Galaxies are humongous systems of stars and interstellar
matter. Galaxies are located in the billions all throughout the
universe and contain very many stars; these numbers range from the
millions to the trillions. Galaxies like our own, the Milky Way,
can be 100,000 light years in diameter. Imagine how large that is!
A light year is 9,365,829,120,000 kilometers. A galaxy can be, as
said, 100,000 times that figure! There are four different types
of galaxies the universe contains—or the only four types that
have been discovered: spiral, irregular, lenticular and elliptical.
Spiral galaxies, like our own Milky Way, have two main parts to
them: the main, flat disk in the center, with the younger generations
of stars arranged in a spiral pattern emerging from the central
disk. Our galaxy, the Milky Way, has several of these arms spiraling
outward from the central disk: arms such as the Orion Arm, in which
we are located, the Sagittarius Arm and more.
Lenticular galaxies in effect spiral galaxies without any arms emerging
from the center. They appear to be simply flat disks in the sky.
The reason why these galaxies have not become spiral is because
all of the interstellar matter they had in the beginning was used
Therefore, Lenticular Galaxies are mostly if not fully composed
of the older generations of stars. Elliptical Galaxies usually appear
to be either strangely circular or highly eccentric in shape. The
galaxies often seem to be just large masses of stars without a common
center because the stars in these types of galaxies do not rotate
together as a group. Elliptical Galaxies, as Lenticular ones, have
little interstellar matter to create new stars with and are, again,
composed of mostly older generation stars.
Irregular Galaxies, as their name suggests, have no particular shapes
as the spiral or Lenticular Galaxies do. This is due to the many
neighboring celestial objects that exert a gravitational pull on
these galaxies making them irregular. For example, it’s as
if you were to take a nice round piece of dough and started pulling
on all sides of it, top and bottom as well; you would receive a
total irregular mess.
Some galaxies float through space by themselves and are lonely wanderers.
But many galaxies occur in large groups in which they create large
gravitational fields that alter the galaxies’ appearances.
The numbers of galaxies in a cluster could range from a few to a
dozen to several thousand. Galaxies are majestic objects that will
forever mystify the imaginations of human beings everywhere.