Tides & the Lunar Cycle

Tidal Range Tides – rise and fall of sea level due to the Moon & Sun’s gravitational pull on the Earth Tidal Range – height difference between high & low tides

Tides Caused by gravitational attraction between the Earth, Moon, and Sun Moon exerts stronger pull than the Sun because it is closer Moon’s gravitational pull on oceans causes bulge on side facing the Moon; opposite bulge due to inertia NOTE: Ocean bulges—towards moon due to gravity; away from moon due to Earth’s rotation (Newtons Laws-Inertia). Students should note that the image is a “model” and all models have limitations. This model is an exaggerated view of the ocean around the Earth…the Earth does not “Spin” INSIDE the ocean. Image courtesy of NOAA Ocean Service Education.

Spring Tides Special tides occur when Sun, Moon, & Earth in straight line; new & full moon. High tides are higher than normal Low tides are lower than normal i.e., greater tidal range Increased tidal range due to greater gravitational pull of both Sun & Moon in line Bullets 2 & 3 NOTE: This means that there is a greater change between high and low tides than normal. This is most notable in Nova Scotia. The Bay of Funday can have tidal changes as much as 46 feet. The tidal forces from the Sun are weaker than those from the Moon, but are still quite strong, causing tides that are about 30% as strong as the Moon's. When the Sun and the Moon are lined up, during a New Moon and during a Full Moon, you get the highest high tides and the lowest low tides, known as Spring Tides. MNEMONIC: Straight Spring (both start with ‘S’)

Neap Tides Special tides occur when Sun, Earth, Moon in perpendicular alignment; 1st & 3rd Quarters High tides are not as high as normal Low tides are not as low as normal i.e., smallest tidal range Sun & Moon’s gravity pull in opposite directions, partially canceling each other out Bullets 2 & 3 NOTE: This means that there is a much smaller change between high and low tides than normal. When the Sun and Moon are at right angles to each other (during the Moon's first and last quarter, or when it appears half-full), you get the lowest high tides and the highest low tides, known as Neap Tides. This is due to the fact that the Moon and Sun are pulling in opposite directions, partially canceling each other out. However, since the Moon is closer, it still exerts a greater gravitational pull that the Sun.

In this animation, the words SPRING TIDES and NEAP TIDES will occur at the top of the screen as the moon revolves around the Earth. ScienceBlogs.com

Bay of Fundy Nova Scotia, Canada Scot’s Bay Nova Scotia, Canada famous for the shape of the bay greatly affecting tidal range Hall’s Harbour Scot’s Bay video Hall’s Harbour video Scott’s Bay video: This time lapse shot at Scot’s Bay, NS, in the Bay of Fundy shows twelve hours of tide in only 120 seconds. People have often found themselves facing peril when they did not keep an eye on the clock while beach combing. When the tide is rolling in at an average rate of 8 feet of depth per hour it can be a chore just staying ahead of it. Hall's Harbour, Nova Scotia video: The world's highest tides occur in the Bay of Fundy in Atlantic Canada. This time lapse movie speeds up by 720 times the fall and rise of the tide – it shows from low tide through high tide and back to low tide.