A major solar flare could potentially bring doom and gloom to our modern civilization, however, so long as the flare or CME remains below the critical threshold of destruction, it can bring a mysterious and beautiful display of shimmering light in the night sky. Instead of reiterating the ‘negative’ and scary aspects of our Sun unleashing hell and fury, which we’ve done our share of here… lets look at the bright side a moment…
The origin of the aurora is the Sun, 93 million miles away. Particles from the Sun are carried out into space along with the hot solar wind. This wind sweeps supersonically toward the Earth at speeds ranging from 300 to 1,000 km per second (670,000 to 2,230,000 miles per hour!) carrying with it the solar magnetic field.
The Earth’s magnetic shield acts as a barrier, protecting us from particles and radiation in the hot solar wind. Most of these particles are deflected by the magnetosphere, but some get trapped. Electrons trapped in the Earth’s magnetic field are accelerated along the magnetic field toward the polar regions and then strike the atmosphere to form the aurora.
This circle is centered over the magnetic pole and is around 3000 km (1,800 miles) in diameter during quiet times. The circle grows larger when the magnetosphere is disturbed.
Auroral features come in many shapes and sizes. Tall arcs and rays start brightly 100 km (60 miles) above the Earth’s surface and extend upward along its magnetic field for hundreds of km.
Auroral arcs can nearly stand still and then, as though a hand has been run along a tall curtain, the aurora will begin to dance and turn.
Most of the auroral features are greenish yellow but sometimes the tall rays will turn red at their tops and along their lower edge. On rare occasions, sunlight will hit the top part of the auroral rays creating a faint blue color. On very rare occasions (once every 10 years or so) the aurora can be a deep blood red color from top to bottom.
Where or when can we see the Aurora?
The geomagnetic field is measured and quantified and categorized in the ‘K-index’. The K-index value ranges from 0 to 9 and is directly related to the amount of fluctuation (relative to a quiet day) in the geomagnetic field over a 3-hour interval. The higher the K-index value, the more likely it is that an aurora will occur.
First, determine your ‘corrected magnetic latitude’ based on your geographical location.
Then, compare that number to the following cross reference list, which shows you the required ‘K-index’ (of a given solar storm effecting the Earth) versus your magnetic latitude location in order to see the Aurora. For example, if you are located at magnetic latitude ’58’, you will need a solar storm producing a K-index of at least ‘4’ to see the aurora during the night.
You can discover the current K-index, here.
Current ‘live’ K index
Credit: Some of the descriptive text was excerpted and then simplified, from a NOAA document in the public domain.