A distant planet can be much harder to see than the star it orbits. Astronomers therefore often look for its effects rather than a direct picture. Small changes in a star's brightness or motion can provide evidence that another world is present.
In the transit method, a planet passes between its star and an observer, blocking a small fraction of the light. Repeated dips can reveal an orbital period, while the depth of a transit helps estimate the planet's size relative to its star. The geometry matters: a planet whose orbit never carries it across the star from our viewpoint will not create a transit for us.
The radial-velocity method examines changes in the star's light caused by motion toward and away from the observer. A star and planet both move around their common centre of mass. Measuring the star's motion constrains the planet's mass, with the orbit's inclination affecting the interpretation. NASA describes these methods as complementary ways of finding and characterising exoplanets.
Imagine a classroom demonstration with a small ball passing in front of a lamp. A light sensor could register a dip, but a hand or another object could also block the light. The illustration captures an important scientific habit: an apparent signal needs examination. Astronomers assess alternative explanations and seek consistent observations before treating a candidate as a confirmed planet.
Finding a world also differs from knowing what conditions exist there. Size and orbital distance are valuable clues, but they do not provide a complete picture of surface temperature, atmosphere, or habitability. A label such as "Earth-sized" describes one property; it should not be read as evidence of oceans, breathable air, or life.
The excitement of exoplanet research lies partly in this progression from a faint signal to a more detailed physical account. Each measurement answers a particular question while leaving others open. When reading a discovery story, ask what was observed directly, what was inferred from a model, and which questions still require new evidence. Those distinctions make the discovery more interesting, not less.
Reference: NASA, How We Find and Characterize Exoplanets: https://science.nasa.gov/exoplanets/how-we-find-and-characterize/