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If you hold up a grain of sand, the patch of sky it covers contains 10,000 galaxies


A grain of sand may be tiny, but the patch of sky it covers when you hold it up at arm’s length is many light years in diameter due to the truly astronomical distances involved. Thanks to observations by telescopes such as Hubble, we can estimate that there are over one hundred billion galaxies in our universe – and they’re just the ones we could see. So, by knowing the proportion of the sky that the grain of sand is covering, we can estimate the number of galaxies in that area.

Stars in your eyes

What’s even more mind-blowing is the number of stars your grain of sand is covering. Galaxies are huge swirling masses of stars, dust and dark matter and each galaxy can contain anywhere from 10 million stars for a dwarf galaxy to a thousand billion stars for a giant galaxy. So even if your grain of sand was hiding only dwarf galaxies, that would be around a hundred billion stars!

Our solar system is located on one arm of the spiral galaxy the Milky Way. If you look up on a clear night and away from city lights you can see a smudge of stars across the sky. What you are seeing is the billions of stars that make up the main body of our galaxy. But what you can’t see is the super massive black hole that is thought to be at the centre of most, if not all, galaxies in the universe.

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