Why do bright rings form around the Sun? (QUESTIONS)

The rings around the Sun are known as haloes. The bright, circular bows form when sunlight is refracted by millions of tiny ice crystals high up in the atmosphere. The ice crystals are often hexagonal or plate or pen-shaped and generally occur in association with high-flying cirrus clouds. The crystals function as small prisms, which bend the sunlight at specific angles. It is quite common to observe a 22 degree halo in the sky, and it is not uncommon to see two bright spots at the edge of the ring – they are known as sun dogs. On the other hand, it is more rare to experience a 46 degree halo appear further away from the Sun, and very rare to see a 9 degree halo occur in a ring close to the Sun. These haloes are only produced, when sunlight is refracted by pyramid-shaped ice crystals. Haloes often occur in the winter, when it is cold, and the Sun is low in the sky. They can also be observed around the Moon, in which case hexagonal ice crystals in thin cirrus clouds cause the phenomenon.

Can a helicopter loop-the-loop? (QUESTIONS)

It is physically possible to make a helicopter loop. But the trick requires very special conditions. First of all, only a skilled, experienced pilot can make the manoeuvre – in “Spectre”, this is done by helicopter acrobat Chuck Aaron. Secondly, the pilot must fly a helicopter which is equipped with an inflexible main rotor, whose rotor blades are hingeless. An inflexible main rotor is designed to tolerate an extra load on its blades, and it makes sure that the helicopter behaves in a predictable fashion during a loop. Ordinary helicopter rotors feature several hinges between blade and hub. A vertical hinge allows the blade to give in a little to the wind, whereas a horizontal hinge allows the blade to move slightly up and down. If the rotor blades are slightly flexible, the pilot can neutralise the difference in lift she experiences during the flight. When the helicopter is in the air, the rotor blade that moves forwards in the flight direc-tion is affected by more lift than the rotor blade on the opposite side, which moves backwards in comparison with the flight direction. In an ordinary, flexible rotor, the difference is adjusted with hinges.

Is Pluto a planet or a dwarf planet? (QUESTIONS)

In 1930, when Pluto was discovered, the new world was proclaimed the ninth planet of the Solar System. In 2006, astronomers revised the definition of a planet, making Pluto a dwarf planet. However, some scientists still insist that Pluto is a planet.

Where does it rain the most? (QUESTIONS)

The village of Mawsynram in the Indian state of Meghalaya is the wettest place in the world – especially during the monsoon. The name means "the abode of clouds", and the average annual rainfall is 11.873 mm.

How are holes in stones created? (QUESTIONS)

Stones with holes appear if some parts of a stone are softer than others. Soft areas wear away faster, as the stone is affected by the wind and weather or by ocean currents and waves. In stones from sediments, such as sandstone and limestone, the holes often reflect some kind of biological activity – a worm may have gnawed through the sediment, leaving a hole that was subsequently filled by a softer material. In stones from magma, holes typically form where the softest mineral grains were located. On the beach, you can find stones with holes including many small perforations and larger, harder ones with only one hole.