Semipääakseli

Semipääakseli, often translated as semi-major axis, is a fundamental concept in astronomy and physics, particularly in the study of ellipses and orbital mechanics. It is a parameter that describes the size of an ellipse. In the context of an ellipse, the semip major axis is half of the longest diameter of the ellipse. This longest diameter is known as the major axis, which passes through both foci of the ellipse and its two vertices. The semip major axis is therefore measured from the center of the ellipse to one of its vertices.

The semip major axis plays a crucial role in Kepler's laws of planetary motion. Specifically, Kepler's first law states that planets orbit the Sun in elliptical paths, with the Sun at one of the foci. The semip major axis of this elliptical orbit is a key factor in determining the orbital period of the planet, as described by Kepler's third law. The relationship between the orbital period (T) and the semip major axis (a) is given by T² ∝ a³, meaning that the square of the orbital period is proportional to the cube of the semip major axis.

In orbital mechanics, the semip major axis is a measure of the size of an orbit. A larger semip major axis indicates a larger orbit and, for bound orbits, a longer orbital period. Conversely, a smaller semip major axis signifies a smaller orbit with a shorter period. This parameter is essential for calculating various orbital characteristics, such as the velocity and energy of an orbiting body. It is a standard unit of measurement in astronomy for describing the size of planetary orbits and the distances between celestial objects.