Since the orbit of Mercury is very close to the Sun, it is difficult to view. The maximum angles from the sun are 18° and 28° at the extremes of its orbit, and the sun moves about 15° per hour. As a result, there is never more than two hours of dark viewing for Mercury. The difficulties are compounded by the eccentricity of the orbit and its inclination to the ecliptic plane (7°, larger than any other except Pluto). With a synodic period of 115.9 days, it is at its maximum extension about six times per year, of which two usually offer good viewing.