Much of the Hindu calendar is based on the sidereal (nirayana) zodiac, the apparent movement of heavenly bodies in relation to the constellations (nakshatras).

The difference between the zodiacs, known as #ayanamsha, is caused by precession of the equinoxes — the small difference in duration between a tropical and a sidereal year.

Because of this the two zodiacs drift apart, and that is why the festival of #MakarSankranti (calculated using the sidereal zodiac) is now celebrated in mid-January.

Much of the Hindu calendar is based on the sidereal (nirayana) zodiac, the apparent movement of heavenly bodies in relation to the constellations (nakshatras).

The difference between the zodiacs, known as #ayanamsha, is caused by precession of the equinoxes — the small difference in duration between a tropical and a sidereal year.

Because of this the two zodiacs drift apart, and that is why the festival of #MakarSankranti (calculated using the sidereal zodiac) is now celebrated in mid-January.

Much of the Hindu calendar is based on the sidereal (nirayana) zodiac, the apparent movement of heavenly bodies in relation to the constellations (nakshatras).

The difference between the zodiacs, known as #ayanamsha, is caused by precession of the equinoxes — the small difference in duration between a tropical and a sidereal year.

Because of this the two zodiacs drift apart, and that is why the festival of #MakarSankranti (calculated using the sidereal zodiac) is now celebrated in mid-January.