Download 15-3 Notes: Galaxies

15-3 Notes: Galaxies
Large groups of stars, dust, and gas are called galaxies. Galaxies come in a variety
of sizes and shapes. The largest galaxies contain more than a trillion stars.
Astronomers classify a galaxy as a spiral, elliptical, or irregular galaxy according to
its shape.
Spiral galaxies, such as the Andromeda galaxy, have a bulge at the center and spiral
arms. The spiral arms are made up of gas, dust, and new stars that have formed.
The galaxy in which we live is a spiral galaxy called the Milky Way. The Milky
Way consists of about 200 billion stars, including the sun. The sun is located about
two-thirds of the way between the center of the galaxy and the galaxy’s edge.
Because most elliptical galaxies are round or oval, they can be thought of as
“cosmic snowballs.” Some elliptical galaxies are slightly flattened. Elliptical
galaxies are among the largest in the galaxies in the universe.
Irregular galaxies are galaxies that have no definite shape. The smallest irregular
galaxies have only about 10 million stars. The largest irregular galaxies can contain
several billion stars.
Galaxies contain not only stars and planetary systems. Large features, such as gas
clouds and star clusters are also located within galaxies.
In space, nebulas are large clouds of gas and dust that are the birthplaces of stars.
Some nebulas glow, others absorb light and hide stars, while others reflect starlight.
A globular cluster is a highly concentrated group of stars that looks like a ball. All
of these stars formed at the same time from the same nebula and orbit a galaxy as a
group. Globular clusters are located in a spherical halo that surrounds spiral
galaxies, such as the Milky Way.
Open clusters are groups of 100 to 1,000 stars that are close together relative to
other stars. They are usually located along the disk of a spiral galaxy. All of the stars
in an open cluster formed at the same time from the same nebula.
Quasars are among the most distant objects in the universe. They are starlike sources
of energy that are located in the center of galaxies. Quasars are among the most
powerful energy sources in the universe and may be caused by massive black holes.
Unit 7 (Ch. 15) – Earth in the Solar System
Bach
04/02/10
Section 15-3 Review
1. What are the main components of galaxies?
Stars, gas, and dust.
2. What are two characteristics of a spiral galaxy?
Spiral galaxies have a bulge in the center and spiral arms. The spiral
arms are made of gas, dust, and stars.
3. What type of galaxies are round or egg-shaped?
Elliptical galaxies.
4. What type of galaxy is the Milky Way galaxy?
A spiral galaxy.
5. Where is the sun located in the Milky Way?
The sun is located about two-thirds of the way between the center and
the edge of the galaxy.
6. What is a nebula?
A nebula is a large cloud of gas and dust that is the birthplace of stars.
7. Where is a globular cluster most likely to be found?
Globular clusters are most likely to be found in the spherical halo
around spiral galaxies or near giant elliptical galaxies.
8. How do quasars differ from galaxies?
Galaxies are large groups of stars, dust, and gas that have different
shapes and sizes.
Quasars are starlike sources of energy that generate energy at a high
rate. They are located in the cores of distant galaxies and may be
caused by massive black holes.
Unit 7 (Ch. 15) – Earth in the Solar System
Bach
04/02/10
15-3 Notes: Galaxies
Large groups of stars, dust, and gas are called ____________. Galaxies come in a
variety of sizes and _________. The largest galaxies contain more than a _________
stars. Astronomers classify a _________ as a spiral, elliptical, or irregular galaxy
according to its _________.
__________ galaxies, such as the Andromeda galaxy, have a bulge at the center and
spiral arms. The spiral arms are made up of ______, dust, and new ________ that
have formed.
The galaxy in which we live is a spiral galaxy called the ________ ______. The
Milky Way consists of about _______________ stars, including the sun. The _____
is located about two-thirds of the way between the center of the galaxy and the
galaxy’s edge.
Because most _______________ galaxies are round or oval, they can be thought of
as “cosmic snowballs.” Some elliptical galaxies are slightly _______________.
Elliptical galaxies are among the ____________ in the galaxies in the universe.
________________ galaxies are galaxies that have no definite shape. The
____________ irregular galaxies have only about 10 million stars. The __________
irregular galaxies can contain several billion stars.
____________ contain not only stars and planetary systems. Large features, such as
gas clouds and star ____________ are also located within galaxies.
In space, __________ are large clouds of gas and dust that are the birthplaces of
stars. Some nebulas ________, others absorb light and hide stars, while others
reflect ______________.
A ____________ ____________ is a highly concentrated group of stars that looks
like a ball. All of these stars formed at the same time from the same __________
and orbit a galaxy as a group. Globular clusters are located in a spherical ________
that surrounds spiral galaxies, such as the __________ _______.
________ ___________ are groups of 100 to 1,000 stars that are close together
relative to other stars. They are usually located along the _______ of a spiral galaxy.
All of the stars in an open cluster formed at the same time from the same ________.
__________ are among the most distant objects in the universe. They are starlike
sources of _________ that are located in the _________ of galaxies. Quasars are
among the most powerful _________ sources in the universe and may be caused by
massive _________ holes.
Unit 7 (Ch. 15) – Earth in the Solar System
Bach
04/02/10
Section 15-3 Review
1. What are the main components of galaxies?
2. What are two characteristics of a spiral galaxy?
3. What type of galaxies are round or egg-shaped?
4. What type of galaxy is the Milky Way galaxy?
5. Where is the sun located in the Milky Way?
6. What is a nebula?
7. Where is a globular cluster most likely to be found?
8. How do quasars differ from galaxies?
Unit 7 (Ch. 15) – Earth in the Solar System
Bach
04/02/10