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3

The volume isn't well-defined, because the radius isn't. There are practical values for the radius such as scale length/height, half-light radius, $R_{200}$, etc. that are commonly used, depending on what you're interested in. But the densities never reach zero, so any value for the radius will be arbitrary. Moreover, you always only observe a 2D projection ...

4

This answer is conjecture, but typically when an object has a nickname that identifier is used frequently as an alternative to the index number. In that case, you would expect a brief search through a page or two of Google to find at least one instance of the object referred to by that name. As there is none, it is likely there is not a common nickname for ...

1

The time it takes for the Sun to complete one orbit around the center of the Galaxy is called a Galactic year. It is estimated to last 225 to 250 million terrestrial years. Now if you know the speed of the Sun in the Galaxy and you know how far the Sun is from the center, you can estimate this period. Let's assume a circular orbit and ignore the (large) ...

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