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Mean longitude is the ecliptic longitude at which an orbiting body could be found if its orbit were circular and free of perturbations. While nominally a simple longitude, in practice the mean longitude is a hybrid angle.〔 〕 ==Definition== * Define a reference direction, (unicode:♈), along the ecliptic. Typically, this is the direction of the vernal equinox. At this point, ecliptic longitude is 0°. * The body's orbit is generally inclined to the ecliptic, therefore define the angular distance from (unicode:♈) to the place where the orbit crosses the ecliptic from south to north as the ''longitude of the ascending node'', . * Define the angular distance along the plane of the orbit from the ascending node to the pericenter as the ''argument of the pericenter'', . * Define the ''mean anomaly'', , as the angular distance from the pericenter which the body would have if it moved in a circular orbit, in the same orbital period as the actual body in its elliptical orbit. From these definitions, the ''mean longitude'', , is the angular distance the body would have from the reference direction if it moved with uniform speed, : measured along the ecliptic from (unicode:♈) to the ascending node, then up along the plane of the body's orbit to its mean position.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「mean longitude」の詳細全文を読む スポンサード リンク
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