What causes the aurora to dance across the night sky?
An aurora can dance across the night sky in a variety of colors, making it one of nature’s most dazzling displays.
The breathtaking phenomenon is a regular occurrence close to the north and south poles, but it can occasionally be seen in more populated areas in Europe and the United States.
In the Northern Hemisphere, the aurora is commonly referred to as the northern lights, or aurora borealis, while in the Southern Hemisphere, it is known as the southern lights, or the aurora australis.
Although the phenomenon occurs in the sky above the Earth, the origin of the lights can be traced back to the sun.
In this photo taken on Wednesday, March 1, 2017, the Northern Lights, or aurora borealis, appear in the sky over Bifrost, Western Iceland. (AP Photo/Rene Rossignaud)
When eruptions occur on the surface of the sun, they can blast a wave of charged particles hurling through space. This is known as a Coronoal Mass Ejection (CME).
“CMEs travel outward from the sun at speeds ranging from slower than 250 km/s [56,000 mph] to as fast as near 3000 km/s [6.7 million mph],” the Space Weather Prediction Center (SWPC) said.
“The fastest Earth-directed CMEs can reach our planet in as little as 15-18 hours,” the SWPC said.
When these waves of charged particles reach the Earth, the planet’s magnetic field funnels them toward the north and south poles where they collide with the planet’s atmosphere.
The interaction between the charged particles and the Earth’s atmosphere results in colorful swirls of light known as aurora.
These amazing displays are not limited to Earth. The aurora has been observed on other planets in our solar system with magnetic fields.
Jupiter’s magnetic field is stronger than any other planet in the solar system and produces aurora over 1,000 times brighter than how they appear on Earth.
Astronomers are using NASA's Hubble Space Telescope to study auroras — stunning light shows in a planet's atmosphere — on the poles of the largest planet in the solar system, Jupiter. This is an image composite of two different Hubble observations. Credits: NASA, ESA, and J. Nichols (University of Leicester)
Due to the Earth’s magnetic field, the aurora is most common in areas close to the poles, such as Canada, Norway, northern Russia and Antarctica.
However, when larger CMEs are blasted toward Earth, it can result in the aurora being visible much closer to the equator.
Moderately strong CMEs have impacted Earth many times in recent years, allowing the northern lights to be seen in areas farther south, including much of Europe, the northern half of the U.S., New Zealand and parts of Australia.
On rare occasions, an incredibly large CME can cause the aurora to be viewed in areas much closer to the equator, including Hawaii and the Caribbean, but such an event would have far-reaching impacts beyond filling the night sky with colorful swirls of light.
In September of 1859, such an event happened in what is now known as the Carrington Event.
According to NASA, the Carrington Event “caused global telegraph lines to spark, setting fire to some telegraph offices and disabling the 'Victorian Internet.””
“A similar storm today could have a catastrophic effect on modern power grids and telecommunication networks,” NASA said.
The frequency that the aurora appears in the night sky is linked with a phenomenon on the sun known as the solar cycle.
The sun goes through one solar cycle every 11 years that consists of a period of high solar activity and a period of low solar activity.
“The peak of the solar cycle is known as solar maximum and the valley of the cycle is known as solar minimum,” the SWPC said.
Around the time of the solar maximum, sunspots, or cooler and darker areas on the surface of the sun, are more common. This correlates to a higher number of CMEs, causing the aurora to light up the night sky more frequently.
The opposite can be said during the solar minimum as the number of sunspots declines. This translates to fewer CMEs, meaning that the aurora is not visible as often.
Currently, the sun is approaching a solar minimum, which will last for several years.
The aurora will still be visible during this period, but it will mainly be limited to areas close to the north and south poles. The aurora will also not be as vivid or vibrant as often as it is around the time of a solar maximum.
The next solar maximum is expected to occur in the early- to mid-2020s, providing aurora watchers with the next great opportunity to see Mother Nature’s light show.
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