Beneath the Earth flows molten rock known as magma. When a volcano erupts, the resulting explosion shoots this magma out into the atmosphere. At this point the magma becomes known as lava. There is no major difference between magma and lava; the terms merely distinguish whether the molten rock is beneath or above the surface. Caused by gas pressure under the surface of the Earth, a giant volcanic eruption can be incredibly powerful with lava shooting up to 600 metres (2,000 feet) into the air.

Lava can reach temperatures of 700-1,200°C (1,300-2,200°F) and varies in colour from bright orange to brownish red, hottest to coldest, respectively. This viscous liquid can range from the consistency of syrup to extremely stiff, with little or no flow apparent. This is regulated by the amount of silica in the lava, with higher levels of the mineral resulting in a higher viscosity. When lava eventually cools and solidifies it forms igneous rock.

Inside lava are volcanic gases in the form of bubbles, which develop underground inside the magma. When the lava erupts from inside the volcano, it is full of a slush of crystalline minerals (such as olivine). Upon exposure to air the liquid freezes and forms volcanic glass. Different types of lava have different chemical compositions, but most have a high percentage of silicon and oxygen in addition to smaller amounts of elements such as magnesium, calcium and iron.

Did you know?
Explosives have been suggested as a means of stopping lava flows since 1881 and have had varying degrees of success. In 1935 and 1942 the US Air Force was unsuccessful in stopping a lava fl ow in Hawaii by dropping bombs on it, but the tactic was partially successful in 1975 and 1976.

Jelly is a soft semisolid containing gelatine (or gelatin). Gelatine is processed from the protein collagen found in skin and bones, so we wouldn’t advise eating jelly if you’re a vegetarian. The molecules in gelatine are intertwined in a triple helix. As they are mixed with hot water their bonds break, unravelling and becoming long stretchy wiggly lines. As the water cools down, the helices start to reform and cross-linking occurs. This creates supermolecules that are so long they span across the whole jelly in a three-dimensional web, and water gets trapped in the spaces giving jelly its wobble.

Dwaine Anthony Clarke, Science Museum

Traditional thermometers contained mercury, which expands with rising temperatures. But most households have digital thermometers now because they’re safer, easier to read, and work faster. Digital thermometers contain an electric resistor, also known as a thermistor, which is temperature-sensitive. When the temperature rises, the thermistor becomes more conductive. This happens at about 37°C (99°F). A microcomputer pinpoints the temperature by measuring the conductivity, and displays it on an LCD screen.

Originally, Anders Celsius pegged his scale with the boiling point of water at 100 degrees and the freezing point of water at 0 degrees, based on the water’s behaviour under pressure, but Carl Linnaeus swapped these after his death. Daniel Gabriel Fahrenheit first based his scale on three states of brine: stable, freezing and boiling. Later his scale was adjusted so there were 180 intervals between the freezing point of water (32°F) and boiling point of water (212°F). The scales intersect at -40 degrees.

Today, the majority of sunless tanning lotions, mousses, sprays and gels contain a safe sugar molecule called dihydroxyacetone (DHA), which darkens skin tone with no side effects.

The concentration of the DHA determines the darkness of the fake tan. DHA reacts with the amino acids present in dead cells on the surface of the skin to alter their colour, producing a yellow/brown tanned appearance. The colour doesn’t come through straight away, however; it develops over a number of hours and often keeps getting darker for 24 hours. Further application of the tanning lotion over a number of days will create a darker tone. Because the tan only affects the already-dead surface skin cells, the colour will of course fade and wear off as the skin is eventually shed.

Asked by Leia Smith

Tungsten (often referred to as wolfram in other parts of the world) has the highest melting point of any metal. Extracted from wolframite, scheelite and other minerals, it is a grey-white metallic element and is incredibly dense and extremely hard. In fact, it is the second hardest material (only beaten by diamond), has a greater density than lead, and does not break down or decompose, meaning it is environmentally friendly. This range of properties means that tungsten is used in many industries and products, from high-speed cutting tools and jet turbine engines, to shotgun ammunition and fishing weights.

Nathaniel Marten, Science Museum

Bigger isn’t better

The larger the star, the shorter its life. Although bigger stars have more fuel, they have to quickly consume it through nuclear fusion to maintain hydrostatic equilibrium.

The same, but different

All stars are made from hydrogen and helium, and they all started out with the same proportions – they contain about 1/4 helium and 3/4 hydrogen.

More red dwarfs

The vast majority of stars are red dwarfs, which can have masses as low as seven per cent t hat of the Sun’s mass. They can burn for no less than 10 trillion years.

Not yellow dwarfs

The name ‘yellow dwarf’ is a misnomer: these can range from white to yellow. The Sun is white, but it appears yellow due to the scattering of light in our atmosphere.

Second best

The brightest star in our sky aside from the Sun is Sirius, which is actually a binary star system about 8.6 light years away from Earth.

Asked by Daniel Price

It wouldn’t be correct to say fire is a gas, but it is mainly made of a mixture of bright hot gases. There’s obviously other stuff to be found there, such as soot. Let’s imagine igniting a pool of petrol. The flame is always above the surface. Some flammable gas is constantly evaporating from the liquid. An initial heat source such as a match provides the energy needed to start the reaction with the oxygen in the air. The heat generated will supply the energy to keep it going and evaporate even more petrol from the liquid. That is the job of the wick in a candle: as the wax melts, it is absorbed by the wick and turns into a gas with the high temperatures.

If we describe the way a flame behaves, we obviously have to say it does so as a gas. Liquids have fixed volume and because molecules in liquids stick together, they are always quite dense compared with the gases in the air. Simply speaking, liquids fall down to the ground as soon as the drops are big enough.

José Monteiro, Science Museum

While a surface temperature of 462°C, Venus is definitely not the ideal holiday destination. Its unique climate contribute to the most powerful greenhouse effect in the solar system, with an atmospheric pressure ago the planet was much like Earth, with a significantly lower temperature and vast oceans of water. However, its proximity to the Sun meant this liquid water evaporated into the atmosphere. This in turn sublimated carbon in rocks and mixed with the oxygen in the atmosphere to form carbon dioxide, which no accounts for about 95% of the atmosphere.

This is known as a ‘runaway greenhouse effect’, as the creation of more carbon dioxide in the atmosphere released more carbon from the ground, repeating the process. Only 10% of incoming solar radiation reaches the surface, but almost all of this stays trapped inside the atmosphere, giving rise to a temperature difference of almost 500°C between the surface and the cloud layer.

Travelling at 38,000 mph, the Voyager 1 probe was launched on 5 September 1977 with the intention of studying Jupiter, Saturn, Uranus and Neptune. Now, 33 years later and almost 11 billion miles from home, it is going where no Earth object has gone before.

Both Voyager probes are approaching the interstellar medium, with Voyager 1 further ahead than its sister ship Voyager 2 (which is travelling at 35,000 mph). It is here that the nature of the environment is expected to dramatically alter.

Dispatched towards deep space, the Voyager probes have functioned far beyond expectations, with their radioactive power packs continuing to work and send data back to Earth, although at such a distance away any radio message takes 16 hours to reach us.

Speaking to the BBC, Edward Stone, the Voyager project scientist, said: “When Voyager was launched, the space age itself was only 20 years old, so there was no basis to know that spacecraft could last so long. We had no idea how far we would have to travel to get outside the Solar System. We now know that in roughly five years, we should be outside for the first time.”

Our solar system is contained inside an area of space known as the heliosphere. Up to the heliosheath our Sun exerts a magnetic and energetic influence, with its solar wind extending to all corners of the system. Upon reaching the heliosheath, the solar wind slows considerably and begins to heat up as it reaches a shockwave known as the termination shock.

Voyager 1 crossed the termination shock in December 2004. Using data from its Low-Energy Charged Particle Instrument, the velocity of the surrounding solar wind has been constantly measured.

At the edge of the heliosphere is the heliopause, where the Sun’s influence is less apparent. It is here that Voyager 1 – and later Voyager 2 – will enter the interstellar medium, the matter between stars in our galaxy.

It is theorised that at this distance from the Sun, over 11 billion miles, the velocity of particles emitted by the Sun will slow to zero. Although it is not quite there yet, once Voyager 1 reaches interstellar space there should be a sudden drop in the density of hot particles and an increase in that of cold particles. The success of the Voyager probes so far has markedly increased our understanding inside our solar system, and its continuing journey will give us unprecedented information on the outside as well.

When things heat up they expand. The yolk of an egg contains lots of water, and this starts to expand upon getting hot. In boiling water this is fine, but in a microwave the yolk can reach temperatures so high that the water vaporises. Eggs have a shell and within that there is also a membrane. If the pressure of the rapidly heating yolk exceeds the breaking pressure of the shell and membrane, the egg will explode.

Rik Sargent, Science Museum