# Tag Info

8

I've been trying to figure out the technical details of astrometry.net for quite some time. As others already pointed out, the main input to the whole process is a list of stars. I will not go into details on how astrometry.net does it, just note that you can either use its internal simplexy algorithm or use SExtractor. In the end you need a list of ...

8

I did some rough calculations, and 100 light-years doesn't seem to be a bad guess. If we assume that the average mass of a halo star is $\sim0.3M_{\odot}$, as would be expected for a typical IMF, and that the total stellar halo mass is $\sim10^9M_{\odot}$ (Deason et al. 2019), then we should expect there to be $\sim3.3\times10^9$ halo stars.$^{\dagger}$ The ...

7

The linked article is copied from a university press release. Arecibo's article is more matter-of-fact but naturally also emphasizes the value of their own work. NASA Goldstone can do planetary radar and remains operational. As this page says: Arecibo has twice the range and can see three times the volume of Goldstone, while Goldstone, whose greater ...

4

Like most asteroids and comets, 1I/'Oumuamua's trajectory was determined entirely by measuring its position in optical images over several days. The earliest data came from automated, ground-based surveys such as Pan-STARRS and the Catalina Sky Survey, then targeted follow-ups from various other asteroid observers. The object's evident extrasolar origin ...

2

In many cases in astronomy, there’s a difference in finding the position of something precisely vs. seeing detailed structure in that object. In the former case, what you need to do is to find the centroid of the image. So even with relatively coarse spatial resolution, you can often get very precise positions because you can centroid the images very well. ...

2

This isn’t code for a full implementation, but you could do something like this: Transform your RA, Dec coordinates (which are spherical polar coordinates, just all with the same $r$) to Cartesian $x, y, z$ coordinates. (The $r$ value you would use here is arbitrary, for example $r = 1$, and should be the same for all stars, not their real distances; you'...

1

Ok, it needed some searching with the right words (astrometry, standard coordinates) to actually find the equations I needed. I'll try to go through the process here to make this a complete answer to my own question. The key equation here is the conversion of Celestial Coordinates (RA, Dec) to Standard Coordinates (X, Y) on a tangent plane of the sky. This ...

1

About 300 light years Wolfram has previously informed me that if our planet is as big as a flea (1MM), the sun is as big as a pigeon (11CM), the average distance of milky way halo stars is 25000 KM, and the milky way would be as big as the solar system, the disk stars would be about 3700 KM distance. If the milky way galaxy was as big as the solar system, ...

1

Based on links on this page, the closest visible star in Orion (that is, the region of the sky called Orion) is Pi3 Orionis (π3 Orionis), a.k.a Tabit, a.k.a al-thābit, a.k.a. Zhāng Qí Liù. This is the point where the arm touches the shield/bow. That page says it is 26.2 light-years away; Wikipedia says its 26.32 ± 0.04 light-years or 8.07 ± 0.01 parsecs away....

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