In the last blog we looked at how the Moon and rotation of the Earth creates tidal movement, with 6 hours between high and low water being a rough rule of thumb. The Moon travelling around the Earth also creates a 50 min lag in our high and low waters each day. This blog will focus on how the sun also plays an important role in our tides.
The Suns gravitaional pull creates either small or large tides known as neaps and springs respectively, which can make either a fast or slow conveyer belt when kayaking in Chichester Harbour. Figure 1 shows the Sun, Moon, and Earth being in alignment with the Moon and Sun working together to create very large tides. This gives us a higher high tide and a lower low tide. In 14 days the Moon will have travelled half way around the Earth and importantly the Sun, Earth and Moon will again be in alignment and creating another Spring tide. With these two different position we get a spring tide and either a full or new Moon.
Seven days after a spring tide the Moon will have travelled one quarter of the way around the Earth, which puts the Sun, Earth and Moon at right angles. This means the Moon and Sun are now working against each other and giving us smaller tides. This gives us a lower high tide and a higher low tide. You will notice in figure 2 the main bulge of water is towards the Moon and not the Sun as the Moon has a stronger influence on tides than the Sun. In this configuration we will see a half moon in the sky.
The tides around Chichester Habpur can range from a spring low tide at 0.4m and high tide at 5.0m, which gives 4.6m of tidal movement where as a neap low tide at 2.0 m and a high at 3.8 will give just 1.8m of tidal movement. These two tidal ranges are quite extreme examples taken near to the equinox of the Earth, this is when our north and south poles are at equal distant from the Sun. The tilt of the Earth on its axis plays another variable into the size of tides with a greater range found during the spring and autumn equinox as seen in figure 3. This also create the phenomenon of tidal bores, for example the Severn Bore. If you look at a tide table you will be able calculate the tidal range for each day needed.
To conclude, a spring tide occurs when the Sun, Moon and Earth are all in alignment and will give us a new or full moon. A neap tide is when they are at right angle to each other and gives us a half moon. The time taken to change from a spring to neap tide is 7 days as the Moon travels around the Earth and with a full cycle of 28 days giving us two spring and two neap tides. Getting these timing right is an important part of at either helping or hindering progress when kayaking.
A bit of trivial knowledge; the saying ‘once in a blue moon’ refers to two full moons on a single calendar months which is not often as the first full moon needs to be within the first two to three days of the calendar month. This then provides another 28 calendar days for the moon to complete another full rotation of the Earth to give a second full Moon at the end of the month.
The Adventure Brand provides a variety of kayaking tours and courses, whether you’re seeking personal guiding technical and safety skills or coaching. Importantly Chichester Harbour, Langstone Harbour, Portsmouth Harbour and the river Hamble provides an excellent teaching and learning environment for kayaking of all abilities. For more information click here or contact Ellis Bird at email@example.com.