By Thomas P.

Going through the era of satellite navigation, we observe that it has gained a great role among us, sidelining inevitably the nautical art which, until a few years ago, constituted the basis of every voyager, depriving them at the same time of a big part of the magic of the voyage!

Certainly, navigation hides within it an amount of scientific knowledge which is, at least some of it, necessary to be aware of, before we decide to go out to the sea. Above all though, it is a fascinating art. An art which emerges from our passion for the sea and it is based on traditional means of navigation.

Navigating with the stars

Of course, long has gone the era of the sextant and of the great seafarer, who were constantly observing the position of the Sun and of Polaris (Pole Star) in order to define their position. Today, a mini GPS gadget is enough to provide us with every information received from the 24 satellites which are in permanent orbit around the earth.

Nevertheless, it is very important and incredibly charming at the same time, to be able to stand on the deck of our boat and have the capability to be orientated by observing the horizon and the sky; to be aware at least of where we are based only on the natural "signs" that surround us.

A look... at the Sky

It is really very interesting to be in the position to recognize some important constellations which concern northern latitudes where our continent also is.

Perhaps, looking towards the night sky, besides the wonderful spectacle, we might at first be disappointed by the thousand stars which look like being accidentally scattered in the celestial dome. However, a closer look will reveal to us some more luminous stars which are in stable positions among them.

The groups of the closest and brightest stars constitute the constellations we are familiar with. Those which are of great interest and are visible only in the north hemisphere, are the Little Bear (Ursa Minor), the Great Bear (Ursa Major) and Cassiopeia.

The Little Bear and Polaris

The stars that constitute the Little Bear are plenty. Noticeable to us are the seven brightest ones of that constellation which, if are united with imaginary lines, they form the well known «ladle». One of these stars is Polaris and this is exactly what makes the Little Bear constellation so important. In particular, the four stars form a small trapezium whereas the other three constitute the tail of the Little Bear or, otherwise known, as the «handle» of this small ladle.

Navigating with the stars

Polaris is the last star in the tail of the Little Bear constellation. The stars which constitute a constellation are symbolized with the small letters of the greek alphabet through which the degree of their luminosity is defined. So, with the letter α the brightest star of the constellation is defined, with letter β the less bright and so on. As it is evident in the figure, the brightest star of the Little Bear is the last one in its tail (α) and the two on the edge of the ladle follow (β and γ). Consequently, those three stars are the most discernible ones with star α being Polaris. That means that the brightest star of this constellation is, therefore, the most discernible one of the Little Bear.

It must become clear here that Polaris is unambiguously the brightest star of the Little Bear but not the brightest in the sky as it is wrongly believed by many people. Generally, it is a star of medium luminosity as well as of little luminosity is the Little Bear constellation. And this is the reason why many times they are difficult to be discerned in the dark sky.

It must become clear here that Polaris is unambiguously the brightest star of the Little Bear but not the brightest in the sky as it is wrongly believed by many people. Generally, it is a star of medium luminosity as well as of little luminosity is the Little Bear constellation. And this is the reason why many times they are difficult to be discerned in the dark sky.

Undoubtedly, Polaris is the most «famous» star in the north hemisphere. It has been given a lot of names such as North Star or Stars of the Seas, since for many years it was the guardian angel of all seafarers sailing in north latitudes.

Pointing always to the North Pole it guided and helped at the orientation of the sailors constituting the only stable reference point during their voyages in the open sea.

Also, with its help, they could define their latitude. These are the reasons why Polaris was and will still be for many years so important, not only to sea navigation but to other things too.
The most important characteristic of Polaris, from which its priceless use comes from, is that it is just above the North Pole manifesting it, always having during the whole year a stable position.

So, no matter where in the north hemisphere we are, we can discern it and very simply, by bringing a vertical imaginary line towards the horizon, we can define with great accuracy the real north.

Navigating with the stars

The Great Bear

It is the most well-known of all constellations, not only for its characteristic shape but also for the fact that it is very easily distinguished due to the great luminosity of its stars.

As in the Little Bear, also in its «elder sister», as the Great Bear is commonly called, only the seven brightest stars are discernible. In reality of course, the stars of the Great Bear are many more and if they were visible to the naked eye and unite them with imaginary lines, we could see a big bear being formed. From this derives the name of the constellation.

Πλοηγώντας με τα άστρα – (μέρος 1ο)

But we clearly discern only seven of the brightest stars of the Great Bear, which if we connect them with imaginary lines, our familiar «Big Dipper» is formed, which is nothing but the tail and a section of the back of the bear (figure 3).

Because of its recognizable identity, the Great Bear is used as a point of reference for the detection of many more constellations. It is of course very useful for the detection of Polaris which is of great interest in ship navigation.

So, when it is difficult to discern the Little Bear and Polaris, we can turn to the Great Bear which is very close to them.

There are many times when, although the Little Bear is not at all visible, only Polaris is discernible. In this case, in order to be certain that we have really detected it, there is nothing else to do but look for the Great Bear.

Therefore, let's see how we can connect those two constellations.
The stars α and β of the Great Bear, those that are on its opposite side and are the brightest, are also known as the «pointer stars». This name is due to the fact that they show us the exact location of Polaris. If we bring this imaginary straight line, which connects the pointer stars of the Great Bear in a direction from β to α and we extend it by multiplying it by five, we will be led to Polaris (Figure 4).

Being aware that the pointing stars of the Great Bear are about 5 degrees away to each other, we understand that the distance of star α of the Great Bear from Polaris is equal to 25 degrees.

Navigating with the stars

The Great Bear of course is not still as we think Polaris is because of its position. Like all stars in the north hemisphere, this also «revolves» around Polaris. But if it is at any point of this particular orbit or, in other words, if it is at any position in the sky, the two pointer stars of the Great Gear always point towards Polaris. This is perhaps the greatest reason why the constellation of the Great Bear is so important to our orientation, a reason that makes its presence invaluable.

Even in the case when Polaris is not at all visible because it might be covered with clouds, we have the capability to estimate approximately its position and consequently that of the north. This happens by knowing that the distance of star «α» of the Great Bear from Polaris is about equal to the quintuple of the distance of the Great Bear pointer stars.

The Great Bear: locate it!

  • In the winter, it is in the east (or, on the right, if you prefer) of Polaris, in upright position, with the «handle» facing downwards.
  • In the spring, it is on Polaris, with the «handle» to its right.
  • In the summer, it is in the west of Polaris with the «handle» upwards.
  • In the autumn, it is located low on the horizon, below Polaris, with the «handle» on its left.

Navigating with the stars

Basically, we observe that the Great Bear «revolves» around Polaris and it is in specific – but the same every time – position in relation to it, according to the seasons of the year. But no matter where it is, if we extend the imaginary line which connects the «pointer stars» between them, we will cross with Polaris.

We should remember that...

  • Polaris is visible only in the north hemisphere.
  • Polaris, no matter where we observe it from, always points to the real north. The point where the imaginary vertical line, which begins from Polaris, cuts our horizon and constitutes the real north.
  • The Little and Great Bear are constellations which help us locate Polaris.
  • By bringing the imaginary line, which connects the «pointer stars» of the Great Bear, and extending it (by multiplying it by five), we intersect with Polaris.
...keep Ribbing!

 

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