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Unit 2 Lesson 2 Stars Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars Florida Benchmarks • SC.8.N.1.6 Understand that scientific investigations involve the collection of relevant empirical evidence, the use of logical reasoning, and the application of imagination in devising hypotheses, predictions, explanations and models to make sense of the collected evidence. • SC.8.N.3.1 Select models useful in relating the results of their own investigations. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars Florida Benchmarks • SC.8.E.5.5 Describe and classify specific physical properties of stars: apparent magnitude (brightness), temperature (color), size, and luminosity (absolute brightness). Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars Reach for the Stars! What is a star? A star is a large celestial body that is composed of gas and emits light. • Stars are made mostly of hydrogen and helium. They also contain other elements in small amounts. • Stars emit light and vary in brightness. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars What is a star? When we say an object is in orbit, we mean that it is traveling around another object in space. Planets in a solar system orbit a star. Copyright © Houghton Mifflin Harcourt Publishing Company What is a star? • The temperatures of stars vary, resulting in differences in color. • Stars range in color from red, which indicates a cool star, to blue, which indicates a very hot star. • The sun is a relatively cool yellow star. Unit 2 Lesson 2 Stars What is a star? • Stars have different sizes, ranging from 1/100 the size of the sun to 1,000 times the size of the sun. • Two or more stars may be bound together by gravity, which causes them to orbit each other. • Three or more stars that are bound by gravity are called multiple stars or multiple star systems. The largest object in our solar system is the sun, which is a medium sized star. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars What is a star? • The sun is a star and is composed mostly of hydrogen and helium. It also contains oxygen, carbon, neon, and iron. • At the center of the sun lies the core, where gases are compressed and heated and temperatures reach 15 million degrees Celsius. • The sun’s core is where matter is converted into energy. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars You’re a Shining Star How is star brightness measured? Apparent magnitude is the measure of a star’s brightness as seen from Earth. • Ancient astronomers, using only their eyes, described star brightness by magnitude. • They called the brightest stars they could see first magnitude and the faintest stars they could see sixth magnitude. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars How is star brightness measured? • Astronomers used telescopes see many stars that are too dim to see with the unaided eye. They added to the magnitude system. • Today, the brightest stars have a magnitude of about –2, and the faintest stars that we can see with a telescope have a magnitude of +30. • Dim stars have positive (larger) numbers, and bright stars have negative (smaller) numbers. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars How is star luminosity measured? When astronomers use the word luminosity, they mean the actual brightness of a star. They measure it on a scale called absolute magnitude. Absolute magnitude is a measure of how bright a star would be if the star were located at a standard distance. • Absolute magnitude is a measure of the brightness of a star whose distance from Earth is known. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars How is star luminosity measured? • Stars with the same absolute magnitude may have different apparent magnitudes. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars How are the sizes of stars measured? • Stars differ greatly in size. • Some are about the same size as Earth, and others are larger than the size of Earth’s orbit around the sun. • Astronomers use the size of the sun to describe the size of other stars. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 2 Stars How are the sizes of stars measured? Solar radius is the unit used to express the size of stars. • Very small stars, called white dwarfs, have about the same radius as Earth, which is approximately 0.01 solar radius. Copyright © Houghton Mifflin Harcourt Publishing Company How are the sizes of stars measured? • Very large stars, called giant stars, typically have sizes between 10 and 100 times the sun’s radius. • Some rare, extremely large stars have sizes of up to 1,000 solar radii. They are called supergiants. The objects of space in order from largest to smallest are: universe, galaxy, star, planet