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GeoWorld focuses on everyone’s favorite planet, Earth. This is the first in a series of ten articles that serve as an introduction to the world around us. You might think of the series as a crash course on earth sciences and geography.

This first article puts Earth in perspective by exploring its natural habitat - the universe.

Of course, the universe is too vast and complex for anyone to really understand. The word universe means everything that exists. Consider Wikipedia’s definition:

Sounds simple enough - but what, or how much, exists? How big is the universe? When was the universe born - or has it always existed? What lies beyond the universe? Is there more than one universe (aka multiverse)?

You won’t find the answers to any of those questions here. Rather, this is a simple overview of the universe. If you already know there are billions (or sextillions) of stars scattered across a domain measured in light years and you know about gravity, which sometimes causes visitors from outer space to crash into Earth, then feel free to skip to the next article, Earth vs World.

6 Universal Basics

Start a discussion about the universe, and people are suddenly full of questions. How big is it? What is it made of? Why is the universe the way it is?

No one knows the answer to the first question, but we can get some ideas by examining the known universe, which is, in a sense, measured by two units - size and time. It’s probably safe to say the universe is made of matter and energy. And the universe makes a lot more sense if we understand the basics of gravity, which helps keep the universe round.

So let’s think of size, time, matter, energy, gravity and round as six universal basics as we take a closer look at each.

Here are two facts about the universe’s size: 1) Everyone wants to know how big the universe is, and 2) no one knows how big it is.

Of course, everyone knows the universe is big - so big it tends to warp space and maybe time itself (along with our minds). In, fact astronomers use time to measure the universe.

Time

To put that in perspective, can you imagine telling someone your best friend lives six and a half days away? Of course not; we normally measure distances in feet, meters, miles, kilometers or city blocks.

But miles are useless in deep space. Instead, the universe is commonly measured in light-years - the distance light travels in one year. At a speed of 186,000 miles per second, that adds up to about six trillion miles (nearly 9.5 trillion km).

Astronomers prefer another unit, the parsec, because it can be more easily derived from and compared with observational data. The parsec is defined as the distance at which an object will appear to move in one arcsecond of parallax when the observer moves one astronomical unit perpendicular to the line of sight to the observer, and is equal to approximately 3.26 light years. GeoWorld will stick with light-years, largely because they’re more familiar to the general public.

Of course, time is useful for more than measuring distances. It can also be used for measuring, well, time.

If you want to read this series of ten introductory articles (highly recommended), continue with Earth vs World.