At one time, the Sun’s southward course commenced on his reaching the middle of Āśleṣā (the ninth constellation) and its northward course on its reaching the beginning of Dhaniṣṭhā (the twenty-third constellation). This must have been the case as we find it so recorded in ancient books.
Whereas at present the one course of the sun (āditya) commences at the beginning of Cancer, and the other at the beginning of Capricornus. That it is so, and different from what it was at one time can easily be ascertained from actual observation as follows:
Either from observing some distant point in the horizon where the sun rises or sets or from observing the ingress or the egress of the end of shadow of a perpendicular rod placed at the centre of a big horizontal circle (the change in the sun’s course can be detected).
अप्राप्य मकरं अर्को विनिवृत्तो हन्ति सापरां याम्याम् । कर्कटकं असम्प्राप्तो विनिवृत्तश्चौत्तरां स ऐन्द्रीम् ॥ ३-०४ ॥
If the Sun should change his course before reaching Makara (Capricornus) he will bring evil on the west and south; and if he should do so before reaching Karka (Cancer), he will bring evil on the north and east.
The Sun when he changes his course from north to south and when in his usual condition will bring on prosperity and increase of crops; but when he undergoes a change either in his usual course or in his usual appearance he causes fear to mankind.