324 The Poetry of Physics and The Physics of Poetry
a tiny component of a system orbiting a nucleus, which has much more
mass. We begin with the electron orbiting the nucleus of the atom. But
once we jump to large aggregates of matter in space we find a similar
structure. Moons orbit planets and planets orbit stars. Stars, which are
members of a galaxy orbit the nucleus of the galaxy, which as we have
discovered is almost always composed of a supermassive black hole. The
sun orbits the center of the Milky Way galaxy every 225 to 250 million
years. In addition to the stars orbiting the center of a galaxy there are
satellite galaxies that orbit still larger galaxies. The Milky Way galaxy
has two smaller satellite galaxies the Large and Small Magellanic Clouds
and several dwarf galaxies that orbit it in a structure self-similar to our
solar system. Our galaxy belongs to the Cluster of galaxies known as the
Local Group with a gravitational center somewhere between the Milky
Way and Andromeda galaxies. Finally The Local Group Cluster is part
of the Virgo Supercluster, which has two-thirds of its galaxies in an
elliptical disk and one-third in a spherical halo. The pattern of smaller
objects orbiting a central nuclear mass is repeated over and over again in
our restless universe and that, my readers, is still another example of the
Poetry of Physics.