The question of how fast one must travel to keep the sun from moving across the sky is a thought experiment rooted in physics. Since the sun’s apparent movement is due to the Earth’s rotation, the challenge is to match that rotational speed exactly. To achieve this, a person would need to continuously move eastward at the same velocity as the ground beneath them is spinning. This constant velocity would effectively freeze the sun in one spot, creating a perpetual noon or sunset.
Defining the Earth’s Rotational Speed
Calculating the required speed involves understanding the fundamental components of the Earth’s movement. The time component is straightforward: the Earth completes one full rotation in approximately 24 hours, which is the period of a solar day. The distance traveled during that time is defined by the Earth’s circumference at the specific location. Because our planet is an oblate spheroid—bulging slightly at the middle—this circumference is not the same everywhere.
The largest circle any point on the surface traces during a rotation is the equator. This means a person standing on the equator must travel the greatest distance in 24 hours compared to anyone else on the planet. Therefore, the rotational velocity is highest at the equator, establishing the maximum speed required for this challenge. The circumference of the Earth at the equator measures approximately 24,901 miles (40,075 kilometers).
The Maximum Speed: Keeping Pace at the Equator
Using the equatorial circumference and the 24-hour rotational period, the maximum speed required to keep pace with the sun can be precisely calculated. This speed is approximately 1,040 miles per hour (1,670 kilometers per hour). To match the rotation and keep the sun stationary, a traveler at the equator would need to maintain this blistering velocity every single second.
This speed far exceeds the typical cruising velocity of commercial passenger jets (550 to 600 miles per hour). At 1,040 miles per hour, the required velocity is significantly faster than the speed of sound at sea level (roughly 767 miles per hour). A person attempting this feat would be traveling at approximately Mach 1.35, consistently breaking the sound barrier.
How Latitude Changes the Required Speed
The speed calculated for the equator is the absolute maximum, and the required velocity diminishes dramatically as one moves toward the poles. This change is due to the planet’s geometry; as a traveler moves away from the equator, the radius of the circle traced during a 24-hour rotation shrinks. The exact speed at any given latitude can be determined by multiplying the equatorial speed by the cosine of the latitude angle.
For instance, at a mid-latitude city near 45 degrees north or south, the required speed drops to approximately 733 miles per hour (1,180 kph). This is still a supersonic velocity, but it is noticeably slower than the speed needed at the equator. At 60 degrees latitude, the required speed is halved to about 520 miles per hour. At the precise North or South Pole, the rotational circle collapses to a single point, meaning the speed necessary to keep up with the sun is effectively zero.
Real-World Limitations of Achieving Solar Speed
While the physics of the calculation are clear, the practical execution of this feat is impossible for a ground-based vehicle. Sustaining a speed of over 1,000 miles per hour requires massive propulsion and aerodynamic engineering, immediately ruling out any standard car or train. The vehicle would have to cope with catastrophic atmospheric drag and friction at supersonic speeds.
A major limiting factor is the lack of a continuous, straight path along any line of latitude. The journey would require crossing vast oceans, mountains, and continents, rendering the use of a land vehicle unfeasible. Furthermore, no existing ground infrastructure, such as road surfaces or tires, is designed to endure speeds exceeding 1,000 miles per hour for a prolonged period. The most realistic method would involve a specialized aircraft flying at high altitude, but constant refueling and navigation challenges remain.