You've probably heard these short beeps known as 'pips' - the Royal Observatory in Greenwich England has been broadcasting these hourly time signals since 1924. You can hear them before the BBC's hourly newscasts.
Click here for a 360 degree panorama of the Greenwich Meridian
The pips mark "Greenwich Mean Time" or GMT. It's come to be known as Universal Time. Times in cities around the world are often expressed as a number of hours "ahead of GMT" or "behind GMT".
So here's the question: When it's noon in the city of Los Angeles, what time is it in Mecca, Saudi Arabia? The answer may depend on whom you ask, some Muslim scientists are calling for abandoning the GMT standard.
In any case, you've got about 5 minutes to come up with the answer.
We asked you to do a little international time conversion for our Geo Quiz today. We wanted to know what time it is in the Saudi City of Mecca when it's noontime in Los Angeles.
Well, LA is currently 7 hours behind GMT or Greenwich Mean Time and Mecca is 3 hours ahead of GMT. So when it's noontime in LA it's 10pm in Mecca.
It's a bit confusing... But time zones around the world are usually compared to Greenwich Mean Time. But now some Muslim scientists are calling for the adoption of MECCA TIME to replace GMT.
Grand Mosque in MeccaGrand Mosque in Mecca
Muslims around the world turn to face Mecca when they perform their daily prayers. And as the BBC's Arab Affairs Analyst, Magdi Abdelhadi reports -- some argue Mecca is a better point than Greenwich to represent the center of the earth.
Listen to his report:
The call was issued at a conference held in the Gulf state of Qatar under the title: Mecca, the Center of the Earth, Theory and Practice. One geologist argued that unlike all other longitudes, Mecca's was in perfect alignment to the magnetic north. He said the English had imposed GMT on the rest of the world by force when Britain was a big colonial power and it was about time that changed.
A prominent cleric, Sheikh Youssef Al Qaradawy, said modern science has at last provided evidence that Mecca was the true center of the earth; proof, he said, of the greatness of the Muslim qibla -- the Arabic word for the direction Muslims turn to when they pray.
The meeting also reviewed what has been described as a Mecca Watch, the brainchild of a French Muslim. The watch is said to rotate anti-clock wise and is supposed to help Muslims determine the direction of Mecca from any point on earth.
The meeting in Qatar is part of a popular trend in some Muslim societies which seeks to find Koranic precedents for modern science. It is called "Ijaz Al-Koran", which roughly translates as the "miraculous nature of the holy text". The underlying belief is that scientific truths were also revealed in the Muslim holy book, and it is the work of scholars to unearth and publicize the textual evidence.
But the movement is not without its critics, who say that the notion that modern science was revealed in the Koran confuses spiritual truth , which is constant, and empirical truth, which depends on the state of science at any given point in time.