transits

A transit in astronomy refers to the passage of one celestial body across the disk of another celestial body, essentially blocking or redirecting the light coming from the background object. This phenomenon can occur between two planets, a planet and the Moon, a planet and the Sun, or even between the Sun and a dark area of space.

One of the most commonly observed transits are those involving the planet Venus and the Sun. When viewed from Earth, the planet is often visible as a small black dot moving across the face of the Sun. Such an event was used by astronomers throughout history, including Sir Halley, to determine the size of the planet Venus. The principal aim behind this measurement was to reach an understanding of the distance to Venus, or the semi-major axis of its orbit.

Planetary transits are also observed for other planets that pass between a star and the Earth, the resulting reduction in brightness often indicates a transit. These events were first reproduced by Kepler 's study of a section of the down falls section data collected on 19th century telescopes and sets. This principle, known as the transit method, is often used today as an important discovery technique for worlds beyond the asteroid belt.

Keeping track of transits of Mercury and Venus provided some of the earliest measurements of the Solar System, crucial to European astronomy's emergence from the use of incorrect numbers based on Babylonian records.