• Ashwini

GS1: The Universe around us!

Updated: May 18, 2020

A very overwhelming ability of humans is the presence of copious, complex and conscious thoughts. This amazing ability distinguishes us from the other species sharing space with us on our planet and, in parallel, this brought in us the curiosity to know beyond the horizon, an innate desire to understand and explain all that surrounds us- our beloved Universe.

The universe is all of space and all the matter and energy within it. It constitutes a vast number of galaxies and solar systems and is expanding ever since its creation after the Big Bang 13.7 Billion years ago.

The study of the structure and history of the Universe is called Cosmology.

Image Credit: NASA, ESA, CXC and STSci-PRCD-07A

Questions that are put forth for consideration before beginning the study of the Universe are, What is up there? How big are they? How far are they? How are they arranged in a vacuum? Oh, is there a vacuum?

We first begin by distinguishing between the planets and the stars. The Planets are celestial bodies which move in an elliptical orbit around the star and do not have the light of their own like stars. They are more or less spherical bodies.

Shape of the Earth is best described as the Geoid.

The Stars are a luminous celestial body, unlike planets. They are balls of incandescent gas that emits intense heat and light. You can observe many fixed luminous stars in the night sky with your naked eyes because those stars are very far from the Earth.

Do you know the nearest star to Earth is the Sun (150 millions km).

In the last few centuries, two famous schools of thought existed to explain the configuration of Earth, Sun and Moon. And these were the Geocentric Model (a) and the Heliocentric Model (b). The Geocentric (Geo-Earth, Centric-Centre) Model enunciated that Earth was the centre of the Universe, not Solar System, while the Moon and the planets along with the Sun revolved around it. This model gained popularity due to the influence of an Egyptian Mathematician, Ptolemy, for he developed equations that appeared to predict the wandering of a celestial body around the Earth. Also, did this theory comfort the thought that the home of humanity occupies the most important place in the Universe, no one thought of breaking the queue. And, if you dare to, then you were supposed to face the consequences.

The second school, the Heliocentric (Helio- Sun, Centric- Centre) Model enunciated the presence of the Sun as the centre of the Universe, with Earth and other planets orbiting around it. In the 15th century, Europe saw the rise of bold thinkers leading to the new age of exploration and scientific temperament. The efforts of Nicolaus Copernicus and Galileo Galilei led to the realization that the Earth and planets did indeed orbit the sun and Sun itself could not be at the centre of the Universe. Afterwards, when Newton explained the theory of gravity, all the equations were balanced.

The revelation of the Universe began from the era of Newton only. They began discussing the Universe in terms of Matter and Energy. The matter is the substance of the Universe which takes up space and is tangible. The amount of matter in an object leads to the concept of mass, greater the mass-more the matter. The force that acts on an object due to gravity is called Weight, which is determined by its mass. The density of an object refers to the amount of mass occupying a given volume of space. Weight can vary depending upon the gravity but the mass remains constant. The matter in the universe can not sit idle. It moves, vibrates, jumps and spins. They pull or push against each other, and they may break or combine. In a general sense, such changes are considered as Work. And the ability to do work is known as Energy. With the improvement in understanding and technology, our concepts were refined and became robust. Stars, as observed with the telescope, are not randomly scattered through the Universe; gravity holds them together in immense groups called Galaxies. The Sun and over 300 billion stars together form the Milky Way galaxy. More than 100 billion galaxies constitute the visible Universe. Now we have to conclude the fact that neither the Sun nor the Earth nor the Milky Way heralds the centre of the Earth.



Stephen Marshak- Essentials of Geology

Arthur Holmes- Principles of Physical Geology

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  • Earth orbits around the Sun in 365.25 days. 0.25 days add to form 1 day after 4 years resulting in the leap year.

  • Earth completes its rotation about its axis in 23.9 days, defining days and nights.

  • Earth's axis of rotation is 23.5 degrees inclined from the normal to the elliptical equatorial plane of planets, giving rise to the seasons on the planet.

  • On two days of the year- Equinoxes, both the hemisphere is equally illuminated by the Sun.

  • Whichever hemisphere is close to the Sun experiences summer, while the one away from the Sun experiences winter.

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