ACytherocentric orbit is an orbit around theplanetVenus. Venus has no moon, but several man-made objects orbit the planet.

The name is analogous to the termgeocentric orbit for an orbit around Earth andheliocentric orbit for an orbit around the Sun. Theapsides of an Cytherocentric orbit are pericytherion, thepericenter (analogous toperigee), and theapocenter is named apocytherion (analogous toapogee).

TheCythero prefix is derived fromKythira or "Cythera." InGreek mythology, Cythera was an island associated with the goddessAphrodite, who is the equivalent of the Roman goddessVenus. Therefore, naming an orbit around Venus "cytherocentric" is a way of referencing Venus' association with this goddess.^{[citation needed]}

Venera 9 was the first satellite to achieve Venus orbit in 20 October 1975.Akatsuki was the latest probe to achieve Venus orbit in 2015.^[1]

Eight probes have achieved Venus orbit:

• 4Soviet Union probes,Venera 9,Venera 10,Venera 15,Venera 16
• TwoNASA probe,Magellan,Pioneer Venus 1
• OneJAXA probe,Akatsuki
• OneESA probe,Venus Express.

In order to enter Venus orbit, a satellite has to perform an engine burn to reduce the speed. Otherwise, the probe moves too fast to achieve orbit and will be aflyby. A noteworthy case is that of Japanese probeAkatsuki, which failed to enter orbit around Venus on 6 December 2010.^[2] JAXA stated on 8 December that the probe's orbital insertion maneuver had failed,^[3] because of a defect in the orbital insertion burn. After the craftorbited the Sun for five years, engineers successfully placed it into an alternative Venusianelliptic orbit on 7 December 2015 by firing itsattitude control thrusters for 20 minutes.

Magellan was the first interplanetary probe to useaerobraking to reduce the apocytherion.^[4] By passing through the dense atmosphere, a probe can reduce its speed and attain the necessarydelta-v.Venus's thick atmosphere supportsaerobraking. This reduces fuel needs.

Asatellite with revolutionary period that matches the planet's rotational period appears fixed at a position in the sky relative to an observer on the planet. Such an orbit on Earth is aGeostationary orbit.^[5]

The height of a stationary or synchronous orbit can be calculated as follows:

${\displaystyle R_{syn}=\sqrt[3]{\frac{G(m_2)T^2}{4{\pi }^2}}}$ ^[6]

where G is thegravitational constant, m₂ is the mass of the celestial body, and T is thesidereal rotational period of the body.

By this formula one can find thegeostationary-analogous cytherostationary orbit. Around Venus, such anorbit would be 1,536,600 km or about 253 Venus radii from the planet's surface^{[citation needed]}. This is because Venus has the slowest rotation rate of any planet. The slower the rotation, the farther away a satellite must be in order to be stationary. Thehill sphere of a celestial body describes the region in which the gravity of that body is dominant. Thehill sphere radius of Venus is about 1 million kilometers; and as the cytherostationary orbital distance lies outside of it, no stable cytherostationary satellite can exist.

• Orbit of Venus
• Areocentric orbit