What are auroras, and why do they come in different shapes and colors? Two experts explain

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Northern lights

Credit: Pixabay/CC0 Public Domain

For thousands of years, humans have observed and been inspired by the beautiful displays of light bands dancing across the dark night sky. Today, we call these lights auroras: the Northern Lights in the Northern Hemisphere, and the Australian Lights in the South.

Nowadays, we understand that the aurora borealis are caused by charged particles from Earth’s magnetosphere and the solar wind colliding with other particles in Earth’s upper atmosphere. trigger these collisions atmospheric particleswhich then releases light as it “relaxes” and returns to its unanimated state.

The color of the light corresponds to the release of separate portions of energy by the molecules of the atmosphere, and is also an indication of how much energy was absorbed in the initial collision.

The frequency and intensity of auroral displays is related to activity on the Sun, which follows an 11-year cycle. Currently, we are approaching the next maximum, which is Expected in 2025.

Sun contacts

These performances have been documented long ago by peoples all over north americaEurope , Asia And Australia.

In the 17th centuryScientific explanations for what caused it Northern lights began to surface. Possible explanations include air from Earth’s atmosphere rising from the Earth’s shadow to become sunlit (Galileo in 1619) and light reflections from ice crystals at high altitudes (Rene Descartes and others).






Fox Fires, a short film based on the Finnish folk tale of the Northern Lights.

In 1716, the English astronomer Edmund Halley was the first to suggest a possible connection to the Earth’s magnetic field. In 1731, a French philosopher named Jean-Jacques d’Ortus de Mairan noticed a coincidence between the number of sunspots and the aurora borealis. He suggested that the aurora borealis are related to the sun’s atmosphere.

Here the correlation between activity on the Sun was associated with the aurora borealis here on Earth, which led to the emergence of scientific fields now called “solar physics” And “space climate“.

Earth’s magnetic field as a particle trap

The most popular source for Northern lights They are particles that travel within the Earth magnetosphereThe region of space occupied by Earth’s natural magnetic field.

Images of Earth’s magnetosphere usually show how a magnetic field “bubble” protects Earth from space radiation and fends off most disturbances in the solar wind. However, what is not usually highlighted is the fact that the Earth’s magnetic field contains its own population of electrically charged particles (or “plasmas”).






A typical representation of Earth’s magnetic field interacting with the solar wind.

The magnetosphere consists of charged particles that escaped from Earth’s upper atmosphere and charged particles that entered from the solar wind. Both types of particles are trapped in the Earth’s magnetic field.

The motions of electrically charged particles are controlled by electric and magnetic fields. Charged particles revolve around magnetic field lines, so when viewed on large scales magnetic field lines They act as “pipelines” for charged particles in the plasma.

Earth’s magnetic field is similar to a standard “dipole” magnetic field, with field lines bunching together near the poles. This grouping of field lines actually alters the particles’ trajectories, effectively managing them to go back the way they came, in a process called “magnetic reversal.”

Earth’s magnetosphere under turbulent solar winds

During calm, stable conditions, most of the particles in the magnetosphere remain trapped, bouncing happily between the north and south magnetic poles in space. However, if there is disturbance in the solar wind (such as a Coronal mass ejection) the magnetosphere gives a “blow”, it becomes turbulent.






Magnetic reversal makes charged particles bounce back and forth between the two poles.

Trapped particles are accelerated and the magnetic field “pipelines” change abruptly. Particles that used to bounce happily between north and south have now moved to their bouncing site to lower altitudes, as Earth’s atmosphere becomes denser.

As a result, the charged particles It is now likely to collide with atmospheric particles as it reaches the polar regions. This is called “particle sedimentation”. Then, as each collision occurs, the energy is transferred to the atmosphere grains, excites them. Once they relax, they emit light that makes up the beautiful aurora borealis that we see.

Curtains, colors and cameras

The spectacular displays of the Northern Lights dancing across the sky are the result of complex interactions between… Solar wind and magnetosphere.

The appearance, disappearance, and brightening of the aurora borealis and the formation of structures such as curtains, eddies, hanging fences, and traveling waves are all visual representations of the invisible, ever-changing dynamics in Earth’s magnetosphere as it interacts with solar wind.






Catching the Northern Lights in the Southern Hemisphere.

As these videos show, auroras come in all kinds Colors.

The most common are green and red, both of which are given off by oxygen in the upper atmosphere. The green aurorae correspond to altitudes close to 100 km, while the red aurorae are higher for altitudes above 200 km.

Blue colors emit nitrogen – which some red colors can also emit. A range of pinks, purples, and even white light is also possible due to a combination of these emissions.

The aurora borealis are much brighter in the images because the camera sensors are more sensitive than the human eye. Specifically, our eyes are less sensitive to colors at night. However, if the aurora borealis are bright enough, they can be a stunning sight to the naked eye.

when and where?

Even under calm space climate In climatic conditions, the aurora borealis can be very prominent at high latitudes, as in AlaskaAnd CanadaAnd Scandinavian countries And Antarctica. When space weather is disturbed, the aurora borealis can migrate to much lower latitudes to become visible across the continent. United StateAnd Central Europe and even the South And Australia.






A rare sight of the Australian aurora from central Australia, with Uluru in the foreground.

The intensity of a space weather event usually controls the range of locations where the aurora borealis are visible. The strongest events are the rarest.

So, if you’re interested in chasing the Northern Lights, keep an eye on the local space weather forecast (weAnd AustraliaAnd United kingdomAnd South Africa And Europe). There are also many space weather experts at Social media And even citizen science projects to catch the Northern Lights (ex Northern lights) that you can contribute to!

Get out and see one of nature’s true beauties – the aurora, earth’s gateway to heaven.

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the quoteWhat are auroras, and why do they come in different shapes and colors? Two Experts Explain (2023, March 29) Retrieved March 29, 2023 from https://phys.org/news/2023-03-auroras-experts.html

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