The discovery of our galaxy
Galaxy means “made of milk” because the Greeks, with their dark skies, saw a brilliant white ribbon that crosses our skies in summer. They imagined it was due to that gentleman Junoesque who spread their milk in the sky, a symbol of abundance. Then came Galileo which explained that, less poetically, that the glow of the Milky Way was the result of countless stars that our eyes could not tell, but his telescope yes. Four centuries of astronomy after him have taught us that in heaven we see the projection of a disk made of stars (more or less like the Sun) and in which we live immersed.
Source: www.nasa.gov; Credit ESA/NASA
Here today, from Kourou in French Guyana, the Gaia mission of ESA is designed to tell us, how it is really done our galaxy, studying many of those hundred billion stars that we know today and compose the galaxy. The mission begins with the glorious Soyuz rocket, the grandson of one that took Gagarin into orbit, now managed in Europe and adapted for launch from the base of the ESA. The satellite will work in a quiet place, away a million and a half miles from any disturbance of the Earth. It’s a special point, discovered by Louis Lagrange, mathematician who studies in Turin, where Gaia will be able to “float” between the Earth and the Sun but will not stand still; however: draw elegant closed orbits around that special spot , turning with the Earth around the Sun the work program provides for measuring the position of a billion (one billion equals a thousand million!) of stars with an incredible angular precision, the same that we would see a shirt button of a man walking on the moon or the spire of a mole that possible Antonelli had built on Jupiter.
Making a three-dimensional map of the galaxy, even with such a powerful tool, it will not be easy. The mission will take five years or more, if everything works fine. In addition to positioning a billion (one thousand million!) stars, they will measure the displacement. Yes, because to make matters worse, the stars, even those “fixed”, they are actually moving, even at tens of kilometers per second. In short, a long and complicated process, where the Italian scientific and industrial community invests heavily, thanks to ASI. Many of INAF Astronomical Observatories, starting with that of Pino Torinese, grinding data with patience do not expect results in a few days. They will come in such time and could be impressive. And we will be able to move in three dimensions in the galaxy, in its center and the spiral arms. We have to understand when and how stars formed in the billions of years of life in the galaxy. But perhaps we must even understand what it is that and if it’s neither stars nor stardust , that is, a phoenix of astronomy , the famous dark matter and that it exists, anyone may say , what it is (and where) no one knows. It is not a recently problem: the Galaxy is much more dark matter than normal matter, that’s what the stars and all of us are made of. And in our galactic neighborhood Gaia will find thousands of planets around Sun-like stars, perhaps in habitable zones: first, we’ll see the home of ET. Closer, we’ll even see the physics of the solar system, with mapping of asteroids, dangerous or not, that run between our planets. Putting together all the data of the mission, finally, this will be the largest experiment ever conducted of general relativity. Again, Einstein will have to bear a difficult examination: so far he has a great book, but who knows, even a small anomaly found by Gaia in his theory, could have a huge impact in cosmology.