Either of the two orbital points nearest or farthest from the center of attraction, the perihelion and aphelion in the case of an orbit about the sun, and the perigee and apogee in the case of an orbit about the earth. The line connecting these two points is called LINE OF APSIDES.
Related Terms 
RESTRICTOR
A device for producing a deliberate pressure drop or resistance in a line by reducing the crosssectional flow area.

GRID RHUMB LINE
A line making the same oblique angle with all grid meridians. Grid parallels and meridians may be considered special cases of the grid rhumb line.

HAND LEAD
A light sounding lead (7 to 14 pounds), usually having a line of not more than 25 fathoms

GROUND LOG
A device for determining the course and speed over the ground in shallow water consisting of a lead or weight attached to a line. The lead is thrown overboard and allowed to rest on the bottom. The course over ground is indicated by the direction the line tends and the speed by the amount of line paid out in a unit of time.

CASE DRAIN FILTER
A filter located in a line conducting fluid from a pump or motor housing to reservoir.

ELASTOHYDRODYNAMIC LUBRICATION
In rolling element bearings, the elastic deformation of the bearing (flattening) as it rolls, under load, in the bearing race. This momentary flattening improves the hydrodynamic lubrication properties by converting point or line contact to surfacetosurface contact.

GRID PARALLEL
A line parallel to a grid equator, connecting all points of equal grid latitude

HARBOR LINE
The line beyond which wharves and other structures cannot be extended

HORIZON
The great circle of the celestial sphere midway between the zenith and nadir, or a line resembling or approximating such a circle. The line where earth and sky appear to meet, and the projection of this line upon the celestial sphere, is called the visible or apparent horizon. A line resembling the visible horizon but above or below it is called a false horizon. The circle of the celestial sphereformed by the intersection of the celestial sphere and a plane perpendicular to the zenithnadir line is called sensible horizon if the plane is through any point, such as the eye of an observer; geoidal horizon if through any sealevel point; and celestial or rational horizon if through the center of the earth. The geometrical horizon was originally considered identi cal with the celestial horizon, but the expression is now more commonly used to refer to the intersection of the celestial

HEADING LINE
The line extending in the direction of a heading
