Tnpsc group 1, 2, 4 syllabus material Nature of Universal Part-7

Introduction

“My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all.”

—Stephen Hawking

Starry night sky is a wonder which has fascinated humans from time immemorial. Our ancestors have observed and documented the objects seen in the night sky.

The field of study of the universe is called astronomy. We know that there are billions and billions of stars in the universe, although only about 2000 or so are visible to naked eye. Have you ever think of the size of our universe? The universe is unimaginably and infinitely big. Universe is commonly defined as the totality of everything that exists or is known to exist.

Even though the spatial size of the entire universe is still unknown, it is possible to measure the observable universe. The universe consists of galaxies, planets, stars, meteorites, satellites and all other forms of matter and energy. And it is a world of wonder. Let us move into this world of wonder to know more interesting facts about the place of residence of our solar system.

astronomical unit

GEO Centric Theory

Sky is a wonder. Sun, Moon, stars all appear to rise in the East and move towards the west, giving us an impression that all these objects are going around the Earth. Just as in a moving bus the distant mountains and trees appear to move backwards, perhaps really Earth is spinning and that is why Sun, Moon and stars appear to go around the Earth. Does the Earth revolve around the Sun, or the Sun revolves around the Earth? How do you know about it?

When you look at the night sky you can see lot of twinkling objects. But a few of them differ from the others. They don’t twinkle and while the other stars hold a fixed pattern from night to night, these drift. They wander across the sky, moving against the backdrop of stars. These are called planets. Our ancestors observed this and they imagined a universe with the Earth at the center, the stars in the distant background, and Sun, Moon and the planets orbiting around us.

Two observations supported the idea that Earth was the center of the Universe. First, from anywhere on the Earth, the Sun appears to revolve around the Earth once in a day. While the Moon and the planets have their own motions, they also appear to revolve around the Earth about once per day. Even the celestial sphere studded with stars appears to rise and set in the evening, and make one complete rotation in a year. Second, the Earth seems to be unmoving from the perspective of an earthbound observer; it feels stationary.

As civilization progressed the early astronomers found two types of motion of celestial objects. Let us take the case of Moon. On a daily basis Moon appears to rise in the east and set in the west.

Thus, one can say that Moon is going around the Earth with a period of one day. But for a careful observer, it was clear that the Moon was also exhibiting another motion. Suppose, the Moon is appearing in the sky today near the star Asvini, tomorrow we will observe that the Moon is near the star Bharani, a star east of Asvini. And the next day it will be near the star Kartikai, east of Bharani.

After 27 days, moving little by little eastwards, the Moon again stations itself near asvini. Thus, everyday Moon appears to move from east to west in one day where as it appears to go in a circle from west to east in the background of stars in about 27 days.

Light year

These two motions were puzzling. Very soon astronomers like Aryabhata said that Earth is spinning in its axis, that is the cause of apparent daily motion from East to West. Whereas the eastward motion of Moon in the celestial sphere with a period of about 27 days, was seen as the ‘actual’ motion of the celestial objects.

Thus, the geocentric model (also known as geocentrism), that is a description of the Universe with spherical and spinning Earth at the center and the Sun, Moon, stars, and planets all orbits the Earth emerged in various cultures. In Greece, this model was put forth by the Greek philosopher Plato and his disciple Aristotle in 6th century B.C.

It was standardized by a Greeco Roman mathematician Ptolemy in the 2nd Century A.D. A similar model is seen in the Siddhanthic astronomy in India like Aryabhateeyam of Aryabhata.

How moon exhibit phases

Astronomers in ancient times also observed certain facts. The Purananuru (65) of Sangam literature, the poet Poet Kalathalaiyar singing in appreciation of Cheraman Peruncheralathan says

“ On the day when the full moon appears, the sunand moon look at each other with their bright light. In the evening time, one sphere hides behind the mountains.”

On the full moon day, when the Sun is setting in the west, precisely at the same time, Moon rises at the East. That is both Sun and Moon are in the opposite side. Likewise when it is waning half moon, the Moon is rises when it is midnight and the waxing half moon rises during noon. From such observations and modelling ancient astronomers could explain why we have waxing and waning of moon.

It is probably easier to understand the waxing and waning of Moon in the order of new moon & full moon and then how the first and third quarter moon (half moon) appear and then the phases in between. Sun is the source of light. Sun light falls on the spherical earth, but only on the side facing Sun. The opposite side of Earth is without sunlight.

As the Earth spins day and night follows as different parts of Earth appear before the Sun. That is at all times one half of Earth is illuminated by Sun and one half is in darkness.

Like wise at all times one half of Moon is illuminated by Sun and the opposite side is shroud in darkness.

As shown in the above diagram, when the moon is positioned between the earth and sun, notice all the illuminated part of Moon is away from Earth. Hence we cannot see any part of the illuminated side of the Moon. Only the dark side of Moon is towards Earth. When the moon is in this position, we have new moon.

Now look at the moon when it is behind the Earth. Now the portion of the moon illuminated by sun is totally towards Earth. The dark side is away from the Earth. This means the moon will appear to be round in the sky. This is full moon.

When the Sun, Earth and Moon are in 90 degree angle how will the moon appear to a person on the surface of the Earth? Now if you look at the portion of moon facing Earth, we will see half if it illuminated and half is dark side. Thus, the moon will appear as half moon. The half moon during the waxing period is called as first quarter and the half moon during the waning period is called as third quarter.

Once we understand those four key moon phases, the phases between them should be fairly easy to visualize. The word crescent refers to the phases where the moon is less than half illuminated. The word gibbous refers to phases where the moon is more than half illuminated.

Waxing essentially means “growing” or expanding in illumination, and waning means “shrinking” or decreasing in illumination. Note all so that these discoveries could be made with naked eye. You do not need telescope or any modern equipment.

TNPSC TAMIL STUDY MATERIAL

10 std tamil study material

அன்னை மொழியே 

இரட்டுற மொழிதல் 

காற்றே வா

முல்லைப்பாட்டு 

காசிக்காண்டம் 

மலைபடுகடாம் 

பெருமாள் திருமொழி 

பரிபாடல் 

நீதி வெண்பா 

திருவிளையாடற்புராணம் 

பூத்தொடுத்தல் 

முத்துக்குமாரசாமி பிள்ளைத்தமிழ் கம்பராமாயணம் 

ஏர் புதிதா ? 

மெய்க்கீர்த்தி 

சிலப்பதிகாரம் 

ஞானம் 

காலக்கணிதம் 

சித்தாளு 

தேம்பாவணி 

9 std tamil study material

தமிழோவியம் 

தமிழ்விடு தூது 

பட்டமரம் 

பெரியபுராணம் 

புறநானூறு

மணிமேகலை 

ஓ , என் சமகாலத் தோழர்களே

உயிர்வகை 

குடும்ப விளக்கு 

சிறுபஞ்சமூலம் 

இராவண காவியம்

நாச்சியார் திருமொழி 

சீவக சிந்தாமணி 

முத்தொள்ளாயிரம்

மதுரைக்காஞ்சி 

ஒளியின் அழைப்பு 

தாவோ தே ஜிங் 

யசோதர காவியம் 

அக்கறை 

குறுந்தொகை 

8 std tamil study material

தமிழ்மொழி வாழ்த்து 

தமிழ்மொழி மரபு 

ஓடை 

கோணக்காத்தும் பாட்டு 

நோயும் மருந்தும் 

வருமுன் காப்போம் 

கல்வி அழகே அழகு 

புத்தியைத் தீட்டு 

திருக்கேதாரம் 

பாடறிந்து ஒழுகுதல் 

வளம் பெருகுக 

மழைச்சோறு 

படை வேழம் 

விடுதலைத் திருநாள் 

ஒன்றே குலம் 

மெய்ஞ்ஞான ஒளி 

உயிர்க்குணங்கள் 

இளைய தோழனுக்கு

7 std tamil study material

எங்கள் தமிழ் 

ஒன்றல்ல இரண்டல்ல 

காடு 

புலிதங்கிய குகை 

கலங்கரை விளக்கம் 

இன்பத்தமிழ்க் கல்லி 

ஒரு வேண்டுகோள் 

விருந்தோம்பல் 

வயலும் வாழ்வும் 

புதுமை விளக்கு 

அறம் என்னும் கதிர் 

மலைப்பொழிவு  

6 std tamil study material

காணிநிலம் 

அறிவியல் ஆள்வோம் 

மூதுரை 

துன்பம் வெல்லும் கல்வி 

ஆசாரக் கோவை 

கண்மணியே கண்ணுறங்கு 

நானிலம் படைத்தவன் 

கடலோடு விளையாடு 

QUANTITATIVE APTITUDE STUDY MATERIAL

Ration and proportional

Simplification

Percentage

Number series

L.C.M and H.C.F

Simple Interest

Compound Interest

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