There's a A transit of Mercury today when the planet Mercury passes directly between the Sun and the Earth, becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Mercury appears as a tiny black dot moving across the disk of the Sun.
Mercury will begin to creep onto the sun's disk at 1235hrs GMT and it will take about 5 hour and 28 minutes to make its way across, with the transit ending at 1804hrs GMT.
The next transit will be on 13th November 2032.