Aurora Visible in the American South: Solar Wind, CMEs, and the Solar Cycle

StarTalk host Neil deGrasse Tyson explains how auroras form when charged solar wind particles interact with Earth's magnetic field and atmosphere, lighting up nitrogen and oxygen as curtains of color. He notes that auroras have been spotted far south into Central Florida during solar maximum, and discusses coronal mass ejections, the geomagnetic dynamo, and how improved predictions help skywatchers know when to look.

Introduction to a Southern Aurora

In this discussion, Neil deGrasse Tyson explores how the most dramatic visual displays in the sky, the auroras, arise when energetic particles from the Sun collide with the Earth's atmosphere. The conversation emphasizes that auroras are not limited to high latitudes but can be seen further south during periods of intense solar activity. Tyson connects everyday sightlines to the physics behind the phenomenon, offering a bridge between captivating sky-gazing and the underlying science.

What Causes the Light Show

The aurora occurs when charged particles from the Sun, part of the solar wind, are directed by Earth's magnetic field toward the polar regions. These particles collide with atmospheric nitrogen and oxygen, transferring energy and exciting those molecules. When they relax back to their ground state, they emit light in distinct colors. The result is shimmering curtains of color that people call the Northern Lights or the Southern Lights depending on the hemisphere.

The Sun-Earth Connection

Tyson describes the solar wind as a swarm of charged particles emanating from explosive events on the Sun, notably coronal mass ejections. The Sun’s magnetic field drives these particles toward Earth, and there is a measurable time delay between solar activity and auroral displays. The discussion also covers the Earth's liquid iron core dynamo that sustains the geomagnetic field and guides particles toward the poles.

Solar Cycles and Solar Maximum

The host explains the roughly 11 year solar cycle, tracked by sunspot counts. Solar maximum means more energetic events and a higher likelihood of auroral sightings, sometimes far south of typical viewing regions. Tyson notes that while solar maxes vary, this cycle has produced stronger activity than in the recent past, contributing to more frequent aurora displays across the United States.

Visibility in a Modern Sky

The conversation then examines why clearer skies and dimmer light pollution in cities enable more people to notice auroras. The International Dark Sky Association has helped cities redesign street lighting to reduce upward glow, improving night-sky visibility. Tyson also points out that advancements in prediction and tracking systems allow observers to know when and where to look for auroras with greater accuracy than in previous cycles.

Practical Takeaways for Skywatchers

For aspiring aurora photographers and enthusiasts, the speakers highlight the importance of monitoring solar activity, choosing dark locations away from city lights, and understanding that even in lower latitudes, bright auroras can cross many degrees of latitude under favorable solar conditions. An anecdote about a Long Island aurora sighting illustrates how southern observers can be treated to an unexpected display during strong solar events.

Conclusion

Tyson closes with a reminder to keep looking up during solar max periods and to enjoy the science behind these beautiful celestial lights, which serve as a vivid reminder of the dynamic Sun-Earth connection.