Gamma rays have less energy than infrared radiation. (True or false?)

Answer to q. 1

FALSE

Answer to q. 2

Planetary motion was a big problem for ancient astronomers. In fact, the word planet comes from the Greek word for wanderer, referring to the eastward motion of the planets against the background of the fixed stars. The planets did not, however, move at a constant rate, and they could occasionally stop and move westward for a few months before resuming their eastward motion. This backward motion is called retrograde motion.

Answer to q. 3

Tides are caused by small differences in gravitational force. As the Earth and Moon orbit around each other, they attract each other gravitationally. Because the side of Earth toward the Moon is a bit closer, the Moon pulls on it more strongly and that pulls up a bulge. Also, the Moon pulls on Earth a bit more than it pulls on Earth's far side and that produces a bulge on the far side. The oceans are deeper in these bulges, and as Earth rotates and carries you into a bulge, you see the tide creeping up the beach. Because there are two bulges, there are two high tides each day, although the exact pattern of tides at any given locality depends on details such as ocean currents, the shape of the shore, and so forth.The Sun also produces tides on Earth, although they are smaller than lunar tides. At new and full moons, the lunar and solar tides add together to produce extra high and extra low tides that are called spring tides. At first- and third-quarter moons, the solar tides cancel out part of the lunar tides so that high and low tides are not extreme. These are called neap tides.

Answer to q. 4

Galileo was the first person to observe the sky carefully through telescopes and apply his observations to the main theoretical problem of the day-the place of Earth. What Galileo saw through his telescopes was so amazing that he rushed a small book into print,Sidereus Nuncius(The Starry Messenger). In that book, he reported two major discoveries about the Solar System. First, the Moon was not perfect. It had mountains and valleys on its surface, and Galileo used the shadows to calculate the height of the mountains. Aristotle's philosophy held that the Moon was perfect, but Galileo showed that it was not only imperfect but was even a world like Earth. Second, Galileo's telescope revealed four new planets circling Jupiter, planets that we know today as the Galilean moons of Jupiter.