Laser Beams is one way to measure the distance to the Moon.
Have you ever wondered how scientists know the exact distance between the Earth and the Moon? It’s not like they can simply measure it with a tape measure! Instead, they use a variety of techniques and tools to calculate the distance. In this blog post, we’ll explore how scientists measure the distance to the Moon.
Around 270 BC, Aristarchus figured out how far the Moon was from Earth by observing a lunar eclipse. At the time, people believed that the Earth was a sphere and the center of the universe, and that the Sun, Moon, planets, and stars all revolved around it. Aristarchus assumed that the Moon moved in a circle around Earth and used the radius of that circle and the time it took the Moon to orbit Earth (about one month) to calculate the Moon’s distance. During a lunar eclipse, when the Moon passes through the Earth’s shadow, the time it takes for the middle of the Moon to cross the center of the shadow (about three hours) can be used to calculate the radius of the Earth. By comparing these measurements, Aristarchus estimated that the Moon was about 60 times the radius of the Earth away from us, which is similar to the current accepted value. Hipparchus would improve on this calculation some forty years later and derived an answer within 2,000 miles of the currently known average distance of the moon from Earth!
- Math In-Depth by NASA!
- Similar Lunar Parallax Method on Khan Academy
- ClassRoom Astronomer Parallax Method
Another method that is commonly used to measure the distance to the Moon is called radar ranging. This technique involves bouncing a radar signal off the surface of the Moon and measuring the time it takes for the signal to return. This technique is used for nearby objects like Venus and the moon. By knowing the speed of the radar signal and the time it takes to travel to the Moon and back, scientists can calculate the distance to the Moon.
- Radar Ranging at University of Nebraska-Lincoln
- More on Radar Astronomy from Brian Koberlein and the National Radio Astronomy Observatory
Yet another method used to determine the distance to the Moon is called the laser ranging technique. This method involves firing a laser beam at a reflector on the Moon’s surface and measuring the time it takes for the beam to return. By knowing the speed of light and the time it takes for the laser beam to travel to the Moon and back, scientists can calculate the distance to the Moon1.
Credit EarthHOW.com
One of the most important historical events that helped scientists accurately measure the distance to the Moon was the Apollo 11 mission. During this mission, astronauts placed a series of reflectors on the surface of the Moon, which allowed scientists to use the laser ranging technique to measure the distance to the Moon more accurately than ever before. The Soviet Union LUNA missions to the moon also play an important part to this day as one of their mirrors has been re-discovered on the moon and can be used for Laser Ranging studies of the moon.
In summary, scientists use a variety of methods to measure the distance to the Moon, including the lunar parallax method, radar ranging, and laser ranging. These methods involve observing the Moon from different locations on Earth, bouncing radar signals off the Moon’s surface, and firing lasers at reflectors on the Moon’s surface. Thanks to these methods, we can accurately calculate the distance to the Moon, which has helped us better understand our closest celestial neighbor.
Footnotes
Author: J. Verne