That's the title of a new Bloc Party song. I haven't decided whether I like it or not. It's a kind of "bangin" track that I would sometimes jump around violently to in my room, and sometimes be utterly bored by. After all, it has a heavy beat, good rhythms, but only 3 words. In fact, put in those terms, the song Count Five or Six by Cornelius is similar. It has five and a half words in the entire song (those being "one, two, three, four, five, si...") and it's amazing because of the repetition and the good beat.
Another thing that those two songs have in common is that they are educational. I knew how to count to five or six. However, I was not entirely sure what retrograde meant. Well, I had some idea, but having found it on wikipedia, it turns out that retrograde motion is simply motion that is the opposite way to normal. So planets can spin in a retrograde way or move in a retrograde way relative to each other. Maybe it would make it clearer if I explained. If you are looking down on the solar system, you can see a planet going round it either clockwise or anti-clockwise. You can also see it is spinning on its axis either clockwise or anticlockwise. If these motions are different to each other, it is called retrograde spin. If the planet goes in the opposite direction round the sun to most of the others, then it is a retrograde orbit too.
I might be wrong, but Mercury is not retrograde in either sense. However, it can appear to have a retrograde orbit from Earth, because the motion we see is its motion relative to us, and we are moving too. Sometimes the stars can move across the sky from East to West, while Mercury will move from West to East. This looks like retrograde motion. But sometimes Mercury will go with the stars from East to West. It just depends where our orbits are relative to each other.
I think I might have complicated things so I apologise if I have... my conclusion is that saying Mercury is Retrograde is describing a temporary phenomenon as viewed from Earth.
I had hoped that it would be a universal truth. A song would be a wonderful way of remembering and spreading scientific knowledge. It's successful because the words sound cool. The question I'd like to ask you is this: if you could have any fact immortalised in a song so that people would remember it forever, what would it be? It should have cool words like "retrograde" and be an interesting fact. My initial suggestions would be
Atmospheric pressure is one BAR
Put your balls in a box to case harden my metal
Coke contains phosphoric acid
Martensite is diffusionless
Coble creep is along grain boundaries
Tungsten is amazing
PS sorry they are all materials science related and a bit obscure, maybe you have better ones
!EDIT! Apparently the song is called "Mercury's in retrograde" !EDIT!