* Astronomy

Title: Transits of Venus and the Astronomical Unit: four centuries of increasing precision
Authors: Costantino Sigismondi

Only seven transits of Venus have been observed and studied up to now since the first astronomical observations with the telescope: 1639, 1761-69, 1874-82 and 2004-12. The measurement of the Astronomical Unit has been one of the main goal of the study of this rare phenomenon, as well as the identification of the planetary atmosphere and its properties, the understanding of the black drop phenomenon and the measurement of the solar diameter. The transit of 1639 observed by J. Horrocks is presented in more detail.

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The second most recent transit of Venus observed from Earth took place on June 8, 2004. The event received significant attention, since it was the first Venus transit after the invention of broadcast media. No human alive at the time had witnessed a previous Venus transit since that transit occurred on December 6, 1882. 
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Transit of Venus 2004

A transit of Venus across the Sun takes place when the planet Venus, passes directly between the Sun and Earth, obscuring a small portion of the sun. During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun. The duration of such transits is usually measured in hours (the transit of 2004 lasted six hours). The next Transit of Venus is the 6th June 2012. If you miss this one the next one is December 2117 and Dec 2125. They occur in pairs of 121.5 years and 105.5 years. These are vary rare!! Remember do not look directly at the sun to observe. You can safely project the image with binoculars.

Title: Venus transit 2004: Illustrating the capability of exoplanet transmission spectroscopy
Authors: P. Hedelt, R. Alonso, T. Brown, M. Collados Vera, H. Rauer, H. Schleicher, W. Schmidt, F. Schreier, R. Titz

The transit of Venus in 2004 offered the rare possibility to remotely sense a well-known planetary atmosphere using ground-based observations for absorption spectroscopy. Transmission spectra of Venus' atmosphere were obtained in the near infrared using the Vacuum Tower Telescope (VTT) in Tenerife. Since the instrument was designed to measure the very bright photosphere of the Sun, extracting Venus' atmosphere was challenging. CO_2 absorption lines could be identified in the upper Venus atmosphere. Moreover, the relative abundance of the three most abundant CO_2 isotopologues could be determined. The observations resolved Venus' limb, showing Doppler-shifted absorption lines that are probably caused by high-altitude winds.
This paper illustrates the ability of ground-based measurements to examine atmospheric constituents of a terrestrial planet atmosphere which might be applied in future to terrestrial extrasolar planets.

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