During exoplanet transits the ratio of the observed flux divided by the out-of-transit stellar flux is called the transit light curve. If during a transit the exoplanet temporarily occults a spot or facula, then the light curve will have a positive or negative bump, but after correction for such occultations the light curve will have a nearly smooth shape determined by the exoplanet’s radius and the illumination along the transit path by an immaculate (unspotted) star. As described in Chap. 16 , any difference between stellar illumination along the transit path and the illumination from the entire heterogeneous stellar disk can change the transit light curve depth. When the decreased radiation from many spots away from the transit path is not compensated by the enhanced radiation from faculae, the effect of this reduced illumination from the entire star is to produce a deeper transit light curve. As a result, the inferred radius of an exoplanet appears to be larger than for the case of an immaculate star. The reverse case of faculae dominating the stellar flux makes the light curve depth weaker during transits and the apparent radius of the exoplanet smaller Even polar spots can impact transit light curves when the exoplanet is in a highly-inclined orbit (Libby-Roberts et al. 2023).