The Sun and the stars surrounding it constitute a part of a spiral galaxy that is always identified with a capital latter "G" - Galaxy - because it is our galaxy.
The position of the Sun in our Galaxy is rather unfortunate as far as the studies of the Galaxy are concerned. We are situated relatively close to the plane of the star disk, and it is fairly complex to identify the Galaxy's structure from the Earth. Besides, there is quite a lot of cosmic matter in the region that is close to the Sun. It absorbs light and makes the star disk virtually invisible because of "blind spots" that are especially prominent if we look in the direction of the star disk's core. Therefore, studying other galaxies plays a tremendous role in understanding the nature of our Galaxy.
The Galaxy is an intricate stellar system that is composed of numerous different objects with a complex relationship between them. The mass of the Galaxy is assessed to be equal to 200 billion masses of the Sun, but only two billion stars are available for observation from the Earth.
The pattern of stars in the Galaxy has two clearly manifested trends. First, there is a strong concentration of stars at the Galactic plane, and secondly, there is a strong concentration of stars at the Galaxy's center. Apart from the higher concentration of stars, a higher concentration of dust and gas is also observed in the Galaxy's plane.
The central and most compact region of the Galaxy is known as the core. The concentration of stars is at its highest at the core. If we were living on a planet located in a stellar system in the vicinity of the Galactic core, dozens stars with would be visible in the sky, shining as brightly as the moon shines on the Earth. Scientists believe that a massive black hole is situated in the center of the Galaxy.
A circular region of the galactic disk contains virtually the entire molecular substance of the interstellar medium. The largest number of pulsars - remnants of supernovas and infrared radiation sources - are also located in the center of the galactic disk. Visible radiation of the central regions of the Galaxy is completely concealed from us by thick layers of absorbing substance.
The Galaxy contains two major subsystems (two components), tied to each other by gravity. The first galactic component is called the halo. Its stars are concentrated at the galactic center. The density of substance is high at the galactic center, and it abruptly drops from the center of the halo to its outskirts. Dense central part of the halo that lies within the limits of several thousand light years from center of the Galaxy is called the bulge.
The second galactic subsystem is a massive stellar disk. The concentration of stars in the disk is much higher than in halo. The Sun is situated in the stellar disk between the spiral branches.
Both the disk and the halo are located in the corona. The size of galactic corona is presently considered to be 10 times larger than size of the disk.
The age of our Galaxy exceeds 12 billion years.
This 3D animation illustrates the structure of our Galaxy. A small yellow circle demarcates the position of the Sun. Distance from the Sun to the center of the Galaxy, as well as the Galaxy's changing size, are also indicated on the diagram.
Press "Run" button and observe the Galaxy rotate. A special input window allows you to observe the galactic rotation from different angles of perspective. "Stop" and "Reset" buttons bring the model to a halt and return it to its initial state, respectively. The model stops when 5 billion virtual years elapse.