01
The dip is exaggerated
A real Earth-sized planet transiting a Sun-like star dims it by less than 0.01% — this diagram uses a far larger dip so it's visible at all.
Exoplanets · Question
How do we find planets we can never directly see?
Most confirmed exoplanets have never been photographed — they're too small, dim, and close to their blinding-bright star. Instead, astronomers watch for something much simpler: a tiny, regular dip in the star's brightness.
Visual model
Drag the planet around its orbit.
What's simplified
Real transit signals are far smaller.
02
Only some orbits align
Transits are only visible if the planet's orbit happens to be lined up edge-on to Earth — most exoplanets orbit at the wrong angle to ever be detected this way.
03
One dip repeats
Astronomers look for the same dip repeating on a precise, regular schedule — a single dip could be measurement noise; a repeating one is a planet.
Misconception check
Quick check.
Quick check
Go deeper
Keep exploring.
Next in this series →
EM spectrum ↗
What infrared and X-ray reveal.
Orbits
Why don't planets fall into the Sun?
The orbital mechanics behind the planet in this diagram.
Learn
How to read space images
A light curve is a measurement, not a photograph — the same distinction this page covers.