Transit of Mercury

We speak about astronomical transit or simply a transit when an astronomical body move between the observer and the celestial body that he observes. In particular the transit was used by Planck to discover exolpanets, but we can use also to observe some events that occur in our solar system. And between 9th and 10th May it occurs the transit of Mercury between Sun and Earth.
In the figure below (via EclipseWise) you can see the visibility of the transit:

More details on: NASA | NakedEyePlanets.com