Re: Is the Earth, on average, moving closer to the sun?

The Earth is not moving closer to the Sun and this is not the reason for global warming and/or global climate change.

The Big Bang theory describes the expansion of the Universe, not the Milky Way galaxy or the Solar System. For more information, please see http://www.umich.edu/~gs265/bigbang.htm

Kepler's Laws describe the motions of the planets, including their constant (i.e., unchanging) elliptical orbit around the Sun. However, in the case of the Earth and most of the other planets, the ellipse is so slight that we assume circular orbits. While it is true that during our year (which takes us one time around the Sun), the Earth is slightly closer at some point, it is not *moving* closer to the sun, as in changing its orbit. Newton told us that objects in motion stay in motion unless acted on by an outside force; therefore, the Earth and all the other planets will stay in their current orbits, unless some external factor causes this to be different. One example would be a large gravitational interaction due to another planet or planetesimal. Our Solar System is over 4.5 billion years old and most, if not all, of these large impacts, ones that would cause planetary orbits to change, finished occurring by 3.75-ish Ga ago. Of course, we still see orbits of small objects change, as in the cases of comets (Shoemaker-Levy 9 in 1994) and Earth-crossing asteroids. The website spaceweather.com lists the orbits of near-Earth asteroids and describes the interactions that caused them to be in these orbits.

Global climate change (my preferred phrase) has to do with human causes, such as the emission of greenhouse gases into our atmosphere. These gases are very efficient at keeping infrared radiation (i.e., heat) near the surface. Please see http://climate.nasa.gov/keyIndicators/ for more information.