If you stare at a light for about 30 seconds then turn it off or look away you will still see a light in front of your eyes. This is called an afterimage, or technically a positive afterimage.

In the back of your eyes are lots of little cells called cones. When certain types of light hit them they fire and send a signal to your brain. Your brain puts together all the signals to make a picture of what you are seeing. But your brain is very clever – we don’t actually see everything all the time, like a movie. Our eyes are moving around and looking at different pieces at different times, our brain smooths it out and fills in the gaps. Sometimes it can make mistakes or take a little while to catch up.

Positive Afterimages

Positive afterimages like seeing a light when it’s been turned off are a mistake by your brain. One of the things your brain does to make the picture you see look full is assume that things stay the same unless there is a signal that draws its attention that something has changed. A good signal is movement, it attracts our attention right away.

When you flick off a light switch there are no clues to tell the part of your brain putting together what you are seeing that the light isn’t there any more, so it keeps putting it in and you ‘see’ it even though it isn’t there.

Negative Afterimages

Negative afterimages are when you keep seeing something but it is the opposite colour. This is when you walk in from a bright day and everything looks dark, or when you are staring at something red and then have blue splotches. Negative afterimages are caused by your eyes and your brains together.

If you stare at something that is brightly coloured for a long time, the cones at the back of your eye get tired and stop firing as much. But even when the signal from your eyes gets tired and switches off, your brain knows the thing is still there and you keep ‘seeing’ it.

When you turn to look at something else, the tired cones stay switched off for a few seconds. But cones for different coloured light in the same area  that aren’t tired will start to fire because of the new light reaching them. Your brain doesn’t know that some cones aren’t signalling because they switched off, it just knows it isn’t getting a signal from them so it assumes there isn’t supposed to be a signal there.

This means the picture your brain puts together of what you are seeing is wrong, and has a dark hole in the middle of it the same shape as the bright object you were looking at first.

There are lots of illusions you can use to see this happening. Stare at the picture up the top for as long as you can, at least 30 seconds. The longer you look at it, the better afterimage you will get. Don’t try to look at details, pick a spot like the nose or the bridge of his glasses and focus on that as tightly as you can. This works because of your eyes and brain, it doesn’t need you to know what you are looking at.

Then look away at a bright white wall or piece of paper. You will see a very clear image of a man’s face. It is actually Pierre Cardin, the image is by Dimitri Parant.

What flag does the afterimage show you?

The quick answer is ‘no,’ frogs don’t have lips. They have some very interesting features in their mouths, but lips like we have belong to monkeys, apes and us.

Primate lips

There are 5 types of large animals we’re most familiar with – fish, amphibians, reptiles, birds and mammals. Mammals have very different mouths to the others because we drink milk as babies. This means our mouths are developed for sucking and we have cheeks that can move and lips that can close around the nipple and help us suck.

Most mammals have thin lips that are attached to their gums, but for monkeys, apes and us our lips are free. This lets us have expressive faces and communicate in our social groups. Apes are the most like us, and chimps even kiss each other.

Photo courtesy of Thomas Lersch

We have very big lips, they are extremely important in communicating. Smiling in happiness, laughing and talking are all uniquely human and all use our lips. The reason they look red is they have very thin skin like the inside of our mouths and you can see the blood underneath.

Frog lips

You can see that there is a border around a frog mouth, but it isn’t plump red lips like ours. It opens so wide because there are no cheeks and inside is very different to ours too.

Starting at the top there are nostrils inside the mouth as well as outside. These are to help the frog breathe. Frogs use their lungs when they are out of the water, but they can also dissolve oxygen in a thin layer of water on their skin and absorb it straight into their blood.

There are two types of teeth in the top jaw – there are small teeth around the edge and two larger teeth called the vomerine teeth just inside the nostrils. But there are no teeth on the bottom jaw. This means frogs can’t chew their food, the tiny teeth are only used for holding it before they swallow.

Moving down are two big round things that are actually the bottom of the eyes! The top of your mouth has a layer of bone, but frogs just have skin and their large eyes are right on top of their mouth. In fact, frogs use their eyes to swallow their food. They push their eyes down and it pushes their food back into their throat. There is a video at the bottom that shows the frog’s eyes pushing in as it swallows.

Right at the back are the openings of the eustachian tubes, these drain the ears and ours go into our noses. In the middle is the throat. Then on either side are the openings of the vocal sac, which is how male frogs sing.

Photo courtesy of Christian Fischer

The tongue is the opposite of ours, it is attached near the front and curls back into the mouth. This lets it shoot out to catch unsuspecting prey.

Have a look at this video, the interesting part is around 2 minutes. The frog catches the fish and then pushes his eyes down to swallow them.

The answer to this one is yes and no. Land animal skeletons and tongues are very different to fish and sharks, with very different jobs.

Land Animals

Our tongues are full of muscles and covered with sensitive skin and lots of nerves. They are very mobile and help mammals eat and drink, move food around while we are chewing and help us move food to our throats to swallow. Bears, elephants and anteaters all use their tongues to help collect food and bring it into their mouths. And many animals lap water using their tongues.

Land animal tongues are covered in tastebuds that warn us what is in our food before we swallow it. Bitter tastes often mean poisons and we can taste if something is rotten much better than with smell or sight. So our tongues help protect us. And in humans they are essential for talking.

Sharks

Fish and especially sharks are built quite differently to us. Remember they don’t have lungs but breath through the gills on their sides. Sharks have a skeleton made of cartilage, like your ears and nose. It is tough but not as strong as our bones. They have a long piece of cartilage running up their front to support the gill arches and this extends all the way forwards into their mouth (or their mouth extends back a long way!).

The very end of this cartilage is called the basihyal (ba-see-HI-al) and this is the shark’s tongue. For most sharks it doesn’t do very much but just sits in the bottom of their mouth. But for other sharks it does very interesting things.

Another of the differences between animals with lungs and fish is that they cannot suck. That may not sound very important, but think about it for a minute. They don’t have hands or claws to bring food to their mouth. They don’t have a tongue to reach out and get it. About the only things they can do are sit there with their mouth open and hope it drifts in, run into it and catch it, or somehow manage to suck it in. Most invertebrates like corals or sponges do the first, herbivores and lots of predators like tuna do the second, and some sharks use their tongue to do the third.

In order to suck, you need to somehow make a hole bigger. This is how we breathe – our ribs open out and make our lungs bigger and this sucks air into them. But sharks don’t have ribs and lungs so they can’t do it that way. Instead there are some sharks that have large basihyals. They use some of the muscles around their throat to pull them down and back, which makes their mouth bigger and creates suction. You can try this yourself by opening your jaw while keeping your lips closed, your cheeks will get sucked in. Then the sharks can either hunt by sucking fish into their mouths, or one type of shark actually suctions on to its prey and takes a bite out of it. This is called a cookie-cutter shark because it looks like it’s cut a round hole in the animal, many of them survive and heal.

Bites taken by a cookiecutter shark by sucking onto the fish using its tongue.

I discovered with this one that different types of bees carry pollen differently, there are two main ways. One important thing to remember is that in spite of what you may see in movies, most of the pollen collecting bees are girls and any pollen that is spread is by accident – the bees would much rather take it home to eat.

Pollen

Pollen is a plant protein, it’s a bit like the meat or milk we eat. So bees use lots of it to feed their babies (larva). Bee larvae are like our babies – they are growing very quickly, so they need lots of protein to help them.

There are two main ways of carrying pollen. One is fairly simple and involves long branched hairs on the bees’ legs or tummies. It makes something a bit like velcro, and when the bee rubs over the pollen it gets caught in the hairs and the bee can carry it back to its hive.

Many bees have curly hairs on their legs or tummy that the pollen is tangled in. Photo by Alexander Klink.

Other bees including honey bees and bumblebees have something called ‘pollen baskets’ on their legs. This is a large flat space or hollow on their hind legs surrounded by hairs to make the ‘basket.’ The inside of their legs have lots of hairs that make brushes or combs. After they have climbed around a flower and have lots of pollen stuck to them they run the combs over themselves to pick up the pollen. Then they mix it all together with a bit of nectar to make it sticky and pack it into the pollen basket.

The big yellow blob on the back leg is pollen in the pollen basket. Photo by Muhammad Mahdi Karim.

Nectar and Honey

The other thing bees collect is nectar, which is sugary water with other things in. Flowers make it to attract bees so they will visit and spread pollen around. Nectar is their other food because it gives them energy. They use it to make honey that they can eat over the winter when there are no flowers around.

When a bee is drinking nectar it goes into a special stomach called the honey sac or honey stomach. When she goes back to the hive she gives the nectar to another bee who keeps it in her mouth. There are things in her mouth called enzymes that start breaking it down, just like your saliva breaks down food like yoghurt in your mouth. Then they spread it out into the honeycombs and fan it with their wings to make it dry out. Once lots of the water is gone and it’s thick, it is honey.

Honey in cells of the comb. Photo by Fir0002/Flagstaffotos

At first this sounds really weird – we use glass for windows so we can see through it, but we also use glass for mirrors and we can see ourselves. Why does it act differently in different things?

The answer is that it isn’t really the glass that makes the mirror.

Good quality glass is transparent and we can see through it clearly. This is why we use it in windows, and also its job in mirrors. Because the glass isn’t what makes the reflection we see, it is only there to protect the metal behind it and let us see through it.

If you have a close look at the edge of a bathroom mirror you will see that the picture is at the back of the glass, not the front. Or if you have a dirty mark or dust on the mirror and you look at an angle you should be able to see that reflect too. If you have a really nice Mum she might let you draw on a mirror with a water-based texta and you will be able to see the reflection of your drawing at the back.

A mirror has three parts -

• the front glass to protect it,
• a really thin layer of silver to reflect,
• a dark layer or backing to stop light coming through from the back.

All metals are shiny and reflect, but most metals react with air very quickly and lose their shine. We use silver in mirrors because it starts off very shiny and it takes much longer to react than most metals. Then to help it even more we use the glass and backing to protect it.

The glass is also good because it is so smooth and flat and lets us use a very thin layer of silver. Silver is expensive and we don’t want to use much, and the flatter it is then the better the reflection it will give us. Try looking at yourself in two spoons – one that is new and has no scratches, one that’s old. You will see a much better picture in the new, smooth spoon. Then try to clean or polish the old spoon and see what happens. Or try the same thing with smooth alfoil, then scrunch it up into a ball and look when it’s all wrinkled.

An activity

Can you do a self-portrait using a mirror? If you have a real mirror from a craft shop you could do a really good one, especially using something like oil pastels or glass paints. But you can have fun with a simple homemade one as well.

• Get some very smooth alfoil and spread it over a book or board so it is supported.
• Either use an easel or look down on it and you’ll see yourself. Make sure there are no lights directly shining on the foil or they’ll drown out your reflection.
• Carefully draw over your reflection to get a picture of you. You might need to experiment to find what will work on the shiny surface, I’ve used textas successfully but you have to be careful to let them dry or they will smudge.

Self-portrait of big girl, little girl just had fun drawing on something different!

Living where we do we get lots of willy-willies. They range from a few leaves swirling around on the ground to columns of dust and leaves that you can definitely feel. When I was in Halls Creek we used to call them ’30 second cyclones’ because they could be strong enough to knock over things in your yard.

Willy-willy is the Australian name for minor whirlwinds and dust-devils. Although they look like smaller versions of tornadoes they form differently. Tornadoes are linked to super-cell thunderstorms or other powerful storms. It is the storm that begins spinning to form the tornado.

Willy-willies are formed by local winds. There may be a windstorm or windblast that helps them or where we are it is just the heat. A rising column of air is caused by a local hotspot, which may be something like a road. Any unevenness or an existing wind can start the column spinning. This is what is happening with the most common small swirls of leaves.

Larger ones can last longer because they become self sustaining. As the air column rises it stretches and gets thinner. This makes it spin faster because of the conservation of angular momentum. This is the trick when an iceskater or dancer pulls their arms and legs in and speeds up, you can also try this on spinning playground equipment. Leaning out will slow you down, leaning in will speed you up.

As it spins faster it can start to pull more air in because of the spin, just like in an emptying bathtub. Plus the rising air leaves low pressure underneath it which is filled by incoming air.

They can become quite large, however they rarely last more than a minute or so. We have fun spotting them out the car window, or if we are outside we try to run and jump in the middle of them. Which instantly makes them collapse! It’s lots of fun though.

Tracks of Martian willy-willies. Both images are from NASA

I suspect big girl was actually asking this to delay being kicked outside, because bouncing the little rubber ball down the hall was not going down well. But it’s a good question anyway, and like all good distractions it led to lots of other things to do.

Bouncing balls is a fun one because kids can actually feel the answer for themselves.

• Get a ball, or better yet several different balls and try to squash them between your fingers.
• Make a note of which ones squash the easiest.
• Now bounce them and see which ones bounce the best.

When you bounce a ball it is being squashed against the ground. It has lots of energy from speeding down, when it hits the ground some of that energy goes into squashing it. Then it springs back into shape, and the ball pushing back out also pushes it up into the air again.

Have a look at this video to see it happening in ultra-slow motion.

There are lots of fun ways to play with bouncing:

• Compare different balls to see which bounces the best. Some of the things that make a difference are what the outside is made of and what is inside – is it hollow or solid?
• Compare bouncing with using a racquet or kicking against a wall.
• Hold two balls together with one on top of the other and drop them. The bottom one will stay fairly still and the top one will shoot off quickly. What is happening is that they both deform, but rather than the bottom one’s energy going into bouncing it, when it pushes back to round it pushes the top one, so it gets double the energy.

Now find all your balls and have fun playing!

“I mean bladder? I mean when you drink it does it go straight through you?”

I was pretty happy to hear big girl ask this, because it was one that confused me for years. I had quite a logical but completely wrong image in my head, I suspect most kids do.

From an early age, when we cough and splutter people say it ‘went down the wrong way.’ Which it does, but very few kids realise that air is going down their throat into their lungs. So when they are told there are different ways for things to go, many kids develop an image of swallowing that includes a ‘drink tube’ and a ‘food tube.’ Given that urine is mostly water, it’s an obvious next step to think anything going down the ‘drink tube’ somehow goes straight to the bladder. Especially once they make the connection or are told that drinking will make you wee.

What really happens?

Firstly, there really are two tubes, but one is for air and goes into your lungs. The other carries all your food and drink down into your stomach.

Once it reaches your stomach even more liquid is added and it is squeezed and mixed to make a type of soup. It moves into your small intestine, which is actually very long. This is where most of the food gets into your body – blood goes very close to the intestines and the tiny dissolved bits of food, too small to see, get pulled through the walls of the intestines and into the blood. Blood is the transport for your body and carries the food and air to everywhere that needs it.

Seeing blood is the transport it also carries your body’s rubbish, including the bits that are used up or broken. A lot of this is filtered out by the kidneys – they act like a very fine net. They catch the rubbish and take out some of the water from the blood at the same time, and this is what makes wee. It goes from your kidneys down to your bladder, and when it’s full it lets you know you need to go to the toilet.

Drinking water puts more water in your body – your blood, your skin, your muscles and even your bones. Some of that water needs to come out and will be pulled out into your bladder. But it isn’t necessarily the same water that just went in.

One of the classics with different levels of answers.

Chlorophyll

Firstly grass is green because plants use light from the sun to make food.  This is called photosynthesis and uses a chemical called chlorophyll that looks green.  It stores light from the sun and transfers the energy into chemical reactions that eventually produce sugar.  Photosynthesis can be written like this:

Water + Carbon Dioxide   — light –> Oxygen + Sugar

If you just mixed lots of water and carbon dioxide together nothing would happen – otherwise we would have sugar falling from the sky!  But chlorophyll helps the reaction, giving us oxygen to breathe and energy from sugar.  This is why plants are so important – without them we wouldn’t be able to breathe or have anything to eat.

In this photo you can see the little round chloroplasts where the chlorophyll is.

Why is it green?

We see because of light bouncing off things and getting into our eyes, the colour that bounces off is what it looks like.  Chlorophyll looks green because it stores the red and blue light and bounces off the green and yellow light which go to our eyes.  However this doesn’t make much sense – most of the light from the sun is yellow and green!  So plants aren’t even touching most of the light they receive.

We don’t really know why this is.  Apart from a few communities in the deep ocean and purple bacteria, all life on earth depends on chlorophyll and photosynthesis.  So if something came along that was more efficient it would have had a good chance of taking over because it would have had more energy and could grow faster, pushing out the inefficient chlorophyll.  This hasn’t happened in billions of years, so there must be a very good reason plants use chlorophyll.

The best guess is that chlorophyll is so good at storing and transferring light energy that this makes up for only being able to use a little bit of it, and molecules that store the abundant green and yellow light aren’t very good at it.  This leads to an exciting idea.  Maybe chlorophyll is unique – maybe it is absolutely the best molecule so if you are going to get energy from light you almost have to use it.  In that case, maybe it is being used by living things in other solar systems too.  What’s really exciting is that we can look for chlorophyll and it’s product, oxygen, on other planets.  Looking at the light coming from stars with very special telescopes we can tell what is there because of the light that is being used and the light that is bouncing off, exactly the same as our eyes do on earth.  We have already found over 500 planets in other star systems and are getting to the stage where we can detect them directly, it may not be too long before we can look for chlorophyll on other planets.

Hat tip to Marita, Ash and Carly for this, when I asked Twitter yesterday what I should write about they suggested mud, photos for iHappy and the water cycle.  And it just so happens that I was thinking it’s a long time since I’ve put a video up, and I have a just turned 5 year old drama queen who has been explaining the water cycle to random strangers for a year or so.

It’s a pretty good explanation, there was no setup here it’s all hers.  She knows the water cycle well because we live in a semi-arid area with wet and dry seasons, so she’s grown up with floodways, dams and even rivers that fill and dry up quickly.   We get to watch the big clouds roll over and the rain pelt down, then see the puddles dry.  And we know where the town water tanks are and have explained how we get our water when there are no lakes or rivers around.  We also spend a lot of time playing with water and the sandpit!

Do you take the chance  to watch the weather?