... 3 Seasons of the year and inclination of the Earth's axis. ... 6 Calendar: solar and sidereal day . ... 9 Retrograde motion of inner and outer planets. ... Center of motion is not Sun but mutual center of gravity. 12a Concept of solving an equation by iteration [see M-2 for "Algorithm"] . ... 17 Concept of mass--gravitational vs. inertia. ... 25 Concept of center of gravity . Principle of rocket motion. ... 8 Size of Earth as estimated by the ancients and by Columbus. 8a The story of Pike's Peak. ...

... The gravity-gradient force on the Moon. 4b Craters of the Moon--why round, why middle higher. ... Intuitive concept of 2nd law--planet or satellite slows down when further away, relation to conservation of energy and analogy to motion of thrown stone. 12a Example of non-algebraic equation (Kepler's) . ... Principle of rocket motion. ... Design of house windows, taking advantage of the Sun's motion. 4a Poem by Vachel Lindsay. 4b The story of exploration of the Moon using space vehicles. ...

... How much brighter is the Sun as viewed from the planet Mercury as compared to Earth ? ... Actually, all of these questions can be answered through a very simple mathematical relationship known as the inverse square law. ... As the distance from the Sun increases the surface area of the sphere grows by the square of the distance. ... Common sense tells us that the Sun will be brighter and the inverse square law tells us how much brighter. ... gr = 0.912 G or 91.2% gravity felt at Earth's surface. ...