Gorgeous auroras were seen rippling across the night sky in unusually southern states on Saturday, when a G2-class geomagnetic storm had been predicted to hit the Earth.
The northern lights were seen across the U.S., including spectacular green lights over Lake Michigan, with a red-hued aurora even being visible using night-time settings on phone cameras as far south as Colorado and Missouri.
The northern lights are usually caused by a coronal mass ejection, or CME, slamming into the Earth's magnetic field and atmosphere, but strangely, solar wind data show no clear signs of a CME impact, despite one being predicted for September 2.
The Aurora Borealis seen over the Kvaloya island at Tromso in the Arctic Circle in Northern Norway. The nothern lights were seen across the U.S. at the weekend, being seen as far south as Colorado...The Aurora Borealis seen over the Kvaloya island at Tromso in the Arctic Circle in Northern Norway. The nothern lights were seen across the U.S. at the weekend, being seen as far south as Colorado and Missouri.Photo by Tim Graham/Getty ImagesCMEs are huge plumes of solar plasma and magnetic field that are spat out from the sun as a result of the sun's twisted magnetic fields suddenly realigning. The CME then flies into space at mind-boggling speeds—up to 6.7 million mph—reaching Earth in only a few days if it happens to be heading in our direction.
The CME will then interact with the Earth's magnetic field and atmosphere, causing geomagnetic storms and resultant auroras in the areas nearest to the poles.
"A geomagnetic storm is the alteration of the Earth's magnetic environment. This means when the magnetic fields that usually surround our Earth start to be distorted," Daniel Brown, an associate professor in astronomy and science communication at the U.K.'s Nottingham Trent University, previously told Newsweek.
"The amount of matter ejected, its speed, the associated magnetic fields as well as how they interact with other already emitted particles from the sun all add up to a bumpy environment moving outwards from the sun for our Earth's magnetic field to travel through."
The Northern Lights illuminate the night sky on August 23, 2016 in Erikslund village at Vaesternorrland County in Sweden. The Northern Lights illuminate the night sky on August 23, 2016 in Erikslund village at Vaesternorrland County in Sweden. JONATHAN NACKSTRAND/AFP via Getty ImagesGeomagnetic storms are classified between G1 (minor) to G5 (extreme), according to NOAA's G scale, with stronger storms causing the northern lights to be visible further south. It's much more rare to see the aurora in southern states.
"The colors in the aurora are the result of particles in the upper atmosphere becoming excited by collisions with particles coming from within the magnetosphere and some from within the solar wind," Brett Carter, an associate professor in space science at RMIT University in Australia, told Newsweek in February. "The different colors are the result of electrons relaxing from different energy levels from oxygen (the most common reds and greens) and nitrogen (dark reds/blues)."
Northern lights seen from further south are generally fainter and more red in color, due to the red light being emitted from oxygen higher in the atmosphere.
A surfer looks at the Northern lights illuminating the sky over the snow covered beach of Unstad, on Lofoten Islands, Arctic Circle, on March 14, 2016. A surfer looks at the Northern lights illuminating the sky over the snow covered beach of Unstad, on Lofoten Islands, Arctic Circle, on March 14, 2016. OLIVIER MORIN/AFP via Getty Images"That red color is usually also rather faint since you do not have that many of the oxygen atoms around at such high altitudes," Brown told Newsweek in February. "But, if you have a strong enough activity like we are getting now, there are enough exciting particles in the coronal mass ejections to interact with more oxygen and make the red brighter."
It's possible that despite a CME not having been detected, a weak one did indeed hit the Earth on Saturday, with its impact being masked by other solar wind. Weaker CMEs can still cause auroras, especially near the equinoxes in September and March, due to the Russell-McPherron effect. This is when solar wind passes through cracks in the Earth's magnetic field, causing more intense auroras than usual.
"The Russell-McPherron effect is more of a geometrical effect to do with the orientation of the solar wind's magnetic field and that of the Earth. There is always a cusp or open region of the Earth's magnetic field around the north and south poles so the 'cracks' are permanent," Ciaran Beggan, a geophysicist from the British Geological Survey, previously told Newsweek.Do you have a tip on a science story that Newsweek should be covering? Do you have a question about the aurora? Let us know via science@newsweek.com.
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