The summer temperatures in the Northern Hemisphere are reaching record highs, with heatwaves sweeping across various countries in the region, causing residents to experience one of the hottest summers in history.
Notably, at this time, the Earth is about to reach its farthest point from the Sun in its orbit this year. This annual event is known as aphelion, a term that originates from the Greek words “apo” (away) and “helios” (Sun), according to the Almanac.
This event has raised many questions: If the Earth is at its farthest distance from the Sun, why is summer still so hot with such high temperatures?
Today, July 6, at aphelion, the Earth will be 1.01 AU from the Sun.
To answer this question, we first need to consider how the Earth orbits the Sun, as well as how our planet rotates on its axis.
Astronomers consider the average distance between the Earth and the Sun to be one astronomical unit (AU), which is approximately 93 million miles (150 million km), according to the definition by the International Astronomical Union (IAU).
However, the Earth’s slightly elliptical orbit around the Sun also means that each year there is a day when the Earth is closest to the Sun (perihelion) and a day when our planet is farthest from its star (aphelion).
In 2023, perihelion occurred on January 4, when the Earth was 0.98 AU from the Sun. According to astronomer Fred Espenak, today, July 6, at aphelion, the Earth will be 1.01 AU from the Sun.
Looking back at history, perihelion and aphelion were first noted by astronomer Johannes Kepler in the 17th century. He calculated that planets have elliptical orbits around the Sun and noted that a planet moves fastest at perihelion and slowest at aphelion. This results in the summer in the Northern Hemisphere being a few days longer than the summer in the Southern Hemisphere.
Although the difference between perihelion and aphelion can be a few million kilometers, this discrepancy has little effect on Earth’s temperatures. In July, the Northern Hemisphere tilts towards the Sun, allowing for full sunlight during summer, resulting in longer and hotter days. Meanwhile, the Southern Hemisphere tilts away from the Sun, resulting in shorter and cooler days.
Even though aphelion occurs just a few weeks after the summer solstice in June, and perihelion occurs close to the December solstice, these events are not related to each other. The precise timing is caused by changes in the eccentricity of Earth’s orbit, according to timeanddate.com, with the dates of perihelion and aphelion drifting one day every 58 years since the 13th century.
