पृष्ठम्:महाभास्करीयम्.djvu/२७५

190 RISING, SETTING AND CONJUNCTION OF PLANETS the Sun and the visible Moon. These correspond to the time to elapse before moonset. The Moon's agra and sankvagra are defined in the same way as in the case of the Sun.¹ The base (bahu or bhuja) for a planet is the distance of the foot of the perpendicular dropped from the planet on the plane of the horizon from the east-west line. It is equal to śankvagra + Rsin (agrā), + or -sign being taken acccording as the sankvagra and the Rsine of the agră are of like or unlike directions. The true value of the Moon's base (usually called spasta-bahu or spasta-bhuja) denotes the north-south distance between the projections of the Sun and the Moon on the plane of the horizon. It is equal to Moon's base + Sun's base, + or - sign being taken according as the bases of the Sun and the Moon are of unlike or like directions. When the Sun is on the horizon as in the case contemplated in the above stanzas, is is equal to Moon's base + Sun's agrā.² The upright denotes the difference between the Rsines of the alti- tudes of the Moon and the Sun. In the present case, the Sun's altitude is zero, so that the upright is equal to the Rsine of the Moon altitude. The base and the upright defined above will be required in the stanzas below. Method for the graphical representation of the elevation of the lunar horns in the first quarter of the month at sunset: 13-17. To the north or south of the Sun is (to be laid off) the (true) base (according to its direction); and to the easts (of the point thus obtained) is (to be laid off) the upright; the line which joins the ends of the base and the upright is called the hypotenuse. (Taking the centre) at the meeting point of the hypotenuse and the upright, draw the Moon's disc. The ¹ Vide supra, chapter III, stanzas 37 and 54, pp. 84 and 93. 2 The Sun's base in this case is the same as the Sun's agră. 3 The upright is laid off towards the east because in the light half of the month the Moon is towards the east of the Sun.