Transcript The Discovery of Galaxies

The Discovery of
Galaxies
GALAXIES
A galaxy is a massive group of stars, gas and dust
all held together by gravity. Galaxies contain
upwards to 100 billion stars. To fully grasp the
concept of what a galaxy is, think of this:
Earth  Solar System  Milky Way Galaxy
Earth is a planet in our solar system. Our solar
system is one of many in the Milky Way Galaxy.
The Milky Way Galaxy is one of many in the
Universe.
THE MILKY WAY
In the summer, you may have seen a hazy white
band in the sky, similar to a group of clouds.
In fact, you have seen the Milky Way (well, actually
only a portion of it). This band occupies about
400 billion stars, including our Sun.
THE MILKY WAY
THE MILKY WAY
THE MILKY WAY
THE MILKY WAY
THE MILKY WAY
The Milky Way is 75 000 light years in diameter.
The nearest galaxy to us is 2.5 million light years
away.
It is a spiral galaxy because of its shape. The Sun
is located near the outer part of the spiral.
STAR CLUSTERS
Open Clusters – collections of 50 to 1000 stars.
ex. Pleiades
Globular Clusters – collections of 100 000 to one
million stars arranged in a
sphere.
ex. Hercules
PLEIADES
HERCULES
TYPES OF GALAXIES
There are 3 types of galaxies:
- elliptical (like a football)
- spiral (like a pinwheel)
- irregular (like something not regular…)
ELLIPTICAL
SPIRAL
IRREGULAR
ANDROMEDA
The closest galaxy to us is called Andromeda. It is
actually visible with the naked eye!
Discovered by Edwin Hubble in 1925, he spotted
individual stars in a nebula, and realized that he
wasn’t looking at a cloud of gas or dust, but
another entire galaxy!
ANDROMEDA
GALAXY CLUSTERS
Galaxies exist in clusters. The Milky Way and
Andromeda are 2 of 30 galaxies that make up a
cluster known as the Local Group. These groups
are organized into superclusters.
Figure 15.12 shows the distinction between these
terms.
GALAXY CLUSTERS
GALAXY CLUSTERS