Precession of Earth and the signs of the Zodiac

This animation shows the Earth’s precession and how it relates to the signs of the Zodiac. As the Earth rotates, it ‘wobbles’ slightly around its axis of rotation, much like a spinning top, tracing small circles on the night sky and changing how we view it. Each full precession cycle takes around 25 800 years to complete.   

This means that the apparent position of the Sun in the night sky on a given date changes depending on how far through the precession cycle the Earth is at that time. Since the Zodiac signs are defined by the Zodiac constellation the Sun is in at a given time, this means that someone’s astrological star sign also changes depending on the year they were born. For example, someone born in late September in the year 200 would be a Libra, while someone born on the same date in 2000 would be a Virgo, a Leo if born in the year 4000, and so on.  

This animation was originally produced for an ESO Chasing Starlight episode on astronomy myth busting.