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1

Before satellites or aircraft were invented, how did people make maps? You start at one point on the ground and carefully measure the angle to some landmark, say a mountain. Then you measure the distance. You make many many such measurements of angles and distances between various objects. Then you scale all the measurements down to something manageable and ...


-2

Actually it is quite simple and this method, Integrated Tomographic Imaging, has produced what is a fairly accurate 'top down' image of the Milky Way. You start with a catalog of known stars their elevation, azimuth, actual estimated brilliance and estimated distance. Sort by brilliance. You then can polar plot in a 3 axis grid system the stars location. ...


21

There's actually an ingenious way to do this! Hydrogen everywhere in the galaxy emits radiation with a wavelength of about 21 centimeters, and this radiation is really easy to detect. Where there's hydrogen, there are stars. Unfortunately, this isn't enough; if you just look straight at the center of the Milky Way, you'll see plenty of 21cm radiation, but ...


7

We determine the shape of the Milky Way simply by measuring the positions of objects within it. Well, I say "simply", but this is an extraordinarily hard thing to do for lots of reasons. As a result there is still lots that we don't know about the Milky Way. For example although we believe the Milky Way is a barred galaxy we don't know how big the bar is. ...


23

We base it on pictures we have of similar galaxies, as we know they occur in general classes, or groups. We also, to some degree, can map the speeds and positions of the various components of the spiral arms and that is confirmation that we have the general shape correct, although from memory, we did recently discover some new galactic features that ...



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