Why do the outer planets take longer to orbit the Sun than the inner planets do?
The outer planets are farther from the Sun than the inner planets, so they travel longer distances and move more slowly in their orbits.
What keeps the planets in orbit around the Sun?
Gravity (the Sun's gravitational pull) keeps the planets in orbit.
What did Johannes Kepler discover about the motion of the planets?
Kepler discovered that planets orbit the Sun in elliptical paths (not perfect circles) and that they move faster when closer to the Sun.
List the four closest planets to the sun.
Mercury, Venus, Earth, Mars
What materials formed the solar system?
A nebula (cloud of gas and dust) collapsed and formed the Sun and planets.
Explain the difference between the geocentric and heliocentric models of the solar system.
The geocentric model places Earth at the center with everything orbiting it, while the heliocentric model places the Sun at the center with planets orbiting the Sun.
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