The evolution of astrometry
Discover how we’ve been charting the skies for over 2,000 years
Astrometry is a branch of astronomy concerned with mapping the sky. Records show that it is one of the first sciences and was practised by several early civilisations. Monitoring the movements of stars and planets served a practical purpose for ancient cultures, from tracking time to aiding navigation and timing rituals .
The first astronomers could track visible celestial bodies and record their periodic motions, but it wasn’t until the third century BCE that attempts were made to estimate their distances using geometry.
The invention of the telescope in the 17th century led to an astronomy revolution. With an enhanced view of the universe, astronomers could collect more evidence to support the heliocentric model — the idea that the Sun, not the Earth, was at the centre of our Solar System. The telescope enabled much more detailed cataloguing of stars’ positions and distances.
The 19th and 20th centuries saw the development of more advanced telescopes, as well as photography, which improved the accuracy and detail of star charts. But Earth’s atmosphere interferes with measurements from the ground as it makes stars appear to flicker. Since the advent of the space age in the 1950s, we have been able to launch telescopes into orbit, overcoming atmospheric interference to see further into the cosmos than ever before.
ESA’S latest mission to chart the skies will rely on the space telescope Gaia, which is currently mapping the position, parallax and annual proper motion of about 1 billion stars. This will provide us with a three-dimensional map of our galaxy in unprecedented detail, as well as a new, definitive stellar catalogue, due to be published in the early 2020s.