Astronomy I Test Study Guide: Chapter 28 Stars and Chapter 26 Sun
Know the following for the test:
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Ptolemy was the astronomer known for first endorsing the Geocentric Model = Earth Center.
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Copernicus was the astronomer known for first endorsing the Heliocentric Model = Sun Center.
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Absolute Magnitude is used to compare the brightness of stars.
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Understand the Big Bang Theory – ball of hydrogen exploded, the hydrogen cloud moved outward with
parts of the cloud condensing into galaxies. Galaxies continue to move outward into space, away from
Earth – red shift. This theory was proposed by American astronomer Edwin Hubble.
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A galaxy is a system that contains millions to billions of stars. Our galaxy is called the “milky way”
galaxy and its shape is known as a spiral galaxy, more specific known as a “barred spiral”. The “milky
way” galaxy contains our solar system.
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Understand the H-R Diagram – know the groups of stars, locations, and characteristics of the four
groups of stars. Identify the temperature, spectral class, and absolute magnitude axis. Identify the
position of the Sun on the diagram. Study the H-R Diagram from your star quiz.
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Constellations are stars that form patterns in the night stars. Some constellations are visible all year
long, they change position in the night sky during the year due to the Earth revolving around the Sun.
These constellations are called circumpolar constellations. Some constellations like Orion are only
visible in certain seasons – fall/winter. Constellations are helpful with direction in the night sky –
Polaris = North Star.
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A nebulae is a cloud of gas and dust in space that forms stars. Stars are made of hydrogen and helium.
Stars “shine” due to converting Hydrogen into Helium which is a process called nuclear fusion. Light
years are used to measure distance between stars.
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Know the life cycle of an average star and a massive star:
Nebula  Protostar Main Sequence small/average star Giant  White Dwarf
large star Supergiant  Neutron Star
 Black Hole
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The Hubble telescope has an advantage over a ground based telescope due no interference with Earth’s
atmosphere, allows the telescope to produce clear pictures of stars and other objects in space.
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The corona is the hottest layer of the sun and only seen during a total solar eclipse.
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Understand Hubble Law – stars moving to Earth have a blue shift, traveling at a slower speed. Stars
moving away from Earth have a red shift, traveling at a faster speed.
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Scientist use a spectroscope to study stars chemical composition – the elements that make up a star.
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The age of the universe is estimated to be about 13.8 billion years of age, our solar system is estimated
to be 5 billion years old, making our solar system a third generation solar system.
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As we speak today, we continue to have a cosmological red shift – galaxies are moving away from each
other in our expanding universe.
Notes: