. Elements of theoretical and descriptive astronomy, for the use of colleges and academies. distance of the moon from the observer decreases. Butthe earths radius is about g^th of the distance of the moonfrom the earths centre: therefore the semi-diameter of themoon in the zenith will be greater than the semi-diameter inthe horizon by -g^th of itself, or by about 15. This increaseis called the augmentation of the moons semi-diameter. 139. Two bodies are said to be in conjunction when they havethe same longitude. They are said to be in opposition whentheir longitudes differ by 180°; and in quad
. Elements of theoretical and descriptive astronomy, for the use of colleges and academies. distance of the moon from the observer decreases. Butthe earths radius is about g^th of the distance of the moonfrom the earths centre: therefore the semi-diameter of themoon in the zenith will be greater than the semi-diameter inthe horizon by -g^th of itself, or by about 15. This increaseis called the augmentation of the moons semi-diameter. 139. Two bodies are said to be in conjunction when they havethe same longitude. They are said to be in opposition whentheir longitudes differ by 180°; and in quadrature when theirlongitudes differ by either 90° or 270°. The moon is an opaque body, which is rendered visible tous by the rays of light which it reflects from the sun. Thephases of the moon are due to the different relative positionsto the sun and the earth which it has while revolving aboutthe earth. In Fig. 54 let E be the earth, and the circle ACFH the orbhof the moon. Since the inclination of the plane of the moonaorbit to the plane of the ecliptic is only a few degrees, we may. centre of the earth, andMthat of the moon. Withthe distance between E andM as a radius, describe the B Fig. 53. ,jy semi-circumference When the moon is in the\ horizon of the point C, itsdistances from C and fromE are very nearly as the moon rises, the THE MOONS PHASES. Ill \si:s. 127 neglect it in this case, and suppose the two planes to the sun lie in the direction ES. Since the distance of the
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