Distance From Earth In “How High The Moon” - Science On

“Somewhere there’s music; How faint the tune! Somewhere there’s heaven; How high the Moon!” – “How High the Moon,” lyrics by Nancy Hamilton and music by Morgan Lewis

As a jazz standard, “How High the Moon” has been recorded and performed by countless jazz musicians, including Benny Goodman & His Orchestra, Les Paul and Mary Ford, and Ella Fitzgerald.

And I realize that the exclamation of “how high the Moon” is just an observation or rhetorical question, but just how high is the Moon?

On average, the Moon is 238,855 miles (384,400 kilometers) from Earth. I say “average” because the Moon follows an elliptical orbit around Earth. The Moon is closest at 225,623 miles (363,104 kilometers) from Earth. Its farthest distance is 252,088 miles (405,696 kilometers).

The Earth has an average diameter of 7,926 miles (12,753 kilometers), while the Moon has an average diameter of 2,159 miles (3,476 kilometers). This means that you could fit 30 Earths or 110 Moons between the Earth and the Moon.

The distance is accurately measured through the use of lasers. During the Apollo 11 mission in 1969, astronauts left the lunar laser ranging reflector on the surface of the Moon. Scientists used this reflector to “bounce” a laser beam off the Moon and measure the time it took for the laser to travel there and back. By combining this time with the velocity or speed of the laser, scientists could then calculate the distance between the Earth and the Moon.

distance to the Moon = (velocity of laser light x time to travel) ÷ 2

More reflectors were placed on the Moon by the Apollo 14 and 15 missions as well as the unmanned Lunokhod mission. With laser and technology advancement, scientists have gotten the accuracy of measurement within about two centimeters.

Prior to the use of lasers and the Apollo program, astronomers would use trigonometry to determine how far the Moon was. To do this, they would consider the parallax, the difference in observed position of an object view along two different lines of sight. Take the simplified example below demonstrating an object against a distant background. Viewer A would see the object amongst a blue background, while Viewer B would see the object against a red background.

The same can be done with the Moon or other solar objects. Two observers separated on Earth could look up at the night sky at the exact same time and see different star placement behind the Moon.

The angular separation, as measured with an instrument, can be combined with the known distance between the two observers to estimate the distance between the Earth and the Moon.

distance to moon = distance between observers ÷ tan (angle)

Keep calm and science on.

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