# Lengths From Very Small to Very Large

Our Universe has very small things (like atoms), and very large things (like galaxies).

And this is where metric prefixes like **milli-** and **kilo-** can be very useful.

Example: the distance between London and New York is about **5,580,000 meters**.

But it is easier to use 5,580 **kilo**meters.

Here is an illustration of sizes, from the very small (a Quark) to the very large (the known Universe):

The sizes are **in meters** using metric numbers.

(Just add the word "meter" after them, so we get "**milli**meter", "**tera**meter", etc.)

### Examples:

A Quark is about a **femto**meter in size.

Cells are about a **micro**meter in size (many different sizes though!)

The Milky Way is about a **zetta**meter in size.

## The Numbers

The numbers (like **10 ^{6}**) use Scientific Notation to show how big the value is.

Example: **10 ^{6}** means to use 10 in a multiplication

**6**times:

10 × 10 × 10 × 10 × 10 × 10 = **1,000,000**

But in practice it is easier to think **"a 1 followed by 6 zeros"**

Which is a million.

The prefix is **mega-**, so a megameter is a million meters.

Example: **10 ^{9}** is a 1 followed by

**9**zeros: 1,000,000,000 (a billion).

The prefix is **giga-**, so a gigameter is a billion meters.

Example: **10 ^{-9}** is a 1 moved nine places the other side of the decimal: 0.000 000 001

It is also called a **billionth**.

The prefix is **nano-**, so a nanometer is a billionth of a meter.

Looking at the illustration we can see that a person is about 1 meter in size, a mountain is about **10 ^{3}** (one thousand) meters in size, and the diameter of the Sun is about

**10**(one billion) meters.

^{9}Example: We could also say the Sun is about a "gigameter" in size

It's diameter is actually 1.392×10^{9} meters, or **1.392 gigameters**, or simply 1.392 Gm

Some Interesting Facts:

- The smallest length with any meaning is the Planck length (about 1.6 x 10
^{-35}meter) - Quarks are very very small (less than 10
^{-19}meters) - A Hydrogen atom is about 100 picometers in diameter (1.06 x 10
^{-10}meters) - Molecules are around the billionths of a meter in size. That is 0.000000001 meters. Some molecules are smaller and some bigger, though.
- A DNA molecule has a width of about 2.5 nanometers (but
*unfolded*is about 2 meters!) - A skin cell is about 30 micrometers across (0.000 030 m)
- People are a little over a meter tall (1.7 m is typical for men)
- Mountains are kilometers in size (Mount Everest is 8,848 m high)
- The Earth is megameters in size (a megameter is a thousand kilometers, and the Earth's diameter is 12,742 km)
- The Sun's diameter is about a gigameter (actually 1.39 x 10
^{9 }meters) - A Light Year is about 10 petameters in size (a petameter is 1,000,000,000,000,000 meters, which is a 1 followed by 15 zeros, or 10
^{15}) - The Milky Way is about 1 zettameter across (1,000,000,000,000,000,000,000 meters, which is a 1 followed by 21 zeros, or 10
^{21}) - The Universe is very very big