Galileo was a prominent defender of the <1> theory of the solar system. He was also the first person to use a <2> in astronomy and made a number of important observations. He observed that the <3> was made of many stars too faint to be seen with the naked eye. He also observed sunspots on the sun, craters on the moon, and the <4> large moons of Jupiter. However, his most important observations were of the phases of Venus. Galileo observed a complete set of phases for Venus, while according to the Ptolemaic theory, Venus should only be seen as a <5>.
Isaac Newton was the greatest scientest of all time making substantial contributions to optics, calculus, and astronomy. He devised 3 laws of motion which are very useful for discussing planetary orbits. The first is known as the law of <6> and states that an object will continue at rest or in uniform motion in a straight line unless acted upon by some force. Newton's second law states that Force is equal to mass times <7>. Netwon's third law states that forces come in <8>. Newton also expressed the Law of Universal Gravitation which states that the force of gravity between two masses is always <9> and is proportional to the product of the masses divided by the <10> squared. @ qu.1.1.blank.1=heliocentric, geocentric, egocentric, ergocentric@ qu.1.1.blank.2=telescope, microscope, stethoscope, periscope@ qu.1.1.blank.3=Milky Way, Solar System, Virgo Supercluster, asteroid belt@ qu.1.1.blank.4=4, 3, 5, 2@ qu.1.1.blank.5=crescent, gibbous, full, first quarter.@ qu.1.1.blank.6=inertia, university administration, the Couch Potato, constant velocity@ qu.1.1.blank.7=acceleration, velocity, momentum, angular velocity@ qu.1.1.blank.8=pairs, groups of 3, one at a time@ qu.1.1.blank.9=attractive, repulsive, perpendicular, negative, positive@ qu.1.1.blank.10=separation, velocity, acceleration, momentum@ qu.1.1.grader.1=menu@ qu.1.1.grader.2=menu@ qu.1.1.grader.3=menu@ qu.1.1.grader.4=menu@ qu.1.1.grader.5=menu@ qu.1.1.grader.6=menu@ qu.1.1.grader.7=menu@ qu.1.1.grader.8=menu@ qu.1.1.grader.9=menu@ qu.1.1.grader.10=menu@