Category Archives: Outreach

Don’t panic: the northern lights won’t be turning off anytime soon

Don’t panic: the northern lights won’t be turning off anytime soon

Image 20170203 13995 1ap4x0d
Truly spectacular.
Moyan Brenn/flickr, CC BY

Nathan Case, Lancaster University

The northern lights are nature’s very own magnificent light show. They are the mesmerising end result of electrically charged particles from the sun colliding with the Earth’s upper atmosphere. Though more frequently witnessed from the polar regions, the UK and other places on similar latitudes are lucky enough for the aurora borealis to occasionally grace their night sky. The Conversation

But recent reports now claim the phenomenon may no longer be visible from places such as the UK – instead confined to the North Pole. But is this correct?

The northern lights are driven by activity on the sun and the sun’s activity waxes and wanes over an 11-year period known as a solar cycle. The number of large-scale aurora events, the type that is visible from places such as the UK, tends to follow this cycle. But each solar cycle is different, with the maximum and minimum activity varying between each cycle.

Predicting solar activity

Current predictions suggest that we are headed for a period of particularly weak solar cycles, where the solar maximum of each cycle will not result in much solar activity. We call this a grand solar minimum.

The number of sunspots observed on the sun.
Global Warming Art/Wikipedia

Grand solar minimums can last for several decades or even centuries and have occurred throughout history. Although solar output does decline during these periods, it doesn’t mean that we are heading for a new ice age.

A study recently published in Nature has modelled the perhaps most well-known grand solar minimum, called the “Maunder minimum”. This particular grand solar minimum started in 1645 and finally ended 70 years later. During this time only 50 sunspots, structures on the sun that act as a measure of its activity, were observed. This is compared to the 40,000-50,000 that we would expect during a period of “normal” activity lasting that long.

Sunspots (black) visible on the sun.
NASA/SDO/AIA/HMI/Goddard Space Flight Center

The authors of the study found that during the Maunder minimum, the solar wind, which drives the aurora, dramatically weakened. They also illustrate that as the solar wind weakens, so too will the aurora.

If we are in fact heading into a new grand solar minimum, it stands to reason that we might see less of nature’s beautiful spectacle. But does that mean we’ll stop seeing it from the UK altogether as some have suggested?

Lessons from the past

Looking back at historical records of aurora sightings might provide the answer. Fortunately, a study has done just that. The authors analysed auroral observations during two grand solar minimums– including the Maunder minimum. They found that the number of aurora sightings from below 56° magnetic latitude (which is similar to geographic latitude but measured from the magnetic pole rather than the geographic pole) did indeed decrease. But they did not stop altogether.

That value of 56° magnetic latitude is actually quite important as it happens to coincide with the magnetic latitude of the UK (more specifically somewhere close to Lancaster, England).

The aurora captured from Groomsport, Northern Ireland (UK).
Philip McErlean/flickr

So what’s my prediction for the aurora over the next century? If the models are correct and we do head into a grand solar minimum, then solar activity is going to decrease – and remain at very low levels for decades to come. With this decrease in solar activity, aurora sightings from outside the polar regions are going to become rarer. But that doesn’t necessarily mean they’ll stop altogether. It also isn’t certain that we are heading for a grand solar minimum or – even if we are – when it might occur.

So while that elusive light show might get even more elusive, don’t fret just yet: the northern lights aren’t going out anytime soon.

Nathan Case, Senior Research Associate in Space and Planetary Physics, Lancaster University

This article was originally published on The Conversation. Read the original article.

Beautiful green ‘airglow’ spotted by aurora hunters

Beautiful green ‘airglow’ spotted by aurora hunters – but what is it?

Nathan Case, Lancaster University

Amateur astronomers and aurora hunters alike have been reporting a green glow across the UK sky. Easily confused with the aurora borealis, or northern lights, the sightings were of another phenomena called “airglow”.

Airglow is the natural “glowing” of the Earth’s atmosphere. It happens all the time and across the whole globe. There are three types of airglow: dayglow, twilightglow and nightglow. Each is the result of sunlight interacting with the molecules in our atmosphere, but they have their own special way of forming.

Dayglow forms when sunlight strikes the daytime atmosphere. Some of the sunlight is absorbed by the molecules in the atmosphere, which gives them excess energy. They become excited. The molecules then release this energy as light, either at the same or slightly lower frequency (colour) as the light they absorbed. This light is much dimmer than daylight, so we can’t see it by eye.

Twilight glow is essentially the same as dayglow, but only the upper atmosphere is sunlit. The rest of the atmosphere and the observer on the ground are in darkness. So, unlike day glow, twilightglow is actually visible to us on the ground with the naked eye.

Chemiluminescence

The chemistry behind nightglow is different. There is no sunlight shining on the nighttime atmosphere. Instead, a process called “chemiluminescence” is responsible for the glowing atmosphere.

Sunlight deposits energy into the atmosphere during the day, some of which is transferred to oxygen molecules (e.g. O₂). This extra energy causes the oxygen molecules to rip apart into individual oxygen atoms. This happens particularly around 100km in altitude. However, atomic oxygen isn’t able to get rid of this excess energy easily and so acts as a “store” of energy for several hours.

Eventually the atomic oxygen does manage to “recombine”, once again forming molecular oxygen. The molecular oxygen then releases energy, again in the form of light. Several different colours are produced, including a “bright” green emission.

Airglow spotted in panoramic shot of the Very Large Telescope.
ESO/Y. Beletsky – http://www.eso.org/public/images/uhd_vlts_pan_cc/, CC BY-SA

In reality, the green nightglow isn’t particularly bright, it’s just the brightest of all nightglow emissions. Light pollution and cloudy skies will prevent sightings. If you’re lucky though, you might just be able to see it by eye or capture it on long-exposure photos.

Not to be confused with aurora

The green night glow emission is very similar to the famous green we see in the northern lights. This is unsurprising since it is produced by the same oxygen molecules as the green aurora. But the two phenomena are not related.

Aurora form when charged particles, such as electrons, bombard the Earth’s atmosphere. These charged particles, which started off at the sun and were accelerated in the Earth’s magnetosphere, collide with the atmospheric gases. They transfer energy, forcing the gases to emit light.

The aurora and airglow captured from the International Space Station.
NASA

But it isn’t just the process behind them that is different. The aurora form in a ring around the magnetic poles (known as the auroral oval); whereas nightglow is emitted across the whole night sky. The aurora are very structured (due to the Earth’s magnetic field); whereas airglow is generally quite uniform. The extent of the aurora is affected by the strength of the solar wind; whereas airglow happens all the time.

Why then did we get a lot sightings from the UK recently, rather than all the time? The brightness of airglow correlates with the level of ultraviolet (UV) light being emitted from the sun – which varies over time. The time of year also seems to have an impact on the strength of airglow.

Airglow captured by Michael Darby from Cornwall, UK. The Milky Way shines through in the centre of the image.
Author provided

To maximise your chances of spotting airglow, you’ll want to take a long-exposure photograph of a clear, dark, night sky. Airglow can be spotted in any direction that is free of light pollution, at about 10⁰-20⁰ above the horizon.

The Conversation

Nathan Case, Senior Research Associate in Space and Planetary Physics, Lancaster University

This article was originally published on The Conversation. Read the original article.

Explainer: what are the ‘nacreous clouds’ lighting up the winter skies? — The Conversation Article

Explainer: what are the ‘nacreous clouds’ lighting up the winter skies?

Nathan Case, Lancaster University

People in the polar regions of the world, such as Scandinavia and Canada, sometimes get to watch majestic, rainbow-coloured clouds drift across an otherwise grey winter sky. Over the past few days, observers from across the UK and Ireland have also been lucky enough to witness this phenomenon, known as “nacreous” (or polar stratospheric) clouds.

In fact, nacreous clouds are so unusual in Britain that AuroraWatch UK, a service that monitors the likelihood of auroal sightings, received reports that these colourful displays were “aurora borealis”, also known as the northern lights, which is caused by collisions of electrically charged particles from the sun colliding with particles in Earth’s atmosphere. However, the two phenomena are not related.

Nacreous clouds typically form in the winter polar stratosphere, a layer of our atmosphere around 15,000 to 25,000m in altitude. The stratosphere is generally very dry and so cloud formation is rare, but it seems as though recent storms may have driven moisture high into the atmosphere. Nacreous clouds will also only form when the temperature in the stratosphere is below a chilly -78°C, which turns any moisture in the air into super-cooled liquid or ice crystals. Such temperatures generally only occur in the winter at high latitudes.

Polar stratospheric cloud .
wikimedia

During the hours of “civil twilight”, when the sun is between 1° and 6° below the horizon, the first or last rays of the day illuminate these high altitude clouds from below. This light is refracted by the ice crystals in the clouds, a process known as cloud iridescence, producing the shimmering rainbow effect.

Destructive force

As pretty as they may look, nacreous clouds have a darker side too. These clouds enhance the breakdown of the Earth’s ozone layer, a vital part of our atmosphere that provides protection from the sun’s harmful ultraviolet rays. The ice crystals in the clouds encourage a chemical reaction between the ozone layer, which is made up of a specific type of molecular oxygen (O3), and gases such as chlorine and bromine. In fact, it is estimated that just one atom of chlorine in the stratosphere can destroy over 100,000 ozone molecules.

Polar Stratospheric Cloud type I above Cirrus.
François Guerraz /wikimedia, CC BY-SA

The presence of these ozone-destroying gases in the stratosphere is a problem of our own making. Although phased out after the Montreal Protocol in 1987, the prime reason for their presence is our use of chlorofluorocarbons (CFCs) in products such as refrigerators and aerosol cans. While usage of CFCs has been significantly reduced, it is estimated that it may take another 50-100 years before the effects of CFCs in the atmosphere is diminished.

Current weather predictions suggest that further sightings of nacreous clouds may be possible in the UK until around Saturday. At this time, the polar vortex (which is responsible for the cold conditions currently in the stratosphere above the UK) moves northward to its usual position.

The Conversation

Nathan Case, Senior Research Associate in Space and Planetary Physics, Lancaster University

This article was originally published on The Conversation. Read the original article.

How can I see the aurora or Northern Lights?

Nathan recorded the following clip for Lancaster University, and AuroraWatch UK, giving a few tips about how best to see the northern lights from the UK.

The tips include:

1 – Head north: the aurora will generally be visible on the northern horizon (in the northern hemisphere)
2 – Find an unobstructed view of the northern horizon: such as a hillside or a northward facing coast.
3 – Find dark skies: city light pollution will tend to be brighter than the aurora, especially when attempting to view by eye. Try seeking out local dark sky areas.
4 – Hope for clear skies: (this one is down to chance!) the aurora occur higher in altitude than clouds, so any clouds will obscure your view.
5 – Sign up to AuroraWatch UK for alerts of increased chance in auroral visibility from the UK.

Nathan also recorded a clip on “5 Surprising Facts about the Northern Lights” which you can watch below.

What’s it like to see auroras on other planets? — The Conversation Article

What’s it like to see auroras on other planets?

Nathan Case, Lancaster University

Witnessing an aurora first-hand is a truly awe-inspiring experience. The natural beauty of the northern or southern lights captures the public imagination unlike any other aspect of space weather. But auroras aren’t unique to Earth and can be seen on several other planets in our solar system.

An aurora is the impressive end result of a series of events that starts at the sun. The sun constantly emits a stream of charged particles known as the solar wind into the depths of the solar system. When these particles reach a planet, such as Earth, they interact with the magnetic field surrounding it (the magnetosphere), compressing the field into a teardrop shape and transferring energy to it.

Because of the way the lines of a magnetic field can change, the charged particles inside the magnetosphere can then be accelerated into the upper atmosphere. Here they collide with molecules such as nitrogen and oxygen, giving off energy in the form of light. This creates a ribbon of colour that can be seen across the sky close to the planet’s magnetic north and south poles – this is the aurora.

Gas giant auroras

Using measurements from spacecraft, such as Cassini, or images from telescopes, such as the Hubble Space Telescope, space physicists have been able to verify that some of our closest neighbours have their own auroras. Scientists do this by studying the electromagnetic radiation received from the planets, and certain wavelength emissions are good indicators of the presence of auroras.

Each of the gas giants (Jupiter, Saturn, Uranus, and Neptune) has a strong magnetic field, a dense atmosphere and, as a result, its own aurora. The exact nature of these auroras is slightly different from Earth’s, since their atmospheres and magnetospheres are different. The colours, for example, depend on the gases in the planet’s atmosphere. But the fundamental idea behind the auroras is the same.

Blue aurora on Jupiter.
NASA/J Clarke

For example, several of Jupiter’s moons, including Io, Ganymede and Europa, affect the blue aurora created by the solar wind. Io, which is just a little larger than our own moon, is volcanic and spews out vast amounts of charged particles into Jupiter’s magnetosphere, producing large electrical currents and bright ultraviolet (UV) aurora.

On Saturn, the strongest auroras are in the UV and infrared bands of the colour spectrum and so would not be visible to the human eye. But weaker (and rarer) pink and purple auroras have also been spotted.

Hubble Space Telescope captures Saturn’s aurora.
NASA/ESA/Hubble

Mercury also has a magnetosphere and so we might expect aurora there too. Unfortunately, Mercury is too small and too close to the sun for it to retain an atmosphere, meaning the planet doesn’t have any molecules for the solar wind to excite and that means no auroras.

The unexpected auroras

On Venus and Mars, the story is different. While neither of these planets has a large-scale magnetic field, both have an atmosphere. As the solar wind interacts with the Venusian ionosphere (the layer of the atmosphere with the most charged particles), it actually creates or induces a magnetic field. Using data from the Venus Express spacecraft, scientists found that this magnetic field stretches out away from the sun to form a “magnetotail” that redirects accelerated particles into the atmosphere and forms an aurora.

Mars’s atmosphere is too thin for a similar process to occur there, but it still has aurora created by localised magnetic fields embedded in the planet’s crust. These are the remnants of a much larger, global magnetic field that disappeared as the planet’s core cooled. Interaction between the solar wind and the Martian atmosphere generates “discrete” auroras that are confined to the regions of crustal field.

A recent discovery by the MAVEN mission showed that Mars also has much larger auroras spread across the northern hemisphere, and probably the whole planet too. This “diffuse” aurora is the result of solar energetic particles raining into the Martian atmosphere, rather than particles from the solar wind interacting with a magnetic field.

If an astronaut were to stand on the surface of Mars, they might still see an aurora but it would likely be rather faint and blue, and, unlike on Earth, not be necessarily near the planet’s poles.

Brown dwarf with red aurora.
Chuck Carter and Gregg Hallinan/Caltech

Most planets outside our solar system are too dim compared to their parent star for us to see if they have auroras. But scientists recently discovery a brown dwarf (an object bigger than a planet but not big enough to burn like a star) 18 light years from Earth that is believed to have a bright red aurora. This raises the possibility of discovering other exoplanets with atmospheres and magnetic fields that have their own auroras.

Such discoveries are exciting and beautiful, but they are also scientifically useful. Investigating auroras gives scientists tantalising clues about a planet’s magnetic and particle environment and could further our understanding of how charged particles and magnetic fields interact. This could even unlock the answers to other physics problems, such as nuclear fusion.

The Conversation

Nathan Case, Senior Research Associate in Space and Planetary Physics, Lancaster University

This article was originally published on The Conversation. Read the original article.

Newsweek article

Connor Gaffey from Newsweek.com today published an article about last night’s spectacular auroral display that was visible from across the UK. Connor spoke with Nathan about how best to see the aurora in the UK and why the display last night was so strong.

Newsweek spoke to Nathan Case, a member of the Aurora Watch U.K. team at Lancaster University, who track geomagnetic activity around the British Isles and sends alerts to users when sightings of the Northern Lights are possible, to find out the best way to see the lights.

Click here to read the full article.

Mapping Aurora with Twitter blog post

As our users will know, we love Twitter here at Aurorasaurus. In addition to using the social media service ourselves (check out the Twitter list of Aurorasaurus Team Members here), we present aurora-related tweets for our users to verify them as aurora sightings (a process called crowdsourcing.) We then use these “verified tweets” in just the same way as the other observations reported via our website or apps, for example, by comparing their location with the modeled auroral ovals.

Read full blog post here.

#Aurorachat

Last week Nathan helped run a tweet-chat about the aurora. Organised by Aurorasaurs (@TweetAurora), members of the public were able to ask questions about the aurora, citizen science and the Aurorasaurus project. Nathan answered questions ranging from “where can I see the aurora?” to “will climate change affect the aurora?”.

 

You can read more by searching for #aurorachat on Twitter (or clicking by viewing the Storify article here).

Aurorasaurus Google Hangout

The Aurorasaurus team ran their first Google+ Hangout today, introducing the project and its scientific aims as well as running through details about citizen science reporting and how to use the website. Nathan introduced himself, answered some questions about the aurorae as well as summarizing how Aurorasaurus will be using the citizen science observations.

Screenshot of Nathan appearing in the Aurorasaurus Hangout.

Screenshot of Nathan appearing in the Aurorasaurus Hangout.

The full blog post can be found here

Skype chat with Class 3 from Ince CE Primary School

Nathan was invited to take part in a Skype chat about “space” with Class 3 from Ince CE Primary School. The children in Class 3 had been learning all about space and human missions to the Moon and so invited Nathan to speak a bit about the work he does and to answer some questions they had. Nathan answered questions ranging from things like “what are stars made of?” to “has a giraffe been to space?”!

Photo of Nathan on Skype Call with Class 3, Ince CE Primary School

Nathan joined Class 3 from Ince CE Primary School for a chat about space during their space week. More info and photo source.

Class 3 saying thank you for the space-themed gifts.

Class 3 saying thank you for the space-themed gifts. Full story and photo source.