Perihelion refers to the point in the orbit of a planet or any celestial object where it is closest to the Sun. It is the opposite of aphelion, which is the point where the object is farthest from the Sun. Perihelion and aphelion are specific terms used to describe the positions of objects in elliptical orbits, such as planets in our solar system.

The term "perihelion" is derived from the Greek words "peri," meaning "near," and "helios," meaning "Sun." It signifies the closest approach of a planet or comet to the Sun during its orbital path. The distance between the planet and the Sun is at its minimum at perihelion.

The perihelion point is not fixed and varies depending on the planet's orbit. For example, in the case of Earth, it occurs around January 3rd each year. This is when Earth is closest to the Sun in its elliptical orbit, at a distance of about 147 million kilometers (91 million miles). The date of perihelion can change slightly due to factors such as gravitational interactions with other planets and the effects of Earth's axial precession.

Perihelion has important implications for the seasons on a planet. Despite being closer to the Sun during perihelion, the seasons are primarily determined by the tilt of a planet's axis. For Earth, it is the tilt of about 23.5 degrees that causes the changing seasons, not the distance from the Sun. In fact, Earth is actually farthest from the Sun during its Northern Hemisphere summer. Other planets with different axial tilts may experience different seasonal patterns due to their perihelion and aphelion distances.