Ancient Photons Hello, fellow stargazers!
So, why did I name the group “Ancient Photons”? Well, it’s simple really. You see, in reality, astronomy is the study of light – Photons.
Those photons, quanta of light, were emitted by the object under study, traveled vast distances through space, and eventually collided with our detectors. Whether that detector is a CCD chip, a strip of film, a spectrograph, or an old-fashioned Mark I eyeball makes no difference. By the time we detect the photon, it is ancient.
Thanks to the speed of light, we can never know the current state of any astronomical object we observe. Think about that for a second. We can never know the current state of any object we see. Be it the light of the most distant object in the observable universe, or your fingertips. Why?
Well, it all has to do with the speed of light. In a star, a lightbulb, or the glowing embers of a campfire, energy is converted from one form to another (including into matter and back) and in the process emits photons. Photons are special. They always move at the speed of light - ~186,000 miles per second in a vacuum. Slightly, ever so slightly, slower in other mediums, such as air and glass.
In this case, we are only concerned about photons that exist in the spectrum of visible light, although photons run the gamut from ultra-high gamma rays to very low-energy radio waves.
So, getting back to the premise that we can never know the current state of any object we see; we have to ask ourselves, why is that?
It is because the speed of light is finite – it takes a given amount of time to travel from where it started its journey until it reaches its destination.
In the case of photons emitted by the sun; once they escape from the sun’s surface and start their journey through space, some will arrive at our detectors (eyes, camera, whatever) in about 8 minutes and 20 seconds. So, by the time the newly emitted solar photon enters our detector, we see it as it was 8 minutes and 20 seconds ago, not as it is now.
Likewise, if a photon strikes your fingertip and is reflected into your eyes, are you seeing your fingertip as it is now? The answer is no. You are seeing it, as it was about 3 nanoseconds ago – or about 3 billionths of a second ago. An exceedingly small amount of time – granted – but still, you are not seeing your fingertip as it currently is.
Let’s move out into space a bit. A photon is emitted from Proxima Centauri and heads in the general direction of Earth. In a little over four and a quarter years that photon will fall upon our detector. Is Proxima still there? We assume it is, but we can never be sure. If by some cosmic disaster, Proxima were to suddenly, right this instant, explode we would be blissfully ignorant of the event for another four and a quarter years.
And that is only the light in our neighborhood of the galaxy. For example, light from the Andromeda Galaxy takes two and a half million years to reach our detectors here on Earth. At the time the photon was emitted from the Andromeda Galaxy Homo habilis -- a species of early humans were emerging. They are commonly known as the first species to use carved stone tools.
And so, the further out into space we look, the further back in time we look. Astronomy is a study, where we depend on photons reaching our detectors here on earth, and for the most part, those photons are ancient.
Hence the name of my new group is “Ancient Photons Observatory”. Stop by and join us as we marvel at our universe.
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