The enormous piece of space debris is expected to pass just 2.5lunar distances from planet Earth – the moon is approximately384,400 km (238,000 miles) from us, meaning the asteroid’s flybywill be at a distance of about 950,000km (600,000 miles).Some astronomers have compared its size to that of a city block,others a football pitch. Its dimensions were widely given as 460feet (140m) long and 210 feet (64m) wide. A professional Americanfootball field is 360 feet by 160 feet, which would make thisasteroid 100 feet longer than a football field, and 50 feet wider,should it live up to calculations.Celestial bodies: What’s thedifference?A meteor is a ‘shooting star’, or the flash of light seen when asmall chunk of space debris burns up in the Earth’s atmosphere.However, the word does not refer to the debris itself – this is ameteoroid. A meteoroid is the interplanetary matter –a small rock or piece ofspace debris that burns up in the Earth’s atmosphere and is thesource of the meteor. A meteorite is a meteoroid that survives the falling through theEarth’s atmosphere and subsequently collides with the Earth’ssurface. Asteroids are generally larger chunks of matter from space, andtend to come from the asteroid belt located between the orbits ofMars and Jupiter. Comets are asteroid-like objects, but have a visible atmospherecalled a ‘coma’ which resembles a kind of ‘shell’ and/or ‘tail’,created by ice, ammonia, or other compounds.Asteroid 2013 ET was first detected on March 3 by the CatalinaSky Survey based at the University of Arizona, and now approachesthe planet less than a week after it first hit astronomers’radars.It will not be quite bright enough to view through standardpersonal binoculars or small ‘backyard’ telescopes, but will bevisible using larger, professional devices in observatories, one ofwhich will broadcast its passage online.Although it was due to be shown via live webcast by the VirtualTelescope Project in Ceccano, Italy, at 19:00 GMT, strong rain andclouds have prevented it from broadcasting the event. Now theonline Slooh Space Telescope, based in the Canary Islands, hastaken the reins, and will give a live webcast from theirobservatory at 20:15 GMT.“We only have a short viewing window of an hour or so…but wewanted to give the general public a front row seat to witness thisnew asteroid in real time as it passes by Earth,” said Sloohpresident Patrick Paolucci, as cited by Space.com.It will be the second in one day, and the third this week.Earlier on Saturday, at 5:57am Moscow time (09:57 GMT), a smallerasteroid passed even closer to Earth. The 2013 EC20, between 9 and40 feet (3 and 10m), came within 169,000 km (some 106,000 miles) –even closer than the moon.The second last asteroid on Monday’s, named 2013 EC, flew within230,000 miles of the planet. Its range fell just inside the moon’sorbit. It was also smaller, at 33 feet (10m) wide.Earthlings have been especially excited about space bodies as oflate, after the planet was hit by a huge meteorite last month. Themeteorite that smashed into the Russian city of Chelyabinsk onFebruary 15 was the largest object to enter the Earth’s atmospherein nearly a century. On the same day it struck, another 164 feet(50m) wide space rock, named 2012 DA14, brushed the planet, closerthan any other in known history.“The recent flurry of asteroidal close calls and near misses,including the double-whammy of DA14 and the Siberian meteor onFebruary 15, is starting to make our region of space seem like avideo game or pinball contest,” said American astronomer andwriter Bob Berman.