On April 21, the sun released huge coronal mass ejection (CME). Magnetic fields pulsed across the surface of the sun’s southern hemisphere; hurling charged particles toward our planet. Two days later in the nighttime hours of April 23, the particles hit Earth’s atmosphere and treated Utah’s skies to a psychedelic light show called the aurora borealis.

The aurora borealis rarely appears as far south as Utah, so the spectacle was a special treat. For the rest of us sad saps who missed it, we’re in luck—Paul Ricketts, director of the South Physics Observatory and astrophotographer, captured the once-in-a-generation event. He talked about the aurora borealis.

What is the aurora borealis?

The sun has magnetic fields that constantly grow, interact and subside across its surface. These fields affect charged particles in the sun’s atmosphere. With a special telescope, you actually see arcs (prominences) and plumes (faculae) undulating on the sun’s chromosphere.

Every so often there are CMEs, which are large bursts of plasma from the sun’s surface. They eject billions of tons of material outwards and carry their own magnetic fields through space. When they’re directed toward Earth, they eventually hit our atmosphere. The lights that we see are the result of that material being funneled through the weakest portions of our magnetic fields at the north and south poles. These charged particles then interact with upper atmospheric air particles and cause them to become energized, then release the excess energy as light.

The colors of the lights depend on the type of air molecule that gets hit—oxygen molecules produce the most common color, yellowish green. Nitrogen molecules produce pinkish lights.

Have you ever seen the aurora borealis in Utah?

We have seen them in Utah before. As far as I know, there have been about five times since 2003 that they have occurred, including this event. But this is likely one of the largest events that Utah has seen in the past 50 years or more! There were two main surges—one around 10:30 p.m. and one a bit after 1 a.m. People all around Utah, including St. George, Emery County and even as far south as New Mexico, witnessed the event.

We saw it farther away from the poles this time because the huge mass of particles released from the sun squeezed our magnetic field and funneled them even farther south than normal. Right now, the sun is nearing its peak in activity. This happens at an 11-year cycle when we see a maximum of flares, coronal mass ejections, sunspots and prominences. If these events occur with high enough magnitude and if they’re pointed at the Earth, they’ll increase the auroral activity to the point we see them even here as far south in Utah.

Will we get to see it again?

It’s quite possible that we’ll be able to see them again. The sun has produced a lot of extra activity in this cycle and that may indicate another big event in the future. Solar activity is not predictable, so we’ll just have to wait and see. In the meantime, people can download a solar activity app that’ll notify them when the chance of an aurora is high.

When I heard of the event, I had to drive out of the city to avoid light pollution. The show was even better earlier in the evening, but light pollution made it impossible to see. So, let’s make our dark skies darker so we can see the next one!