Sunday, 11 December 2016

The Northern and Southern Lights

WHAT IS AN AURORA?
High-speed particles from the Sun, mostly electrons, strike oxygen and nitrogen atoms in Earth’s upper atmosphere. Credit: NASA
The South Pole Telescope under the aurora australis (southern lights). Credit: Keith Vanderlinde


For many people around the world the ability to see the Aurora Borealis or Aurora Australis is a rare treat. Unless you live north of 60° latitude (or south of -60°), or who have made the trip to tip of Chile or the Arctic Circle at least once in their lives, these fantastic light shows are something you’ve likely only read about or seen a video of.

But on occasion, the “northern” and “southern lights” have reached beyond the Arctic and Antarctic Circles and dazzled people with their stunning luminescence. But what exactly are they? To put it simply. auroras are natural light displays that take place in the night sky, particularly in the Polar Regions, and which are the result of interaction in the ionosphere between the sun’s rays and Earth’s magnetic field.

Basically, solar wind is periodically launched by the sun which contains clouds of plasma, charged particles that include electrons and positive ions. When they reach the Earth, they interact with the Earth’s magnetic field, which excites oxygen and nitrogen in the Earth’s upper atmosphere. During this process, ionized nitrogen atoms regain an electron, and oxygen and nitrogen atoms return from an excited state to ground state.


Aurora

An aurora, sometimes referred to as a polar light, is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions. Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere), where their energy is lost. The resulting ionization and excitation of atmospheric constituents emits light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes.

Most auroras occur in a band known as the auroral zone, which is typically 3° to 6° wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the auroral oval, a band displaced towards the nightside of the Earth. Day-to-day positions of the auroral ovals are posted on the internet. A geomagnetic storm causes the auroral ovals (north and south) to expand, and bring the aurora to lower latitudes. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis (1860), and later Hermann Fritz (1881) and S. Tromholt (1882) in more detail, established that the aurora appeared mainly in the "auroral zone", a ring-shaped region with a radius of approximately 2500 km around the Earth's magnetic pole. It was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The instantaneous distribution of auroras ("auroral oval") is slightly different, being centered about 3–5 degrees nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. The aurora can be seen best at this time, which is called magnetic midnight.

In northern latitudes, the effect is known as the aurora borealis (or the northern lights), named after the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas, by Galileo in 1619. Auroras seen within the auroral oval may be directly overhead, but from farther away they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction.

Its southern counterpart, the aurora australis (or the southern lights), has features that are almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone.[8] It is visible from high southern latitudes in Antarctica, Chile, Argentina, New Zealand, and Australia. Auroras also occur on other planets. Similar to the Earth's aurora, they are also visible close to the planets’ magnetic poles. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs,[9] which can be sub-visual.


WHAT IS AN AURORA?

Auroras are electrically charged particles from solar winds that enter the Earth’s atmosphere and react with its gases.

Solar winds are part of “space weather”, which is a stream of highly energised particles and electromagnetic radiation emitted from the sun. The particles are blown around in space at a very high speed and temperature – just like they are being blown about in the most extreme wind ever!

What usually protects the Earth from solar wind is the magnetosphere, which is constantly changing in size depending on the solar winds. The magnetosphere stops solar winds and other cosmic rays from entering the Earth’s atmosphere (and killing us all). However, an aurora is formed when some of the charged particles from the solar winds breaks through the magnetosphere at the north and south poles and reacts with the Earth’s atmospheric gases. Energy is transferred between the gases and solar wind electrons. Any excess energy becomes the pretty lights that you see in the aurora.

The colours of the aurora are due to a number of factors: the type of gas molecule, the electrical state at the time of collision, and the type of solar wind particle that the gas collides with.

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NORTHERN & SOUTHERN AURORAE ARE SIBLINGS, BUT NOT TWINS

Seen the Northern Lights and you’ve seen them all, hm? Not so.

It is commonly assumed that the aurora borealis in the Northern Hemisphere and the aurora australis in the Southern Hemisphere are mirror images of each other — but new research has revealed differences between the events.

The aurorae, commonly known as the Northern and Southern Lights, are spectacular natural light displays in the Earth’s upper atmosphere. The phenomenon is caused by charged particles from the solar wind striking atoms and molecules in the atmosphere.

It’s intuitive to think the Northern and Southern Lights are identical, because the charged particles causing the aurora follow the symmetric magnetic field lines connecting the two hemispheres.

But  study co-authors Nikolai Østgaard and Karl Magnus Laundal, both of the University of Bergen in Norway, report in the journal Nature this week that there are differences between the phenomena.

“Here we report observations that clearly contradict the common assumption about symmetric aurora: intense spots are seen at dawn in the Northern summer Hemisphere, and at dusk in the Southern winter Hemisphere,” they write. “The asymmetry is interpreted in terms of inter-hemispheric currents related to seasons, which have been predicted but hitherto had not been seen.”

Østgaard and Laundal based their report on observations from a new set of global imaging cameras at each pole. The authors suggest that the observed asymmetry confirms the existence of inter-hemispheric, field-aligned currents related to the seasons, which had been predicted but never before observed.




The Northern and Southern Lights

The northern lights can be green, pink, red, blue or violet in color © iStockphoto.com/Constance McGuire

Southern lights as seen from space. Picture taken by the Expedition 32 crew onboard the International Space Station from an altitude of about 240 miles (386 kms). NASA

What Are Northern and Southern Lights? An aurora is a natural electric phenomenon that creates bright and colorful light displays in the sky. They are common at higher latitudes, mostly within the Arctic and the Antarctic Circles.

In the Arctic Circle, they are known as aurora borealis or the northern lights, while in the Antarctic Circle they are called aurora australis or the southern lights. These dramatic and colorful lights are created when electrically charged particles from solar winds enter the Earth’s atmosphere and interact with gases in the atmosphere.

Best Places to See Northern Lights? If one were to look from space, they would see a ring-shaped aurora spanning around 2500 miles (4000 kms) around both poles. This auroral zone covers Central and northern Alaska and Canada, Greenland, northern Scandinavia and Russia in the Northern Hemisphere, and Antarctica in the Southern Hemisphere. In the south, auroras can sometimes be seen from southern Australia, New Zealand, and Chile.

When's the Best Time to See Auroral Lights? While auroral activity and auroras can occur throughout the year, day and night, the best time to view them is at night during the winter months. This is because, during the winter, areas around the North and the South Poles have longer periods of darkness. Auroras are best observed around midnight – when it is darkest – on a clear night, and at a location that is away from the city. Light sources – artificial or natural, like from a full Moon – can make it very hard to view the aurora.

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WHAT CAUSES THE NORTHERN AND SOUTHERN LIGHTS

Today I found out what causes the Northern and Southern Lights (aurora borealis and aurora australis respectively).

Simply put, these lights are caused by very fast moving electrons striking atoms in the Earth’s upper atmosphere, primarily oxygen and nitrogen atoms which make up most of our atmosphere.  When this happens, it can put these atoms in an excited state.  During the process with which they return to their normal state, they emit this excess energy in the form of visible photons.

So where do these fast moving electrons come from?  Charged particles from the sun’s corona are constantly striking near the Earth and are more or less deflected by the Earth’s magnetic field, which in turn protects life on the Earth from being harmed by these solar winds. When these charged particles encounter the Earth’s magnetic field, they end up traveling along the field lines with some of them ending up interacting with the magnetic field lines, cutting across the field, thus producing a current which can accumulate to upwards of 10 million megawatts!

This current ends up creating a fairly unstable state in the magnetosphere.  Occasionally, some of this current is discharged causing electrons in the magnetosphere to spiral down towards the poles and through the Earth’s upper atmosphere.  As it descends into the atmosphere, it collides with primarily oxygen and nitrogen.  When this happens, the atoms move to high energy orbitals.  This state is fairly unstable for these atoms and they will return fairly quickly to their normal orbitals.  To do so, they must release the excess energy they have stored up from this collision by emitting a photon.  With enough of these atoms going from the high orbital state to the low orbital state, it will produce enough light to be viewable to the naked eye by people standing in appropriate locations on Earth.

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What turns on the Northern and Southern Lights - Aurora Borealis and Aurora Australis?

The Aurora Borealis and Aurora Australis are seen in the northern and southern hemispheres respectively. Aurorae are generally confined to higher latitudes but large displays associated with violent magnetic disturbances can be seen from as far south as southern Britain.

Both are due to the interaction of a stream of particles from the Sun with the Earth's atmosphere. They have been associated with magnetic activity since the 18th century. Their association with sunspot activity, and later with solar flares, gave the key to understanding their cause
Aurorae are often bright enough to be seen with the naked eye. They often take the form of curtains of light in which the folds rapidly move and vary in brightness. Often the curtain rests on an arc of light. Colours are seen in the brightest displays and can be seen to be red and green.

The lowest part of an aurora is at a height of about 100km above the Earth's surface while the top of a display may extend to several thousand kilometres.


The Northern Lights - where, when and what

Where can we see the northern lights? The Northern Lights, as the name suggests, are especially related to the polar regions. They occur most frequently in a belt of radius 2500 km centered on the magnetic north pole. This so-called auroral zone extends over northern Scandinavia, Island, the southern tip of Greenland and continuing over northern Canada, Alaska and along the northern coast of Siberia. The coasts of the Norwegian counties of Troms and Finnmark lay where occurrence is greatest, making northern Norway, due to its ease of access and mild winter climate, an attractive destination for people interested in observing this atmospheric phenomenon. The Northern Lights can be seen from regions both north and south of the auroral zone, but the likelihood decreases with distance. There is a corresponding auroral zone around the southern magnetic pole, but these 'Southern Lights' are largely only seen from Antarctica and the surrounding ocean. Of the populated regions in the southern hemisphere, the Southern Lights, may only be glimpsed from Tasmania and southern New Zealand. The Northern and Southern Lights occur simultaneously and are almost mirror images of each other.

How often can you see the Northern Lights? In Troms and Finnmark, we can see the Northern Lights every other clear night, if not even more frequently. From southern Norway, sightings would be only a few times a month while in central Europe hardly more than a few times a year and they have even been seen from the Mediterranean but only a few times each century. To the north of the auroral zone, on Spitzbergen, the Northern Lights are a common sight, although they don't appear as often as in northern Norway.

When can we see the Northern Lights? We associate the Northern Lights with wintertime, although in reality they are present the year round; it's just that we can't see them when the nights are light as the background sky has to be fairly dark. In practice, in northern Norway we are restricted to the period starting at the beginning of September and extending until the middle of April. On the other hand, if the Northern Lights are strong enough, they may still be seen against a twilight sky, and it is not unusual to see them from Tromsø on an August evening. The Northern Lights are often referred to as 'night aurora' because they occur on the night side of the Earth and they commonly appear in the early evening and continue late into the night. Although this is the most usual form of aurora, during winter on Spitzbergen, where it is dark even at midday, it is possible to observe the rarer 'day aurora' which occurs on the 'day side' of the Earth. The aurora lies well above the highest clouds, so we need clear skies to be able to see it. In fact, cloudy skies are the greatest obstacle for auroral observations in northern Norway and for this reason the inland regions are better suited than near the coast. The days around full moon are not conducive to viewing the Northern Lights because the background sky becomes so light. Finally, one should avoid cities and areas with much street lighting in order to experience the Northern Lights to the full.

How high up are the Northern Lights? Most aurorae occur between 90 and 130 km above sea level, but some, particularly the ray-like forms, extend to several hundred kilometers up. In comparison, the usual altitude for a jet aircraft is around 10km and the ozone layer lies between 20 and 30km so we have to be almost up at the heights of satellites orbits to be at the same height as the aurora. A consequence of its great height is that the aurora is visible at horizontal distances of several hundred kilometers. Thus an aurora over Bear Island will be visible from both Spitzbergen and Tromsø, and one over Tromsø can be seen in the northern sky from central Norway.

What exactly are the Northern Lights? The Northern Lights stem from when large numbers of electrically charged particles (electrons) at high speed stream in towards the Earth along its magnetic field and collide with the highest air particles. The air then lights up rather like what happens in a fluorescent light tube. The resulting colours reflect which gases we find up there, the most usual yellow-green colour coming from oxygen. Red colouring is also due to oxygen with a contribution from nitrogen. The violet we often see at the lower edge of the aurora is due to nitrogen, as is most blue colouring. The charged particles originate from the sun, and it is the 'weather' conditions on the sun that decide whether or not we will see the aurora. Particles can stream out from the sun and some are captured by the Earth's magnetic field and find their way into the polar regions. On the way, they travel out into the night side of the Earth and gain extra energy - we still lack understanding of exactly what happens out there!


Aurora Borealis: What Causes the Northern Lights & Where to See Them

The northern lights, or aurora borealis, offer an entrancing, dramatic, magical display that fascinates all who see it — but just what causes this dazzling natural phenomenon?

At the center of our solar system lies the sun, the yellow star that sustains life on our planet. The sun's many magnetic fields distort and twist as our parent star rotates on its axis. When these fields become knotted together, they burst and create so-called sunspots. Usually, these sunspots occur in pairs; the largest can be several times the size of Earth's diameter.

At the center of the sun, the temperature is 27 million degrees Fahrenheit (15 million degrees Celsius). As the temperature on its surface rises and falls, the sun boils and bubbles. Particles escape from the star from the sunspot regions on the surface, hurtling particles of plasma, known as solar wind, into space. It takes these winds around 40 hours to reach Earth. When they do, they can cause the dramatic displays known as the aurora borealis.

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The Five Best Places to See the Southern Lights—Aurora Australis
Southern Lights From Stewart Island, New Zealand
The Aurora Australis in Full Flow

Why are the Southern Lights no where near as popular as the Northern Lights?

Well it’s all about land. Head high up to the Northern Hemisphere towards the Arctic Circle and there is land aplenty. You have Northern Canada, Greenland, Norway, and Russia all heading high up to where the Aurora comes out to play. This makes finding a nice location with accommodations very easy. You can go on trips and spend days relaxing in comfort while the night sky lights up for you. However, the Southern Hemisphere is a little different.

Due to the nature of the land masses in the south, there are very few places that reach down low enough towards Antarctica that will give you ideal Aurora viewing spots. If you look at a map of the polar regions you will see the south is just surrounded by water. Of course you could go and camp out on the Antarctic ice but that is not something your average person can do.

Despite the fact that viewing the Southern Lights can be very tricky, there are places you can go where you can see them. So we have put together a list of our top 5 places to view the Southern Lights.

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THE BEST TIMES AND LOCATIONS TO SEE THE SOUTHERN LIGHTS IN NEW ZEALAND
THE WORLD’S MOST REMARKABLE LIGHT SHOW!

New Zealand is known for a lot of natural wonders, and Aurora Australis (The Southern Lights) has to be one of the most wonderful of all. But with the right conditions and the right location, the Aurora Australis will give you a night to remember.

Aurora Australis may be lesser known than Aurora Borealis (The Northern Lights), but it is just as impressive! Only a few of us have had the privilege to see the electric phenomenon because we struggle to get far enough south. That’s with the exception of Australia, Chile, New Zealand and Antarctica. So if you have chosen New Zealand as your work and travel destination, then here’s yet another reason you have made the right decision! In New Zealand, you can see the aurora activity as a green and pink hue over the horizon and even dancing green veils lighting up the sky. To increase your chances of seeing the Southern Lights on your travels, you need a combination of the best time, the best weather conditions, and being in the right place.

THE BEST TIME TO VIEW THE SOUTHERN LIGHTS - Unfortunately, the Southern Lights are not very predictable. They don’t run on a schedule. In fact, they tend to occur with only 30 minutes notice! Although auroras happen all year round, the best time to see them in New Zealand is during the winter months (March to September). The widest part of the aurora is when the sun is on the opposite side of the Earth to where you are, so around midnight is best.

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