Magnetic-field lines around a bar magnet are easily imaged using iron filings and a piece of paper. However, applying such a technique to the Sun is not so simple, unfortunately, as knowledge of its field could help predict changes in solar wind that affect our planet. The Tibet ASγ Collaboration now shows that a 'shadow' cast on the Earth by the Sun is a sensitive probe of this complex magnetic structure.
Cosmic rays travel to Earth from outside the Solar System. The Sun blocks some of them, creating a cosmic-ray shadow. The researchers analysed data taken from the Tibet Air Shower Array — a γ-ray detector high in the foothills of the Himalayas — to monitor how the intensity of this shadow varied between 1996 and 2009: the shadow is darker when solar activity is at a minimum, they found.
Comparing these data with the predictions of two different theoretical models of the magnetic field in the solar corona, it seems the results support a model that incorporates the influence of electric currents flowing through the corona.
Rights and permissions
About this article
Cite this article
Gevaux, D. In the shadow of the Sun. Nature Phys 9, 454 (2013). https://doi.org/10.1038/nphys2722
Published:
Issue Date:
DOI: https://doi.org/10.1038/nphys2722
