The Aurora Borealis, which are commonly known as the Northern Lights, are a captivating phenomena.
The shimmering colors of green, red and violet light occur due to the relationship between the Earth and the Sun. While they typically occur in higher latitudes, recent events prove that it can happen across the country, including portions of South Central Texas.
But what exactly are the Northern Lights, and what has to happen for San Antonians to catch a glimpse?
The science behind the lights
The lights start 93 million miles away. The auroras occur when charged particles from the sun are carried by solar wind to Earth where it interacts with the magnetic field.
When the sun erupts with more intense bursts of energy - such as from solar flares or coronal mass ejections (CMEs) that wind becomes supercharged.
Earth’s magnetic field normally deflects much of the activity on a day to day basis, but during solar storms, the magnetic field is temporarily distorted. That allows some of those particles to funnel down towards the North and South Poles.
At the poles, they collide with atoms and molecules (primarily nitrogen and oxygen) while also emitting energy in a form of light. However, the colors can vary by altitude.
- Green: oxygen at ~100km altitude
- Red: oxygen above 300 km altitude
- Purple/Blue: nitrogen molecules only
Where the lights are typically seen
The auroras are typically and most commonly seen in the polar regions, which some call the Auroral Oval, which typically sit around 60° latitude. Those ovals, however, aren’t a fixed location.
When a strong solar storm hit, they can expand dramatically southward, reaching midwestern states like Kansas or even the Lone Star State.
Technology impacts
While the auroras are breathtaking to view, the same solar storms that create them can disrupt technology. Below are the lights’ effects on everyday technologies:
- Power grids: strong geomagnetic currents can overload transformers and cause blackouts
- Satellites: increased radiation interferes with GPS, communications, and weather monitoring systems
- Aviation: polar flight routes may be diverted due to radiation hazards
- Communications: radio signals, especially at high frequencies, can be degraded or lost
What needs to happen for San Antonio to see the lights
Shockingly, the Alamo City has seen the Northern Lights a handful of times over the last few years.
For the lights to be visible here, Earth would need to experience an extreme geomagnetic storm, measured by a KP Index of 8 or 9 (on a scaled between 0 and 9).
That level of disturbance typically happens only during the most powerful solar events, perhaps a few times in an 11-year solar cycle.
However, in order for them to reach us, several conditions must align:
- Peak activity: often a few hours (between sunset - midnight)
- Clear, dark skies: away from city lights
- Low light pollution and eyes adjusted to the dark
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