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# Astronomy

#1) (A) Issac Newton's Law of Universal Gravitation is: Two bodies attracted to each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. This means that the further apart these two attracting bodies are from each other, the less the gravitational force between them is. The force of gravity depends on the product of the mass of the two attracting bodies. If the distance between the two bodies doubles, the force between them becomes one quarter of the force it was before.
The Law of Universal Gravitation is vital because it mathematically proves Kepler's Three Laws of Planetary Motion. The Planets follow the same laws of motion as objects on the surface of the earth. (B) Newton discovered other types of orbits that have circular of elliptical paths. However, if the velocity of an orbiting body were increased, its orbital path would change to a parabola or hyperbola and it would escape the gravitational pull of the sun. It would then leave the solar system. Parabolas are the orbital paths of objects in the form of an open curve. If one cuts out an angle in a circular cone, it would follow this path parallel to the sides of the cone. Hyperbolas occur when a plane cuts across two parallels half-cones.
Kepler's laws applies to any situation where two bodies in the universe orbit each other due to their mutual gravitational attraction, not just two planets. For example: Moon's that orbit planets, such as the four Galilean Moons that orbit Jupiter.
#2)(A) The reflecting telescope, which uses a mirror to attract light was perfected by Isaac Newton in 1668 although it was developed by John Gregory in 1663. The refracting telescope, which uses a lens to attract light was developed by a Dutch optician in 1608 named Hans Lippershey. Two other inventors were Zacharias Jannssen and Jacob Metius.

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