In celestial mechanics, '''true longitude''' is the ecliptic longitude at which an orbiting body could actually be found if its inclination were zero. Together with the inclination and the ascending node, the true longitude can tell us the precise direction from the central object at which the body would be located at a particular time.
==Calculation== The true longitude {{math|''l''}} can be calculated as follows:<ref name=Moulton_1970>{{cite book|last=Multon|first=F. R.|date=1970|title=An Introduction to Celestial Mechanics|edition=2nd|pages=182–183|location=New York, NY|publisher=Dover}}</ref><ref name=Roy_1978>{{cite book|last=Roy|first=A. E.|date=1978|title=Orbital Motion|page=174|ISBN=0-470-99251-4|location=New York, NY|publisher=John Wiley & Sons}}</ref><ref name=Brouwer_Clemence_1961>{{cite book|last1=Brouwer|first1=D.|last2=Clemence|first2=G. M.|date=1961|title=Methods of Celestial Mechanics|url=https://archive.org/details/methodsofcelesti00brou|url-access=registration|page=[https://archive.org/details/methodsofcelesti00brou/page/45 45]|location=New York, NY|publisher=Academic Press}}</ref>
:{{math|1=''l'' = ''ν'' + ''ϖ''}}
where: *{{math|''ν''}} is the orbit's true anomaly, *{{math|''ϖ'' ≡ ''ω'' + ''Ω''}} is the longitude of orbit's periapsis, **{{math|''ω''}} is the argument of periapsis, and **{{math|''Ω''}} is the longitude of the orbit's ascending node,
==References== {{Reflist}}
{{Orbits}}
{{DEFAULTSORT:True Longitude}} Category:Orbits Category:Equations of astronomy
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