Moon Phases & Tides Reading Comprehension

Revolution & Rotation

Just like the Earth, the moon also revolves and rotates. The moon rotates on its own axis every 27.3 days and revolves around the Earth every 27.3 days. This causes the same side of the moon to always face the Earth. Since Earth is revolving it takes an extra 2.2 Earth days for the sun, moon and Earth to line up, causing the phases of the moon to make a complete cycle approximately once per month, every 29.5 days to be exact. As the moon circles the Earth, we can only see a portion of the lit up side. When we can see 100% of the lit up side, this is a full moon. When we can't see any of the lit up side, this is called a dark moon or new moon.

What are the different phases of the moon?

 

The revolution or orbit of the Moon around the Earth makes the Moon look as if it is changing shape in the sky. This is caused by the different angles from which we see the lighted part of the Moon's surface. These are called "phases" of the Moon. There are four major phases and four minor phases during a cycle that repeats itself every 29.5 days. The phases always follow one another in the same order, here are the phases of the moon starting with the New Moon are: 

• New Moon

• Waxing Crescent 

• First Quarter 

• Waxing Gibbous 

• Full 

• Waning Gibbous 

• Third Quarter 

• Waning Crescent 

We'll start with what is called the New Moon phase. This is where we can't see any of the lit up side of the moon. The moon is between us and the sun. As the moon orbits the Earth we can see more and more of the lit up side until finally the moon is on the opposite side of the Earth from the sun and we get a full moon. We usually only see one Full moon a month, but sometimes we see a full moon twice a month, this is known as a “Blue Moon”. A blue moon can also be the third of four full moons in a season, this happens every 2.5 years. As the moon continues to orbit the Earth we now see less and less of the lit up side. So what does waxing and waning mean? As the New moon begins its orbit and we see more and more of the moon, this is called Waxing. After the moon gets to its Full phase, we start to see less and less of the moon, this is called Waning. 

What Causes Tides?

Basically, tides are caused by the moon’s gravity. The moon pulls water on the Earth toward itself, causing a bulge on the side of the Earth near the moon. The Earth rotates one full turn in 24 hours, but the bulge of water stays on the side of the Earth facing the moon. The bulge stays in place as the Earth moves under it. There are really two bulges of  water on the Earth. One bulge is toward the moon, the other bulge is on the far side of Earth from the moon. Water is drawn away from the areas between the high tides, which causes low tides to form. Think of it as a rubber band around a ball, as two sides pull further away from the ball the other two sides get closer.

The pull increases on the Earth when the sun and moon are aligned. This causes bigger high tides and lower low tides. These alignments happen when the Moon is full or new - so twice a month. This is called Spring Tides, though they happen year round. The opposite effect occurs when the Moon and Sun are at right angles. From Earth, the Moon will be in its quarter phase. This causes less of a pull on the Earth and the tides are milder. This is called the Neap Tide and also happens twice a month.

Total Eclipse

So what is a total solar and lunar eclipse? This is when the Sun, Earth, and moon line up perfectly. Not everyone can see the eclipses. Only certain locations on Earth can see the eclipse and for a total eclipse this location is a very small area since it needs to be lined up perfectly. This causes two different shadows, umbra and penumbra. The umbra is in the area of total darkness which is the total eclipse and the penumbra is in the area of partial darkness which is the partial eclipse. The angle between Earth’s orbit and the orbit of the moon is 5.15° and without this tilt we would have total solar and lunar eclipses every month!

Tidal Changes

The tides rise and fall because of the pull of gravity between the moon and Earth. The sun also pulls on the Earth, but it is so far away that its pull is less than half of the moon’s force. Luckily, Earth’s gravity keeps our oceans on the Earth, but the tug of war between the Earth and the moon results in our changing tides. The sun also affects tides. The combined forces of the sun & the moon on Earth result in tidal ranges that vary based on the positions of the 3 bodies. A tidal range is the difference between levels of ocean water at high tide and low tide. The most extreme tidal change is seen in the Bay of Fundy in Nova Scotia where the water can rise and fall more than 50 feet (15.24 meters) throughout the day. Other factors that may affect tides are storms and the shape of the coastline.