An armillary sphere is a spherical astrolabe, showing the great circles in their unflattened orientation: The great circle of the ecliptic (the path of the Sun) is marked off in degrees of celestial longitude and in the 12 signs of the Zodiac. The great circle of the celestial equator is marked off in hours and degrees now called Right Ascension. Two partial circles at 23.5° from the celestial equator and parallel to it are the Tropic of Cancer in the north and Tropic of Capricorn in the south.