How to Determine the Size of the Dark Matter Hallow of a Galaxy

Astronomy is not something you can do, like in a couple of days. Takes years, sometimes decades. You have to look at old data that previous generations of astronomers have compiled. Based on all the data that we have, we can then arrive at good, at a good idea of how far a galaxy is and how much mass it contains. And similarly, for our own galaxy, we can do such things. For our galaxy. It is slightly difficult because we can't see the entire ay. But once again, we can doing these things. We can determine the size of the dark matter hallow of the galaxy.