The word perigee describes the point in the Moon’s orbit when it is closest to Earth—but behind that simple definition is a lot of fascinating science and some very real effects on our oceans, our sky, and even our cameras. When the Moon sweeps through perigee, tides can rise higher, coastal risks can increase, and photographers around the world rush outside to capture what many call a “supermoon.”
This guide breaks down what perigee really is, why it happens, how it affects tides, and how you can make the most of it with your own Moon photos.
What Is Perigee, Exactly?
The Moon doesn’t orbit Earth in a perfect circle—it follows an ellipse. That means there’s a closest point and a farthest point in its orbit:
- Perigee – the point where the Moon is closest to Earth
- Apogee – the point where the Moon is farthest from Earth
On average:
- Mean Earth–Moon distance: ~384,400 km
- Typical perigee distance: ~363,300 km
- Typical apogee distance: ~405,500 km
So at perigee, the Moon can be more than 40,000 km closer than at apogee. That’s enough to make the Moon appear up to about 14% larger in diameter and around 30% brighter compared with an apogee full Moon (often called a “micromoon”).
Why the Orbit Is Elliptical
The elliptical shape of the Moon’s orbit isn’t a design flaw; it’s a consequence of gravity. The main players:
- Earth’s gravity dominates the Moon’s path.
- The Sun’s gravity tugs on the Earth–Moon system, slowly rotating the ellipse over time.
- Other planets (especially Jupiter and Venus) add tiny perturbations.
Because of these influences, the line joining perigee and apogee slowly turns in space, a process called apsidal precession, which takes about 8.85 years to complete a full rotation.
Perigee and the “Supermoon” Phenomenon
You’ll often hear social media hype about a supermoon. Astronomers don’t use that as a formal scientific term, but it’s widely accepted in popular astronomy.
A supermoon occurs when:
- A full Moon happens close to perigee, or
- A new Moon happens close to perigee (not visible, but still important for tides).
Different organizations define a supermoon slightly differently, usually as a full Moon occurring within about 90% (or a given number of kilometers) of its closest possible approach to Earth (source: Time and Date).
How Much Bigger Is a Supermoon?
From a naked-eye standpoint, the difference is subtle but real:
- Up to 14% larger apparent diameter vs. an apogee full Moon
- Up to 30% brighter overall illumination
Side-by-side photographs or careful measurements show this clearly, but in the moment, your brain tends to normalize the view—especially against a dark sky with no fixed-size reference.
How Perigee Affects Tides on Earth
The Moon’s gravity is the primary driver of Earth’s tides. When the Moon is at perigee, its gravitational pull on Earth’s oceans is slightly stronger, subtly amplifying the normal tidal cycle.
The Basics of Tidal Forces
Tides arise because gravity changes with distance:
- The side of Earth facing the Moon feels a slightly stronger pull.
- The far side feels a weaker pull.
This difference stretches Earth’s oceans, creating tidal bulges. As Earth rotates, coastlines move in and out of these bulges, producing:
- High tide – when a location rotates into a bulge
- Low tide – when it rotates away from a bulge
Perigean Spring Tides (a.k.a. “King Tides”)
Tides respond not just to perigee, but also to the Moon’s phase and the position of the Sun.
- Spring tides happen around the full Moon and new Moon, when the Sun, Earth, and Moon align. This alignment increases tidal range—higher highs, lower lows.
- When a spring tide lines up with perigee, we get perigean spring tides, often called king tides in popular usage.
During a perigean spring tide:
- High tides can be noticeably higher than average.
- Low tides can be somewhat lower than average.
The difference in water level might be measured in tens of centimeters to perhaps half a meter above normal spring tides, depending on the location, coastline shape, and local geography.
Why Perigee Matters for Coastal Flooding
On its own, perigee doesn’t cause catastrophic floods. But it can stack with other factors:
- Storm surge from strong storms or hurricanes
- Long-term sea-level rise
- Persistent onshore winds
- Low atmospheric pressure
When these combine with a perigean spring tide, coastal communities can see:
- “Sunny day” or nuisance flooding in low-lying areas
- Higher risk of storm surge damage during coastal storms
- Increased erosion along vulnerable shorelines
That’s why coastal planners track dates when perigee coincides with full or new Moons—they’re key windows of elevated risk.
Visual Changes: How Perigee Affects the Moon’s Appearance
From your backyard, perigee translates to a slightly larger, brighter Moon. The difference is modest, but with a bit of planning you can really see (and capture) it.
Apparent Size and Brightness
Compared with an average full Moon:
- A perigee full Moon appears a few percent larger and brighter.
- Compared specifically with an apogee full Moon, the contrast becomes more striking in photos.
The human eye isn’t great at noticing small incremental changes in size against a dark sky. That’s why you’ll often see:
- Comparison images: same focal length, one photo at perigee, one at apogee
- Stacked frames showing outlines of both Moons overlaid
These reveal just how much perigee enlarges the Moon visually.
The Moon Illusion vs. Perigee
People often say “the Moon looks huge near the horizon.” That’s the Moon illusion—a psychological effect, not an astronomical one. The Moon is actually slightly farther away when it’s on the horizon than when it is overhead, due to geometry.
Perigee is different:
- It’s a real change in distance and angular size.
- It applies regardless of whether the Moon is on the horizon or high in the sky.
You’ll notice the size increase most clearly with a camera and fixed focal length, not just by eye.
Perigee and Moon Photography: Getting the Best Shots
For photographers, perigee is an excellent excuse to plan a Moon shoot—especially when a full Moon occurs near perigee, generating the “supermoon” buzz.
Essential Gear and Settings
You don’t need top-end gear, but some basics help:
- Camera: DSLR, mirrorless, or a good bridge/compact camera with strong zoom
- Lens:
- 200–300 mm (full-frame equivalent) for moderate close-ups
- 400–600+ mm for detailed lunar disks
- Tripod: Strongly recommended for sharp images
- Remote shutter / self-timer: Reduces camera shake
Starter settings (adjust as needed):
- Mode: Manual
- Shutter speed: ~1/125 to 1/250 sec (the Moon is bright and moves fast)
- Aperture: f/5.6–f/11
- ISO: 100–400
- Focus: Manual, set to infinity or fine-tuned with live view
Planning a Perigee Moon Shoot
The magic is less about perigee itself and more about composition and timing. Use apps or websites that provide:
- Moonrise and moonset times
- The Moon’s azimuth (direction) and altitude
- Dates when a full Moon aligns closely with perigee
Plan shots where the Moon rises or sets behind something recognizable:
- City skylines
- Mountains or cliffs
- Famous landmarks
- Trees or church spires
Because perigee makes the Moon a bit bigger, those foreground–Moon composites look more dramatic.
Tips for Eye-Catching Perigee Moon Photos
To maximize visual impact:
-
Shoot at moonrise or moonset
- You can balance the Moon’s brightness with the warm light of dusk/dawn.
- The low moon near the horizon works beautifully with foreground silhouettes.
-
Use a long focal length
- Compress the scene so the Moon looks huge relative to foreground objects.
-
Bracket your exposures
- Take multiple shots at slightly different exposures to avoid blowing out lunar details.
-
Check the weather early
- High clouds can soften the Moon’s brightness nicely, but solid overcast will hide it altogether.
-
Try time-lapse or sequences
- Capture the Moon rising or setting, or a side-by-side comparison of a perigee and non-perigee full Moon over months.
Beyond Tides: Other Subtle Effects of Perigee
The most obvious physical effect of perigee is its influence on tides, but scientists also track:
- Small variations in Earth’s rotation – tidal forces cause tiny changes in the distribution of mass in the oceans, which can slightly affect rotation rate.
- Crustal flexing – the solid Earth also “tides” by a few tens of centimeters, rising and falling as the Moon moves, especially at perigee.
- Satellite orbits – precise orbit determination for satellites must account for the exact position of the Moon, especially near perigee.
These effects are mostly invisible in daily life, but they matter for geophysics, navigation, and satellite operations.
Simple Timeline: The Rhythm of Perigee
You don’t have to memorize astronomical tables, but it helps to understand how often perigee comes around.
- The Moon orbits Earth in about 27.3 days (sidereal month).
- It moves from perigee back to perigee in about 27.6 days (anomalistic month).
That means:
- Perigee happens roughly once a month, but at different lunar phases.
- Every few months, perigee will line up closely with a full Moon or new Moon, triggering especially strong “supermoon” tides.
Check online perigee calendars or astronomy apps to find:
- Exact perigee distances and times
- Phase of the Moon at perigee
- Dates of perigean spring tides relevant for your coastline
FAQ: Perigee, Supermoons, and Tides
Q1: What’s the difference between perigee and apogee Moon?
A: The perigee Moon occurs when the Moon is at its closest point to Earth in its orbit, making it appear slightly larger and brighter. The apogee Moon is when the Moon is farthest from Earth, appearing smaller and dimmer. When a full Moon happens close to perigee, people often call it a “supermoon,” while a full Moon near apogee is sometimes dubbed a “micromoon.”
Q2: Do perigee full moons cause earthquakes or extreme disasters?
A: There’s no solid scientific evidence linking perigee itself to major earthquakes or global disasters. While tidal forces are slightly stronger at perigee, they are still tiny compared with the stresses driving plate tectonics. What perigee does reliably influence is the height of tides, especially during perigean spring tides, which can worsen coastal flooding when combined with storms and sea-level rise.
Q3: How often do perigee supermoons happen?
A: Because the lunar phase cycle (about 29.5 days) and the perigee cycle (about 27.6 days) don’t match perfectly, a perigee full Moon occurs a few times a year. Some years feature three or four consecutive “supermoons,” while other years might have only one. Astronomical calendars list these dates in advance so you can prepare for both higher tides and better Moon photo opportunities.
Bring Perigee Down to Earth
Perigee may sound like an abstract orbital concept, but it quietly shapes everyday experiences—from the height of the sea along our coasts to the brightness of the Moon in your evening sky. Understanding perigee helps you:
- Anticipate higher-than-usual tides and potential coastal flooding
- Appreciate the subtle but real changes in the Moon’s size and brightness
- Plan striking Moon photographs that take advantage of the Moon’s closest approach
The next time you hear that a “supermoon” is coming, treat it as more than just a headline. Check the perigee timing, look up local tide forecasts if you live near the coast, and grab your camera to make the most of the Moon’s visit.
Start now: look up the upcoming perigee dates for your location, mark the next perigee full Moon on your calendar, and plan a tide check or a photo session. With a little preparation, you can turn perigee from a distant astronomical term into a vivid, memorable experience in your own sky and along your own shoreline.
Learn how astronomy, psychology, and spiritual traditions intersect by visiting SpiritualMindScience.com for deeper insights.