For millions of people in the world living along the ocean, the daily fluctuations of the oceans’ water level are important factors of life. Tides occur because of the gravitational attraction between the Earth, the Sun and the Moon. The Sun and Moon actually tug at the Earth’s oceans, causing a tidal bulge (the tidal influence of the Moon is about twice that of the Sun). Each coastal location experiences approximately two high tides and two low tides each day; when it is high tide at one coastal location, it is low tide along a different coast a quarter of the way around the Earth. Because tides occur due to the gravity of both the Sun and Moon, there are two different classifications of tides, which depend on the orientation of the Sun and Moon.

A spring tide occurs when the Sun, Moon and Earth are all in a line (full or new moon), and causes the greatest tidal differences because the Sun and Moon act together to create one large tidal bulge.

A neap tide, on the other hand, occurs near a quarter moon phase when the Sun and Moon are at right angles from each other, causing a smaller tidal bulge. In addition to the effect of the orientation of the Sun and Moon, the distance to the Moon will also affect the tide levels. During perigee (when the Moon is nearest to the Earth), the gravitational pull of the Moon is about 40% greater than if it were at apogee. The world’s greatest tides occur in the Bay of Fundy in Nova Scotia. The greatest variation occurs in Minas Basin, on the eastern extremity of the Bay of Fundy, where if the Moon is near perigee during a spring tide, the water level can be as much as 16 metres higher at high tide than at low tide. The location and shape of the shoreline combined with the depth of the water are the key reasons that the Bay of Fundy experiences such dramatic tidal variations.