On October 10, 2024, the sky lit up with a spectacular aurora visible as far south as South Carolina and Arizona. This rare event was caused by an intense solar storm during a period called solar maximum. Scientists measure and explain events like these using numbers and data about the Sun and Earth’s magnetic field, such as speed, Bz, density, Bt, and Kp index. Let’s break it down!
What Is Solar Maximum?
The Sun goes through an 11-year cycle where its activity increases and decreases. Right now, it’s at its most active phase, called solar maximum. During this time, the Sun has more storms and explosions, which send huge amounts of energy into space. These events, like solar flares and coronal mass ejections (CMEs), can create incredible auroras on Earth.
How Did the October 10 Aurora Happen?
In early October, the Sun released a CME—a giant bubble of charged particles (plasma) and magnetic fields. When the CME reached Earth’s magnetic field on October 10, the collision created a powerful geomagnetic storm, leading to the stunning aurora. Scientists tracked the storm using key measurements:
Speed:
The solar wind from the CME was traveling at an incredible speed of over 700 kilometers per second (km/s). The faster the solar wind, the more energy it delivers to Earth’s magnetic field.
Density:
The density of the solar wind (how many particles are packed into a certain space) was high during the event, meaning more charged particles hit Earth’s atmosphere. Typical densities are around 5 particles per cubic centimeter (cm³), but during this storm, it was much higher.
Bt:
Bt is the total strength of the magnetic field carried by the solar wind. During the October storm, the Bt was very strong, around 20 nanoteslas (nT) or higher, making it a significant event.
Bz:
Bz is the most important part of the solar wind’s magnetic field because it tells us how well the solar particles can interact with Earth’s magnetic field. If the Bz is negative, it means the solar wind can easily connect with Earth’s magnetic field, leading to stronger auroras. On October 10, the Bz dipped to -10 nT or lower, which allowed lots of solar particles to flood into the atmosphere.
Kp Index:
The Kp index measures how strong a geomagnetic storm is on a scale of 0 to 9. During the October 10 event, the Kp index reached 8, which is considered a major storm. This level of activity is rare and can push auroras much farther south than usual.
What Are Auroras Made Of?
When the charged particles from the solar wind hit gases in Earth’s atmosphere, they create colorful lights. Here’s how the colors happen:
Green and red: Caused by oxygen at different heights in the atmosphere.
Purple and blue: Caused by nitrogen when it’s hit by high-energy particles.
Why Does Solar Maximum Matter?
Events like this aurora are exciting, but solar maximum also comes with challenges. The energy from solar storms can:
Disrupt satellites: GPS and internet signals can get scrambled.
Affect power grids: Strong storms can cause blackouts on Earth.
Pose risks for astronauts: Solar radiation can harm people in space.
That’s why scientists carefully monitor measurements like speed, Bz, and Kp to predict and prepare for solar storms.
How Can You See an Aurora?
If you want to catch an aurora during solar maximum, here’s what to do:
Watch for high Kp numbers: A Kp index of 5 or more means auroras might be visible.
Look north: Auroras usually appear closer to the poles, but strong storms can bring them south.
Go somewhere dark: City lights make it harder to see the glow.
Use a camera: Even a cellphone camera can make the northern lights easier to see.
The October 10 Aurora: A Solar Show to Remember
The aurora on the night of October 10th and the morning of the 11th was one of the strongest in years, lighting up the skies with green, purple, and pink colors and although not as strong the lights were visible on the 6th-8th. Thanks to solar maximum, we might see more big storms like this in the coming months. So keep an eye on the Sun and the Kp index—you never know when the next amazing aurora will appear!