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A diagram of the orbit of comet 3D/Biela, with various important points and directions indicated, suitable for explaining orbital elements.

Creator: Louis H. Strous

The thick blue curve is the comet's orbit. The grey grid indicates the plane of the orbit of the Earth (the ecliptic). The grid points are spaced 1 Astronomical Unit apart. The thin grey curve is the vertical projection of the comet's orbit unto the ecliptic. The yellow lines connect points on the comet's orbit with the corresponding points projected vertically unto the ecliptic. The comet traverses the orbit in the counterclockwise direction.

The meaning of the labels and lines is as follows:

A	the descending node of the orbit, where the orbit goes from "above" to "below" the ecliptic.
B	the vertical projection of the aphelion unto the ecliptic.
C	the aphelion of the orbit, where the orbit is furthest from the Sun.
D	the ascending node of the orbit, where the orbit goes from "below" to "above" the ecliptic.
E	the vertical projection of the perihelion unto the ecliptic.
F	the perihelion of the orbit, where the orbit is closest to the Sun.
Z	the location of the Sun (at the intersection of AD, BE, and CF).
${\displaystyle \gamma }$	the direction of the vernal equinox.
AD	the line of nodes of the orbit.
CF	the line of apsides or major axis of the orbit.

The thick red line points from the Sun towards the vernal equinox. This direction corresponds to an ecliptical longitude of 0 degrees and is the direction compared to which the orbital element longitude of the ascending node is measured. The thin red line likewise indicates an ecliptical longitude of 90 degrees. The two red lines together define the plane of the Earth's orbit, the ecliptic, relative to which the orbital element inclination is measured.

This diagram was created by the author using the ANA data processing package (http://ana.lmsal.com, with some adjustments by the author). The orbital elements were taken from http://ssd.jpl.nasa.gov/data/ELEMENTS.COMET archive copy at the Wayback Machine. They are: perihelion = 0.87907300 AU, eccentricity = 0.75129900, inclination = 13.21640°, longitude of ascending node = 250.66900°, argument of perihelion = 221.65880°.

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Under the following conditions:

• attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
• share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.

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