Geomagnetic activity may cause more frequent displays of auroras around the equinoxes. (Image credit: Westend61 via Getty Images)
The Sun is about to enter the Northern Hemisphere, which means we will be able to see magnificent auroras in the coming weeks.
At 9:01 UTC (5:01 a.m. EDT) on March 20, our star will cross the celestial equator during the spring equinox. Earth's axis will be pointed sideways toward the sun, meaning the Northern Hemisphere will experience more daylight hours from now until the June solstice.
Besides the start of astronomical spring, this also signals the approaching end of the aurora hunting season north of the equator, as regions around the Arctic Circle at 66 degrees north latitude will see sunrises and sunsets significantly earlier and later, respectively, until the solstice. Soon, there won't be enough darkness.
However, the aurora season can end with a bang thanks to celestial geometry. An equinox occurs when the Earth's axis is perpendicular to the sun, and every location on the planet receives roughly equal amounts of sunlight and darkness. This can cause an “equinox effect” that increases the likelihood of polar activity around the spring and fall equinoxes.
The northern lights are caused by the interaction of charged particles from the sun — known as the solar wind — with the Earth's magnetic field. During the equinoxes, the likelihood of favorable interactions between the solar wind's magnetic orientation and the Earth's magnetic field increases because the Earth's magnetic poles are at right angles to the direction of the solar wind's flow, according to Live Science partner site Space.com.
“The Earth and Sun’s magnetic fields are inherently better aligned around the equinoxes, and so the likelihood of an exact inverted alignment around the equinoxes is increased simply because it’s perpendicular,” said Tom Kerss, author of Northern Lights: The Complete Guide to the Auroras (Collins, 2021) and chief aurora hunter for Hurtigruten Astronomy Cruises. “The transmission efficiency is increased because it opens holes in the Earth’s magnetic field shockwave and allows solar wind to penetrate into the geospace environment.”
David Hathaway, a solar physicist at NASA's Ames Research Center, explained that this means more geomagnetic disturbances, which are nearly twice as likely to occur in the spring and fall as in the winter and summer months.
This alignment results in an increase in the frequency of auroras during these seasons, although this is not necessarily observed in the more southern latitudes of the Northern Hemisphere. This is due to the presence of powerful geomagnetic storms, which are not dependent on the season; instead, they depend on the sun's activity, which is currently at its peak due to solar maximum.
Will the aurora season end with a bang? That remains to be seen, but the “equinox effect” could continue for several more weeks, so those in northern latitudes should be on guard.
Jamie CarterNavigate Social LinksLive Science Contributor
Jamie Carter is a freelance journalist and regular Live Science contributor based in Cardiff, UK. He is the author of A Stargazing Program For Beginners and lectures on astronomy and the natural world. Jamie regularly writes for Space.com, TechRadar.com, Forbes Science, BBC Wildlife magazine, and Scientific American, among many other publications. He edits WhenIsTheNextEclipse.com.
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