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 is the Sun orange when white stars are hottest? – Rain, age 6, Toowoomba.

Hi Rain. Thanks for sending in your excellent question.

The reason the Sun shines so bright is that it’s hot. And the colour it glows depends on how hot it is.

You are right that a star that glows white is hotter than one that glows orange.

And it’s true the Sun often looks orange. But it isn’t really orange. It is white. Well, it’s a bit on the yellow side but it’s mostly white.

But even white stars aren’t the hottest.

The blue giants that burn bright and briefly

The very hottest stars actually glow blue. We call them blue giant stars.

These blue giants are around 80 times larger than our Sun – so they are really, really big. They live and die very quickly. They are so hot and so big they burn through their fuel very quickly and last just a few million years.

That might sound like a long time but it’s not much compared to how long our Sun will live.

When our Sun was a million years old, it was still just a child. It’s about 5 billion years old now and will live to about 10 billion years. So you could say the Sun is now middle-aged. It’s about halfway through its life.

So blue giants are hottest, white stars are very hot, but there are also orange stars that burn less hot. There are even red stars, which are a bit cooler again. They are a half or even a quarter the size of our Sun and while they are still burning hot, they are nowhere near as hot as our lovely Sun.

So why does the Sun look orange, then?

A lot of the pictures we take of the Sun make it look orange because of special filters we use to take the photo. The Sun is putting out so much light that we would not be able to photograph the detail on its surface unless we cut some of the brightness out. That’s what the filters do.

At sunrise and sunset, the Sun can look especially orange to our eyes. That’s because, at those times of day, its light has to travel through a lot of the Earth’s atmosphere (the layer of swirling air that surrounds our planet). And all the dust and stuff in the atmosphere makes the light scatter and change so it looks less blue and more orangey-red.

Only Bored Astronomers Find Gratification Knowing Mnemonics

In the olden days, astronomers used letters to try to sort different types of stars. As we learned more about stars, the order changed, and labels became quite mixed up! Today we still use this naming system to remember the order of stars from hottest to least hot. It goes like this: O, B, A, F, G, K, M. (Some versions have more letters at the end).

The O-stars are the blue giants, while our Sun is a “G-class” star. That means it’s not the hottest but it’s not the coolest either.

Those letters are hard to remember, so astronomers came up with different tricks to remember it. One memory trick is called a “mnemonic” where you pretend each letter stands for a word. It’s easier to remember a sentence instead of a bunch of letters.

One student in my class came up with this mnemonic: “Only Bored Astronomers Find Gratification Knowing Mnemonics” (gratification means something like happiness).

Another one I like is: “Orange Butterflies And Frogs Get Knitted Mittens”.

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.

Belinda Nicholson, Lecturer, University of Southern Queensland

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 are there waves? - Evie, age 5.

Thanks for a great question, Evie.

When you look at the waves breaking at the beach, those waves might be at the end of a long journey. The waves might have been created thousands of kilometres away, or they could have been created near you.

There are lots of types of waves in the ocean, but the waves you usually see at a beach are created by the wind. When the wind blows over a smooth ocean, it creates little waves or ripples on the surface. If the wind continues to blow, the waves grow bigger.

Faster, bigger, longer

The faster the wind blows (like in a strong storm out at sea), the bigger the waves will grow.

The further the wind blows (or the bigger the area of the storm), the bigger the waves will grow.

And the longer the wind blows (like in a storm that lasts a long time), the bigger the waves will grow.

If the wind stops, or changes direction, the waves will stop growing, but they won’t stop travelling.

They will keep travelling away from where they were created in a straight line, sometimes for days, until they run into something like a beach where they are stopped because they break. That’s why there are still waves at the beach, even when it is not windy.

Waves trip over themselves

Imagine you were running really quickly. But then suddenly, you ran into thick gloopy mud. Your feet would slow down, but the top half of your body would still be going fast. You’d trip over.

Waves do the same thing and that is when they break.

As waves approach the shore, the water is shallower, and the bottom of the wave starts to feel the sand and rocks and seaweed. The bottom of the wave slows down, and soon, the top of the wave is going faster than the bottom part of the wave, so the top spills forward and topples over in a big splash.

Waves can travel a long way

Scientists who study the ocean (called oceanographers) have measured waves created in the Southern Ocean, and seen them travel all the way across the Pacific Ocean and break on the beaches of North America more than a week later.

Try counting the seconds between waves breaking on the beach. If the time between waves is 10 seconds or more, the waves have come from a long way away. If the waves were created nearby, the time between waves will be short, perhaps five seconds or fewer.

Sometimes when we look at the sea we might see different waves (some big, some small) all happening at the same time. These waves were created at different places, perhaps by different storms, but ended up in the same spot at the same time.

Freak waves

During big storms, waves can get very big. If big waves from two different storms meet together, that can create enormous waves that we call “freak waves”. The largest waves measured are around 25 metres high (that’s five giraffes standing on top of each other!) and they can tip over ships.

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.

Mark Hemer, Senior Research Scientist, Oceans and Atmosphere, CSIRO

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.

Where are all the other galaxies hidden? – Sasha, age 7, Sydney.

Hi Sasha,

Thanks for sending in your question.

Almost everything in our universe is high above the clouds, even higher than an aeroplane. If you keep going up, up, up… you get to outer space. There is a lot of empty space up there, as well as some fascinating things like planets, stars and beautiful clouds of gas.

Imagine that you could launch yourself on a very fast spaceship — travelling as fast as lightning — the first place you would reach would be the planets in our solar system: Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. At that speed, you could travel to the planets in a few minutes. Which would you visit first?

If you went even further, travelling for almost five years on your spaceship you would reach the nearest stars. Many of these stars live in twos or threes, and have their very own planets too. We don’t know whether there are any animals, plants, birds or fish on these planets, or perhaps creatures that we don’t have here on Earth. Maybe that’s a mission for astronaut Sasha. Can you imagine what life on other planets might be like?

If you zoom even further on your spaceship, travelling for thousands of years, you will start to see that we live in a huge spiral galaxy containing two hundred billion stars. It’s called the Milky Way and you can see it glowing in the night sky as a band of light. Have you ever seen the Milky Way?

Now, keep travelling out of our Milky Way, for more than two million years (you’ll be very old by then). You will finally reach the nearest spiral galaxy, called the Andromeda galaxy. It’s hard to believe, but all the other galaxies are even further away than this. Some galaxies are so far away they would take thousands of millions of years to reach.

So to answer your question Sasha, the other galaxies are there, but they are hiding a very long way away. That’s why we can’t easily see them when we look up at the night sky. Luckily, we don’t have to fly in a spaceship for millions of years to find other galaxies. Scientists like me, astronomers who study space, can use huge telescopes to study the light coming from galaxies and see what they are up to.

Galaxies are fascinating. Like people, some are young and others are old. Some galaxies are made up of hot stars that have only recently been born, like baby stars. Other galaxies are colder and contain mostly older stars. Galaxies can be active too. As gravity pulls them towards one another, they can merge together and collide. This will eventually happen to the Milky Way, which will collide with the Andromeda galaxy in about four billion years’ time. When that happens, the Sun will keep shining but our night sky will look very different.

I hope you will keep looking up at the stars, astronaut Sasha. It’s a fascinating place out there. Let me know if you find life on those planets!

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

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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.

Lisa Harvey-Smith, Astronomer, CSIRO

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 eggs have orange stuff inside? – Rafael, age 7.

This is a very interesting question. That orange stuff is called a yolk. It’s a great source of vitamins, minerals, fats and proteins packaged up by the female animal for an embryo (the developing cells that turn into a baby).

You probably know that the yellow bit inside a chicken’s egg is the yolk, but in fact a lot of animals lay eggs that have yolks in them. However, not all animal eggs have a yolk!

A contest called evolution

To understand why different animal species have different types of eggs, you need to know that all living things change slowly over time, through a process called evolution.

When a living thing is born with a special difference – what we would call a “trait” – sometimes this trait helps them live and survive better than someone who doesn’t have that trait. This trait may help them live longer and have more babies.

Because of these differences in survival, eventually, the trait that lets one individual living thing live and prosper will become quite common and be found all throughout a species.

Back to eggs

Imagine you are a worm living millions of years ago. You produce heaps and heaps of eggs that develop quickly into little worms. But most of the babies die because they are small and have to find food straight after hatching. They can’t go far because they are very little and so most starve to death (or are eaten by bigger creatures).

But what if some of those eggs happened to contain a little bit of fat from the mother? Compared to its brothers and sisters, the fat will allow the worm to spend just a little bit more time growing inside the egg and less time looking for food after hatching.

The worms that were lucky enough to have that fat inside the egg are more likely to survive long enough to have their own babies. And they pass on the fatty-egg trait to their own worm kids. Soon this fatty-egg trait becomes quite common.

So the worm who was able to feed its babies when they’re still inside the egg had more babies survive, and a yolk evolved.

Which eggs have a yolk and why?

Eggs with tiny bits of yolk are found in animals such as earthworms, leeches, clams, mussels, starfish, sea urchins, and marine arthropods (shrimp, lobsters, crabs) and some insects. These animals produce huge numbers of eggs.

Most of the babies that grow in these sorts of eggs have to go through a lot of steps before they reach the adult stage. First they have to grow into a larvae (which is what we call a junior body, and often looks a bit like worm).

The babies have to change into a larvae so they can eat, and after having eaten a bit they develop into an adult (think of caterpillars that eventually turn into butterflies).

Animals that produce eggs with a bit more yolk have babies that can fully develop and skip the larvae step, such as in hagfish and snails.

Big yolks for big babies

Eggs with really large yolks are found in animals that produce very few eggs, and the offspring can use the yolk to develop completely. These sorts of eggs are found only in cephalopods (squid, octopus and nautilus) and some vertebrates (animals with backbones).

Vertebrates that produce eggs with large yolks include bony fish, cartilaginous fish (sharks and rays), reptiles, birds and egg-laying mammals (platypus and echidnas).

The rest of the mammals (animals that don’t lay eggs) have found a different system. They have a placenta, which is a kind of a feeding sack linking mother to embryo inside the mother’s body. This system allows the developing embryo or fetus to get nutrients straight from the mother. That’s how you were grown!

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.

Maggie J. Watson, Lecturer in Ornithology, Ecology, Conservation and Parasitology, Charles Sturt University

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