On Saturday evening before Mother’s Day, Australians witnessed a rare celestial spectacle: a breathtaking display of aurora australis, also known as the southern lights.

Social media was flooded with photos of the vivid pinks, greens and blues lighting up the skies from local beaches and backyards all over the country.

Auroras are normally visible near Earth’s north and south poles. In Australia, they are typically only seen in Tasmania. However, due to rare and special space weather conditions, this time people could see them as far north as Queensland.

The Australian Space Weather Forecasting Centre first issued a potential extreme (G5, most severe level) geomagnetic storm warning on Saturday morning.

Lucky Australians who received this warning, and those who happened to look outside that evening, were rewarded with an amazing spectacle. However, by sunset on Sunday, the chance of aurora had subsided, leaving many hopeful viewers in the dark.

What happened? Why are auroras so hard to predict, and how reliable are aurora forecasts? To answer this, we need to know a bit more about space weather.

What is space weather?

Auroras on Earth are related to the Sun’s magnetic field. The Sun’s activity increases and decreases over an 11-year period called the solar cycle. We are currently approaching the solar cycle maximum, meaning there’s a higher number of sunspots on the Sun’s surface.

These sunspot regions have intense magnetic fields, which can lead to huge explosions of electromagnetic radiation called “solar flares”, and eruptions of material into space, called “coronal mass ejections”.

When this material is directed towards Earth, it collides with Earth’s protective magnetic field, kicking off a series of complex interactions between the magnetic field and the plasma in the ionosphere, part of Earth’s upper atmosphere.

The charged particles resulting from these interactions then interact with the upper atmosphere, causing beautiful and dynamic auroras. The conditions in space produced by this chain of events are what we call “space weather”.

Everyday space weather generally poses no threat, but these events – known as geomagnetic storms – can impact power supply, satellites, communications and GPS, potentially leaving lasting damage.

Saturday’s dazzling display was produced by the most intense geomagnetic storm since November 2003. Fortunately, this time there have been no reports of major disruptions to power grids, but SpaceX’s Starlink constellation was reportedly impacted.

Why are geomagnetic storms hard to predict?

Last weekend’s geomagnetic storm was caused by a large and complex region of sunspots that launched a series of solar flares and a train of coronal mass ejections.

Space weather prediction is challenging, and the physics is complex. Even when we see an eruption on the Sun, it’s not clear if or when it will hit Earth, or how strong the effects might be.

Predicted arrival times can be off by up to 12 hours, and it is only when the eruption arrives at monitoring spacecraft close to our planet that can we can gauge the strength of an impending geomagnetic storm.

As a result, aurora hunters really only have up to a few hours advanced notice to decide whether venturing outside is worthwhile or not.

Can we expect more auroras soon?

At the time of writing, the sunspot region responsible for the recent display is still spitting out X-class flares and eruptions, but it’s no longer facing Earth directly. It is possible this region will still be active when it faces Earth again, but this remains to be seen.

However, as we approach solar cycle maximum, other large complex sunspot regions are likely to form and, if the conditions are right, produce more spectacular aurora displays.

How to check for aurora forecasts?

Thousands of Australians lined the beaches looking towards the horizon on Sunday night hoping for a second show, only to be disappointed. Official space weather and aurora forecasts provide a wide range of possibilities that must be communicated with the appropriate nuance.

The most reliable sources of information about space weather and aurora are agencies such as the Bureau of Meteorology’s Australian Space Weather Forecasting Centre or the United States NOAA Space Weather Prediction Center.

Not only do they provide aurora forecasts, but they also play a vital role in safeguarding infrastructure from the negative impacts of space weather.

Space weather research

Looking ahead, scientists in Australia and around the world are working hard to improve our understanding and prediction of space weather events.

By studying the Sun’s magnetic activity and developing advanced forecasting models of the complex processes that happen between the Sun and Earth, we can better predict and prepare for future space weather events.

A better understanding will help protect important technologies that we rely upon. It will also alert people to step outside and witness a phenomenon that not only lights up the sky, but ignites a profound sense of wonder.

Correction: this article was amended to correct the name of the Australian Space Weather Forecasting Centre.

Brett Carter, Associate Professor, RMIT University and Hannah Schunker, ARC Future Fellow, University of Newcastle

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Last week, a huge solar flare sent a wave of energetic particles from the Sun surging out through space. Over the weekend, the wave reached Earth, and people around the world enjoyed the sight of unusually vivid aurora in both hemispheres.

While the aurora is normally only visible close to the poles, this weekend it was spotted as far south as Hawaii in the northern hemisphere, and as far north as Mackay in the south.

This spectacular spike in auroral activity appears to have ended, but don’t worry if you missed out. The Sun is approaching the peak of its 11-year sunspot cycle, and periods of intense aurora are likely to return over the next year or so.

If you saw the aurora, or any of the photos, you might be wondering what exactly was going on. What makes the glow, and the different colours? The answer is all about atoms, how they get excited – and how they relax.

When electrons meet the atmosphere

The auroras are caused by charged subatomic particles (mostly electrons) smashing into Earth’s atmosphere. These are emitted from the Sun all the time, but there are more during times of greater solar activity.

Most of our atmosphere is protected from the influx of charged particles by Earth’s magnetic field. But near the poles, they can sneak in and wreak havoc.

Earth’s atmosphere is about 20% oxygen and 80% nitrogen, with some trace amounts of other things like water, carbon dioxide (0.04%) and argon.

When high-speed electrons smash into oxygen molecules in the upper atmosphere, they split the oxygen molecules (O₂) into individual atoms. Ultraviolet light from the Sun does this too, and the oxygen atoms generated can react with O₂ molecules to produce ozone (O₃), the molecule that protects us from harmful UV radiation.

But, in the case of the aurora, the oxygen atoms generated are in an excited state. This means the atoms’ electrons are arranged in an unstable way that can “relax” by giving off energy in the form of light.

What makes the green light?

As you see in fireworks, atoms of different elements produce different colours of light when they are energised.

Copper atoms give a blue light, barium is green, and sodium atoms produce a yellow–orange colour that you may also have seen in older street lamps. These emissions are “allowed” by the rules of quantum mechanics, which means they happen very quickly.

When a sodium atom is in an excited state it only stays there for around 17 billionths of a second before firing out a yellow–orange photon.

But, in the aurora, many of the oxygen atoms are created in excited states with no “allowed” ways to relax by emitting light. Nevertheless, nature finds a way.

The green light that dominates the aurora is emitted by oxygen atoms relaxing from a state called “¹S” to a state called “¹D”. This is a relatively slow process, which on average takes almost a whole second.

In fact, this transition is so slow it won’t usually happen at the kind of air pressure we see at ground level, because the excited atom will have lost energy by bumping into another atom before it has a chance to send out a lovely green photon. But in the atmosphere’s upper reaches, where there is lower air pressure and therefore fewer oxygen molecules, they have more time before bumping into one another and therefore have a chance to release a photon.

For this reason, it took scientists a long time to figure out that the green light of the aurora was coming from oxygen atoms. The yellow–orange glow of sodium was known in the 1860s, but it wasn’t until the 1920s that Canadian scientists figured out the auroral green was due to oxygen.

What makes the red light?

The green light comes from a so-called “forbidden” transition, which happens when an electron in the oxygen atom executes an unlikely leap from one orbital pattern to another. (Forbidden transitions are much less probable than allowed ones, which means they take longer to occur.)

However, even after emitting that green photon, the oxygen atom finds itself in yet another excited state with no allowed relaxation. The only escape is via another forbidden transition, from the ¹D to the ³P state – which emits red light.

This transition is even more forbidden, so to speak, and the ¹D state has to survive for about about two minutes before it can finally break the rules and give off red light. Because it takes so long, the red light only appears at high altitudes, where the collisions with other atoms and molecules are scarce.

Also, because there is such a small amount of oxygen up there, the red light tends to appear only in intense auroras – like the ones we have just had.

This is why the red light appears above the green. While they both originate in forbidden relaxations of oxygen atoms, the red light is emitted much more slowly and has a higher chance of being extinguished by collisions with other atoms at lower altitudes.

Other colours, and why cameras see them better

While green is the most common colour to see in the aurora, and red the second most common, there are also other colours. In particular, ionised nitrogen molecules (N₂⁺, which are missing one electron and have a positive electrical charge), can emit blue and red light. This can produce a magenta hue at low altitudes.

All these colours are visible to the naked eye if the aurora is bright enough. However, they show up with more intensity in the camera lens.

There are two reasons for this. First, cameras have the benefit of a long exposure, which means they can spend more time collecting light to produce an image than our eyes can. As a result, they can make a picture in dimmer conditions.

The second is that the colour sensors in our eyes don’t work very well in the dark – so we tend to see in black and white in low light conditions. Cameras don’t have this limitation.

Not to worry, though. When the aurora is bright enough, the colours are clearly visible to the naked eye.

Timothy Schmidt, Professor of Chemistry, UNSW Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

As spring started springing, and leaves started to reappear on the trees, Robi-Jo wanted to find out why some trees lose their leaves and others don’t. He joined our host Eloise to ask Paul Ashton, a botanist at Edge Hill University, who took them into the secret life of our big leafy friends!

The Conversation’s Curious Kids podcast is published in partnership with FunKids, the UK’s children’s radio station. It’s hosted and produced by Eloise Stevens. The executive producer is Gemma Ware.

Email your question to curiouskids@theconversation.com or record it and send your question to us directly at funkidslive.com/curious.

And explore more articles from our Curious Kids series on The Conversation.

Disclosure statement:

Paul Ashton does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Sound credits

The sound of a cricket bat swing is from nextmaking, and the sound of a lunchbox flying and falling in the grass are courtesy of copyc4t and DrMrSir respectively. All via freesound.org.

Eloise Stevens, Host, The Conversation's Curious Kids podcast, The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Why don’t ladybirds have tails? – Lotte, aged 2.

Thank you, Lotte, for this great question.

Let’s start by thinking about animals that do have tails and what they have in common.

Dogs, elephants, cats, birds, monkeys, and fish – they all have tails and use them for many different things like balancing, swishing flies away, or hanging onto things. And what do all these animals have in common? A backbone!

That’s because a tail is actually an extension of a backbone. (Humans used to have tails! Our early ancestors did but then we changed over time and now only a little stump of a “tailbone” remains.)

So to answer your question, ladybirds do not have tails because they do not have a backbone.

They have something called an “exoskeleton” instead. I will explain what that word means.

Insects have their skeletons on the outside

Exoskeleton means a skeleton that is on the outside. And ladybirds are a type of insect – just like beetles, bees, stick insects, and flies.

An insect’s exoskeleton is a hard outer shell that protects important stuff on the inside of their body (like its stomach, and special tubes that help it breathe).

Parts of the ladybird body

A ladybird’s body is divided into three sections: a head, a thorax, and an abdomen.

The head has eyes, mouthparts, and antennae. Antennae help them sense what’s in front of them and how far away it is.

The thorax is where all the legs and wings are connected to the body. Ladybirds have six legs and two pairs of wings.

The tough pair of outer wings is tough is called the “elytra”. The second pair is hidden underneath and ladybirds stretch these wings out only when they need to fly.

Bright colour means ‘don’t touch!’

Ladybirds come in red, orange, yellow, blue, brown, and black. Most of them have black dots or patterns on them.

We think that ladybirds use their colours to warn other animals (like birds or spiders) to not to eat them. They’re using their bright colour to send a message that says “Hey! I taste bad, so don’t eat me!”

Their predators recognise what these colours mean and avoid eating them.

Ladybirds are beautiful and smart, aren’t they?

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Heshani Edirisinghe, PhD student, Massey University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Why do leaves fall off trees? - Emma, age 5.

Great question! The short answer is that leaves fall off trees when they aren’t doing their job any more.

A leaf’s job is to turn sunlight into food for the tree. To do this, the leaf needs water. This water comes from the soil, and is sucked up through pipes in the trunk and branches all the way to the leaves – this can be a very long way for tall trees!

If there isn’t enough water, the leaf can be damaged and stop working. The tree doesn’t want to waste all the good things in the leaf, so it takes the nutrients from the leaf back into the stems and roots. This way, they can be recycled.

When the leaf is empty, the tree stops holding onto it and it falls to the ground, or blows away in a gust of wind.

What are deciduous trees?

Some trees lose their leaves every year. These trees are called deciduous trees, and they lose their leaves in response to the seasons. Deciduous trees mostly come from places where winter gets cold and snowy.

When it is very cold, the water in the tree can freeze – the leaves stop working and can even be damaged by the ice crystals. These trees know to prepare for this, and start taking nutrients out of the leaves when the days get shorter in autumn – this is when we can see them changing colour.

But there are deciduous trees in tropical places where it never gets cold. Winter in these places is very dry. When the rainy season ends, the tree knows that it will not have very much water for a few months, so it lets go of its leaves.

Trees hibernate too

When the tree is leafless, it can’t make food. But it doesn’t get hungry. Instead, it rests.

Just like a bear goes into hibernation and snoozes all through winter, trees have a long sleep until the water in the pipes starts moving again. This can be in spring, or when it starts to rain again. Then, they wake up and put out new leaves, so they can start making food again.

Some trees hold onto their leaves all year long. These trees are called evergreens, because they stay “ever green”. But the leaves on these trees all die and fall off eventually. That happens when the leaves are old or damaged. Leaves don’t work very well after they’ve been munched on by an animal.

Leaves are really important for the tree, but sometimes it’s better for the tree to let them go. They can save all the good bits and when there is enough water, they can use them to grow brand new leaves.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Matilda Brown, PhD, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.