Today we are providing you short notes about universe, galaxy, milky way, stars, sun, meteors, comets, big bang theory and planets. We will try to define them in few words. Glossary of these astronomy terms are very easy to memorize even for school kids for their school projects. So let’s check out definitions of space and planetary related terms.
Definition of Universe
Universe is infinite in time and space which includes planets, stars, asteroids, comets, constellations, galaxies and all the matter and energy.
Definition of Galaxies
Galaxies are association of billions of stars (star clusters) or groups of stars which are bound gravitationally, and intersteller matter. There are millions of galaxies; each galaxy is composed of millions of stars. A single galaxy with its constituents of stars makes a stellar system.
Definition of Milky Way
The name of our Galaxy. Also the name given to the band of diffuse light seen in the night sky that originates in the disk of our Galaxy.
Definition of Stars
These are massive, luminous bodies of plasma. The illumination is being the effect of nuclear fusion reactions of hydrogen.
Definition of Planets
These are non-luminous or non-radiating bodies, and are formed by the consolidation of gaseous nebula enriched with various elements.
Definition of Solar System
It is the arrangement of all the 8 planets in a systematic order by Sun’s gravitational force. The solar system is divided into two groups –
- Terrestrial group of planets or inner group of planets.
- Giant planets or outer group of planets.
Both these groups are separated by a zone of asteroids.
Definition of Inner Group of Planets
The planets Mercury, Venus, Earth and Mars form their inner group of planets. Their locations depend on the basis of their relative density. They are characterized with –
- Relatively smaller masses with higher densities
- Relatively slow speed of rotation
- Less number of natural satellites (moon)
Definition of Outer Group of Planets or Giant Planets
This group of planets includes Jupiter, Saturn, Uranus and Neptune. Pluto is now not regarded as planet of our solar system. It is regarded as dwarf planet. The outer planets are characterized by –
- Larger masses with low densities
- Relatively high speed of rotation
- High number of natural satellites
There are over 1700 identified planets outside our solar system, identified in 2014.
Definition of The Sun
Sun is a typical star where all the planets are revolving around by its gravitational force. The sun and these planets make the solar solar system.
Definition of The Earth
Earth is the third planet from the Sun. It is the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System’s four terrestrial planets. It is sometimes referred to as the blue planet. Earth formed approximately 4.54 billion years ago, and life appeared on its surface within its first billion years. Earth’s biosphere then significantly altered the atmospheric and other basic physical conditions, which enabled the proliferation of organisms as well as the formation of ozone layer, which together with earth’s magnetic field blocked harmful solar radiation. Earth has one natural satellite i.e. moon.
Definition of Meteors
These are also comic bodies which lose their orbital path and thrown off in the space. Some of them fall on the earth. During their path the cosmic body burns and they are called meteorites. The earth receives at least 10,000 tones of meteoric and cosmic materials every year.
Definition of Comets
These are the bodies of solar system; they are most remote from the Sun. These are countless in number. Their orbit is eccentric and consist of head and tail. They reappear periodically.
Definition of Big Bang Theory
The recent big band theory tells us how the universe began and is evolving. In essence, it is a theory that was created to explain two facts that we know about the universe – it is gradually expanding and cooling.
In the 1920s, Edwin Hubble found that galaxies far from own Milky Way are moving away from us. In fact, the further away galaxies are, the faster they are receding. So he concluded that the whole universe must have been expanding. Working backwards this means that at one stage the universe must have come from a single point. The big bang describes how the universe grew to form all the stars and planets we see around us now. During the big bang was first created and then stretched.
The easiest way to understand this tricky concept is to think of the universe as a fruitcake in an oven. Imagine you are a bit of fruit inside the cake. As it bakes, the cake rises and all the other bits of fruit around you move further and further away. No matter whereabouts in the cake you are, everything around you is moving away at the same rate. But unlike the fruitcake, there is no centre to the universe.
Read all our notes here >> Physical Geography