State that: (a) galaxies are each made up of many billions of stars (b) the Sun is a star in the galaxy known as the Milky Way (c) other stars that make up the Milky Way are much further away from the Earth than the Sun is from the Earth (d) astronom

What is a Galaxy? 🌌

A galaxy is a huge collection of stars, gas, dust, and dark matter. Think of it like a bustling city where each star is a house. Each galaxy contains billions of stars (often 10⁹ to 10¹²).

Our Sun in the Milky Way ☀️

The Sun is just one of the many stars in our galaxy, the Milky Way. It sits about 27,000 light-years from the galactic centre, in a region called the Orion Arm.

Distances to Other Stars 🚀

Other stars in the Milky Way are much further away from Earth than the Sun. For example:

• Proxima Centauri – 4.24 light-years
• Betelgeuse – 642.5 light-years
• Vega – 25 light-years

Light‑Years: The Cosmic Unit of Distance ✨

A light-year is the distance light travels in one year in a vacuum. Since light moves at \$c \approx 3.00 \times 10^8\ \text{m s}^{-1}\$, one light-year is:

\$1\ \text{ly} = c \times 1\ \text{yr} \approx 9.46 \times 10^{15}\ \text{m}\$

Use light-years to compare cosmic distances easily.

Quick Reference: Distances in Light-Years

Exam Tips for IGCSE Physics 0625 📚

1. Remember that a galaxy is a collection of billions of stars.
2. State that the Sun is a star in the Milky Way.
3. Explain that other stars in the Milky Way are farther from Earth than the Sun.
4. Define a light-year and give its value in metres.
5. Use the city analogy to describe a galaxy for clearer answers.