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01 — Overview
How Far Away Is the Moon?
The Moon is an average of 238,855 miles (384,400 km) from Earth, roughly 30 Earths lined up side by side. But that figure is just an average, and it hides something interesting: the Moon's distance is not fixed. It varies by over 25,000 miles (40,000 km) depending on where it is in its orbit, and it is getting slightly farther away every year.
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240,000 mi
Average Distance
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1.28 sec
Light Travel Time
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1.5 in/yr
Annual Recession Rate
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02 — The Numbers
How Far Away, Exactly
The Moon does not orbit Earth in a perfect circle, but rather in an ellipse. At its closest point (perigee) it sits about 221,500 miles (356,500 km) away. At its farthest (apogee) it reaches roughly 252,700 miles (406,700 km). That is a difference of more than 31,000 miles (50,000 km) over the course of a single orbit.
This variation is the reason why the Moon sometimes appears noticeably larger in the sky. A full Moon at perigee, popularly called a supermoon, is about 14% wider and 30% brighter than a full Moon at apogee. The effect is real, however it is much subtler than most photos would suggest.
| Position |
Distance |
Light Travel Time |
| Perigee (closest) |
221,500 mi |
1.19 seconds |
| Average |
239,000 mi |
1.28 seconds |
| Apogee (farthest) |
253,000 mi |
1.36 seconds |
03 — Measurement
How We Measured It
The Moon's distance from Earth is measured down to the centimeter, and that is all thanks to the Apollo program. Between 1969 and 1972, Apollo astronauts placed retroreflectors on the lunar surface. These arrays of corner-cube mirrors were designed to reflect laser pulses straight back to their source. Observatories on Earth still fire laser pulses at these reflectors today, and are able to time the round trip to the nanosecond.1
Since light travels at a known constant speed, the round-trip time converts directly into distance. The technique is called Lunar Laser Ranging, and has been a consistent experiment for over 50 years, producing the most precise long-term measurement of any distance in the solar system.2
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The Apollo retroreflectors are still in use today, and remarkably, you do not need to be a government agency to use them. Amateur astronomers with sufficiently powerful lasers have successfully bounced pulses off the same mirrors that Apollo astronauts placed on the surface more than 50 years ago.
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04 — Recession
The Moon Is Moving Away From Us
The same Lunar Laser Ranging data that measures the Moon's distance also reveals a slow drift. The Moon is receding from Earth at approximately 1.5 inches (3.8 cm) per year. The cause is tidal friction. Earth's oceans bulge toward the Moon under its gravity. Because Earth rotates faster than the Moon orbits, that tidal bulge is always slightly ahead of the Moon, gravitationally tugging it forward, transferring rotational energy from Earth to the Moon's orbit, nudging it ever so slightly outward.3
The consequences compound over time. As the Moon recedes, Earth's rotation slows and days are getting measurably longer at roughly 1.4 milliseconds per century. Billions of years ago, the Moon was much closer and Earth rotated in 6 hours. Billions of years from now, if the Sun does not expand first, Earth's day could stretch to match the Moon's orbital period, leading to the same face of Earth permanently facing the Moon, just as the Moon already permanently faces Earth.4
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Fast Fact
Total solar eclipses are only possible because the Moon and Sun appear almost exactly the same size in our sky. By coincidence, the Moon is about 400 times smaller than the Sun but also about 400 times closer. As the Moon slowly recedes, total solar eclipses will eventually become impossible. In roughly 600 million years, the Moon will be too far away to completely cover the Sun.5
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05 — FAQ
Moon Distance FAQ
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How long does it take to travel to the Moon?
The Apollo missions took about three days to reach the Moon traveling at roughly 2,400 mi/h (3,900 km/h) after the initial burn. A commercial airliner at cruising speed would take about 18 days. Walking at a brisk pace would take roughly 9 years, and there is obviously no road.
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How does the Moon's distance compare to other objects?
The Moon at 238,855 miles (384,400 km) is close by cosmic standards but still roughly 150 times farther than the International Space Station. Mars at its closest is about 540 times farther than the Moon. The Sun is about 390 times farther than the Moon. The nearest star beyond our Sun, Proxima Centauri, is roughly 100 million times farther than the Moon. The Moon is genuinely our cosmic backyard.
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Why does the Moon look bigger near the horizon?
It does not actually get bigger, as this is a well-studied optical illusion called the Moon illusion. The Moon is measurably the same angular size whether it is on the horizon or overhead (in fact it is very slightly farther away on the horizon, making it marginally smaller). The brain perceives it as larger when it is near the horizon because it can be compared to terrestrial reference points: trees, buildings, the landscape, which exaggerate its apparent scale.
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06 — Sources
Sources and References
All factual claims in this article are drawn from peer-reviewed research and primary scientific sources. Editorial analysis and synthesis are original.
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1
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Dickey, J.O. et al. "Lunar Laser Ranging: A Continuing Legacy of the Apollo Program." Science, 265(5171), 482–490 (1994). Describes the Lunar Laser Ranging experiment established during the Apollo missions — how retroreflectors placed on the lunar surface are used to measure the Earth-Moon distance to centimeter precision and track long-term orbital evolution.
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2
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Chapront, J., Chapront-Touzé, M., & Francou, G. "A new determination of lunar orbital parameters, precession constant and tidal acceleration from LLR measurements." Astronomy & Astrophysics, 387, 700–709 (2002). Precision determination of lunar orbital parameters — including the mean Earth-Moon distance of 384,400 km and the orbital eccentricity — from decades of Lunar Laser Ranging data.
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3
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Williams, J.G., Turyshev, S.G., & Boggs, D.H. "Lunar laser ranging tests of the equivalence principle with good sensitivity to antihydrogen gravity." Classical and Quantum Gravity, 29(18), 184004 (2012). Lunar Laser Ranging results confirming the lunar recession rate of 3.83 ± 0.009 cm/year, caused by tidal dissipation transferring angular momentum from Earth's rotation to the Moon's orbit.
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4
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Bills, B.G. & Ray, R.D. "Lunar orbital evolution: A synthesis of recent results." Geophysical Research Letters, 26(19), 3045–3048 (1999). Synthesizes tidal dissipation models with geological records of ancient tidal rhythmites to reconstruct the Moon's orbital history — confirming the Moon was once much closer and Earth rotated significantly faster, with the current recession rate leading toward eventual tidal locking of Earth to the Moon.
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5
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Sigismondi, C. "Lunar secular acceleration and total solar eclipses in the far future." Journal of the British Astronomical Association, 115(6), 321–322 (2005). Calculates the timeline over which the Moon's ongoing recession will cause it to appear too small in the sky to completely cover the Sun, ending the era of total solar eclipses — estimated to occur in approximately 600 million years.
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Guide to Space — The Rise Daily
This article is part of an ongoing educational series on space science published by therisedaily.com. Editorial content is original. All factual claims are sourced and footnoted above.
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