Earth, moon, and Sun
Earth in space
#1 How does Earth move in space?
Earth moves through space in two major ways: rotation and revolution. Earth rotates on its axis around the sun. Earth rotates on its axis once every 24 hours, this rotation is called a day. Earth makes a full rotation around the sun every year, which is 365 days or 366 days on a leap year.
#2 What causes the cycle of seasons on Earth?
Earth has seasons because its axis is tilted as it revolves around the sun. If Earth’s axis were straight up, temperatures would remain fairly constant year round and seasons would be fairly the same. As Earth revolves around the sun, the north end of its axis is tilted away from the sun for a part of the year this is during winter. The axis faces toward the sun in the summer. Seasons are opposite for people on the southern end of the axis. Changing seasons are not caused by the distance between the sun and Earth.
Gravity and Motion
#1 What determines the strength of the force of gravity between two objects?
The strength of the force of gravity between two objects depends on two factors: the masses of the objects and the distance between them.
The force of gravity is measured units called newtons named after Isaac Newton.
All objects around you, including Earth, are pulling on you, just as you are pulling on them. We don't notice the pull because gravity's strength depends on the mass of each object.
#2 What two factors combine to keep the moon and Earth in orbit?
Inertia and Gravity are the two forces that combine to keep Earth in orbit around the sun, and the moon in orbit around Earth.
Earth’s gravity pulls the moon toward it, preventing the moon from moving in a straight line. The moon keeps moving ahead because of its inertia.
Phases, Eclipses, and Tides
#1 What causes the phases of the moon?
The changing relative positions of the moon, Earth and the sun cause the phases of the moon, eclipses, and tides.
The moon rotates around Earth, also rotating on its own axis. The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth. Half of the moon is almost always in sunlight.
#2 What are solar and lunar eclipses?
A solar eclipse occurs when the moon passes directly between the Earth and sun, blocking sunlight from Earth. A lunar eclipse occurs when the Earth blocks sunlight from the moon.
#3 What causes the tides?
Tides are caused mainly by differences in how much the moon’s gravity pulls down on different parts of Earth. The force of gravity pulls the moon and Earth including bodies of water. The area of Earth, where moon is closest to, has the strongest force of gravity with high tides. At the opposite side of the world, the force of the moon's gravity is weaker and high tides are also formed here.
#1 What features are found on the moon's surface?
Features on the moon's surface include maria, craters, and highlands. Recent photos show much more detail than what could be spotted with a telescope.
Maria: Dark, flat areas on the moon's surface
Craters: Large round pits on the moon
Highlands: Light colored features on the moon's surface
#2 What are some characteristics of the moon?
The moon is dry and airless. Compared to Earth, the moon is small and has large variations in its surface temperature. The moon is very different from Earth and requires bulky space suits to keep you protected from sunburn and to provide air for you to breathe.The moon's diameter is 3,476 kilometers, which is about one-fourth Earth's diameter. The temperature on the moon changes so much because it has no atmosphere,they range from 130 degrees Celsius in direct sunlight to -180 degrees Celsius at night. The moon has no liquid water but large patches of ice near its' poles are possible.
#3 How did the moon form?
Scientists theorize that a planet-sized object collided with Earth to form the moon. Material from the object and Earth's outer layers was ejected into orbit around the Earth, where it formed a ring. Gravity caused this material to combine to form the moon.