The ancient Greeks learned that the Earth was round because of the shape of the shadow it cast during a (1)______ Another Greek philosopher named (2) _____observed that ships disappear as they sail along the horizon. Ancient astronomers observed the changes in the appearance of the moon within (3) _____days. A 4).______ occurs when the earth casts its shadow on the moon when the Earth is between the sun and the moon. On the other hand, a (5). _____occurs when the moon is in between the sun, the earth, and the moon partially or completely blocks out the sun. Astronomers believe that many (6)______have planets circling around them, just as the sun does. (7)______developed tools such as a sextant in order to observe the heavenly bodies and get ccurate data describing them. He discovered that the universe is changing with the appearance of a new star in a constellation called (8) _______and the appearance of a comet. Johannes kepler, a mathematician formulated the Laws of Planetary Motion. The first law explains that the shape of a planet's orbit around the sun is an (9)______ and not a perfect circle. The second law of planetary to the sun and slowest when it is (10)_______ to the sun and slowest when it is (11)______from the sun. The third law of planetary motion states that the ratio of the (12)_____of the period to the (13)_______of their average distance from the sun is the same for every one of the planets ​