
nautical circle: generic term for a circular mathematical instrument of use in navigation, but likely to carry a range of mathematical and astronomical scales.

nautical hemisphere: a combination of graduated arcs and circles used for navigational calculations, see article on the nautical hemisphere.

navicula dial: type of altitude dial in the shape of a ship.

nocturnal: instrument for finding the time at night from the orientation of the stars, see article on the nocturnal.

nocturnal and quadrant: compound instrument which combines both the functions of a nocturnal and quadrant, usually on two different sides of the same instrument, with equal importance given to each.

nocturnal and sundial: compound instrument which combines both the functions of a nocturnal and sundial, usually on two different sides of the same instrument, with equal importance given to each.

nonius: a way of subdividing a quadrant of a circle to provide fine discrimination of parts of degrees, comparable in purpose to the later vernier scale. The name comes from the latinized surname of the 16thcentury Portuguese mathematician Pedro Nu?ez.

Nuremberg hours: system of hour reckoning, see article on time and date.

octant: the eighth part of a circle or an instrument measuring up to 45 degrees.

old quadrant: type of horary quadrant, see article on the quadrant.

opposition: two planets 180? from each other in the ecliptic are said to be in opposition. This relative position had important astrological significance.

ordinary hours: system of hour reckoning, see article on time and date.

orthographic planisphere: flat map produced by orthographic projection.
