Whale trapped in tidal power station

A six-metre-long humpback whale has strayed into the reservoir of the Annapolis tidal power station in the Canadian Bay of Fundy. The power plant’s turbines have been shut down to avoid injuring the whale. It remains to be seen how long the operators can economically justify an outage.

Since 1984, the Annapolis tidal power plant has been located in the area with the world’s largest tidal range. At high tide, billions of tonnes of ocean water are artificially dammed there. At low tide, the water shoots back through the turbines into the ocean and generates about 20 megawatts of electricity. Animal rights activists have long been against the operation of the power plant. Whales have often swum into the reservoir and cannot find their way back through the sluices. For an animal threatened with extinction, this is a life-threatening situation.

The voice of the moon

The voice of the moon” is what Canadians at the Bay of Fundy call the deafening roar of trillions of litres of ocean water shooting into the bay at high tide. Within just six hours, the 60-kilometre narrow and 220-kilometre long bay on Canada’s east coast fills up like a bathtub. Every day, residents and tourists experience the impressive natural spectacle: the change between low and high tide like no other. This is because the Bay of Fundy experiences the largest tidal range in the world. Between 15 and 21 metres of difference in height make up the ebb and flow here. You could sink a four-storey house in it.

Ebb and flow

Anyone who has spent a holiday on the North Sea or the Atlantic knows the problem: you go to the beach for a swim and the water is much further away than the last time you went. The water level has dropped: it’s low tide. If you want to go into the water now, you either have to walk a long way over wet sand and mud or wait a few hours until the tide comes in and the water rises again.

The tides alternate in a regular rhythm. This change is called the tide. The time interval between high and low tide is just over six hours. There are twelve hours and 25 minutes between one high tide and the next. How much the water rises and falls depends on the coast. On the North Sea, the difference between high and low tide measures about two to three metres. Elsewhere, however, it is much greater: in the Bay of Fundy in Canada, the water level fluctuates by 15 to 21 metres – that is the highest tidal range in the world!

But why does the water in the oceans slosh back and forth? The solution lies in the gravitational pull of the moon. This force causes two huge tidal mountains under which the Earth rotates. One of the two is directly caused by the moon’s gravitational pull, because it draws the water towards it. The second flood mountain is on the exact opposite side of the Earth. This is because the Earth does not rotate perfectly evenly due to the Moon’s gravitational pull, but “wobbles” somewhat. As a result, there is a centrifugal force that pulls the water away from the moon. Both flood peaks are about half a metre high.

Not only the moon, but also the gravitational pull of the sun affects the water. When the sun and the moon are in line, the joint gravitational pull causes the tide to rise higher than normal: there is a “spring tide”. If, on the other hand, the sun and moon are at a 90 degree angle to the earth, then their forces partially cancel each other out. The result is a less high tide, the neap tide.

What is the moon?

It is the brightest celestial body in the night sky: the moon. On full moon nights, it shines so brightly that some people have trouble sleeping. It appears as big as the sun and the stars look like tiny points of light next to it.

But the impression is deceptive: in reality, the moon (diameter: 3474 km) is only about a quarter as big as the earth (12742 km) – and the sun (1.39 million km) is even four hundred times bigger. The moon only appears to be the same size because it is so close to us – the sun (distance to earth about 150 million km) is also about four hundred times further away than the moon. (384400 km, an aeroplane needs 18 days to cover this distance).

The bright light is also deceptive: unlike the sun, the moon does not shine by itself, but is illuminated by the sun. Part of this light is then reflected back from the moon’s surface and hits the earth. It is only because the moon is so close to us that enough light arrives on Earth to light up the night for us – at least when the moon does not seem to have disappeared without a trace …

Why do planets have moons?

Earth has one, Mars two, Jupiter and Saturn even over sixty each! Only two planets in the solar system have to manage without moons: Mercury and Venus, all the other planets have at least one moon. But why do most planets have moons? And what is a moon actually?

For us, the moon is first of all the bright circle that is in the sky at night. It looks small, but in reality it is a large sphere of rock 3475 km in diameter orbiting the Earth. And it is exactly the same with the other planets: They are also orbited by smaller or larger celestial bodies in regular orbits. Astronomers also call these celestial bodies “moons”.

To get a moon, a planet usually has two possibilities: Either the moon is formed together with its planet, or the planet is formed first and later captures a smaller celestial body.

These smaller celestial bodies are asteroids that fly through the solar system without a master. When they come close to a much larger planet, they are attracted by its gravity. This forces the asteroid into orbit around the planet – the planet has been given a moon. This “capture” of a moon works better the heavier the planet is. That is why the large and heavy planets Jupiter and Saturn have the most moons in the solar system.

Other moons have formed from dust remnants left over when their planets were formed: In the beginning, the solar system was nothing but a large disc of dust, gas and ice. In the middle, the matter concentrated particularly strongly – this is where the sun was formed, surrounded by the rest of the disc of dust, ice and gas. In this disc, the same thing happened again on a small scale: Again, compact clumps formed – the planets – and the remaining dust gathered in a disc. And if there was enough matter in this disc, even smaller lumps were formed there: moons. (Only if the gravitational pull of the planet was very strong, the lumps were broken up again immediately. This was the case, for example, close around Saturn, which is still surrounded by dust rings today).

Both moons that were formed from the dust remnants and the captured moons are much smaller than their planets.

The Earth is the great exception: its moon is much larger than it should be compared to the Earth. Therefore, it could neither have formed from dust remnants nor been captured just like that. Instead, the Earth owes its moon to a cosmic catastrophe that almost destroyed the planet:

Shortly after the Earth was formed, it collided with a celestial body about half the size of itself. The force of this impact cannot be imagined: The explosion was so powerful that the young Earth largely melted again – and so did the other celestial body. Part of the molten mass was hurled away and gathered in orbit to form a second sphere. Over time, these two spheres cooled and became solid again. Today, the larger sphere orbits the sun as the Earth – and the smaller one orbits the Earth as the moon.

A small blue dot

You have to look for a while in this picture: The sensation is a “pale blue dot”, a tiny light blue dot in the nothingness. It’s hard to imagine that this little dot should be our home!

This picture shows the Earth. It was taken by the Voyager 1 probe from the edge of the solar system – 6.4 billion kilometres from Earth. It is part of a unique group photo of our solar system, which is composed of a total of 60 individual photos and contains all the planets except Mars and Mercury.

While the image has no scientific value, it shows a fascinating and eerie view of our planet: From this distance, Earth is just a tiny grain of sand in space, our island in the middle of an empty, hostile nothingness.

The Voyager 1 probe and its identical sister, Voyager 2, were launched in 1977 to explore the outer solar system. It visited Jupiter in March 1979 and Saturn in November 1980. It provided impressive close-up images of the moons and rings of both planets. As the probe continues its journey, scientists hope to obtain new and interesting measurement data from the edge of the solar system – and the region beyond.

Before it left the solar system for good, however, the scientists activated the camera one last time to take these pictures.

A record for aliens

As with previous probes, NASA has also equipped Voyager 1 and 2 with a message to extraterrestrials. For this purpose, a copper plate was attached to the probe and covered with gold. On the front is engraved instructions on how to play the images and sounds on the back. This contains greetings in 55 languages, animal voices and other sounds from nature, music (including Bach and Mozart) and a personal address by the then US President Jimmy Carter, just like on a record. In addition, photos of life on earth and scientific graphics are stored there.

The idea behind it: These probes will leave our solar system and fly out into the void of space. There is nothing there to damage or decompose the probes. Therefore, they could be those man-made objects that exist the longest ever – estimated up to 500 million years!

The researchers were attracted by the following idea: what if in the distant future, far away from the solar system, extraterrestrial astronomers discover, capture and study one of the probes? They then decided to give their extraterrestrial colleagues some information about the probe’s builders, a kind of cosmic message in a bottle.

However, space is unimaginably vast and empty. Therefore, it is very unlikely that aliens will actually find the probe. And even if they do: Earth will look very different then – and probably no humans will be alive then either.