Every year, Earth follows an elliptical orbit around the Sun, meaning its distance from the Sun changes throughout the year. One of the most important points in this orbit is perihelion, the moment when Earth is closest to the Sun. But what actually happens during perihelion? Does it affect our seasons, weather, or climate?
In this topic, we’ll explore what perihelion is, when it occurs, and its impact on Earth.
Understanding Perihelion and Aphelion
Earth’s orbit is not a perfect circle but an ellipse. This means there are two key points in its journey around the Sun:
- Perihelion – The point in Earth’s orbit where it is closest to the Sun.
- Aphelion – The point in Earth’s orbit where it is farthest from the Sun.
How Close Is Earth at Perihelion?
At perihelion, Earth is about 147.1 million kilometers (91.4 million miles) from the Sun. In contrast, at aphelion, it is about 152.1 million kilometers (94.5 million miles) away. This means there is a difference of about 5 million kilometers (3 million miles) between the two points.
When Does Perihelion Occur?
Many people assume that perihelion happens during summer because Earth is closer to the Sun. However, this is not true.
- Perihelion occurs in early January each year, typically between January 2 and January 5.
- Aphelion happens in early July.
This might seem surprising, but it shows that Earth’s distance from the Sun does not determine the seasons.
What Happens When Earth Reaches Perihelion?
1. Earth Moves Faster in Its Orbit
Because Earth follows Kepler’s Second Law of Planetary Motion, it moves faster when it is closer to the Sun. This means:
- Earth’s orbital speed is highest at perihelion, about 30.3 km/s (18.8 miles per second).
- At aphelion, Earth moves slower, around 29.3 km/s (18.2 miles per second).
This difference slightly shortens the length of winter in the Northern Hemisphere and summer in the Southern Hemisphere.
2. The Sun Appears Slightly Larger in the Sky
Since Earth is closer to the Sun at perihelion, the Sun appears about 3% larger in the sky compared to aphelion. However, this change is so small that most people don’t notice it.
3. Slight Increase in Solar Energy
At perihelion, Earth receives about 7% more solar energy than at aphelion. This extra energy does not cause noticeable temperature changes because seasons are determined by Earth’s axial tilt, not its distance from the Sun.
4. Shorter Winter in the Northern Hemisphere
Because Earth moves faster in its orbit at perihelion, the duration of winter in the Northern Hemisphere is slightly shorter than summer. In contrast, the Southern Hemisphere experiences a longer summer and shorter winter.
5. Minor Atmospheric and Oceanic Effects
The increased solar radiation at perihelion can have small effects on Earth’s atmosphere and oceans, including:
- Slight changes in global wind patterns.
- Minor variations in ocean currents.
- Small fluctuations in weather patterns.
However, these effects are too small to cause major climate changes.
Does Perihelion Affect Seasons?
Many people believe that Earth’s seasons are caused by its distance from the Sun, but this is incorrect. Seasons are primarily caused by Earth’s axial tilt (23.5 degrees).
- When the Northern Hemisphere is tilted toward the Sun (June), it experiences summer, even though Earth is farther from the Sun (aphelion).
- When the Southern Hemisphere is tilted toward the Sun (December), it experiences summer, even though Earth is closer to the Sun (perihelion).
This proves that Earth’s tilt, not its distance from the Sun, is the main driver of seasonal changes.
Interesting Facts About Perihelion
- Earth’s orbital shape changes over time – The orbit becomes more or less elliptical over thousands of years due to gravitational influences from other planets.
- Other planets also have perihelion and aphelion – For example, Mars has a much more elliptical orbit than Earth, making its perihelion and aphelion distances much more extreme.
- Perihelion shifts over time – Due to gravitational interactions and the precession of Earth’s orbit, the date of perihelion slowly changes over thousands of years.
When Earth reaches perihelion, it is at its closest point to the Sun, moves faster in orbit, and receives slightly more solar energy. However, these factors do not significantly impact seasons because Earth’s tilt is the main reason for seasonal changes.
Perihelion is a fascinating reminder of how Earth’s motion is governed by physics, and it plays a role in the subtle variations of our planet’s climate and orbital dynamics.
