Sao is a prograde irregular satellite of Neptune. It was discovered by Matthew J. Holman et al. on August 14, 2002.^[3] Matthew J. Holman is a Smithsonian Astrophysicist and lecturer at Harvard University. ... JJ Kavelaars is a Canadian astronomer who was part of a team that discovered several moons of Saturn, Uranus, and Neptune. ... August 14 is the 226th day of the year in the Gregorian Calendar (227th in leap years), with 139 days remaining. ... For album titles with the same name, see 2002 (album). ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... A gigametre (American spelling: gigameter) (symbol: Gm) is a unit of length equal to 109 metres. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... Inclination in general is the angle between a reference plane and another plane or axis of direction. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... In astronomy, a Julian year is a unit of time defined as exactly 365. ... In geometry, a diameter (Greek words diairo = divide and metro = measure) of a circle is any straight line segment that passes through the center and whose endpoints are on the circular boundary, or, in more modern usage, the length of such a line segment. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... Albedo is a ratio of scattered to incident electromagnetic radiation power. ... In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. ... Asteroids are assigned a type based on spectral shape, color, and sometimes albedo. ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... Prograde motion is the motion of a planetary body in a direction similar to that of other bodies within its system, and is sometimes called direct motion, especially in astrology. ... In astronomy, an irregular satellite is a natural satellite following a distant, inclined, often retrograde orbit and believed to be captured as opposed to a regular satellite, formed in situ. ... Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ... Matthew J. Holman is a Smithsonian Astrophysicist and lecturer at Harvard University. ... August 14 is the 226th day of the year in the Gregorian Calendar (227th in leap years), with 139 days remaining. ... For album titles with the same name, see 2002 (album). ...

Irregular satellites of Neptune.

Sao orbits Neptune at a distance of about 22.4 million km and is about 44 kilometers in diameter (assuming an albedo of 0.04).^[2] Albedo is a ratio of scattered to incident electromagnetic radiation power. ...

Sao follows an exceptionally inclined and moderately eccentric orbit illustrated on the diagram in relation to other irregular satellites of Neptune. The satellites above the horizontal axis are prograde, the satellites beneath it are retrograde. The yellow segments extend from the pericentre to the apocentre, showing the eccentricity. Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... (This page refers to eccitricity in astrodynamics. ... Prograde motion is the motion of a planetary body in a direction similar to that of other bodies within its system, and is sometimes called direct motion, especially in astrology. ... A diagram of Keplerian orbital elements. ... A diagram of Keplerian orbital elements. ...

The satellite is in so-called Kozai resonance, i.e. its inclination and eccentricity are coupled (the inclination of the orbit decreases while eccentricity increases and vice versa).^[3] In celestial mechanics, the Kozai mechanism is a secular perturbative effect resulting in the periodic sychronised changes of the eccentricity and the inclination of the orbit of the perturbed body. ...

Sao, or Neptune XI, like many of the outer satellites of Neptune, is named after one of the Nereids; Sao was assocated with sailing and is referred to as "The rescuer" or "Safety". Prior to January 29, 2007, Sao was known provisionally as S/ 2002 N 2. In Greek mythology, the Nereids (NEER-ee-eds) are blue-haired sea nymphs, the fifty daughters of Nereus and Doris. ... January 29 is the 29th day of the year in the Gregorian calendar. ... This article or section does not cite its references or sources. ...

See also

• irregular satellites

In astronomy, an irregular satellite is a natural satellite following a distant, inclined, often retrograde orbit and believed to be captured as opposed to a regular satellite, formed in situ. ...

External links

• Matthew Holman's Neptune's page
• David Jewitt's pages
• Scott Sheppard's pages

References

1. ^ Discovery Circumstances from JPL
2. ^ ^{a b c d} S. Sheppard, D.Jewitt and J.Kleyna A Survey for "Normal" Irregular Satellites Around Neptune: Limits to Completeness, The Astronomical Journal, 132 (2006), pp. 171–176. Preprint.
3. ^ ^{a b} M. Holman, JJ Kavelaars, B. Gladman, Grav, Tommy; Gladman, Brett J; Fraser, Wesley C; Milisavljevic, Dan; Nicholson, Philip D; Burns, Joseph A; Carruba, Valerio; Petit, Jean-Marc; Rousselot, Philippe; Mousis, Oliver; Marsden, Brian G; Jacobson, Robert A Discovery of five irregular moons of Neptune, Nature, 430 (2004), pp. 865-867. Final preprint(pdf)

• Ephemeris from IAU
• Mean orbital parameters from JPL