Astronomy-Fact or Fiction?
Planets
MYTH 1: The Earth is the largest object in the solar system.
FACT: The sun is the largest object in the solar system. It contains 99 percent of the mass of the
solar system. Jupiter is the largest planet in the solar system, and Earth is the fifth-largest.
MYTH 2: The Earth is the center of the solar system.
FACT: The Sun is at the center of the solar system, and the planets, asteroids, moons, dwarf
planets, plutoids, and comets orbit the Sun. The Earth is the third planet from the Sun.
MYTH 3: All the planets are the same size as Earth.
FACT: The planets are different sizes. Listed from smallest to largest, the planets are Mercury,
Mars, Venus, Earth, Neptune, Uranus, Saturn, and Jupiter. Jupiter is roughly 10 times larger than
Earth. Mars is about half the size of Earth. Venus and Earth are roughly the same size.
MYTH 4: The solar system is made up of only the Sun and eight planets.
FACT: The solar system also contains the planets’ moons, dwarf planets, plutoids, scattered gas
and dust, asteroids, and comets.
MYTH 5: Stars and galaxies are part of our solar system.
FACT: There is only one star, the Sun, in our solar system. The solar system resides in the Milky
Way Galaxy. Many other stars are outside our solar system, but are part of our Milky Way
Galaxy. About 50 billion galaxies are outside our galaxy. Galaxies contain from tens of millions
to trillions of stars.
MYTH 6: The rings of Saturn are solid disks.
FACT: The rings of Saturn are not solid. Thousands of rings, made of pieces of ice, orbit the
planet Saturn. The pieces of ice are about one meter apart, and can be as small as dust specks or
as big as a house. The ice pieces collect into ring shapes because of gravity.
MYTH 7: Spacecraft can land on the surfaces of Jupiter, Saturn, Uranus, and Neptune.
FACT: Spacecraft cannot land on these planets because these giant planets are made mostly of
gas. They may have solid cores, but the temperature and pressure of the gas would increase as
the spacecraft moved toward the core. The spacecraft would be destroyed before it reached that
solid core.
MYTH 8: The planets are evenly spaced between the Sun and Neptune.
FACT: The planets are not evenly spaced. The inner planets (Mercury, Venus, Earth, and Mars)
are closer together than the outer ones (Jupiter, Saturn, Uranus, and Neptune). The distance
between planets generally increases as the planets get farther and farther from the Sun. The
planets in the inner solar system are tens of millions of kilometers apart; the planets in the outer
solar system are hundreds of millions of kilometers apart.
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MYTH 9: Pluto is the most distant and last object in the solar system.
FACT: Pluto is not the last object in the solar system. Pluto resides within a region of icy objects
called the Kuiper Belt. The Kuiper Belt extends from Neptune’s orbit outward. Beyond Pluto’s
orbit is another vast region of icy objects called the Oort Cloud, which is where comets are
formed.
MYTH 10: Gravity exists only on Earth.
FACT: Gravity exists on other planets and moons. Gravity pulls objects toward the center of the
planet, causing them to accelerate and drop toward the planet. In fact, objects stay in orbit
because of gravity. Without gravity, a satellite launched from the Earth would simply drift off
endlessly into space, traveling in a straight line, instead of circling the planet. Gravity also pulls
objects toward the center of the planet, causing them to accelerate and drop toward the planet.
Moon
MYTH 1: The Moon is only visible at night.
FACT: The Moon appears in the daytime sky just as often as the night sky.
MYTH 2: The Moon and the Sun are the same size.
FACT: The moon and the sun are different sizes, but sometimes they appear to be about the same
size in our sky. In fact, the more distant Sun is much bigger than the Moon. The Sun is a large
object that is far away, so it appears smaller than it really is. The Moon is a small object that is
closer to Earth and therefore appears large.
MYTH 3: Both sides of the Moon are visible from Earth.
FACT: Only one side of the Moon is visible from Earth. The other side, called the far side of the
Moon, is not visible from Earth. The Moon makes exactly one turn on its axis (28 days) as it
makes one orbit around Earth (28 days).
MYTH 4: There is a side of the Moon that is always dark, called the “dark side of the Moon.”
FACT: It is true that at any given moment, one half of the Moon is dark. It is not always,
however, the same half.
MYTH 5: We can tell how far away a celestial object is by looking at its size in the sky.
FACT: We cannot tell how far away a celestial object is just by looking at it. Large objects that
are far away will appear small, and small objects that are close to Earth can appear large.
The Sun and other Stars
MYTH 1: The Sun is not a star because it doesn’t shine at night.
FACT: The Sun is the closest star to Earth and provides us with most of our energy and light.
When we experience darkness, we are facing away from the Sun. When we experience daylight,
we are facing the Sun. We can’t see other stars during the day because the Sun’s light illuminates
Earth’s atmosphere.
MYTH 2: The Sun is a burning ball of fire.
FACT: The Sun is glowing, not burning like a fire. The Sun glows because its temperature is
about 5,500°C (about 10,000°F). This heat is not produced by burning (a chemical reaction), but
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rather by fusion (a nuclear reaction). This nuclear fusion takes place deep in the Sun’s core at a
temperature of about 15,000,000°F. As the heat travels out through the Sun’s layers, it becomes
much cooler, but still hot enough to glow in visible light. For comparison, the temperature of a
wood fire is less than a 1,000°F.
MYTH 3: All stars are exactly the same.
FACT: All stars are not the same. Stars vary in brightness, color, mass, temperature, and age.
MYTH 4: The stars in a constellation are close to each other.
FACT: The stars that make up a constellation are the brightest ones in that region of the sky, but
they are not close to each other.
MYTH 5: Stars live forever.
FACT: Stars do not live forever. Stars’ life spans range from millions to trillions of years,
depending on the type of star. The shortest-lived stars last about 50 million years.
MYTH 6: All stars will end their lives the same way-as supernovae.
FACT: Not all stars will end their lives in violent explosions, called supernovae. Only massive
stars become supernovae. The Sun and other less-massive stars will gently puff off their outer
layers to form shells of glowing gas called planetary nebulae.
Galaxies
MYTH 1: Most galaxies are easily viewed with the naked eye.
FACT: Most galaxies are so far away that people can view them only with the help of telescopes.
Only three galaxies can be seen with the unaided eye: the Andromeda Galaxy and the Large and
Small Magellanic Clouds. These galaxies appear as cloudy patches or fuzzy spots in the sky
when viewed with small telescopes.
MYTH 2: All galaxies are the same.
FACT: The shapes of galaxies vary. Galaxy shapes include spiral, elliptical, irregular, and
barred spiral. Galaxies also differ in color, composition, orientation, age, size, the number of
stars within them, and their distance from Earth.
MYTH 3: Galaxies are composed of material that is different from stars.
FACT: Galaxies are large collections of stars, gas, and dust held together by their gravitational
attraction.
MYTH 4: Galaxies are static, remaining unchanged with time.
FACT: In fact, galaxies are dynamic and change over millions of years. Stars are born and die in
galaxies. A galaxy also can interact with another galaxy, which alters both galaxies’ shapes.
MYTH 5: An object that appears faint in the sky is actually faint, and an object that appears
bright in the sky is actually bright.
FACT: The brightness of an object depends on its true brightness and its distance from Earth.
Faint objects can appear bright if they are nearby, while bright objects may appear faint if they
are very distant.
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Telescopes and Space Technology
MYTH 1: Telescopes have always been powerful tools that astronomers use to look at objects
very far away.
FACT: Telescopes began as simple “spyglasses” and have evolved into powerful tools.
MYTH 2: Space-based telescopes such as the Hubble Space Telescope are manned satellites
with astronauts living and conducting research on them.
FACT: Space-based telescopes are unmanned and controlled from Earth. Astronomers request
observation time on the telescopes and conduct their research from Earth.
MYTH 3: Space-based telescopes can observe celestial bodies such as planets better than
observatories on earth because they are closer to them.
FACT: Space-based telescopes produce clearer images than ground-based telescopes because
they are above Earth’s atmosphere. The Earth’s atmosphere distorts our view of objects in space.
MYTH 4: Space-based telescopes take pictures of celestial objects, like taking snapshots with the
family camera.
FACT: Space-based telescopes do not use film to take images. The telescopes instead take digital
images, which are transmitted to Earth. Scientists, however, do not think of space-based
observatories as giant digital cameras in space, but rather as scientific instruments that observe
objects for analysis.
MYTH 5: NASA has “warp-drive” technology.
FACT: Warp drive is an imaginary device used in science fiction. Objects cannot travel faster
than the speed of light (300,000 km. per second, or 186,000 miles per second).
MYTH 6: NASA spacecraft can travel at or near the speed of light.
FACT: Spacecraft travel much more slowly than the speed of light. For example, the Cassini
spacecraft was successfully launched on October 15, 1997 and reached Saturn in July 2004. The
Apollo missions took slightly more than three days to travel from the Earth to the Moon. At the
speed of light, it would take about one second to reach the Moon and 75 minutes to reach Saturn.
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