In geometry, the major axis o an ellipse is its langest diameter: a line segment that runs throu the centre an baith foci, wi ends at the widest pynts o the perimeter. The semi-major axis is ane hauf o the major axis, an thus runs frae the centre, throu a focus, an tae the perimeter. Essentially, it is the radius o an orbit at the orbit's twa maist distant pynts. For the special case o a circle, the semi-major axis is the radius. Ane can think o the semi-major axis as an ellipse's lang radius.
The semi-minor axis (an aa semiminor axis) is a line segment associatit wi maist conic sections (that is, with ellipses an hyperbolas) that is at richt angles with the semi-major axis an haes ane end at the centre o the conic section. It is ane o the axes o symmetry for the curve: in an ellipse, the shorter ane; in a hyperbola, the ane that disna intersect the hyperbola.