The autumn equinox is now upon us! Today marks the moment that the sun crosses the celestial equator, ushering in the beginning of astronomical autumn in the northern hemisphere, which brings with it the inevitability of longer nights, perfect for stargazing.
In 2025, the autumn equinox will occur on Sept. 22 at 2:20 p.m. EDT (1820 GMT), when the sun moves southward across the celestial equator. The celestial equator is an imaginary projection of Earth's equator into space, forming a circle around the sky that divides the northern and southern celestial hemispheres. The sun's drop across the equator is due to a 23.5° tilt in Earth's rotational axis, which shifts our star's apparent path in the sky as our planet goes about its yearly orbit.
