The Vastness of the Universe

Maps of the universe can understate the sheer vastness of space.  Even when distances are to scale, the size of celestial bodies are overly large and for good reason.  If the size of the objects were true to scale, they would be too small to see.  To get a grasp of the true nature of space, I am going to scale various systems using 10 miles as a base.  This is still pretty large but as the average commute in the United States is about 10 miles, this is a scale that is familiar in our day-to-day lives.

We’ll start with the Earth-Moon system.  The Moon is on average 238,855 miles from Earth.  Here, we’ll put the scale at 1 mile = 24,000 miles.  So, if we shrink the Earth and Moon to this scale, Earth will sit in the center while the Moon resides 9.95 miles away.  How big is the Earth?  The diameter of the Earth would be 1741 feet, about 100 feet less than the CN Tower in Toronto.  The troposphere, the lowest layer of the atmosphere where weather occurs and humans live, would only extend about 20 inches above the surface.  Here, you can see why astronauts comment on how from space, the atmosphere appears as a fragile protective layer that just hugs the Earth’s surface.  The upper layers of the atmosphere extend out 66 feet above the surface.  Also at 66 feet, you’ll find the Hubble Space Telescope.  The drag from the tenuous upper atmosphere will be enough to bring the Hubble down to Earth in the 2020’s just as happened to Skylab in 1979.  Here, you can appreciate the accomplishment of the Apollo program which traveled, on this scale, 9.95 miles to the Moon as opposed to 66 feet to reach Earth orbit.

Next up is the Solar System.  We’ll change the scale to 1 mile = 1 billion miles.  At this scale, the distance from the Earth to the Moon shrinks to 15 inches.  The Earth itself is half an inch or about the size of a marble.  In this model, we’ll put the Sun at the center and the table below will show what the Solar System looks like at this scale.

Object Diameter Distance from Sun
Sun 4.75 feet
Mercury 0.19 inch 190 feet
Venus 0.48 inch 354 feet
Earth 0.50 inch 491 feet
Mars 0.27 inch 748 feet
Asteroid Belt 0.01 – 0.03 inches 1080 to 1570 feet
Jupiter 5.50 inches 0.48 miles or 2,550 feet
Saturn 4.59 inches 0.89 miles or 4,688 feet
Uranus 2 inches 1.8 miles
Neptune 1.94 inches 2.8 miles
Pluto 0.09 inch 3.67 miles
Kuiper Belt 0.001 to 0.09 inches 2.5 to 4.5 miles
Voyager I & II

12.5 & 10.3 miles

On this scale, a trip to the Moon is 15 inches, to Mars some 250 feet.  As NASA people like to say, Mars is hard.  Going from the Moon, to the planets, and as we’ll see, to the stars each involves an exponential leap.  The Voyager missions, in space since 1977, have just reached the outer edges of our 10 mile map.  Note how much more massive the Sun is compared to the planets as it contains 99% of the mass in the Solar System.  Also note how tiny the asteroids are and on this scale, there is an average of 38 inches of separation between the objects in the asteroid belt.  Contrary to what you see in many sci-fi stories, there is plenty of space in an asteroid belt to navigate through.  Beyond the asteroid belt lie the gas giants.  This region was far enough from the Sun and cold enough to allow hydrogen compounds to freeze and utilize the abundant hydrogen in the solar nebula to form these giant planets.  In turn, the gas giant Jupiter’s gravity disrupted the formation of a planet in the asteroid belt.

Now, we’ll examine our neck of the woods in the Milky Way by taking a look at a region 10 light years from the Sun.  On this scale, we’ll put 1 mile = 1 light year.  Maps of our stellar neighborhood are not as ubiquitous in grade school as the Solar System so below is a look at our closest neighbors.

The Closest stars
Stellar Neighborhood 12.5 light years from Sun. Credit: Richard Powell

This region is embedded in what is called the Local Bubble, a peanut shaped area 300 light years across marked by tenuous, hot stellar gas.  It is thought that a series of supernovae 10-20 million years ago cleared out much of the interstellar gas in the Local Bubble.  On this scale, the solar system shrinks to 9 feet and the Sun is the size of a grain of sand.  The nearest star, Proxima Centauri, would be 4.24 miles away.  So, the leap from a Voyager type mission to visiting the nearest star on this scale is 9 feet to 4.24 miles.  The brightest star in the night sky, Sirius, would be 8.6 miles away.  Wolf 359 is not visible to the naked eye, but known to Star Trek fans where Star Fleet is destroyed by the Borg, would lie 7.8 miles away.  Galaxies often collide, but because of the spacing, stars rarely do.  This is key due to an impeding event to occur to the Milky Way in a few billion years.
Credit: Andrew Z. Colvin/Wiki Commons

The Local Galactic Group consists of some 54 galaxies clustered within 10 million light years.  Most are small, dwarf galaxies.  Here, we’ll use the scale 1 mile = 1 million light years.  The Milky Way would be 1/10th (528 feet) of a mile wide.  The Solar System lies 137 feet from the center of the Milky Way and is 0.0001 inches wide, about 1,000 times thinner than a human hair.  The closest galaxies to the Milky Way, the Magellanic Clouds, lie about 830 feet away.  The Andromeda Galaxy (M31), would be 2.5 miles away.  The Andromeda galaxy is larger than the Milky Way and would span over 1,100 feet across.  Compare this to the size and spacing to stars.  Galaxies are much larger and tend to collide into each other.

Until the 1920’s, the Milky Way was the only known galaxy.  Other galaxies were observed but were thought to be spiral nebulae within the Milky Way.  Edwin Hubble, working at Mt. Wilson, was able to resolve stars within the Andromeda Galaxy and determined it was situated beyond the Milky Way.  Taking measurements of other galaxies, Hubble also discovered the universe was expanding causing galaxies to race away from each other.  When galaxies are close enough, at times the gravitational attraction to each other is greater than the effect of the expansion of the universe.  The result is a collision between galaxies such as below.
NGC 2623, two colliding spiral galaxies. Credit: Hubble Legacy Archive, ESA, NASA

The same will happen to the Milky Way and Andromeda galaxies in a few billion years.  Stars will not collide but some may be ejected in the process.  The end result is the two galaxies will merge to form a giant elliptical galaxy.

Galaxies are not the only objects to collide in the universe, galaxy clusters also can collide.  Some 150 million light years away (or 150 miles using the current scale) lies the Great Attractor.  This region lies behind the center of the Milky Way and thus, is not open to optical observation.  It is hoped that infrared and radio observations, which can peer behind the veil of dust at the galactic center, can someday provide details what the Great Attractor is.

The largest structures in the universe are galactic superclusters.  The Milky Way and Local Group reside in the supercluster Laniakea which is some 520 million light years in length.  Superclusters form filament type structures with large voids in between.
Credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder)

To get a proper perspective on our home supercluster, lets use a scale of 1 mile = 50 million light years.  On this scale, Laniakea stretches out the entire 10 miles.  the Local Group of galaxies would be 1/5 of a mile (1,056 feet) wide.  The Milky Way would be about 10 feet across.  And as we can see from the image above, Laniakea is just a small part of the web of superclusters throughout the universe.

I have heard many students after taking an astronomy course say that it made them feel like an ant.  I remind them of what Fritz Zwiky said – each person in this vast universe is unique and thus, irreplaceable.  And that is of no small significance.

*Image atop of post is the Milky Way from the delicate arch in Natural Bridges National Monument in Utah.  Credit:  Jacob W. Frank/National Park Service

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