Unit 2 Lesson 3 What Are Stars and Galaxies? Copyright © Houghton Mifflin Harcourt Publishing...

Unit 2 Lesson 3 What Are Stars and Galaxies?

Copyright © Houghton Mifflin Harcourt Publishing Company


Florida Benchmark


• SC.5.E.5.1 Recognize that a galaxy consists of gas, dust, and many stars, including any objects orbiting the stars. Identify our home galaxy as the Milky Way.


Twinkling Stars


• Astronomy is the study of objects in space and their characteristics.

• Astronomers are scientists who study astronomy.

• Astronomers use tools such as telescopes to study objects in space.


Twinkling Stars


• Stars are huge balls of hot, glowing gases that produce their own heat and light.

• The sun is the closest star to Earth.

• The sun looks larger than other stars only because it is so close to Earth.

A Star Is Born

• Stars form when gravity causes gas and dust particles in space to pull together.

• The particles are squeezed together. Eventually, they start releasing heat and light.

• Stars are classified by color, temperature, brightness, and size.



A Star Is Born

• How does the brightness, size, and color of the sun compare to other stars in the image below?



Going Galactic


Features of Galaxies

• The universe is everything that exists.

• The universe is full of billions of galaxies.

• A galaxy is a group of billions of stars, the objects that orbit the stars, gas, and dust.


Features of Galaxies

• Our home galaxy is known as the Milky Way.

• Large distances separate galaxies.

• Powerful telescopes help scientists to study galaxies far away.



Types of Galaxies

• Galaxies are classified by their shapes.

• Pinwheel-shaped galaxies are called spiral galaxies.

• Barred spiral galaxies, such as the Milky Way, are spiral galaxies with a center shaped like a long bar.



More Types of Galaxies

• Irregular galaxies do not have a particular shape. The stars are randomly scattered.

• Irregular galaxies have lots of gas and dust to form new stars.

• About 20 percent of all galaxies are irregular.



More Types of Galaxies

• Elliptical galaxies are brightest at their center. They can be shaped like a perfect sphere or a flattened globe.

• Elliptical galaxies have old stars and too little gas and dust to form new stars.

• About 60 percent of all galaxies are elliptical.



Cosmic Crashes

• Sometimes galaxies collide, or crash together, in space.

• Gravity pulls galaxies toward each other. Galaxies are always moving.

• When galaxies collide, large amounts of dust and gas get pressed together.



Cosmic Crashes

• A starburst, or rapid formation of many stars, can happen when galaxies collide.

• Scientists think that many irregular galaxies were once spiral or elliptical galaxies that collided.



Unit 2 Lesson 3 What Are Stars and Galaxies? Copyright © Houghton Mifflin Harcourt Publishing...

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