Teacher Content Knowledge:
Overview
To effectively teach this unit, the teacher must be familiar with the planets of the solar
system, characteristics of each (including size and composition), their moons, the sun, the
distances of the planets from one another and their distances from the sun, the gravitational pull
of each planet and how to determine the weight of an object on the other planets based on that
object’s weight on Earth.
The Sun
The sun is the center and the largest body in the solar system. The surface of the sun
averages about 10,000 degrees F. The sun is a ball of burning gas and is made up of 74 percent
hydrogen, 25 percent helium and 1 percent of smaller elements, including iron, carbon, lead and
uranium.
The Planets
Mercury
Mercury is the closest of the eight planets to the sun. Mercury is a rocky planet with
craters, similar to Earth’s moon. Mercury’s core is made up mostly of iron. Its surface
temperature ranges from a low of about -300 degrees F to a high of about 800 degrees F.
Mercury revolves around the sun four times as fast as Earth, therefore it’s year is equivalent to
only 88 Earth days. Mercury spins so slowly on its axis that a day on Mercury is equivalent to 59
Earth days. Mercury is 3,031 miles in diameter and 36 million miles from the sun.
Venus
Venus is the second planet from the sun, and the closest planet to Earth. Venus’ 40-milethick, cloudy atmosphere is made up of poisonous gases. Even though Mercury is closer to the
sun, Venus is hotter than Mercury. Venus’ temperature remains constant at approximately 864
degrees F because its gaseous atmosphere insulates the heat from the sun. Venus is very close in
size to Earth and is often referred to as Earth’s twin for that reason. Venus is a very dry, rocky
planet. Venus’ gaseous clouds reflect sunlight and make it a very bright planet. It is so bright that
it can be seen from Earth, even during the day. Venus is 7,521 miles in diameter, and 67.2
million miles from the sun.
Earth
Earth is the third planet from the sun. Earth’s surface is solid and rocky. Earth is covered
mostly (75 percent) by water and ice. Earth spins on its axis at 1,000 miles per hour. Our year,
365 days, is the amount of time it takes for Earth to make one complete trip around the sun. Our
month, approximately 28 days, is the amount of time it takes for Earth’s moon to revolve around
the planet. Many things work together to make Earth the only “livable” planet. Earth is just the
right distance from the sun to be neither too hot, nor too cold. Earth’s atmosphere is filled with
breathable oxygen. The Earth’s atmosphere also helps prevent Earth from overheating. It absorbs
some heat/warmth, but also reflects heat to keep the planet from overheating. Because Earth is
tilted on its axis, we experience seasonal changes. Earth is 7,926 miles in diameter, and 93
million miles from the sun.
Mars
Our solar system’s fourth planet is Mars. Also known as the “Red Planet,” Mars is
covered in rocky, red, dusty soil. The reddish color is a result of the amount of iron in the dusty
soil. It has huge, extinct volcanoes and an enormous canyon called “Valles Marinaris”. Mars’
thin, poisonous atmosphere is made up mostly of carbon dioxide. The atmosphere is very cold
and thin, making it impossible for liquid water to exist on its surface. Mars is 4,220 miles in
diameter, and 142 million miles from the sun. It takes Mars 24 hours and 37 minutes to rotate
completely and 687 Earth-days to orbit the sun.
Jupiter
The fifth planet from the sun, and the largest of the eight planets, all of the other planets
combined could easily fit inside of Jupiter. Jupiter is made of hydrogen, helium and methane
gases. This enormous planet radiates almost as much heat as it takes in from the sun. Jupiter has
63 moons. Jupiter’s brownish red stripes are ammonia hydrosulfide and its white clouds are
made of ammonia. Jupiter has no solid surface to walk on. Like Saturn, Jupiter has rings, but
they are much thinner and much more difficult to see from Earth. Jupiter has four rings. The
largest planet, Jupiter is 88, 400 miles in diameter, and 484 million miles from the sun.
Saturn
Saturn is the most commonly known “ringed” planet. It has thousands of rings. Saturn’s
rings are made up of rock, dust, and ice. Saturn has the most rings of all of the “gas giant”
planets. Saturn is the most distant planet that can be seen by the naked eye. Like Jupiter, Saturn
has no solid surface to walk on. Instead, Saturn’s surface is frozen and slushy. Also like Jupiter,
Saturn’s atmosphere is made of hydrogen and helium gases. Saturn is the least dense of all the
planets and, if it were possible to drop it into water, it would float much like a cork. Saturn’s
rings are very bright and scientists divide them into seven different bands. Saturn is considered
the most beautiful planet in our solar system. It is 74,600 miles in diameter, and 887 million
miles from the sun. It takes Saturn 10 hours and 39 minutes to rotate completely and 29.5 Earthyears to orbit the sun.
Uranus
Uranus is the seventh planet from the sun. Like Jupiter and Saturn, Uranus is considered
a gas giant. Uranus’ atmosphere is made up mostly of hydrogen and helium gases. There is also a
significant amount of methane gas, which contributes to its blue-green color. Uranus is
approximately eight times the size of Earth. It is 31,700 miles in diameter and 1,784 million
miles from the sun. It takes Uranus 17 hours and 14 minutes to rotate completely, and 84 Earthyears to orbit the sun. Uranus’ axis is tilted 98 degrees, tilting it almost completely on its side.
Uranus’ north pole faces the sun for 42 years at a time, and faces away for another 42 years at a
time. That causes Uranus to be sunny for 42 years and dark for 42 years. There is no solid
surface on Uranus. Uranus has 27 known moons.
Neptune
Neptune is the eighth planet from the sun, and is the smallest of the gas giants. Like the
other gas giants, Neptune has no solid surface to walk on. Its atmosphere is made up of
hydrogen, helium and methane. Neptune’s axis is almost perfectly upright. Neptune is 30,800
miles in diameter and is 2,794 million miles from the sun. It takes Neptune 16 hours and 7
minutes to rotate completely and 163.7 Earth-years to orbit the sun. Neptune has 13 moons and 9
rings.
Weight in Space
In order to effectively teach about weight in space, the teacher must be familiar with the
concepts of weight, mass and gravity.
Weight
For the purpose of the unit, weight will be defined as “a measurement of the force on an
object caused by gravity trying to pull the object down.”
Mass
For the purpose of this unit, mass will be defined as “the amount of stuff contained inside
an object.”
Gravity
For the purpose of this unit, gravity will be defined as “an attractive force; an objects
gravity pulls other objects toward it.”
Weight in Space
Earth’s moon has zero gravity. That doesn’t mean that when a person is on the moon they
have no mass, they always have mass because mass is the amount of stuff contained inside an
object. Their weight, however, would be zero, because when there is zero gravity, an object is
weightless.
Earth’s gravity is 1, so the mass of an object is equal to its weight on Earth.
The other planets each have a different level of gravity. To determine the weight of an
object on any planet with a gravity other than 1, students will multiply the mass by the gravity of
each planet. Students will use the weight of celebrity Justin Bieber to practice determining
weight in space.