The distance from the center of a lens to one of its focal points is the focal length of the lens.
The length of the semi-major axis multiplied by the eccentricity.
Most orbits are elliptical; all NATURAL orbits are. There are two foci, or focuses, to an ellipse. The distance between the foci determines how eccentric, or non-circular, they are. If the two foci are in the same place, then the ellipse becomes a circle. So a circular orbit would have only one focus.
A half of a hyperbola is defined as the locus of points such that the distance of the point from one fixed point (a focus) and its distance from a fixed line (the directrix) is a constant that is greater than 1 (the eccentricity). By symmetry, a hyperbola has two foci and two directrices.
The one with the largest available focal length.
Foci, (the plural of focus), are a pair of points used in determining conic sections. They always fall on the major axis of symmetry of a conic. For example, in a circle, there is only one focus, the centerpoint. Every distance from the focus to any other point on the circle will be the same. In a parabola, the distance from any point of the parabola to the focus equals the distance from the centerpoint to the directrix. In a hyperbola, the difference of the distances between a point on the hyperbola and the focus points will be constant, and in an ellipse, the sum of the distances from any point on the ellipse to one of the foci is constant.
One.
Planets don't have circular orbits; all orbits are ellipses. A circle has one center, but an ellipse has two focuses, or "foci". The further apart the foci, the greater the eccentricity, which is a measure of how far off circular the ellipse is. Venus has the lowest eccentricity, at 0.007. Neptune is next with an eccentricity of 0.011. (Earth's orbit has an eccentricity of 0.017.) So, Venus has the shortest focus-to-focus distance.
The path itself is called its orbit. The shape is an ellipse, with the sun sitting at one of the foci.
CONCAVE LENS : lens that atleast possess one end inwards is called as concave lens. CONVEX LENS : lens that atleast possess one end outwards like the exterior of the sphere is called convex lens. According to the medical values convex lens are used for long sight vision problem and concave lens for short sight vision problems.
probably the sun since one of earths eliptical foci is the sun
An ellipse has 2 foci. They are inside the ellipse, but they can't be said to be at the centre, as an ellipse doesn't have one.
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.