What Northern Lights look like – arch, band, coronas
Aurora Borealis can appear in many different shapes. Early at night, it is usually a grand arc stretching across the sky from east to west. Usually it is green and with fuzzy edges. The bottom of the arc is quite sharp while the upper edge is blurred.
Sometimes, the arc can be active and start moving so it looks like curtains. You may see rays of light that appear in the same direction as the Earth’s magnetic field. The length of the arc can reach up to 1000 km or more, while its width can be limited to as little as 100 m.
An aurora band is similar to an arc but crimped or curled into a spiral.
If you stand right underneath the northern lights in the same direction as the magnetic field, the Aurora rays appear to originate from one single point and radiate outwards. This is called a corona.
If you are watching the same Northern Lights, but from a location further south or north, it will appear as an arch.
The most intense Northern Lights, which appear after solar storms, the entire sky can be filled by incredible shapes and colors including green, red, blue and violet. On these occasions, the light can be strong enough to read a text in a book or magazine.
The shades and shapes change very suddenly. The most intense activity may not last more than 10 minutes so the trick is to check the sky often!
When the extra energy transmitted to the magnetosphere from the solar storm is reducing, you may see pulsating Northern Lights. Underneath, you may see pale patches of light appearing and disappearing randomly and with different duration but usually only a few seconds. These types of Northern Lights are most common after midnight.
The most common Aurora is called “Different” Northern Lights. They are difficult to see because they lack shapes and may just appear as a soft glow over big sections of the sky.
In fact, there is always Northern Lights somewhere on the sky even if you can’t see it. Around the Earth’s magnetic poles there is always a ring of Aurora but you may be in the wrong location. Or, you may be in the right location but still can’t see it because of clouds, daylight or bright summer nights.