Unit 2 Lesson 3 What Are Stars and Galaxies?
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
A Star Is Born
• How does the brightness, size, and color of the
sun compare to other stars in the image below?
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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Unit 2 Lesson 3 What Are Stars and Galaxies?
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.
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