Lecture 2: Page 6

Page 6, Motions in the Sky: [Previous Page] [First Page] [Class Home Page]

The Milankovitch Hypothesis

Many might think the Winter is when we are further from the Sun. You now know that it's not the distance, but the inclination to the Sun that gives us our seasons. However! There is a slight effect as the Sun-Earth distance changes in the year.

The Earth's orbit is 98.3% circular. The 1.7% `egg-shaped-ness' means we are slightly closer at some points than at other points in the orbit. Closest approach to the Sun is called Perihelion, the furthest point is called Aphelion (`A' for away). Lucky for us in the Northern hemisphere the Earth is closest to the Sun during Northern Winter, which helps to minimize the freeze!

In the 1920s, a Yugoslavian scientist Milutin Milankovitch presented an `astronomical theory' for long term global changes in climate which result from slow changes in the Earth's orbit around the Sun. The Earth-Sun distance changes due to changes in: (1) the orbits `squashed-ness', (2) the amount of the tilt (varying from 22^o to 24^o), and finally, (3) precession. Imagine how things will change due only to precession in 12,000 years. Our Winters will be much colder and our Summers unbearably hot!