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Auroras


Image credit: NASA/Bin Li

A ribbon of green aurora appears in the night sky over snowy mountains and a body of water.

Also known as the northern lights (aurora borealis) or southern lights (aurora australis), auroras are colorful, dynamic, and often visually delicate displays of an intricate dance of particles and magnetism between the Sun and Earth called space weather.

When energetic particles from space collide with atoms and molecules in the atmosphere, they can cause the colorful glow that we call auroras.

Quick Facts

Why Are Auroras Colorful?

  • An aurora can appear in a variety of colors, from an eerie green to blue and purple to pink and red. When particles from space bombard gases in the atmosphere, they can give the atoms and molecules of the gases extra energy that’s released as tiny specks of light.

    The color of an aurora depends on the type of gas that is hit and where that gas is located in the atmosphere.

    Oxygen excited to different energy levels can produce green and red. Green occurs roughly between 60 to 120 miles (100-200 km) altitude, and red occurs above 120 miles (200 km).

    Excited nitrogen gas from about 60 to 120 miles (100-200 km) glows blue. Depending on the type and energy of the particle it is interacting with, nitrogen can give off both pink and blue light. If it is below about 60 miles (100 km), it gives the lower edge of the aurora a reddish-purple to pink glow.

    Sometimes, the light emitted by these gases can appear to mix, making the auroras seem purple, pink, or even white.

    Image credit: Neil Zeller, used with permission

An infographic shows atoms and molecules, denoted as grey circles, in Earth’s atmosphere at different elevations about the ground. In the top band of the infographic, showing the region 120 miles above Earth, oxygen atoms turn red when struck by an electron, shown by pink dots and arrows. The next band down, stretching to 60 miles above the surface, nitrogen atoms turn blue when hit by an electron shown by a pink arrow. A secondary electron — another pink arrow leaving the blue electron — hits an oxygen atom which glows green. In the bottom band, below 60 miles, the pink electron arrows strike nitrogen molecules, shown as double circles, which turn pink. Vertical bands on the right side of the infographic show how these particle interactions create the colors of the aurora at different altitudes, from red high in the atmosphere to green in the middle and pink closer to the surface.
The colors of an aurora reveal where the lights were created as well as what atoms and molecules created them.
NASA/Aurorasaurus
ColorAltitudeComposition
Red≥120 miles (≥200 km)Oxygen
Green60-120 miles (100-200 km)Oxygen
Blue60-120 miles (100-200 km)Nitrogen
Pink≤60 miles (≤100 km)Nitrogen

Researching Auroras

Ground-Based Measurements

Using ground-based scientific equipment, we can learn a lot about auroras. With tools like magnetometers that show changes in Earth’s magnetic field and radar networks that monitor particle activity in the upper atmosphere, scientists can analyze the various effects that occur during auroral displays. Some ground stations even provide real-time views of auroras using special wide-field cameras called all-sky imagers.

Different countries and agencies collaborate to conduct aurora research using ground stations worldwide, representing just how collaborative science can truly be.

Stories About Ground-Based Research
A collection of time-lapses An animated GIF shows time-lapse views of green auroras from multiple all-sky cameras across Canada.
All-sky imagers across Canada capture the progression of auroras.
NASA/Goddard Space Flight Center/Scientific Visualization Studio/Tom Bridgman

Aurora Science Made EZIE

The Electrojet Zeeman Imaging Explorer (EZIE) is an upcoming mission to image the magnetic fingerprint of the auroral electrojets, electric currents in the atmosphere linking the magnetosphere to the aurora.

Learn More About EZIE

NASA/Johns Hopkins Applied Physics Laboratory

Discover the Physics of Auroras

  • Magnetospheres and Geomagnetic Storms

    Many planets, including Earth, are surrounded by a large magnetic shield called a magnetosphere. On Earth, this shield stems from the churning molten metal core inside the planet and extends far out into space.

    Our magnetosphere protects us from harmful charged particles in the space environment. As these particles collide with the magnetosphere, they can transfer energy to the magnetosphere itself. However, if certain regions become overloaded, a geomagnetic storm can erupt, just as rain clouds swell with water droplets preceding a thunderstorm.

    During a geomagnetic storm, much of the accumulated energy in the magnetosphere flows down along Earth’s magnetic field lines, precipitating into the atmosphere like a summer downpour on the prairie. This type of particle precipitation injects millions of amps into the atmosphere, leading to impressive auroral displays in places far from Earth’s poles.

    This simulation demonstrates a geomagnetic storm hitting Earth’s magnetosphere on February 3, 2020. This particular storm was average in strength, but still destroyed dozens of commercial satellites.

    The green colors show the density of the magnetic current. Lines tracing out the magnetic field are purple in regions of weaker magnetism and orange-yellow where the magnetic field is strongest. Blue lines represent the velocity of the solar wind. They have been calibrated to appear brightest when moving toward Earth. Learn more here: https://svs.gsfc.nasa.gov/5193/
    NASA/Goddard Space Flight Center/Scientific Visualization Studio/AJ Christensen
  • The Heliosphere and Solar Wind

    Just as planets with churning cores like Earth produce magnetic shields, the Sun’s dense, ever-roiling interior also produces a magnetic shield — on a much larger scale. The Sun’s magnetic shield is called the heliosphere, and it fills the solar system.

    As the Sun seethes, it radiates its energy throughout the heliosphere. Planets and other objects in the solar system experience much of this radiation as a continuous stream of charged particles and magnetic fields blowing by. This stream of fields and particles is called the solar wind.

    When the solar wind blows past Earth, it buffets Earth’s magnetosphere like a strong breeze flapping a flag.

    This animation shows the Earth being bathed by energetic particles from the Sun. The view then transitions to a top-down view of the solar system, showing the solar wind flowing out toward the edges of the system. A final transition shows the heliosphere being buffetted by the interplanetary medium from the rest of the galaxy.
    This animation illustrates how the solar wind moves through the solar system and interacts with forces beyond the solar system. It shows three perspectives: orange dots represent the solar wind flowing around Earth’s magnetic shield; a top-down view of the solar wind spreading through the solar system as the Sun rotates; and a zoomed-out look at the heliosphere — the Sun’s protective bubble — surrounded by the slower-moving interstellar medium (blue dots).

    Both the solar wind and interstellar medium consist of streaming energetic particles, but the interstellar medium originates from within our galaxy instead of within the Sun. Notice how the interstellar medium flows around the heliosphere, similar to how the solar wind moves around Earth’s magnetosphere. Learn more here: https://svs.gsfc.nasa.gov/20299/
    NASA/Goddard Space Flight Center/Conceptual Image Lab/Jonathan North
  • Coronal Mass Ejections

    Occasionally, magnetic storms on the Sun eject large amounts of solar material into the solar atmosphere. These huge, flying blobs of Sun-stuff are called coronal mass ejections, or CMEs.

    If directed at Earth, fast-moving CMEs can reach our planet in as little as 15 hours. (The Sun is approximately 93 million miles away from Earth. A CME arriving here in 15 hours means that it’s traveling around 6.2 million miles per hour, or about 0.9% the speed of light. At those speeds, you could fly from San Francisco to Washington, D.C. in ~1.5 seconds!)

    As they billow away from the Sun, fast CMEs can overtake slower-moving charged particles ahead of them in the solar wind. These particles are accelerated as they’re swept into the careening solar ejecta, increasing the risk and intensity of a radiation storm when they reach Earth.

    Under certain conditions, CMEs can supercharge the magnetosphere as they blow past, creating powerful geomagnetic storms in response.

    An animation of a coronal mass ejection from the Sun as seen from various instruments. SDO shows the event starting on the Sun itself in red, then SOHO shows the plume of matter spewing off and out into space in red and blue.
    On May 1, 2013, the Sun emitted a huge amount of solar material from its eastern limb (left edge). Instruments on multiple Sun-monitoring spacecraft caught the coronal mass ejection (CME) in various wavelengths of light.

    This animation combines perspectives from the NASA Solar Dynamics Observatory (SDO) and the ESA/NASA Solar and Heliospheric Observatory (SOHO) to show the progression of the CME out into space. Learn more about this animation here: https://svs.gsfc.nasa.gov/10785/
    NASA/ESA/SOHO/Goddard Space Flight Center
  • Magnetic Reconnection

    As we’ve seen, the solar wind emanating from the Sun flows around Earth’s magnetosphere like a river rushing around a rock. This onrush of charged particles stretches Earth’s magnetosphere away from the Sun, creating a long wake known as the magnetotail.

    The magnetic shields of the Sun and Earth are polarized, like refrigerators and the magnets that adhere to them. The polarity of Earth’s magnetic shield is mostly stable, but the Sun’s can vary due to its more dynamic nature.

    Sometimes, the magnetic polarity of the solar wind is opposite that of Earth’s magnetosphere. When the solar wind buffets the magnetosphere under these conditions, the field lines of the Sun and Earth snap together, similar to when an everyday magnet connects to a fridge. This is called magnetic reconnection.

    The continuously blowing solar wind then pushes these newly connected Sun-Earth field lines, wrapping them around the magnetosphere and stretching them out toward the magnetotail. Eventually, these field lines stretch to their limit and snap like a rubber band. This severs the direct Sun-Earth magnetic connection, releasing energy back along the field lines and reinstating the original magnetic configuration in the process.

    This animation starts with a close-up view of the Sun, radiating light and energetic particles as the solar wind. The view transitions to Earth, surrounded by blue magnetic field lines, which curve and form the magnetosphere. Solar wind from the Sun approaches the magnetosphere from the left of the frame, compressing Earth's magnetic field, causing fluctuations and bright yellow-orange impacts. The magnetosphere stretches and reacts to the pressure, culminating in a burst of light and energy in the tail region of the magnetosphere during magnetic reconnection. The sequence ends with a zoomed-in view of Earth, showing vibrant pink auroras at the poles against a backdrop of stars, showing the after effects of energy from reconnection raining down on them..
    This animation is an artistic interpretation of magnetic reconnections and the resulting geomagnetic substorm that rains down energetic particles at Earth’s polar regions.

    Two reconnections are shown here: the first occurs when the Sun’s magnetic field disconnects from itself and reconnects to Earth’s magnetic field; the second occurs in the magnetotail as the field lines get squeezed too close together. Learn more about this animation here: https://svs.gsfc.nasa.gov/20097/
    NASA/Goddard Space Flight Center/Conceptual Image Lab/Walt Feimer

Geomagnetic Substorms

While the huge auroral displays caused by geomagnetic storms are fun to see, they’re relatively rare since the Sun’s and Earth’s magnetic fields need to align just right for them to occur. Auroras that stay near the Arctic and Antarctic circles are much more frequent. They’re created by geomagnetic substorms, magnetic disturbances affecting portions of the magnetosphere. Geomagnetic storms, in contrast, are large-scale disturbances that distort the whole geomagnetic system. The everyday flow of charged particles within Earth’s magnetosphere can create small regions of magnetic imbalance that cause geomagnetic substorms.

A time-lapse view from the International Space Station shows the Southern Lights, aurora australis, on June 25, 2017.

   

This short video features commentary by David Sibeck, project scientist for NASA’s Time History of Events and Macroscale Interactions During Substorms (THEMIS) mission, discussing a visualization of magnetic reconnection and geomagnetic substorms. Learn more about this video here: https://svs.gsfc.nasa.gov/11309
NASA/Goddard Space Flight Center/UNH/J. Raeder

Views from the Space Station

Auroras Seen from Orbit

The International Space Station orbits roughly 250 miles (400 km) above Earth’s surface. At that height, astronauts regularly fly over (and sometimes through!) brilliant auroral displays. Many astronauts document their auroral experiences with photos and videos, but did you know the space station has high-definition cameras on board? Photos and time-lapses are uploaded regularly to NASA’s online Gateway to Astronaut Photography of Earth.

Explore Auroras from the Space Station about Auroras Seen from Orbit
An animated GIF showing a view of auroras from the international space station. The aurora appears like moving ribbons of green light snaking across the atmosphere at night.
A time-lapse view from the International Space Station shows the southern lights, aurora australis, on June 25, 2017.
NASA/Johnson Space Center/International Space Station/Earth Science and Remote Sensing Unit