Celestial Information: The aurora season is again

STEAMBOAT SPRINGS – It has been a long time since the Aurora Borealis was seen in the sky over northwest Colorado. The last good thing I can remember was March 17th, 2013. While most people were sitting comfortably in their bed in the early hours of St. Patrick’s Day, a billion dollar cloud of hot plasma was ejected from the sun days earlier, slammed into Earth’s protective magnetic field, triggering a moderate geomagnetic storm that sent aurors as far as northern Colorado.

In general, we see aurors this far south of the Arctic Circle only a few times a decade, as the sun approaches the peak of its 11-year sunspot cycle. During these “solar maximum” times, dozens of sunspots, solar flares, and coronal mass ejections can erupt on the sun before it settles down for another decade.

When a sunburst spits charged particles (mostly protons and electrons) into space, they can become entangled with the Earth’s magnetic field and create colorful, dancing lights above the magnetic poles in the upper atmosphere. Galileo, the famous Italian astronomer, coined the term “aurora borealis” or “northern dawn” to describe it in the 17th century.

The sun’s 11-year heartbeat has been strong for the past century, although the most recent cycle known as solar cycle 24 was somewhat anemic. After a much longer than usual solar minimum between 2008 and 2010, scientists predicted that the maximum of cycle 24 could be the least active since 1906. In fact, the peak of sunspot activity for Cycle 24 came in April 2014, with the lowest number of sunspots counted in over a century.

Even if the last sunspots of cycle 24 fade in the sun, sunspots of the new sunspot cycle 25 appear more and more frequently. Early projections by some solar astronomers predict another weak solar cycle, similar to cycle 24, which will peak sometime in 2025. More recently, another group of solar scientists has predicted that cycle 25 could be one of the most active ever recorded. This just goes to show that the science of predicting how the sun will behave is uncertain at best. Only time will tell which forecasting model is correct.

Meanwhile, as solar cycle 25 increases, aurora sightings are increasing around the world. Several moderate geomagnetic storms have already crossed the northern US border, and more are imminent.

Historically, March is the best month for aurora sightings, especially around the spring equinox, which falls on March 20th this year. The Russell-McPherron Hypothesis explains that at the time of the equinox, the Earth’s axis is best aligned with the incoming solar winds so that they can penetrate Earth’s atmosphere and trigger bright auroral displays.

With the new cycle of 25 sunspots appearing on the sun and the spring equinox just around the corner, a new aurora season is dawning. Hopefully the sun will send us aurors in the coming weeks and months.

Daily updates on all astronomical topics, including aurora forecasts and warnings, can be found on NASA-sponsored spaceweather.com. You don’t want to sleep through Colorado’s next auroral storm.

Jimmy Westlake is the former full-time professor of physics at Colorado Mountain College Steamboat Springs and the past director of the Rollins Planetarium at Young Harris College, Georgia and the St. Charles Parish Planetarium, Louisiana. His column “Celestial News” appears monthly in Steamboat Pilot & Today. Check out Jimmy’s new 2020 Cosmic Calendar of Celestial Events on his website at jwestlake.com. It has 12 of his best astro photos and a daily list of cool celestial events for you and your family to enjoy all year round.

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