The sun crosses the celestial equator this week, meaning that the March equinox is upon us.
The celestial equator is the projection of the Earth’s equator up into the sky. Because Earth rotates on a tilted axis, which always points in the same direction, our orientation to the sun changes throughout the year. When we are in the hemisphere tilted towards the sun, our parent star appears higher in the sky than the celestial equator and we experience summer with its longer days. Likewise, when the axis is pointed away, the sun never rises as high as the celestial equator and we experience winter with shorter days.
The longest day is known as the summer solstice and the shortest is the winter solstice. As the day length gradually changes from one to another, so there comes a point when the day lengths are roughly equal because the Sun is on the celestial equator. There are two each year, one in March and the other in September. This year, the March equinox takes place on 20 March at 03:06 GMT. This means that in certain westward time zones, the equinox will actually fall on 19 March local time.
