Today we reach our final step in the cosmic ladder as we look beyond our home, the Milky Way.

Despite its vast scale, over 100,000 light years across, the Milky Way is insignificant on the scale of the universe. Why is this? There’s nothing unique about the Milky Way, in fact it is one of thousands of similar galaxies that we can see with amateur grade equipment.

Our nearest galactic neighbor is the famous Andromeda Galaxy, at 2.5 million light years away. Not only is it the closest, it appears to be very similar to our own galaxy in terms of structure and mass, given us a good idea of what the Milky Way would look like if we could see it from a distance.

In the accompanying image of the Andromeda Galaxy, you can see numerous stars across the field. These aren’t part of the Andromeda Galaxy, these foreground stars are actually nearby stars in the Milky Way as we peer out through them to see the much further Andromeda Galaxy!

How many galaxies are there? To answer this, one technique that curious scientists employed was to aim the Hubble Space Telescope at a seemingly empty patch in deep space and instead of taking an image with an exposure of a few hours, as is typical, they captured 22 days(!) worth of exposure on a single patch, and the results are breathtaking.

In the resulting Hubble Deep Field images, we can see over 3000 galaxies in a single frame, from a point in the early universe in which most galaxies hadn’t even had time to start forming stars.

There are an estimated 100 billion galaxies in the known universe, collectively containing more stars than all the grains of sands on Earth’s beaches combined.

“It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.” - Carl Sagan

Next week we’re talking about myths and misconceptions, you send us your questions if you’d like to see something specific covered.

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Stay well, and clear skies!

Cosmic Ladder: Step 5 - The Universe Beyond