Cosmology Asteroid Mining Space Station
Cosmology Asteroid Mining Space Station
A website about the Universe would not be complete without an introduction to the sizes and distances involved. For the Universe is a truly grand design.
When we humans think of "small" we are likely to think of things like a grain of sand, or an insect, or a poppy seed. And when we think of "large" we might think of things like redwoods, or mountains, or even the Earth itself.
But, in truth, these objects represent only a tiny slice in the range of sizes in the Universe. To help illustrate just how incredibly vast the range of sizes present in the Universe truly are, we'll take two of the examples mentioned above to demonstrate.
A desert sand dune.
How small is a grain of sand? Sand grains fall in a size range between 0.6 and 2 millimeters in diameter. Smaller sizes would be grit or powder, while larger sizes would be gravel, rocks, boulders, etc. For our size demonstration, we'll assume that a "typical" grain of sand would be 1 millimeter in diameter. Further, let's assume that the particular grain of sand we are using is a perfect cube. Thus, the volume of this grain of sand would be exactly one cubic millimeter (1/1000th cc).
Avogadro's Number - When dealing with the VERY small (atoms and molecules), scientists use a unit called a Mole (or Mol). These numbers represent the relative mass (weight) of a substance in grams based on that substance's molecular weight. Avogadro's Number is the number of atoms or molecules in a mole of a substance. This number is about 602,404,000,000,000,000,000,000 (6.02404 X 1023 or over 600 sextillion atoms/molecules).
With this huge number, and a few more, such as the density (2.648 gm/cc) and molecular weight (60.0843) of silica (the primary ingredient in sand), we can determine the approximate number of molecules of silica (SiO2) in that grain of sand. The actual number of molecules in our grain of sand turns out to be about 26,548,795,476,000,000,000 (over 26 quintillion).
So, as you can see, compared to a molecule, a grain of sand is gargantuan!
Our home among the stars.
How big is the Earth? By human standards, the Earth is humongous; 1.4 X 1021 tons (1.4 sextillion tons). But it is nowhere near the largest object in space.
The most easily visible objects in our galaxy are stars. Our sun is just one of them. Although our sun is not a "typical" star (it's in the top 5% of stars by mass), it's still a good one to use as a basis for comparison. The mass of the Sun is 333,000 times the mass of the Earth. Pretty huge, eh? But our sun is only one star among billions in our galaxy. The mass of the Milky Way galaxy is about 2 X 1011 (200 billion) times the mass of the Sun (to the edge of the visible disk), or about 66.6 quadrillion times the mass of the Earth. Now that's enormous! This alone would be something special but for the fact that it's still only a small part of the Universe as a whole.
Hubble Deep Field - North.
Hubble Deep Field - The Hubble Space Telescope has opened our eyes to the true vastness of the Universe at large. The main project which made this possible was Hubble Deep Field North and South. Hubble exposed two tiny areas of "blank" sky to it's cameras for many hours to see what it could see. What it found were thousands of galaxies like our Milky Way. By extrapolation, astronomers were able to estimate the total population of galaxies in the Universe. It turns out to be over 100 billion major galaxies. So, if you take 66.6 quadrillion times 100 billion (the number of Earth masses in the Universe), you can see that our Earth is pretty insignificant in the grand scheme of things.
Full Sky Survey of the Cosmic Background Radiation courtesy of WMAP.
The Wilkinson Microwave Anisotropy Probe (WMAP) has just given us even more revelations about the mass/energy in the Universe. It turns out that normal matter and energy like atoms, molecules, electrons, and photons (known as "baryonic" particles) represent only about 4.4% of the Universe. About 22 percent is "dark matter," and 73 percent is "exotic dark energy." So it seems that all the planets, stars, nebulae and galaxies we see through a telescope represent only a tiny fraction of the material that makes up our Universe.
Now for some more mind-numbing numbers.
When we plan a trip, we'd usually like to know the distance to our destination. Of course, these distances are measured in Miles or Kilometers. The circumference of the earth at the equator is 24,901.55 miles (40,075.16 kilometers). If the oceans weren't there, it would take a person walking at a steady pace of 3 miles per hour, 24 hours a day, over 345 days (nearly a year) to circumnavigate the globe. Of course, we humans are pretty slow moving.
The fastest known speed for anything in our Universe is the speed of light, which is about 186,300 miles per second. While our human walker will take months to get around the Earth, a beam of light could circumnavigate the globe nearly 7-1/2 times in one second. Now that's fast!
Since the speed of light is the fastest speed we know of, it's used a lot in astronomy to measure distances in space. These units of distance are based on the distance a beam of light can traverse in a given unit of time. The most common of these units is the Light Year. One light year is equal to about 5,875,156,800,000 miles (just under 6 trillion miles). That's nearly 236 million times the circumference of the Earth! It would take our human walker over 249 million years to travel one light year.
Proxima Centauri, our nearest stellar neighbor.
The nearest star to the Earth is Proxima Centauri (above). This tiny (relative to the sun) red dwarf, visible only in telescopes, is about 4.25 light years from Earth. Over a billion years would be required for our walker to get to this nearest of the stars.
Our view of the Milky Way in the Near Infrared (courtesy Caltech 2MASS).
The Sun and Proxima Centauri are only two of an estimated 400 billion stars in our Milky Way Galaxy. The majority of these stars are spread out in a disk-like system about 90,000 light years in diameter and about 10,000 light years thick. This is equivalent to over 63 trillion cubic light years! We won't even begin to guess how many aeons our walker would require to cover all that space.
The size of our galaxy is truly enormous. And for the longest time, we believed that our galaxy WAS the universe. But thanks to some pioneering work by a few dedicated astronomers, especially Edwin Hubble (for whom the Space Telescope was named), we now know that our galaxy is only one among billions of galaxies.
Galaxies come in all sizes and shapes; from (relatively) tiny dwarf irregular systems containing a few million stars, to enormous eliptical galaxies containing trillions of stars. And the distances between galaxies are just as varied.
Two of the nearest galaxies to our own are the Large and Small Magellanic Clouds (above, left and center), only about 180,000 light years away. The nearest large galaxy is the Great Andromeda Galaxy (above, right), about 2.9 million light years distance. 2.9 million light years! That works out to over 32 times the diameter of our entire galaxy. In other words, if you lay 32 Milky Ways edge to edge you would not quite reach Andromeda.
Australopithecus africanus lived from 3.3 to 2.5 million years ago.
Another way to put it is that it takes a beam of light 2.9 million years to reach us from Andromeda. The light you see today from Andromeda started it's journey when the early hominid Australopithecus Africanus (above) walked the Earth.
As vast as the distance between the Milky Way and Andromeda is, this, too, represents only a small fraction of the distances within the Universe. These two galaxies form the core of a loose configuration of about 30 galaxies contained within a volume of space about 10 million light years in diameter, known as the Local Group. This group, in turn, is only a small "suburb" of a much larger group known as the Virgo Cluster, which contains about 2,000 galaxies spread over a volume fully 100 million light years in diameter.
The Virgo Galaxy Cluster.
The Virgo Cluster, in turn is only one among millions of clusters and superclusters (clusters of clusters) populating the Universe at large, and spanning distances in excess of 10 billion light years.
As you can see, the Universe is a much larger (and smaller) place than most people realize. To even begin to grasp the fantastically huge numbers involved in astronomy and astrophysics is truly a stretch of the imagination. If nothing else, it's certainly a humbling experience.
We humans are fortunate, indeed, to be able to view and analyze our surroundings to such a remarkable degree. And we are especially fortunate to be living in this particular period of our history. We have learned more about the world around us in the last 75 years than in all of human history.
A thousand years ago, our Earth was the center of the Universe, with the stars and planets circling us embedded on celestial spheres. And a hundred years ago, our Milky Way galaxy was the sum total of the Universe. We now know that the Earth is but a mote of dust, circling a tiny spec of a star called the Sun, circling a vast conglomeration of stars, dust and gas called a galaxy, only one among billions of galaxies.
