Geography-1: Astronomy Basics

Important Prelims Topics

Age/ Size of Universe, Cosmic Horizon, Big Bang Theory, Expansion of Universe, Cosmic Microwave Background, Hubble Constant, Doppler Effect, Blue and Red Shift, Black Holes, Wormholes and Cosmic Strings, Dark Matter & Dark Energy, Galaxies Basics, Milkyway and Andromedia, Radio Galaxies, Magellanic Clouds, Intersteller Medium, Nebula, Quasar, Stellar Evolution, Sun & Solar System, Planets and Planetary Rings, Satellites, Meteors, Comets, Cosmic Rays.

Basic Facts about Universe

The universe is all of space, time, matter, and energy that exist. Universe is not just space, but space is just the framework or the scaffolding in which the universe exists. As Space and time are intimately connected in a four-dimensional fabric called space-time.

Age of Universe

The universe is not infinitely old. According to modern astronomical measurements, the universe began to exist about 13.7 billion years ago.

Size of Universe

It has not yet been scientifically determined exactly how large the universe is. It may indeed be infinitely large, but we have no way yet to confirm this possibility scientifically.

Cosmic Horizon

The farthest limit to our viewing is called the cosmic horizon, which is about 13.7 billion light-years away in every direction. Everything within that cosmic horizon is called the observable universe.

Structure of Universe

The structure of the universe—as opposed to the structure of matter in the universe— is determined by the shape of space. The shape of space is, surprisingly, curved.

On a very large scale—millions or even billions of light-years across—space has a three-dimensional “saddle shape” that mathematicians refer to as “negative curvature”.

Big Bang Theory

According to the Big Bang theory, the universe began to exist as a single point of space-time, and it has been expanding ever since. As that expansion has occurred, the conditions in the universe have changed—from small to big, from hot to cold, and from young to old—resulting in the universe we observe today.

Big Bang theory developed as independent works on Einstein’s General Theory of relativity by Willem de Sitter (1917), Alexander Friedmann (1922), Georges Lemaître (1927), Robertson, and Walker.

In 1929, Edwin Hubble analyzed and concluded that the galaxies are drifting apart. This became one of the cornerstone of the Big Bang theory.

Big Bang theory remains a theory as of now. The key evidences to Big Bang theory include expansion of universe and the cosmic microwave background radiation.

Expansion of the Universe

Universe is expanding but the scientists say that this expansion has not been at same rate all the times. Scientists say that for a very small fraction of second (Planck Time or 10 Scientists say that for a very small fraction of second (Planck Time or 10-43 seconds), universe underwent hyperinflationary expansion, which suddenly expanded the diameter of universe by at least a factor of ten billion billion. This is the so called Hyperinflationary model of expansion of universe.

Long after the hyperinflation ended, the expansion returned to an almost-constant rate, slowed down very slightly, and then billions of years ago started speeding up. Right now, the expansion rate of the universe is slowly but surely increasing. We live in an accelerating universe.

Cosmic Microwave Background

In the 1960s, astronomers at Bell Telephone Laboratories in USA were testing some of their instruments when the detected an ubiquitous microwave static that came from all directions in the sky. This discovery was later used as a proof to big bang theory.

Cosmic Microwave Background refers to the leftover energy from the hot, early universe that still fills space and permeates the cosmos in every direction.

Hubble Constant

The expansion rate of the universe is called the Hubble Constant in honor of Edwin Hubble (1889–1953). Currently the best measured value of the Hubble Constant is about 73 kilometers per second per megaparsec.

This implies that if a location in space is one million parsecs from another location, then in the absence of any other forces or effects the two locations will be moving apart from one another at the speed of 263,000 kilometers per hour!

Hubble measured the galaxies’ Doppler effect—the shift in the observed color of objects moving toward or away from an observer—by mounting a machine called a spectrograph on a telescope. He split the light from distant galaxies into its component parts and measured how far the wavelengths of emitted light shifted toward longer wavelengths.

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