Mary Ann (10) asks “Why are most leaves on trees green?”

Mary Ann. I sometimes think it is amazing that  leaves are so successful because they reflect green light ….the don’t want it.

Remember that white light from the Sun is a mixture of all different colours.Below you can see the result of white light being passed through a prism. the chlorophyll in leaf absorbs the deep blue and the red light and reflects the green light.

For red leaves the chlorophyll is hiding in the colour of the leaf. Our eyes cannot see it.
If you want to know a little bit more then ask another question.

(Anyone reading this post who wants to ask a question or make a comment please feel free to do so)

“When the Sun blows up will Mercury smash into Earth?” asks Flynn and Freddie (10)

 

Below is a short video of the expansion of the Sun. Again this is a hypothesis based upon observations of our Universe.

The expansion is thought to be caused by firstly the Sun running out of fuel (it uses  Hydrogen, converting it by a fusion reaction to Helium). As the Sun cools the centre will expand, (any thoughts on what might cause this?) pushing out the rim of the Sun and consuming Mercury, Venus and The Earth and eventually it becomes a Red Dwarf. It is suggested that Mars will survive.

What is the difference between a hypothesis and a theory?

Hope this helped. Please comment or ask another question.
(Anyone reading this post who wants to ask a question or make a comment please feel free to do so)

“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)

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)

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)

Shabaar (9) asked “Can humans cause an ice age?”

The last ice age ended about 11,700 years ago. It started almost 3 million years before that and was thought to have been caused by changes in the way that the Earth moved around the Sun.

So can we cause a new ice age? From this evidence it seems unlikely that we (humans) can cause a future ice age. With our production of greenhouse gases (Carbon Dioxide, Carbon Fluoride compounds and other related gases) it likely that we will be warming the atmosphere rather than making it colder. This may cause weather extremes which might make life on our planet (for humans) unacceptable. See the following link

Science Master Special – What might plants need to grow?

1. Air (Oxygen and Carbon Dioxide)
2. The Sun or some light or maybe some darkness.
3. Warmth (heat), or maybe some coolness.
4. Water (moisture, dampness)
5. Soil, rocks, compost, sand.
6. Time, lots or maybe little.
7. Creatures, in or above the soil. These could be giant worms or miniscule creatures.
8. Plant food. Fertilisers, minerals.

 

This list was helped by The Nuffield Space Project P77

Jessica(8) asked several great questions about the Solar System

Jessica. I have asked my team to answer the information based questions. I will try to help you with the other questions.

Jessica asked about Dwarf planets, the temperature of the Sun, The Earth’s layers and the size of Jupiter. Here are the comments from my team.

solarsystem1solarsystem2

 

I was interested in your question about Venus having an opposite spin to that of Earth. Earth has (if you are above the North Pole) a Counter (Anti) Clockwise spin while Venus (if you are above Venus’s North Pole)has a Clockwise spin. Most of the other planets spin in the same direction as the Earth. Here is a little experiment…..

Pick up a pencil and holding it upright begin turning it in a clockwise direction,  now still turning the pencil, turn the pencil through 180 degrees. Which way is the pencil now rotating, clockwise or anti clockwise?  It is thought that close to the beginning of the Solar System a close encounter with another large object caused the axis of Venus to move through 180 degrees. Is that a theory or a hypothesis?

To your question about the position of Mercury – I have no idea why it is the nearest planet to the Sun. At the beginning of the Solar System you have the Sun surrounded by orbiting space dust. This dust slowly collects together and the planets begin to be formed. The closest ring of dust to the Sun formed the closest planet (Which we call Mercury).

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

stopspin-copy

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.