The vast emptiness of space often defies intuition, especially regarding distances between celestial bodies that appear close in illustrations. A common thought experiment asks: how many of the solar system’s other planets could you physically line up side-by-side in the gap between Earth and its Moon? The answer highlights a profound truth about astronomical scale, revealing that the Moon is much farther away than most people imagine. This calculation provides a tangible way to grasp the immense distance separating our planet from its only natural satellite.
Defining the Earth-Moon Distance
The distance separating the Earth and the Moon, known as the lunar distance (LD), is the fundamental measurement required for this thought experiment. On average, the center of the Earth is separated from the center of the Moon by approximately 384,400 kilometers (238,855 miles). This figure is an average because the Moon orbits Earth in an ellipse, not a perfect circle.
This elliptical path means the distance constantly changes. When the Moon is at its closest point (perigee), the distance shrinks to about 356,500 kilometers. Conversely, when the Moon reaches its farthest point (apogee), the distance stretches to roughly 406,700 kilometers.
The average distance of 384,400 kilometers is the figure most commonly used. Scientists measure this distance with precision using the lunar laser ranging experiment. This involves bouncing powerful laser beams off retroreflectors left on the Moon’s surface by Apollo astronauts, allowing scientists to determine the separation down to the centimeter level.
Calculating the Planetary Fit
To determine how many planets fit in the gap, one must sum the equatorial diameters of the solar system’s other seven planets: Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune. The total width of all these planets, placed end-to-end, is just slightly less than the average distance to the Moon.
The calculation includes the four terrestrial planets and the four gas giants:
- Mercury: 4,879 kilometers
- Venus: 12,104 kilometers
- Mars: 6,779 kilometers
- Jupiter: 139,822 kilometers
- Saturn: 116,464 kilometers
- Uranus: 50,724 kilometers
- Neptune: 49,244 kilometers
The total length created by lining up all seven planets side-by-side is approximately 380,012 kilometers. Comparing this total to the average Earth-Moon distance of 384,400 kilometers shows they fit with space left over. After placing the seven planets in the gap, a remaining distance of about 4,388 kilometers still exists. This remaining space is roughly the size of Mercury, meaning an eighth, smaller planet could almost fit in the remaining void.
Visualizing the Scale of the Solar System
The fact that all other planets can be stacked between the Earth and the Moon demonstrates the true astronomical scale of the lunar distance. This tight fit reveals that the space between our planet and its satellite is far more expansive than simple diagrams often suggest, which frequently show the Earth-Moon system positioned unrepresentatively close together.
The seemingly large Earth-Moon distance is dwarfed when compared to the vast emptiness of the rest of the solar system. For instance, the distance between Earth and Mars varies dramatically due to their orbits, but at its closest, the two planets are separated by approximately 55 million kilometers. That separation is over 140 times greater than the average distance to the Moon.
Even the closest planet, Venus, is separated from Earth by a minimum distance of about 40 million kilometers. This comparison emphasizes that the space between Earth and the Moon is an isolated pocket of comparative closeness within a truly immense solar system. The surprising planetary fit serves as a powerful reminder that empty space is the dominant feature of our cosmic neighborhood.