Celestial News: Aurora season returns
For Steamboat Pilot & Today
STEAMBOAT SPRINGS — It’s been a long time since the aurora borealis has been seen in the skies over northwest Colorado. The last good one that I can recall was on March 17, 2013. While most folks were snug in their bed during the wee hours of that St. Patrick’s Day morning, a billion-ton cloud of hot plasma, ejected from the Sun days earlier, slammed into the Earth’s protective magnetic field and sparked a moderate geomagnetic storm, sending auroras as far south as northern Colorado.
We generally get to see auroras this far south of the Arctic Circle only a few times a decade, when the Sun is near the peak of its 11-year sunspot cycle. During these times of “solar maximum,” dozens of sunspots, solar flares and coronal mass ejections can erupt on the sun before it quiets down for another decade.
When a solar eruption spews charged particles (mostly protons and electrons) into space, they can become entangled with the Earth’s magnetic field and generate colorful, dancing lights in the upper atmosphere over the magnetic poles. Galileo, the famous Italian astronomer, coined the phrase “aurora borealis,” or “northern dawn,” to describe them in the 17th century.
The sun’s eleven-year heartbeat has been going strong for the past century, although the most recent cycle, known as solar cycle 24, was a bit anemic. After a much longer than usual solar minimum between 2008 and 2010, scientists predicted that the maximum of cycle 24 might be the least active since 1906. Indeed, the peak of sunspot activity for cycle 24 came in April 2014 with the fewest number of sunspots counted in over a century.
Even as the last sunspots of cycle 24 fade on the sun, sunspots of the new sunspot cycle 25 are now popping up more and more frequently. Early forecasts by some solar astronomers predict another weak solar cycle, similar to cycle 24, peaking sometime in 2025. More recently, another group of solar scientists has predicted that cycle 25 could be one of the most active on record. This just goes to show that the science of predicting how the sun will behave is uncertain at best. Only time will tell which forecast model is correct.
In the meantime, as solar cycle 25 ramps up, aurora sightings around the world have been on the increase. Several moderate geomagnetic storms already have crossed the northern U.S. border and more are in the offing.
Historically, March is the best month of all for aurora sightings, especially around the time of the spring equinox, which this year falls on March 20. The Russell-McPherron hypothesis explains that the Earth’s axis at the time of the equinox is best aligned with the incoming solar winds to allow them to penetrate into the Earth’s atmosphere and spark bright auroral displays.
So, with new cycle 25 sunspots popping up on the sun and the spring equinox right around the corner, a new aurora season is dawning. Hopefully, the sun will start sending auroras our way in the weeks and months ahead.
For daily updates on all things astronomical, including aurora forecasts and alerts, visit the NASA sponsored website spaceweather.com. You don’t want to sleep through Colorado’s next auroral storm.
Jimmy Westlake is the former full-time professor of physical sciences at Colorado Mountain College Steamboat Springs and former director of the Rollins Planetarium at Young Harris College in Georgia and the St. Charles Parish Planetarium in Louisiana. His “Celestial News” column appears monthly in the Steamboat Pilot & Today. Check out Jimmy’s new “2020 Cosmic Calendar” of sky events on his website at jwestlake.com. It features 12 of his best astro-photos and a day-by-day listing of cool celestial events that you and your family can enjoy watching all year.
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