Washington

Light entertainment: the aurora as it was seen at the Brno Observatory in the Czech Republic. Credit: JAN SAFAR

Aside from lighting up night-time skies with colourful auroral displays last week, a magnetic storm that originated on the Sun acted as a showcase for the growing fleet of ‘space weather’ stations positioned at various points in the inner Solar System.

The first spacecraft to detect the storm was the Advanced Composition Explorer (ACE), parked in a stable orbit 1.5 million kilometres from the Sun. At 16:00 Universal Time (ut) on 6 April, ACE detected a shock wave associated with a gust in the solar wind of between 375 and 600 kilometres per second. The blast of atomic particles hit the Earth's magnetosphere less than an hour later and triggered the auroras.

Images from the US–European Solar and Heliospheric Observatory revealed the origins of the outburst in a solar flare that produced a large coronal-mass ejection at 15:41 ut on 4 April.

According to a Space Weather Scale introduced last November by the US space agency NASA, this was a category 4 geomagnetic storm (category 5 is the highest). Storm activity is expected to pick up in the next couple of years as the Sun reaches its solar maximum.