Solar Flares: The Aurora

Fiona Hamilton
1 day ago
3 min read

Solar flares can contain as much energy as a billion hydrogen bombs. They are intense explosions of light and matter from the Sun and occur almost daily. Solar flares are measured by their intensity, in a similar manner to earthquakes, each level being ten times stronger than the last.

The weakest flares, the ones that don’t really affect Earth, are labeled A, B, and C, with A being the weakest. Ten times stronger than C is M. M-class solar flares can cause radio blackouts in polar regions and occasionally small radio storms. X solar flares are the largest on the scale, and while the other four are divided into numbers 1-9 (ex., M3 class solar flare), X solar flares scale up to infinity, up to X28 in recent history.

Solar flares often occur near Sunspots. Sunspots are spots on the Sun that are about the size of Earth, where the magnetic field is unusually strong, about 2,500 times stronger than Earth’s magnetic field. The magnetic field of the Sun is a mess and looks quite unlike those of the planets. Here’s a depiction of Mercury’s magnetic field as viewed from the north and south poles:

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Now take a look at the Sun’s magnetic field:

Image credit: NASA/Solar Dynamics Observatory

The Sun’s magnetic field lines are all over the place, and it’s where those lines are strongest that sunspots form. Because these spots of the magnetic field are so strong, the magnetic pressure increases in that zone, which slows down hotter gas within the star from reaching the surface in that area. Because the spots are cooler than the rest of the Sun, they appear dark.

So, do we have anything to worry about solar flares?

In general, no. The strongest flares can cause disruption to our electronics, but it’s unlikely that any solar flare will be powerful enough to incinerate us. Most of the energy carried by solar flares is captured by our atmosphere and magnetosphere and transported to the poles, where the energy turns into the stunning auroras we call the northern and southern lights.

Aurora borealis; Image credit: Joseph Bradley

The northern lights, or the aurora borealis, are known for their stunning colors and guest appearances in the cold regions of the northern hemisphere. The colors of an aurora are dependent on both the altitude and the elements in the air. At the highest altitude, oxygen turns red, but between 60-120 miles up, it appears as the classic green. But where oxygen turns green, nitrogen turns blue, and even pink, lower in the atmosphere. These beautiful color arrays are caused when atoms that have been excited by the solar flare’s energy cool down, releasing light.

Lately, the northern lights have been seen further and further south. Why is this? Well, the sun operates on a cycle of about eleven years, during which the number of sunspots on the sun reaches a minimum or a maximum. The most recent maximum was just about a year ago, so the sun has been more active than usual as of late. Solar flares have been more frequent and more powerful, meaning they strongly affect our magnetic field, stretching and snapping magnetic field lines and producing auroras further south than normal.

Photo taken of the Aurora Borealis from the International Space Station in October 2024

So, how far south can the aurora borealis go? Currently, the furthest south it’ll likely be seen is in the northern United States, especially as we return from a solar maximum and near another minimum. However, the northern lights have been seen as far south as Hawai’i. A year ago, a huge solar flare of about class X6 sparked an aurora that could be seen, though faintly, all of the way here in Hawai’i. This wasn’t actually the first time this had happened. Records from over a hundred years ago report aurora sightings on the islands.

So who knows, maybe in another decade, we’ll be able to see the aurora here again.

Sources:

NASA -

Auroras - https://science.nasa.gov/sun/auroras/

Solar storms and flares - https://science.nasa.gov/sun/solar-storms-and-flares/

Solar flares FAQs - https://science.nasa.gov/blogs/solar-cycle-25/2022/06/10/solar-flares-faqs/

NOAA -

Sun and sunspots - https://www.weather.gov/fsd/sunspots

Solar flares - https://www.swpc.noaa.gov/phenomena/solar-flares-radio-blackouts

Solar cycle data/graph - https://www.swpc.noaa.gov/products/solar-cycle-progression

ESA -

Solar flares - https://www.esa.int/Science_Exploration/Space_Science/What_are_solar_flares