How to wrap one’s mind around large numbers: from galaxies to yourself.
The screenshot above, from the website ‘Scales of the Universe’, shows the typical scale of everyday life. We live on the scale of meters, kilometers, and miles, and for everyday purposes this suffices quite nicely.
To get a sense of how the Earth sizes up to the rest of the Universe, why not do so ‘Cosmos’-style?
Here are the inner planets:
Earth is largest at 12,756 km in diameter, followed very closely by cloudy Venus at 12,105 km. Rust-coloured Mars is about half the size of Earth, and barren Mercury only a third as large.
Next are the gas giants:
There’s a very good reason we call them ‘giants’.
The smallest is Neptune, the blue ball on the right, at just over 49,000 km wide. Uranus, the blue ball nearest to Earth, is slightly larger at over 51,000 km. The ringed planet Saturn is roughly twice the size of Uranus, whereas Jupiter, the largest of the planets, comes in at over 142,000 km, or around 11 times the size of Earth.
Now that we got 1% of the mass of the Solar System out of the way, let’s meet the other 99%:
Yes, that big orange ball hogging the viewing space is the Sun. It is over 1.3 million kilometers wide. If a beam of light (called a photon) were to travel the diameter of the Sun, it would spend roughly 4.4 seconds trying to reach the other side. Light only needs about one second to fly to the Moon from the Earth, at a top-speed of nearly 300 million meters per second (m/s).
And this is where using our old, Earthly measurements starts to become cumbersome and useless…
From now on, we will have to use units based on that light beam of ours. For example, the Sun is roughly 4.4 light-seconds wide, and the distance from the Earth to the Moon is about one light-second.
So now, let’s go meet the stellar neighbourhood!
It is okay if you do not recognize the names of the stars in the bottom-right panel. They are the largest stars ever discovered in the Milky Way, and were only found recently by astronomers using advanced telescopes. VV Cephei is 2.4 billion kilometers in diameter, or just over two light-hours. If that star sat where our Sun is now, it could swallow Saturn in its orbit.
Once we leave the realm of stars, we will have no choice but to make use of a unit called the light-year (as you might be able guess, it is how far light can travel through a vacuum in a year).
Our Milky Way galaxy is around 100,000 light-years (ly) across, which means that, travelling at the speed of light, a trip from one edge to the other would take 100,000 years.
Going intergalactic, the present separation between the Milky Way and the Andromeda galaxy is 2.8 million ly. That means that we are seeing the Andromeda galaxy where it would have been in outer space back when the first Oldowan tools were being used by the Homo habilis, 2.5 million years ago.
Now, we will be doing some serious time-travel:
The galaxies that make up the Local Group are all floating about in a region roughly 10 million ly across. Some famous members of this group include the Milky way and Andromeda.
The Local Group is part of a massive clustering of galaxies called the Virgo Supergroup. This agglomeration is over 100 million ly across. Light from the furthest of these galaxies left for Earth as an 8 km-wide asteroid was helping wipe out the dinosaurs.
The edge of the observable Universe, defined by the Cosmic Microwave Background (CMB), is a dizzying 48 billion ly across.
This is what unimaginable size looks like.
The interactive infographic for this article is perhaps the greatest webpage ever designed by mankind to give Regular Joe’s a pleasantly visual sense of the scale of various things, from the smallest of the small, to the Observable Universe in all its unimaginable glory. Check it out!
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planets, earth, venus, mercury, gas giants, neptune, uranus, saturn, milky way, andromeda, vv cephei