What is the coldest known location in our Solar System?
Asked by: Sasha Wright, Coventry
Until recently, Pluto had the distinction of being both the outermost planet and coldest known place. Now it’s neither, having been demoted from planet status in 2006 and last September (2009) losing its frosty reputation to somewhere much closer to home: the Moon. NASA’s Lunar Reconnaissance Orbiter recorded a temperature of -240°C inside a crater at the Moon’s south pole, where the Sun has never shone. That’s 20°C colder than the surface of Pluto.
Who owns the Moon?
Asked by: Finn Bogdan, Switzerland
Officially, nobody. The issue of owning extraterrestrial space or objects is governed by the United Nations’ Outer Space Treaty, first enacted in 1967. It forms the basis of international space law. Article II of the treaty states “outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.”
Some entrepreneurs have argued that this doesn’t apply to private individuals and they are therefore free to claim (and sell off) portions of outer space, including lunar real-estate! However, legal bigwigs insist that nations take responsibility for not only state and corporate functions but also private citizens.
There is also a legal concept called corpus possessionis which implies that for something to be ‘owned’ it must be ‘controlled’ – something not possible unless an individual can access and defend their lunar real-estate. In reality, anyone buying a piece of the Moon owns nothing more than an expensive bit of paper.
What is tidal locking?
Asked by: Dennis Lund, Salisbury
Tidal locking is the phenomenon by which a body has the same rotational period as its orbital period around a partner. So, the Moon is tidally locked to the Earth because it rotates in exactly the same time as it takes to orbit the Earth. That is why we only see one side of the Moon. If both bodies are of comparable size and are close together, both bodies can be tidally locked to each other – this is the case in the Pluto-Charon system.
Tidal locking is a natural consequence of the gravitational distortions induced by a body on another.
Why is the Moon white?
Asked by: Edward Seymour, Hove
Despite appearances, the Moon is not entirely devoid of colour. Apollo astronauts described its colour as ‘brownish’. Careful study shows that the dark areas, or ‘maria’, display hints of blue or brown while the highland areas have faint traces of yellow, pink and pale blue. These differences are mainly due to varying amounts of metals such as iron or titanium in the surface minerals.
Unfortunately, the human eye isn’t sensitive enough to pick out these slight differences in colour from a distance. However, much of the lunar surface contains minerals that are naturally grey and these dominate the colour we perceive from Earth.
Is the flag still on the Moon?
Asked by: Harriet Fyfe, Falkland Islands
Six flags were planted on the Moon – one for each Apollo landing. Apollo 11’s flag was too close to the lander and was knocked over by the rocket exhaust when Armstrong and Aldrin took off again. But high resolution images from the Lunar Reconnaissance Orbiter show that the other five are still standing. The flags were made of ordinary nylon though, so they have all long since been bleached white by the Sun.
Why is the far side of the Moon so heavily cratered?
Asked by: Colin Gray, by email
It’s often thought that the far side of the Moon is more exposed to incoming impacts, leaving it more battered than the side facing us.
In fact, calculations show both sides have been equally affected. The key difference is the far side has a much thicker crust. This thickness has prevented fresh, molten rock emerging from below to cover as many of its craters.
What if Earth had two moons?
Asked by: Simon Turner, Bridgwater
The consequences of a second moon orbiting the Earth depend on how massive that moon is and how far from the Earth it orbits. The most obvious effect would be that the ocean tides would be altered. Tides could be either smaller or higher and there could be more than two high tides per day. If the gravitational influence of a second moon were extreme, it could lead to phenomenally huge ocean tides (up to a kilometre high) which would also result in frequent tsunamis. It could also lead to enhanced volcanic activity and earthquakes.
What would happen if we blew up the Moon?
The gravitational binding energy of the Moon is 120 million, trillion gigajoules. This means that unless you deliver that much energy in one go, the Moon will just crack apart and reform into a sphere. To blow it up, you’ll need to drill mine shafts hundreds of kilometres deep, all over the Moon, and drop a total of 600 billion of the largest nuclear bombs ever built down them.
Any Moon debris that falls on Earth will only have about 1 per cent of the impact energy of a similar-sized asteroid, because of the lower orbital speed. But smaller stones would still be lethal as they would be so numerous. The kinetic energy of the stones would be absorbed by the atmosphere as they burned up, heating the atmosphere until all life was incinerated.
The remaining debris will spread out into rings around the planet. Without the stabilising tidal drag from a single moon, the Earth’s axial tilt will wobble far more than it does now. Over tens of thousands of years, Earth could tilt all the way past 45°, so that most of one hemisphere faces the Sun continuously, and the other is in perpetual darkness.
How does a laser beam measure the distance to the Moon so accurately?
Asked by: Colin Gray, Castle Cary
In 1969, the Apollo 11 astronauts placed the first of four mirrors on the Moon that reflect back laser beams to reveal the distance to the Earth. The beams travel at the speed of light and their journey times are measured to within a few million-millionths of a second, the distance can be recorded to within a few millimetres.
What would happen if there were no Moon?
Asked by: Derek Palmer, Eton Wick
The most immediate effect (other than the lack of moonlight, of course) would be on the Earth’s tides. With only the Sun’s gravitational influence, the difference between high and low tides would be reduced dramatically – as would tidal drag, which slows the Earth down at a rate adding about 0.002 seconds to the length of a day each century. Long term, the effects would be far more serious.
The climate of the Earth is sensitively dependent on the 23.5° tilt of the Earth’s axis, and without the stabilising presence of our relatively huge Moon, the gravity of the other planets would produce big changes in this angle – as it does with Mars, whose tilt changes by 60° over a few million years.
Image © iStock
Are there really still human footprints on the Moon?
Asked by: Maya Goldsworthy, by email
Yes there are, even though nobody has stepped on the lunar surface since the last Apollo mission in 1972. The footsteps will be there for many years to come too. The Moon is geologically dead so the marks won’t be wiped out by earthquakes or volcanoes. Neither is there any wind to disturb them or rain to erode them.
Why can we only see one side of the Moon?
Asked by: Greg Ganter, California
The time taken for the Moon to spin on its axis is almost exactly the same as the time it takes to orbit the Earth. Hence, the Moon always keeps the same side pointing our way. This is not a coincidence. Over billions of years, the Earth’s gravity has forced the Moon to spin synchronously with its orbit.
However, things are a bit more complicated than that. Viewed from Earth, the Moon appears to rock slowly backwards and forwards so that we see a slightly different face throughout the lunar month. There are two main reasons for this. First, the Moon’s orbit around Earth is elliptical not circular so its rotation is sometimes ahead, and sometimes behind, its orbital motion. And second, the Moon’s rotation axis is not at right angles to its orbit around the Earth so we can sometimes see ‘over’ or ‘under’ its poles. Over time this means we actually get to see about 59 per cent of the Moon’s surface.
Why are solar eclipses rarer than lunar eclipses?
Asked by: Liza Dennis, Brighton
Solar eclipses are not actually rarer than lunar eclipses – in fact, they occur in about equal numbers, usually about two of each per year.
For example, between 2000BC to 3000AD there will be 11,898 solar eclipses and 12,064 lunar eclipses. However, at any one location on Earth, it is much less common to see a solar eclipse than a lunar one. And the reason for this is entirely due to geometry.
A lunar eclipse, when the Moon moves through the shadow of the Earth, is visible from wherever the Moon is above the horizon, which is over half of the Earth. However, when the Moon appears to move in front of the Sun during a solar eclipse, the shadow cast by the Moon is much smaller than Earth. It’s only about 480km (300 miles) wide when cast onto the Earth’s surface.
Solar eclipses are therefore only visible from within a narrow path across the Earth, making it difficult to get to a location to see one. This is why they are visible less often from any given location.
Image © Alamy
Can a moon have a moon?
Asked by: Ceri Rideout, Ammanford
Astronomers are pretty certain there are no moons orbiting moons in our Solar System. Although possible, it is likely that the gravitational tug of the parent planet would quickly destabilise the orbit of the moon’s moon, eventually pulling it out of its orbit. However if the moon’s moon is small, the distance to the parent planet is large, and there are negligible tidal forces, then such a system could exist.
Image © iStock
If you could drive a car upwards at 60mph, how long would it take to get to the Moon?
Asked by: Matt B, Glastonbury
Astronomer Fred Hoyle was the first to point out that if you could drive a car upwards at 95km/h (60mph), it would only take about an hour to get into space. To get to the Moon would take a little longer though, since it's 400,000km (250,000 miles) away - around 10 times the circumference of the Earth. So it would take as long as driving around the world 10 times - just under six months. Your only real problem (apart from the lack of air for your lungs and for burning the petrol) would be finding a garage to refuel - and that has a loo!
Could an asteroid impact push the Moon closer to us?
Asked by: Rob Harper, London
The Moon is very big, and any small object hitting it would have very little effect on its motion around the Earth, because the Moon’s own momentum would overwhelm that of the impact. Most asteroid collisions would result in large craters and little else; even the largest asteroid known, Ceres, wouldn’t budge the Moon.
However, if an object of similar mass and velocity to the Moon were to hit it, the Moon’s orbit could well be altered, though it’s more likely the Moon would be destroyed by such an impact. If the Moon were to orbit closer to Earth we would experience much larger tides, along with longer and more frequent solar eclipses.
Image © iStock
How often do large meteorites hit the Moon?
Asked by: Jenny Smith, Peterborough
The Moon is constantly being bombarded with meteorites, but most of them are no bigger than specks of dust. Larger impacts have been observed regularly over the years. In February 2014, Spanish astronomers recorded the impact of a meteorite weighing about 400kg. It was travelling at about 64,374km/h (40,000mph) and probably resulted in a crater 40m wide. Just six months earlier a NASA telescope spotted the impact of a 40kg object. However, the actual yearly rate of these impacts is unclear because astronomers have not yet observed enough of them.
Image © iStock
How long will the man-made objects on the Moon last?
Asked by: Steve Cameron, by email
It has been estimated that there are more than 180 tonnes of man-made material on the Moon, ranging from bags of human body waste to crashed spacecraft. But there is very little to affect this material – no wind, pollution or water to erode, rust, dissolve or abrade it – although the action of sunlight, particularly UV radiation, has probably already bleached the US flags left there by the Apollo astronauts. While the constant bombardment by energetic micrometeorites is likely to gradually erode this material over time, current research suggests it could survive for up to 100 million years!
Image © NASA
Why is the Moon moving away from us?
The famous English astronomer Edmond Halley first suspected the Moon was receding nearly 300 years ago, after studying records of ancient eclipses. His suspicions were finally confirmed in the 1970s, when laser beams bounced off mirrors put on the Moon by US and Soviet missions showed that it is moving away at the rate of 3.8cm per year.
It’s driven by the effect of the Moon’s gravity on the rotating Earth. Tides raised in the oceans cause drag and thus slow the Earth’s spin-rate. The resulting loss of angular momentum is compensated for by the Moon speeding up, and thus moving further away.
At least, that’s the basic idea, but there’s a problem. At the current rate of recession, the Moon must have separated from the Earth just 1.5 billion years ago – far more recently than geological evidence suggests.
Creationists have used this to question the standard scientific account of the origin of the Earth and Moon. However, astronomers point out that the recession rate will have been slower in the past because of continental drift, which altered the size and depth of the oceans and thus the amount of tidal drag. Taking this into account pushes the date of separation back by several billion years – in line with the geological evidence.
Image © NASA
Why is there poo on the Moon?
The Apollo landers were designed to lift off from the lunar surface at a particular weight. Since the Apollo astronauts were charged with bringing large amounts of Moon rock back home, the weight of those samples was offset by leaving behind unwanted items. This discarded junk included, among other things, two golf balls, 12 cameras, 12 pairs of boots, a gold-plated telescope, and a total of 96 bags of ‘human waste’ – urine, faeces and vomit!
Although not the best example of green thinking, this detritus will have had no permanent effect on the lunar environment. Any microorganisms present in the human waste could not have grown under the harsh conditions of the lunar surface. It is possible, however, that some could have survived for a time as dormant, inactive spores. So, after 50 years on the lunar surface the human waste, which is now probably just bags of dust, may contain important information on the survival of microorganisms in space.
Astrobiologists would like to see if any of those microorganisms have undergone any genetic mutations due to the harsh lunar environment, or have indeed survived in a dormant state. They hope one day that private companies may eventually return this human waste for study!
How did the Moon form?
One possibility is that the Moon was originally an independent dwarf planet that was captured by Earth’s gravity. Mars is thought to have snagged its two moons, Phobos and Deimos, this way.
Alternatively, the Moon and Earth could have formed together, from the same dust and gas. This is more consistent with the Moon’s orbit but it doesn’t explain why it is much less dense than Earth.
But the theory currently preferred by astronomers is that a Mars-sized planet, called Theia, collided with Earth 4.5 billion years ago. The Moon was formed from the lighter crustal elements that were blasted into space by the impact, leaving Earth’s denser core behind.
Image © iStock
What time is it on the Moon?
Asked by: Sam Gormley, via Twitter
Fundamentally, and ignoring the complications of Einstein’s Special Relativity, it’s the same time as it is here on Earth. But this is a bit of a cheat, of course, because we haven’t defined how we are measuring time.
There are many ways to define the ‘time’ at a particular location. Here on Earth our usual system (‘solar time’) is defined by the motion of the Sun in the sky (although we usually keep track of time with an atomic clock). This means that the local time depends on where you are on Earth and we get around this complication by having many different time zones.
Now, we could also define a similar time system based on the motion of the Sun as seen from the Moon. Such a system exists (Lunar Standard Time) but it is not much more than an interesting exercise in physics.
What is more useful, however, is a definition of time that doesn’t vary with location. This is called Universal Time (UT) and is a modern form of Greenwich Mean Time. It is the same everywhere in the Universe. So, the UT time on the Moon is the same as the UT time on Earth.
Has Earth ever had more than one moon?
Asked by: Richard Ward, Lutterworth
No observations or theoretical claims for additional moons of the Earth have ever been substantiated. However, some astronomers have speculated that there may have been a companion moon very early in Earth’s history. An impact with this ‘other’ moon may help explain how the Moon’s nearside is low and flat and is dominated by volcanic maria (or ‘seas’), whereas the far side is mountainous and deeply cratered. It can also explain the distribution of certain chemical elements on the Moon. However, other processes can also account for these observations, so the ‘other moon’ idea is still hypothetical.
The Earth does, however, have some very small satellites that could be classed as moons. In 2006 a tiny asteroid, 2006 RH120, was discovered in Earth’s orbit. This ‘captured’ object remained in Earth orbit for 13 months before returning to a solar orbit. These ‘temporary’ moons are thought to be quite common.
Is it coincidental that the human menstrual cycle is about the same length as the Moon cycle?
Asked by: Alex Sutherland, Banffshire
Charles Darwin thought that the 28-day human menstrual cycle was evidence that our ancestors lived on the seashore and needed to synchronise with the tides. The Moon’s phase certainly has an effect on the behaviour of many animals. Fiddler crabs are more active at full and new Moons because the tides are higher, so their burrows are uncovered for longer. Gerbils avoid foraging at night during a full Moon, because the extra light makes them more likely to be eaten by owls. But the human menstrual cycle is only the same length as the lunar month – it isn’t synchronised with a particular phase.
One frequently cited study, published in the American Journal Of Obstetrics And Gynecologyin 1980, found some evidence of synchronisation, but the effect was very weak. Of the sample of 312 women, 244 had cycles that were longer than 29 days or shorter than 27, and only 70 per cent of the rest actually started their period within two weeks of the full Moon.
If locking our reproductive cycle to the lunar month was advantageous, you might expect other animals to do the same. Orangutans and possums have 28-day cycles, but our closest relatives, the chimpanzees, have 35-day cycles. Non-primate mammals have an oestrous cycle, which works differently to menstruation, but none of them synchronise their reproduction with the phases of the Moon.
What size Moon structure could we see from Earth?
Asked by: David McLellan, Glasgow
The average human eye has a resolving power of around 1/60th of a degree, meaning that under good conditions it can see objects at distances up to roughly 3500 times the size of the object. The Moon being around 380,000km away, means that under ideal conditions we should be able to see objects around 100km across.
Why doesn’t our moon have a name?
Astronomical objects acquire their names either via long-standing tradition, or through being named by their discoverers. Of all the satellites of the planets, the Moon has the distinction of being the only one known since the dawn of history, and so has no discoverer as such. It has thus retained its traditional name of ‘the Moon’, befitting its unique status.
How far apart are the Sun, Moon and Earth during eclipses?
Asked by: Ashley Martin, Chawton
It depends on the type of eclipse. During a total eclipse of the Sun, the Moon covers the whole solar disc, and to do this the Sun has to be around 400 times further from the Moon than the Moon is from the Earth. If the ratio is smaller, the Moon no longer completely covers the solar disc, and so produces an annular eclipse, which features a ring of light around the Sun.
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