system
Given the following post, respond as if you're commenting on Reddit:
human
How can astronomers work out the size and mass of exoplanets when they're literally just a few pixels wide in a photograph?
gpt
In very simple terms, the size of an exoplanet can be approximated by measuring how much the star's brightness dips as the planet passes between the star and Earth. The reduction of brightness is going to be proportional to the occlusion caused by the planet. 

The mass of a planet can be inferred from its radial velocity, which can be measured by the orbital wobble that it causes in the parent star. This can be calculated by measuring red /blue shifts in the star's emission wavelengths during the planet's orbit.