Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s3.71

v2.c12.s3.71

The cause of mean motions of planets has already been discussed above. The numbers of the revolutions of planets in the Zodiac during the period of one Kalpa or one Mahāyuga have already been given as mentioned by different siddhāntas. There is a noteworthy point about Mercury and Venus; and it is that because they are always found near the Sun, their revolutions in the Zodiac are assumed to be always equal to those of the Sun; and hence, our authors of the works have assumed for them the same number of revolutions and mean motion as for the Sun. But having regarded the conjunction (Śīghra) of Mercury and Venus as some planets, the numbers of their revolutions given by them in the works happen to be equal to those of their actual revolutions round the Sun; and although our astronomers had no idea that planets revolve round the sun, it is worth remembering that they had given importance to the revolutions of the ‘Śīghras’ of Mercury and Venus.