How Big are the Mountains on the Moon?

~ J.S. Pailly

Hello, friends!

So I’ve fallen down a research rabbit hole, or maybe I should say I’ve fallen into a research crater.  I’ve been studying the topography of the Moon: mountains, valleys, craters, cliffs, etc, etc.  Some of these lunar land forms sound like they are stupidly big.  2 or 3 kilometers tall, in a surprising number of cases, or 2 or 3 kilometers deep.  Photos taken from space or by Earth-based telescopes don’t necessarily give you a good sense of just how stupidly large these things are.

Of course we have stupidly large land forms here on Earth, too.  Mt. Everest rises about 8.5 kilometers above sea level, and Mauna Kea (in Hawaii) stands more than 10 kilometers above the ocean floor.  The tallest mountains I’ve seen, personally, would be the Rocky Mountains in the western United States.  According to the Google machine, the tallest of the Rocky Mountains stands about 4 kilometers above sea level; however, if you’re in a place where you can see the Rockies, you’re not standing at sea level.  So I’m guessing that when I saw them, the Rocky Mountains were looming roughly 2 or 3 kilometers over me—comparable to many of the lunar land forms I’ve been reading about.

But here on Earth, mountains like the Rockies or the Alps are exceptional, whereas on the Moon, mountains that big (or cliffs that tall, or craters that deep) seem to be fairly ordinary.  I’m guessing this is due to gravity.  It’s easier to be a big mountain when the pull of gravity is so much less.

So if you and I were standing on the surface of the Moon, is that what the landscape would look like around us?  Rocky Mountain size mountains all around us?  In some regions, yes.  But also no.  Before you try to imagine what the lunar landscape would actually look like, to your human eyes, I need to tell you how your human eyes may play tricks on you when you’re on the Moon.

Here on Earth, when you see a tall mountain in the distance, how can you tell it’s a tall mountain in the distance and not a small hill right in front of you?  Well, certain visual cues help your brain figure that out.  Roads and cars, trees and buildings, birds or other wildlife… you know how big or small these things are, and seeing these things will help you guesstimate how large a nearby hill/far off mountain must be.

The atmosphere also plays a role in this.  Air is not 100% transparent, so even on a clear and sunny day, distant mountains will tend to look a little hazy—noticeably hazier than a nearby hill would look.

But there’s no air on the Moon, so you won’t see any atmospheric haze.  None whatsoever.  There are also no trees on the moon, nor any roads or buildings (yet).  So those visual cues are also missing.  As a result, an optical illusion comes into play which can make nearby hills almost indistinguishable from far off mountains.

Noticing the size of rocks and boulders might help, but the only way to really recognize the sheer scale of some of these lunar land features (as seen from the lunar surface) is to move around, change perspectives, and try to judge size and distance by parallax.

A few weeks ago, I went planet hunting with my telescope.  Mercury, Venus, and Mars were clustered together in the sky, and I didn’t want to miss that.  I also took a look at the Moon that night.  I’ve seen the Moon in my telescope many times, of course.  I always enjoy looking at the shadows cast by mountains, craters, etc.  But thanks to this new “research crater” I’ve fallen into, that night was the first time I fully appreciated the significance of those shadows.  Those are big shadows.  They must be big shadows in order for me and my relatively small telescope to see them so clearly all the way from Earth.  It takes some stupidly tall mountains and stupidly deep craters to cast such stupidly big shadows across the lunar surface.

WANT TO LEARN MORE?

To make landing on the Moon safer and easier, the Apollo missions mostly stuck to flat terrain regions.  Mostly.  The exception is Apollo 15, which landed near a mountain range called Montes Apenninus.  Click here to learn more about Apollo 15 and the terrain around the Apollo 15 landing site.

Additionally, I found this video from Astrum really helpful in understanding the true size and scale of lunar surface features.  The video also talks about how your eyes can deceive you when viewing the lunar landscape.

14 thoughts on “How Big are the Mountains on the Moon?”

  2. I’ve generally only encountered this subject before when reading about art and it tends to boggle my mind. Every time it’s explained in a different manner, it helps me to understand, so thank you. I also really enjoyed this.

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    1. Glad you enjoyed! Researching this was a pleasant mingling of my interests. That atmospheric haze effect is an important thing for artists to know about. It’s a great tool for communicating size and distance in a painting, but I never before thought about how it applies (or rather, doesn’t apply) to an airless world like the Moon.

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  3. It’s all about perspective. The tallest mountains here in Colorado are about 14,000 feet above sealevel, but wherever you are viewing them, you are stasrting at roughly 5000 feet or more. They would in fact be much more impressive if they rose to 14,000 feet as viewed from somewhere on an ocean beach. Also, your piece reminds me of an activity I did in college many (many) years ago where we measured the height of a lunar mountain (Mons Piton or Mons Pico) as seen in a small telescope by measuring the length of the shadow and knowing the age of the Moon in the lunar cycle (which would tell us the angle of the Sun above the horizon. I might have used a modified version of that in some of my classes years later.

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    1. That’s really awesome! I hadn’t even thought about that, but it totally makes sense that you could measure the height of mountains based on the length of their shadows. That is so cool!

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      1. I don’t know if I have a copy of the old exercise, but I will try to look it up. As I recall, we measured the length of the shadow by timing how long it took for it to drift past a marking in the eyepiece reticle, then knowing the angular speed of the Moon in the sky and its known size, you could figure out the actual length of the shadow. After that a little simple trig gave the approximate height of the mountain above the average terrain.

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      2. Wow, that really is cool. It’s one thing to learn these sorts of facts about space (or any topic, really) but to actually know how we figure this stuff out and to do it yourself… that’s really exciting. I’m really glad you shared this.

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      3. I managed to find my field notes from freshman year in college, 53 years ago, about measuring the height of a mountain on the Moon. It wasn’t all that accurate, but I have put it into a PDF file you are welcome to download if you want. It’s probably not very clear, but essentially you can estimate the angle of the Sun in the sky at that location on the Moon just by knowing the phase, and you can estimate the length of the shadow by comparing to objects on the Moon of known length. Those two facts enable you to figure out the Mountain height by simple trig. Of course it doesn’t start from absolutely zero knowledge, but most discoveries are firmly rooted in previous discoveries. Anyway, only if you are interested. No worries if you aren’t.
        Here’s a link: https://bit.ly/44EqBH6

        LS

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      4. Thanks for this. This is, in fact, very helpful to me.

        Also, you make a good point about new discoveries being built upon previous discoveries. At the very least, I’d imagine we had to know the exact distance of the Moon before anyone could try to figure out the size of its surface features.

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  4. When Carol and I visited Denali in Alaska, we were told it was the highest mountain in the world from its base elevation (the land surrounding it) to its peak. I don’t have a citation for that, but I’ll check my previous posts and see if I have an academic reference for that claim. My photo doesn’t prove much, but it’s pretty:

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  6. Feel free to delete this if it’s getting us too far off your wonderful original post. ..

    I know this is wikipedia, but it seems to have real data: The highest mountains above sea level are generally not the highest above the surrounding terrain. There is no precise definition of surrounding base, but Denali,[1] Mount Kilimanjaro[2] and Nanga Parbat[3] are possible candidates for the tallest mountain on land by this measure. The bases of mountain islands are below sea level, and given this consideration Mauna Kea (4,207 m (13,802 ft) above sea level) is the world’s tallest mountain and volcano, rising about 10,203 m (33,474 ft) from the Pacific Ocean floor. Mount Lamlam on Guam is periodically claimed to be among the world’s highest mountains because it is adjacent to the Mariana Trench; the most extreme claim is that, measured from Challenger Deep 313 kilometres (194 mi) away, Mount Lamlam is 37,820 feet (11,530 m) tall.[4][5] Ojos del Salado has the greatest rise on Earth: 13,420 m (44,029 ft) vertically to the summit[citation needed] from the bottom of the Atacama Trench, which is about 560 km (350 mi) away, although most of this rise is not part of the mountain.

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    1. I remember Denali, Mauna Kea, and Kilimanjaro came up in my research for this post. It sounded like a really strong case could be made for Denali being that tallest, as measured from its base. So what they told you in Alaska is legit.

      The question “what’s the tallest mountain on Earth?” is a surprisingly tricky question. I decided not to get into that in this blog post, because I didn’t want to get too sidetracked from talking about the Moon. But it is a really interesting question.

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