by James Morris
Earlier this month, Elon Musk launched a Tesla into space, revitalizing our collective interest in space travel. The stunning photos of Earth from space also invite us all to think about where we are.
Take a look at a map and you will often see an icon stating, “You are here.”
Or pull out your phone and open one of the map apps, and there you are, that pulsating dot indicating your location.
And knowing “you are here” can be a comfort, indicating that you are around to listen, help out, and be supportive.
So, where are you? A mathematician might specify your location as a point in space. On a plane, it takes two coordinates to specify a point. One determines where the point is along a horizontal axis, and the other along a vertical axis. That point is a place, not a thing. It denotes where, not what.
The Earth is not a plane, but you can specify where you are using two coordinates – latitude, which tells you how far above or below the equator you are, and longitude, which tells you how far east or west you are from the Prime Meridian. The Prime Meridian is a reference line running from north to south through the Royal Observatory in Greenwich, England.
Your phone provides latitude and longitude information thanks to the Global Positioning System (GPS), a group of satellites that circle the Earth. Your phone and other devices communicate with these satellites to specify where you are.
To be even more precise, a third coordinate is needed – elevation. Elevation tells you where you are relative to sea level. Sea level changes daily due to the tides, so when you say “sea level,” you are referring to the average sea level between low and high tides.
You, along with all living organisms, occupy a layer – called the biosphere – at, above, and below sea level. The Rüppell’s vulture, a bird with a 10-foot wingspan, holds the record for the highest flight ever recorded. In 1975, one was sucked into the engine of a plane flying a mile-and-a-half above the summit of Mt. Everest. There are also deep-sea fish that live in the depths of the ocean. In 2014, a snailfish was found about 5 miles below the surface of the water.
These high flyers and deep swimmers define the extremes of height and depth for living organisms. However, compared to the size of the planet, the biosphere is actually an exceedingly thin layer blanketing the Earth.
Space is literally all around you. On Earth, the space in which you live and move about is the air, or atmosphere. Air seems empty, but it’s not. It’s made up of gases, and gases have substance. Think of a tree, which is largely built by converting carbon dioxide gas in the air into the substance of the tree.
Moving out from the Earth’s atmosphere, you next encounter the vacuum of space. But again, it is not completely empty. There is no air, but there are electromagnetic waves in the form of light from our sun and other stars. There are comets, asteroids, and planets.
There is the background radiation left over from the Big Bang about 14 billion years ago, still reverberating like a drum. There is dark matter and dark energy, which can’t be seen but can be detected by their effects on other objects. Together, they make up a staggering 95% of the universe. This means that everything you are familiar with is just a small fraction of the universe.
There are also human-made objects, such as the International Space Station, the Hubble Space Telescope, and space probes like Voyagers 1 and 2. And there are satellites orbiting the Earth, some of which are part of the Global Positioning System that you use to pinpoint where you are.
These objects move about in space. It was Albert Einstein who taught us that space itself is the gravitational field generated by objects. This field has a shape and emanates from any object with mass, like the Sun and Earth. In other words, there would be no space if not for the objects within it.
Where are you in space? The Earth is the third planet from the Sun, further than Mercury and Venus, but closer than Mars, Jupiter, Saturn, Uranus, and Neptune.
Between Mars and Jupiter is the asteroid belt, a ring of rocky objects that circle the sun. The region contains billions of asteroids, but they are spread out in a vast region of space, so it is not hard to navigate through it and, if you could stand on an asteroid, you probably wouldn’t see another one.
Pluto, discovered in 1930 as the ninth planet, was recently downgraded to a dwarf planet. It is now considered part of the Kuiper belt, which includes thousands of small, icy objects that form a ring just beyond the orbit of Neptune.
The Sun, planets, asteroid belt, and Kuiper belt make up the solar system. The solar system is just one of many solar systems that make up the Milky Way Galaxy. When you look up into space at night, you might see a passing plane, satellite, or even the International Space Station. You might notice a planet, like Venus or Jupiter. And you see stars dotting the sky. All of the stars you see at night are in, and make up, the Milky Way Galaxy.
If you look up on a really dark night, away from urban light pollution, you may be able to see a white band across the sky, the “milky way” itself. The Milky Way Galaxy is a flat, spiral galaxy, with arms radiating outward. You are located in one of these arms (the Orion arm). When you look up, you are seeing the galaxy edge on, from within, so most of the stars form a band across the night sky.
At the center of the Milky Way is a supermassive black hole. You can find the center of the galaxy by looking at the constellation Sagittarius, which is visible just above the horizon on summer nights in the Northern hemisphere.
Looking away from the center, you come to other galaxies. Your closest neighboring galaxy is the Andromeda Galaxy. The Milky Way and Andromeda Galaxies are part of the Local Group, which in turn is part of the Virgo Supercluster.
Recently, scientists found that this supercluster is part of an even larger supercluster called Laniakea (“immeasurable heavens” in Hawaiian), with more than 100,000 galaxies. Laniaikea is just one supercluster of galaxies among many that make up the universe.
So, where are you? You can tell someone where you are with a place (“I’m in the coffee shop”) or by an address (with building number, street name, city, state, and country). You can specify your location precisely by GPS coordinates (with latitude, longitude, and elevation coordinates, triangulated by satellites orbiting the planet), or by cosmological address (Earth, Solar System, Orion Arm, Milky Way Galaxy, Local Group, Virgo Supercluster, Laniakea, Universe).
Regardless of how you describe your location, you are always here.
© James Morris 2018