PANTS ON: A Newbie’s Guide to Aurora Terms

by Laura Brandt (with lots of help from Dr. Liz!)

Since joining Aurorasaurus, I have learned a lot about auroras and the ways aurora chasers and scientists describe them. I’ve been taking notes and want to share my list of key terms—by a newbie, for newbies, and reviewed by a subject matter expert—as a big welcome to the amazing world of auroras! In this blog post, we walk you through these terms, starting with the visible and moving on to the mostly invisible. The text heading each set of words aims to distinguish the important differences between similar-sounding terms and clear up some common misconceptions. We hope this post helps start your journey in aurora citizen science, and helps to clarify why “when can I see the aurora” is a surprisingly complicated question to answer.

The entries below are beginner-level starting points to explore complex subjects, so there are links in each for finding out more. We’re also excited about a new, beginner-level NASA resource on some of these terms—be sure to check out the growing Heliopedia! For an intermediate-level list of definitions, visit the SWPC Space Weather Glossary. It’s also important to note that while I am writing from the context of Western science, there are many ways of knowing about the aurora. Click here to watch a film by the University of Alaska Fairbanks (UAF) about how some of Alaska’s Indigenous people describe and experience the powerful Northern Lights. UAF also has educational materials on their Cultural Connections website, including a poster series that translates scientific aurora terms into different languages. To find out more about common aurora questions, visit the Learn section of the Aurorasaurus site. 

Let’s get started with some basic terms used by aurora chasers and citizen scientists.

Aurora chasing communities are fun groups of people who love the night sky, and have their own ways of talking about the Northern and Southern Lights.

A man stands in snow taking a photo of aurora

Aurora, photo by Alberta Aurora Chaser and Aurorasaurus Ambassador Hugo Sanchez

“Pants On!” a quirky Alberta Aurora Chasers slang phrase for “there’s a high probability that aurora will be visible, time to bundle up and prepare to go outdoors to watch!”

A woman joyfully motions toward the sky

Aurora, photo by Christy Turner Photography

Lady Aurora: an affectionate name for the aurora, used by many aurora chasers and groups. She likes to dance!

Two men watch aurora

Citizen scientists and Aurorasaurus Ambassadors Vincent Ledvina and Andy Witteman chasing aurora in Alaska. Photo by Vincent Ledvina

Citizen science: NASA’s citizen science projects are collaborations between scientists and interested members of the public. Through these collaborations, volunteers (known as citizen scientists) have helped make thousands of important scientific discoveries. The term “citizen science” is in the process of changing and we are interested in its evolution to something more inclusive. For example, one misconception about citizen science is that you have to be a citizen to participate—anyone can take part! As that conversation is actively underway, we will use NASA’s term for this post. 

Two smiling women hold a poster between them

Aurorasaurus project manager Laura and founder Dr. Liz hold a conference poster by Aurorasaurus Ambassador Michael Hunnekuhl

Aurorasaurus: A citizen science project that maps the aurora in real-time using citizen science reports and crowdsourced data from Twitter. This helps scientists with aurora data, and helps the public see whether and where the aurora is shining in real time. The project has made a number of discoveries, including that social media is effective for detecting large natural events; that crowdsourcing the verification of citizen science data works; and that space weather alerts are more accurate when integrated with citizen science data. You can see our live aurora map and submit your own observations by going to www.aurorasaurus.org

 

Many aurora chasers and citizen scientists are also accomplished astrophotographers.

They capture beautiful (and scientifically useful) photos of aurora!

Aurora, STEVE, and stars light the sky and reflect in water

Aurora, STEVE, and the Milky Way, photo by Krista Trinder

Astrophotography: the practice of taking pictures of the night sky, including auroras. Chasers also talk about taking pictures of the stars when no auroras are visible. Even if you don’t have a fancy digital camera, you can still take part! Check out this free smartphone astrophotography guide from NASA. 

A photo shows the Milky Way, a meteor, a nova, and lightning sprites

Multiple phenomena in a composite photo by Daniel Korona, via NASA’s Astronomy Photo of the Day

Single exposure vs. stacked images: a “single exposure” is a single photo that you might snap on a camera. Sometimes photographers take multiple photos from the same location within a short period of time. Special software can then put them together, or “stack” them, to make a final image with less noise. Stacking images is a common practice when photographing low-light subjects like the night sky—though not necessary for aurora, which is brighter than most astrophotography targets. Artistic “composite” photos, made by combining pictures taken at different times or places, are not necessarily the best for aurora science either, though they are beautiful.

 

Aurora chasers tell us that one of the things they love most is that each aurora is different.

To make this wide variety easier to study, scientists classify the Lights into different types. Here are some basic categories—but there are many more types!

A red glow lights the sky

Diffuse aurora, photo by Larry Koehn, from spaceweather.com

Diffuse aurora: these usually have little motion, are quite dim, and might even be confused with clouds. (But if you can see stars through the glow, then it is likely an aurora, not a cloud.) They can be green, whitish, or blood red and spread over a wide area, typically closer to the equator than the “discrete” auroras described below. Diffuse red glows can be visible at great distances because they are so high in altitude. You can find out more about diffuse auroras and how they form in our Aurorasaurus Journal Club reading of the classic article by Dr. Syun-Ichi Akasofu, “The Development of the Auroral Substorm.” 

A green swirling aurora lights the sky

Discrete aurora, photo by Senior Airman Joshua Strong, courtesy of United States Air Force, CC-NC-SA

Discrete aurora: Discrete auroras are bright thin bands — most common pictures of auroras are of this type. They typically have a definite lower border and can stretch high into the sky, like curtains, when viewed from the side. From below they are very narrow. They can wave slowly or race across the sky, particularly on the part closest to the Earth’s nearest pole. They are broadest, brightest, and/or most active around midnight local time! We ask about types of aurora on our citizen science report form, because each is caused by a different process.

An animated gif shows pulsating aurroa

Pulsating aurora, photo by Poul Jenssen

Pulsating aurora: diffuse auroras can have pulsating patches which occur on the equatorward side of the auroral oval and turn on and off every few seconds. Video photography may be best for seeing them. They also have irregular shapes that reappear. They are quite dim and usually occur late in the night/early in the morning, after the main arcs have subsided. Some of what causes these unique shapes is unknown. 

STEVE curves up from the horizon like a feather in the sky

STEVE, photo by Vincent Ledvina

Subauroral phenomena: these occur closer to the Earth’s equator than the regular diffuse or discrete aurora and are more rarely studied; however, new cameras are aiding in documenting them. STEVE is an example of one type, and proton aurora is another. Keep reading to find out more about both!

A hand holds a pendant with coiled wire and beads

Pendant inspired by proton aurora science! Watch a basic explanation here. Images of proton auroras are surprisingly difficult to come by! We would be very interested in replacing this placeholder with an actual photo. If you have one that you would be willing to let us use, please let us know at aurorasaurus.info (at) gmail.com!

Proton aurora: a rare kind of aurora that is usually extremely dim to the human eye. Aurora chasers originally thought the mysterious STEVE might be some kind of proton aurora, but the differences between what they saw and proton aurora caught the interest of aurora scientists and led to research and discoveries. 

A clear STEVE lights the sky against the Milky Way

STEVE, photo by Catalin Tapardel

STEVE: a purplish arc with green “picket fence” features that runs east to west and appears closer to the equator than regular aurora. The name “STEVE” stands for “Strong Thermal Emission Velocity Enhancement.” While this phenomenon has been observed for centuries by both laypeople and scientists, in 2018 a team of citizen scientists and scientists published the first scientific paper on it. Collaborations involving citizen scientists are still discovering new things! Click here to watch a video that describes the story of STEVE.

 

We are often asked, “How can I see the aurora?”

In order to answer this question, let’s dive deeper into some of the science behind the Lights. 

A diagram labels the Sun, the boundary of the Earth's magnetic field, the Earth, auroras around the north and south poles, and the tail of the Earth's magnetic field

This diagram with artwork by Hannah Foss illustrates some of the spaces and phenomena that connect the Sun and Earth. It was created by the University of Alaska Fairbanks Museum of the North. They and traditional knowledge holders are working together to translate an “Anatomy of the Aurora” version of the poster into multiple languages. You can download it in two dialects of Iñupiaq from their Cultural Connections website. Western science is a newcomer to the observation of the aurora, and we recommend exploring these resources created by traditional knowledge holders.

 

Space is not empty!

In our solar system, it is a soup of dancing plasma, carried by the solar wind.

A stream of plasma jets out of the Sun

Plasma of the Sun, image by Hinode’s Solar Optical Telescope, Jan. 12, 2007

 

Plasma: the fourth state of matter. When a gas is superheated, its atoms split apart into electrons (negatively charged) and “ions” (positively charged). The charged particles move on their own, dancing to magnetic fields in space. Some people call plasma “ionized gas.” While in our daily lives we might encounter it in fire, lightning, or electric sparks, it actually makes up the vast majority of the universe. Click here to listen to a NEW podcast interview about plasmas in the universe with plasma physicist Dr. Doug Rowland!

solar wind streams toward the left of the gif like rapid mist

GIF excerpt from highly-processed STEREO spacecraft data of the normally-invisible solar wind. Data credit: Craig DeForest, SwRI. NASA’s Goddard Space Flight Center visualization

Solar wind: a gusty stream of material that flows from the Sun in all directions, all the time, carrying the Sun’s magnetic field out into space. While it is much less dense than wind on Earth, it is much faster, typically blowing at speeds of one to two million miles per hour. The solar wind is made of charged particles — electrons and ionized atoms — that interact with one another and the Sun’s magnetic field. Solar wind particles interacting with the Earth’s magnetic field are a major driver of aurora. Pro tip: You might see the solar wind’s magnetic field called the “interplanetary magnetic field” or “IMF” for short. Click here to explore an Aurorasaurus blog post and check out this solar wind sea shanty!

 

The Earth is surrounded by a magnetic bubble called the magnetosphere.

It exists inside a larger magnetic bubble called the heliosphere. This in turn is formed by the flowing “interstellar medium” of outer space.

The Sun, tiny and sparkling in the center, is surrounded by illustrated shells representing parts of the heliosphere protecting from interstellar radiation

Still illustration of the heliosphere with the Sun sparkling in the center, from a NASA video

Heliosphere: the space environment that originates in the Sun and surrounds the solar system. Made up of the flowing solar wind, which ultimately travels past all the planets to three times the distance to Pluto, the heliosphere is defined by the furthest reaches of the Sun’s magnetic field in space. The heliosphere is filled with radiation as well as magnetic fields that trail all the way back to the Sun. The heliosphere itself acts as a giant shield for the solar system, protecting the planets from galactic cosmic radiation. The NASA Voyager 1 and Voyager 2 spacecraft flew to the edge of the heliosphere and beyond—click here to follow their ongoing adventures!

A hand opens the 3D Printed Magnetosphere Model, revealing the internal structures

3D printed magnetosphere model created by Aurorasaurus, NASA’s STEAM Innovation Lab and NASA’s Magnetosphere Multiscale Mission (MMS)

Magnetosphere: the Earth has a magnetic field, or “magnetosphere,” with a north and south pole, kind of like a bar magnet or “dipole.” Solar wind plasma blows from the Sun and squishes the sunward side of our magnetic field. The plasma stretches the side farther away from the Sun into a long “magnetotail.” The magnetosphere’s outer boundary is where the solar wind meets the Earth’s magnetic field. Click here to explore an Aurorasaurus blog post about a 3D printed model of the magnetosphere, and find out more about how scientists study the magnetosphere here

A woman gives a space weather forecast

Still of space weather forecaster Tamitha Skov, “The Space Weather Woman,” from her website

Space Weather: the science behind and the forecasting of the ever-changing conditions in the solar system that may affect human-made assets. While the Earth’s magnetic field mostly protects the planet, some space weather can interfere with satellites and other technology. NOAA’s Space Weather Prediction Center (SWPC, pronounced “SWIP-see”) tracks space weather and issues alerts for a number of different customers. Some of these are relevant for aurora chasers. Other agencies also employ space weather forecasters. For those interested in graphs and charts, a list of scientific space weather resources is available here.

 

The terms “solar storm” and “geomagnetic storm” are often used interchangeably.

However, solar storms are shorter releases of matter, magnetism, and energy from the Sun, while geomagnetic storms are their longer-lasting effects on Earth. Not all solar storms hit Earth or cause geomagnetic storms. 

The Sun sneezes a mass of plasma at the Earth's magnetosphere

Artist illustration of material from the Sun headed toward the Earth’s magnetosphere. Created by NASA

Solar storms: eruptions of mass and energy from the solar surface. These launch hot plasma and magnetic fields out from areas near the surface of the Sun into the solar system. Sometimes these particles make it all the way to the Earth and beyond by flowing along the Sun’s magnetic field.

An illustration shows a large area of intensity near Antarctica.

This visualization of a 2003 geomagnetic storm affecting the South Pole is from the Polar spacecraft with “false-color” data overlaid using colors that represent auroral intensity. Red marks the highest intensity, blue the lowest. NASA/Goddard Space Flight Center Scientific Visualization Studio

Geomagnetic storm: when a large solar disturbance arrives at Earth, it buffets the magnetosphere more than usual. If the arriving solar magnetic field is directed southward, it interacts strongly with the northward-facing magnetic field of the Earth (see Bz). The Earth’s magnetic field is then peeled open like an onion, allowing energetic solar wind particles to stream down and hit the atmosphere over the poles. Geomagnetic storms can be measured by instruments on the Earth’s surface. There is a very small decrease in magnetic field strength that lasts about six to twelve hours, after which the magnetic field gradually recovers over a period of several days. Click here for more info about geomagnetic storms from the Space Weather Prediction Center, which monitors them.

 

The Sun drives solar storms. Sometimes—but not always—a solar flare can herald the launch of a CME toward Earth.

Solar flares are visible to instruments, but we can’t always tell if a CME is on the way to Earth, so we have to wait until it reaches a place where our satellites can detect it and the key direction of its magnetic field, which is called Bz. Forecasting CME arrival times is by its nature difficult to do with high accuracy. Until an hour or so before a geomagnetic storm, there can be a window of uncertainty for when the CME arrives of plus or minus 12 hours—a whole day in total! 

Animated gif of the Sun sneezing a large volume of matter off the right hand side

The European Space Agency/NASA Solar and Heliospheric Observatory captured this imagery of a coronal mass ejection as it left the sun in the direction of Earth and Mercury on July 16, 2013. Image by ESA&NASA/SOHO

Coronal mass ejection (CME): a huge bubble of radiation and particles from the Sun that explodes into space at very high speed when the Sun’s magnetic field lines suddenly reorganize. When charged particles from a CME reach enter the magnetosphere, they can trigger auroras. CMEs drive the biggest solar storms, and so can be a higher threat for severe space weather. The largest incidents are rare, but scientists constantly monitor the Sun for such events. How large can CMEs be? Click here for a video about the journey of an extremely large CME that occurred in 2012!

An image of the Sun with a large white sparkle-shaped flare

Image of a very large solar flare on the Sun taken by NASA’s Solar Dynamics Observatory on February 15, 2011. Much of the vertical line in the image is caused by the bright flash saturating the SDO sensor. Credit: NASA/SDO

Solar flare: the way magnetic fields on the Sun move and change can sometimes cause a sudden explosion of energy called a “solar flare” that releases large amounts of radiation into space. In scientific imaging of the Sun through special filters, it looks like a bright flash of light. If a solar flare is very intense, the radiation it releases can interfere with radio communications on Earth. Solar flares can sometimes—but not always—be accompanied by CMEs that can cause aurora. Click here to find out more about how scientists develop ways to predict solar flares. 

 

When particles arrive at Earth, they are caught and accelerated in the magnetosphere.

They then stream down through the upper atmosphere near the planet’s poles, driving the aurora and its related processes.

An animated graphic says "Welcome to the Ionosphere" as it rises above Earth's surface to the edge of space

Illustration from “Welcome to the Ionosphere” video by NASA Goddard Space Flight Center

Ionosphere: the Earth’s ionosphere is made up of charged particles, or plasma, and is the place in the upper atmosphere where auroras occur. It occurs between about 50 to 400 miles (80 to 640 kilometers) in altitude, far above clouds and planes. It overlaps the top of the electrically neutral atmosphere and the edge of space. Click here for a fun video about the ionosphere!

Snowy pine trees frame an aurora-filled sky

Aurora, photo by Vincent Ledvina

Aurora: Named for the Roman goddess of dawn, the aurora is a display of light in the night sky resulting from the raining down (precipitation) of electrons and protons from the magnetosphere into the Earth’s upper atmosphere. The aurora borealis and aurora australis — also called the northern lights and southern lights — occur at the north and south poles. Solar wind particles funnel around to the long tail of the magnetosphere, where they become trapped. The particles are then accelerated toward Earth’s poles, driven by a process called magnetic reconnection. At the final step of the process in Earth’s upper atmosphere, they ricochet off of atoms and molecules providing them with extra energy that is released as a burst of light. These interactions continue at lower and lower altitudes in the ionosphere until all the incoming energy is lost. When we see the glowing aurora, we are watching a billion individual collisions, lighting up the invisible magnetic field lines of Earth. Find out more about aurora science on the Aurorasaurus Learn page and blog!

A map of North America has an intense auroral oval overlaid on it

Image of the auroral oval in December 2015 by NOAA / NASA, retrieved by Sky & Telescope

Auroral oval: because of the way the Earth’s magnetic field is shaped, auroras occur in a roughly oval shape around the planet’s north and south magnetic poles. The oval can expand toward the equator during strong geomagnetic storms, but usually sits at about 65-70 degrees latitude. The Earth rotates beneath the auroral oval. In order to see auroras, you need to be underneath or close to the auroral oval. Scientists created a forecasting tool and real-time model of the auroral oval called OVATION Prime, which you can see in action on the Aurorasaurus map. Click here to watch a journal club exploration of a well-written, intermediate-level paper on this topic!

Green swirls of aurora grace the sky

Active auroral substorm, photo by Donna Lach

Substorm: a word for the daily, natural progression of auroras. They happen every few hours and take place at high latitudes in the auroral oval. Substorms are the natural results of the magnetosphere taking in, storing, and releasing energy. They were explored in the 1950’s by Dr. Syun-Ichi Akasofu of the University of Alaska Fairbanks, who figured out some of the ways that auroras behave on a global scale, that was later confirmed by images from satellites. You can find out more in this Aurorasaurus Journal Club reading of his classic article, “The Development of the Auroral Substorm.” The peaks of substorms are the times that the aurora dances most brightly and at the lowest latitudes, but the timing of the peaks is very difficult to predict, and not predicted by SWPC! 


A Bz south magnetic field reconnects with the Earth's

Diagram of a solar wind Bz south magnetic field reconnecting with the Earth’s Bz north magnetic field. Adapted from clip in COMET Met Ed Aurora Science lesson.

Bz: an important term for aurora chasing. Magnetic fields, called B by physicists, are carried through the heliosphere by the solar wind and are constantly changing direction and strength. The most important direction to aurora chasers is “Bz” because of the way it interacts with the Earth’s magnetic field.
There is a special location between the Earth and the Sun (close to the Earth) called L1. From this monitoring location, it takes the solar wind approximately an hour to reach Earth so this vantage point is naturally helpful for aurora chasers. There are two space weather satellites there, DSCOVR and ACE, measuring the interplanetary magnetic field, solar wind velocity, and other quantities. At L1 a coordinate system is used in which the “positive Bz” (aka “Bz north”) is in the same direction as the Earth’s magnetic field (technically speaking, the tangent.)
Why does this matter? When it comes to magnets, opposites attract. So if the solar wind near Earth has a “Bz south” magnetic orientation, also called “negative Bz,” it is the opposite of the Earth’s magnetic field. That makes it more likely to connect with the Earth’s magnetic field and drive processes that can cause aurora. If incoming solar wind has a “Bz north” or “positive Bz” orientation—the same as the Earth’s—it is largely deflected by the planet’s magnetic field. 
In other words, for aurora chasing, Bz south is a good thing! There are more details in our blog post on Bz. 

An illustrated fox watches an illustrated aurora, with different levels of intensity on a toggle at the bottom

Still from KpFox showing an artistic take on moderate, Kp5 conditions. KpFox was created by Aurorasaurus Ambassador Jeremy Kuzub

Kp Index: a global scale of disturbances in the Earth’s magnetic field, which ranges from 1-9. It is based on measurements of the Earth’s magnetic field from Earth at certain latitudes where geomagnetic storms cause changes. Higher numbers mean stronger activity, by a factor of 10. Since the Kp Index applies to the entire planet, it helps predict the presence of auroras on Earth, but can’t tell you if auroras will show up in any specific location. You can find out more in our blog post, and explore a visualization on the Kp Fox site by Aurorasaurus Ambassador Jeremy Kuzub. Click here to explore the official Kp Index website!

A graph shows highs and lows over time

Solar Wind Power chart on Aurorasaurus.org

Solar Wind Power: a measurement of the strength of the solar wind, based on real-time measurements from the ACE satellite, which sits between the Earth and the Sun and provides about an hour’s notice of activity. Like Kp Index, Solar Wind Power applies to the entire Earth, so while it can’t predict whether the aurora will show up at your location, it can help you decide whether it’s a “pants on!” kind of night since the plot is color-coded to tell you what levels may mean for your latitude. Solar wind power also is calculated more frequently than Kp, and takes into account the varying effects of Bz and solar wind speed on driving aurora.
You can see the current Solar Wind Power on the Aurorasaurus websiteClick here to explore a scientific paper by Dr. Syun-Ichi Akasofu, in which he calculates the parameters on which Solar Wind Power is based.

A similar estimate is “hemispheric power,” the power of the aurora in either the northern or southern hemisphere, measured in gigawatts (GW). It is measured by the OVATION Prime aurora model and serves as a good proxy for how strong the aurora is overall: higher values of hemispheric power or “hem pow” correspond with higher chances of seeing aurora. 

Because of all these things, the question “when can I see the aurora?” turns out to be surprisingly complex. The short answer is: there’s no way to know for sure, so the goal is to be in the right place at the right time, with fingers crossed! Use estimates like the Kp Index and Solar Wind power to see if space weather and Bz might be favorable with an hour of advance warning. Find a location under the auroral oval with a good view toward the pole and clear, dark sky. Keep an eye on Aurorasaurus and aurora chasing groups to see if others are seeing the aurora—and don’t forget to make a citizen science report of any you see! Even when everything looks favorable, aurora chasing requires a certain amount of luck—and Lady Aurora can also surprise you when the factors don’t look promising. The uncertainty is part of the sport and fun of chasing the aurora.

I hope these help you start to explore the amazing science of auroras! There are many more resources to explore on the Aurorasaurus website and blog. Have a safe, well-prepared, and wonderful time on your first aurora chase!

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