A whimsical artist's view of our home planet. Earth, also called the world (and, less frequently, Gaia or, in Latin, Terra) is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to accommodate life. Valentine's Day, also known as Saint Valentine's Day or the Feast of Saint Valentine, is a holiday observed on February 14 each year. It is celebrated in many countries around the world, although it is not a holiday in most of them. The day was first associated with romantic love in Medieval Europe, when the tradition of courtly love flourished. In 18th century England, it evolved into an occasion in which lovers expressed their love for each other by presenting flowers, offering confectionery, and sending greeting cards. Valentine's Day symbols that are used today include the heart-shaped outline, doves, and the figure of the winged Cupid. No artist credited, dated May 2, 2013.