Astrophysics

5. The scientist who formulated the laws of motion and universal gravitation.
7. A historical instrument used to solve problems relating to time and the position of the Sun and stars.
9. A small circle whose center moves along the circumference of a larger circle, used to explain planetary motion in the geocentric model.
12. An Italian astronomer and physicist who improved the telescope and made significant discoveries, including the four largest moons of Jupiter.
13. The effect whereby the position or direction of an object appears to differ when viewed from different positions.
14. A German astronomer who discovered the three laws of planetary motion.
15. motion The apparent backward movement of a planet in the sky as seen from Earth.
17. A Roman-era astronomer who proposed a geocentric model of the universe that was widely accepted for over 1,400 years.
18. The force that attracts a body toward the center of the Earth, or toward any other physical body having mass.
20. Brahe A Danish astronomer known for his accurate and comprehensive astronomical observations.

1. model The ancient belief that Earth is the center of the universe and that other celestial objects revolve around it.
2. A Renaissance-era astronomer who formulated a model of the universe that placed the Sun rather than Earth at its center.
3. The part of a sundial that casts the shadow.
4. of planetary motion Three scientific laws describing the motion of planets around the Sun, formulated by Kepler.
6. An optical instrument that makes distant objects appear magnified.
8. The study of the movements and relative positions of celestial bodies interpreted as having an influence on human affairs and the natural world.
10. model The astronomical model in which the Sun is the center of the solar system.
11. An oval shape that describes the orbits of planets, as discovered by Kepler.
16. chart A map of the night sky showing the positions of stars and constellations.
19. A property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.