Why the Moon is iron-poor and what it means for understanding Earth's neighbor.

Moon myths busted—and what they really tell us about our lunar neighbor

Let’s take a moment to think about the Moon. It’s been a fixture in skies and stories for as long as people have looked up and wondered, “What’s going on up there?” When you’re part of the LMHS NJROTC Academic Team, you get a chance to connect big ideas about science with the curiosity that makes sailors and scientists alike lean in a little closer. Here’s a clean, friendly guide to the question many of us have tussled with: which statement about the Moon is true? Let’s walk through it together, no heavy lab gear required.

Iron content: is the Moon iron-poor?

Here’s the thing that often surprises people: yes, the Moon is iron-poor compared with Earth. The Moon’s makeup is dominated by silicate minerals—think rocks like you’d find in volcanic basalt and crustal rocks. Iron is present, but not in Earth’s abundance. If you had to put a rough number on it, the Moon’s overall iron content sits at about 10% of its mix. That’s not a lot when you compare it to Earth, where iron plays a much bigger role in the crust and mantle. It’s a simple, clean way to say: the Moon isn’t iron-rich the way Earth is.

This isn’t just a trivia fact. It helps explain why the Moon’s interior behaves differently from Earth’s. A smaller iron supply means a different density structure, a smaller core, and a geologic history that’s more quiet than ours in many places. You can think of it this way: Earth is a bustling metal core surrounded by dynamic, molten rock. The Moon is a quieter neighbor, with a thinner interior that tells a different story in rocks and mountains.

Why the other statements aren’t true (and what that means)

Choice A says: Visible starlight is the same on the Moon as on Earth. If you’ve ever watched a night sky without a city’s glow, you might imagine starlight would look the same everywhere. But our planet’s atmosphere does a lot of work—scattering light, making the sky bright during the day, and washing out faint stars at night in cities. On the Moon, there’s almost no atmosphere to scatter or filter light. That means space is incredibly dark, and stars shine with a clarity that’s hard to replicate on Earth. It’s not that the stars themselves change, but the way we experience their light does. So, no, starlight isn’t the same on the Moon as it is here on Earth. The Moon’s airless environment makes for a sky that’s stark and quiet, perfect for science-and-sky nerds to ponder.

Choice B claims the Moon is roughly one-quarter the size of Earth. This one trips people up because it’s easy to mix up diameter, volume, and mass. The Moon’s diameter is indeed close to a quarter of Earth’s — a little more, a little less depending on how you measure. But size isn’t the whole story. When you stretch that tiny diameter into volume and mass, the Moon is much, much smaller than a simple quarter-size hint suggests. Think of it like this: a small cookie cutter can produce a much smaller volume than a larger one, even if they look similar at a glance. In real numbers, the Moon’s volume and mass are far shy of a quarter proportion. It’s a good reminder that “size” can be a slippery metric unless you specify what you’re actually measuring.

Choice C says the Moon circles the Earth every 30 days. And this is the classic slip you’ll see in pop science and even some classroom posters. The Moon’s orbital period around Earth is about 27.3 days if you measure sidereal time (that’s the Moon completing a full orbit relative to the distant stars). There’s also a 29.5-day cycle called the synodic month, which is what you see from Earth when you watch the phases of the Moon from new to full and back again. So, if you’re aiming for precision, 27.3 days is the sidereal orbital period. The 30-day figure is a nice rough number, but not the exact science. It’s a small difference that matters if you’re tallying orbital mechanics or plotting missions that rely on precise timing.

Choice D says the Moon is iron-poor. This one—the correct choice—lines up with current scientific understanding. It’s about composition, not mood. The Moon does have iron, mainly in its core, but not in the same proportions you’d find in Earth’s crust and mantle. That’s what many science teachers and textbooks highlight when they point out the Moon’s silicate-dominated exterior and relatively modest iron inventory. It’s a crisp, defensible truth that helps explain other lunar features, from rock formations to magnetic history clues scientists have studied from lunar samples.

What this tells us about the Moon, in practical terms

• The atmosphere—or lack of it—changes how we see the sky. The Moon’s airless environment means stars appear brighter and more numerous than you’d expect when you’re under a city’s glare. If you’ve ever watched a night scene on a desert road or in a high-altitude environment, you know how vast the sky can look when there’s little to dim it. Imagine that on a world where there’s no air to blur the view. That clarity is a reminder of the Moon’s quiet, ancient nature.

• Size is more than a single number. It’s tempting to say “a quarter the size,” but that’s a partial truth. Size can mean diameter, volume, mass, gravity, or even the way a body responds to heat and motion. The Moon’s diameter is about a quarter of Earth’s, but its mass is only about 1/81 of Earth's mass, and its volume is about 1/50. Those different numbers aren’t just trivia; they explain why the Moon’s surface features and tides are so different from ours.

• Iron content shapes the Moon’s story. Iron’s role in a planet or moon isn’t just a count of atoms; it helps determine core size, magnetic history, and even how the body holds onto heat over time. The Moon’s relative iron-poor nature provides a window into its origin and evolution, including the idea that it formed from debris after a colossal impact early in the solar system’s history.

Bringing it home to curious minds and the NJROTC lens

If you’re part of a team that loves to map, measure, and reason through physical relationships, the Moon offers a great practice ground. It’s not just about memorizing which statement is true; it’s about building a framework to test ideas, compare data, and weigh explanations. Here are a few angles you can explore that feel practical and engaging:

• Orbital mechanics in action. The Moon’s orbit isn’t just a line around Earth; it’s a complex dance influenced by gravity, inertia, and the Sun’s pull. If you’ve ever tried to predict lunar phases or track a transit, you’re exercising the same muscle that navigators use when plotting courses at sea.

• The role of atmosphere in perception. The Earth’s atmosphere acts like a filter and a lens. On the Moon, the lack of atmosphere gives us a different lens to study stars and the night sky. It’s a cool contrast that helps explain why telescopes and space probes measure the same objects in different ways.

• Rocks as storytellers. Lunar rocks aren’t just “rocks.” They are records—bits and pieces that tell us how the Moon formed and what it experienced during its early days. The Apollo samples, collected and transported back to Earth, opened windows into meteorology of space, volcanic processes, and the core’s history.

• Real-world references you can check. Agencies like NASA have a treasure trove of images, mission notes, and data. The Lunar Reconnaissance Orbiter scans the Moon’s surface, giving scientists and students alike a detailed look at craters, plateaus, and maria. If you’re curious about the terrain you’d want for a hypothetical lunar outpost, these tools are a great starting point.

A few quick contrasts you can remember without overthinking it

• Moon vs Earth atmosphere: Moon has virtually no atmosphere; Earth’s atmosphere is a bustling, protective blanket. The result is very different night skies and weather dynamics.

• Size vs mass: The Moon is roughly a quarter of Earth’s diameter, but its mass is far smaller—around 1/81 of Earth’s. That discrepancy matters for gravity, tides, and heat retention.

• Iron content: Moon is iron-poor compared with Earth, even though it has iron in its core. This difference helps explain a lot about how the Moon formed and how its surface records volcanic and impact histories.

A friendly wrap-up

So, which statement about the Moon is true? The Moon is iron-poor. While it isn’t completely devoid of iron, it carries far less iron than Earth does, and its rocky exterior is dominated by silicate minerals. It’s a neat reminder that truth in science often comes in shades of nuance: diameter isn’t the whole story, orbital periods require precise terms, and the sky’s brightness is shaped by a planet’s cloak of air.

If you’re ever up before dawn, or you’re out with friends on a clear night, you can test these ideas with a simple thought experiment. Look up, imagine the Moon’s quiet interior, and notice how the sky feels different when you’re listening to the absence of atmosphere rather than the hum of it. It’s not just a science lesson; it’s a moment to savor how human curiosity can turn a simple rock into a story about formation, motion, and the quiet drama of the cosmos.

As you move through topics in the program, keep this approach in mind: ask a clear question, test it against what we know from rocks and orbits, and then connect the dots back to the everyday world. The Moon isn’t just a distant object in the sky; it’s a compact classroom—one that teaches us about composition, gravity, time, and the way even modest bodies can reveal big truths about our place in the solar system.

If you’re ever curious to dig deeper, there are plenty of accessible resources that bring lunar science to life. NASA missions, lunar geologic maps, and student-friendly mission briefs can widen the lens and spark new questions. And who knows? The next time you glance upward, you might spot a crater’s shadow and hear in your mind the rhythm of a sidereal month, reverberating with the same precision and wonder that mathematicians, navigators, and scientists have relied on for generations. The Moon keeps pace, and so can you.