Exoplanet Discovery Calculator

The transit method finds planets by the tiny dip in starlight as they pass in front.

How the Math Works

The Exoplanet Discovery Calculator uses the transit depth formula to determine how much a planet blocks its star's light when crossing in front of it. The calculation squares the ratio of the planet's radius to the star's radius (depth = (R_planet ÷ R_star)²). This works because when a planet transits its star, it creates a shadow that reduces the observed brightness. The fraction of light blocked equals the fraction of the star's surface area that the planet covers, which is why we square the radius ratio - area scales with the square of linear dimensions.

Practical Applications

To use this calculator, input the radius of the planet and the radius of its host star in the same units. For example, if a planet has a radius 6,000 kilometers and its star has a radius 700,000 kilometers, you would calculate (6,000 ÷ 700,000)² = 0.000074, or about 74 parts per million of the star's brightness blocked. Astronomers use these depth measurements from transit observations to determine planet sizes and identify potentially habitable worlds that might support liquid water and life.

Day-to-Day Use

While you may not calculate transit depths daily, this technology impacts our everyday lives in surprising ways. The same principles help astronomers discover thousands of exoplanets, many of which may host alien life. Understanding planetary systems also informs our search for resources and future space exploration. Additionally, the precise measurement techniques developed for exoplanet detection have improved GPS accuracy, medical imaging, and other technologies we use regularly. It's a reminder that the math behind cosmic discoveries powers both scientific breakthroughs and practical applications on Earth.

Worked example

An Earth across a Sun-like star → about 84 ppm (0.0084%).

FAQ