Red light of the visible light spectrum has longer wavelengths than blue.

Answer to q. 1

TRUE

Answer to q. 2

A spiral density wave is a stable concentration of interstellar gas and dust. Clouds of gas and dust moving at different orbital velocities approach the dense area of the wave and collide with the material in the density wave. This collision increases mass density and triggers star formation.
The young stars created in this process will include O and B stars, which will make the arms visible with their high luminosity. The OB associations will create emission nebulae, causing a wave of star formation. The newly-formed stars will continue on the orbital track of the original cloud, passing through the leading edge of the density wave and continuing through the disk. The short-lived O and B stars will go through their entire evolutionary cycle before exiting the area of the density wave, so they are only seen in the region of the wave.

Answer to q. 3

After the Principia was published, physicists and astronomers understood that the motions of celestial bodies are governed by simple, universal rules that describe the motions of everything from orbiting planets to falling apples. Suddenly the Universe was understandable in simple terms, and astronomers could accurately predict future planetary motions.

The Principia also changed science in general. The works of Copernicus and Kepler had been mathematical, but no book before the Principia had so clearly demonstrated the power of mathematics as a language of precision. Newton's arguments in his book were such powerful illustrations of the quantitative study of nature that scientists around the world adopted mathematics as their most powerful tool.

Finally, the Principia changed the way people thought about nature. Newton showed that the rules that govern the Universe are simple. Particles move according to just three laws of motion, and attract each other with a force called gravity. These motions are predictable, and that makes the Universe seem like a vast machine, but one whose operations are based on a few simple rules. The Universe is complex only in that it contains a vast number of particles. In Newton's view, if he knew the location and motion of every particle in the Universe, he could, in principle, derive the past and future of the Universe in every detail. This idea of mechanical determinism has been modified by modern quantum mechanics (laws that govern behavior of particles inside atoms), but it dominated science for more than two centuries. During those years, scientists thought of nature primarily as a beautiful clockwork that would be perfectly predictable if they knew how all the gears meshed.

Answer to q. 4

Stars rotate around the galactic center in ways that are controlled by the way the mass of the galaxy is distributed. A star that has distributed matter inside and outside of its orbit will orbit according to one principle, a star that is orbiting outside of the mass will follow another (Keplerian) principal.
We observe that the orbital periods of stars follows the pattern of an orbit inside of a distributed mass, rather than changing to a Keplerian orbit pattern after crossing the boundary of visible matter. This means that there must be mass outside of the visible region of the galaxy. This mass does not emit or absorb photons of electromagnetic energy, so it is termed dark.

Answer to q. 5

Gravity is universal, so the Sun also produces tides on Earth. The Sun is 27 million times more massive than the Moon, but it lies almost 400 times farther from Earth. Tides on Earth caused by the Sun are less than half as high as those caused by the Moon. Twice a month, at new moon and at full moon, the Moon and Sun produce tidal bulges that add together and produce extreme tidal changes: At those moon phases, high tides are exceptionally high, and low tides are exceptionally low. Such tides are called spring tides. Here the word spring does not refer to the season of the year but to the rapid rising up of water. At first- and third-quarter moons, the Sun and Moon pull at right angles to each other, and the tides caused by the Sun partly cancel out the tides caused by the Moon. These less extreme tides are called neap tides, and they do not rise very high or fall very low.

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