The 235th 'Galactic Tick Day', since the idea's inception in 1608, was observed on September 29, 2016. Earth, along with the rest of the Solar System, completes one revolution around the Milky Way galaxy's centre every 225 million years. The shift of one centi-arcsecond, or around 0.0000027 degrees, is called a Galactic Tick, an event happening once every 1.7361 years.