It was wonderful to see Leo Houlding in Antarctica enjoying one of nature’s spectacular heavenly glories of a ‘solar corona’ (Gazette, January 4).

The caption comments on the science behind the apparition but in a confused way.

The term ‘solar corona’ can carry two very different notions - readily identifiable according to whether the definite or indefinite article is used. The caption firstly describes ‘THE solar corona’ as the sun’s plasma gaseous atmosphere of extremely high temperature - a correct description for the term but not for what is captured in the beautiful image. ‘THE solar corona’ is seen only at a total eclipse, or by using special astronomical instruments at observatories or on a satellite.

The second usage of the term refers to ‘A solar corona’ or halo which appears when ice crystals in the Earth’s stratosphere refract solar light to produce a large ring in the sky. This was hinted at later the photograph’s caption and is the correct interpretation for the photograph. Such coronas come and go according to local meteorological conditions.

The caption makes no reference to the bright coloured spots at two points around the halo. These are ‘parhelia’ commonly known as ‘sun-dogs’ and may be seen anywhere at the time of ‘A solar corona’ as they were for the accompanying photograph taken from my garden.

Dr David Clarke

Retired astrophysicist