It is a vast expanse of space where everything in existence lies.

Different Views on the Universe

Big Bang Theory: Origins and Evidence

It was given by George Lemaitre.

• It states that the universe came into existence around 13.8 billion years ago. The universe started as just a single point called the singularity – infinite mass with zero volume. 
• During the Big Bang, the single point inflated and exploded violently which resulted in expansion of the universe.

Evidences Supporting Big Bang

• Distance between galaxies increased (Red Shifting of Galaxies)
• Faint glow of light present in the Universe (Cosmic Microwave Background Radiation)

Galaxies

It is a huge collection of dust, gas, and billions of stars and their solar systems which are held together by gravity.

Types of Galaxies

Milky Way Galaxy: Structure and Neighbors

• Location: Our solar system is located in this galaxy.
• Size: Around 1,00,000 light-years across
• Age: Around 13.6 billion years.
• Type: Spiral Galaxy.
• Structure:
  • Sagittarius A*: It is a supermassive black hole in the middle of our Milky Way galaxy. Everything in our galaxy revolves around this black hole.
  • Galactic Bulge: It is a tightly packed region of gas, dust, and stars in the immediate surrounding of the Sagittarius A*.
  • Galactic Disc: It is located beyond the galactic bulge. It hosts billions of stars, including our Sun.
• Nearest Neighbour: Andromeda

Science of Stars

Stars are a giant, glowing ball of gas and dust which are held together by gravity.

Characteristics:

• Mainly composed of hydrogen and helium.
• Vary in size, mass and temperature.
• The colour of the star is determined by its temperature. The hottest stars are generally blue, while the coldest stars appear red. 

Life Cycle of a Star

Constellation

A group of stars with a constant shape. 

• Visibility of a particular constellation depends on the location and time. 
• Generally named after objects, animals, and even mythological figures.  
• At present, there are 88 officially recognized constellations. 
• Used to name stars, meteor showers, and navigation.
• Examples: Ursa Major, Orion, Hunter, Ursa Minor, and The Little bear.