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Astrophysics

Sunlight under Scrutiny


artist

© D. Ducros/ESA

Artist's rendering of the Columbus laboratory docked at the International Space Station



On February 7th, 2008, the American space shuttle Atlantis took off and “docked” three days later with the International Space Station (ISS). It delivered the European Columbus laboratory 1, which carries many internal payload racks–autonomous and independent laboratories–and which is also fitted with mounting points for external payloads. One of these external platforms is SOLAR, a set of three instruments dedicated to observing the Sun.
SOLSPEC (SOLar SPECtrum measurement) is one of the three instruments, and was jointly built by the Service d’Aéronomie 2 in France, the Institut d’Aéronomie Spatiale in Belgium, and the Heidelberg Observatory in Germany. The latest version of this solar spectrometer will measure the Sun spectrum irradiance (light power received by Earth as a function of radiation wavelength) over a period of several years with unequaled accuracy.
As Gérard Thuillier, principal investigator of SOLSPEC explains: “Measurement accuracy will be around 1%, compared to 30% in the 70’s and 6% achieved in 1983 with the first version of SOLSPEC on board SpaceLab I.”
The measurements from SOLSPEC are eagerly awaited not only in solar physics, but also in atmospheric and climate sciences, because physical and chemical atmospheric processes depend on the amount of energy injected by sunlight as a function of wavelength. Researchers compare their theoretical predictions with the measurements carried out in space to determine whether their models correctly describe the Sun’s properties. “The interest in greater measurement accuracy is obvious. It is possible that future data will lead to some big shake ups in current modeling,” explains Gérard Thuillier. Apart from SOLSPEC’s accuracy, scientists are also interested by the extended length of time it will be operational on the ISS. The spectrometer could remain on board the space station for nearly ten years. SOLSPEC should thus give new insights into the link between the Sun’s eleven-year activity cycle and atmospheric variations. “This is a great opportunity for studying a nearly complete solar cycle,” concludes Gérard Thuillier.

Mathieu Grousson

Notes :

1. This pressurized laboratory will be used by astronauts for experiments in biology, physiology, materials science, fluid physics, technology, life sciences and education.
2. CNRS / Université Paris-VI / Université Versailles-Saint-Quentin-en-Yvelines.

Contacts :

Gérard Thuillier
Service d'aéronomie, Verrières-le-Buisson.
gerard.thuillier@aerov.jussieu.fr


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