Confusing Stationary Bike Calories.

Hi,

I am new to MFP and was trying to log in some exercises just now. However I seem to be confused with the intensities of thw stationary bike, how fast is 'moderate' and how fast is 'vigorous'. I haven't got a heart monitor yet so it will be great if anybody could classify these intensities according to speeds.

Ah and yes, I just did it a stationary bike session of 10 minutes at an average speed of 20 mph.

Any help would be awesome!!