07-06-2008 Earth – home sweet home (Article 140)

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Simon Kenny
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Joined: Tue Feb 12, 2008 9:17 pm
Location: Shannon, Co. Clare, Ireland

07-06-2008 Earth – home sweet home (Article 140)

Post by Simon Kenny » Wed Dec 31, 2008 10:43 am

Earth — home sweet home (Article 140)

Shannonside Astronomy Club has been producing short pieces on various astronomy topics for the Limerick Leader for over two and a half years now and we have dealt with our neighbouring planets and other Solar System residents. We have described the creation and evolution and location of other stars and star clusters and indeed our own Milky Way galaxy. We have described the presence and sheer abundance of other galaxies in the universe and included discussion on very exotic things like black holes and quasars, all the while demonstrating the sheer enormity of the known universe. But, we have said very little about our home planet Earth, our own backyard, so to speak.

This article can only attempt to give a quick overview of Earth and many more articles are required to go deeper and attempt to explain the checks and balances that go into making the Earth ‘tick’.

Between 1968 and 1972 when astronauts first travelled from Earth to the moon they often reported that our planet Earth is the most beautiful sight visible from space. The famous image of Earth with this article -- known as ‘The Blue Marble’-- was taken on Dec 7th 1972 from the Apollo 17 spacecraft that was some 18,000 miles from Earth and heading to the Moon. NASA credits this image to the entire crew of Apollo 17: Eugene Cernan, Ronald Evans and Jack Schmitt.

No other world in our solar system has Earth’s contrast between white clouds and blue oceans and the magnificent green colour of vegetation. There would be no comparison with the Moon whose surface has been bombarded for billions of years by interplanetary debris. Whilst Earth would have been equally bombarded in the violent past of our solar system its atmosphere and weathering capability has removed almost all traces of this pulverisation.

To an interstellar traveller Earth would certainly seem like a very tranquil and inviting place to visit. Yet this apparent tranquillity is deceptive. From 18,000 miles what looks like a solid surface is actually in a state of very slow but yet constant motion that is driven by the movement of molten rock within ‘The Blue Marble’s interior. The relentless sunlight from our parent star gives the Earth the energy to create huge storms. What we cannot see in this image are the colossal clouds of sub atomic particles that wander around outside our planet in two enormous radiation belts (Van Allen belts) and are influenced by Earth’s magnetic field. Nor, in this image, can we see trace gases in Earth’s atmosphere whose amounts may decide the future of our climate with inevitable knock on effects.

To put Earth into perspective, with respect to the other ‘terrestrial’ planets of Mercury, Venus and Mars, Earth is the largest of these and has a mass greater than the combined mass of Mercury, Venus and Mars and is unlike the arid surfaces of these three insofar as Earth has 71% of its surface covered in water. But this is just the beginning of trying to understand how Earth ‘ticks’.

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