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Name: _____________________________________
Date: ________________ Period: ___
SPACE SCIENCE Reading Review
The universe is estimated to be over 10 billion years old. The universe is composed of galaxies,
stars, planets, asteroids, comets, and meteors, each having different properties. Our solar system
exists within the Milky Way galaxy. The known components of our solar system are the Sun,
four terrestrial planets (Mercury, Venus, Earth, Mars), four gas giants (Jupiter, Saturn, Uranus,
Neptune), Pluto (one of the three dwarf planets), as well as numerous moons, comets, asteroids,
and meteors. Each of these celestial objects has its own unique characteristics.
1. How old is the universe? ______________________________________
2. True or False. Asteroids and comets have the all same physical properties. ___________
3. List the components of our solar system: Our star, the ____________________, Four
terrestrial planets  ______________________________________________________,
Four gas giants  _______________________________________________________,
Dwarf planets such as ______________, and other celestial objects such as __________,
_________________, ________________________, and _____________________.
The universe, all of space and everything in it, contains billions and billions of stars and galaxies.
A galaxy is a giant structure that contains hundreds of billions of stars. Galaxies have been
classified into three main categories based mainly on shape: spiral, elliptical, and irregular.
Spiral galaxies consist of a central nucleus of bright stars and flattened arms of stars that spiral
around the nucleus. The spiral arms contain millions of young stars, gas, and dust. Elliptical
galaxies vary in shape from nearly spherical to flattened disks. They are different from spiral
galaxies in that they do not have spiral arms. This indicates that elliptical galaxies have no
young stars and contain very little gas and dust. Finally, irregular galaxies do not have any
particular shape. Irregular galaxies have young stars and a lot of gas and dust. Irregular galaxies
tend to be smaller and fainter than other types of galaxies and appear to have an uneven
distribution of stars throughout the galaxy.
4. What is the definition of the universe? ________________________________________
5. How many galaxies in the universe? __________________________________________
6. How many stars are in galaxies? _____________________________________________
7. Define a galaxy. __________________________________________________________
8. By which characteristic are galaxies classified? _________________________________
9. What are the three main categories of galaxies? _________________________________
10. Fill in the chart with the correct characteristics of each type of galaxy.
Draw shape
Types of stars
A lot or a little
Other
(young or old)
Gas and dust
characteristics
Spiral
Elliptical
Irregular
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Our solar system is a just a small speck within the Milky Way Galaxy. The Milky Way Galaxy
is a spiral galaxy. The Milky Way Galaxy has a diameter of about 100,000 light years, with the
sun being located about 30,000 light-years from the center of the galaxy.
11. What type of galaxy is the Milky Way? _____________________________
12. Draw the milky way galaxy.
13. True or False. Our solar system is located in the center of the Milky Way galaxy.
_______________
Stars are huge spheres made mostly of gasses and can produce their own light. Light is released
as a result of nuclear fusion in the core of stars. Astronomers classify stars according to their
size, temperature, and brightness. A star’s temperature is indicated by its color. Cooler stars
appear red in the night sky and hotter stars appear blue. Brightness, the amount of light stars
give off, varies from star to star. How bright a star looks from Earth depends on both how far the
star is from Earth and how bright the star actually is. Apparent magnitude is how bright a star
appears from Earth whereas absolute magnitude is how bright a star would appear if it were a
standard distance from the earth. A star’s temperature and brightness can be plotted on a graph
known as the Hertzsprung- Russell Diagram.
14. What are stars made of? ___________________________________________________
15. What do stars produce? ________________________
16. How are three ways stars are classified? _______________________________________
___________________________________________________________________________
17. What color are cool stars? _________________________
18. What color are the hottest stars? _____________________________
19. True or False. Every star gives off the same amount of brightness. _____________
20. What characteristics of a star are plotted on the Hertzsprung Russell Diagram?
________________________________________________________________________
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A collection of planets, moons, asteroids, comets, and meteoroids orbiting around a central star is
known as a solar system. None of these objects except the star can produce its own light. The
closest star to Earth is the sun, the center of our solar system. Its mass makes up 99.8% of the
total mass in the solar system. Due to its size, the sun’s gravitational pull is strong enough to
hold all of the planets and celestial bodies in orbit. Like Earth, the sun has an interior and an
atmosphere. The interior of the sun, the core, acts like a giant furnace releasing energy from
nuclear fusion. The temperature inside the sun’s core can reach up to 15 million degrees Celsius.
The sun’s atmosphere is divided into three layers: the photosphere, chromosphere, and corona.
On the photosphere, there are darker areas where the gases are cooler than the surrounding gases.
These areas are called sunspots. These sunspots usually occur in pairs or groups. Prominences
are reddish loops of gases that connect two sunspots. Occasionally, when these loops connect,
there are explosions of gases called solar flares. This can cause fluctuations in our weather and
radio communications on Earth.
21. What is a solar system? ___________________________________________________
_________________________________________________________________________
22. What is the only celestial object that can produce light? _________________________
23. What is the closest star to Earth? ___________________
24. What is in the center of the solar system? ___________________________
25. What holds all the planets, asteroids and comets in orbit around the Sun? ____________
26. What is the temperature of the sun’s core? _____________________________________
27. What are the darker spots on the outside of the sun’s photosphere called where gases are
cooler? __________________________
28. What can cause changes in our weather and radio communications on Earth?
_______________________________
The four inner planets, Mercury, Venus, Earth and Mars, are more similar to each other than they
are to the four outer planets. They are called the terrestrial planets because they are smaller and
have rocky surfaces. The word terrestrial comes from the Latin root word terra, which means
“Earth.” Unmanned space missions have collected data regarding conditions on Mercury,
Venus, and Mars. The probe Mariner10 photographed Mercury in 1974. Most of what we know
about Venus comes from data collected by the Megellan probe in 1990. Various missions to
Mars, such as Pathfinder in 1997, have collected data utilizing a remote-control rover called
Sojourner. Evidence from these space missions indicates that terrestrial planets are similar in
that they all show evidence of geologic activity such as volcanoes.
29. List the four inner planets. __________________________________________________
30. What is another name for the inner planets? ____________________________________
31. True or False. Unmanned space mission indicate that the terrestrial planets are very
similar to each other. ___________________
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The four outer planets (Jupiter, Saturn, Uranus, and Neptune) are known as the “gas giants,”
because they are much larger than Earth and are made almost entirely of gases. Since the gas
planets have so much mass compared to the inner planets, they exert a much stronger
gravitational force. Pluto is considered a dwarf planet. Most of what is known about the outer
planets has come from observations by the NASA space probes Voyager 1 and Voyager 2.
32. List the four outer planets. __________________________________________________
33. What is another name for the outer planets? ____________________________________
34. List three ways the outer planets are different from earth.
a. __________________________________________________________________
b. __________________________________________________________________
c. __________________________________________________________________
Orbiting many planets are smaller satellites called moons. A moon is a spherical object that
orbits a planet. Just like the terrestrial planets, some moons also show evidence of geologic
activity. For example, Earth’s moon has evidence of moonquakes and lava flows. Also, one of
Jupiter’s many moons, Io, is the only satellite in our solar system known to have active
volcanoes. In addition, it has lava flows, volcanic deposits, and large volcanic craters.
35. What does a moon orbit around? __________________________________
36. What is another name for a moon? _________________________________
37. True or false. Some moons have evidence of earthquakes, known as moonquakes, and
volcano activity. ___________________
Additional celestial objects within our solar system include comets, asteroids, and meteoroids.
Asteroids are objects revolving around the sun that are too small and numerous to be considered
planets. Most asteroids can be found orbiting the sun in a region between Mars and Jupiter
known as the Asteroid Belt. Smaller pieces of rock and dust found in a solar system which are
similar to asteroids are known as meteoroids. When meteoroids enter an atmosphere they burn
up which causes a streak of light in the sky. This streak of light is called a meteor. If the
meteoroid is too large and does not completely burn up in the atmosphere, it will strike the
surface and become a meteorite. Finally, a comet is a ball of ice and dust whose orbit is a long,
narrow ellipse. Gas and dust found in the tail of the comet are illuminated by the sun, which
causes the comet’s fiery appearance in the night’s sky.
38. Why are asteroids not considered planets? ___________________________________
_________________________________________________________________________
39. Where are asteroids located in the solar system? ________________________________
40. Explain or draw the process of a meteoroid becoming a meteor and then a meteorite.
41. What is a comet made of? _________________________
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