Constellations
Author: Róża Chojnacka
A brief history
The celestial sphere is divided into 88 areas called constellations. The constellations visible in the northern sky often refer to ancient Greece and Rome (for example Perseus or Hercules). Most of the names for the southern constellations appeared in 18. century on the maps of the French astronomer, de Lacaille ( Telescopium, Horologium). For the centuries, the borders among the constellations were changing and moving, depending on the people who made the observations and presented them on maps. In other word, the same star could belong to one constellation in the opinion of person 1, and to the other one, if we asked someone else.
This mess was over in the late twenties of 20. century, when International Astronomical Union described a constant number of constellations and their exact borders. They are drawn along vertical and horizontal lines of right ascension and declination, but for the epoch 1875 (in astronomy, the term „epoch” means a moment for which celestial coordinates or orbital elements are specified. In the case of the coordinates, the location of an object can be computed by taking into account precession and proper motion).
The names of constellations can be different in different languages, but the astronomers unsually use the latin names. English language uses them as well.
Groups of stars
A group of stars consists of some stars, whose arrangement on the sky has been given its own name, and which do not form a complete constellation. One of the best known ones is undoubtedly Big Dipper, seven the brightest stars of Ursa Major. Other groups include Hyades and Pleiades in Taurus or Little Dipper in Ursa Minor.
Zodiac in astronomy and astrology
The zodiac is formed of twelve constellations that played a significant role in cultures of ancient civilizations. They are so important, because the Sun, the Moon and the planets are moving on the top of them. That is why the zodiac constellations lie on the way of the Sun on the cellestial sphere. To the constellations, there are assigned zodiac signs. All of them spread on 30 degrees of the ecliptic. Most of those constellations show animals.
The zodiac signs were introduced to the astronomy just to supply the needs of calendar makers. Nowadays, the play no role. Only the symbol of Aries is associated with the Spring Equinox. However, they are the base of astrology, a pseudo-science that reached the biggest popularity in the Medieval ages. The astrologers thought that the future history of every single person and whole nations depends on the arrangement of the stars and planets. It was the astrologer who had to pay attention to make the horoscopes true. The astrology has not changed for ages and nowadays it still cheats naive people, suggesting them it is a real "science".
Moreover, the precession moved the zodiac about 30 degrees to the east, so the constellations do not match to the signs. The changes made in 1928, when the borders were set up, caused that the Sun and planets sometimes move on the top of Sextans or Orion. Today, we define the zodiac as a part of the sky that spread on 8 degrees on every side of the ecliptic, so it contains also small parts of those „additional” constellations.
See also
How to observe the sky?
In the beginning, we should get a rotable map of the sky (it is available in every astronomical observatory or on the Internet). The best to light the map is a lamp with the red light. It could be screened with a piece of PTFE. You can take a red lamp from your bike, as well. Thanks to it, our eyes will not be stabbed by the flash of the bright light. Sometimes, it is useful to have a compass. When we are ready to go, we set the map and hold it like we read a book. We must turn to the north direction, as the map shows at the bottom. We compare the map with the stars on the sky we can see. Next, we check other directions, every time rotating the map so that the description of the direction was at the bottom of it.
The classification
It is the best to start the recognition of constellations from the ones around the pole. The visibility of the southern constellations depends on the season of the year. Thankfully, all of them have its own, characteristic constellations. The winter – Orion, Taurus, Gemini and Auriga. The spring – Leo, Hydra, Boötes. The summer – Cygnus, Lyra, Aquila. The autumn – Pegasus and Andromeda. In the summer, the night could not be dark enought, but even then we can follow the bright stars of Deneb, Vega and Altair. On the southern hemisphere, there will be visible Crux, which has a shape of a latin cross. If we lenghten its axis four times, we reach the southern pole of the sky.
Central constellations
As I previously mentioned, the easiest is to start the exploration of the sky from the constellations around the pole. They are visible whole year and moreover, they are the best known ones, like Big Dipper, which is a part of Ursa Major. Using the stars from this constellation, you can find Cassiopeia, Cepheus, Ursa Minor and Draco.
Winter constellations
On the northern hemisphere, the winter sky is dominated by a wonderul constellation of Orion that has a shape of a sandglass. It is very easy to recognize; there is a bright, orange star called Betelgeuse in its north-eastern part, and three stars in the center. If we lengthen the line described by them, we will reach the Aldebaran star in Taurus and in the opposite direction – Sirius in Canis Major. The line that connects Rigel and Betelgeuse shows us Gemini, whereas the connection between Bellatrix and Betelgeuse points to Procyon in Canis Minor. The brightest stars form a hexagone. The center is Betelgeuse and the vertices are: Aldebaran, Capella, Castor and Pollux, Procyon and Sirius.
Spring constellations
In spring, we can find a triangle formed by three stars: white-yellow Regulus in Leo, bluish Spica in Virgo and orange Arcturus in Boötes. Those three constellations are the best visible ones in spring and they are easy to remember. Under Big Dipper we see Canes Venatici, and between them and Virgo we could find a group of very dark stars – Coma Berenices. Under Leo, Virgo and Libra, there spreads Hydrus with the head directed to the north. Between Virgo and Hydrus we can also find Corvus and Crater. Under Hydrus, there is Pyxis, Antlia and the highest part of Centaurus. To the east from Boötes, there is Corona Borealis, to the west from Leo we see Leo Minor, and to the south - Sextans.
Summer constellations
Bright summer nights and relatively long twilight cause some constellations not to be widely known. However, this is the best season to contemplate the Milky Way splitting the sky. The night sky of summer is dominated by famous Summer Triangle that consists of Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila). If the sky is cloudless, we can see such constellations, as: Hercules, Corona Borealis, Lyra, Telescopium, Cygnus, Aquila, Piscis Austrinus, Sagittarius, Hydrus, Ophiuchus, Aquarius and many more.
Autumn constellations
The constellations that lead us through the autumn sky are Pegasus and Andromeda. There are Piscis and Aquarius under them. To the west from Aquarius, there is Cetus with Mira the star. Above the head of Cetus, we see Aries and Summer Triangle. Among the autumn constellations, the highest one is Perseus with Algol. To the east from Perseus, there could be found even winter constellations: Taurus, Auriga, Orion and Gemini. Over the western horizon, the summer constellations fall down: Hercules, Aquila, Lyra and Cygnus.
The end
This is the end of my story about constellation. For those ones who became interested in the observations, I would recommend to buy some books, like "The Sky: A User's Guide" by David H. Levy. Worth installing, there is also a computer programme "Stellarium", which is a simulation of the night sky and all the visible events.
Translated by Tomasz Jędrzejewski