Today in this blog post I will describe the size and scale of the universe from my understanding. To start off, light from the sun takes approximately 8 minutes to reach Earth, yet light from the farthest parts of the observable universe would take 13.8 billion years. Keep in mind, counting one billion seconds, one second per each number, would take nearly 100 years (34,722.2 days). In another scale such as the galactic scale, according to NASA’s Cosmic Distance Ladder, the Milky Way galaxy contains over 100 billion stars, with an estimated 2 trillion galaxies in the observable universe. With in these trillions of galaxies exists large voids out side of galactic clusters. As seen in the image above there is pockets density in the red and green and pockets of empty space between them, spanning hundreds of millions of lightyears.
For me, one of the biggest challenges in studying astronomy is truly understanding the scale of space and time. When humans have walked the earth for hundreds of thousands of years, it is hard to recognize that our collective existence is a mere flash in the grand scheme of the universe’s 14-billion year life. Every era of the universe feels unfathomably lengthy, and I doubt I could ever recognize the brevity of some cosmic events when duration is viewed this way.
This is why I find a tool such as the cosmic calendar so helpful. By scaling the unfathomable span of a universe down to a single year, from the Big Bang to NOW, astronomers can relate cosmic events to durations of time they have actually personally experienced.
Within the cosmic calendar, the earth only formed about four months ago. The dinosaurs ruled this young planet for a meager four days. Primitive humans appeared at 9 pm on the final day of the calendar. Imagine all of human history taking place in just three hours. Will we get as many days as the dinosaurs, or will we render this planet uninhabitable before a cosmic disaster can wipe us out? If the earth is swallowed by the sun in a few billion years, think about how compressed our measly existence would be by then.
Finally, within the cosmic calendar, the average college student is about 0.05 seconds old. The life I’ve lived so far has been brief. If the “cosmic viewer” began to blink the moment I was born, they might not yet be finished. 21 years is my personal reference period for the world, and squashing my life to this barely significant duration is what finally helped me “get” just how short our time here has been.
Depending on the moon’s location around the Earth, it causes the sun to light up different parts of it. As seen in the picture above, there are 8 different moon phases: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, and waning crescent. Waxing phases light on the right side of the moon, illustrating that it will be growing. Waning phases light up the left side of the moon, illustrating that it is slowly losing more and more visibility. Today (9/2/24) the moon phase is waning crescent to near new moon phase, making tomorrow the start of a new cycle. Typically, it takes the moon about 1 month to complete one whole moon phase cycle. Source 1
A sight everyone has seen is the moon, shining brightly over the dark shadows of night. But have you ever wondered why it looks so different all the time? The answer is that the moon is just a rock, not a glowing one, so all of the light we see is just reflected sunlight. Since the moon orbits around us, the side of the moon that we see each day is a little different from the last, and sometimes sunlight doesn’t fully reach the side that we can see. This cycle takes around 30 days before resetting, which is why we often say that the full moon signifies the end of a month.
Take a look at the chart below and try to see what phase the moon is in today!
People create so many different apps for observation for so many unique purposes such as understanding the scale of the universe, observing the Solar System day or night, and learning mind-blowing facts about space. For my first official blog, I wanted to explore a few other options outside of Stellarium that are available for free use.
Skyview Lite
Skyview Lite is a phone app. In the grand scheme of this blog, it is fairly basic. This app follows the mobile device camera and highlights where popular constellations and planets are located. It is all real-time so it is not as useful if you are using an app to determine where a star system or planet will be at a specific time. However, it is great fun at night to find what you can see with a little bit of help.
Celestia
This app is slightly different than the others introduced. Rather than observing from Earth, this website allows the viewer to explore space through a 3D simulation. While it is different, this app is great for understanding the actual scale of the universe introduced in class. The viewer can see their distance from the selected object as well as its radius. The user can even follow the orbit of a planet by changing the time. This allows them to see how far a planet will move from the starting point over a specific period. Celestia also has a “Solar System Browser” and a “Star Browser.” Both options allow the user to quickly jump to other planets, stars, and systems. While there are many great aspects of Celestia, it is very easy to lose track of where you are. If you lose Earth, you most likely are not getting back without restarting the program. This program is available for Windows and macOS here.
This is a photo I took on the Celestia app. The top left corner shows the distance and radius.
Sky Chart / Cartes du Ciel
The final program is Cartes du Ciel. This is by far the most advanced and difficult-to-use program. However, it provides great detailed information for those truly enthusiastic about astronomy. Upon starting the program, the user is prompted to pick any observatory around the world. If you complete this step, a large program opens with constellations, star systems, planets, asteroids, comets, and more based on the cardinal direction you look from the observatory. If clicked on, each will open a long list of information about the object. You can see distance, system, classification, and much more. Unfortunately, the times and dates chosen are limited to the past. This is because the app is based on results from real observatories. Cartes du Ciel is an app for avid astronomy fans with the patience to learn the inner workings of such an intricate system. The download for Cartes du Ciel can be found here.
I took these images from the Cartes du Ciel app. They are from the Vanderbilt University Observatory.
by me, On Staten Island Ferry in front of Statue of Liberty
My name is Elias Ibrahim and I will talk a little about me. I am from Memphis, TN and I am currently a freshman at Vanderbilt University and I also take astro2110 . I am a Jazz studies Major and my primary instrument is piano. My music and musical journey can be found here
covering a wide range of topics dealing with our solar system
The Grandfather Paradox The Grandfather Paradox is a concept in theories about time travel. More specifically, the paradox introduces the dilemma that if you were to travel back in time to a point before your grandfather met your grandmother, and you happened to prevent them from meeting (i.e. killing your grandfather), you would, by extension, prevent yourself from being born. But, if it was actually the case that you were never born, how could you have traveled back in time to commit this act in the first place? And if you didn’t go back in time to kill your grandfather, then you would still be alive, meaning that you would be able to go back in time and kill your grandfather. This concept creates a seemingly unsolvable loop- a paradox. In short, the Grandfather Paradox serves to illustrate the complex contradictions that arise when we think about altering events that have already occurred. It suggests that if time travel were possible (if we were to come up with a time machine to the past, today), there would need to be some sort of mechanism that prevents this contradiction from happening. Some hypotheses lie along the lines of alternate timelines/parallel universes, but the backing to these theories are far from absolutely conclusive. Instead, one could argue that it’s equally as easy (or easier) to conclude from this paradox that time travel is simply a physical impossibility.
The Speed of Light When we look at an object in space (a star, for example), what we actually are seeing is the light emitted from such object. When emitted, light travels through space at a finite speed (approximately 300,000 km/s), meaning that it takes some ‘X‘ amount of time for this light to reach us. Generally, X is dictated by the distance between the observer (us) and the source of light. Because of this, the farther an object is, the longer it takes for its light to travel to us. Some examples include the Sun, which is 93 million miles away, and has its light take 8m20s to reach observers on Earth1. The Moon, on the other hand, is much closer at an average distance of about 240,000 miles, resulting in a “light travel time” of around 1.33 seconds. On much smaller scales this truth holds, but is considerably more difficult to notice. Due to this discrepancy between the time the light is emitted and the moment where it reaches the observer, whenever the light arrives at us, we’re actually observing this object as it was in the past. In the case of the Sun, we see it as it was 8m20s ago (8.33 light-minutes). In the case of the Moon, we see it as it was 1.33 seconds ago (1.33 light-seconds). Andromeda (the closest galaxy to our own Milky Way) is roughly 2.5 million light years away (Image 1), meaning the light takes 2.5 million years to travel to us.
(Image 1 displaying the distance, in light years, between the Milky Way and Andromeda galaxies. Image taken from http://www.waitbutwhy.com)
Observing the Past Through the Speed of Light Now imagine a hypothetical alien civilization in Andromeda. If they were to have a powerful enough telescope, they would be able to observe Earth as it was 2.5 million years ago. They would be observing the Earth at/around the time of an Ice Age, allowing them to gather insights on aspects of humanity’s past. This is because the light (and the information it carries) from Earth during that period would just now be reaching Andromeda’s point in space. However, such alien civilization would only be able to observe this past- they have no ability to interact with it. In a way, this hypothetical is a form of a time capsule, where information about the past is encoded in the light that travels across the Universe. And at the same time, every different point of view (Earth, the Sun, Andromeda, a Supercluster, or ANY OTHER PLACE IN THE UNIVERSE) serves as its own time capsule. While holding the Grandfather Paradox to be true, we can consider this idea of light travel-time as a loophole around the contradictions of the paradox. If us, humans, were to somehow, magically teleport to Andromeda today and looked back at Earth, we would see it as it was 2.5 million years ago. This ability to observe the past serves as the closest fathomable alternative to traveling in time, allowing you to observebut not interact with the Universe of the past.
