Final answer:
The fraction of a star's light blocked out by an exoplanet during transit can be calculated using the transit depth, which is determined by the area of the exoplanet compared to the area of the star.
Step-by-step explanation:
In a transit, the fraction of a star's light blocked out by an exoplanet can be calculated using the transit depth. The transit depth is determined by the area of the exoplanet compared to the area of the star.
Mathematically, the transit depth is given by the formula TR², where T is the size of the exoplanet and R is the size of the star. The transit depth represents the fraction of light blocked by the exoplanet during its transit.
For example, if the transit depth is 0.05, it means that 5% of the star's light is being blocked by the exoplanet.