The Sun may appear rather tranquil to the eye, especially at a time when it is going through a period of what astronomers call "minimum activity". To the instruments of the SOHO spacecraft, however, this comparatively minor star is in a ceaseless turmoil.

These four images, at different wavelengths corresponding with different temperatures of the Sun, were taken by the SOHO's extreme ultra-violet-imaging telescope (EIT) - developed by Belgium, France and the USA. They reveal short, hair-like, jets of strong emissions, or, in simple terms, giant flames, shooting into the Sun's atmosphere.

Revealing the Sun's atmosphere to an extent not seen clearly before, these "spicules" tell of energetic upheavals which heat some parts of the atmosphere to 2 million¡C. The temperature profile varies greatly from place to place. The temperatures soar to over 2 million¡C in the outer atmosphere, while the lower atmosphere and the visible surface are relatively cool.

In some regions, cool gas follows magnetic pathways high above the Sun's visible surface. Elsewhere, violent activity raises the temperature locally, at low altitudes. The high-temperature images contain large, dark, regions called coronal holes, which remain relatively cool. Also visible are plumes stretching far into space from the North and South poles.

Only spaceborne instruments such as the EIT can see the hot regions of the Sun's disc, because the Earth's atmosphere absorbs ultra-violet rays produced at high temperatures.

Source: Flight International