“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. 

This gives the route to determining the distance between the Earth and a Star.


(revised 14/05/17)


“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)

Akshita (12) asks “In a circuit of 5 light bulbs and 2 batteries why do all of the light bulbs come on at the same time when you switch the switch?”

Hello Akshita, I asked my friends about your question.

Thank you team. You are right metals are much more important than the plastic coating. You could replace the plastic coating with paper or rubber or cloth BUT the metal has to be a metal. Why. It’s all to with things called electrons. Most elements

  • An element is a group of atoms that all have the same number of protons (positively charged particles) in their nucleus. Oxygen is the most abundant element on the Earth, Iron is the most abundant metal element.

have electrons that are tightly held by the nucleus but metals are different. The outer electrons of metals are rather loosely held by the nucleus and are free to move around within the metal structure. So if we looked at a circuit which was not connected to a battery (switch is Off) and looked closely at a small section of the wire you would see something like this …

The little red dots depict the outermost electrons of the metal atoms (the element nuclei are the positive circles).  You have to imagine that the electrons are constantly moving around within the metal structure and probably keeping quite close to their parent atom.

Now close the switch.

The battery is now pushing the electrons around the wire (- to +). This push is a bit like a long chain being pushed or pulled. All the electrons in the wire experience the push simultaneously (like the links in the chain) so when the switch is closed all the lights in the circuit will experience the ‘push’ and the electrons in the vicinity of the bulb filament will give up some of the energy of the push to the filament which will be converted to heat energy and create a hot filament which is then partly converted to light energy.

This is a lot to think about Akshita, you, and any other reader can ask another question or Leave a Comment in the Reply Box below.

How do we know what organelles inside a cell looks like? – asks Anne (7th Grade)

How do we know what organelles inside a cell looks like? Anne, a fascinating questions. I have to be honest I have no idea what an organelle is (I am traditionally what might be called a physical scientist) – I know a lot about physics and chemistry but very little about biology and botany. I do have a team who can set me on the trail of answering you question so here goes…..over to you team.


Thanks team. Some other questions ‘bounce’ around my mind. Why can’t light bounce of the organelles? I then realised that it is thought that light is in fact particulate  in nature. Scientists think that light might consist of particles – called photons. These photons are basically to big to bounce of such a small particle as an organelle. They could bounce off but when you look at them after the bounce they will not be able tell you anything about the thing they bounced off.

As my team suggest electrons are much smaller than photons, so when they bounce of the organelle they will reflect what the organelle at that point looks like. To do this scientists use special microscopes called electron microscopes  that instead of firing light (photons) at the thing they want to look at fire electrons and look at how the electrons have changed after they have bounced of the thing you are looking at.

Anne, hope this makes sense. Thanks for the question. Unsure about what I have said then you can ask another question.

Ratterson asks -‘What is Newton’s third law of motion?’

Hello Ratterson. I am real, so that is my first answer. I have my own thoughts on Newton’s third law , but firstly I will ask my friends to think about it.


Thanks team. I think I agree. When somebody fires a gun the bullet is pushed forwards and the gun is pushed backwards, the forces are equal and opposite. I can remember a little experiment that I once carried out. I sat on a trolley with lots of sandbags on it. one by one I threw the sandbags of the trolley and the trolley began to move! And it moved faster and faster as I continued to throw the sandbags off it. I was forcing the sandbags in one direction and I was being pushed in the opposite direction.

Why is the sky blue in the day and black in the night? asks Lamar (12)

Lamar – a brilliant question. I will ask my friends to think about it.


Lamar. I hope that you have had the opportunity of passing ‘white light’ through a prism and see the fantastic ‘spectrum’ of coloured light that results. If not then try ‘creating’ white light by using torches and  coloured cellophane (blue, red, green) on each torch and shining them at a white piece of cardboard. Let me know what happens.

Things then get a little difficult. You have to think of the Sun’s white light reaching the atmosphere of the Earth. The two major components of the atmosphere are nitrogen and oxygen. The structure of the molecules of these two components makes them very receptive to the blue part of the white light from the Sun. The air molecules absorb this blue part and then re-emit it in all directions. This is a process called ‘scattering’. Thus the blue sky. The rest of the (white minus some blue) sunlight passes onwards.

At night the Sun is shining on another part of the Earth, so no white light is falling on your part of the Earth. No light ….blackness.

Lamar . An interesting question, a complex answer. Feel free to ask another question.

Natalie’s question was linked to chemicals and what happens when you add a chemical to a chemical.

Natalie, a great question. Before answering it I thought that we needed to think about what was meant by the term ‘Chemical’. So I asked my team.


So the salt that you put on your food is a chemical. The food is made up of chemicals. Water is a chemical and so is Oxygen, the gas that you breathe. Washing up liquid is made of chemicals as is milk and butter.

Sometimes, very, very rarely adding one chemical to another causes an explosion. So there is no need to worry. Please ask another question.

Luie asks ” What is the most deadly gas?”

Luie I asked my friends for help on this question. They had some interesting thoughts.

posinous gases

Luie, it is not quite true that there is only one gas that is not poisonous. Air consists of a variety of gases that are not poisonous, we breathe them in all the time and they don’t poison us. There is however one gas that is used by our body and is more important than the others. What is it? If you know then you could tell me by using the ‘Leave a Reply’ box

Did you know that Hydrogen Sulphide (bad eggs) is more poisonous than Hydrogen Cyanide (almond smell), why ???

Because our nose is much more sensitive to Hydrogen Sulphide than Hydrogen Cyanide. By the time you can smell the almond smell you are dying.