08-09-2007 The Sun (Article 102)

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Simon Kenny
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Location: Shannon, Co. Clare, Ireland

08-09-2007 The Sun (Article 102)

Post by Simon Kenny » Wed Feb 04, 2009 11:20 am

The Sun (Article 102)

In our cool, rainy climate, the lack of sunlight is a regular source of complaint. Our position at 52 degrees North provides a constant reminder of the Sun’s importance to life on earth: its seasonal coming and going determines the cycle of life. Its energy, mostly as heat, drives the global weather systems, constantly witnessed in our own changeable weather. The Sun’s tremendous energy can be somewhat appreciated in the vicious storms that lash our coasts during winter months.

People understood the Sun’s power from earliest times. The Sun determined the time of day, the time of the year, when to plant and harvest. Religious festivals were based on its seasonal coming and going. It was frequently worshipped as a god. It so dazzled us in every way, that serious scientific study of the Sun only began relatively recently. The source of the Sun’s massive energy output was a complete mystery until Einstein formulated his Theory of Relativity a century ago. Only recently has the eleven year cycle of its sunspots been carefully studied, because of the associated risks to astronauts and satellite communications.

Recent studies show the Sun isn’t quite the stable, unchanging source of light and heat that people once thought. It is a boiling, seething sphere of gases, mostly hydrogen, about 1.6 million km in diameter and like any boiling fluid, it occasionally belches and splutters hot fluid from its surface, some falling back, more escaping into space. The stuff that escapes is extremely energetic plasma and if it comes our way, within a few days of leaving the Sun, it can cause magnificent auroral displays at night. It is these Coronal Mass Ejections (CMEs) that can cause much damage to satellites and astronauts exposed to them above the Earth’s protective magnetic field. Even electronic equipment on the ground isn’t immune to damage from these energetic visitors from the Sun.

The source of the Sun’s energy is in its core. Here, hydrogen experiences enormous gravitational compression and is heated to over 15 million degrees Kelvin. These extreme conditions are needed to initiate and sustain the thermonuclear fusion reactions in the Sun’s core. In this process, hydrogen is changed into helium, and the by-product is a massive output of energy across the electro-magnetic spectrum: the best known to us are light, heat and ultraviolet rays.

Fortunately, the Sun’s energy output remains remarkably stable and this has made the emergence of life on Earth possible. Stars that are bigger than the Sun are more unstable and are subject to massive periodic explosions of plasma from their surfaces that would kill off any emergent life in their neighbourhoods. So, while our friendly neighbourhood star has its moods, it is generally very civilised and predictable. Thanks to that, we are here! Clear skies.
(Warning: do not use a telescope or binoculars with the Sun above the horizon — instant blindness will occur).

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