negative declination

At the other point the Sun is moving from positive to negative declination and that is the autumnal equinox, falling on September 23, the beginning of the northern autumn.

Unlike the fixed stars, the Sun changes its position on the celestial sphere, being at a positive declination in summer, at a negative declination in winter, and having exactly zero declination (i.e., being on the celestial equator) at the equinoxes.