Ch.2 Homework answers

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Ch.2 Homework answers

One can observe all the stars, the equator. From the North Pole, only half of the sky can be seen throughout the year, not subject to any change.

Four ways to demonstrate the Earth is spherical

Watching a ship as it sails off to sea. As the vessels move toward the horizon, it sinks first, then the mast, instead of getting smaller and smaller until its visibility disappears.

If one pays attention during the lunar eclipse, you may note that indeed the Earth is spherical. During this time, the Earth crosses between the Moon and the Sun. Hence, the Earth’s shadow is cast onto the Moon in the night sky by the Sun.

Traveling through different time zones. At an elevation of 35,000 feet, the Earth’s curvature is somewhat visible and even more visible at a 50,000 feet elevation.

When watching a sunset from point A, one notices a clear horizon that certainly will be in the front, while behind you is somewhat an elevated point that one can quickly access (point B).

According to geocentric, the heavenly bodies rotate on epicycles lying on the deferents, thus making the Earth overtake the planets far from the Sun and it and certainly appear as if they are going backward in their orbits. Heliocentric theory hold that retrograde motion comes as a result of the Earth passing the outer planets that move slower than the Earth, making them look as if they are going backward relative to the background stars.

Galileo’s model placed the Earth at the center of the universe and other heavenly bodies circling it. On the other hand, the Copernicus model puts the Sun at the center of the universe, and planets, Moon, stars circle around it.

Galileo discovered that the Sun is at the center of the universe instead of the Earth, which was the common belief at the time. He found that the Sun had a dark sunspot. He also discovered the four moons of Jupiter, Callisto, lo, Europa and Ganymede. Galileo also made discoveries on the phases of Venus; more importantly, he noted and proved that Venus does not orbit the Earth. Previously it was thought that the Milky Way was a cloud, which he proved is was not; instead, it is comprised of numerous stars.

Hipparchus came up with star maps, where starts were ranked by calling the first magnitude the “brightest” and second magnitude were those “less bright.” Six magnitudes was the name given to the faintest. It is the reason why it appears to go backward, with smaller numbers indicating brighter stars.

During the day, circumpolar stars are on the horizon; hence, they can be spotted since they orbit the north pole star.

The Sun moves at about 1 degree each day, which equates to 4 minutes of the right rise. It takes 365 and ¼ days for the Sun to go back to its point of origin.

On average, the Moon moves at about 13.2 degrees every day. It takes roughly 27.3 days for the Moon to return to its original location.

Zodiac constellations are once in a year passed by the Sun and are 12 specific constellations. Other constellations are generally a group of stars forming a certain pattern, and their traditional mythological figures are used to their naming and identification.

The popular geocentric model made the people thought that the Sun was a planet circling the Earth. The Sun has nine planets, asteroids, and comets revolving around the milky way galaxy. Contrary to the idea, Moon revolves around the planets. The stars and the planets have a different composition, and there are numerous stars, but the Earth and the Sun are close.

The ecliptic plane and the celestial equator are not the same. The ecliptic plane is the plane of the Earth’s axis around the Sun. On the other hand, the Earth’s projection of the equator onto the sky is called the celestial equator.

Asterism can be defined as a group of stars or star patterns that do not form their constellation but are seen in the night sky. Examples of asterisms include The Summer Triangle and The Great Square of Pegasus.

Pythagoras believed the Earth is spherical, basing his argument on observing the terminator line of the Moon circling the orbit, which has a round shape. In his thought, he concluded that if the Moon is spherical, even the Earth must be spherical.

The Moon appears to be passing in front of the Sun during the solar eclipse. It made Aristotle conclude the Sun is further away from the Earth than the Moon.

Aristotle deduced the Earth is spherical by observing the circular shadow cast by the Earth during the lunar eclipse. Also, when people move to the South, they tend to see fewer polar stars, and no polar stars are seen at the pole.

Hipparchus discovered precession by comparing his 200 BC records’ circa with older charts. He found out that the equinoxes during his time displayed similar positioning among the stars compared to those of 150-year-old maps showed. It resulted from the gyroscopic wobble of Earth’s spin axis, and it takes approximately 26 000 years to complete.

Ptolemy had to introduce multiple epicycles since he must have accounted for the retrograde motion of the planets observed occasionally.

Copernicus wanted to develop a new system for predicting planetary position since he viewed the Ptolemaic model as unclear, perhaps not precise for planet positioning prediction. Institutions like the churches were invested in the notion that the Earth is placed in the middle of the universe, which is not the case.

What makes the geocentric and heliocentric models to choose between them is the fact that people do not feel the Earth’s motion even though it is moving, making it easier to place the Earth in the middle. The two theories were not precise on their philosophical reasoning on placing either the Sun or the Earth at the center of the universe.

It would display crescent phases as the larger part of the bright side will not be facing the Earth.