The universe is big. Or as Douglas Adams described it in his bestselling novel "The Hitchhiker's Guide to the Galaxy": you just won't believe how vastly, hugely, mind-bogglingly big it is. Scientists currently estimate its size to be 91 billion lightyears in diameter. However, this is obviously rather difficult to determine. Because how do we define our universe in the first place? Some say that the universe is everything within our space-time environment which could have a chance to interact with us and vice versa. How plausible this definition may seem at a first glance, it's also quite restrictive because some parts of the universe may expand faster than light can traverse it so any message we send will never arrive at its destination. That's a direct consequence of the speed of light being constant and finite and so far Einstein has always been proven right. So we must assume that regions of our universe exist which are just as much part of reality as we are but which will forever remain beyond our reach of interaction or observation. Therefore we'll never know how big the universe really is.
The part of the universe which we can interact with, on the other hand, is the observable universe and the edge of that is, indeed, almost 46 billion lightyears away, which makes it just over 91 billion lightyears across. This edge is very close to the actual age of the universe times the speed of light (13,9 billion lightyears), but this is not a correct representation since our galaxy and the edge of the universe have travelled substantially further apart since the Big Bang and our universe is still expanding at a breathtaking rate.
Today, I want to show you some of the furthest objects that I've ever observed with my humble, homemade 18" telescope: a cluster of galaxies, scientifically denominated Abell 2666. I was able to identify 5 members of this cluster, with NGC7768 being the prominent one, near the centre of the field of view. The other 4 are a lot less obvious and I challenge you to find them all! :-) Contrary to some of my colleagues who try to sketch every little detail they thought they perceived during their observation, I try to give my audience an experience as close as possible to really looking through the eyepiece. The details are still there but you'll have to look for them very carefully, just like I had to do for a considerable time when I made my observation. The central galaxy immediately draws the attention, being easily visible with its 12.3 magnitude. The faintest on the other hand is close to mag. 16 and therefore at the limit of what you can expect to see through a similar telescope. NGC7768 is a fairly primitive galaxy and still fully under development. Analysis with the Hubble space telescope revealed a disk of dust and at least one star forming region.
Imagine that every little patch you see on my sketch is a complete galaxy, just like Andromeda, Triangulum, the Pinwheel or our own. The distance of this particular cluster is estimated between 340 and 360 million lightyears, so at not even one hundredth of the distance to the edge of the observable universe! So yes... the universe is big!
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