“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)


“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.



Niamh (10) asks “How do scientists know what the weather is going to be like in the future?

Niamh, that is a question that I have asked several times over the last 20 years ….. and the answers have changed. I asked my team about their thoughts.

Niamh, the weather forecasts were initially based upon previously recorded weather patterns. Records of the what happen to the weather go back to the 19th century  and the weather experts of today look for patterns in past weather to predict what is going to happen in the future.

All the past patterns have now been computerised so part of the role of the forecasters is to get the computers to analyse the patterns and then make suggested predictions.

Nowadays the weather experts ( they are called meteorologists) also have satellite images  to help them predict the weather. They also use other sensors like weather balloons which record air pressure and temperature at different levels in their location.

Niamh, for the distant future it is very difficult to predict what the weather will be like. The weather is one of those magnificently independent variables that we still cannot control.

Niamh if you or any other reader would like to make a comment please go to the Leave a Reply box below. Or ask another question.

Ujala asked questions about where Science came from.

Many thanks for the question Ujala. I hope my friends answers satisfy your curiosity. Interestingly although ‘Natural Philosophy’ and ‘Science’ were names that evolved 2500 years ago there is evidence that ancient civilizations practiced ‘science’ more than 4000 years ago in Africa where they used measurements to create maps of plots of land by the Nile – Geometry is a scientific tool.

Any reader can ask another question or leave a Comment in the Leave a Reply box below

Why do we have droughts? asks Lisa (10)

It is a difficult question to answer. There are a lot of possible things that could cause a drought, however one of the most interesting is the effect of atmospheric pressure.

If you listen to weather forecasts you would have heard of a low and high pressure areas. You might have also noticed a pattern. When the weather forecast talks about low pressure it is normally accompanied by rain while high pressure is accompanied by sunny periods and dryness. Dryness over a long period of time could mean the loss of a lot of ground water and therefore create a drought. You get long periods of high pressure over deserts,

So why does this happen?

When you have high pressure dry air descends from the colder air higher in the atmosphere (cold air is more dense and heavier than warm air. In low pressure the movement of the air is in the opposite direction with the warmer, ground level air rising carrying with it water vapour which eventually forms clouds as it gets colder.

Lisa, there are some difficult ideas here. Think about them and then ask another question.That’s the way science works.

Revised (03/02/17)

Abdul (10) asked “Why do heavy things fall faster than light things?

Abdul, a great question. I can remember asking this question to a class of 9yr olds. Our investigations started by dropping a sheet of A4 paper and timing how quickly it reached the floor. We had to make the test fair and then recorded our answers. We then all screwed up our piece of A4 paper and then predicted how long it would take to drop the same distance, again making sure the test was fair.

Several in the class said that the results of the test was unfair, because the sheet of paper had been made heavier. A mass balance proved that was not the case. So why had the screwed up ball of paper fallen faster? Your thoughts please.

So how can we test if heavier things fall faster than light things? Is it true or not true? What things do we need to change and what things do we need to make sure are the same. We need a fair test. Let me know your answers.

Mitchell (10) asked ‘What would happen if the Earth stopped spinning’


A great question Mitchell. Can you think of any other thing that might happen?

Firstly the speed at which the spin happens is measured at the equator. Any idea at what the speed would be at the North and south poles? If the Earth suddenly stopped spinning what would be the effect at the poles?

How long will each day and night be? Remember although it is not spinning it would still be orbiting the Sun.

Interestingly, because of the Earth’s spin the Earth has a bulge around its equator.  Remove the spin and the Earth will become a true sphere. This will however cause a redistribution of the Earth’s oceans. The world after the spin will look a little bit like it is depicted in the video below, a big continent in the equatorial area with an ocean either side of it.

Another thing that will happen is that the Earth will lose it’s magnetic field. No longer will you be able to hold a compass and see the pointer pointing to the north pole.

Soham asked a question about forces.

Soham’s question was  …”What is the force if mass is 10N and final final velocity is 100 m/s and initial velocity is 0 m/s and time taken is 7.98s.” force-times-acceleartion

Soham. Please do not expect me to give an answer to your question. You have all the information that will allow you to make the calculation yourself. Acceleration is change of speed divided by time taken and you have your mass (in grammes) and you have Newton’s brilliant formula.  Thanks for the question.

Soham (10) ask “Why is the sky blue”

Soham, I have tried with my friends to answer this question previously. Have a look at my a previous answer.

Think about it and if there is something that you are unsure of ask another question. Sometimes other questions help. They  help all of us to understand some of the strange aspects of our lives.

Soham(10) asks – “Why do Chameleons change their colour and how ?”


Thanks team, some good answers. On most occasions it is suggested that a Chameleon changes colour for defensive purposes.  It seems that they can do this by changing the tension in their skin. Not something that we can do very easily. For the Chameleon, part of the skin is a compound that can be stretched and it is this compound that changes the light colours that are absorbed by the skin and those that are reflected. Thus the colour change.

Reflection of light of things depends on the material and the light that is falling on it. Suppose green light was shone on a red object in a dark room. Would you see it? Sometimes you can also notice that changing the temperature of a material changes the way it reflects light. Running a hot iron over a red material changes the ‘redness’ of the material because of the effect of the heat on the compound that the red dye is made of. Some experiments that you might try (with the help of an adult).