Editing Orbital inclination (section)

===Exoplanets and multiple star systems===
The inclination of [[exoplanet]]s or members of [[Star system|multi-star star systems]] is the angle of the plane of the orbit relative to the [[plane of the sky]]: a plane perpendicular to the line of sight from Earth to the object: .<ref name="Campante">{{cite journal
|author=Tiago L. Campante
|date=27 October 2016
|title=Spin-orbit alignment of exoplanet systems: Analysis of an ensemble of asteroseismic observations
|url=https://www.cambridge.org/core/services/aop-cambridge-core/content/view/10DAA84B787CEF3DE91E5398CFB20123/S1743921316006232a.pdf
|journal=Proceedings of the International Astronomical Union
|publisher=Cambridge University Press
|volume=11
|issue=General Assembly A29B
|pages=636–641
|doi=10.1017/S1743921316006232
|bibcode=2016IAUFM..29B.636C
|s2cid=126328423
|access-date=27 February 2022
}}</ref>
* An inclination of 0° is a face-on orbit, meaning the plane of the exoplanet's orbit is perpendicular to the line of sight with Earth.
* An inclination of 90° is an edge-on orbit, meaning the plane of the exoplanet's orbit is parallel to the line of sight with Earth.

Since the word "inclination" is used in exoplanet studies for this line-of-sight inclination, the angle between the planet's orbit and its star's rotational axis is expressed using the term the "spin-orbit angle" or "spin-orbit alignment".<ref name="Campante"/> In most cases the orientation of the star's rotational axis is unknown.

Because the [[doppler spectroscopy|radial-velocity method]] more easily finds planets with orbits closer to edge-on, most exoplanets found by this method have inclinations between 45° and 135°, although in most cases the inclination is not known. Consequently, most exoplanets found by radial velocity have [[Binary mass function|true masses]] no more than 40% greater than their [[minimum mass]]es.{{citation needed|date=May 2014}} If the orbit is almost face-on, especially for superjovians detected by radial velocity, then those objects may actually be [[brown dwarf]]s or even [[red dwarf]]s. One particular example is [[HD 33636]] B, which has true mass 142 M<sub>J</sub>, corresponding to an M6V star, while its minimum mass was 9.28 M<sub>J</sub>.

If the orbit is almost edge-on, then the planet can be seen [[transit method|transiting]] its star.