A jet airliner leaves a vapor trail as the planet Mercury is seen, lower left quadrant, transiting across the face of the sun in Las Vegas. Mercury passes between Earth and the sun only about 13 times a century.

Tiny Mercury, the solar system's innermost planet, sailed across the face of the sun on Monday, a celestial dance that occurs about once every decade as Earth and its smaller neighboring planet align in space.

The journey, which astronomers refer to as a "transit," began with what looked to be a small, black dot on the edge of the sun at 7:12 a.m. EDT (1112 GMT), images relayed live on NASA TV showed.

Over the next seven and a half hours, Mercury, which travels at a speed of 30 miles (48 km) a second, crossed the face of the sun, a spectacle last seen in 2006.