Surya Siddhanta
छायाभूमौ विपर्यस्ते स्वच्छायाग्रे तु दर्शयेत् । ग्रहः स्वदर्पणान्तःस्थः शङ्क्वग्रे सम्प्रदिश्यते॥
Exhibit, upon the shadow-ground, the planet at the extremity of its shadow reversed : it is viewed at the apex of the gnomon in its mirror. [As a practical test of the accuracy of his calculations, or as a convincing proof to the pupil or other person of his knowledge and skill, the teacher is heje directed to set up a gnomon upon ground properly prepared for exhibiting the shadow, and to calculate and lay off from the base ct the gnomon, but in the opposite to the true direction, the shadow which a planet would cast at a given time; upon placing, then, a horizontal mirror at the extremity of the shadow, the reflected image of the planet's disk will be seen in it at the given time by an eye placed- at the apex of the gnomon. The principle of the experiment is clearly corroct, and the rules and processes taught in the second and third chapters afford the means of carrying it out, since from them the shadow which any star would cast, had it light enough, may be as readily determined as that which the sun actually casts. As no case of precisely this character has hitherto been presented, we will briefly indicate the course of the calculation. The day and night of the planet, and its distance from the meridian, or its hourangle, are found in the same manner as in the process previously explained (p. 192, above), excepting that here the planet's latitude, and its declination as affected by latitude, must be calculated, by ii. 56-58; and then the hourangle and the ascensional difference, by iii. 34-36, give the length of the shadow at the given time, together with that of its hypothenuse. The question would next be in what direction to lay off the shadow from the base of the gnomon. This is accomplished by means of the base (bhuja) of the shadow, or its value when projected on a north and south line. From the declination is found, by iii. 20-22, the length of the noon-shadow and its hypothenuse, and from the latter, with the declination, comes, by iii. 22-23, the measure of amplitude (agrd) of the given shadow; whence, by iii. 23-25, is derived its base. Having thus both its length and the distance of its extremity from an east and west line running through the base of the gnomon, we lay it off without difficulty.]
english translation
chAyAbhUmau viparyaste svacchAyAgre tu darzayet । grahaH svadarpaNAntaHsthaH zaGkvagre sampradizyate॥
hk transliteration by Sanscript