Free Astronomy Magazine September-October 2016

35 SPACE CHRONICLES the University of Arizona, USA, and one of the co-authors of the new study. “For about half of the plan- et’s orbit, which lasts 550 Earth- years, three stars are visible in the sky; the fainter two are always much closer to- gether, and change in apparent separation from the brightest star throughout the year,” adds Ke- vin Wagner, the study's first au- thor and discoverer of HD 131399Ab. For much of the planet’s year the stars would appear close together in the sky, giving it a familiar night-side and day-side with a unique triple sunset and sunrise each day. As the planet moves along its orbit the stars grow further apart each day, until they reach a point where the setting of one coincides with the rising of the other — at which point the planet is in near-constant day- time for about one-quarter of its orbit, or roughly 140 Earth-years. SEPTEMBER-OCTOBER 2016 T he background artist's impression shows a view of the triple-star sys- tem HD 131399 from close to the giant planet orbiting in the system. The planet is known as HD 131399Ab and appears on the left in the picture. [ESO/L. Cal- çada/M. Kornmesser]