Thursday, February 21, 2008
Friday, February 8, 2008
Jean-Pierre Houdin said the 4,500-year-old pyramid, just outside Cairo, was built using an inner ramp to lift the massive stones into place.
Other theories contend that the three million stones - each 2.5 tons - were pushed into place using external ramps.
Mr Houdin studied the problem for eight years and used a computer model to illustrate how he thought it was done.
"This is better than the other theories, because it is the only theory that works," said Mr Houdin as he unveiled his theory with a 3D computer simulation.
He believes workers used an outer ramp to build the first 43 metres (47 yards) then constructed an inner ramp to carry stones to the apex of the 137m pyramid.
The pyramid was built to house the tomb of Pharaoh Khufu, also known as Cheops.
The Grand Gallery inside the pyramid, another source of mystery for Egyptologists, housed a giant counter-weight used to hoist five 60 ton granite beams into position above the King's Chamber.
"I've been teaching them myself for 20 years but deep down I know they're wrong."
Mr Houdin said that an outer ramp all the way to the top of the pyramid would have blocked sight lines and left little room to work, while a long, frontal ramp would have used up too much stone.
Further confusing matters, there is little evidence left of external ramps at the site of the Great Pyramid.
Mr Houdin said the pyramid could have been built by 4,000 people using his technique instead of 100,000, as postulated by other theorists.The architect is now assembling a team to verify his theory on site using radars and other non-invasive means.
Tuesday, February 5, 2008
The reptiles change colour for a variety of purposes - communication, camouflage and temperature control.
However, the reason why they first evolved this ability to flash bright colours was previously unclear.
Scientists report in the journal Plos Biology that it was to allow them to signal to other chameleons.
Co-author Dr Devi Stuart-Fox, from The University of Melbourne, Australia, told BBC News: "[Our research] suggests that chameleons evolved colour change for signalling, to fend off rivals or attract a mate, and not so they could match a greater variety of backgrounds."
Dr Stuart-Fox's team looked at the colour changing ability of 21 southern African dwarf chameleon species (Bradypodion spp), to compare species colour changing ability and consider evolutionary relationships.
As chameleons have a different visual system to humans, they have a fourth type of cone which is ultra-violet (UV) sensitive, the researchers had to first measure what the chameleons were actually seeing.
The Melbourne-based researcher explained: "We measured colour with a spectrometer, which measures both the UV and visual colour range, and combined this with information on the chameleon visual system to model chameleon colour perception.
By setting individual chameleons up in a duel with a series of opponents, the colour range between the submissive and dominant colours could be measured.
"If a male is challenged by another male they both begin by showing their brightest colours - until one figures out the other is going to win and changes to a submissive, dark, 'don't beat me up colour'," said Dr Stuart-Fox.
The team also looked at how chameleons change colour in response to a predator, by presenting them with a model bird or snake.
It was shown that the most dramatic colour changes were used to socially signal to other chameleons."We found that chameleon species that changed colour the most had displays that were most conspicuous to other chameleons. But they didn't have a greater range of background colours in their habitats
Saturday, February 2, 2008
There was no chance of it hitting the planet, but astronomers trained telescopes and radar on the object to learn as much about it as they can.
The asteroid - which carries the rather dull designation 2007 TU24 - passed by at a distance of 538,000km (334,000 miles), just outside Moon's orbit.
Scientists who study so-called near-Earth objects say similar-sized rocks come by every few years.
The moment of closest approach for 2007 TU24 is 0833 GMT. The asteroid is only expected to be visible through amateur telescopes that are three inches (7.6cm) or larger.
Detailed observations of 2007 TU24 could reveal whether the asteroid is a solid object or simply a loose pile of space rubble.
Knowledge of how asteroids are put together will be key to working out how we might defend ourselves against future, more threatening rocks.
An explosive attack - so popular with Hollywood scriptwriters - may not be the most effective approach. Many scientists believe that giving a hostile object a gentle nudge over a long period of time may in fact be our best strategy.
Given the estimated number of near-Earth asteroids of this size (about 7,000 discovered and undiscovered objects, says the US space agency), an object similar to 2007 TU24 would be expected to pass this close to Earth, on average, about every five years or so.
The average interval between actual Earth impacts for an object of this size would be about 37,000 years, Nasa adds.
A little over a year-and-a-half ago, a 600m-wide (2,000ft) asteroid known as 2004 XP14 flew past the Earth at just about the Earth-Moon distance.
The asteroids' names include the year in which they were first identified.