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27 November 2014
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Last updated: 08 May 2006 1124 BST
Picture: Mark Lawrik-Thompson
Graphic: Astronomy: your questions answered
Norfolk astronomer and Chairman of the Norwich Astronomical Society Mark Thompson is here to answer your questions about space.
Picture: Comet Hyakutaki
Hyakutaki comet

How do astronauts breathe in space? How far apart are the earth and sun?

Read the answers to your questions by local astronomer, Mark.


My friend told me that there is a black hole in the center of the solar system and that because of that we will never even be able to leave our solar system even if we tried! Is it true?
JOSEPH, AGE 11, STOKE-ON-TRENT

Answer: Your friend is almost right. We think there is a black hole at the centre of our Galaxy, not our Solar System. The Sun is at the centre of the Solar System and there is certainly no black hole there. In fact a number of space craft are now heading on their way out of our Solar System, the Voyager and Pioneer probes.

If there was nothing before the big bang, where did the matter come from in the big bang?
KYLE, AGE 15, GOBLES, MICHIGAN

Answer: What a good question. There are many answers to this, some of which are somewhat complicated to explain so I'll pick one of the easier ones.

One idea explains that not only space, but time was also made when the Universe formed in the explosion we call the Big Bang. If time was made at the Big Bang, then time didn't exist before it so it's somewhat meaningless to ask what happened before! So that matter didn't actually have anywhere to come from!

Seem a strange answer? Think about this though. If you got in a car with a compass and headed north, eventually you would reach the North Pole (ignoring the fact of all the water and snow between here and there). Anyway, when you get to the North Pole, you have reached the most northerly point on the Earth, there is nowhere further north!

In the same way, one theory says that there is no time before the big bang, you are at the very beginning! Hard to get your head round that one!

How big is the solar system?
AURELIE, AGE 9, OTTAWA

Answer: The edge of our Solar System is found at a place called the heliopause and is thought to be about 23 billion kilometers from the Sun. This means that the Universe is 46 billion kilometers from one side to the other. That's pretty big.

Can black holes be a time machine?
SOFIA, AGE 10, COLOMBIA

Answer:Black holes themselves cannot be used as time machines. If they were to join up to form wormholes (we have not found a wormhole yet, they are just theoretical) then the wormholes could be used as time machines. We would need to learn a lot more about them though before we could.

Yesterday I found something really strange written in the Egyptian news. It says that the new planet, Sedna, will be hitting the Earth in the year 2036. I just want to know if this information is right or not because I think it would be a major disaster. Thanks. HUSSEIN, CAIRO, EGYPT

Answer: There is no scientific evidence that suggests Sedna will hit the Earth in 2036 or any other year.

Why does Earth have seasons?
ARNELL, AGE 11, KITCHENER

Answer: The Earth has seasons because it is tilted at an angle. Imagine the Sun sitting in the middle of a huge piece of paper. The Earth moves around the Sun once every year along the sheet of paper in a path that is like a squashed circle.

The Earth also spins around an axis, like a bike wheel and takes one day to do that. Now, the axis that the Earth spins around does not point straight up and down, its tilted over.

This means that when the top half (the northern half) of the Earth points to the Sun, we get summer and at the same time, the bottom half (the southern half) is pointing away from the Sun and gets winter.

My question is relatively basic but I do need some clarification. I was always under the impression that a light year is the distance light travels within a year (6 x 10/12).

However, recently I have come across a reference book that suggests that one light year represented by this equation is only 6 billion miles.

Do astronomers reflect 6 billion miles as a light year or 6000 billion miles as a light year? Your answer is very important to me, and I would appreciate your help in this.
DAVID, BRISBANE, AUSTRALIA

Answer: The confusion arises not in the definition of the length of a light year but instead in the definition of a billion.

The British billion is a million million (1 followed by 12 zeros) whilst the American billion is a thousand million (1 followed by 9 zeros).

Convention in science is still a little uncertain about this but the trend is toward the American version. Most astronomers will tell you that a light year equals approximately 6 thousand billion miles.

Can you see artificial satellites with the naked eye?
ROSS, SAUNDERSFOOT

Answer: It is very easy to see satellites with the naked eye. Just look out on any dark clear night and you will sometimes see lights steadily moving across the sky.

Check out (the Βι¶ΉΤΌΕΔ is not responsible for the content of external websites) and it will tell you when you can see satellites and even the International Space Station.

What is a fireball?
LAETITIA, AGE 11, ARIZONA

Answer: A fireball is just a very bright meteor! What's a meteor? A meteor is a piece of rock or dust that falls through the atmosphere of the Earth.

As it falls, it gets hotter and hotter and starts to glow. Really big pieces of rock glow brighter and we see these as fireballs. Sometimes, they can be so bright that they will cast shadows.

How big is the universe?
ELENAR, EDINBURGH

Answer: The Universe goes on forever and ever; we say that the Universe is infinite.

Why is it not usual to express the earth-moon distance in astronomical units?
JOYCE

Answer: An astronomical unit is equal to the average distance between the Sun and Earth (150 million km or 93 million miles). The distance to the Moon is on average 380,000 km.

That's equal to about 0.0025 astronomical units. The answer to your question is that it's just easier to work with in kilometres rather than astronomical units as the units are too big. It's a bit like measuring your height in kilometres rather than metres.

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Astronomy index

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International Space Station

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New Planet

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Planets Pluto, Neptune and Uranus

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Venus passes in front of the Sun

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