Northern Lights Should be Visible as Far South as Maryland
Tonight, Friday September 12, 2014 the aurora borealis, or northern lights, might be visible as far south as Maryland in the East, and Nebraska to the west, according to Space.com.
Massive solar flares that occurred earlier this week on the sun just now reaching Earth. The charged particles, known as ions, upon entering the earth atmosphere will excite the cloud of gases surrounding the earth, making them glow. Usually, the aurora borealis, are only visible much closer to the magnetic north pole or close to the southern pole, where they are known as the aurora australis.
While the light will be technically visible far south on the eastern seaboard, in order to have a chance to see the lights you will have to move out of the cities with a clear view northwards.
Auroras seen near the magnetic pole may be high overhead, but from farther away, they illuminate the northern horizon as a greenish glow or sometimes a faint red, as if the Sun were rising from an unusual direction. Discrete auroras often display magnetic field lines or curtain-like structures, and can change within seconds or glow unchanging for hours, most often in fluorescent green. The aurora borealis most often occurs near the equinoxes.
- Red: At the highest altitudes, excited atomic oxygen emits at 630.0 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under some circumstances with more intense solar activity. The low amount of oxygen atoms and their very gradually diminishing concentration is responsible for the faint, gradual appearance of the top parts of the “curtains”.
- Green: At lower altitudes the more frequent collisions suppress this mode and the 557.7 nm emission (green) dominates; fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays its role here as well, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the bottom parts of the curtains.
- Yellow and pink are a mix of red and green or blue.
- Blue: At yet lower altitudes atomic oxygen is not common anymore, and ionized molecular nitrogen takes over in visible light emission; it radiates at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the bottoms of the “curtains”, show up at the highest levels of solar activity.