Ask mr Brain..all will be explained

PUBLISHED : Friday, 13 August, 1999, 12:00am
UPDATED : Friday, 13 August, 1999, 12:00am

Why do aircraft have to fly above altitudes of 10,000 metres? Is it not safer to stay at a lower altitude? No, it is actually the opposite. Below 10,000 metres, air currents fall and rise. Thunder and lightning also take place in this layer of the atmosphere.

If aircraft fly in this area, they will be affected by the upwards and downwards air currents and will have difficulty maintaining stability during flight. They may also be hit by thunder and lightning.

There is also more moisture in the air below 10,000 metres and frost may form on the aircraft.

Above 10,000 metres, air currents are more stable and there is less going on. The air is thinner and there is less water vapour, so frost will not easily form on the aircraft's body.

What is Halley's comet? When will we see it again? In 1705, Edmund Halley used Isaac Newton's newly formulated laws of motion and predicted that the comet seen in 1531, 1607 and 1682 would return in 1758 (unfortunately, after his death).

The comet did indeed return as he predicted and was later named in his honour.

The comet travels around the sun in an elliptical orbit. It travels to the outermost reaches of our solar system before swinging around the sun. As it comes near the sun, its nucleus, a huge ball of ice and dust, is heated and releases dust and vaporised gases. These form the fan-like tail seen in the sky during the comet's visit.

Halley's nucleus is about 16 kilometres by eight kilometres by eight kilometres and is very dark. The density of the nucleus is very low, indicating it is probably porous, maybe because it is largely dust re maining after the ice has vaporised. The average period of Halley's orbit is 76 years but you cannot calculate the exact date of its reappearance by simply adding 76 years to 1986, the last time it was visible from earth.

The gravitational pull of the larger planets alters the orbital period from revolution to revolution. Non- gravitational effects, such as the reaction from gases boiled off during its passage near the sun, also play a role in altering the orbit.

Halley is almost unique among comets in that it is both large and active and has a well-defined, regular orbit. It will return to the inner solar system in the year 2061.

How long is the longest snake in the world? The longest snake in the world is the reticulated python, which measures about 10.7 metres.

The second longest is the green anaconda, which is about 8.5 metres long. The green anaconda is also the heaviest snake, weighing in at 227 kilograms.

Lengthwise, it is followed by the Indian python, diamond python and king cobra.

The most deadly snake is the taipan, followed by black mamba and tiger snake, with a mortality rate of 100 per cent without prompt anti- venom treatment.

The shortest snake in the world is the thread snake, at about 11.5 centimetres long. The oldest snake is a male boa constrictor, which is 40 years old.