Ponder Earth’s magnetic field as a shield protecting us from harmful cosmic radiation. Known as “geomagnetic” because it starts at our solid iron outer core, (miles below the surface) and reaches to the outer atmosphere. (creating a magnetosphere, the point in space beyond the ionosphere where charged particles protect us from solar wind and radiation). Without it – our ozone layer would wither, and we would succumb to ultraviolet radiation. In other words, life could not exist.
When strong solar winds impact the magnetosphere, they “distort” our magnetic field creating “openings” – the near side to the sun being “compressed” and far side of the planetary field is bulged outward.
- As the charged particles of solar winds and flares hit the Earth’s magnetic field, they travel along the field lines.
- Some particles get deflected around the Earth, while others interact with the magnetic field lines, causing currents of charged particles within the magnetic fields to travel toward both poles — this is why there are simultaneous auroras in both hemispheres. (These currents are called Birkeland currents after Kristian Birkeland, the Norwegian physicist who discovered them — see sidebar.)
- When an electric charge cuts across a magnetic field it generates an electric current (see How Electricity Works). As these currents descend into the atmosphere along the field lines, they pick up more energy.
- When they hit the ionosphere region of the Earth’s upper atmosphere, they collide with ions of oxygen and nitrogen.
- The particles impact the oxygen and nitrogen ions and transfer their energy to these ions.
- The absorption of energy by oxygen and nitrogen ions causes electrons within them to become “excited” and move from low-energy to high-energy orbitals (see How Atoms Work).
- When the excited ions relax, the electrons in the oxygen and nitrogen atoms return to their original orbitals. In the process, they re-radiate the energy in the form of light. This light makes up the aurora, and the different colors come from light radiated from different ions.
Two recent solar events – CME’s (coronal mass ejection) are poised to deliver Aurora magic in regions unaccustomed to their magnificence. Solar wind from the first eruption have arrived, with stronger consequences from the second ejection expected in the next few hours. What this means is Auroras could be visible far below normal latitudes. Some scientists project as far south as Mexico.
If you feel so inclined – go outside, cast your gaze northward, and watch for tell tale green ripples across the sky. Best time to view is between midnight and dawn – obviously clear skies away from city lights are advisable.