A corona is a type of plasma

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 "atmosphere" of the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse

Solar eclipse

As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...

, but also observable in a coronagraph

Coronagraph

A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved...

. The Latin root of the word corona means crown.

The high temperature of the corona gives it unusual spectral

Spectroscopy

Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...

 features, which led some to suggest, in the 19th century, that it contained a previously unknown element, "coronium

Coronium

Coronium was the name of a suggested chemical element, hypothesised in the 19th century. It was named after the solar corona.During the total solar eclipse of 7 August 1869, a green emission line of wavelength 530.3 nm was observed in the coronal spectrum...

".