On February 14th, 1990, as it was speeding out of our solar system, and traveling around 38,000 miles per hour, the Voyager 1 spacecraft turned back toward home and snapped this picture of Earth.
Having just completed one of the first close up tours of the outer planets Jupiter and Saturn, Voyager 1 was positioned around 3.7 billion miles (or 5.5 light-hours) from home. Scientist and astronomer Carl Sagan, who was largely responsible for convincing NASA to take the image, reflected on its significance in the passage below from his book, Pale Blue Dot. Click the orange button on this sound file to hear it in his own voice:
From this distant vantage point, the Earth might not seem of any particular interest. But for us, it’s different. Consider again that dot. That’s here. That’s home. That’s us. On it, everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there—on a mote of dust suspended in a sunbeam.
The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner, how frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds.
Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves. The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand.
It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we’ve ever known.
- Carl Sagan, Pale Blue Dot
I selected the quote above as an introduction to this first article because of the sentimental feelings I have for it. I can recall hearing the passage, in Carl Sagan’s own voice like the clip above, for the first time around the age of 15, and feeling a profound sense of wonder at the vastness of space and the smallness of our entire world. He had a way of writing and talking that naturally inspires the listener and I credit much of my interest in astronomy to this inspiration. He has since become a favorite author of mine and will doubtlessly show up again in future articles.
Now, as it did then, the passage elicits in me feelings of being incomprehensibly small and insignificant on the grand scale of the universe. Similar to how we humans might view an ant or a bacterium. This idea of our world being a tiny place is an appropriate segway into the topic of this first article, which will be a brief overview of the size and structure of the known universe and our position within it. A sort of “you are here” type map which will be helpful to those unfamiliar with astronomy and could be used as a reference to help better understand later topics. I will also briefly cover some of the timescales involved in studying the universe.
One of my main goals with this blog is get the reader thinking about what else is out there. Most of us get so lost in our day-to-day lives here on Earth, hardly giving a passing thought to the entire rest of the universe, which lays right above our heads at all times, night or day. Why aren’t people more curious about this huge bubble of space we live inside of?? How did we get here in the first place and what does our existence even mean? How incredible is it that we are literally made of inanimate space dust, yet we are able to study and contemplate the universe itself? These are the types of things I think about all the time and I’d like to share my passion for trying to understand them with you.
So let’s start with the most basic of questions one can ask when studying the universe: how big is it? Most people are well aware that the universe is vast, but just how vast are we talking? For the purpose of this article, I’m only going to consider the observable universe, which is a gigantic sphere having a diameter of about 93 billion light-years with the Earth at its center. There are other definitions of the word “universe,” but I will cover those in a later article, as they relate to what’s outside of that sphere. The observable universe is what we can be reasonably sure of since, afterall, we can directly see all of it with large and sensitive telescopes. How big exactly is 93 billion light-years, though? It turns out, the average person (myself included), is fairly incapable of truly comprehending such a large distance. We have absolutely nothing in our daily lives with which to experience that distance. But there are learning tools and comparisons that can help a little. For example, since 93 billion light-years is just the distance that light travels in 93 billion years, it helps to understand how fast the speed of light actually is. Light travels at a constant speed of around 670 million miles per hour. A beam of light would travel the distance around the equator of the Earth about 7.5 times in a single second. The light beam would reach the sun in about 8 minutes and the planet Saturn in about 1 hour and 26 minutes. In short, light is fast and the distance that it covers in 93 billion years is incredibly huge.
The distances involved in astronomy are so huge that they prohibit us from traveling to even the nearest star, at least with the technology available now and in the near future. The most interesting feature of these distances, though, is that they permit the study of the early history of our Universe. This is due to the speed of light being finite. Here on Earth, we basically witness things happening in real time. The time it takes light to travel from a source, such as a light bulb, around the room and then to our eye is so tiny that it’s virtually indistinguishable from being instantaneous. Out in the rest of the Universe though, where the distances are so vast, light actually takes an appreciable amount of time to reach us. Since the light travels for such a long period of time before getting to Earth, we actually get to see objects as they were when the light left them, even if that happened thousands or millions or even billions of years ago. When we look far out into space, we are therefore also looking back in time. Telescopes really are like time machines. For example, when we look at a galaxy that’s 40 million light-years away from us, we are seeing it as it was 40 million years ago. It’s this property of light that creates the edge of the bubble that is our observable universe. More on this later…..
Another great tool I know of to help understand the size of the universe is a series of diagrams, each centered on the Earth, that progressively zoom further and further out until they show the entire observable universe. Such a series of illustrations can be found in the book Nightwatch by Terrence Dickinson. I would highly recommend this book to anyone interested in learning about or practicing astronomy. The illustrations themselves were done by astronomical artist Adolf Schaller and I’ve included them below with my own descriptions. Each illustration is drawn to scale and depicts a cube-shaped volume of space that is one million times larger in volume than the drawing before it. In other words, the length, the width, and the height of the cube are each multiplied by 100 with each successive zoom out. We start with a cube that comfortably fits the Earth:
Step 1. Earth Diameter: 7,926 Miles (12,756 km)
Step 2. This next size cube contains the Earth and our only natural satellite, the moon. Here at only step 2, we reach the furthest extent of space that humans have traveled. Don’t get me wrong, the moon is still a whopping 238,900 miles away, but it’s right next door on the scales of the universe.
Step 3. The orbits of the inner planets Mercury, Venus, Earth, and Mars are partly shown in this next step. The moon, which is around one quarter the size of Earth, is no longer visible in this image.
Step 4. Our entire solar system. From this distance, the orbits of the inner planets are barely visible around the faint sun. At this point in the tour, we’ve reached the most distant area of space that human-made machines have explored (well, actually there a few that are probably a little bit outside this cube by now, but not much). The Voyager I, Voyager II, Pioneer 10, Pioneer 11, and New Horizons spacecrafts have all left our solar system and are currently bound for far off stars. All of them will likely outlive our species, and are carrying messages from the human race to anyone or anything that might eventually find them. I plan to write a future article that digs more deeply into the Voyager missions.
Step 5. Backing out another step, we see the sun as just a bright star. This is how an observer from a nearby star would see our entire solar system. It’s also how we see other stars. It’s estimated that around half of all stars in our night sky have one or more planets orbiting them, yet we have only been able to directly photograph very few of the thousands we’ve discovered so far because the light from the stars is simply too bright and tends to overpower the small amount of light that is reflected off the planets. We have other ways to detect these so-called exo-planets, but I’ll save that topic for a future article.
Step 6. If you look closely, you can now see the other stars in our stellar neighborhood. Most prominent in this category would be Sirius, which happens to be the brightest star in our night sky. Some stars may look close to us in this drawing, but keep in mind that each time we've zoomed out, this cube of space around the earth has been increasing in volume one million times. Even the closest star to the sun, Proxima Centauri, is 4.25 light-years away. The fastest man-made object ever, The Parker Solar Probe, reached a top speed of 430,000 mph. It would still take an object traveling that fast over 6500 years to reach Proxima Centauri, and again, that's the closest one.
Step 7. Here we can see some familiar objects, stars, and parts of constellations. Many of them are bright and familiar because of their relative proximity to us. The Orion Nebula, for example, is about 1340 light-years away from us. While that is indeed an incredibly far distance, it's right in our backyard when compared to the scales of our entire galaxy. Several of the objects I've imaged, including the Pleiades, the Orion Nebula, the Flame Nebula, and the Horsehead Nebula are contained in this volume of space. They can be viewed in the STAR CLUSTERS & NEBULAE section of my portfolio. The image below is not one of the 11 steps in our progression outward, but it's a good intermediate stage between steps 7 and 8 that shows where the sun and many other objects similar to the ones above are located within our galaxy.
Step 8. Here is our Milky Way Galaxy. The disk-shaped cosmic structure we live within. A vast collection of dust, gas, and hundreds of thousands of stars all slowly swirling around a supermassive black hole.
Formerly known as island universes, galaxies are the basic building blocks of the cosmos. Mind boggling distances of millions of light-years separate these enormous conglomerates of matter. Indeed, every star you see in the night sky and in my astrophotos (with the exception of some brighter stars in nearby galaxies) is located in our own galaxy. The other photo shown here was taken by a friend of mine, Alan Del Ponte, and it shows how we see the Milky Way from our vantage point within it. On a clear dark Summer night, in an area free from light pollution, even the naked eye can make out the lanes of dust and gas within the bright arch of light extending overhead. Our galaxy also has two nearby small satellite galaxies called the large and small Magellanic clouds. We don’t see them where I live in North America, but they can be seen easily from the southern hemisphere. There are also a few nearby tiny dwarf galaxies barely visible.
Step 9. Around 100 years ago, it was still thought that our galaxy was the only one and that all those faint smudges of light we saw in the night sky were some other type of smaller objects that existed within our own galaxy. In 1929 Edwin Hubble discovered (using a familiar type of star he found in the Andromeda Galaxy) that those fuzzy patches of light were incredibly far away from us. Too far, actually, to be within the bounds of our own Milky Way Galaxy, which means they had to be other galaxies. This discovery tremendously expanded the size of the known universe and put Hubble’s name in the history books forever. Read more about it in the text for the Andromeda Galaxy image that can be found in the GALAXIES section of my images portfolio. This illustration shows The Milky Way and our nearby neighbors, which astronomers call the Local Group. The scale used here is enormous. Even the Andromeda Galaxy, our closest large neighbor, is around 1.5 million light-years away from us.
Step 10. Backing out one more step, we begin to see the overall structure of the universe itself on the grandest of scales. Groups of galaxies, millions upon millions of them, are arranged into long filament structures creating a cosmic web of sorts. When we gaze into the universe with our most powerful telescopes, we see these filament structures and countless galaxies in every direction.
The famous image below was taken by the Hubble Space Telescope. It fixed its nearly 8-foot wide mirror upon a seeming empty region of space, which would cover the same area of the sky as a grain of salt held at arm's length. For 10 days in late 1995, Hubble imaged this area of space with long exposures. The resulting image mosaic consists of around 100 hours of total exposure time and was the first image of its kind, displaying around 3000 never before observed galaxies from the early universe. The faintest galaxies in the image are up to 10 billion years old, meaning that the light Hubble captured from them started its journey before our sun or Earth even existed.
Step 11. This illustration attempts to show our entire observable universe. Most astronomers believe the universe is about 13.7 billion years old. Because of this (and the finite speed of light), there exists a barrier, beyond which we cannot see. Before a certain point, the early universe was dark and opaque to light. Eventually, the hot soup of elementary particles leftover from the big bang began to cool and combine into ordinary atoms, which made the universe transparent to light.
Shortly after, the first stars and galaxies formed out of gravitationally collapsing clouds of hydrogen gas, and visible light began streaming through the cosmos for the first time. That early light represents the edge of our observable universe. The light from anything that lays beyond about 13.7 billion light-years away from us, hasn't yet had time to reach us and this is what creates the boundary of what we can see. There is very likely a whole lot more universe out there (it's looking like it might even extend infinitely), but we will never see it. Only theoretical models can predict what might lay beyond and I hope to write more in the future about that fascinating field of study, known as cosmology.
So if the very first stars and galaxies began producing light around 13 billion years ago, we would expect the observable universe to be about 26 billion light-years in diameter, right? 13 billion light-years in either direction from our point at the center? As I stated near the beginning of this article, it's actually about 93 billion light-years in diameter. This is because the universe itself is expanding. Space is stretching in all directions. When we look out into space, we see every other galaxy (except for a few closer ones that are bound to us by gravity) receding away from us. Every point in space is getting further and further away from every other point.
In fact, much to the surprise of scientists when it was first discovered, the expansion is accelerating. The more time that passes, the faster the universe expands. So the edge of our observable universe is now around 46.5 billion light-years away, but when the light from it first left, it was only about 13 billion light-years away. In the time since, space has stretched and the bubble of our observable universe has expanded.
An interesting consequence of this is that the light itself has also stretched as the space that contained it expanded. When light waves are stretched, their wavelengths get longer and they shift in color towards the red side of the visible spectrum. This redshift can be precisely measured and it's one method that astronomers use to study the expansion of the universe and the distances to far away objects. In the case of very distant objects, light can be stretched so far that it moves out of the red part of the spectrum and into the infrared part. The James Webb Space Telescope, launched Christmas day 2021, is equipped with sensors to detect this infrared light and this will allow it to peer back in time even further than Hubble has been able to. Webb should be able to view the very first stars and galaxies that ever formed around 13.6 billion years ago and study the early universe in much greater detail than has been possible before.
So far in this article, I've tried to convey how absolutely huge the universe is. Hopefully, some of the graphics and comparisons I've used have made the sizes and distances easier to understand. I'd also like to talk briefly about the timescales of the universe. Just as 13.7 billion light-years is a difficult distance to comprehend, 13.7 billion years is a difficult time frame to grasp. An entire human lifetime is a small fraction of the blink of an eye compared to that span of time. I know of a few comparisons to help understand it, though. One of them is the "Cosmic Calendar" that Carl Sagan originally used in his series Cosmos, where the entire span of the history of the universe is scaled to one regular calendar year. I might elaborate on this concept more fully in a later article. Another example I'd like to mention here, though, is an exhibit that exists at the Hayden Planetarium in New York City. It consists of a 120 yard-long (360 feet) corridor that represents all of time since the big bang around 13.7 billion years ago. As you progress along the timeline, you move closer and closer to present day. At the very end of this corridor, there is a human hair. The width of that human hair represents, to scale, the amount of time that our species has existed. It's mind boggling that we've been able to accumulate so much information about the history of the universe when we weren't even around for basically all of it.
This concludes our little tour of the universe and I hope you found it interesting and engaging. The cosmos truly is enormous and ancient beyond our wildest expectations, and if you ask me, there's no subject more fascinating to learn about. Some topics may be difficult to comprehend at first, but I encourage you to always keep trying to learn about them. Often, it's just a matter of hearing it explained a certain way and then things begin to click. I'd love to hear your feedback on this first article, along with any suggestions for future articles or topics you'd like me to explore further.