The highest high tides – the so-called "spring" tides – occur when the Earth, Moon, and Sun are aligned (such an alignment is called a conjunction when the Moon and Sun are closest, and an opposition when they are furthest apart). A conjunction should be distinguished from a syzygy – which is every serious Scrabble player's favorite word – in that in a syzygy, heavenly bodies are aligned in both the vertical and horizontal planes; a solar eclipse occurs during a syzygy, but not during a conjunction.

The additive effect of the solar and lunar gravitational fields during conjunctions and oppositions is what causes the tides to "spring" up (the term has nothing to do with the season of Spring). Because the mareoscope shows the relative positions of the Earth, Moon, and Sun over the course of a synodic month, it's possible to see approximately when spring tides and neap tides happen – a neap tide occurs when the Moon, Earth, and Sun form a 90º angle (quadrature) and it's the tide when there's the least difference between high and low water marks ("neap" comes from an Anglo-Saxon word meaning "without power"). The spring and neap tide conjunctions and quadratures are shown on the mareoscope by a crosshairs, centered on the Earth.