What Moon Phases Are Present During the Neap Tide?
The moon phases present during neap tides are the first quarter and third quarter (also called last quarter). A neap tide is one of the two twice-monthly periods when the tidal range — the difference between high and low tide — is at its smallest. This happens because the Sun and Moon pull on Earth’s oceans from roughly 90-degree angles during those quarter phases, so their gravitational effects partially cancel instead of combining.
What Is a Neap Tide
A neap tide is a period of minimal tidal range that occurs about twice a month, roughly a week after each spring tide. During a neap tide, high tides are lower than average and low tides are higher than average, so the total swing between them is small.
Tides are driven mainly by the gravitational pull of the Moon, with a smaller contribution from the Sun. Because the Sun is so much farther away, its tidal influence is weaker than the Moon’s even though it’s far more massive. Still, the Sun’s pull is enough to either reinforce or counteract the Moon’s, depending on how the two bodies are aligned relative to Earth.
When the Sun, Earth, and Moon line up — at new moon or full moon — their pulls add together and produce large tidal ranges (spring tides). When the Sun and Moon sit at right angles as seen from Earth, their pulls work against each other and produce small tidal ranges (neap tides). The National Oceanic and Atmospheric Administration describes the Sun’s tide-generating force as roughly 46% of the Moon’s, which is why the Sun can meaningfully shift the range but never dominate it.
The basic geometry
- Spring tides: Sun, Earth, and Moon roughly in a straight line (new or full moon).
- Neap tides: Sun and Moon roughly 90 degrees apart in the sky (first or third quarter).
These alignments recur predictably because the Moon completes a full cycle of phases — from new moon back to new moon — in about 29.5 days, a period called the synodic month.
Moon Phases During Neap Tides
If you’re asking what moon phases are present during the neap tide, the answer is simple: neap tides coincide with the first quarter and third quarter (last quarter) moon phases. At both of these points, the Moon appears half-lit from Earth, and it sits about 90 degrees away from the Sun in the sky.
- First quarter moon: Occurs about a week after the new moon. The Moon has traveled a quarter of the way around its orbit, so the Sun-Earth-Moon angle is approximately 90 degrees.
- Third quarter moon: Occurs about a week after the full moon, again placing the Sun-Earth-Moon angle near 90 degrees.
At either quarter phase, the tidal bulges raised by the Moon and the smaller bulges raised by the Sun act at cross-purposes rather than in tandem. The result is a weakened combined tide — the neap tide.
It’s worth noting that the actual neap tide doesn’t always land exactly on the day of the quarter moon. Because of factors like the time it takes for water to respond (tidal lag) and local geography, the smallest ranges typically appear a day or two after the quarter phase, depending on your location.
Why Quarter Moons Cause Neap Tides
The key to understanding neap tides is vector addition of gravitational pulls. When two forces act in the same direction, they combine; when they act at right angles, they partly offset each other’s tidal effects.
How the 90-degree alignment works
At quarter moon, the Moon is pulling on the ocean on one side of Earth while the Sun is pulling from a direction 90 degrees away. The Moon’s tidal force tries to stretch the oceans along the Earth-Moon line, and the Sun’s tidal force tries to stretch them along the Earth-Sun line, at a right angle to the first.
Because the Sun’s tidal contribution is weaker, it doesn’t erase the Moon’s effect — it just reduces the net range. The high tides during a neap tide are pulled down a bit, and the low tides are pushed up a bit, so the difference between them shrinks. This is why neap tides produce the mildest high and low tides of the month.
A short worked example helps: suppose at a given coastal location a spring tide range is about 3 meters. A week later, near quarter moon, the neap range at the same spot might be closer to 1.5 meters — the Sun partway cancels the Moon’s tide-raising pull rather than adding to it. The exact numbers vary by coastline, but the pattern — smaller range at neap, larger at spring — holds worldwide. NASA explains that the Moon’s gravity, combined with the Sun’s, governs the tidal cycles we observe, including the twice-monthly shift between spring and neap.
Why the range is minimized
The tidal range is simply the vertical difference between consecutive high and low water. During neap tides:
- High tides reach less extreme heights than at spring tide.
- Low tides don’t retreat as far.
- The gap between them is at its narrowest for the month.
This matters for boaters, fishermen, and coastal planners, since a smaller range changes how much water is available in harbors and shallows at any given time.
Neap Tides vs Spring Tides
The clearest way to see which moon phases belong to each tidal pattern is to compare them side by side.
| Tidal type | Moon phase | Sun–Earth–Moon angle | Tidal range |
|---|---|---|---|
| Spring tide | New moon | ~0° (in line) | Largest |
| Spring tide | Full moon | ~180° (in line) | Largest |
| Neap tide | First quarter | ~90° | Smallest |
| Neap tide | Third quarter | ~90° | Smallest |
Spring tides occur at new and full moon, when the Sun and Moon align and their gravitational pulls reinforce each other, producing the biggest high and low tides of the month. Neap tides occur at first and third quarter, when the pulls work at right angles and the range shrinks.
This creates a predictable rhythm: spring tide, then roughly a week later a neap tide, then another spring tide, and so on, cycling about twice per month. The schedule repeats with the lunar phase cycle rather than the calendar month, which is why peak tides drift through the year.
Key Takeaways
- Neap tides occur during the first quarter and third quarter (last quarter) moon phases.
- A neap tide is a twice-monthly period of smallest tidal range, with lower high tides and higher low tides.
- They happen because the Sun and Moon pull from about 90 degrees apart, so their gravitational effects partly cancel.
- Spring tides — the opposite pattern — occur at new moon and full moon, when the Sun and Moon are aligned and their pulls combine.
- The spring-to-neap cycle repeats roughly twice a month, tracking the ~29.5-day lunar phase cycle.
