Changes

About every two years, Venus "catches up with" and passes the Earth as they both orbit the Sun. This is called a "conjunction" of Venus and the Earth. During a conjunction, Venus is almost directly between the Earth and the Sun. It would seem as if Venus could be seen silhouetted against the Sun on every conjunction, but in fact the orbits of the planets are slightly tilted with respect to each other, so at a conjunction Venus almost never lines up perfectly, but appears to pass above or below the Sun. Very rarely—at intervals of over a century—conjunction occurs at the point in the orbits where they are both in the same plane. When this occurs, a ''transit of Venus'' can be observed. Transits of Venus occur in pairs, eight years apart; then over a century passes before the next one.  

About every two years, Venus "catches up with" and passes the Earth as they both orbit the Sun. This is called a "conjunction" of Venus and the Earth. During a conjunction, Venus is almost directly between the Earth and the Sun. It would seem as if Venus could be seen silhouetted against the Sun on every conjunction, but in fact the orbits of the planets are slightly tilted with respect to each other, so at a conjunction Venus almost never lines up perfectly, but appears to pass above or below the Sun. Very rarely—at intervals of over a century—conjunction occurs at the point in the orbits where they are both in the same plane. When this occurs, a ''transit of Venus'' can be observed. Transits of Venus occur in pairs, eight years apart; then over a century passes before the next one.  

One of the rare transits of Venus occurred on June 8, 2004; another will occur on June 6, 2012; then there will be no more until 2117, probably not within the lifetime of those reading this. A transit of Venus cannot be seen with the naked eye. Observing a transit of Venus requires '''great attention to eye safety''' and a telescope ''equipped with a safe sun filter'' or a special transit viewer.  

One of the rare transits of Venus occurred on June 8, 2004; another will occur on June 6, 2012; then there will be no more until 2117, probably not within the lifetime of those reading this. A transit of Venus cannot be seen with the naked eye. Observing a transit of Venus requires '''great attention to eye safety''' and a telescope '''equipped with a safe sun filter''' or a special transit viewer.  

The planet Venus is about the same size as the Earth. Before explorations made by spacecraft made it clear just how harsh conditions on Venus are, science-fiction writers used to speculate that the temperature and climate of Venus might be within the range of life as we know it on Earth.

The planet Venus is about the same size as the Earth. Before explorations made by spacecraft made it clear just how harsh conditions on Venus are, science-fiction writers used to speculate that the temperature and climate of Venus might be within the range of life as we know it on Earth.