TL;DR
Two moon methods determine approximate direction. The crescent method: draw a line between the two horn tips of a crescent moon and extend it to the horizon — the contact point is approximately south (northern hemisphere). The shadow stick method: identical to the sun version but requires a full or near-full moon bright enough to cast a distinct shadow. Both methods are rough — useful for maintaining a general direction, not for precise bearings.
Why Moon Navigation Is Tricky
The moon is only useful for navigation when it's visible and bright enough to cast a meaningful reference. This is about 7-10 days per lunar month (roughly waxing crescent through full moon through waning gibbous). The new moon is invisible, and a thin crescent barely helps.
The moon's path across the sky is also more variable than the sun's — it follows a slightly different arc each night due to its orbital inclination. Moon navigation gives approximate direction with higher uncertainty than star or sun methods.
That said, it's worth knowing for nights when stars are partially obscured but the moon is visible and bright.
The Crescent Moon Method
When the moon is in crescent phase (first or last quarter), the two pointed ends are called horns. Drawing an imaginary line between the horn tips and extending it to the horizon indicates approximate south in the northern hemisphere.
The technique:
Error sources: The curvature of the line isn't quite straight due to the moon's orbital angle. In practice, accuracy is 15-30 degrees — useful for rough orientation.
The intuition: The illuminated side of the crescent faces the sun (which is below the horizon). The line between the horns, extended, points toward the sun's general position relative to the horizon. Because the sun is roughly south (in the northern hemisphere), the horn-to-horizon line points south.
The Shadow Stick Method by Moonlight
A bright full or near-full moon creates shadows usable with the same technique as the sun shadow stick.
Requirements:
- Full moon, or nearly full (last or first quarter — within 3-4 days of full)
- Open sky with unobstructed moonlight
- Flat, clear ground for shadow marks
Procedure: Identical to the sun shadow stick. Wait 20-30 minutes between marks (the moon moves more slowly than the sun). The first mark is west, the second is east.
Accuracy: Better than the crescent method when the moon is bright enough to work with. Comparable to the sun shadow stick but with slightly more error because the moon's arc isn't as precisely east-west as the sun's midday position.
The Moon's Timing
The moon's position in the sky correlates with its phase and the time of night:
| Phase | Rises | Highest | Sets | |---|---|---|---| | New moon | Sunrise | Noon | Sunset | | First quarter (waxing half) | Noon | Sunset | Midnight | | Full moon | Sunset | Midnight | Sunrise | | Last quarter (waning half) | Midnight | Sunrise | Noon |
Practical application: A first-quarter moon (the right half illuminated in the northern hemisphere) reaches its highest south point at approximately sunset. At 9 PM, it's in the southwest. At midnight, it's setting in the west.
A full moon rises in the east at sunset and is due south at midnight. Knowing what phase the moon is in lets you use its position as a rough clock-and-compass combined: if the full moon is overhead (highest point), it's approximately midnight and you're facing south.
Combining Moon and Stars
On nights when both the moon and stars are visible, use stars for accurate direction and moon for quick reference checks. If the moon's direction estimate and Polaris agree roughly, you have good orientation confidence. If they disagree significantly, trust Polaris.
The moon is more visible than faint stars through light haze and urban light pollution. On nights when Polaris isn't visible, a visible moon plus knowledge of the crescent method gives you at least a rough heading.
Sources
- Tristan Gooley - The Natural Navigator
- Harold Gatty - Finding Your Way Without Map or Compass
- U.S. Army Survival Manual FM 21-76
Frequently Asked Questions
Is moon navigation reliable enough to actually use?
It's reliable for rough direction-finding — maintaining a general heading, not taking precise bearings. Accuracy is typically 15-30 degrees, worse than a good compass but useful when disoriented. The crescent moon method is the most teachable and fastest to apply. It's worth knowing as a backup to star navigation on nights when stars are partially obscured but the moon is visible.
Can I use the shadow stick method with moonlight?
Yes, if the moon is bright enough to cast a distinct shadow (full or near-full moon). The exact same procedure as the sun shadow stick applies. However, the moon moves along a different path than the sun and moves more slowly, so wait at least 20-30 minutes between marks for a useful shadow movement. Full moon shadow navigation is significantly more accurate than crescent moon horn-pointing.
Does the moon always rise in the east and set in the west?
The moon follows roughly the same path as the sun across the sky: rising in the east, arcing through the south (in the northern hemisphere), and setting in the west. With variations by phase and season, this holds. Like the sun, the exact rising point varies from northeast to southeast depending on the time of year and the moon's orbital position.