Types of Glaxies

Introduction to Galaxy

Astronomy 2023

What makes up the universe?

• A galaxyis a large collection of stars,

gas, and dust held together by gravity.

• Small galaxies, called dwarf galaxies,

may contain a few billion stars. Giant
galaxies may contain hundreds of
billions of stars.

What makes up the universe?

• Our solar system is located

in the Milky Way galaxy.
The Milky Way is classified
as a spiral galaxy.

What makes up the universe?

Types of Galaxies

• Spiral galaxies are shaped like pinwheels. They

have a central bulge from which two or more
spiral arms extend.

Spiral Galaxy

1.
The most common type of galaxy is called a "spiral
galaxy."

2.
Not surprisingly, spiral galaxies look like spirals,
with long “arms” winding toward a bright bulge at
the center.

3.
About 77% of the observed galaxies in the universe
are spiral galaxies.

4.
Our own galaxy, the Milky Way, is a typical spiral
galaxy

Types of Galaxies

• Elliptical galaxies look like spheres or ovals and

do not have spiral arms.

Elliptical Galaxies

● They are generally round but stretch longer along one

axis than along the other.

● Elliptical galaxies contain many older stars, up to one

trillion, but little dust and other interstellar matter.

● The universe's largest known galaxies are giant

elliptical galaxies, which may be as much as two
million light-years long.

Type of Galaxies

• Irregular galaxies appear as splotchy,

irregularly shaped “blobs.” They are very active
areas of star formation.

Irregular Galaxies

● Approximately 3% of galaxies

observed cannot be classified as
either ellipsoidal or spirals.

● These galaxies have little symmetry

in their structure and are termed
irregular galaxies.

Lenticular Galaxy

● Lenticular galaxies are disc galaxies (like

spiral galaxies) which have used up or lost
most of their interstellar matter and therefore
have very little ongoing star formation.

● As a result, they consist mainly of aging stars

and will produce the least amount of stars.

How are distances in the universe measured?

• Distances between most objects in the universe are so large

that astronomers measure distances using the speed of light.

• A light-year is the distance that light travels through space

in one year.

• Light travels through space at about

300,000 km/s, or about 9.5 trillion kilometers in one year.

Unit 1Lesson 1 Structure of the Universe

How are distances in the universe measured?

Unit 1Lesson 1 Structure of the Universe

• The universecan be defined as space and all the

matter and energy in it.

• Throughout the universe, there are areas where galaxies

are densely concentrated.

• These areas are called clusters and superclusters.

• Clusters contain as many as several thousand galaxies.

• Superclusters can be made up of 10 or more clusters of

galaxies.

What is the structure of the universe?

• The universe also contains huge spherical areas

where very little matter exists. These areas are
called voids.

• Astronomers have begun to think of the universe as having a

structure similar to soap bubbles.

• Clusters and superclusters are located along the thin bubble

walls.

• The interior of the bubbles are voids. It takes light hundreds of

millions of years to cross the largest voids.