Orbital eccentricity

The eccentricity, also called " Numeric eccentricity " or " orbital eccentricity ," in astronomy is a dimensionless quantity that serves as a web property to describe the form of a Keplerian orbit in celestial mechanics. It is the numerical eccentricity (defined therein) of each track. The eccentricity characterized the different train types, the solutions of the Kepler problem ( two-body problem ) are. This corresponds to

• The value 0 is an ideal circular path,
• A value greater than 0 and less than 1 in an elliptical orbit ( with increasingly elongated, narrow shape, the larger the value is )
• The value 1 of a parabolic orbit and
• A value greater than 1, of a hyperbolic track.

Note that in most cases, " e" is used as the symbol size, while used in mathematics for the eccentricity " ε " and "e" for the linear eccentricity is reserved. In astronomy, the linear eccentricity is, however, not used as an absolute size.

Term origin

The word eccentricity comes from the Latin ex, for " outside ", and from the centrum, for the "center ", ie excentricus " off-center " for. The name goes back to Tycho Brahe.

The so-called tychonische world system is a mixture of geocentric and heliocentric world view. The earth is the center of the world, which revolves around the sun. The other planets are acting in the so-called " eccentric " orbits around the sun.

Connection with other web elements

For an orbit in the form of a Kepler ellipse applies:

Eccentricity

For some cases is also the eccentricity angle φ as a path element an application:

The eccentricity is the deviation of the true anomaly ν (small Ny ) of the secondary crown SN from a right angle.

This relationship is especially true if you handled directly with the Kepler equation.

Examples

Among the planets in the solar system has the orbit of Venus with the least eccentricity 0.0067 (that is on kreisähnlichsten ) and the orbit of Mercury with 0.2056 the largest. The values ​​for the other planetary orbits, including for their mean distance from the Sun can be found in the list of the planets of the solar system.

Significantly greater eccentricity of the orbits have some transneptunischer objects: Pluto with 0.2502, 0.4383 with Eris and Sedna with 0.8587.

Orbits of comets generally have a very high eccentricity comets with an orbital period of more than 200 years, the value is often just under 1 153P/Ikeya-Zhang has in an orbital period of around 366 years orbital eccentricity of 0.99.