1. Star Systems and Galaxies
What are the differences between the planets and stars? What are the major types of galaxies?

2. Galaxy: the term derives from Greek and Latin words for milk
Galaxy: the term derives from Greek and Latin words for milk. Our galaxy is called the Milky Way because of its filmy white appearance in the night sky.
star: a giant ball of gas primarily hydrogen and helium.
Planet : an object that orbits a star. Earth is an example of a planet.
What do stars and planets have in common? Both are round astronomical bodies.
What makes up a planet? Some are made of Rocky and metallic materials and others are mostly liquid and gas. Stars and planets have a clear physical relationship with each other in a solar system.
Solar system; A SOLAR SYSTEM contains a star and the planets and other objects that revolve around the star.
Our solar system contains the Sun, Earth, and planets and objects that revolve around the sun. The farthest planet from the sun, Neptune, is 30 times as far away from the sun as Earth.

3. Most stars, are members of groups of two or more stars, called star systems.
How many stars are in our solar system? Just one, the sun.
Star systems that have two stars are called double stars or binary stars. The prefix bi- means two. One star in a binary star system is much brighter and more massive than the other.
Astronomers can detect the dim companion by observing the effects of its gravity. The dim star’s gravity causes the bright star to wobble. Astronomers use the same method to detect planets around other stars.
Larger groupings of stars are called star clusters
A galaxy is a huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity. Galaxies are much larger than solar systems or star systems. Our galaxy is about 100,000 times as big as our solar system.
Stars may be found in clusters. What do all of the stars in the cluster has been,? They formed around the same time, and they’re about the same distance from Earth.

4. Page 101 assess your understanding. Questions 1A,1B,1C.

5. Major types of galaxies
Galaxies can be classified into the following types: spiral, elliptical, irregular, quasar.
Spiral: the arms contain gas, gas and many bright, young stars.
Elliptical : it has many stars packed into a ball shape, but little gas and dust. They look like round or flattened balls. They contain only old stars.
Irregular: it has many bright, young stars and lots of gas and dust
Quasar: an active, young galaxy with a huge black hole at its center.
What holds galaxies together? Gravity.
Gravity is what causes the gas in a nebula to pull together and form a star. It is also what holds Earth in orbit about the sun, and the moon in orbit about Earth.

6. Types of Galaxies at a glance:
Spiral: it has a spiral shape and lots of bright stars. It looks like a pinwheel. Its arms are full of young stars and new ones form there.
Elliptical: it looks like a round ball.
Quasar: it has gas revolving around a black hole.
Irregular: it does not have a regular shape.
Students: Page 103 apply it.

7. Classwork:
Using construction paper draw the four types of galaxies( spiral, elliptical, irregular, quasar ) and mention their differences.