V - Factary

Van Allen Belts

See radiation belts.

VIRGO

No, not the star sign! This is a piece of equipment on board the SOHO satellite which is studying the Sun. It measures changes in the intensity of electromagnetic radiation from the Sun. VIRGO stands for : Variability of solar IRradiance and Gravity Oscillations.

Volt (V)

The SI unit which measures electrical potential difference or electromotive force. It is named after the Italian physicist Alessandro Volta and is one of those units which looks horrible when translated into SI basic units. A volt is equivalent to m².kg.s^-3.A^-1

Volts, e.m.f. and Potential Difference (PD)

These terms are often a source of confusion since they are both measured in the same unit - the volt.

If you are measuring the voltage of a power supply (like a cell, battery or transformer) the term e.m.f. is used to describe this voltage. It stands for 'electro-motive-force'. The electro part is about the electrons flowing in the circuit; the motive part is the motion and the force bit is what pushes things around the circuit - which is exactly what a power supply does.

When you are measuring the voltage anywhere else in a circuit, this is called the Potential Difference (or P.D.) and it's also measured in volts.

Volta, Alessandro (1745-1827)

Volta was an Italian physicist who transformed the study of electricity by inventing the voltaic cell. Prior to his invention, it was only possible to generate small and unreliable electric currents. Thus the work of people like Humphrey Davey and Michael Faraday owes much to Volta's efforts.

Not to be confused with the (generally more famous) French writer Voltaire - a very different person and after whom the volt was not named!

Voyager 1

Voyager 1 was launched from Cape Canaveral on Sept. 5, 1977, carrying scientific instruments for planetary exploration and a message to the universe in the form of recordings of different languages and images.

It is currently over 11 billion kilometres from Earth. Although heading in a different direction, it 'overtook' the Pioneer 10 spacecraft in terms of distance from the Sun in February 1998 making it the most distant man-made object.

Voyager 1 still returns data, even though the power of the signal reaching NASA antennas is 20 billion times weaker than the power delivered by a digital watch battery. Voyager I is expected to have enough power from its plutonium radio-active power source to operate until about 2020. By then it will be over 22 billion kilometres away and of course will not stop its journey but will just be unable to communicate with controllers on Earth. What are the chances that some alien civilisation will find it one day and bring it back to us - 'is this your spacecraft I found wandering in the galaxy?'

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