Introduction

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.

Mayflies are amazing creatures; some species live just a few minutes as adults.

In contrast, humans are among the longest-lived animals, sometimes reaching ages of one hundred years or more. But to a star, people would seem like mayflies.

Consider the sun, which is thought to have formed about 4.5 billion years ago - and it’s a youngster. Based on current interpretations of astronomical observations, the universe is estimated to be about 13.73 billion years old.

In comparison, the average human lifespan is probably about 50-75 years. Thus, 13.75 billion years is probably the equivalent of more than 140 million human generations (or approximately 138 million centuries). And since the average human lifespan was probably less than fifty years in the distant past, we could be talking about even more generations.

Centuries and even millennia (a millennium equals a thousand years) clearly have little meaning in deep space. Like geologists and paleontologists, astronomers measure time in millions or billions of years. However, astronomers may also describe events that occur in days, hours or even fractions of a second.

Size

Let’s take a break from time and talk about size for a while.

Heavenly Bodies

Astronomers fall back on smaller, more familiar units of measurement when sizing up heavenly bodies. Simple comparisons can be convenient, too.

For example, Earth has a diameter of 7,926.41 miles (12,756.32 km) at the equator (7,901 miles/12,715.43 km at the poles), ranking as the fifth biggest planet in our solar system. The largest planet is Jupiter, the fifth planet from the sun. It has two and a half times the mass of all the other planets combined.

(Above) This image shows the relative sizes of, from left to right, Mercury, Venus, Earth and Mars.
(Below) Earth is puny compared to Jupiter. In fact, that reddish spot on Jupiter (the Great Red Spot) is a centuries-old storm that’s two or three times as big as Earth. For some really cool pictures comparing the planets, check out POV-Ray Planet Render.

The sun is more than 1,000 times as big as Jupiter - and our sun is not a big star, with a diameter of less than half a million miles (approximately 432,450 miles/695,500 km).

Consider the comparisons below. The picture on the left compares Jupiter, the Sun and a well known star named Sirius. The next picture shows Sirius in comparison with Arcturus and Aldebaran. In the third picture, we downsize Aldebaran to illustrate the relative sizes of Rigel, Antares and Betelgeuse. And the last picture shows Betelgeuse nested inside VY Canis Majoris, the biggest known star, with a diameter roughly 2,000 times that of the Sun (1.7 billion miles or 3 billion km). However, one astrophysicist believes Canis Majoris is only 600 times as big as the sun.

Interstellar Distances

We might use miles to measure the distance between Earth and the moon or some of the closer planets. But when we talk about interstellar distances - the distances between stars - it’s back to light-years.

But let’s size up our solar system first. Our solar system has a radius of approximately 2.79 billion miles or 30.07 AU, as measured from the Sun to the most distant planet, Neptune. (Pluto isn’t considered a true planet.) The diameter of our solar system is twice the radius, or 5.58 billion miles (60.14 AU).

But our solar system also includes non-planetary bodies, like Pluto...and even that isn’t the end of the story.

The real edge of our solar system is something called the Oort Cloud, a region where the Sun’s gravity loses dominion over its surroundings. The Oort Cloud is estimated to reside in a sphere about 18 trillion miles (193,548.38 AU) from the Sun. That gives our solar system a diameter of about 36 trillion miles.

Our solar system is just one of countless similar systems that make up the Milky Way Galaxy. The diameter of a typical galaxy is 30,000 light years. The Milky Way Galaxy is thus pretty big, at a diameter of roughly 100,000 light years.

The typical distance between two neighboring galaxies is about three million light years. Our nearest sister galaxy, the Andromeda Galaxy, is roughly 2.5 million light years away.

The yellow rectangle above represents the Milky Way Galaxy, while red represents the distance between the Milky Way and the Andromeda Galaxy.

The diameter of the observable universe (that portion of the universe visible from Earth) alone is thought to be at least 93 billion light years (8.80 X 10²⁶ meters) - and the universe may be infinite in volume. Since the universe may be expanding faster than the speed of light, we’ll probably never know exactly how big it is.

If we were able to travel at the speed of light, it would therefore take a spaceship eight minutes to reach the sun, 4.22 years to reach the next nearest star (Proxima Centauri) and 93 billion years to reach the edge of the known universe - assuming the univers was standing still. In fact, the edge of the universe is racing away from us as the universe expands.

Even if we could fly to the Edge in just 93 billion years, things could still get kind of weird, considering the universe is thought to currently be about 14 billion years old. So the universe would be more than eight times as old by the time our spacecraft arrived at the current boundary of the observable universe (if it wasn’t expanding).

Some astronomers have suggested that it may be impossible to travel at the speed of light. That could make traveling to other stars virtually impossible. With our current technology, it would likely take nine months to reach Mars, one of the three nearest planets. (Mars, Venus and Mercury can all be closest to Earth, depending on their orbits.) That’s one and half years round trip - about 550 days cooped up in a spaceship.

Star Counts

Counting the stars in just one small patch of night sky can be a daunting challenge.

Light-years and parsecs aren’t the only units we can use to gauge the universe’s size. Astronomers and amateurs alike adore star counts. After all, numbers are easy to understand, and who could not be impressed by the staggering number of stars in the universe?

Yet, once again, the human mind is slammed by the numbers. There are probably more than 100 billion (10¹¹) galaxies in the observable universe alone, suggesting a rough estimate of around one sextillion (10²¹) stars in the observable universe. However, a 2010 study by astronomers resulted in a figure of 300 sextillion (3×10²³).

So far we’ve learned that the universe is big - so big that we may never know how big it is. But what’s it made of and, more important, what makes it tick?

Anyone with a basic understanding of science knows the universe is made of matter and energy, right? In fact, the bulk of the universe is thought to be made of something called dark matter and dark energy, which are poorly understood. So let’s tackle conventional matter and energy first.

Matter

Matter is basically anything that takes up space. Anything in the universe that occupies space and has mass - a measure of the amount of matter in a given sample - is composed of matter. The amount of force required to move an object, or the resistance of that object, is a measure of its mass.

The Law of Conservation of Matter and Energy says that matter cannot be created nor destroyed. The total quantity of matter and energy that is in the universe is constant.

Note that matter can be transformed. For example, several elements can be combined to form a particular type of metal, just as we can combine ingredients to make a loaf of bread. But we cannot make matter magically appear or disappear, though we might create the illusion that we can do so.

The Law of Conservation of Matter and Energy has a corollary in the political/economic dictum there is no free lunch.

But what’s matter itself made of? Earlier generations of students were taught that matter is made of atoms, which in turn combine to form molecules. Simple, huh?

Once again, science has revised the rules. Scientists have now designated quarks (of which protons and neutrons are made) and leptons (related to electrons) as the fundamental building blocks of matter. If you aren’t confused yet, brace yourself: There are now a bewildering variety of definitions for the word matter - not to mention different kinds of matter.

Like something from a comic book, antimatter is a form of matter that’s more or less wired backwards; when matter and antimatter come into contact with each other, they annihilate each other.

Antimatter is a very rare and fleeting phenomenon on Earth (associated with radioactive decay or cosmic rays), and it appears to be far scarcer than matter in the observable universe. The apparent imbalance is one of physics’ biggest mysteries.

Not Alone

Extraterrestrial Life

Of course, one of the questions everyone asks about the universe is whether there’s life anywhere besides Earth. No one knows the answer, and it’s possible we may never know.

The late astronomer Carl Sagan suggested that it might be impossible to travel at the speed of light. If so, that might leave intelligent races effectively stranded in their home galaxies. And if there is life out there, there may very well be thousands, millions or billions of planets with life. So why should another race visit Earth when there are so many other inhabited worlds to explore?

Moreover, how could another race know about Earth when people have only been transmitting light and radio signals for a century or so? For all practical purposes, we’re probably invisible.

In the meantime, people continue searching for extraterrestrial (extra-terrestrial?) life, advertising our presence as loudly as they can. But is this smart?

Renowned physicist Stephen Hawkins points out that beckoning another race we know nothing about could be - welll, stupid. It might be compared to a man who knows nothing about Africa standing in the middle of a savanna making loud noises, hoping to discover other life forms - only to get eaten by a lion.

Alien races aren’t the only potential danger.

Visitors from Outer Space

Do you know what created the craters that pockmark the moon? If you answered volcanoes, you’re wrong; there are no volcanoes on the moon.

Those famous lunar craters are impact craters, souvenirs of collisions with meteors and other space travelers. They’re also a remidner that Earth isn’t immune from such collisions.

In fact, scientists believe that some of Earth’s biggest extinction events were caused by enormous meteors plowing into the planet. The most famous extinction os probably the one that wiped out the dinosaurs about 65.6 million years ago, apparently caused by a meteor that struck near what is now Yucatan, Mexico.

Fortunately, you really don’t need to worry about evil space aliens or rogue meteors. It could well be another fifty million years before Earth is struck by another monster meteor.

Of more immediate concern is the militarization of space. The United States’ ravenous war machine is guided largely by satellites orbiting Earth, and the U.S. is developing a new generation of space-based weapons. After witnessing the horrible war crimes the U.S. has committed - using everything from atomic bombs to Agent Orange to depleted uranium - people in other countries are understandably scared.

Thus, we are now witnessing two space races - a scientific space race intent on learning more about the universe we live in and a military space race. Between spy satellites that listen in on our phone calls and e-mails and military spacecraft that can strike any spot on the planet within hours, we need to take control of our government back from corporate interests. This and related topics are discussed in more detail on the website Politix.

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