Week 2

How do the positions of the Earth, Sun, and moon affect tides?

learning intentions

to explain the phases of the Moon and their relationship to the positions of the Earth, Sun, and shadows.
to analyse and interpret lunar cycles and their effects on tides.

success criteria

I can name and draw the 6 phases of the moon and understand the relative position of the earth moon and sun at that point.
I can explain the causes of the tidal bulge and it's movement around the globe
I can graph the connection between the phases of the moon and the tide at Murray (Mer) Island

Tasks

Knowledge & understanding

Perspective and Phase of the Moon on Google Classrooms or Toddle - 2 worksheets
Graphing Tides Worksheet on Google Classroom

Literacy & research

Continue with your assignment

Knowledge and understanding

phASES OF THE MOON

The appearance of our Moon is constantly changing. One day it may look like a thin crescent, and two weeks later it looks like a circular disk.

Watch this video to see how the Moon appears to change shape over the course of a year.

But why does the Moon’s shape appear to change?

buac18-vid-moonphases2018.mp4

This simulation below shows two different perspectives, or views, of the Moon. One section shows the Sun–Earth–Moon system from overhead, as if you were in space above Earth’s North Pole. The other section shows what the sky looks like to a person located on Earth who is standing where the stick figure is on the globe.

Task 1: Observing Moon and Sun

Use this simulation below to explore how the motion of the Moon is related to the Moon’s appearance from Earth and answer the questions on Google Classrooms

Tides

You walk along a beach, seashells, driftwood and seaweed left by the retreating tides at your feet. Look up at the Moon, and you’re seeing the main cause of the surge and retreat of oceans from our shores. As distant as the Moon may seem, its gravitational pull on Earth plays a huge role in the formation of tides.

When you see the tide roll in or out, what you’re really seeing is a cycle of small changes to the distribution of our planet’s oceans. As the Moon’s gravity tugs at Earth, it shifts Earth’s mass, distorting its shape ever so slightly into that of a football ― elongated at the equator and shortened at the poles. This effect on the solid Earth can be detected by scientific instruments, but we can watch the same changes to Earth’s oceans just by visiting the beach.

In this simplified animation, Earth’s oceans bulge out on both the side closest to the Moon and the side farthest from the Moon. These bulges create high tides. The low points are where low tides occur. Credit: NASA/Vi Nguyen.

It might seem strange that the ocean would bulge on the side farthest from the Moon as well as the side closest to it. This happens because the Moon’s gravity affects the entire Earth, pulling at every point on our planet. The strongest pull occurs on the points closest to the Moon, and the weakest on the points farthest away, but every bit of water is affected.

Now think about pouring a bucket of water out on a table. It’s easier to slide the water around on the table rather than lift it directly upwards. When the Moon’s gravity pulls at Earth, the water doesn’t float outward, it just gets pushed and squeezed around on the globe, directed by both gravitational pull and other forces, until it ultimately ends up bulging out on the side closest to the Moon and the side farthest away.

The Moon’s gravitational pull on Earth, combined with other, tangential forces, causes the ocean bulges that create tides. Credit: NASA/Vi Nguyen.

Our observer sees the tides rise when passing through the bulges, and fall when passing through the low points. Of course, in reality the Earth isn’t a smooth ball, so tides are also affected by the presence of continents, the shape of the Earth, the depth of the ocean in different locations, and more. The timing and heights of the tide near you will be affected by those additional elements. Credit: NASA/Vi Nguyen.

As Earth rotates within this layer of water, its landmasses pass through the two bulges. These bulges are Earth’s high tides. Most shorelines experience two high and low tides per day. One high tide to high tide cycle (or low tide to low tide cycle) takes a little over 12 hours.

Can you easily predict the tides by following the path of the Moon? Not really! First of all, because the Moon is orbiting in the same direction as the Earth rotates, it takes extra time for any point on our planet to rotate and end up exactly below the Moon. The extra time is ~50 mins. This means that the high tide bulges are never directly lined up with the Moon, but a little ahead of it.

In addition, Earth isn’t a perfect, smooth sphere. The tides we actually see at our shores are affected by everything from the shape of Earth’s continents to wind and storms. To get a true estimate of the tides near you, you’ll have to check the local tides forecast.

Here Comes The Sun

Now, the Moon is the biggest influence on Earth’s tides because of its proximity ― but it isn’t the only influence. The Sun ― with about 27 million times the mass of the Moon ― is always the gorilla in the room when it comes to solar system equations. But it’s a distant gorilla, about 390 times farther away than the Moon, which gives it a little less than half of the Moon’s tide-generating force. Yet it still plays a role.

Twice a month, when the Earth, Sun, and Moon line up, their gravitational power combines to make exceptionally high tides where the bulges occur, called spring tides, as well as very low tides where the water has been displaced. About a week later, when the Sun and Moon are at right angles to each other, the Sun’s gravitational pull works against the Moon’s gravitational tug and partially cancels it out, creating the moderate tides called neap tides.

You can tell when a spring tide or neap tide is happening without being anywhere near the water. Spring tides always happen when the Moon is at the full or new phase, which is when the Sun, Moon and Earth are in alignment. Neap tides occur around the first and last quarter phase of the Moon, when the Moon’s orbit around Earth brings it perpendicular to the Sun.

task 2: Complete the graphing Tides worksheet on Google Classrooms in pairs

Page updated

Report abuse