If there’s one straightforward lesson from astronomy, it’s that we’re tiny. We’re small compared to the Earth’s vast size, which is small compared to the Sun, which is tiny compared to the space that contains our solar system, which is a tiny dot in one arm of the Milky Way galaxy, which is one of roughly two trillion galaxies in the observable universe.
It’s almost impossible to try to grasp the universe’s size directly. Because it’s far beyond the size of anything we interact with daily, it’s hard to comprehend. It’s easier if we scale it to the size of the United States, and see how big it makes things we’re more familiar with (e.g. the size of the Earth). We can go step by step through some of the steps between the size of the Earth and the size of the Milky Way.
To begin, we need the size of the United States. We can use the distance from Portland, Maine to Los Angeles (about 2,600 miles) as an estimate of its size. This lets us start to scale. The Earth’s diameter is about 12,700 km, but the distance to the Moon is 384,000 km. So, if we scaled down the Earth and the Moon to put the Earth in Los Angeles and the Moon in Maine, the Earth’s diameter would be about 86 miles. If one “corner” of the Earth were in Los Angeles, the opposite side would only reach about halfway to Nevada.
The Sun is much further away. The Sun is about 150 million km from the Earth, almost 400x further than the Moon. If we scaled down the universe to fit the Sun in Maine while keeping the Earth in LA, the Earth would only be .22 miles wide. Viewed from above, a circle containing the Earth would be .6 square miles – about .1% of Los Angeles’s actual 487 square miles.
This shows how little space the Earth truly takes up, relative to its distance from the Sun. But what if we go a step further? What if we put one edge of the Milky Way in Los Angeles, and the other side in Maine? The short answer: things stop making sense. The Milky Way is 1,000,000,000,000,000,000 km across, or 621 million billion miles. To scale that down the to the size of the US (2,600 miles), the Earth would become 53 nanometers. A fingernail is somewhere around .4mm thick. So if we scaled down the Milky Way to the size of the US, you could fit 7,500 Earths side-to-side and it would only be as wide as your fingernail is thick.