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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Astronomy and climate
From: George Huxtable
Date: 2004 Dec 4, 16:01 +0000
From: George Huxtable
Date: 2004 Dec 4, 16:01 +0000
Apologies, in advance, for the lack of navigational content in this message. It's just an example of the subtle way that astronomical factors can affect Earth's climate, over historical (well, archaeological) periods of a few thousand years. Just in terms of the Earth-Moon-Sun system; nothing to do with interplanetary chaos. What controls the Earth's weather is mainly radiation from the Sun. The Earth's elliptical orbit round the Sun means that when it's closest to the Sun (early in January), the heat and light received by the Earth is about 7% greater than it is 6 months later, when the distance is greatest. That's quite a big difference. It's also a convenient difference, for those of us that live in the northern hemisphere, in that we get our 7% boost just around the coldest time of the year. It helps to ameliorate the changes, to make northern climates more equable than they would have been otherwise. Not so for those in Southern latitudes, however. Their increased Sun energy is around midsummer, when it's needed least. As a result, southern climates are more extreme than they would have been otherwise. However, in 9,000 years time, around 11000 AD, mainly because of the precession of the Earth's axis, it will all be the other way round, and northern climates will be correspondingly more extreme between winter and summer; and in the south, more equable. And that would also have been the case around 9000 BC. All this is quite inevitable, and has nothing to do with global warming or greenhouse gases. There's another effect, caused by slow changes in the tilt of the Earth's axis (obliquity), by getting on for a degree either way, which can also affect the variability of the seasons over a similar timescale. George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================
