The speed of light!

I recently read "A briefer history of time" By Stephen Hawking(in record time!), which is an updated and shortened version of his 1988 book "A Brief History of Time". And it was an awesome book! 


But perhaps the part of it that really struck me, was the part where he talks about how we(humanity) figured out that light is not instant. Because, from what we can tell, in our everyday life, light is as good as instant. 


But as most of us know, light, like everything else, takes time to travel, and has a set speed. So this guy by the name of Ole Rømer figured it out in 1676!!! He noticed that the eclipses on Jupiter, were not happening at regular intervals. And as was already known at the time, eclipses always happened at regular intervals. That is how many ancient civilizations, inlcluding the egyptians and the mayans were able to predict eclipses here on earth. They can be predicted because moons orbit their planet at a constant speed, so we can predict their location at any given time. So when he was observing the moons of Jupiter, he noticed they did not occur at regular intervals. It was almost as if they would speed up and slow down at different times. But all known orbits at the time had a constant speed. He realized that as the earth and Jupiter were moving towards each other, the eclipses would 'happen faster'. And as Jupiter and the earth were moving away from each other, the would 'happen slower'. This was puzzling. So he concluded that the reason this was happening is because the light traveling from Jupiter to earth was taking longer to arrive when we were moving away, and less time when moving towards each other! So it wasn't that the moons were speeding up and slowing down. It was that the light had to travel further at times to get to us than at other times. It may sound simple to us now. But if we try to remember that we haven't always known that, it is quite amazing, to me at least. That this guy discovered something that is not obvious to any of us in our daily lives, and most certainly not to any of them back 334 years ago! 


Just for fun, here are some times it takes light to travel from:


Moon to Earth                              1.3 sec
Sun to Earth                               8.3 min
Alpha Centauri(nearest star) to Earth      4.4 years!
Across our galaxy                          100,000 years!
From the Andromeda Galaxy to Earth         2.5 Million years!! 


So apparently, we have learned a lot from Jupiter! I can think of 2 major things right away that revolutionized astronomy. Galileo, in the 1600's confirming that the Earth was not the center of the universe(the catholic church didn't like that!), and that not everything revolved around the earth. He was the first to notice that Jupiter had its own moons, and that they clearly rotated around Jupiter, so clearly, not everything was rotating around the earth. And Ole Rømer realized light was not instant while observing Jupiter. 


So, in conclusion, Jupiter is awesome! I was able to see it when we went stargazing on Saturday Aug 14th to the Bong Recreational Area(that's what the park is called! haha) under really dark skies(for Milwaukee/Chicago area, I remember El Paso skies being darker in the north east and east montana). 

This is more or less what it looks like through my small telescope! 

We looked at it long enough to see one of the moons hide behind Jupiter. And there was some guys there with awesome giant motorized telescopes that had GPS and auto locate objects in the sky! They were awesome! I will get one! Sometime...