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Global topographic map of Venus, with all probe landings marked (red: returned images; with additional black dot: analyzed samples). There have been 46 space missions to the planet Venus (including gravity-assist flybys). Missions to Venus constitute part of the exploration of Venus.
While Venus approaches Earth the closest, Mercury approaches Earth more often the closest of all planets. [11] That said, Venus and Earth still have the lowest gravitational potential difference between them than to any other planet, needing the lowest delta-v to transfer between them, than to any other planet from them. [12] [13]
Knowing Greenwich time and local time, the navigator can work out longitude. [1] Local time can be determined from a sextant observation of the altitude of the Sun or a star. [8] [9] Then the longitude (relative to Greenwich) is readily calculated from the difference between local time and Greenwich Time, at 15 degrees per hour of difference.
A diagram of a typical nautical sextant, a tool used in celestial navigation to measure the angle between two objects viewed by means of its optical sight. Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the ...
Consequently, Venus transits only occur when an inferior conjunction takes place during some days of June or December, when the orbits of Venus and Earth cross a straight line with the Sun. [189] This results in Venus transiting above Earth in a sequence currently of 8 years, 105.5 years, 8 years and 121.5 years, forming cycles of 243 years.
The following outline is provided as an overview of and topical guide to Venus: . Venus – second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period (243 days) of any planet in the Solar System and rotates in the opposite direction to most other planets.
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The Mission Profile presented in 1956 consisted of a 154-day travel from Earth to Mars, followed by a 113-day travel to Venus including passing by the planet and using the gravitational attraction for a course correction, followed by the 98-day return to Earth. [5] Crocco proposed the first Mission to be launched in June 1971.