The "Dagwood Sandwich" Moon. Earlier models of Ganymede's oceans were based on the assumption that the existence of salt didn't change the nature of liquid very much with pressure. However, Dr. Vance and his colleagues found, through laboratory experiments, that salt does increase the density of liquids under the extreme conditions hidden deep within Ganymede and similar icy moons with subsurface bodies of water. Imagine adding table salt to a glass of water. Instead of increasing in volume, the liquid will actually shrink and become denser. The reason for this is that salt ions lure water molecules. Have you ever had one of those days fishing where it seemed like you could do no wrong? Like everything you tried resulted in fish being caught? And not only fish being caught, but large fish being caught? This was all probably due to the moon and what phase the moon was in. That's right, something as simple as what phase the moon is in can have an effect on your fishing success. So here you have two definitions of a blue moon but the one for a calendar blue moon does not describe the true meaning of a blue moon. Here's why: