Context: Early on July 5, the Earth reached aphelion, its farthest distance from the sun in our year-long journey around our nearest star.

What is Aphelion? 

• Aphelion is a term used in astronomy to denote the point in the orbit of a planet or celestial body where it is farthest from the Sun. 

• The Earth’s orbit around the Sun is not a perfect circle but rather an ellipse, with the Sun situated at one of the two foci of the ellipse. 

• Aphelion marks the moment when Earth is at its maximum distance from the Sun along this elliptical path.

• The concept of aphelion was crucial in Johannes Kepler‘s formulation of his laws of planetary motion during the 17th century.

What exactly are Aphelion and Perihelion?

• Aphelion refers to the point in Earth's orbit when it is farthest from the Sun, occurring around July 4 each year. At this juncture, the distance between Earth and the Sun extends to approximately 152.5 million kilometers. Conversely, Perihelion denotes the opposite scenario, where Earth is closest to the Sun, happening around January 3 annually, with a distance of approximately 147.5 million kilometers.

• The distance variations between Aphelion and Perihelion may seem subtle, only about 5 million kilometers apart, but they play a crucial role in shaping Earth's climate and seasons. The Earth-Sun distance impacts the amount of solar energy received, influencing seasonal variations and temperature patterns across the globe.

Implications for Earth's Seasons

• The timing of Aphelion and Perihelion influences the occurrence of seasons on Earth.

• Contrary to common belief, Earth's distance from the Sun during each season is not the primary determinant of seasonal changes. Instead, it is the tilt of Earth's axis that plays a pivotal role.

• However, the slight distance variation during Aphelion and Perihelion does contribute to subtle differences in solar radiation received, impacting regional climates.

How far is the Earth from the Sun at aphelion? 

• At aphelion, which occurs around July 4th– 5th each year, the Earth is approximately 152.1 million kilometers (about 94.5 million miles) away from the Sun. 

• This distance is about 3.3% greater than its average distance from the Sun, known as its semi-major axis, which is about 147.1 million kilometers.

Does aphelion affect temperatures on Earth? 

• Aphelion has a slight effect on temperatures on Earth, but its impact is minimal compared to other factors such as axial tilt and atmospheric circulation patterns. 

• Despite being farther from the Sun during aphelion, the Earth’s tilt towards the Sun during the northern hemisphere’s summer results in warmer temperatures for that region. 

• This phenomenon is primarily responsible for the seasons on Earth.

What would happen if there were no aphelion? 

• If Earth’s orbit were perfectly circular, without aphelion or perihelion (the closest point to the Sun), the distance between Earth and the Sun would remain constant throughout the year. 

• This scenario would result in less variation in seasonal temperatures between the northern and southern hemispheres. 

• The distinct seasons that we experience today, which are essential for ecological diversity and agricultural cycles, would be significantly altered.

Conclusion

• In conclusion, Aphelion and Perihelion are fundamental concepts in astronomy and planetary motion, offering valuable insights into Earth's orbit, seasonal variations, and solar energy dynamics.