Abuja Map for From the zenith to the unobstructed horizon there are degrees; degree is equal to arcminutes or , arcseconds. Delta Effect. The theory that, as a comet makes a close approach to Earth within about . AU, the outer edges of the growing coma may go undetected by the human eye. Descending node. The point at which an orbit crosses the plane of the ecliptic, as the comet moves from the north of it to the south of it. Dust. Abuja Map 2016.