That's not a silvery mirror in the night sky, and there's a reason why the sea isn't even saltier. Plus, can soaking in a hot bath affect male fertility, and how spinning electrons cook your dinner
*Q How does the moon shine; what causes the reflection and how? *asks Manish Kunwar
A As Professor Manuel Grande from Aberystwyth University explains, the moon isn't simply a silvery mirror. "It's very hard to get a surface which is either completely white or completely black," he says. "Actually the moon is pretty black. In visible light it reflects about 12%. But there's an awful lot of sunlight falling on it, so it looks quite bright."
And the reflections can cause difficulties. "When we built our X-ray spectrometer for SMART-1, the first European moon mission, we actually had a lot of trouble keeping this reflected sunlight out of the instrument." In fact, he says: "In low moon orbit, the amount of light is not so different to what you see from a plane on Earth if you're flying over a desert."
But what is the moon actually made of? "Most of the surface is made of either anorthosite (a type of feldspar) – the light, silver-coloured material you see towards the edges of the disk – or else basalt [which forms] the dark areas: seas or maria. The ilmenite (titanium-rich) areas are particularly black," he says.
*Q Why did the salt content of the oceans remain nearly constant over millions of years despite the fact that rivers carry huge amounts of salt into the sea? *asks Thoralf Schubert
A Levels of rainfall, evaporation and melting sea ice all affect the salinity of seawater by adding or removing water, but the total amount of salt in the ocean remains pretty much constant. When rain (which is slightly acidic) falls, it washes over land, weathering and eroding rocks and carrying off salts, chiefly calcium carbonate and silicates, into streams which wend their way to the seas. Chloride ions are not a major component of river water; it is thought that they ended up in the oceans as a result of volcanic processes which occurred in the early history of the planet.
At first glance, it seems like a one-way street. However, the salt content of the oceans is not continuously increasing. Instead, a "steady-state condition" exists, meaning that the input of salts into the oceans pretty much balances the output.
These depend on the type of salt. Calcium and carbonate ions, for example, are used by marine creatures such as crustaceans to make their shells. After they die, the shells form sediments on the ocean floor and eventually result in the formation of limestone.
Salts can also be locked up in clays at the bottom of the ocean, while regions around hydrothermal vents on the ocean floor can both spew salts into the water and remove them.
Although calcium and carbonate ions are part of a relatively rapid cycle, sodium and chloride ions hang about in the oceans for millions of years, but can form solid deposits (usually in enclosed seas) if enough water is evaporated.
Furthermore, when seawater crashes over coasts (which has happened a lot this year), some of it settles on the land, leaving salt residues.
*Q Does taking a hot bath affect male fertility? *asks Chris Davies
A Taking a long soak in a hot bath might seem heavenly, but as Dr Allan Pacey from the University of Sheffield points out, the body is carefully designed to keep certain areas cool. "The sperm production process requires testicles to be a few degrees cooler than body temperature. This is why they hang outside the body," he says. "So theoretically, anything that increases the temperature of the testicles for any length of time might hinder sperm production and therefore reduce male fertility."
But it isn't only the hot tub that has been suspected of causing problems: "Previous reports have suggested that spending too long in a bath or saunas or using a working laptop on your lap might raise testicular temperature sufficiently to do this. However, undertaking definitive studies is difficult because men often undertake a range of activities that might affect their testicles."
One such factor is a chap's choice of trousers. "In a recent multicentre study, researchers at the universities of Sheffield and Manchester found that wearing loose pants was linked with better sperm quality," says Pacey. "Therefore, it might be concluded that wearing restrictive underwear or spending too long in a hot bath might harm sperm production. But that exact study has never been done."
*Q How does a microwave oven work? And is it safe to stand near it? *asks mathsdude
A A microwave oven uses electromagnetic radiation (essentially high frequency radio waves) to heat up food. These microwaves are produced by a nifty device called a magnetron, which contains a metal filament that heats up and emits electrons. The electrons are spun around by a magnet and in the process cause the radiation of microwaves, which are then directed towards the cooking chamber. When the oven is turned on, the food inside heats up.
But, you'll notice, only the food gets hot – the dish it sits on remains cold. This is because the microwaves energise only water molecules and your food is packed with water. Why water? Well, a water molecule is polar; it has a positively charged region and a negatively charged region, meaning that it can interact with an electric field.
To understand how this works, first think of a person holding the end of a rope that is attached to a wall and waggling it up and down. You'd see that the rope flips between peaks and troughs at specific locations while other points in the rope don't appear to move at all. This is called a "standing wave".
Inside the microwave oven, the metal walls reflect the electromagnetic radiation and, like the rope-wagglers, create standing waves. Within the cooking chamber, the peaks and troughs of the electric and magnetic fields are flipping more than two billion times a second. The polar water molecules interact with the electric field and, as it flips, they rotate to change their orientation. This generates friction and hence heat and it is this heat that cooks the food.
A turntable is needed to make sure that the food is heated evenly, otherwise the standing waves would result in hot spots at the peaks and troughs of the electric field and cold spots at the points midway between. One bonus of using a microwave oven is that microwaves penetrate into the food, meaning your meal is rapidly heated right the way through. Contrast this to heating your dinner up on the hob; there, heat is transferred through a laborious game of pass-the-parcel from the outside to the centre.
And there is no need to fear a microwave oven. The door is made of glass with a mesh that reflects the microwaves back into the chamber and prevents the radiation escaping.
Keep the questions coming by emailing science.questions@observer.co.uk. Please include your full name and where you live Reported by guardian.co.uk 9 hours ago.
*Q How does the moon shine; what causes the reflection and how? *asks Manish Kunwar
A As Professor Manuel Grande from Aberystwyth University explains, the moon isn't simply a silvery mirror. "It's very hard to get a surface which is either completely white or completely black," he says. "Actually the moon is pretty black. In visible light it reflects about 12%. But there's an awful lot of sunlight falling on it, so it looks quite bright."
And the reflections can cause difficulties. "When we built our X-ray spectrometer for SMART-1, the first European moon mission, we actually had a lot of trouble keeping this reflected sunlight out of the instrument." In fact, he says: "In low moon orbit, the amount of light is not so different to what you see from a plane on Earth if you're flying over a desert."
But what is the moon actually made of? "Most of the surface is made of either anorthosite (a type of feldspar) – the light, silver-coloured material you see towards the edges of the disk – or else basalt [which forms] the dark areas: seas or maria. The ilmenite (titanium-rich) areas are particularly black," he says.
*Q Why did the salt content of the oceans remain nearly constant over millions of years despite the fact that rivers carry huge amounts of salt into the sea? *asks Thoralf Schubert
A Levels of rainfall, evaporation and melting sea ice all affect the salinity of seawater by adding or removing water, but the total amount of salt in the ocean remains pretty much constant. When rain (which is slightly acidic) falls, it washes over land, weathering and eroding rocks and carrying off salts, chiefly calcium carbonate and silicates, into streams which wend their way to the seas. Chloride ions are not a major component of river water; it is thought that they ended up in the oceans as a result of volcanic processes which occurred in the early history of the planet.
At first glance, it seems like a one-way street. However, the salt content of the oceans is not continuously increasing. Instead, a "steady-state condition" exists, meaning that the input of salts into the oceans pretty much balances the output.
These depend on the type of salt. Calcium and carbonate ions, for example, are used by marine creatures such as crustaceans to make their shells. After they die, the shells form sediments on the ocean floor and eventually result in the formation of limestone.
Salts can also be locked up in clays at the bottom of the ocean, while regions around hydrothermal vents on the ocean floor can both spew salts into the water and remove them.
Although calcium and carbonate ions are part of a relatively rapid cycle, sodium and chloride ions hang about in the oceans for millions of years, but can form solid deposits (usually in enclosed seas) if enough water is evaporated.
Furthermore, when seawater crashes over coasts (which has happened a lot this year), some of it settles on the land, leaving salt residues.
*Q Does taking a hot bath affect male fertility? *asks Chris Davies
A Taking a long soak in a hot bath might seem heavenly, but as Dr Allan Pacey from the University of Sheffield points out, the body is carefully designed to keep certain areas cool. "The sperm production process requires testicles to be a few degrees cooler than body temperature. This is why they hang outside the body," he says. "So theoretically, anything that increases the temperature of the testicles for any length of time might hinder sperm production and therefore reduce male fertility."
But it isn't only the hot tub that has been suspected of causing problems: "Previous reports have suggested that spending too long in a bath or saunas or using a working laptop on your lap might raise testicular temperature sufficiently to do this. However, undertaking definitive studies is difficult because men often undertake a range of activities that might affect their testicles."
One such factor is a chap's choice of trousers. "In a recent multicentre study, researchers at the universities of Sheffield and Manchester found that wearing loose pants was linked with better sperm quality," says Pacey. "Therefore, it might be concluded that wearing restrictive underwear or spending too long in a hot bath might harm sperm production. But that exact study has never been done."
*Q How does a microwave oven work? And is it safe to stand near it? *asks mathsdude
A A microwave oven uses electromagnetic radiation (essentially high frequency radio waves) to heat up food. These microwaves are produced by a nifty device called a magnetron, which contains a metal filament that heats up and emits electrons. The electrons are spun around by a magnet and in the process cause the radiation of microwaves, which are then directed towards the cooking chamber. When the oven is turned on, the food inside heats up.
But, you'll notice, only the food gets hot – the dish it sits on remains cold. This is because the microwaves energise only water molecules and your food is packed with water. Why water? Well, a water molecule is polar; it has a positively charged region and a negatively charged region, meaning that it can interact with an electric field.
To understand how this works, first think of a person holding the end of a rope that is attached to a wall and waggling it up and down. You'd see that the rope flips between peaks and troughs at specific locations while other points in the rope don't appear to move at all. This is called a "standing wave".
Inside the microwave oven, the metal walls reflect the electromagnetic radiation and, like the rope-wagglers, create standing waves. Within the cooking chamber, the peaks and troughs of the electric and magnetic fields are flipping more than two billion times a second. The polar water molecules interact with the electric field and, as it flips, they rotate to change their orientation. This generates friction and hence heat and it is this heat that cooks the food.
A turntable is needed to make sure that the food is heated evenly, otherwise the standing waves would result in hot spots at the peaks and troughs of the electric field and cold spots at the points midway between. One bonus of using a microwave oven is that microwaves penetrate into the food, meaning your meal is rapidly heated right the way through. Contrast this to heating your dinner up on the hob; there, heat is transferred through a laborious game of pass-the-parcel from the outside to the centre.
And there is no need to fear a microwave oven. The door is made of glass with a mesh that reflects the microwaves back into the chamber and prevents the radiation escaping.
Keep the questions coming by emailing science.questions@observer.co.uk. Please include your full name and where you live Reported by guardian.co.uk 9 hours ago.