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Archive Astronomy Questions of the Week - International Year of Astronomy 2009

Where does a storm last for several centuries?

Week 26

 Jupiter's Great Red Spot
zum Bild Jupiter's Great Red Spot

The longest documented storm on Earth lasted for just five weeks. Last year, astronomers observed a storm on Saturn that lasted for more than five months. However, on Jupiter, scientists in the 17th century observed a gigantic 'red eye' - known as the Great Red Spot – that has been observed continuously ever since and can be seen with amateur telescopes. In reality, the 'spot' is a hurricane in Jupiter's atmosphere. The largest storm in our solar system is twice as far across as the diameter of Earth.

Jupiter is the largest planet in the Solar System. It is what is known as a gas giant, which is mostly made of hydrogen and helium and has no solid surface.

The planet with the spectacular coloured storms

The cloud layers are always moving in Jupiter's atmosphere. Their lively colours range from white, orange and yellow to brown and are thought to be created by chemical reactions of trace elements with sulphur - whose compounds are known to be very colourful. The colour of the Great Red Spot is most likely due to the presence of phosphorus.

Astronomers still don't understand why this gigantic storm in Jupiter's southern hemisphere has lasted so long. The winds in its interior blow at speeds up to 400 kilometres an hour. It is possible that the Great Red Spot swallows up smaller storm systems and this is what has kept it going for such a long time.

Henning Krause
German Aerospace Center

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Last update: 22/07/2009 11:54:08