Earth's Magnetic Environment and Our Cosmic Address
Big idea: Earth is both a magnetized planet and one member of an enormous hierarchy: planet, planetary system, galaxy and observable universe.
Learning goals
- describe Earth's field with magnetic field lines;
- explain compass alignment, the magnetosphere and auroras;
- distinguish planets, stars and galaxies;
- use astronomical unit and light-year as scale units;
- locate the Solar System within the Milky Way.
A planetary magnetic field
Currents in Earth's electrically conducting, moving outer core generate a large-scale magnetic field. Near the surface it resembles a tilted dipole, but it is not a rigid bar magnet. A compass needle experiences a torque and aligns approximately with the local horizontal field. Magnetic and geographic poles are different, and the field changes gradually with time.
Magnetosphere and solar wind
The solar wind is a stream of charged particles from the Sun. Earth's field redirects many particles and forms the magnetosphere: compressed on the sunward side and stretched into a tail on the night side. Some particles are guided toward polar regions, collide with upper-atmosphere atoms and produce auroral light.