There’s a blaze of light across the sky! A fireball is seen by thousands, and mobile phone and dashcam footage soon appears on social media.

But what have people just seen? A mix of social media hashtags suggests confusion about what has streaked overhead. Was it a Soviet Venus probe? Was it one of Elon Musk’s satellites or rockets? Was it a meteor? Was it a comet?

While these objects have some similarities, there are crucial differences that can help us work out what just passed over our heads.

Shooting stars, meteors and comets

Shooting stars can often be seen on dark, clear nights in the countryside as brief flashes of light travelling across the sky. Usually, they are gone in just a second or two.

Shooting “stars” are not stars, of course. They are produced by dust and pebbles burning up high in the atmosphere, typically above 50km in altitude. Comets are often a source of this dust, and regular showers of shooting stars happen when Earth travels through comets’ orbits.

Sometimes shooting stars burn with colours that reflect their composition – including iron, magnesium and calcium.

Meteors and shooting stars are actually the same thing. But when people talk about meteors, they often mean bigger and brighter events – bolides. Bolides result from rocks and boulders plunging into Earth’s atmosphere, resulting in bright flashes of light that can outshine all the stars and planets in the night sky.

Bolides can reach the lower atmosphere and sometimes produce audible sonic booms. Occasionally pieces of the bolide – meteorites – even make it to Earth’s surface.

While bolides can survive longer than shooting stars, they also don’t last for long. As they are initially travelling at tens of kilometres per second, they don’t take long to traverse the atmosphere.

The Chelyabinsk meteor, the largest bolide known to impact Earth in over a century, shone brightly for only 20 seconds or so.

If you see something blaze across the sky, it almost certainly isn’t a comet. Comets are so far away from us that their vast speeds are imperceptible to the human eye. Furthermore, while comets are sometimes depicted as fiery, their glow is more subtle.

Space junk

Maybe the bright flash you just saw was space junk? Perhaps. The number of orbital rocket launches and satellites has increased rapidly in recent years, and this has resulted in some spectacular reentries, which are often discarded rocket stages.

Like meteors, space junk travels at vast speeds as it travels through the atmosphere and it begins burning up spectacularly. Also like meteors, you can see colours indicative of the materials burning up, such as steel and aluminium. However, there are a few things that distinguish space junk from meteors.

When rockets and satellites are launched into orbit, they typically travel along paths that roughly follow Earth’s curvature. So when space junk begins to enter the atmosphere, it’s often travelling almost horizontally.

Space junk also travels at slower speeds than shooting stars and meteorites, entering Earth’s atmosphere at roughly 8km/s rather than tens of kilometres per second.

Because of these factors, space junk can take minutes to enter the atmosphere and travels hundreds of kilometres in the process. Over this time, the space junk will slow down and break up into pieces, and the more solidly constructed parts might make it down to Earth.

The slower pace of space junk fireballs gives people time to grab phones, take footage and post on social media, perhaps with a little colourful commentary added for good measure.

Rockets

While space junk can produce a light show, rockets can also put on amazing displays. If you happen to be near Cape Canaveral or Vandenberg Space Force Base in the United States, or Wairoa in Aotearoa New Zealand, then it’s not unexpected to see a rocket launch. You get smoke, flames and thundering noise.

But in other parts of the world you may get a different view of rockets.

Rockets that bring satellites into our orbit accelerate to 8km/s. As they do, they travel many hundreds of kilometres at over 100km altitude. American satellite launches often travel near the coast, passing major cities including Los Angeles.

As rockets approach orbit, they are more subtle than the flames and noise of liftoff. Rockets produce plumes of exhaust gases that rapidly and silently expand in the vacuum of space.

While these plumes are typically seen near launch sites, they can be visible elsewhere, too.

Sometimes rocket engines are ignited after reaching an initial orbit to boost satellites to higher orbits, send probes into the Solar System or slow rockets down for reentry. Rockets may also vent excess fuel into space, again producing plumes or spirals of gases. While not necessarily a common occurrence, these have been seen all over the world.

Do look up

There’s a lot to see in the night sky – the familiar Moon, stars and planets. But there’s the unexpected, too – something blazing across the sky in minutes or even mere seconds. While fireballs may be puzzling at first, they are often recognisable and we can figure out what we’ve just witnessed.

Have you had the good fortune to see a fireball for yourself? If not, pop outside on a clear dark night. Perhaps you will see something unexpected.

Michael J. I. Brown, Associate Professor in Astronomy, Monash University

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

I heard that we see upside down, but our brain flips the image. How does it do that?

–Jasmine, Mount Evelyn, Victoria

Our eyes work thanks to light. Objects we can see are either sources of light themselves – like a candle or a phone screen – or light bounces off them and makes its way to our eyes.

First, light passes through the optical components of the eyes such as the cornea, pupil and lens.

Together, they help focus the light onto the retina that senses light, while also controlling the intensity of light to help us see well while avoiding damage to the eye.

The function of the lens is to correctly focus light that comes from objects at different distances. This process is known as accommodation.

While performing this important task, light passing through the lens becomes inverted. This means that light from the top of the object falls lower on the retina than light from the bottom, which falls higher on the retina.

So, light exiting the lens to land on the retina is indeed flipped upside down. But that doesn’t mean the brain is actually flipping the picture “back”. Here’s why.

The orientation doesn’t actually matter

While the light being interpreted by the brain is “upside down” compared to the real world, the question is: is that actually a problem for us?

From your own experience you can tell the answer is probably no. We seem to navigate and interact with the world just fine.

So, where in the brain is the image flipped or rotated 180 degrees to be the “right way up” again?

You may be surprised to learn that vision scientists reject the idea a flipping or rotation needs to happen at all. This is because of how our brains process visual information.

The object you perceive is “encoded” by the firing of various neurons – brain cells that process information – in various locations in the brain. This pattern of firing is what encodes the information about the object you’re focusing on. That info takes into account the object’s relation to everything else in the scene, your body in the world, and your movements.

As long as the relative encodings of these are all consistent with one another, as well as stable, there’s no need for a flip to happen at all.

We can function with ‘upside down’ goggles!

Several studies have looked at how we adapt to large changes in visual input by asking people to wear goggles that flip the image coming in.

This means the image lands on the retina the “right way up”, so to speak, but upside down from what the brain has learned it should be.

In the 1930s, two scientists in Austria performed the Innsbruck Goggle Experiments. For weeks or even months at a time, participants in these studies wore goggles that altered the way the world around them looked. This included goggles that turn the incoming image upside down.

As you can imagine, people wearing these goggles at first found it really difficult to get by in their day-to-day activities. They would stumble and bump into things.

But this was temporary.

Participants reported seeing the world upside-down for the first few days, with difficulties navigating the environment, including trying to step over ceiling lights that appeared to them as on the floor.

Around the fifth day, however, performance seemed to improve. Things that were at first seen upside down now appeared the right way up, and this tended to improve with more time.

In other words, with continued exposure to the upside-down world, the brain adapted to the changed input.

More recent studies are beginning to identify which areas of the brain are involved in being able to adapt to changes in visual input, and what the limits of our ability to adapt might be.

Adaptation may even allow “colour blind” people to see colour better than is predicted from their condition.

Daniel Joyce, Senior Lecturer in Psychology, University of Southern Queensland

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

This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky! You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

If an insect is flying in a car while the car is moving, does the insect have to move along with the car at the same speed? – Sarah, age 12, Strathfield.

Hi Sarah, great question!

Imagine that as you get into a car, an insect flies in with you.

When the car starts to move, the force (push) of the seat makes you move with the car. This is only needed while the car is speeding up (accelerating). Once the car is at steady speed, no push is needed anymore.

If the road is very smooth, you can only tell that you’re moving by looking out of the window.

If you throw a ball straight up inside the car, it goes up and comes down. The motion from your point of view is no different than if the car wasn’t moving at all. The ball does not get “left behind” by the car. (But please don’t throw balls in a moving car!)

This is because everything in the car has been accelerated (sped up) to the same speed – you, the ball, the air and the insect.

Try this: make a small pendulum by tying an object to a piece of string. While the car is speeding up you will see that it hangs at an angle, with the string pulling the object forward to make it speed up.

But it hangs straight down when the car is at a steady speed, just as it does when the car isn’t moving. The string doesn’t need to pull the object forwards when at steady speed.

Now back to the insect. Imagine the insect flew in and landed on the seat next to you. The seat pulls it forwards with the car. This pull is the friction force of the seat on the insect. It speeds up as the car speeds up.

But once the car is at steady speed, the insect doesn’t need to be pulled along any more, and it won’t be able to tell that the car is moving. It can fly around just as if it were in the room of a house. It does not have to fly forwards to keep up with the car.

Just like the pendulum, it doesn’t need a force to push or pull it forwards. (But it does have to hover, or it will fall down.)

But what if the insect flies into the car and doesn’t land?

Then it will have to fly forwards a little bit to speed up with the car, while the car is speeding up. But it doesn’t actually have to fly forwards very much – nowhere near as much as if it was trying to keep up with the car from the outside.

This is because insects are very light, so air has a big effect on them. The air in the car is pushed forwards by the car, and the air pushes the insect forwards. This push is called air resistance or drag. This push would probably be enough for a mosquito, but not a Christmas beetle.

So if the insect wants to stay right in front of your nose, it must fly forwards just a little bit when the car is speeding up. But when the car is at constant speed it needs only to hover.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. You can:

* Email your question to curiouskids@theconversation.edu.au
* Tell us on Twitter by tagging @ConversationEDU with the hashtag #curiouskids, or
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Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.

Kate Wilson, Senior Lecturer, School of Engineering and IT, UNSW Sydney

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

This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome: find out how to enter at the bottom. You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Why do people grow in certain sizes? - Audrey, age 6, Brisbane.

About 150 years ago, there was a very curious English person who asked the same question. His name was Sir Francis Galton.

One day, Sir Francis Galton looked at his friends. He saw that most of his taller friends had taller parents and most of his shorter friends had shorter parents. Francis Galton was one of the first scientists to do some tests to work out why this was the case. He published his findings in a book. Not all of his ideas were correct, though. Some of his ideas were actually very wrong. But he made a start on what we now call “genetics” or the science of genes. I’ll explain what that means.

Children and parents

Children with brown hair often have parents with brown hair. Children who are good runners, often have parents who are very good runners. Children who are a bit shy often have parents who can be a bit shy.

Like parents and children, brothers are sisters are quite alike too.

Do you look like your brother or sister? Have you had grown-ups saying to you: “Oh, you look just like your mum (or dad)!”

The reason behind all this is a thing called DNA. That stands for “deoxyribonucleic acid”, but don’t worry, everyone just calls it DNA.

Humans have a special code, and it’s called DNA

Every human carries an instruction booklet with a very special code. Actually, we carry trillions of instruction booklets. In each booklet, the same special code is written. The code, called DNA, is made out of only four letters, A, C, T, and G. This looks simple, but it is very cleverly set up.

Our eyes can’t read the code, but our bodies can. The code tells our body what to do and how to look. For example, it tells our hair to grow curly or straight, or to make our eyes brown or blue. But also, how much to grow and when to stop growing. Some people have instruction booklets with a code that tells their bodies to grow tall. Other people have a code that tells their body to grow to a smaller size.

Did you know that DNA code is unique for every person? That means there is nobody in the entire world with the same code as you – unless you have an identical twin brother or sister.

Your code is very similar to your biological parents’ code. This is because they pass on their code to you. You share half of your DNA code with your mother and half of your code with your father. If you’re adopted – or your parents used a donor egg or donor sperm – then you share half your DNA code with the person whose egg and person whose sperm were used to make you.

So your code that tells your body what size to grow in is similar to your biological parents’ code on what size to grow in.

Even though our DNA code is very similar to our biological parents’ DNA code, we all still turn out a little bit different. This is because you have your own experiences.

Experiences are a part of being human

Every human being has experiences. An experience is something we do, or something that happens to us. Eating is an experience.

Some experiences we share, others we experience on our own.

For our body to follow the code in our instructions booklets, it needs energy. Energy comes from eating food, and more importantly, eating healthy food. If we don’t eat, we won’t grow. Even if the code in our instruction booklets is telling our body to grow tall. Some children get to eat lots of food that makes them grow. Other children may not get enough food or don’t eat healthy food.

Getting sick is also an experience. Some diseases may make you grow less. These days, we are getting sick less than humans did in the past and have more healthy food than the people who lived a long time ago. That’s why we are all a bit taller than the people who lived a long time ago.

So, both your DNA code and your experiences make you grow to a certain size.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. You can:

* Email your question to curiouskids@theconversation.edu.au
* Tell us on Twitter by tagging @ConversationEDU with the hashtag #curiouskids, or
* Tell us on Facebook

Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.

Anna Vinkhuyzen, Research Fellow, Institute for Molecular Bioscience, The University of Queensland

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