Looking at a lighter flame the other day I wondered whether the inside of the flame was hollow(devoid of flame)? Obviously fuel can only burn with the presence of oxygen this would suggest that just the outside of the flame where it comes in contact with oxygen is actually burning, if so how thick is this 'flame wall'?

Observed this with birds in flight

Recently i have wondered about how the moon and sun affect gravity here on earth. I was wondering wether the force of gravity would change during night or day due to the position of the sun and the moon and their gravitational pulls. But just as I sat down to work this out (being the cool 16 year old I am) I also remembered that the sun and moon would also pull on the earth. so the question is would the pull the on the earth be the same as that on you and therefore cancel out any effects or do you infact become magically (or marginally) lighter at night or day due to this affect?