I often think about the following line: There was once a day when you and your friends went out to play for the very last time, and nobody knew it.
To me, this rings especially true; because the past can be a painful reminder of the way things were, the way we yearn for them to return to or, simply out of nostalgia. However, we cannot change the past. We cannot change what was, relive what we did or visit those memories (in real life). But that doesn't mean the past is all negative. Interesting, sure. Negative? I hope not. But, the past can also be right in front of us, if we know where and how to look.
First thing to consider is that the past IS all around you, if you know where to look for it. And obviously I'm not talking about the picture of your beloved pet or the photos from that camping trip where all your friends went and you all had a blast! No, to find the past, here in the present, you must look up...Just be careful, because the first place to look at, to see the past is the sun. Yes, that sun.
On average, the sun is approximately 93,000,000 miles from Earth, or 149 million kilometers. Astronomers call this distance an "Astronomical Unit" or AU; as distances get bigger, astronomers need other units of measure such as the AU. We also must know some standards as we look towards the past, the first is the speed of light. Light is THE FASTEST thing, ever. Nothing can travel faster than it. Star Wars, Star Trek and most Science Fiction depicts traveling faster than light: warp speed, light speed (or Ludacris Speed for my Spaceballs fans out there) but as of now, March 2024, we do not have the means to do so. Even still, if you want to get nerdy about it, warping space (a la Star Trek) means that you're still not going faster than light, you're warping the space and traveling through that warped space. But I digress.
Light, which is made of photons travels at 186,000 miles per second (300,000 kilometers per second) or at a mind-boggling 671 million miles per hour!!! At that speed, you could circle the equator almost 24 times in one second!! This incredible speed is also the speed at which radio signals and other forms of electromagnetic radiation travels at as well. The above animation (from Wikimedia Commons) helps illustrate the speeds involved when discussing light. Here we see a photo traveling at light speed, crossing the distance between the Earth and Moon in real-time. So, we're all on the same page now about speed? Great!
Knowing that light has a finite speed means we can measure it across vast distances, including the AU that separates Earth and the Sun. At that distance and speed, the light that is shining on Earth right now, took just about eight minutes from the time it left the surface of the sun! 93,000,000 miles in eight minutes seems fast, and it is! But that light is "old", and while eight minutes might not seem a long time, children find is fascinating to think that if I could turn off the sun, they wouldn't know it until those very same eight minutes had elapsed. And yes, that means that sunlight is from the not-very-distant past! But this is only our local star at eight light-minutes away. Look at something like Pluto and you're looking at it, as it was five-and-a-half hours ago! That's less than a quarter of one day. Hardly the past, but it is. (What were you doing 5.5 hours ago?) But even Pluto's distance of 3.7 billion miles (5.9 billion km), this is "around the corner" cosmically-speaking. Now it's time to get moving, metaphorically speaking.
What I next want you to consider is the distance we're talking here. Remember earlier in this post I spoke of distance? Well the next unit of measure is a Light Year. The easiest way to calculate this mind-bogglingly large number is to take the speed of light in miles per hour (670,616,629 mph) and multiply by the number of hours in a year (which is 8,766). Once you have a calculator big enough to do that equation, you get the number 5,878,625,370,000 miles! For our purposes here to say 6,000,000,000,000 TRILLION miles!!
Yes, that's a really big number, but that's only in ONE light-year. (Ponder this quickly, one estimate of the diameter of the known universe is 28 billion light years!) You get the idea, space is big. REALLY big!
Now I would like you to turn your attention to the Alpha Centauri system, our closest stellar neighbor. Located in the southern constellation of Centaurus, this is one of the brightest stars in the sky, bummer we can't see it here in New York.
At just over four light-years away, this star's light left it, just as the world was learning about how dangerous COVID-19 would be (and become)! Kobe Bryant would die on January 26. April 5 would see the first case of COVID-19 in a zoo animal is reported: a four-year-old female Malayan tiger at the Bronx Zoo in New York City. An annular solar eclipse would happen in June, Pope Benedict XVI becomes the longest-lived pope at 93 years, 4 months, and 16 days, surpassing Pope Leo XIII, who died in 1903, and as the year came to a close, the number of confirmed cases of COVID-19 passes 80 million worldwide. All this while the light was leaving the Alpha Centauri system four years ago.
Much like other star systems out there, Alpha Centauri A and B (seen in the image) is a triple star system! The smallest of the three and not seen in this image, is Proxima Centauri, fascinating in its own right because in 2012 an Earth-sized planet was discovered orbiting it, but too close to its star to host life. Still, think about how you, me and the world has changed since that light left the Alpha Centauri System. That light is four years old, but when you look further out, you look further back in time.
I'm a huge fan of space. I love it with every fiber of my being and so now I have to let my space nerd out. There is another, well-known star called Betelgeuse and yes, you say it like the name of the Tim Burton movie. This is easily one of my favorite stars, yep, we space nerds have favorite stars. Betelgeuse is a red supergiant star in the constellation of Orion, currently visible in the night sky.
You can see Betelgeuse in this photo of the constellation, it is the bright orange star in the upper left. OFFICIALLY known as Alpha Orionis, this beast of a star is just about 640 times bigger than the sun! The distance of Betelgeuse has been somewhat difficult to determine even with it being a very bright (and variable star). Using parallax -the apparent change of the position of an object, measured in seconds of arc, caused by the change of position of the observer of that object- mistakes have been made over the years to try to accurately pin down a measurement. So I will use the updated results from Atacama Large Millimeter Array (ALMA) radio telescope bank in northern Chile. Those measurements put Betelgeuse at a ESTIMATED distance of 724 light-years (other parallax measurements put it at 548 light-years). To travel back in time, you'd have to go back to the year 1300 BCE (Before Common Era) and in March of that year, King Edward I of England ("Edward Longshanks") convenes the 47th meeting of parliament in 25 years at Westminster for a two week session; before dissolving two weeks later, the parliament approves the articuli super cartas, a 20-article amendment to the original Magna Carta. This is what it is to know what the world was like when the light from Betelgeuse left the star.
The last stop on our trip into the past is one of the largest stars ever found and one of the most luminous stars in the entire Milky Way! VY Canis Majoris (abbreviated to VY CMa) is also a red supergiant star located in the southern constellation of Canis Major. A truly colossal star, should we somehow be able to swap it, with our sun, the surface of the VY CMa would extend past Jupiter or 464.5 million miles! We must assume these numbers are the most accurately accepted values, and if we do, and if we could travel at light speed, we would need six hours to circumnavigate it, as opposed to the roughly 14.5 second needed to do the same to our sun!
This image helps illustrate the size, but we've been talking distance. VY CMa's current estimated distance is 3,820 light-years (give or take 230 light-years)! Using Wikipedia as a starting spot, we "travel" to 1796 BCE! The Near East (a transcontinental region around the East Mediterranean encompassing parts of West Asia, the Balkans, and North Africa, including Egypt) is in the Middle Bronze Age (approximately 3300 BCE- 1200 BCE) and written languages were starting to develop. In the 1790s BCE, circa 1792 BCE, Hammurabi starts to rule in Babylon and the Middle Kingdom of Egypt was ruled by the Thirteenth Dynasty. In what would become northern India, the Cemetery H culture develops and becomes known for their use of cremation on their dead and, estimates put the entire population of Earth at roughly 85 million, or the current population of Türkiye (Turkey).
How different life was on earth over 3,800 years ago?!
Through all of this "travel" we have seen how it is possible to travel through time, all you need to do is look up into the night sky and know that we can use that distance and time to help us learn about our own past. Everyone asks "Are we alone out there?" I think we're not, but when you consider that even VY CMa's sunlight is over 3,800 years old, if there are other civilizations out there, it's highly likely we're just not existing at the same time to see them or be able to contact with them due to these impossibly large distances. An interesting thing to consider is that any being around a distant star would see the sun as it was from the same distance they are away, meaning they see sunlight the way it was, not as it is. Heck, if they had a sufficiently powerful telescope, a civilization 66 million light years away would see dinosaurs roaming around and not the life modern humans have made.
Who knows, maybe there's someone, something looking at a small, yellow star wondering what's happening in the solar system we call home?
Think about that one...