For thousand of years, astronomers and astrologers believed that the Earth was at the center of our Universe. This perception was due in part to the fact that Earth-based observations were complicated by the fact that the Earth is embedded in the Solar System. It was only after many centuries of continued observation and calculations that we discovered that the Earth (and all other bodies in the Solar System) actually orbits the Sun.
Much the same is true about our Solar System’s position within the Milky Way. In truth, we’ve only been aware of the fact that we are part of a much larger disk of stars that orbits a common center for about a century. And given that we are embedded within it, it has been historically difficult to ascertain our exact position. But thanks to ongoing efforts, astronomers now know where our Sun resides in the galaxy.
Size of the Milky Way:
For starters, the Milky Way is really, really big! Not only does it measure some 100,000–120,000 light-years in diameter and about 1,000 light-years thick, but up to 400 billion stars are located within it (though some estimates think there are even more). Since one light year is about 9.5 x 1012 km (9.5 trillion km) long, the diameter of the Milky Way galaxy is about 9.5 x 1017 to 11.4 x 1017 km, or 9,500 to 11,400 quadrillion km.
It became its current size and shape by eating up other galaxies, and is still doing so today. In fact, the Canis Major Dwarf Galaxy is the closest galaxy to the Milky Way because its stars are currently being added to the Milky Way’s disk. And our galaxy has consumed others in its long history, such as theSagittarius Dwarf Galaxy.
And yet, our galaxy is only a middle-weight when compared to other galaxies in the local Universe. Andromeda, the closest major galaxy to our own, is about twice as large as our own. It measures 220,000 light years in diameter, and has an estimated 400-800 billion stars within it.
Full Article: http://www.universetoday.com/65601/where-is-earth-in-the-milky-way/
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There are assumptions that goes with measuring our position in Milky way. What is dangerous is that some of these assumptions are also what we seek to prove! Do phyc work the same way across our galaxy? Specifically, is the gravitantional constant same throughout? They determine the location of stars using cepheid variability, a phenomena discovered in a group of stars that were clumped together in a cloud. What is overlooked is the possibility that cepheid variability was a thing perculiar to that cloud. Measuring distances using cepheid is just like that of using redshifts. They empody unwaranted assumptions.
'we finaly discovered that the earth orbit the sun'
Unfortunately, our scientists teaches interlectual assumptions as though unquestionable facts, greatly misleading ley people. Nobody can prove that the earth move around the sun or vice versa! Corpenican revolution was a dramatic change in HOW WE THINK about the universe and not the much about the change in the body of facts. There is the use of Occum's Razor in deciding between Ptolemy model and the Corpenican model of which the ley person is never told of till be grow interlectually enough to press the priest against the wall! But logically, being favoured by Occam's Razor does not mean truth. Farther more, the way mainstream use Occam's Razor is ill defined. It allows them to chose arbitrarily what they want!
'as we discover more about the universe, our place in it shrink..'
This is what they are especting to find and thus they see! It is such preconceived ideas that taints the sunglasses. There are discoveries that destroy this view, that the earth occupy insignificant place in the universe, but they are left to obscurity and left in pending till someone in mainstream finds a farfetched way of debunking it. One such a discovery, which should have been anounced from roofs is the so called 'axis of evil'. It is a mind shattering evidence that the earth occupies a very significant place in the known universe. There is an axic passing across the earth from the cosmic north pole all the way to the cosmic south!!