Organization of the Universe, and its Development: The Stellar Evolution

Origin of the Universe

Cosmology is the specialized branch of astronomy which deals with the study of the structure, dynamics, and development of the universe. Cosmologists believe that the best explanation for the origin of the universe is that it began with an explosion, a Big Bang, about 13.8 billion years ago. So that’s how old our universe is.

The Big Bang Theory

1. Started as strong radiation
2. Grew into a large fireball. Hot matter flung out in all directions
3. This hot, swirling matter started cooling down, forming clumps of matter
4. These clumps formed the planets, stars, galaxies, our solar system, and all other forms of matter that we know today

The universe continues to expand even today!

The Hubble Space Telescope

Orbits in the Universe

All planets move around the sun in paths called orbits. Moons move around their planets in their own orbits. There are millions of rocky chunks called meteors and asteroids which also have their own orbits. There are millions of comets, made of dust and frozen gas with long trailing tails, which move in their own orbits. Everything in the universe is in constant motion!

These orbits could be roughly circular or extremely elliptical. Most planets have roughly circular orbits, but more distant bodies, such as comets, have hugely elliptical orbits.

Shooting Stars are not Stars!

Small chunks of rock which are mere debris in space are known as meteorites. These often get pulled into the Earth’s atmosphere by the strong gravitational force of Earth. As they fall, they burn up in a blazing trail which we call “shooting stars”. They’re not really stars!

Galaxies

Millions of stars together form a galaxy. Our solar system resides in the Milky Way galaxy. There are millions and millions of other galaxies in our universe!

A Star is Born!

1. Stars are created from giant, swirling gas clouds.
2. The dust and cloud get pulled together by gravity to form a dense ball.
3. As the star gets squeezed it becomes very hot.
4. The star expands to let the heat out and starts glowing brightly.
5. The expansion and contraction make the star bright and dim and bright again.
6. The expansion and contraction become rapid and the star throbs and pulsates.
7. Eventually, the star explodes into many pieces of material and gas.

Check Point

1. The best explanation for the origin of our Universe is known as the _________.
2. We can monitor and study the Universe with –
   1. Spacecraft such as the Hubble Space Telescope
   2. Probes
   3. Simple Telescopes
   4. All of the above
3. The shapes of orbits are often _________ or _________.
4. Millions of stars together form a _________.
5. Debris falling on Earth with a blazing trail could be –
   1. A Comet
   2. A Meteorite
   3. A Star
   4. A Shooting Star

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