Sun–Earth–Moon Relationships
What causes day and night on Earth?
Earth’s rotation on its axis causes day and night.
What is a moon phase?
A moon phase is the portion of the Moon’s sunlit side that we see from Earth as the Moon orbits Earth.
What force pulls objects toward each other and keeps planets in orbit?
Gravity
What name is given to the cloud of gas and dust that formed the Sun and planets?
The solar nebula (or nebula).
Define "orbit"
An orbit is the curved path an object follows around another object because of gravity.
How long does it take Earth to complete one orbit around the Sun?
One year (about 365 days, or more exactly 365.25 days)
Name the phase that comes right after the new moon.
Waxing crescent
What two factors affect the strength of gravity between two objects?
The masses of the objects and the distance between them.
What caused particles in the early solar nebula to stick together and grow into larger bodies?
Collisions slowed particles and electrostatic forces, then gravity for larger clumps, caused particles to stick and accumulate (accretion).
What is a planetesimal?
A planetesimal is a small, early body formed by the sticking together of dust and rock in the solar nebula; these are the building blocks of planets.
Describe the main reason we have seasons on Earth.
Seasons occur because Earth’s axis is tilted about 23.5°, so as Earth orbits the Sun different hemispheres get more direct sunlight at different times of year.
What causes a lunar eclipse?
A lunar eclipse happens when Earth moves between the Sun and the Moon and Earth’s shadow falls on the Moon.
Explain how gravity and inertia together keep Earth orbiting the Sun
Inertia (Earth’s tendency to move in a straight line) makes Earth move forward; gravity from the Sun pulls Earth inward. The combination causes Earth to follow a curved path (an orbit) around the Sun.
Why are the inner planets rocky while the outer planets are mostly gas and ice? (Give a simple, grade-appropriate reason.)
Closer to the young Sun it was hotter, so light gases and ices couldn’t stay and only rocky materials condensed; farther out it was cooler so ices and gases could condense and form large gas/ice giants.
Define "rotation" and give one effect of a planet's rotation
Rotation is a spin of a planet on its axis. One effect is day and night.
Explain why different places on Earth have different lengths of daylight at different times of year.
Because Earth’s tilted axis changes the angle and path of sunlight during the orbit, locations nearer a hemisphere’s pole have longer or shorter daylight periods depending on the season (e.g., summer → longer days).
How is a solar eclipse different from a lunar eclipse? Include which body is casting the shadow
In a solar eclipse the Moon passes between the Sun and Earth and the Moon’s shadow falls on Earth. In a lunar eclipse Earth passes between the Sun and Moon and Earth’s shadow falls on the Moon.
If you doubled the distance between two objects, what happens to the gravitational force between them (stronger, weaker)? Explain briefly.
The gravitational force becomes weaker; specifically, gravity decreases with the square of the distance, so doubling the distance makes the force about one-fourth as strong.
Describe one piece of evidence that supports the idea that the solar system formed from a rotating disk of gas and dust.
Most planets orbit in the same direction and lie in roughly the same plane, and the Sun and planets rotate in ways consistent with formation from a rotating disk.
What is the difference between a meteor, meteorite, and meteoroid? (Short definitions)
Meteoroid — a small rock or particle in space. Meteor — the streak of light when a meteoroid enters Earth’s atmosphere. Meteorite — a fragment that reaches Earth’s surface.
Draw (or describe) the positions of the Sun, Earth, and Moon during a full moon and explain why the Moon appears full.
During a full moon the Earth is roughly between the Sun and Moon (Sun — Earth — Moon in a line). The side of the Moon facing Earth is fully lit by the Sun, so we see the entire sunlit face and it appears full.
Explain why we don’t have a lunar eclipse every month, even though the Moon orbits Earth every month
The Moon’s orbit is tilted about 5° relative to Earth’s orbit around the Sun, so most months the Moon passes above or below Earth’s shadow; an eclipse only happens when the Moon, Earth, and Sun line up near the orbit nodes.
Describe how gravity influenced the early movement of material in the forming solar system to create planets.
Gravity pulled gas and dust together in the rotating solar nebula; small clumps stuck together (accretion) and gravity made them grow into planetesimals and then protoplanets, attracting more material and clearing their orbits.
Explain the role of gravity in the process of accretion (how planetesimals became planets).
As planetesimals grew, their gravity increased, pulling in more material and causing collisions that allowed them to grow into protoplanets; gravity helped them attract and hold on to more mass until planets formed.
Provide a short explanation of what a model is in science and why scientists use models to study the solar system.
A model is a simplified representation of something real (like a diagram, computer simulation, or scale model). Scientists use models to test ideas, explain observations, and make predictions when the real thing is too large, distant, slow, or complex to study directly.