The Speed of Light
Light travels at approximately 300,000 kilometres per second. While that seems incredibly fast, space is so vast that even light takes a long time to cross it.
Examples:
Moon → Earth: ~1.3 seconds
Sun → Earth: ~8 minutes
Nearest star → Earth: ~4.24 years
Seeing the Past
When you look at the night sky, you are not seeing objects as they are now — you are seeing them as they were when their light left them.
Some galaxies visible through telescopes may no longer exist in their current form.
This makes astronomy unique: it allows us to observe the history of the universe directly.
Why This Matters
By observing objects at different distances, astronomers can:
Study how galaxies evolve
Understand how stars are born and die
Learn how the universe itself has changed over time
Key Takeaways
Light has a finite speed
Distance equals time in astronomy
Telescopes are time machines