The Earth is one of the planets that moves around the Sun and forms
unity with it. The Sun is a relatively small star and it is only one of
many billions of stars, that are grouped in galaxies. All stars we can
see from Earth without special means are part of our galaxy, this galaxy
is called The Milkyway, because of its milky appearance.
At night we may observe the Milkyway as a vague silver ribbon on the sky.
However looking through a telescope, it appears that the Milkyway is built up
out of countless individual stars that seem to be placed very near to each other.
This occurs because from Earth we see The Milkyway Galaxy 'on edge'.
Four hundred billion suns.
The total swarm of suns in the Milkyway has a size of more than one hundred
million times the size of our own planetary system, from end to end it
spans 100,000 lightyears.
It is calculated that 400 billion stars belong to the our galaxy, the
total mass is about 300 billion times the mass of our Sun.
The Milkyway is part of a larger cluster
of some 30 star galaxies, of which the Andromeda nebula is the nearest to us.
The Andromeda is our nearest neighbor galaxy, it is a
spiral galaxy and looks just like the Milkyway. |
Spiral shape.
The Milkyway is a spiral galaxy with a large concentration of stars in the middle. The center (or nucleus) of the Milkyway is thick, like other spiral galaxies, where the spiral arms sprout. The Sun and Earth are located on one of these spiral arms at about 25,000 lightyears from the center, which is at two-thirds the distance of the center to the edge. Our milkyway is rotating around the center, it takes 250 millions years for the Sun to complete one orbit. From the southern hemisphere of the Earth we are looking to the middle of The Milkyway, from the northern hemisphere the are looking to the edge. It is impossible for us to observe the nucleus as the greatest part of our galaxy is hidden by interstellar dust. There are indications that there is a blackhole in the center of The Milkyway. It is also possible that in the large hollow areas around the galaxy there is a giant quantity of invisible (dark) matter that could be found. |