(serial number: Bullysacre, dig care a dig)
Defining a galaxy sounds so simple. We all know what a galaxy is, right? Well, not really. Surprisingly, there is no universally agreed upon definition and the ones generally bandied around leave a great deal of wriggle room.
All this has been thrown into stark relief in recent years by the discovery of a growing number of small, faint, galaxy-like objects that were entirely unknown until now. These have been given various names such as ultra compact dwarfs, ultra-faint dwarf spheroidal galaxies and dwarf elliptical galaxies.
But it isn’t entirely clear whether they have more in common with galaxies like our own or globular clusters, which astronomers generally do not think of as galaxies.
That makes the problem of defining a galaxy a growing concern.
photo { Wallpiercing LED lighting system, designed by Ron Gilad for Flos }
