What is Aurora?

• An Aurora is a display of light in the sky seen in high latitude regions caused by the collision of charged particles with atoms in the atmosphere.
• It is also known as a Polar light.
• They occur commonly at high northern and southern latitudes.
• Aurora is less frequent at mid-latitudes and seldom seen near the equator.
• The colors of auroras include greenish, red, blue, violet, pink, and white.
• The colors appear in a variety of continuously changing shapes.
• Auroras result from emissions of photons in the Earth’s upper atmosphere.
• They originate from ionized nitrogen atoms regaining an electron and electrons from oxygen and nitrogen atoms returning from an excited state to the ground state.
• The solar wind coming from the sun is the origin of the charged protons and electrons that excite oxygen and nitrogen causing auroras.
• The color of the aurora depends on the type of atom that is excited and how its electrons return to the ground state.

Science behind their occurrence

• Auroras indicate that Earth is electrically connected to the Sun.
• They are caused by energy from the Sun and electrically charged particles trapped in Earth’s magnetic field.
• The typical aurora is provoked by collisions between fast-moving electrons from space with the oxygen and nitrogen in Earth’s upper atmosphere.
• The electrons come from the Earth’s magnetosphere, which is controlled by Earth’s magnetic field.
• The electrons transfer their energy to the oxygen and nitrogen atoms and molecules, making them “excited”.
• When the gases return to their normal state, they emit photons, small bursts of energy in the form of light.
• A large number of electrons coming from the magnetosphere can cause the oxygen and nitrogen to emit enough light for the eye to detect, resulting in beautiful auroral displays.

Coronal mass ejection

• A coronal mass ejection (CME) is a significant release of plasma and accompanying magnetic field from the solar corona.
• CMEs can eject billions of tons of coronal material and carry an embedded magnetic field that is stronger than the background solar wind interplanetary magnetic field strength.
• They often follow solar flares and are usually present during a solar prominence eruption.
• CMEs are often associated with other forms of solar activity, but a broadly accepted theoretical understanding of these relationships has not been established.
• CMEs most often originate from active regions on the Sun’s surface, such as groupings of sunspots associated with frequent flares.
• Near solar maxima, the Sun produces about three CMEs every day, whereas near solar minima, there is about one CME every five days.
• The solar flares and coronal mass ejections are driven by magnetic reconnections happening in the Sun’s corona.
• Magnetic reconnection is a process where oppositely polarity magnetic field lines connect, leading to the generation of heating, solar flares, and solar jets.
• The Halloween solar storms were a series of solar flares and coronal mass ejections that occurred from mid-October to early November 2003.
• This series of storms generated the largest solar flare ever recorded by the GOES system.
• Satellite-based systems and communications were affected, and aircraft were advised to avoid high altitudes near the polar regions.
• It is essential to measure the coronal magnetic fields regularly because the solar corona is highly dynamic and varies within seconds to a minute time scale.

Do other Planets get auroras?

• Planets with atmosphere and magnetic field can have auroras
• Gas giants in our solar system (Jupiter, Saturn, Uranus, and Neptune) have auroras
• Auroras on these planets are formed under different conditions than Earth’s auroras
• There are two types of auroras: aurora borealis (northern lights) and aurora australis (southern lights)
• Northern lights are named after the Roman goddess of dawn and the Greek name for the north wind
• Northern lights have had many names throughout history
• Auroras can be seen near the magnetic pole or illuminate the northern horizon
• Discrete auroras often display magnetic field lines or curtain-like structures
• Auroras can change within seconds or glow unchanging for hours
• Aurora borealis occurs near the winter equinox when it is dark for long periods of time
• Aurora borealis’ southern counterpart, aurora australis, has almost identical features
• Aurora australis is visible from high southern latitudes in Antarctica, South America, New Zealand, and Australia.

Why do auroras come in different colors and shapes?

• The color of aurora depends on the gas being excited by electrons – oxygen or nitrogen
• High energy electrons cause oxygen to emit green light
• Low energy electrons cause red light in oxygen
• Nitrogen generally gives off blue light
• Blending of colors can create purples, pinks, and whites
• Oxygen and nitrogen emit ultraviolet light, which can be detected by special cameras on satellites.

Effects

• Auroras affect communication lines, radio lines, and power lines.
• It should also be noted here that Sun’s energy, in the form of the solar wind, is behind the whole process.
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Magnetosphere

• The magnetosphere is the area of space around a planet controlled by its magnetic field.
• The shape of Earth’s magnetosphere is influenced by the solar wind, which compresses its sunward side to a distance of 6 to 10 times the radius of Earth, creating a supersonic shock wave called the Bow Shock.
• Most solar wind particles are heated and slowed at the Bow Shock and detour around Earth in the Magnetosheath.
• The solar wind drags out the night-side magnetosphere to possibly 1000 times Earth’s radius, forming the Magnetotail.
• The outer boundary of Earth’s confined geomagnetic field is called the Magnetopause.
• The Earth’s magnetosphere is highly dynamic and responds dramatically to solar variations.

Space Missions to study Auroras

• NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission aims to solve the mystery of what initiates the violent eruptions of the aurora during substorms in the Earth’s magnetosphere.
• Arase Mission/ERG is a Japanese mission focused on the formation of radiation belts associated with magnetic storms in geospace.
• The mission aims to understand the acceleration and loss mechanisms of relativistic particles during space storms in the inner magnetosphere.