Hesperus

Hesperus is the personification of the evening star in Greek mythology and a name historically used for the planet Venus when it appears as the western evening star after sunset. The term derives from the Greek Hesperos, meaning west or evening, and it is often contrasted with Phosphorus, the Morning Star.

In myth, Hesperus is typically portrayed as a divine figure associated with the western skies. In many traditions, he is the son of Astraeus (the star-maker) and Eos (the goddess of the dawn), and he is frequently linked with Phosphorus, the Morning Star, with both names later identified with Venus. The Hesperus–Phosphorus pair reflects the star’s appearance at dusk and dawn.

Astronomically, Hesperus refers to Venus when seen in the western sky after sunset. For centuries, observers treated Hesperus and Phosphorus as two separate stars or deities, even though both names referred to the same planet, Venus. Modern astronomy uses Venus as the single planetary object, regardless of its appearance.

In philosophy, the sentence "Hesperus is Phosphorus" is famous for illustrating sense versus reference. Philosopher Gottlob Frege used it to show that two names can refer to the same object while conveying different meanings, a distinction central to his theory of language.

Culturally, Hesperus appears in literature as well. Henry Wadsworth Longfellow's ballad The Legend of Hesperus, published in the 19th century, tells of the evening star guiding a vessel, reinforcing the star’s symbolic association with western skies and maritime lore.