The Earth’s orbit around the Sun is not a perfect circle but an ellipse, meaning its distance from the Sun changes throughout the year. The point where Earth is closest to the Sun is called perihelion. But when does perihelion occur? How does it affect our planet? Let’s explore the science behind perihelion, its timing, and its impact on Earth’s climate.
When Does Perihelion Occur?
Perihelion occurs every year in early January, usually between January 2 and January 5. The exact date varies slightly due to gravitational interactions with other celestial bodies.
At perihelion, Earth is about 147.1 million kilometers (91.4 million miles) from the Sun. This is about 5 million kilometers (3.1 million miles) closer than its farthest point, known as aphelion, which occurs in early July.
Why Does Perihelion Happen in January?
The timing of perihelion is determined by Kepler’s laws of planetary motion, which describe how planets move around the Sun. Earth’s orbit is influenced by gravitational forces from the Sun and other planets, leading to slight variations in timing from year to year.
Does Perihelion Affect Earth’s Seasons?
1. No Direct Impact on Seasons
- Many people assume that Earth is warmer in January because it is closer to the Sun. However, this is not true.
- Seasons are caused by Earth’s axial tilt (about 23.5°), not its distance from the Sun.
- When it is winter in the Northern Hemisphere, the Southern Hemisphere experiences summer, and vice versa.
2. Slight Increase in Solar Energy
- Although perihelion does not cause seasons, it does increase the amount of solar energy Earth receives by about 7% compared to aphelion.
- This extra energy is more noticeable in the Southern Hemisphere, which has more ocean coverage, helping to regulate temperature changes.
The Difference Between Perihelion and Aphelion
| Feature | Perihelion | Aphelion |
|---|---|---|
| Date | Early January | Early July |
| Distance from Sun | ~147.1 million km | ~152.1 million km |
| Solar Energy Received | 7% more | 7% less |
How Perihelion Affects Earth’s Climate
Although the difference in distance between perihelion and aphelion is small, it does have some effects:
1. Slightly Shorter Winters in the Northern Hemisphere
- Since Earth moves slightly faster in its orbit when it is closer to the Sun, winter in the Northern Hemisphere is shorter, while summer is slightly longer.
- Conversely, the Southern Hemisphere has longer but milder summers due to the moderating effect of the oceans.
2. Changes in Orbital Eccentricity Over Time
- Earth’s orbit gradually changes shape over thousands of years due to gravitational interactions with other planets.
- These changes, known as Milankovitch cycles, influence long-term climate patterns, including ice ages.
Will the Date of Perihelion Change in the Future?
Yes! Over thousands of years, perihelion is slowly shifting due to a process called axial precession.
- In about 10,000 years, perihelion will occur in July instead of January.
- This shift may contribute to changes in Earth’s climate over long timescales.
Perihelion occurs in early January when Earth is closest to the Sun, but this does not cause seasons. Instead, Earth’s axial tilt is responsible for seasonal changes. While perihelion brings a small increase in solar energy, its effects are subtle and more noticeable in climate patterns rather than day-to-day weather. Over time, the timing of perihelion will continue to shift due to natural orbital changes, shaping Earth’s long-term climate history.
