Chapter 35 - Galaxies, stars and solar system

What is a star?

A star is an object made up of gas that is luminous due to nuclear reactions.

What is the process that forms a star?

Stars form from nuclear fusion reactions between hydrogen atoms, creating helium and releasing energy.

What happens to a star when it runs out of hydrogen?

When a star runs out of hydrogen, it may die, explode in a supernova, or turn into a red giant, eventually becoming a white dwarf.

What are the four phases of a star's life cycle?

Phase 1: Formation, Phase 2: Stable period, Phase 3: Red giant, Phase 4: White dwarf.

What is the main sequence star phase?

The stable period in a star's life when it balances gravitational forces and heat energy, using up hydrogen for billions of years.

Describe a red giant star.

A red giant is a large star that forms when it exhausts hydrogen, burning helium and expanding its outer parts.

What is a white dwarf?

A white dwarf is a small, dense star that forms after a red giant sheds its outer layers, having about one-quarter of its original mass left.

How does light from stars reach us?

Light from stars takes time to travel through space to Earth, causing us to look back in time when we observe stars.

What defines a galaxy?

A galaxy is a collection of millions or billions of stars, along with gas and dust, held together by gravity.

What is our galaxy called?

Our galaxy is called the Milky Way.

What holds planets in orbit around the Sun?

The gravity of the Sun, being greater than that of the planets, holds them in their respective orbits.

What are the three types of planets in our solar system?

The three types are terrestrial planets, Jovian planets, and dwarf planets (planetoids).

Name the terrestrial planets in our solar system.

The terrestrial planets are Mercury, Venus, Earth, and Mars.

What are Jovian planets?

Jovian planets, or gas giants, are Jupiter, Saturn, Uranus, and Neptune, mostly composed of helium and hydrogen.

What is a planetoid?

A planetoid is a dwarf planet that is too large to be an asteroid but too small to be a full-fledged planet.

How do planets maintain their orbit?

Planets orbit the Sun due to the Sun's gravity pulling them inward while they also tend to move away into space.

How many moons does Earth have?

Earth has one moon, while some planets like Jupiter have many more.

Why is Earth unique in the solar system?

Earth can sustain life due to its suitable temperature, gravity, and atmosphere containing essential gases.