Aphelion is the point in an object's orbit where it reaches its greatest distance from the Sun. At this location, the object moves at its slowest orbital speed due to the Sun's weaker gravitational pull. The term comes from Greek words meaning "away from the Sun."</p><p>Earth reaches aphelion around July 4th each year, when we're approximately 94.5 million miles (152.1 million kilometers) from the Sun—about 3 million miles farther than at perihelion in January. Surprisingly, this means Earth is actually farthest from the Sun during Northern Hemisphere summer! This counterintuitive fact demonstrates that seasons are caused by our planet's tilted axis, not our distance from the Sun.</p><p>Comets provide dramatic examples of aphelion effects. Halley's Comet travels from 0.6 AU at perihelion to 35 AU at aphelion (beyond Neptune's orbit), taking 76 years to complete its highly elliptical journey. At aphelion, it becomes a frozen, inactive chunk of ice and rock.</p><p>German astronomer Johannes Kepler first described these orbital mechanics in his laws of planetary motion (1609-1619), explaining how objects speed up when approaching the Sun and slow down when moving away. Understanding aphelion helps astronomers predict orbital periods, plan spacecraft missions, and study how solar radiation affects planetary climates throughout their orbital cycles.