The universe

What are celestial objects?

Natural objects found in space, such as stars, planets, and galaxies.

What are star clusters?

Groups of stars held together by gravity.

What are the main types of galaxies?

Spiral, elliptical, and irregular.

What is the Milky Way galaxy?

The galaxy that contains our solar system.

What is the solar nebular theory?

The theory that the solar system formed from a cloud of gas and dust.

What is the Big Bang Theory?

The theory that the universe began from a hot, dense point and expanded.

What is the Sun today?

A medium-sized, main sequence star.

What is luminosity?

The amount of energy (light) a star gives off.

What is the Hertzsprung–Russell (H-R) diagram?

A graph that shows stars’ temperature, brightness, and size.

How do stars die? (Low-mass stars like the Sun)

They become a red giant, then a white dwarf.

What is a white dwarf?

The hot, dense core left after a small star dies.

How will the Sun die?

It will expand into a red giant and end as a white dwarf.

How do massive stars die?

They explode in a supernova.

What is a supernova?

A powerful explosion when a massive star dies.

Star temperature and colour

• Hottest stars: Blue

• Hot stars: White

• Medium temperature stars: Yellow (like the Sun)

• Cool stars: Orange

• Coolest stars: Red

👉 Rule to remember:
Blue = hottest, Red = coolest