Bellringer Stars are classified by properties such as temperature, color, size, absolute brightness, and apparent magnitude. Some of these factors are directly related. Which of the following factors is most directly related to the temperature of a star? Apparent magnitude color Life cycle stage size

Bellringer 2. Uri looks through a telescope for two stars. He knows that both stars have the same absolute brightness and that the second star is twice as far from Earth as the first star. How bright will the second star appear compared to the first star? It will appear brighter than the first star. It will appear dimmer than the first star. It will appear as bright as the first star. It will appear redder than the first star.

Bellringer 3. Stars seem to be made up of similar chemical elements. Which characteristics are used to differentiate among stars? Size, age, and speed of revolution Age, speed of rotation, and color Weight, age, and temperature Age, temperature, and size

Benchmark C – voice level 0 H – raise hand for teacher A – guided notes M – none P – independent Benchmark SC.8.E.5.5 Describe and classify specific physical properties of stars: apparent magnitude (brightness), temperature (color), size, and luminosity (absolute brightness). Essential Questions What relationship exists between the temperature and brightness of most stars? * What relationship exists between the solar radius and brightness of most stars? * What is the difference between the apparent magnitude and absolute brightness of a star? How is the Hertzsprung-Russell Graph used to classify and compare stars? 4

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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. 6

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. 7

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. 8

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. 9

What is a star? The sun’s atmosphere has several layers and extends millions of kilometers into space. The photosphere is the layer of the sun’s atmosphere we see from Earth. It has an average temperature of 5,527 °C. Energy is transferred from the sun’s core to the photosphere and escapes into space as visible light, other forms of radiation, heat, and wind. 10

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. 11

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. 12

How is star luminosity measured? Stars with the same absolute magnitude may have different apparent magnitudes. 13

Too Hot to Handle How are the surface temperatures of stars measured? Stars have different colors. The differences in the colors of stars are due to differences in their surface temperatures. The same is true of all objects that glow. 14

How are the surface temperatures of stars measured? If an object’s color depends only on temperature, the object is called a blackbody. As the temperature of a blackbody rises, it glows brighter and brighter red. As it gets hotter, its color changes to orange, yellow, white, and blue-white. 15

How are the surface temperatures of stars measured? Stars that have the lowest surface temperatures (below 3,500 °C) are red. Stars that have the highest surface temperatures (above 25,000 °C) are blue. 16

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. 17

How are the sizes of stars measured? Very small stars, called white dwarfs, have about the same radius as Earth, which is approximately 0.01 solar radius. 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. 18

How are the sizes of stars measured? Compare the sizes and temperatures of the red, blue, and yellow stars. Stars can be classified based on their color and luminosity. The color tells us the temperature of the star. The luminosity tells us how bright the star is, which can help us identify the size of the star and the distance. 19

HR Diagram Investigation Worksheet C – level 1 H – raise hand and wait for teacher A- HR diagram assignment M – remain in seat P- ind. or group assistance HR Diagram Investigation Worksheet

Bellringer CYU Stars are classified by properties such as temperature, color, size, absolute brightness, and apparent magnitude. Some of these factors are directly related. Which of the following factors is most directly related to the temperature of a star? Apparent magnitude color Life cycle stage size

Bellringer CYU 2. Uri looks through a telescope for two stars. He knows that both stars have the same absolute brightness and that the second star is twice as far from Earth as the first star. How bright will the second star appear compared to the first star? It will appear brighter than the first star. It will appear dimmer than the first star. It will appear as bright as the first star. It will appear redder than the first star.

Bellringer CYU 3. Stars seem to be made up of similar chemical elements. Which characteristics are used to differentiate among stars? Size, age, and speed of revolution Age, speed of rotation, and color Weight, age, and temperature Age, temperature, and size

Stations Station 1: Station 2: Station 3: Station 4: Herztsprung-Russell diagram Station 2: Penda – “Star Properties” Station 3: Modeling Star Magnifier LAB Station 4: Achieve 3000 – “Starry, Starry Night” C – voice level 1 H – raise hand and wait for teacher A – assigned station assignment M – only when rotating to new station P – independent of group assistance

Wrap Up What relationship exists between the temperature and brightness of most stars? * What relationship exists between the solar radius and brightness of most stars? * What is the difference between the apparent magnitude and absolute brightness of a star? How is the Hertzsprung-Russell Graph used to classify and compare stars?

Exit Ticket C – voice level 0 H – raise hand and wait for teacher A – exit ticket M – remain in seat P - independent