An infographic shows how a planet moving in front of a star in transit tells us different things as does the exoplanet traveling behind its star in an eclipse.

Scientists used the James Webb Space Telescope to observe the exoplanet WASP-18 b and its star before, during and after the planet was eclipsed. By measuring the change in light when the planet travels behind the star, the planet’s brightness is revealed. From these measurements, scientists were able to make a temperature map of the planet’s day side. Displayed temperature range: 2,800 to 4,800 degrees Fahrenheit (1,500 to 2,600 degrees Celsius).

Visual description

A graphic is headlined Transits & Eclipses

Telescopes see an exoplanetary system as a fuzzy spot of light.

Total Light = The brightness of the spot includes the combined light from the star and its exoplanets.​

Transit: Exoplanet passes in front of star

Eclipse: Exoplanet passes behind star

By watching how the total brightness of a system changes over time, astronomers can discover – and learn about – exoplanets.

The light blocked during a transit reveals the exoplanet's size

The light blocked during an eclipse reveals the exoplanet's brightness

How the brightness changes during an eclipse tells us about the exoplanet's general appearance.

Gradual dip indicates a more uniform glow.​

Sharper dip indicates a brighter spot.

Sensitive JWST eclipse observations of exoplanet WASP-18 b helped astronomers calculate a thermal map for its atmosphere.​


NASA/JPL-Caltech (R. Hurt/IPAC)