GRAVITY is part of the Very Large Telescope Interferometer (VLTI) at the European Southern Observatory in Chile. The instrument operates in the near infrared and combines the light of four telescopes, whereby it achieves the spatial resolution of an equivalent telescope with 130 meters in diameter. Due to its high sensitivity and accuracy, it allows researchers to render very small and faint cosmic objects visible. GRAVITY also measures distances very accurately and is therefore very suitable for the measurement of movements. For example, with the help of GRAVITY, the motion of a star around the black hole at the centre of our galaxy could be observed, confirming the predictions of general relativity.