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Ans. 5: If the stars move across the sky in circles centered directly overhead, the loacation of the observer would either be north pole or the south pole. This could be the location because the earth moves around the axes. This can be exaplained by looking at the following justification: Anyone who would be looking at the sky, would be always standing at the top of the earth. Therefore, the objectcs present at the celestial sphere which are classified relative to the ground willl occur at the same point of the sphere.

In order to locate a person, we can mark the horizon diagonally to the mid of the celestial sphere, in such a way that the centre of the earth and the slestial sphere are identical. The observer’s view of the sky doesn’t matter, whether the sky’s view of the observer is the cut off position that is spotted by the horizon therfore the horizon is always kept perfect. The next points for reference would be the North Celestial Pole and the South Celestial Pole. If the person is standing at the equator, the pole would be horizontal through the Earth.

If the observer is located at one of the poles, then these poles would go from the earth vertically. The north and the south celestial pole would be marked at the intersections. These intersections would be the result of exrtending the earth’s pole out to the celestial sphere. If we are at the southern hemisphere, the south celestial pole would be below the horizon, which makes it to be on the opposite side of the celestial sphere and for northern hemisphere, this situation is inverted. Ans. 9: Ptolemaic Model:

The Ptolemaic model describes the obvious movement of the planets in a very direct and a straight way. this apporach is achieved by supposing that each planet of the solar system moves on a small and tiny sphere or circle. This circle is better known as epicycle. This epicycle moved on a larger sphere or circle. This larger sphere is called as a deferent. It was assumed, that the stars move on a celestial sphere around the outside of the planetary spheres. Copernican Model: Copernican Model is better known as the sun centred solar system.

This model explained that the true movement of the planets is not in a uniform circular motion, around. Due to this reason, the Copernican’ model would still need to have those small nad tiny circles on which the planets move, called the epicycles. The main feature of the Copernican model that differs this model from the ptolemaic model was the retrograde loops. These loops of the planets, the way they are seen from the Earth, arise physically as a result of the plantes motion altogether combined with the Earth’s motion.

The Ptolemaic model was considered wrong because it was not precise and as the time passed by the predictiopn in the model proved to be worse and worse. Although this model was very good to predict the position of the planets. Rather than having larger epicycles, earth moving around the sun could also explain the retrograde motions of the planets. Ans. 10: The ptolemaic model accounts better for variations in the brightnesses of the various planets with time. The ptolemaic model contains Epicycles. These epicylces are tiny circles on which the planets move.

The epicycles were establish to clarify variations in brightness of the planets as compared to the eccentrics. Eccentric circles are the circular paths that are intended to be seen from some internal point moved from the centre of the circle. These circles allow better estimations of the celestial movements. The copernican model doesnot account for the brightness issue because the Planets in the solar system closer to the Sun tend to moved faster rather than the planets which are further away from the sun.

This way, at times a planet could be on the similar side of the sun as the earth and this could make them appear brighter and on the other hand, a planet that could be on the opposite side of the sun from the earth will tend to appear dimmer because it was far away. Therefore the ptolemaic model tends to take care the issue of brightness of the planets as it has different circles for all the planets to revolve around. This makes each planet to appear brighter individually. Ans. 15: High tides are the result of the difference between the gravitational pull of the Moon on the either side of the Earth.

The Tidal forces gradually slow down the rotation of the Earth. These Tidal forces slowly increase the dimensions of the orbit of the Moon. The level of the sea rises atleast twice a day. This level is divded into 2 parts. When the sea reaches the highest level, it is said to be high tide. The sea is said to be at low tide when it is at its lowest level or somewhere in between the midway to the highest level. the tides of the earth are defined as the deformation of the ocean and also of the Earth. A gravitational pull is exterted by the moon toward the earth.

This is done when the moon is pulled on by the earth. As you get away from the moon, the gravitational force applied by the moon or any other object decreases gradually. Theorotically the pull by the moon on the near by side of the earth is about 7% greater. Therefore it can be said that the difference between the earth’s turn in its axis and the high tide is a result of the gravitational pull by the moon.

References: Wikibooks (2008). Astronomy. Retrieved September 7, 2008, from http://en. wikibooks. org/wiki/Astronomy

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