Our sun and its planets are part of the Milky Way. Therefore, the Milky Way is our home galaxy. If a distant alien wanted to send a letter to the government, he would have to address it as follows for the ‘pan-galactic post office':
A martian, on the other hand, could just skip the last two address lines.
Besides the sun, the Milky Way accommodates about 100 billion other stars that all rotate around the galaxy center. The Milky Way resembles a flat disk and has a spiral structure. More precisely, it corresponds to a SBc-type galaxy, a spiral with a central bar.
The sun resides in the outer part of a spiral arm. From this position we can observe the disk of the Milky Way from the side. We see a milky band spanning across the night sky. Our perspective resembles the one of a small beetle on the edge of a plate. From this viewing angle, it doesn’t see the plate as a round disk, but as a flat stripe.
The size of the Milky Way is incredibly large: It will still take more than 20’000 years until our radio programs will finally be broadcasted into the galactic center area. So, from there, you would have no chance of being up to date with news from earth. With our naked eyes, we see only the closest couple of thousand stars in our neighborhood. These stars form our familiar sky with its well known stellar constellations.
- masse : 200 Mia de masses solaires
- Diamètre du disque : 98'000 années-lumière
- Épaisseur du disque (étoiles) : 3260 années-lumière
- Épaisseur du disque (poussière et gaz) : 652 années-lumière
- Distance soleil - centre : 28'000 années-lumière
- Vitesse de rotation du soleil : 220 km/s
- Période de rotation du soleil : 240 millions d'années