1. Stars and Galaxies

2. Gravitational Pull-Key Terms Mass- the amount of atoms inside an object. Mass does not change. Weight- the pull of gravity on the mass of an object. Weight changes depending on gravity. Gravity- the force that attracts one physical object to another.

3. Gravitational Pull All objects with mass have gravity. Large objects have a higher gravitational pull. Large= More Gravitational Pull Small= Less Gravitational Pull

4. Gravitational Pull Distance also impacts the amount of gravitational pull an object has. The closer 2 objects are together the higher the gravitational pull. Example- The Earth and Sun have a higher force of gravity than the Sun and Neptune.

5. Gravitational Pull  Which of the following has the most gravitational pull with the Sun? Mars or Pluto  Which scenario describes the star and planet with the largest gravitational force? Each star has the same mass. 1. Planet A- Distance=2 Size=2 2. Planet B- Distance=1 Size=2 3. Planet C- Distance=2 Size=1

6. What Makes Up the Universe? Star- a ball of mostly hydrogen and helium gas that shines extremely brightly. The sun is an example of a star. Clusters- a large group of stars that were formed at about the same time. Galaxy- a huge group of single stars, star systems, star clusters, and dust bound together by gravity. Galactic Cluster- a group of galaxies bound by gravity. This is the largest known gravitationally bound object in the universe.

7. Size Comparison Star  Star Cluster  Galaxy  Galactic Cluster

8. Stars Stars are classified by color, temperature, composition, and brightness.

9. Classifying Stars (Color and Temperature) The color of a star helps Astronomers predict the temperature of a star.  Red Stars- Temperature 3,200 Celsius  Yellow Stars- Temperature 5,500 Celsius  Blue Stars- Temperature 20,000 Celsius

10. Classifying Stars (Size) The largest stars are called giant stars or supergiant stars. Stars about the size of our sun are considered to be medium sized stars. White dwarfs and neutron stars are both smaller than our sun.

11. Classifying Stars (Chemical Composition) Stars vary in their chemical composition. Most stars are made up of the following: 73% Hydrogen 25% Helium 2% Various Elements.

12. Classifying Stars (Brightness) The brightness of a star depends on its size and temperature. Apparent Brightness- a star’s brightness as seen from Earth. Absolute Brightness- is the brightness a star would have if it were at a standard distance from Earth.

13. Galaxies There are 3 types of galaxies. 1. Spiral Galaxies- -Bulge in middle -Arms that spiral outward -Ex. Milky Way 2. Elliptical Galaxies -Shaped like a ball -Contain old stars 3. Irregular Galaxies -Do not have a regular shape -Contain large amounts of dust and gas

14. The Solar System, The Milky Way, and The Universe The Sun and the planets that we are familiar with are considered to be our solar system. The Sun is the center of our solar system. Our solar system is located in one of the spiral arms extending from the Milky Way Galaxy.

15. The Solar System, The Milky Way, and The Universe Our solar system is located in a spiral galaxy called the Milky Way. From the side, the Milky Way resembles a disk with a bulge in the middle. From the top, the Milky Way resembles a pin wheel (spiral shape).

16. The Solar System, The Milky Way, and The Universe The Universe is defined by astronomers as all of space and everything in it. The Milky Way is one of billions of galaxies in the Universe.

17. Checking Understanding List the following in order from smallest to largest. Galaxies, Galactic Clusters, Stars, Clusters 1. 2. 3. 4.

18. Checking Understanding List the following in order from smallest to largest. The Universe, the Solar System, the Milky Way Galaxy 1. 2. 3.