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Earth, Moon, Sun
Objective
The student knows that there are recognizable patterns in the natural world and among the Earth,
Sun, and Moon system. The student is expected to identify and compare the physical
characteristics of the Sun, Earth, and Moon.
Foundation
Our Solar System is one of thousands, perhaps millions, of similar systems scattered throughout
the void of space. Each of these systems has similar characteristics. In the center of the system
there is a star around which orbit a varying number of planets, moons, asteroids, rocks, dust, and
gas. Our Sun is a medium size star, and within our Solar System there are eight recognizable
planets. Listed from the planet nearest to the Sun to the farthest, they are Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus and Neptune. The International Astronomical Union, the
recognized authority in naming heavenly objects, formally classified Pluto as a dwarf planet in
2006. The dwarf planet Pluto and a collection of similar icy bodies orbit far from the sun in an
area known as the Kuiper belt.
Planets revolve around the Sun in an orbit. An Earth year is based on the time it takes the Earth
to complete an orbit of the Sun one time. The time it takes a planet to orbit the Sun is dependent
upon its distance from the Sun. The farther the distance from the Sun, the more time it takes,
simply because it has more distance to travel. While the planets are orbiting the Sun, they are
also rotating on an invisible central axis. The time it takes for our Earth to rotate, or spin, one
time is the length of one of our days (24 hours.) Although it appears that the Sun is moving
across our sky, it is actually the rotation of the Earth on its axis which makes it seem so. All
planets rotate, but at different speeds, so that a “day” would be a different length of time on
different planets. The four planets closest to the Sun (Mercury, Venus, Earth, and Mars) are
called the Inner Planets. They are spheres of rock. The four remaining planets are called the
Outer Planets. Jupiter, Saturn, Uranus, and Neptune are giant balls of gas.
There are moons, asteroids, rocks, bits of dust, and gases orbiting around many of the planets.
Moons are generally round spheres of rock, while asteroids can be large, irregularly shaped
chunks of rock.
The physical characteristics of the Sun, Earth, and Moon are quite different. About the only thing
similar in each one is that they are spheres, but even then, their sizes are not close. The Earth is
four times larger than the Moon, and the Sun is a million times bigger than the Earth. The Sun is
a ball of flaming, exploding gases with no real surface. The Earth and Moon are spheres of rock,
but after that their similarities fade. The Earth has water and an atmosphere of gases which
sustain life, whereas the Moon has no atmosphere and is devoid of life. The Moon’s surface is
scarred and cratered from being struck by many asteroids, but the atmosphere of the Earth causes
most of the asteroids aimed at Earth to burn up before they reach the ground. Because of that, the
Earth’s surface has oceans of water, along with landforms covered with forests, plants, and living
creatures.