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7

To elaborate on Conrad Turner's excellent list: The disk structure is even more easily seen in the infrared, where dust extinction is much less than in the optical. See for instance this image from the 2MASS infrared survey: Stars are not really (as Milan van Dijck suggests) used for mapping the spiral arms. Rather the gas clouds of gas in between stars ...

-2

You can see that the milky way appears as a stream across the night sky. We can calculate the distance between us and the stars in this stream, therefor we also know the distance between those stars (by using the Pythagorean algorithm for example). Because we now know the distance between them, we know their relative position of each other (by ...

7

It is clearly a disk galaxy since the Milky-Way is a stream across the sky and so we conclude that the Galaxy is a highly flattened structure. We observe that external galaxies which are highly flattened are almost all spirals of some form. (Also the stellar populations and arrangement of globular clusters are similar to those of external spirals) Radio ...

3

The Sun orbits in the Galactic potential. The motion is complex; it takes about 230 million years to make a circuit with an orbital speed of around 220 km/s, but at the same time it oscillates up and down with respect to the Galactic plane every $\sim 70$ million years and also wobbles in and out every $\sim 150$ million years (this called epicyclic motion). ...

4

All quoted text in this answer is from image captions in the Wikipedia article on the Milky Way. 360-degree panorama view of the Milky Way (an assembled mosaic of photographs) by ESO This magnificent 360-degree panoramic image, covering the entire southern and northern celestial sphere, reveals the cosmic landscape that surrounds our tiny ...

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