Weather is basically a snapshot of actual or predicted atmospheric conditions in a particular place at a particular time.

A complete weather picture will give local or regional information about temperature, barometric pressure, cloudiness, precipitation (rain, snow, hail, mist or fog), wind speed and direction.

This picture may also include details of weather systems that are, or will be, creating weather conditions in a particular place: areas of high and low pressure, warm and cold fronts, hurricanes, thunderstorms and tornadoes.

Which planets have weather?

Any planet that has an atmosphere can have weather. In our solar system, Earth, Mars and Venus have different atmospheres and different weather, while Jupiter, Neptune, Saturn and Uranus have weather in a very big way. Only Mercury and Pluto have no real atmosphere and so no real weather.

What causes weather?

On Earth, weather is caused mainly by radiation from the sun, which - because the Earth is round - affects different areas of the globe in different ways. Weather is the atmosphere's response to this unequal distribution of solar energy. For example, air masses and storms help to carry heat from the tropics towards the poles.

On planets such as Jupiter and Saturn, weather has a second driving force: heat generated by energy released from the core of the planet itself.

Does the Sun have weather?

The Sun is one of more than 100 billion stars in our galaxy and by far the largest object in our solar system. It contains more than 99% of the total mass of the solar system, and has an 11-year solar cycle. At the peak of each solar cycle, solar flares - huge weather systems which blast gigantic clouds of charged particles into space - occur daily. These are so powerful, they affect other planets, including Earth.

The Sun has the most violent weather in the solar system. The outer 125,000 miles (200,000km) of its atmosphere is completely covered by an ever-changing network of 'convective cells'. Each cell has a broad area of hot rising gas surrounded by a smaller area of cooler sinking gas. The cells are usually about 600 miles (1,000km) across, but 'supergranules' may be up to five times as large. Sunspots are areas where strong magnetic fields cut down the flow of gases that feed the convective cells.

Is there weather in space?

The Earth and other planets in the solar system don't sit in empty space. They are surrounded by solar wind - charged particles blasting into space at a million miles per hour from the outer region of the Sun's dense atmosphere. Space also contains dust and cosmic rays, electric and magnetic fields.

The density of the space 'atmosphere' may be extremely low, but it can still show the violent and dramatic changes known as space weather. Now and again, solar flares shoot out huge clouds of material called 'coronal mass ejections'. These are carried outwards as a shock wave moving through the solar wind at up to 600 miles per second (1,000kps), posing a threat to space stations, satellites, and even to planets themselves.

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