Whichever segment it is to which you are referring, it does not need to be red; it can be any color.

The segment that intersects both foci is called the semi-major axis. The segment that is perpendicular to the semi-major axis with one end midway between the foci is called the semi-minor axis.

The equation to find the semi-minor axis of elliptical orbit is b=a*sqrt(1 - e^2), where b is the semi-minor axis, a is the semi-major axis, and e is the eccentricity. Therefore, using 17.8AU as the semi-major axis and 0.967 as the eccentricity, the semi-minor axis is calculated to be 4.53AU or 6.62*10^11 m.

To describe the size of an ellipse.

The square root of ( a squared plus b squared ), quantity divided by a, where a is the length of the semi-major axis and b is the length of the semi-minor axis.

The square root of ( a squared plus b squared ), quantity divided by a, where a is the length of the semi-major axis and b is the length of the semi-minor axis.