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Perihelion and aphelion
Intermediate
Closest and farthest points to the Sun; speed is highest at perihelion.
Closest and farthest points: r_p = a(1 − e), r_a = a(1 + e). Speed is greatest at perihelion; angular momentum is conserved: r_p v_p = r_a v_a.
Halley's comet: 0.59 AU to 35 AU.
Seasons on Earth are not caused by perihelion.
In more detail
Perihelion is the closest point of an orbit to the Sun, and aphelion is the farthest point. Their distances depend on the semi-major axis and eccentricity.
Real-world uses
- Earth is closest to the Sun in early January, at perihelion.
- Comets are most visible near their perihelion passage.
- Comets are fastest at their closest approach to the Sun, which is why they glow brightly as they pass through the inner Solar System.
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Frequently asked questions
Does the closest point cause the seasons?
No. Seasons are caused by Earth's axial tilt, not its distance from the Sun.
What are the general terms?
Perigee and apogee refer to the closest and farthest points from Earth.
Where is a planet slowest in its orbit?
At aphelion, its farthest point from the Sun, where it moves most slowly.
Related topics in Gravitation & Orbits
Kepler's third law · Elliptical orbit energy · Eccentricity · Orbital transfers · Gravity assist · Tides