Jeremiah Horrocks first observing the transit of Venus by causing the sun's disc to be thrown through a tube so as to show the planet crossing the sun's face. From a painting (1891) by Eyre Crowe. Jeremiah Horrocks (1618-1641) was an English astronomer and the first person to demonstrate that the Moon moved around the Earth in an elliptical orbit. He was the only person to predict the transit of Venus of 1639, an event which he and his friend William Crabtree were the only two people to observe and record. Transits of Venus across the disk of the Sun are among the rarest of planetary alignments. Only eight such events have occurred since the invention of the telescope. A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and Earth (or another planet), becoming visible against the solar disk. During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun. Venus transits are historically of great scientific importance as they were used to gain the first realistic estimates of the size of the Solar System. This image has been color enhanced.