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Here is a drawing of neap tides.

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Tidal energy or tidal power can be defined as the energy that is the result of the moon and the sun’s gravitational influence on the ocean. Height differences between high and low tides create tidal currents in coastal areas, and these currents can be strong enough to drive turbines.

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Last updated June 12, 2013 by Mathias Aarre Maehlum

For centuries, mankind has exploited this massive energy source. In the recent years, we have learnt how to generate electricity from it. 450 TWh is the estimated yearly potential of electric power that can be produced from tidal energy. In addition to this comes a large and not yet estimated potential in river flows.

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What is Tidal Energy?

Tidal energy or tidal power can be defined as the energy that is the result of the moon and the sun's gravitaional influence on the ocean. Height differences between high and low tides create tidal currents in coastal areas, and these currents can be strong enough to drive turbines.

Tidal energy has been used for other purposes since the Roman times. If you want to learn more about these methods go to The History of Tidal Energy (coming soon). This article will focus solely on tidal power generation.

Where is Tidal Energy Used?

As tidal power generation is relatively new, there are not a lot of tidal energy companies out there developing investing in this technology yet. However, there are several tidal power plants in use and more is coming. Some of these are solely for research and experimental purposes, but the number of commercial tidal energy power plants is increasing.

La Rance tidal power station was the first large large-scale tide energy project and was opened already in 1966. It lays in the water-rich river Rance in the north-western France. This is a tidal power plant with a total installed capacity of 240 MW capacity generated from 24 turbines. Annual production of electricity is about. 0.6 TWh (600 GWh), which means that the average effect of day throughout the year is 68 MW. La Rance is a form of what we call a tidal barrage power plant.

Tidal Barrage Energy

A tidal barrage power plant consists of three main parts: The first being the barrage itself, holding the water back during high tide. The second part is the sluice gate that let water through the third part, the turbine and generator, resulting in electricity generation.

The sluice gates are left open during high tide and closed during low tide to create a water level differential, creating a potential difference that powers the turbine when the water is released.

Tidal Stream Generator

Tidal stream generators are very similar to wind turbines except their below the water surface instead of above or on land. The turbine and generator converts the movement of water coming from change in tide, the kinetic energy, into electricity. Water is 830 times denser than air and therefore can generate electricity at lower speeds than wind turbines.

Dynamic Tidal Power

Dynamic tidal power is still in the development stage. The theory of this technology is that we can exploit tidal flows and their interaction between potential and kinetic energy.

Advantages of Tidal Energy

There are several advantages with tidal power generation. The greatest benefit after the fact that tidal energy is both a renewable and a green energy source is the incredible potential it posses. The large density of water, almost 1 000 times greater than in air, results in very large amounts of energy to get out of the tidal currents even if the speed is low.

Tidal currents are very predictable, and therefore very favorable with respect to the planning of production and maintenance.

For a full overview over the advantages of tidal energy as well as the disadvantages go to Tidal Energy Pros and Cons.

I hope you learned by reading this article how tidal energy works and realize what big potential these methods of harnessing energy really have. More tidal energy and tidal power facts can be located in the Tidal category.

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How Does Tidal Power Work? - Energy Informative

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Last updated June 12, 2013 by Mathias Aarre Maehlum For centuries, mankind has exploited this massive energy source. In the recent years, we have learnt how to generate electricity from it. 450 TWh is the estimated yearly potential of electric power that can be produced from tidal energy.

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Here is an image showing how the moon and the sun's gravity affects the tides. The photo shows us neap and spring tides.

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Here is a song about spring and neap tides!

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This is a drawing including spring tides.

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Tides commence every day four times, two low tides and two high tides. Every day the tides occur at different times and go out and in a little more. There are two different types of tides, neap, lower highs and higher lows, and spring, higher highs and lower lows.

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A solar eclipse is a natural event that takes place on Earth when the Moon moves in its orbit between Earth and the Sun (this is also known as an occultation). If the Moon was only slightly closer to Earth, and orbited in the same plane and its orbit was circular, we would see eclipses each month. The lunar orbit is elliptical and tilted with respect to Earth’s orbit, so we can only see up to 5 eclipses per year.

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What is a Solar Eclipse?

A solar eclipse is a natural event that takes place on Earth when the Moon moves in its orbit between Earth and the Sun (this is also known as an occultation). It happens at New Moon, when the Sun and Moon are in conjunction with each other. If the Moon was only slightly closer to Earth, and orbited in the same plane and its orbit was circular, we would see eclipses each month. The lunar orbit is elliptical and tilted with respect to Earth's orbit, so we can only see up to 5 eclipses per year. Depending on the geometry of the Sun, Moon and Earth, the Sun can be totally blocked, or it can be partially blocked.

During an eclipse, the Moon's shadow (which is divided into two parts: the dark umbra and the lighter penumbra) moves across Earth's surface. Safety note: do NOT ever look at the Sun directly during an eclipse unless it is during a total solar eclipse. The bright light of the Sun can damage your eyes very quickly.

Facts about Solar Eclipses

Depending on the geometry of the Sun, Moon, and Earth, there can be between 2 and 5 solar eclipses each year.

Totality occurs when the Moon completely obscures Sun so only the solar corona is showing.

A total solar eclipse can happen once every 1-2 years. This makes them very rare events.s.

The longest a total solar eclipse can last is 7.5 minutes.

The width of the path of totality is usually about 160 km across and can sweep across an area of Earth's surface about 10,000 miles long.

Almost identical eclipses occur after 18 years and 11 days. This period of 223 synodic months is called a saros.

During a total solar eclipse, conditions in the path of totality can change quickly. Air temperatures drop and the immediate area becomes dark.

If any planets are in the sky at the time of a total solar eclipse, they can be seen as points of light.

Solar Eclipse Types

Total Solar Eclipse

A total solar eclipse occurs when the Moon completely blocks the solar disk. In a total solar eclipse, the narrowest part of the path (where the Sun is completely blocked and the Moon casts its darkest shadow (called the umbra)) is called the "zone of totality".

Observers in this path see a darkened Sun (often described as a "hole in the sky") with the ghostly glow of the solar corona extending out to space. A phenomenon called "Bailey's Beads" often appears as sunlight shines out through valleys on the lunar surface. If the Sun is active, observers can also see solar prominences, loops, and flares during totality. A total solar eclipse is the ONLY time when it is safe to look directly at the Sun. ALL other solar observations (even in partial phases) require special solar filters so that you do not harm your eyes.

Total solar eclipses have not always been visible from Earth. In the past, the Moon was too close to Earth and during eclipses it completely blotted out the Sun's disk. Over time, the lunar orbit has changed at the rate of just over 2 cm per year and in the current epoch, the alignment is nearly perfect at times. However, the Moon's orbit will continue to widen, and in perhaps 600 million years, total solar eclipses will no longer occur. Instead, future observers will see partial and annular eclipses only.

Annular Solar Eclipse

Not every solar eclipse is a total one. When the Moon is farther away in its orbit than usual, it appears too small to completely cover the Sun's disk. During such an event, a bright ring of sunlight shines around the Moon. This type of eclipse is a called an "annular" eclipse. It comes from the Latin word "annulus" which means "ring".

The period of annularity during such an eclipse can last anywhere from 5 or 6 minutes to up to 12 minutes. However, even though the Sun is mostly covered by the Moon, enough bright sunlight escapes during annularity that observers cannot ever look at the Sun directly. These events require eye protection throughout the entire eclipse.

Partial Solar Eclipse

A partial solar eclipse occurs when Earth moves through the lunar penumbra (the lighter part of the Moon's shadow) as the Moon moves between Earth and the Sun. The Moon does not block the entire solar disk, as seen from Earth. Depending on your location during a partial eclipse, you might see anything from a small sliver of the Sun being blotted out to a nearly total eclipse.

To view any eclipse safely, use approved filters or use an indirect method of viewing, such as projecting sunlight through a telescope and onto a white piece of paper or cardboard. NEVER look at the Sun through a telescope unless it has the appropriate filter. Blindness and severe eye damage can result due to improper observation technique.

When is the next Solar Eclipse?

Eclipses can occur each year, and they are predictable. There are several places online where you can get up-to-date calendars for all the types of solar eclipses.

mreclipse.com - MrEclipse.com is the page of retired NASA astrophysicist Fred Espenak. He provides a wealth of information about both solar and lunar eclipses.

eclipse.gsfc.nasa.gov - The NASA Eclipse Web Site is the official NASA site for eclipse information.

timeanddate.com - Timeanddate is a reliable source of eclipse calendars for both solar and lunar eclipses.

Solar Eclipse Photo - www.lucnix.be

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Solar Eclipse Facts - Total, Annular & Partial Solar Eclipses

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What is a Solar Eclipse? A solar eclipse is a natural event that takes place on Earth when the Moon moves in its orbit between

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Here is a photo of what a solar eclipse would look like if you were in space.

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Here is a song about solar eclipses!

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Total Solar Eclipse/Total Solar Eclipse 2017/Solar Eclipse 2017 for Kids

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Here is a drawing of a Solar Eclipse. As shown bellow the moon is blocking the sunlight from a part of the Earth, so it looks as if its night during day.

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A solar eclipse occurs when the moon blocks most, or all the light from the sun. When this happens it appears to look like night time in the middle of the day.

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Total eclipses are a freak of cosmic happenstance. Ever since the moon formed, about 4.5 billion years ago, it has been inching away from our planet (by about 1.6 inches, or 4 centimeters per year). The setup right now is perfect: the moon is at the perfect distance for Earth's shadow to cover the moon totally, but just barely. Billions of years from now, that won't be the case.

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Lunar eclipses happen when Earth positions itself between the sun and the moon, casting a shadow across the lunar surface.

They can only occur during a and are a popular event for skywatchers worldwide as they do not require any specialist equipment to enjoy (unlike solar eclipses).

In 2023, Earth will experience two lunar eclipses. The first lunar eclipse of 2023 was a penumbral lunar eclipse on May 5 and was visible across parts of Africa, Asia and Australia. The second and final lunar eclipse of 2023 will be a partial lunar eclipse on October 28 and will be visible across parts of E. Americas, Europe, Africa, Asia and Australia To find out when, where and how to see this year's lunar eclipses, check out our lunar eclipses 2023 guide.
Related: Night sky guide, what you can see tonight
What are lunar eclipses?

A lunar eclipse is caused by Earth blocking sunlight from reaching and creating a shadow across the lunar surface.

The sun-blocking Earth casts two shadows that fall on the moon during a lunar eclipse: The umbra is a full, dark shadow, and the penumbra is a partial outer shadow.

1. Total lunar eclipse: Earth's shadow is cast across the entire lunar surface.

2. Partial lunar eclipse: During a partial lunar eclipse, only part of the moon enters Earth's shadow, which may look like it is taking a "bite" out of the lunar surface. Earth's shadow will appear dark on the side of the moon facing Earth. How much of a "bite" we see depends on how the sun, Earth and moon align, according to NASA.

3. Penumbral lunar eclipse: The faint outer part of Earth's shadow is cast across the lunar surface. This type of eclipse is not as dramatic as the other two and can be difficult to see.

(Image credit: Future)

There are three types of lunar eclipses depending on how the sun, Earth and moon are aligned at the time of the event.

What happens during a lunar eclipse?

Why does the moon turn red during an eclipse?

During a total lunar eclipse, the lunar surface turns a rusty red color, earning the nickname " blood moon". The eerie red appearance is caused by sunlight interacting with Earth's atmosphere.

When sunlight reaches Earth, our atmosphere scatters and filters different wavelengths. Shorter wavelengths such as blue light are scattered outward, while longer wavelengths like red are bent - or refracted - into Earth's umbra, according to the Natural History Museum. When the moon passes through Earth's umbra during a total lunar eclipse, the red light reflects off the lunar surface, giving the moon its blood-red appearance.

"How gold, orange, or red the moon appears during a total lunar eclipse depends on how much dust, water, and other particles are in Earth's atmosphere" according to NASA scientists. Other atmospheric factors such as temperature and humidity also affect the moon's appearance during a lunar eclipse.

How often do lunar eclipses happen and how long do they last?

In astronomical terms, a lunar eclipse is a relatively common phenomenon, with about three lunar eclipses occurring every year, according to the National History Museum. Approximately 29% of lunar eclipses are total lunar eclipses, according to TimeandDate.com.

A solar eclipse always occurs about two weeks before or after a lunar eclipse.

A total eclipse can be seen from any given location - on average - once every 2.5 years.

A lunar eclipse usually lasts a few hours according to the National Weather Service with totality (the duration of total obscuration of the moon) ranging between 30 minutes to over an hour.

Lunar eclipses are more easily observed than solar eclipses, as they can be viewed with the unaided eye by any observer situated where the moon is above the horizon.

(Image credit: NASA/JPL-via Kieth Burns)

(Reminder: Never look directly at the sun, even during a total solar eclipse, without protection such as verified eclipse glasses; serious and permanent eye damage can result.)

How to see a lunar eclipse

(Image credit: NASA)

Lunar eclipses are among the easiest skywatching events to observe.

To watch one, you simply go out, look up and enjoy. You don't need a telescope or any other special equipment. However, binoculars or a small telescope will bring out details on the lunar surface - moonwatching is as interesting during an eclipse as it is at any other time. If the eclipse occurs during winter, bundle up if you plan to be out for the duration - an eclipse can take a couple of hours to unfold. Bring warm drinks and blankets or chairs for comfort.

Scientists like to watch lunar eclipses, too.

"We can get really good science out of what happens to the surface of the moon during total lunar eclipses, but again, the cool thing is that the moon changes color," Noah Petro, a research scientist at NASA's Goddard Space Flight Center in Maryland, told Space.com. "It's something fun to see - it's benign, but it's a change. And anytime we see [a] change in the skies, it's always kind of exciting."

If you hope to snap a photo of a lunar eclipse, here's our guide on How to photograph a lunar eclipse with a camera. And if you need imaging equipment, our best cameras for astrophotography and best lenses for astrophotography have recommendations to make sure you're ready for the next eclipse.

What is a total lunar eclipse?

Why do lunar eclipses occur?

What's the difference between a lunar eclipse and a solar eclipse?

Lunar eclipse FAQs answered by an expert

We asked meteorologist Joe Rao, a few commonly asked questions about lunar eclipses.

Additional resources

Learn more about lunar phases and eclipses with NASA Science. Explore Hanwell Community Observatory's fact sheet for more lunar eclipse information. Discover why we don't have a lunar eclipse every month with the Rice Space Institute at Rice University.

Bibliography

NASA. Blood Red Moon: Total Lunar Eclipse. NASA. Retrieved May 10, 2022,

O'Callaghan, J. (2019, July 16). Lunar eclipse guide: What they are, when to see them and where. Natural History Museum. Retrieved May 10, 2022.

NASA. ( 2017, May 3). What is an Eclipse? NASA. Retrieved May 10, 2022.

Hocken, V., Kher, A. Total Lunar Eclipse. timeanddate.com. Retrieved May 10, 2022.

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What are lunar eclipses and how do they occur?

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Lunar eclipses occur when Earth blocks the sun and casts a shadow over the surface of the moon. We explore the different types of lunar eclipses here.

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Below is a photo of a Lunar Eclipse. This shows us where the umbra and the penumbra are. This also shows that the umbra will always

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Here is a song all about lunar eclipses!

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Lunar Eclipse for Kids/Lunar Eclipse 2018 /Lunar Eclipse Song

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Here is a drawing of a Lunar Eclipse.  As shown below Earth is casting a shadow on the moon.

S- Sun E-Earth M- Moon

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A lunar eclipse occurs on a full moon, and it should look as if the moon is no longer in the sky.  This can occur only when the sun, Earth, and moon are in a line. Also, a lunar eclipse happens when the moon moves into the earth's shadow, or its umbra.

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The Moon moves in a circle around, or orbits, planet Earth. The Moon is Earth’s only natural satellite. Half of the Moon’s surface is always lit up by the Sun. As the Moon orbits Earth, you can see a different part of the sunlit half of the Moon every night. The Moon makes a complete circle around Earth, called a revolution, in about 28 days.

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Phases of the Moon - PowerKnowledge Earth & Space Science

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If you want to see how the lunar cycle works, you can try an experiment. Place a round object on a table to stand for Earth. Use another round object to stand for the Moon. Have a friend shine a flashlight from one side to stand for the Sun.

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Below is a photo of the phases. This shows us where the phases are and when they would occur. (Sun is on the left)

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Here is a song that explains the phases of the moon.

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Here is a drawing consisting the phases of the Moon. The white is the part of the moon that is lit up.

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The moon circles around the Earth in a time period of 29.5 days. Each day you can see the moon a little bit more or less as it moves into a "new" phase. There are eight major phases, new moon, waxing crescent, 1st Q, waxing gibbous, full moon, waning gibbous, 3rd Q, and a waning crescent.