Within the group of instruments used to observe the sky we have the celestial planisphere. It is also known as the celestial plane and is nothing more than a mathematical tool used to understand the sky above the horizon. The advantage it offers over other observation instruments is that you can observe the horizon at any time and any day of the year. Its predecessor is the astrolabe, and like this one, the celestial planisphere is designed for a specific latitude.
In this article we are going to tell you everything you need to know about the celestial planisphere, how it is used and what it is for.
What is the celestial planisphere
When we talk about the celestial planisphere or a type of mathematical tool that serves to know the sky on the horizon. The advantage it provides over other instruments for observing the sky is that we can see it at any time and day of the year. This instrument is designed to observe the sky from a specific latitude. In this case, the planisphere is 37 degrees north and it will not be suitable for another northern location with a very remote attitude. Nothing more to say that it will be useless if used in the southern hemisphere.
Its degree of correction is degrees above or below within 37 degrees north. That is, it can be used perfectly in Andalusia, Ceuta, Melilla and other bordering areas as well as any town in the world with similar latitude. The celestial planisphere consists of two flat and circular discs whose centers pivot on the same axis. The basis of this instrument is the star chart that indicates all the constellations and stars that can be observed in the sky. It also offers you up to a declination or angular distance to the north celestial pole. This decline can be observed in order to know the interests of the planisphere.
It has a spherical section in a plane and always supposes distortions. For the celestial planisphere we have chosen the projection that maintains the angular distances is even if the figures are directed somewhat more laterally. The other disk of which it is formed is opaque except for a small transparent window which is what represents the sky above the horizon. The edge of the window is the horizon of the sky and is where we can find the cardinal points. The north and south points are opposite and divide the window into two equal halves. However, the projection system places the east and west cardinal points as not equidistant.
How the celestial planisphere works
In order to use the celestial planisphere we must use the black background chart. The brightest stars in the sky that can be seen at this latitude are represented on this chart. Some of the names of the stars are presented in a pinkish color, the Milky Way It is presented in violet, the constellation lines in red and the names of the constellations in ocher. Other colors that we can distinguish in the black background chart are the equatorial coordinate system that is expressed in a dark blue color, the celestial Equator in a celestial color and the ecliptic in a yellow color. The ecliptic is the path of the sun between the stars.
Many people wonder why the planisphere only works at about 37 degrees north latitude. This is due to this latitude is the average of the Andalusian towns and since not all planispheres contemplate from our latitudes, this more adapted planisphere has been developed. It was created in Andalusia and hence this latitude.
How is this made
You can make a celestial planisphere in a simple way. It is nothing more than a cutout and the most important thing is to print it with a certain quality and have a good skill cutting the papers with the scissors. We can print the star chart on a normal size sheet. It is advisable to do it on white cardboard or photographic paper so that it has a higher quality in its use. Later, we will print the front and back sides but with a light colored cardboard. Then we can cut the edges of the images into several pieces. Here we will include the window of the front face that will point us to the sky.
Next, we fold the gray tabs on the front face and we will enter glue through the gray area. We will glue the front and back pieces and we will leave the printed faces towards the outside. Once we have finished all these steps we will see that we have a kind of envelope. The above is hollow and in it We will introduce the cut-out spherical letter with the printed side facing the window.
Once we have finished preparing the manufacture of our celestial planisphere, we just have to learn to use it with the passage of time. At first it may cost us more, but then we get used to it more easily.
How it is used
Since we have indicated how to create your own celestial planisphere, we are going to show you how you should use it. On the edge of the star chart we want printed we will place the days and months of the year. In the semicircle of the front face are the hours from 18 hours in the afternoon until 06 hours in the morning. The zones are local hours and not official hours. This means that the mean solar time of each locality depends on the geographical coordinates where we are. We can approximately take two hours off the official time if we are in summer time and one hour if we are in winter time.
If you are in another country but with a similar latitude, you should only know the difference between its official hours and its local time. In this way, you can use the same celestial planisphere. Next, you must look north and you must remember that the pole star is located in the center of the star chart. Rotate the entire planisphere so that the north of the window coincides with the north horizon. The windows must always be above the horizon as it represents the sky and no one from the stars looking at the ground. You must look for similarities between the brightest stars in the sky with those that shine on the chart from a similar position. This is how you can, little by little, identify the different stars and constellations.
I hope that with this information you can learn more about what the celestial planisphere is and how it is used.