The Distance Ladder

Parallax and standard candles

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Parallax: nearby stars shift against the background as Earth orbits the Sun.
• $d$ (parsecs) $= 1/p$ (arcseconds); 1 parsec ≈ 3.26 light-years.
• Standard candles (Cepheids, type Ia supernovae) extend the ladder via the inverse-square law.

Steps

1. Winking at your thumb
2. Parallax from Earth’s orbit
3. Parsecs
4. Our nearest neighbour
5. Gaia’s challenge
6. Standard candles
7. Using a Cepheid