xkcd.WTF!?

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Moon

I mean, it's pretty, but it doesn't really affect us beyond that. Except that half the nights aren't really dark, and once or twice a day it makes the oceans flood the coasts.

Explanation

The Moon is a celestial body orbiting Earth, first formed approximately 4.5 billion years ago - about 50 million years after the initial formation of the solar system. As of the date of this comic, the Moon is still orbiting the Earth[citation needed] at a distance of approximately 384,400 kilometers, or about 238,900 miles.

This comic points out how weird it is to have such an enormous celestial body near to us. The Moon has a radius more than one quarter of Earth's, and is around one eightieth of Earth's mass, and is so close that major surface features are visible, even with the naked eye, and much more clearly visible with even a simple telescope. Celestial distances tend to be so large that only truly immense objects can be seen without magnification, and even those tend to appear only as points of light to the naked eye. The second nearest body of notable size, Venus, is approximately 46.576 million kilometers away at its closest. The fact that there's "another world" that's close enough that humanity has always been aware of it, but distant enough that it couldn't be reached until a space program was developed, is a striking feature of Earth that we take for granted, only because it's always been that way.

While it's not uncommon for planets to have orbiting moons, no other planet in the solar system has a moon that's so large, in relation to the planet. Of the other rocky planets, only Mars has moons, and the largest of those is only 14 miles across.

Pluto and Charon are closer in size, than even the Earth/Moon system, but this meant that they had actually become seriously considered as a double(/binary) planet pair, had not Pluto been redesignated as a "dwarf planet". There is the possibility a term such as "double dwarf planet" could be adopted, at some point, as "double minor planet" is sometimes already used for binary asteroid systems. The lesser bodies of the Pluto-Charon system may then even be considered as circumbinary moons.

Other than this, Earth is the only accepted planet we're currently aware of that has a satellite that's so visible from its surface.

The title text sarcastically claims that, other than being "pretty", the Moon doesn't impact us, then subverts it by mentioning substantial impacts it has on Earth. Having such a large satellite so close has impacts that we take for granted only because we're used to them, but if they hadn't always existed, they'd seem unbelievable. One is that, for half the lunar cycle, the moon reflects enough light to produce visibility at night. The other impact is tides, since the gravitational pull of the Moon is large enough to alter the surfaces of oceans, causing shorelines to shift on a daily cycle. The text mentions these dismissively, in a deliberate contrast with their huge significance. Moonlight alters the illumination cycle of the planet to a significant degree, which changes how both humans and other animals operate at night, even before the advent of artificial lighting. Tides had major impacts on the development of life, continue to affect ecosystems, and play an essential role in our ability to interact with the oceans. If someone from a planet without such a large moon were to observe these impacts, they'd likely be shocked and amazed by them, but we barely notice them.