In the 1920s Edwin P. Hubble, the astronomer for whom the space telescope is named, realized
that the mysterious objects outside the Milky Way were also galaxies. Of the billions that
exist, galaxies take three basic forms: spiral, like our Milky Way, the Cartwheel,
and NGC 1365 (at left); elliptical, such as
M87 in the constellation Virgo;
or irregular, like the Large Magellanic Cloud.
Some 50 million light-years beyond us is the Virgo cluster, comprising 3,000 separate known
galaxies. Near the edge of the universe, more than 11 billion light-years away, are quasars,
high-energy sources of light just now reaching us. That light may emanate from the cores of galaxies.