Science: Technoquest - Elephants, giraffes and Shuttle trash

Questions for this column can be submitted to sci.net@campus.bt.com

How big is the biggest elephant?

The Science Museum has records of an elephant that was 4.10 metres high and weighed an amazing 10.7 tonnes. But on average African elephants weigh around 5.6 tonnes, and are about 3.2 metres high.

What is a planetary nebula?

Nebulae form at the end of a star's life. When a star runs out of its basic fuel, hydrogen, it starts burning its waste - helium. This raises the temperature, and the internal pressure, which makes the star expand - but this expansion lowers the temperature and pressure, so the star's gravity makes it contract again. This cycle repeats until the star "pulses" rapidly, and begins throwing out its mass from its surface in a "superwind". It blows in gusts which rip the envelope of gas from the star in just 1,000 years. The expelled material forms an expanding shell of gas heated by a hot core. Astronomers call this a "planetary nebula" because, seen through a basic telescope, it looks like a planet with moons round it. The hot core looks like the central star of the nebula, which will keep expanding until it dissipates.

How many vertebrae does a giraffe have?

Our backbones are made up of several small bones called vertebrae. Even though a giraffe is much taller than we are, they have exactly the same number of vertebrae - just 24. The difference is, theirs are rather larger in every dimension.

What do they do with rubbish on the Shuttle?

Bring it all back, including what's in the toilet - except the urine, which is often dumped overboard. Rubbish is carefully stowed in containers and the US space agency Nasa is currently developing a "trash-compactor".

You can visit the Technoquest site at http://www.campus.bt.com/CampusWorld/pub/ScienceNet. Questions and answers provided by Science Line's Dial-a-Scientist, 0345 600444.