What ancient Greek astronomer created the first known star catalog, classifying stars by brightness?
What system did Hipparchus develop to measure the brightness of stars?
Hipparchus discovered the slow wobble of Earth's axis. What is this called?
Hint: It causes the position of the North Star to change over thousands of years.
What are Kepler's three laws of planetary motion about?
Kepler's first law states that planets orbit the Sun in what shape?
Kepler's second law (the law of equal areas) means that a planet moves faster when it is where in its orbit?
What force did Isaac Newton identify as the cause of planetary orbits?
Newton's law of universal gravitation states that gravitational force depends on what two factors?
Whose observational data did Kepler use to formulate his laws of planetary motion?
What major work did Newton publish in 1687 that unified celestial and terrestrial mechanics?