1. What is the Speed of Light in Miles Per Hour?

Definition: The speed of light in a vacuum is a fundamental physical constant important in many areas of physics, exactly 670,616,629.3844 miles per hour.

Importance: This value is crucial for astronomical calculations, telecommunications, and understanding the fundamental laws of the universe.

2. About the Exact Value

The exact speed of light is defined as:

Precision: This value is exact by definition, as the meter is defined in terms of the speed of light.

3. Conversion Details

Base Value: The speed of light in vacuum is exactly 299,792,458 meters per second.

Conversion: To convert to miles per hour:

• 1 meter = 0.000621371 miles
• 1 hour = 3600 seconds
• Therefore: 299,792,458 m/s × 0.000621371 mi/m × 3600 s/hr = 670,616,629.3844 mph

4. Practical Applications

Astronomy: Used to calculate interstellar distances (light-years).

Physics: Fundamental in Einstein's theory of relativity (E=mc²).

Technology: Critical for GPS systems and fiber optic communications.

5. Frequently Asked Questions (FAQ)

Q1: Why is the speed of light considered a constant?
A: According to Einstein's theory of relativity, the speed of light in vacuum is constant regardless of the motion of the source or observer.

Q2: Does light always travel at this speed?
A: No, light travels slower when passing through materials like water or glass, but 670,616,629.3844 mph is its speed in vacuum.

Q3: How was the speed of light first measured?
A: Early measurements used astronomical observations, while the first terrestrial measurement was by Hippolyte Fizeau in 1849.

Q4: Why is this value exact now when it used to be measured?
A: Since 1983, the meter has been defined as the distance light travels in 1/299,792,458 seconds, making the speed of light exact by definition.

Q5: How does this compare to other speed measurements?
A: It's about 874,030 times faster than the speed of sound in air (767 mph) and could circle Earth's equator about 7.5 times in one second.