Space FAQs

If black holes drain all light and life like a plughole in a sink then what is the polar opposite? What acts as the constantly running tap that maintains the natural flow of things? And I won't accept stars or the sun as an answer.

Black holes are relatively small and don't actually consume much material. They only consume matter that happens to be going in their direction. Even then, matter tends to orbit the black hole for a long time before finally losing its momentum and falling in.

You won't accept stars or the Sun? Why not? Stars, the Sun and black holes themselves all contribute to the amount of material and energy that's being reprocessed in the Universe. The Universe started off with a certain amount of energy and today there is exactly the same amount of energy as there was then. What's different now is that some of the energy is in the form of mass. That's hard stuff, like stars, planets and people! Black holes compress mass into a very dense ball – contributing to the total mass and energy of the Universe. So black holes don't act as a sink and there is no need for an ever-running tap of energy in the Universe.

Will Earth be pulled into a black hole in the middle of the Milky Way galaxy?

It's unlikely that our solar system would be pulled into a black hole in the centre of our galaxy, the Milky Way. Black holes don't have a stronger pull than any ordinary object with the same mass. And black holes actually have a small mass. So, for example, the Sun could turn into a black hole and apart from being very dark Earth would continue to orbit just as before – we wouldn't be sucked in. If there were a black hole in the centre of our galaxy it would consume any dust and gas that happens to fall inwards, but it wouldn't exert a strong inward pull on us.

Either way, it would be hard to tell whether we are slowly spiralling into the centre of the galaxy. And there is another possibility – we could be moving away from it, as the Moon is moving away from Earth. And even if we are spiralling inwards, the Sun would be long dead before we reached the centre.

I've heard that an asteroid will hit Earth on 1st February 2019. Is it true?

At first it was thought there was a small chance the asteroid might hit us. But scientists have now gathered more accurate data that tell us it will whiz safely by. The problem with making such predictions is that the position and speed of objects in space can only ever be measured with a limited degree of accuracy. although they may have a good idea of where an asteroid is and where it's going on one particular day, small errors in the estimation of its trajectory will grow into enormous errors over decades.

Read more about the story on the BBC News site.

Is the Hubble telescope able to see black holes?

Hubble looks at many objects in space that are likely to contain black holes, but we can't look closely enough to confirm their presence. Black holes are controversial creatures, although most scientists believe they exist and are pretty sure what they look like (a large light emission, also containing X-rays). Quasars are very bright galaxies, visible by telescope, that are thought to contain huge black holes – billions of times the mass of the Sun.

Take a look at the Hubble archive of the Space Telescope Science Institute. Try the Hubble Site for photos.

Why do some people believe the Moon landings were faked?

The idea that the Moon landings were elaborate fakes is quite popular amongst conspiracy theorists. They have a number of pieces of evidence they point to when making this claim. The lack of stars in the background of pictures taken on the Moon is often mentioned. But the reason there are no stars is because the brightness of the surrounding rocks outshines the dim stars in the background. Exactly the same thing happens here on the Earth from light pollution, which is why it's best to look at the stars in the darkness of the countryside.

There are also a number of people who believe that the technology to get us to the Moon wasn't around in 1969. The technological problems of forging six lunar landings would have been immense. There is, of course, lots of evidence to say that the Moon landings actually happened. Ultimately, over 10,000 people are involved in every launch of the space shuttle today – have all of them kept the secret?

The Bad Astronomy site gives its opinion on the conspiracy theory of Moon landings.

Part of the evidence for believing the Moon landings were faked are photographs that show shadows pointing in the 'wrong' direction. I heard that the only source of illumination on the Moon is the Sun. In the photos the Sun was in the wrong position to have cast the shadows. Is there any other explanation for the shadows pointing the wrong way?

The shadows can be explained by the fact that the moon gets illumination from Earth as well as the Sun. From the Moon, Earth would be much brighter than a full Moon is here, because the Earth is so much bigger than the Moon. Another source of illumination comes from the Moon's surface, which is covered in a white-grey dust, that too reflects an appreciable amount of light.

Also, shadows are complex, they can create the illusion of pointing the 'wrong' way, even when they are illuminated by only one light source. There are some nice images showing how this works and more on the Moon's light and shade at Bad Astronomy.

Can you tell me about stars, like our Sun, and their life cycle?

The Sun is thought to have condensed from a cloud of dust and gas. As it condensed, the gas reached a high enough density in the centre for hydrogen atoms to fuse into helium. After this, the Sun settled down into its current hydrogen-burning phase, and it has remained in this phase for the last 4.6 billion years.

The Sun will continue with business as usual for another 5 billion years. It will continue to generate energy by nuclear fusion of hydrogen – combining several hydrogen atoms to create helium. But over time, helium levels will increase and it will become the dominant element. This will happen at the core first until there is no hydrogen left there.

Hydrogen-burning will then move out into a shell around the core, gradually spreading out through the Sun and using up fuel as it goes. This creates instability inside the star, and will make it swell to a vast, cool red giant, large enough to engulf the Earth's orbit.

Throughout this, the temperature and pressure inside the core build up. Eventually they reach a point where helium fusion can begin, generating energy in the core again, and producing heavier elements. The helium-burning will signal a return to relatively normal behaviour for the Sun, but only for a few million years – stars burn helium much more quickly than they burn hydrogen.

Eventually, all the helium in the core will be used up, and helium-burning will follow the hydrogen-burning outwards to a shell, consuming the helium the hydrogen shell has produced on its way. The Sun's internal pressure will overcome gravity again, and it will swell back to a 'red giant'. But this time, the Sun is unable to generate enough energy to begin burning the heavier elements at its core, and it really will be the end. The expansion will continue, and the outer layers of the atmosphere will be puffed off in a series of concentric shells, forming a glowing planetary nebula. Only the core of the Sun will remain, as a slowly cooling, dense 'white dwarf star'.

I would like to find out the scale for each of the individual planets in our solar system.

Our solar system has 9 planets. In order of increasing distance from the Sun, they are – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. Four of these, Mercury, Venus, Mars and Pluto, are smaller than Earth, and the remaining four, Jupiter, Saturn, Uranus and Neptune, are larger. Pluto is the smallest planet of our solar system and Jupiter is the largest.

Mercury is about one twentieth the size of Earth. Its diameter is 4,880 km (3,032 miles)

Venus is eight tenths the size of Earth. Its diameter is 12,104 km (7,521 miles)

The diameter of Earth is 12,756 km (7,926 miles)

Mars is about half the size of Earth. Its diameter is 6,794 km (4,222 miles)

Jupiter is 1,316 times larger than Earth. Its diameter is 142,984 km (88,850 miles)

Saturn is 755 times larger than Earth. Its diameter is 120,536 km (74,900 miles)

Uranus is about 44 times larger than Earth. Its diameter is 51,118 km (31,760 miles)

Neptune is also about 44 times the size of Earth. Its diameter is 49,532 km (30,780 miles)

Pluto is one 200th of the size of Earth. Its diameter is about 2,274 km (1,413 miles)

Can I see the ISS from Earth?

Yes, and once you know where to look it's almost impossible to miss. The International Space Station (ISS) appears as a bright, fast moving object that covers the sky in a matter of minutes. It's about as bright as Venus. Other satellites will be dimmer and may appear to twinkle in the same way as stars do. Sightings of the ISS are predicted a couple of weeks in advance and posted on several websites.

To find the times when it will be orbiting over your neck of the woods try Nasa's International Space Station and J-Pass sites or try the Heavens Above astronomy site.

The information that these sites provide includes the date and time that the ISS is visible, the direction that it is flying from and to, and its maximum elevation. The maximum elevation tells you its height above the horizon – the higher it is, the closer to 90 degrees, the easier it will be to see.

Armed with the predictions, the only thing left to do is hope for a clear night! Once the conditions are right, wrap up warm and find a dark place away from streetlights. Scan the area of the sky in the direction the ISS is predicted to come from. You might find a compass handy to help you get your bearings. The one acre of solar panels on the ISS reflecting light from the Sun down onto Earth is what makes it so bright and easy to see. The solar panels also make the ISS twinkle as it passes overhead.

Why do astronomy telescopes rotate 360 degrees in 24 hours in the opposite direction to the Earth's rotation?

Each day, Earth spins around on its axis one complete turn of 360 degrees. A slowly rotating telescope which is trained from Earth on a specific object in space will keep its view fixed on that object despite the fact that the Earth is moving underneath it. To us this seems like the telescope is moving in the opposite direction to the direction of the Earth's rotation, but in reality the telescope is just fixed on the celestial object, and it's the Earth that's moving.

Is there life on other planets? And are there planets in other galaxies?

We don't yet know if there is life on other planets. Some people suspect there may be microscopic life on other planets in our solar system but there's no sign of intelligent life.

There are planets orbiting stars like the Sun in other galaxies beyond our own. Over 100 planets have been found orbiting stars within our galaxy alone – it seems to be common. As yet we can't see these planets as the stars that they orbit are just too far away. But perhaps with better telescopes in the future we may even be able to detect planets in other galaxies. Then, who knows?

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