Polaris won’t be North Star forever

Hi,
today I will write about precession and what effect it has on our sky.


Polaris is the North Star or Pole Star. This means that it is close to the celestial pole. Celestial pole is a point created by expanding the Earth’s axis of rotation and piercing through the celestial sphere which is imaginary “area” where stars sit. (For Earth based observations you do not really need to take into account that the stars are in completely different distances from us)

Precession is shown by the circle on the top.

But Polaris was not always the North star. For example when the Great Pyramid of Giza was build aobut 4600 years ago, there were two shafts from the tomb added. One points towards some random stop in the sky and the other one to Polaris.. oh wait but 2600 BC it pointed to Orion’s Belt and the star Thuban in the constallation of Draco. Orion was in Egyptian mythology connected to the god of dead Osiris and Thuban used to be the star closest to celestial pole. WHY?

Orange circle shows how the celestial pole’s position will change during the next years

 

Because of precession. That is an effect on Earth by Moon and Sun. The same way as gyroscope creates a kind of cone shape with it top, Earth also rotates like this but very slowly, it takes about 26000 years to rotate once. This type of precession is also called axial precession.

On the southern hemisphere the South Star is Sigma Octantis. It has very high magnitude so it is barely visible and not very good for naked eye observation. This will of course also change in the next hundreds of years.

Because of precession astronomers have to update every 50 years the positions of stars and objects, right now we are in what is called J2000 epoch and the next one will be J2050.

Dragallur

1st picture: By NASA, Mysid – Vectorized by Mysid in Inkscape after a NASA Earth Observatory image in Milutin Milankovitch Precession., Public Domain, https://commons.wikimedia.org/w/index.php?curid=3993432
2nd picture: By Tauʻolunga – self, 4 bit GIF, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=891838

 

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How to! 1) Using stars to navigate

Hi,
here it goes, here it comes. Just because of random I just made another series which may not continue anymore but I don`t care I made it just for fun and today I will write about really practical skill if you dont know where the hell you are. You just have to know couple of things.


So I will start with the easiest skill which you probably already know.
It is always crucial to know the constant direction in which you want to walk. If you have compass it should not be a problem unless when you are in the mountains there may appear bubble because of different pressure and it wont disappear again so watch out for this because then it wont be so accurate.

So the easiest thing is to find Polaris or North Star on the northern hemisphere. It is one of the most bright stars and and also Polaris is exactly at the point around which whole sky is rotating so it will always be on the same spot as you can see on the picture with high exposure.


You can find it when extending the big dipper, which is very bright constellation, 5 times.

Polaris will always point to the north and it should rise as you go north and set while you go south. This concept is very useful when measuring your latitude.

For this you need something to measure degrees. I heard that your fist on the length of your arm is about 10° or you can use watch that are not digital because the difference Image titled Navigate by the Stars Step 4between two numbers should be 30°. If you are PRO then you will have sextant of course :D. You should measure 90° on poles and zero on equator.

To know your longitude it is a bit more complicated. You need clockwatch which has some time like Greenwich, just that you know where this time is. Then during day you will measure when the Sun is highest which can be almost anytime since your watch are not on the time zone where you are.

Then because there is 24 time zones you know that for one time zone there is 15° of longitude + you will add half hours or whatever you measured when was the Sun highest. Then you will know how much you moved to west or east. With the method of sextant you can easily measure where is your place on the Earth. I will make sure to try it when it will be clean sky to see how accurate it is. Anyway if you want this to be useful you have to check the map to see the coordinates of some cities.

But you can use any star to orient yourself!
Put two tall things about meter apart. Than line up the tops of the things with any star and wait to what direction it moves.

  • If the star rose, you’re facing east.
  • If the star sank, you’re facing west.
  • If the star moved to the left, you’re facing north.
  • If the star moved to the right, you’re facing south

Btw. for this last one thanks to wikihow article, I did not know that.Image titled Navigate by the Stars Step 8

Also on south to know south, use South cross. Line up the two stars that
are making the T and they should point Alpha Centauri, the closest star and Alpha Centauri points to south.
Dragallur

Polaris photo 1st and 2nd
Sextant photo and South cross photo