Galaxies Lesson

Galaxies

This fuzzy band of light in the night skys is the Milky Way, our Galaxy

Galileo discovered that the light in it is actually stars.

What is a Galaxy?

What Is a Galaxy?

Galaxies are huge clusters of stars, gas, and dust bound by the force of gravity. Galaxies can contain billions of stars and are quite massive in size! For example, Andromeda, a nearby galaxy similar to the Milky Way, measures an astounding 1,290,000,000,000,000,000 miles across!

Light Years

• Distances in space are so large that it makes calculations using ordinary units of measurement, such as miles or kilometers, impractical. As a result, scientists defined a unit of measure, called the light year, to determine distances in space. A  light year is the distance light travels through space in one earth year. Light travels through space at a speed of 186,000 miles per second.

• Something that is one light year away is about 5,866,000,000,000 miles away. Alpha Centauri is one of the closest stars to Earth. It is about four light years away.

The Shapes of Galaxies

Galaxies are huge, yet they are very unique, and there are billions of them in the universe. Galaxies are different ages, sizes, and distances from Earth. Astronomers classify galaxies by shape: spiral, elliptical, and irregular.

Spiral Galaxies

• Called this because they appear to form a spiral shape

• Stars are still forming in these types of galaxies

• One of the more common types of galaxies

Spiral Galaxies

get their name for their arms of gas, dust, and stars that spiral out from a densely packed cluster of stars in the center. Spiral galaxies typically have a mix of stars, some young and some old.

The Milky Way

The Milky Way is a special type of spiral galaxy, called a barred-spiral galaxy. Barred-spiral galaxies have a thick bar of stars and gas passing through their centers. From Earth, the fuzzy white band of the Milky Way doesn’t look like a spiral; it looks like a stripe. That is because you are looking at the Milky Way sideways, from inside one of its spiral arms.

Multiple Choice

What type of galaxy is the Milky Way?

• Spiral

• Elliptical

• Irregular

• Transition

Elliptical Galaxies

An elliptical galaxy has a shape like a stretched circle, or oval. Elliptical galaxies usually include only old stars. This is because they contain little gas or dust.

Elliptical Galaxies

• Seem to be older

• Stars formation is no longer occurring

• Lack dust and gas

• Might be the result of galaxies colliding

Irregular Galaxies

As their name suggests, irregular galaxies have no distinct or orderly shape. Many new stars are born in irregular galaxies. This is because these galaxies contain far more gas and dust than elliptical or spiral galaxies.

Irregular

• Usually smaller

• Believed to form for 2 reasons - too small to form into a structure, or a massive collision caused them to lose their structure

Black Hole

a region in space where it is theorized that no mass or light can escape

The speed of a galaxy

The sun circles the center of the Milky Way at a speed of about a half a million miles an hour. Even at that rate, it takes the sun more than 200 million years to make one complete orbit Opens in modal popup windowaround the center of the galaxy!

Holding it all together

How do each of these gigantic galaxies stay clumped together? What keeps everything in the universe from spinning out into space? The law of universal gravitation holds each galaxy together. This same force causes you to return to the ground after you jump into the air. In the next lesson, you will learn more about the force of gravity

Open Ended

What are the different types of galaxies?

Multiple Choice

One of the more common types of galaxies which have stars still forming within them are...

• Elliptical

• Spiral

• Irregular

• Transition

Multiple Choice

This type of galaxy is generally considered to be older and is no longer forming stars.

• Spiral

• Irregular

• Elliptical

• Transition Galaxies

Multiple Choice

What type of galaxy is this?

• Spiral
• Elliptical
• Irregular 
• Irrational

Multiple Choice

A flat, disk-shaped galaxy with a central bulge and winding "arms" that extend outward.

• irregular galaxy

• spiral galaxy

• elliptical galaxy

• random galaxy

Multiple Choice

The type of galaxy that is composed of the older stars and low-mass stars.

• Spiral
• Elliptical
• Irregular
• Constellation

Match

Match the following terms with their definitions

• Galaxy

• Star

• Universe

A large grouping of stars, planets, gas, and dust in space held together by gravity.

A self-luminous celestial body consisting of a mass of gas held together by its own gravity.

All space and the matter space contains.

• A large grouping of stars, planets, gas, and dust in space held together by gravity.

• A self-luminous celestial body consisting of a mass of gas held together by its own gravity.

• All space and the matter space contains.