The metric system is based on "tens", and it provides a useful method for describing the sizes of objects. It is also easy to understand, thanks to the evolutionary accident that gave human beings 10 fingers.
The symbol "^" means "to the exponent". The expression 10^2, "ten to the two" is the same as one hundred, or 100. 10^3 is the same as one thousand, or 1000, and so on.
Each step represents a magnification of 10, and begins at the edge of the Universe,
A Vast Distance from Earth
10^25 meters, a billion light-years from Earth - Nothing but an all surrounding black void, sprinkled with faint spots of light.
10^24 meters, a hundred million light-years - The points of light grow slightly larger. Ahead is a colossal supercluster of galaxies.
10^23 meters, 10 million light-years - One point of light is now a smudge. It is the Milky Way galaxy, home to 400 billion stars.
Approaching the Milky Way Galaxy
10^22 meters, 1 million light-years - The spiral structure of the Milky Way becomes evident. It is flanked by two companions, the Magellan clouds.
10^21, 100 thousand light-years - The giant spiral of the Earth's home galaxy fills the view. A huge collection of stars, rotating once every 250,000 years.
10^20 meters, 10 thousand light-years - Countless stars, appearing like millions of sand-grains, hide the Sun and her planets.
10^19 meters, 1 thousand light-years - A mass of bright stars, encompassing our solar system.
10^18 meters, 100 light-years - The sun still too faint to see.
10^17 meters, 10 light-years - The view appears like that of the sky, as seen from Earth on a dark, cloudless night.
Approaching the Sun
10^16 meters, 1 light year - A point of light grows larger, a single small orb, one out of trillions.
10^15 meters, 1 trillion kilometres - The Sun grows larger.
10^14 meters, 100 billion kilometres - From this distance, if the orbits of the planets were drawn out, they could be seen as small ellipses around the Sun.
10^13 meters, 10 billion kilometres - The planetary orbits trace large paths across the view, with the Sun at one focus of the ellipses.
10^12 meters, 1 billion kilometres - The orbits of the inner planets come into view. The third from the Sun is focussed upon, appearing as a pale blue dot.
10^11 meters, 100 million kilometres - The orbit of the Earth sweeps the view.
Approaching the Earth
10^10 meters, 10 million kilometres - The orbit of the Moon can be seen surrounding the tiny Earth.
10^9 meters, 1 million kilometres - The Earth is apparent, and the Moon’s orbit fills the view.
10^8 meters, 100 thousand kilometres - The Earth’s oceans can be seen below a cloudy vale.
10^7 meters, 10 thousand kilometres - The continents become visible.
10^6 meters, 1 thousand kilometres - A river inlet can be seen. Vague shapes indicate cities and towns.
Approaching Home
10^5 meters, 100 kilometres - A town is directly below, a grid system of streets reveals the efforts of human minds.
10^4 meters, 10 kilometres - A group of streets is below, a large park lies to the north, and a river to the east.
10^3 meters, 1 kilometre - The garden of a house comes into view. The trees and a small pond can be seen.
10^2 meters, 100 meters - Two shapes lie in the centre of the garden, a small black shape moves rapidly across the grass.
Approaching Life
10^1 meters, 10 meters - The shapes resolve into a couple asleep on the grass. A black dog plays with a ball.
10^0 meters, 1 meter - The scale of a human being. A plate of food and a magazine can be seen.
10^-1 meters, 10 centimetres - A close-up of the human hand. From this point, the view goes beyond the smallest scale resolvable by the human eye.
References:
Morrison, Philip & Morrison, Phylis. Powers Of Ten, About the Relative Size of Things in the Universe. Scientific American Books, 1982.
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