Monday, April 23, 2007



The two spacecraft that make up the NASA STEREO mission were launched last October. One probe is now travelling in an orbit ahead of the Earth while the other lags behind. Together the probes are imaging the Sun in 3D.

They also have a unique perspective - they can view the space between the Sun and the Earth (the so-called Earth-Sun line), giving scientists their first views of this region of space.

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The Rutherford Appleton Laboratory (RAL) in Oxfordshire and the University of Birmingham led an international effort to develop two identical Heliospheric Imager (HI) instruments. One HI is mounted on each of the two spacecraft so astronomers can watch the Earth-Sun line. In particular, this view gives scientists a ringside seat when giant clouds of material (Coronal Mass Ejections or CMEs) travel from the Sun to the Earth.

CMEs can be made up of more than 1000 million tonnes of charged particles and travel at up to 1000 km per second. When a CME reaches the Earth it can have dramatic effects; compressing the terrestrial magnetic field, generating displays of the northern lights, disrupting radio communications, overloading power grids and damaging satellites.

Images and animation available @

Heavenly Music
from The Royal Astronomical Society

Astronomers have found that the atmosphere of the Sun plays a kind of heavenly music. The magnetic field in the outer regions (the corona) of our nearest star forms loops that carry waves and behave rather like a musical instrument.

In recent years scientists have worked hard to better explain and predict the dynamic behaviour of the Sun. For example, missions like STEREO and Hinode watch as material is ejected towards the Earth, events which are controlled by the solar magnetic field.

Scientists combined observations with new theoretical models to study the magnetic sound waves that are set up along loops in the corona. “These loops can be up to 100 million kilometres long and guide waves and oscillations in a similar way to a pipe organ.”

The acoustic waves can be extremely powerful and reach amplitudes of tens of kilometres per second. “The waves are often generated at the base of the magnetic pipes by enormous explosions known as micro-flares. These release energy equivalent to millions of hydrogen bombs. After each micro-flare, sound booms are rapidly excited inside the magnetic pipes before decaying in less than an hour and dissipating in the very hot solar corona.”


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