Eisenhauer, Perrin, Brandner, Straubmeier, Richichi, Gillessen, Berger, Hippler, Eckart, Schoeller, Rabien, Cassaing, Lenzen, Thiel, Clenet, Ramos, Kellner, Baumeister, Hofmann, Gendron, Boehm, Bartko, Haubois, Klein, Dodds-Eden, Houairi, Hormuth, Graeter, Jocou, Naranjo, Genzel, Kervella, Henning, Hamaus, Lacour, Neumann, Haug, Malbet, Laun, Kolmeder, Paumard, Pfuhl, Perraut, Ziegleder, Rouan, Rousset, 2008. GRAVITY: getting to the event horizon of Sgr A*.