The Moon will start to cover the Sun tomorrow on 2^nd July 2019 at 15:23:51 local time La Silla/Chile ( 21:23:51 CEST). About an hour later at 16:39:24 (22:39:34 CEST) the short totality phase will follow. This is an unique opportunity for astronomers to conduct their special eclipse experiments.

Einstein & the theory of relativity

100 years ago, on 29^th May 1919, a famous solar eclipse experiment was conducted. Led by the British astrophysicist Arthur Stanley Eddington astronomers travelled to the island of Principe (Caribbean) and Sobral (Brazil) to measure the gravitational deflection of light as postulated by Einsteins general relativity.

To deflect light, you need to have a high-mass object like our Sun. While observing a star, which is close to the Sun at the time of the observation, it appears that this star is at a different position then it should be. The light of this star is gravitationally deflected by our Sun. Normally an optical observation is not possible because our Sun is to bright to observe close-by stars, but not during a solar eclipse. Only then, these stars can be seen. Good to know: the deflection is very minimal and is not visible to the naked eye.

The goal of the Eddington expedition was to observe stars close to the sun to then measure the deflection. For that, both expeditions took photos from the totality and compared them to photos from the same region, recorded half a year before the expedition.  And so, the scientist measured the deflection of the light and delivered the first indication of the correctness of general relativity.

Tomorrow the Eddington experiment will be repeated in La Silla. This will be done with the help of the TAROT telescope (Télescope à Action Rapide pour les Objets Transitoires), a fast moving, optical telescope

Additional planned experiments (excerpt):

• Scientific observations oft he the solar atmosphere
• Spectrographic measurements  of the solar corona with the 3.58 m NTT (New Technology Telescope)
• Measurements of linear polarization of the solar corona
• Imaging of the eclipse in various wavelength with the REM (Rapid Eye Mount telescope)
• As well as observing Mercury’s exosphere in collaboration with ESA for the BepiColombo mission

List of all experiments: https://www.eso.org/public/announcements/ann19031/

I will get to take a tour of the NTT an the 3.6 m telescope and try to post as many updates as possible from the solar eclipse event. The ESO will be live-streaming the eclipse:

ESO Live Webcast

In Chile it is currently winter. Moreover, the eclipse will take place shortly before sunset, therefore clouds might block the view to the Sun. If we have clear skies, you will learn in my next blog post

Sources:
https://www.mpg.de/9236014/eddington-sonnenfinsternis-1919
https://en.wikipedia.org/wiki/Solar_eclipse_of_May_29,_1919

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