Stretching Space

Cosmological redshift

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

• Expansion stretches light: $1 + z = \lambda_{\text{obs}}/\lambda_{\text{emit}} = 1/a$.
• Redshift tells us how much the universe has grown since the light left.
• The most distant galaxies known have z > 10.

Steps

1. Light stretched with the universe
2. A third of the size
3. Looking back in time
4. Why JWST sees in infrared
5. A shifted line
6. Farther than its age
7. Light that first moves away