“How do you measure the distance to the Sun and stars?’ asked Julian (12)


Julian, quite a challenging question. I will only be trying to answer the first part – the Sun-Earth distance and the Earth-Stars distance.? Even then as my team suggests, I might be introducing mathematical terms that you have not met yet, but I have included links to other sources of help.

To answer the first question I recommend you read a Universe Today article   It is an excellent historical review of the problems that the early scientists had in determining the Earth-Sun distance. The answer finally came from observations of the movement of the planet Venus across the face of the Sun. In it the writer refers to a Nasa document that tries to explain the methods used. In present times the distance to the Sun is measured by ‘bouncing’ a radar pulse of of it.

Determining the distance to the other stars becomes possible once the Earth-Sun distance was known. It uses a technique called parallax.  I would like to illustrate this with a question which tackles a simpler problem. ‘How far is my finger away from my nose?’

Try this little experiment, put a finger in an upright position in front of your nose. Now close one eye and note the position of the finger. Close that eye and open the other one. The finger moves! Now suppose, with help, you could measure the amount of movement. You could end up with diagrams like those below. Did you make a note of the position of your finger relative to your nose? No – you can now see how you could work this out.

Now let’s do a little geometry and add an axis

We can then measure the angle of the apparent movement

You end with a right angled triangle ABC, knowing the angle x AND the distance between your eyes you should be able to do a bit of trigonometry using TAN x = opposite/adjacent (Tan x = AB/BC) and work out the distance of your finger from your face. For an introduction to trigonometry please look at this site.

Amazingly this is (in a crude way) the same process by which astronomers can measure the distance to the stars. Instead of using the distance between your eyes they use the orbit of the Earth. They look at a star and make a note of it’s position and then do the same thing 6 months later when the Earth is at the opposite side of the Sun. They therefore have AB (the distance between the Sun and the Earth and they have the angle through which the star has apparently moved. 

(revised 24/04/16)


Elizabeth (9) asked “How doesn’t stainless steel stain?”

Elizabeth I would like you try an experiment. Gather together some different nails. If you can, find a stainless steel nail, steel nail, iron nail and as many different nails that you can. Try and get two of each. Find two jam jars and put one set of clean nails in one jar and the other set of clean nails into the other jar. Why do I suggest cleaning the nails?

Fill the first jar with tap water and the second with water that has been boiled and cooled. Cover both with cling film and leave for about 7 days. What happens ?????

Relook at what you did at the start. What did  you see in the tap water that you added? How did this compare to the boiled water? What did you see when you boiled the water?

Most of the stains on metals are caused by interactions with water and oxygen.

When steel and iron are attacked on their surface by the oxygen from the water you get  things called oxides created as the oxygen (a very reactive gas) reacts with the metals surface. For most metals the compound (oxide) that is formed is fairly ‘soft’ and is washed away creating new sites for oxygen attack. With stainless steel it is the chromium in the stainless steel that reacts with the oxygen creating an invisible layer of Chromium Oxide and this is such a hard substance that no other substance can stain the steel.

If you rub the stainless steel implement hard with a scraper you might get rid of the strong oxide and create a stain by attacking the surface of the steel with another substance. Try it (with permission).

Elizabeth and others, quite a detailed answer. If you want to ask further questions please ask.

“If I was sucked into a black hole what would make me die?” asked James (12)

James, thank you for your question. I had a similar question from  Sheereen  click here to see my, and my friends answer.

It is thought that a ‘black hole’ is produced when a rather large star comes to the end of it’s life. It collapses in on itself and forms an object of incredibly concentrated matter. As ‘gravity’ is a property of the quantity of matter (see my answer to Ernie’s question) the collapse causes an immense increase in the gravity from the  smaller collapsed star.  

It is unlikely that our Sun would end in this way as it is classified as a smallish star. It is likely to become something called a ‘Red Dwarf’ star.

The ‘black hole’ is explained by the fact that this concentration of gravity ‘pulls’ light into it, thus the ‘hole’.

Now if you were close to the collapsed star in your spaceship you would also be pulled into it and unfortunately be added to the mass of the collapsed star. Sorry, you will be crushed.

(slightly revised 20/4/2016)

Donna (7) asks “Where do clouds come from?”

Donna, many thanks for the question. Before trying to answer it I thought I would ask my team a question.

Donna, what do you think about the puddles question? Think about how you would answer it and then go to my answer to a previous question.

Now to your question. Firstly I have created a little animation to show how the puddle disappear. You have to imagine that the shapes are water particles (molecules is the proper word). In the puddle they are all moving around. Most of them like being with the other particles BUT some are just moving around a little bit too fast and manage to escape from the puddle. When the Sun begins to warm the puddle it makes more water particles move around faster and more escape. This goes on until the puddle disappears.


The water particles are very small and are are lifted by the air up into the sky. High above the ground the air is quite cold so the water particles ‘slow down’. When they are moving ever so slowly if they meet another water particle they join up with each other and form droplets of water. This is how a cloud begins to form.

At home look at the steam from a kettle, BE VERY CAREFUL AND CONSULT AN ADULT.  At the exit of the kettle spout you can see nothing, BUT just above this the hot water particles begin to cool down and slow down and reform clouds of water.

(revised 21/4/17)

“Is a shadow a reflection?” asks Jack (7)

Thank you team. Some excellent observations. You noticed that the shadow had no detail on it, no colour, no lines, no images of seeds in the fruit. It was just black. On a dark night, under street lights look at your shadow. Other than your shape what detail does it have? It changes now and again, but why?

Now the reflection? If you look into a mirror what do you see? Is it like your shadow? How different is it?

Look at the two images of the fruit. The first image of the the fruit is the ‘real’ image. What about the image just below it (on the shiny surface)? Is it the real image? How did it get there?

Think about this – where did it come from? Now think about your image in a mirror, where did that come from?

You can create you own image of a reflection and a shadow. Get a mirror and a small screen. Put the object on the mirror and the screen behind it and use a torch to shine on the object.

Jack, this a great question. Lot’s to think about. Do you want to ask another question? Then click on the Reply button below.


“Why can heavy things float”? ask Aiden (10)


Aiden, great question,a difficult answer. I hope that you have investigated which things float and which things sink. You should be able to look around you and say ‘That floats’ and ‘That sinks”. Think about this – when something sinks it seems to be breaking the surface of the water. What is it breaking? I pass this back to my team.

The attractive forces between water molecules are called intermolecular forces. Look at this post to find out more.  When the much bigger metal boat hits the water, because of it’s design (spread out) there are lots more water particles that push on the boat and keep it floating.  Squash the boat up into a small lump of metal  and drop it into the water. What do you think will happen? Let me know what you think by leaving a comment in the ‘Leave a Reply’ box below.



A question “How does the world work”

Some time ago a well known scientist (James Lovelock) suggested that the Earth (our planet) was special. He claimed that the Earth itself was a living thing and had control over its environment. He gave the Earth the name Gaia (a Greek name for the goddess of the Earth) and suggested that the planet’s objective was to support life on it, at all cost.

It has been argued, by those who support this idea, that there is a lot of evidence from investigating the Earth’s history over the last 3 billion years, that suggest the idea is valid. Below are some of those arguments. What do you think?

The Gaia idea is something called an hypothesis (an idea). It has yet to be proven. If proven it can then be called a theory.


“When you shake a fizzy drink that is full when you open it and it explodes?” asked Ruby (8)

When you open the bottle you should hear a gentle fizz. When you pour the drink into a glass you get a bigger fizz and lots of bubbles. If you had ice in the glass you would get even more bubbles. This is because the surface of the glass and the ice cubes are full of little gullies and points. The gas bubbles that were hidden in the liquid attach themselves to the gullies and start to get bigger, (bubbles grow by being joined by other bubbles) and bigger and then when they are big enough, because they are lighter than the liquid, they rise to the surface.

Here is a little experiment for you to try —put the ice cube in your mouth and get your tongue to smooth it, for a few minutes. Think about what I have said and try and predict what the outcome will be when you pour a new bottle of drink over it. Now add the carbonated drink and test your prediction.

Now what happens if you shake the bottle before opening it. This is where you get the explosion!  Here is my possible explanation……. look at the bottle of drink.

(1) There is an empty space at the top of the bottle. It’s not empty, it is full of Carbon Dioxide gas.

(2) When you shake the bottle that gas mixes with the liquid and because bubbles attract other bubbles the gas in the liquid becomes more bubbly.

(3) The bubbles that were hidden in the liquid join the new shaken bubbles. Undo the top and these new bigger bubbles all escape at the same time pushing the liquid before it – the  explosion.

Look at this previous post.


Ruby (8) asked “What type of chemical is in capsicum that hurts when police put it in eyes?”

Yes, a great question Ruby. There is this temptation to relate Capsaicin to Black Pepper, however this is not true. The black pepper seeds are from a plant in the vine family of plants. The Capsicum family is the home of the chillies and the chemical Capsaicin which is a chemical in the alkaloid family. Capsaicin is not only used in pepper sprays it also has some curative properties, for example it is an effective pain killer.

I think it is very interesting that certain chemicals, particularly those derived from plants can be used for destructive purposes and for curing purposes. Just a thought.