Page 3: Astronomy of the Milky Way
Observation with the naked eye
We can observe the Milky Way during a moonless night with a sky devoid of light pollution. Unfortunately, most of us live in urban areas.
Here in Europe, I have friends who have never seen the Milky Way in their lifetime.
For my work as a geologist of often travel in the remote areas of Canada, my home country. I take this opportunity to contemplate the sky in all its splendor.
In France, you can see the Milky Way in areas like the Larzac plateau.
During your travels take the time to consult the map of light pollution indices:
Modern astronomy
With the arrival of modern astronomy, we realized that we were in the middle of a great spiral of stars and is only one among the tens of thousands so far enumerated.
Curiously, we use the word 'galaxy' to designate these spirals. Note that this word comes from the Greek galaktos kyklos, 'circle of milk' which simply meant the Milky Way. Each galaxy is made up of billions of stars, dust, gas, vacuum and dark matter.
This image of the Milky Way gives the impression that we see our galaxy on its slice. In fact, we are located on this disc. From here we look towards the thickest part of the Milky Way, the galactic center that corresponds to the constellations of the Serpent and Scorpio. Which means that behind us is the thinnest part of our galaxy. Our Galaxy contains between 100 and 400 billions stars.
With a powerful telescope, we can see other galaxies beyond ours. From the top, a galaxy is a circular spiral. Looking in angle, a galaxy is seen as an oval. Looking on its slice it is seen as a stick. In our night sky, the stars visible to the naked eye are especially the stars of our galaxy.
We recommend this great video by Harry Evette. It will give you a 3D perspective of different galaxies, their size (in light years measurement) and an appreciation of their variety.
A map of our galaxy
We are 27,000 light-years away from the center of our galaxy. By astronomical triangulation, we can map the arms of our galaxy. Our solar system is located on the yellow arm. We see 12 lines aiming at the points which correspond to the constellations located on the Milky Way: Ori = Orion, Aur = Auriga (the Coachman), Cas=Cassiopeia, Cep = Cepheus, Cyg = Cygnus (the Swan), Aql = Eagle, Sgr = Sagittarius, Nor = Norma (the Rule), Cen = Centaurus, Vel = Vela (the Sail), Pup = Puppis (the Stern), CMa = Canis Major (the Great Dog). Not to be confused with the 12 constellations of the zodiac located on the ecliptic. GC = Galactic Center
Credits: Rursus
Our galaxy could very well look like UGC 12158, a galaxy visible in the constellation Pegasus. Credits: ESA / Hubble & NASA
The Milky Way as a loop
To decode the ancient myths, it is important to understand how our ancestors were thinking.
For this we must see the Milky Way as a loop that closes on itself.
If you downloaded the Stellarium free software you will be able to do the following exercise
1- Use the stereographic projection (the default one);
2- Eliminate the terrestrial horizon;
3- Step back to get the full sky (mouse wheel);
4- Drag sky to close the loop (click & drag the mouse);
5- Remove or put on the constellations images as needed.
By viewing the following 3 slides, you note the thick left portion with the constellations of the Serpent (Ser) of Ophiuchus / Serpent (Oph) and Scorpion (Sco); it is the galactic center. The red arrow indicates a thin part almost missing; it's outside of our galaxy. Just above this narrow section is the constellation Perseus (Per) holding the head of the Medusa and below Auriga (Aug). Throughout the world, the myths of the cut head evoke this strangeness in the thickness of the Milky Way.
To understand the thought of our ancestor, seeing below, the path of the sun on the ecliptic (circle of red dashes). We see the 4 fundamental positions of the sun:
1- At the autumnal equinox,
2- At the winter solstice,
3- At the spring equinox,
4- At the summer solstice.
In green, it is the natural part of the cosmos delimited by the Milky Way (the galactic equator). It will be noticed that at the autumnal equinox (1), the sun leaves the natural/terrestrial world to penetrate the supernatural world/ocean. At the winter solstice (2), the sun is deep in the ocean world, in the supernatural of death. At the equinox of spring (3) the sun comes out of the sea to hover above the earthly world. He will be at his highest at the summer solstice (4).
It is good to remember that illustrating a spherical world is a mental exercise that requires multiple projections. In the following two projections of our globe, the red line is the Tropic of Cancer. On the top left we see a cylindrical projection of the world and below the complete Stellarium sky with the same projection. On the top right, we see the world seen from above the North Pole with the Tropic of Cancer closed in a loop, bellow, the Stellarium sky with the Milky Way as a closing loop.
