I want you to imagine that it’s 9.00 in the evening and we are going to watch the night sky. Man has always enjoyed watching the night sky. Astronomers have observed the apparent movements of stars and planets from ancient times. Let’s have a look to the south. This “S” stands for south. The sky is full of stars, many of them especially bright, as Sirius, Rigel, Betelgeuse, or Aldebaran. There are other bright celestial objects in the sky, as planet Mars. Some of these stars form groups of stars called constellations. For example, my favourite one is Casiopea, this one. In fact, in our culture the names of the constellations usually come from the Greek mythology. But, actually, a constellation has no real meaning as the stars are at very different distance from us and appear together only because of a visual effect. So, they form a group but they are not really together. Take for example these three bright stars in Orion constellation and let’s see how far they are from us. This one is about eight hundred light years from us, while this one is about one thousand and three hundred light years. Let’s see what happens as time goes by. A star describes a complete circle in the sky, one per day. However it can disappear below the observer’s horizon if it is not close enough to the celestial pole. It’s now 6.00 a.m. As you can see another fantastic constellations have appeared to the south, as Scorpio, with one of the brightest stars in the night sky, Antares, and Sagittarius, which is also very beautiful. But now I want you to show another well known constellation. Let’s go back in time until 9.00 in the evening, but now let’s look to the north and find the Ursa Minor, next to Ursa Major. Take the line between these two stars until it intersects this star here; this star is called Polaris. Observe what happens when we advance in time through the night. All stars move in circles except the Polaris, which remains fixed. Why does Polaris remain fixed? Why do stars move in circles? Why do planets show retrograde motions? Which is the reason of seasons, the reason of the phases of the Moon and the phases of planet Venus? Well, it seems like we need to learn a bit more about basic astronomy.
Issuu converts static files into: digital portfolios, online yearbooks, online catalogs, digital photo albums and more. Sign up and create your flipbook.