it would be only a couple of million light years away from Keenan's System; so although that is only a possibility, perhaps the appellation is not entirely unwarranted.)

Based on a recessional velocity of 8045 km/sec, NGC 5217 is about 375 million light years away. Given that and its apparent size of 1.5 by 1.4 arcmin, it is about 160 thousand light years across.

A gravitationally interacting pair with NGC 5216, referred to as Keenan's System, or Arp 104. Based on a recessional velocity of 2935 km/sec, NGC 5218 is about 130 million light years away, in fair agreement with a redshift-independent distance of 165 million light years. Whatever the actual distance, the galaxy is obviously at essentially the same distance as its companion, NGC 5216, so I have adopted a common distance of 160 million light years for comparison purposes. Given that and its apparent size of 1.85 by 1.0 arcmin, NGC 5218 is about 85 thousand light years across. The overall extent of Keenan's system, including the trails of gas extending between and beyond the pair, is estimated at about 250 thousand light years. (This pair was featured as the Astronomy Picture of the Day for July 2, 2010. Unfortunately, the accompanying description of the system contained a factor of ten error in distances and dimensions. This appears to be the result of an all-too-common propagation of incorrect data across the Internet; but LEDA and NED make it clear that the system is much more distant than usually stated, and even the NOAO site, although giving incorrect dimensions for the system, correctly states that it is well over 100 million light years away. The APoD caption also incorrectly states that Keenan discovered the system. William Herschel was the first to record the nebulae; Keenan discovered the bridge of stellar material connecting the pair.)