- noun a trumpet-shaped, petal-like outgrowth in flowers such as narcissi
- The outermost portion of the Sun’s atmosphere, extending more than 10 solar radii and maintaining a temperature of 1 000 000° or more. The material of the corona is not very dense and acts mainly as a medium through which solar energy passes almost unaltered. The corona gives out some radiation of its own at X-ray and other wavelengths but is best seen during eclipses. Patterns within the corona vary with the stage of the sunspot cycle, which dictates the shape of the Sun’s magnetic field and the distribution of the charged particles affected by it. Because of their high temperatures, coronas of stars other than the Sun can be observed in X-rays.