# How to use *Perigee* in a sentence

An Anomalistic month is the time in which the moon passes from

**perigee**to**perigee**, &c.The problem of determining an orbit may be regarded as coeval with Hipparchus, who, it is supposed, found the moving positions of the apogee and

**perigee**of the moon's orbit.A line joining the moon in

**perigee**and in apogee is called the " line of apsides."In the case of the motion of the moon around the earth, assuming the gravitation of the latter to be subject to the modification in question, the annual motion of the moon's

**perigee**should be greater by I 5" than the theoretical motion.It may be considered as arising from a semi-annual variation in the eccentricity of the moon's orbit and the position of its

**perigee**.AdvertisementThis is a cycle of 18 years II days, or 223 lunations, discovered at an unknown epoch in Chaldaea, at the end of which the moon very nearly returns to her original position with regard as well to the sun as to her own nodes and

**perigee**.Thus the apogee and

**perigee**became two definite points of the orbit, indicated by the variations in the angular motion of the moon.His most important contribution to the subject consisted in working out by extremely elegant mathematical processes the method of determining the motion of the

**perigee**.The first of the outstanding gravitational problems with which they grappled was the unaccountably rapid advance of the lunar

**perigee**.The eccentricity of the ellipse is in the general average about 0.055, whence the moon is commonly more than i' further from the earth at apogee than at

**perigee**.AdvertisementThe Babylonians knew of the inequality in the daily motion of the sun, but misplaced by to' the

**perigee**of his orbit.Then, by an obvious law of kinematics, the angular motion round the earth would be most rapid at the point nearest the earth, that is at

**perigee**, and slowest at the point most distant from the earth, that is at apogee.Assuming the mean motion of the moon to be known and the

**perigee**to be fixed, three eclipses, observed in different points of the orbit, would give as many true longitudes of the moon, which longitudes could be employed to determine three unknown quantities - the mean longitude at a given epoch, the eccentricity, and the position of the**perigee**.We may conclude the ancient history of the lunar theory by saying that the only real progress from Hipparchus to Newton consisted in the more exact determination of the mean motions of the moon, its

**perigee**and its line of nodes, and in the discovery of three inequalities, the representation of which required geometrical constructions increasing in complexity with every step.By taking three eclipses separated at short intervals, both the mean motion and the motion of the

**perigee**would be known beforehand, from other data, with sufficient accuracy to reduce all the observations to the same epoch, and thus to leave only the three elements already mentioned unknown.Advertisement