DENVER (KDVR) — Fall officially starts in Colorado at 7:03 p.m. on Thursday evening. Fall is the season between the autumnal equinox and winter solstice.

The seasons all depend on the location of the Earth compared to the location of the sun.

Each year, around Sept. 22 the autumnal equinox happens. This is when there are equal parts, or 12 hours, of daylight and night in a 24-hour period.

An equinox happens twice a year, once in the fall and once in the spring also called the spring equinox.

During an equinox, the sun is shining directly over the Earth’s equator meaning that everyone across the world sees an equal 12 hours of sunlight on that given day.

After the autumnal equinox, the amount of sunlight gets shorter each day until the winter solstice as the sun moves south of the equator.