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Sunday, September 18, 2005


Mercury at Inferior conjunction

Image credit SOHO/NASA
The bright spot above the coronagraph disk is Mercury, at inferior conjunction today (Sunday 18 Sept). The spike through it is due to CCD saturation. Inferior conjunction is when a planet lies between us and the Sun (naturally this can only happen to Venus and Mercury). Because of SOHO's L1 position, Mercury is not in front of the Sun under the coronograph disk (and the geometry is only rarely right for Mercury to pass across the Sun's disk from Earth anyway, it happens around 13 times a century). The close proximity of Mercury to the Sun of course means that it will be invisible to us. It returns to the evening sky in late September, and in Early October will have a great conjunction with Jupiter.

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