Gravitational Lensing
![An image of the galaxy cluster Abell 1689 actings as a gravitational lens, with arcs of background galaxies around it.](/sites/default/files/learn/Abell_1689_Gravitational_Lensing.jpg)
cluster Abell 1689.
Credit: NASA
In partnership with the Faulkes Telescope Project
Occupation: Astronomer and Professor
Year born: 1960
Occupation: Computational Cosmologist
Year born: 1951
Research Areas: Supercomputer Simulations, Galaxy Formation
Occupation: Physicist & Author
Year born: 1942
Research Areas: Cosmology, Theoretical Physics
The Extremely Large Telescope (ELT) will be the world's largest optical telescope. The telescope is being built by the European Southern Observatory (ESO). The ESO is made up of 16 countries which includes the UK and Ireland. The ELT is due to be complete at the end of 2027.
Measuring distances in astronomy is difficult but crucial.