A transit occurs when a planet passes between a star and its observer. Transits within our solar system can be observed from Earth when Venus or Mercury travel between us and the Sun.

How often do planetary transits occur?

How frequently do transits occur? Transits are much rarer than eclipses. A Mercury transit occurs, on average, once every seven years.

Why is Venus called Earth's sister?

Venus is sometimes called Earth's sister planet because it's the nearest planet to Earth and it's nearly the same size. But unlike Earth, Venus is obscured by a blanket of dense carbon dioxide. ... This was evidence that Venus orbited the Sun, not the Earth.