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Unit 2 Lesson 2 Stars
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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.
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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).
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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.
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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.
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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.
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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.
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Unit 2 Lesson 2 Stars
How is star luminosity measured?
• Stars with the same absolute magnitude may
have different apparent magnitudes.
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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.
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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.
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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