Home > Amateur Astronomy, Astronomy, Exoplanets, General Astronomy, Solar System, Transits, Venus > Venus Transit And Lunar Mirror Could Help Astronomers Find Worlds Around Other Stars

Venus Transit And Lunar Mirror Could Help Astronomers Find Worlds Around Other Stars


When Venus passes in front of the Sun it hides a part of our star’s rotating surface. Because of rotation, the spectrum of the Sun (created splitting the different colours of light using a spectrograph) is slightly different on each side. On one side, the solar surface is rotating towards the observer and so its light will be ‘blueshifted’, meaning the lines seen in a spectrum move towards shorter wavelengths. On the other, the surface is rotating away from the observer, so its light is ‘redshifted’, meaning that the lines move towards longer wavelengths.

By looking at the reflected light from the lunar surface, this is averaged out as a broadening of the various lines. When Venus moves in front of the Sun from east to west, it first blocks out the surface moving towards us and then the surface moving away from us. This causes a distortion in the spectral lines known as the “Rossiter-McLaughlin effect”.

The astronomers realised that the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph installed on a 3.6m telescope at La Silla in Chile, part of the European Southern Observatory (ESO), would be sensitive enough to detect the effect and that the Moon would be in the right place too. The Moon was slightly ahead of the Earth in its orbit, so ‘saw’ the transit a couple of hours later than terrestrial observers. This also meant that the Moon was in the night time sky in Chile, making it possible for the La Silla telescope to operate safely and observe the change in the solar spectrum.

Full Story: http://www.ras.org.uk/news-and-press/219-news-2012/2203-venus-transit-and-lunar-mirror-help-astronomers-find-worlds-around-other-stars

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