Next week, Japanese space agency JAXA will launch Solar-B, an orbital observatory designed to investigate the causes of solar flares and coronal mass ejections, the huge eruptions from the surface of the Sun.

Although flares themselves are reasonably well understood, the mechanism that produces them is not, and scientists are not able to make good predictions about solar weather patterns.

Watching the Sun is not easy, however, as anything in orbit around Earth will have days and nights - periods when it cannot see the Sun.

"The Sun behaves unpredictably and will be as likely to flare during spacecraft night when Solar-B would be behind the Earth," says Professor Len Culhane, principal investigator of the EIS instrument.

To maximise viewing time, the craft will be inserted into a particular kind of polar orbit that will allow it to observe the Sun for nine months of the year.

The craft, a joint project between Japan, the US, and the UK, will carry three telescopes to study the sun in different wavelengths: optical, X-ray and extreme UV. The latter, the Extreme Ultraviolet Imaging Spectrometer (EIS), was provided by the UK, and is designed to catch the tiniest changes in the solar surface in the build up to a flare.

This so-called "trigger phase" is key to being able to make predictions about flares and CMEs.

"Solar flares are so fast and furious they can cause communication black-outs at Earth within 30 minutes of a flare erupting on the Sun's surface," says Professor Louise Harra, the UK Solar-B project scientist based at UCL's Mullard Space Science Laboratory.

"It's imperative that we understand what triggers these events with the ultimate aim of being able to predict them with greater accuracy." ®

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