coronae

Coronae is the plural of corona, a Latin word meaning crown. In science, the term is used in several fields to describe crown-like structures that surround, envelope, or extend from a central body. The common idea across contexts is a peripheral or halo-like feature.

In astronomy, the solar corona refers to the Sun’s outer atmosphere. It extends millions of kilometers into space and reaches temperatures of several million kelvin, far hotter than the solar surface. The corona is visible during total solar eclipses or with specialized instruments called coronagraphs. Its structure includes loops and streamers shaped by magnetic fields and it is the source of the solar wind. The coronal heating problem concerns why the corona is so hot compared with the Sun’s surface. Stellar coronae are analogous outer atmospheres of other stars, detected mainly through X-ray emissions and varying with magnetic activity, rotation, and age.

In biology and protistology, corona or coronae describe crown-like structures in various organisms. Some ciliates possess a ciliary corona—a ring or crown of cilia around a feeding or locomotor region. The term is used in the plural to describe multiple such crown-like structures across different species or taxa.

In high-voltage engineering, corona discharge is a partial electrical discharge that occurs in the air around energized conductors. This ionization creates a visible glow, ozone, and energy loss. The plural coronae appears in some technical writings to refer to multiple discharge regions.