Astronomy

We do not know for sure, 100%, that there are any black holes. However, beyond reasonable doubt, when the compact object in an X-ray binary system is shown to be more massive than about 3 times the mass of the Sun, then this compact object is a black hole.

With regard how many there are in total, it is thought that many, perhaps most; galaxies contain a massive black hole in their centers. If this is the case, then there will be almost as many black holes as galaxies - a great number!

This is difficult to call. The stable figure for several years was 16. However, recently another 23 or so moons have been discovered and are currently being classified.

As we study the planet more and more, and with more sophisticated technology, more and smaller objects are noted. Whether these count as moons or just clumps of rock caught in orbit by the planet is highly debatable. The total count of moons for Jupiter, as at May 2005, was a staggering 63!

It is thought that the sun is approaching roughly the halfway point of its life.

In addition, the solar system - the system of the sun - lives and dies with its star, at least in turns of being active, because it is the heat and energy from the sun that sustains the reactions on the planets that are within the reach of its light and gravitational force.

The sun has several billion years to go yet until it cools and expands, so we are no immediate danger from the sun - in fact, we can guarantee that by the time the sun is big enough, nothing we recognize as human will exist.

The great red spot is a storm on Jupiter that has been raging for around 300 years or so - that is when it was first spotted.

That is quite a storm really is not it, and we do not know when it will die out. It is also rather large as the question implies.

The answer is that it is estimated something in the region of two earths would fit into the great red spot alone, which gives some idea of the colossal scale of the gas giant that is Jupiter in comparison to the smaller ball of rock that is planet Earth.

Venus is like Earth in some ways, mainly cosmetic, but very different in others.

However until we studied Venus in general it was thought to be a sister planet but the reality is very different. In terms of similarities are the two main facts:

1) It is the closest to Earth in the solar system, very close indeed in planetary terms

2) The second thing is that it is a small rocky planet, of almost the same size as earth

However as you will see in the differences to Earth question I just answered, the differences between the two planets Earth and Venus are much more profound than the similarities.

Saturn is much further from the Sun than the Earth is. Therefore, for it to complete its orbit around the sun once takes much longer than for Earth due to the much wider circle it has to go around in order orbiting (well, ellipse).

Therefore, the length of a year on Saturn is approximately 29.5 Earth years.

So if you want to feel a lot younger and be a child again, define your age in Saturn years instead of Earth years!

Venus is different to planet earth in quite profound ways. We focus, being alive, on the fact that Venus could surely not support life. This focuses us in on some massive differences between the two planets.

First, up, Venus rotates extremely slowly compared to earth.

It also has a magnetic field that is almost non-existent - not good for life! Of course, the temperature means it is so dry and there is hardly any water.

There is extreme pressure on the surface and temperature, and the atmosphere is very dense with a run away greenhouse effect.

Saturn is like earth in the sense that it is one of the planets of the solar system.

Earth is also a planet. They also both are alike in that they go around the sun.

Also they both have moons, though earth has just one and Saturn has so many that we still don't know what they all are and more and more are being found around Saturn all of the time.

Therefore, in these ways they are similar.

This often confuses people that there are stars that have been through their entire life cycle yet there are many stars still forming.

Well part of the answer is that a large star burns quicker and dies quicker so might have its whole life cycle in the fraction of the time a star as if our own Sun does which is perhaps mid sized.

Therefore, it might take a billion years for a large star to go through its lifecycle and if stars started to form around a billion years after the big bang, then after 2-3 billion years stars could have burnt out, thus they could have died already.

A very interesting questions this about the speed of the solar wind. This depends on conditions in and around the sun and how particularly active it is at the time and therefore varies greatly. It moves between around 200 to 900 kilometers per second.

The Mean Distance of Moon from Earth is 238,712 miles (384,400 km).

The greatest distance is 252,586 miles.

The shortest distance is 221,331 miles.

Interestingly, the Moon used to be much closer to the earth, and may have had a pivotal role in the evolution of life on the planet and the whole history of the planet before us, that led to our creation.

The implication of this is also that the Moon will not always be with us - the Earth is slowly losing its grip on the Moon and at some stage long, in the future, the Moon will actually escape Earth's gravitational pull and out of Earth's gravitational grasp.

Venus has a very strange atmosphere, compared with the similar sized planet next to it - Earth.

The atmosphere is virtually all carbon dioxide - in the region of 9%. The rest is mainly made up of nitrogen. There is thick cloud made of not water but acids like sulphuric acid - nasty stuff indeed.

The pressure is massive in the atmosphere of planet Venus - indeed Venus would crush us, as it is 90 times that of earth!

The temperature on Venus is also massive, around 500 Celsius - even some metals would be liquid on the surface of Venus!

Of course, no one knows exactly how old the earth is, however science can give what it believes to be accurate estimates of the age of the earth using various dating techniques.

At present, the generally accepted estimate is that the Earth is between some 4.5 to 4.6 billion years old. This is based partly on radiometric dating techniques and partly on extrapolation back in time and looking at the universe around us.

A day on Saturn is hard to measure, however scientists now believe that the value of a day on Saturn in terms of length is around 10 hours and as such being ten hours compared to our 24 it is less hours than a day on earth.

One interesting theory is that most of the water came to earth from comets.

The idea is that loads of small comets, about the size of small houses, come into the atmosphere every day.

They vaporize in the atmosphere, leaving their water behind.

The idea is that 10 of these very minute for billions of years over the course of the history of the planet would lead to virtually all the water in the oceans and atmosphere!

This would be significant, as it would give an alternative explanation for the standard idea that the water came from gaseous emissions from the crust of the Earth in the early days post its initial formation...

How the moon formed is a good question. Over time, the theories have abounded as to how the moon was formed, and what it consists of.

The current theory that seems to fit the facts the best is that it is actually very old earth rocks. At some stage a huge collision took a massive chunk of rock out of the earth and flung it out into space - this rock became the moon.

If a human was to float in space and he look up would there be other planets on top of the planets in out galaxy. He would not be able to see the other planets without a telescope from space either, or at least not in any detail.

Under general relativity, it is seen that gravity can literally warp space-time around it.

Therefore, anything that passes through the gravitational warping will itself be influenced.

Around a massive object like the sun, there is a slight warping of space-time, and therefore everything that passes through that is affected.

This is what causes the slight bending, you notice in light waves even though they cannot have mass in the standard model (as it takes infinite energy to accelerate anything that has mass to light speed)

The gravitational pull in this instance would be the same from all directions, so the net effect would be no movement.

Of course, you would have to be completely encircled by the massive objects like in the centre of a ring for instance.

The answer seems to be yes, the moon is gradually escaping from the earth's gravitational pull.

However, it is possible that this will reach a steady state, when the pull of the moon is less on the earth it will slow down or stop the rate at which the earth is slowing down its spin from the friction caused. This in turn will place a greater pull back on the moon and hence it may reach a steady distance from the earth.