Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

has an

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...

with a semi-major axis of , and an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.007.Jean Meeus, ''Astronomical Formulæ for Calculators'', by Jean Meeus. (Richmond, VA: Willmann-Bell, 1988) 99. Elements by Simon Newcomb The low eccentricity and comparatively small size of its orbit give Venus the least range in distance between

perihelion and aphelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any elli ...

of the planets: 1.46 million km. The planet orbits the Sun once every 225 days and travels in doing so,Jean Meeus, ''Astronomical Algorithms'' (Richmond, VA: Willmann-Bell, 1998) 238. The formula by Ramanujan is accurate enough. giving an average

orbital speed In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter or, if one body is much more mas ...

of .

Conjunctions and transits

When the geocentric

ecliptic longitude The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System b ...

of Venus coincides with that of the Sun, it is in

conjunction Conjunction may refer to: * Conjunction (grammar), a part of speech * Logical conjunction, a mathematical operator ** Conjunction introduction, a rule of inference of propositional logic * Conjunction (astronomy), in which two astronomical bodies ...

with the Sun – inferior if Venus is nearer and superior if farther. The distance between Venus and Earth varies from about 42 million km (at inferior conjunction) to about 258 million km (at superior conjunction). The average period between successive conjunctions of one type is 584 days – one

synodic period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets, ...

of Venus. Five synodic periods of Venus is almost exactly 13 sidereal Venus years and 8 Earth years, and consequently the longitudes and distances almost repeat. The 3.4°

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

of Venus's orbit is great enough to usually prevent the inferior planet from passing directly between the Sun and Earth at inferior conjunction. Such solar transits of Venus rarely occur, but with great predictability and interest.

Close approaches to Earth and Mercury

In this current era, the nearest that Venus comes to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

is just under 40 million km. Because the range of heliocentric distances is greater for the Earth than for Venus, the closest approaches come near Earth's perihelion. The Earth's declining eccentricity is increasing the minimum distances. The last time Venus drew nearer than 39.5 million km was in 1623, but that will not happen again for many millennia, and in fact after 5683 Venus will not even come closer than 40 million km for about 60,000 years. The orientation of the orbits of the two planets is not favorable for minimizing the close approach distance. The longitudes of perihelion were only 29 degrees apart at J2000, so the smallest distances, which come when inferior conjunction happens near Earth's perihelion, occur when Venus is near perihelion. An example was the transit of December 6, 1882: Venus reached perihelion Jan 9, 1883, and Earth did the same on December 31. Venus was 0.7205 au from the Sun on the day of transit, decidedly less than average. Moving far backwards in time, more than 200,000 years ago Venus sometimes passed by at a distance from Earth of barely less than 38 million km, and will next do that after more than 400,000 years. Venus and Earth come the closest, but they come less often closer than Venus and Mercury. While Venus approaches Earth the closest, Mercury approaches Earth more often the closest of all planets. That said, Venus and Earth still have the lowest

gravitational potential In classical mechanics, the gravitational potential at a location is equal to the work (energy transferred) per unit mass that would be needed to move an object to that location from a fixed reference location. It is analogous to the electric ...

difference between them than to any other planet, needing the lowest delta-v to

transfer Transfer may refer to: Arts and media * ''Transfer'' (2010 film), a German science-fiction movie directed by Damir Lukacevic and starring Zana Marjanović * ''Transfer'' (1966 film), a short film * ''Transfer'' (journal), in management studies ...

between them, than to any other planet from them. The distance between Venus and Mercury will become smaller over time primarily because of Mercury's increasing eccentricity.

Historical importance

The discovery of

phases of Venus The phases of Venus are the variations of lighting seen on the planet's surface, similar to lunar phases. The first recorded observations of them are thought to have been telescopic observations by Galileo Galilei in 1610. Although the extreme cr ...

by Galileo in 1610 was important. It contradicted the model of Ptolemy which considered all celestial objects to revolve around the Earth and was consistent with others, such as those of Tycho and Copernicus. In Galileo’s day the prevailing model of the universe was based on the assertion by the Greek astronomer Ptolemy almost 15 centuries earlier that all celestial objects revolve around Earth (see Ptolemaic system). Observation of the phases of Venus was inconsistent with this view but was consistent with the Polish astronomer Nicolaus Copernicus’s idea that the solar system is centered on the Sun. Galileo’s observation of the phases of Venus provided the first direct observational evidence for Copernican theory. Observations of transits of Venus across the Sun have played a major role in the history of astronomy in the determination of a more accurate value of the astronomical unit.

Accuracy and predictability

Venus has a very well observed and predictable orbit. From the perspective of all but the most demanding, its orbit is simple. An equation in ''Astronomical Algorithms'' that assumes an unperturbed elliptical orbit predicts the perihelion and aphelion times with an error of a few hours. Using orbital elements to calculate those distances agrees to actual averages to at least five significant figures. Formulas for computing position straight from orbital elements typically do not provide or need corrections for the effects of other planets. However, observations are much better now, and space age technology has replaced the older techniques. E. Myles Standish wrote ''Classical ephemerides over the past centuries have been based entirely upon optical observations: almost exclusively, meridian circle transit timings. With the advent of planetary radar, spacecraft missions, VLBI, etc., the situation for the four inner planets has changed dramatically.'' For DE405, created in 1998, optical observations were dropped and as he wrote ''initial conditions for the inner four planets were adjusted to ranging data primarily...'' Now the orbit estimates are dominated by observations of the Venus Express spacecraft. The orbit is now known to sub-kilometer accuracy.

Table of orbital parameters

No more than five significant figures are presented here, and to this level of precision the numbers match very well the VSOP87 elements and calculations derived from them, Standish's (of JPL) 250-year best fit,Standish and Williams(2012) p 27 Newcomb's, and calculations using the actual positions of Venus over time.

Dust ring

Venus' orbital space has been shown to have its own dust ring-cloud, with a suspected origin either from Venus trailing asteroids, interplanetary dust migrating in waves, or the remains of the Solar System's circumstellar disc out of which its proto-planetary disc and then it self, the Solar planetary system, formed.

References

{{Venus Dynamics of the Solar System Venus