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I know that Sirius A and B orbit each other. I'd like to ask how large is their relative apparent motion in arc seconds, seen from Earth?

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From Sirius A to Sirius B on the sky is around 3 arcsec on average.

The separation between Sirius A and Sirius B actually varies from 3 to 11 arcseconds b/c of their orbital motion over a long period of time (Here).

I believe you're referring to that. There's a lot of information (and even some graphs and diagrams) here: Here. The information on that website is sort of vague, but I think it'll be helpful in visualization.

Hope that helps!

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  • $\begingroup$ not the separation between the two, the movement of Sirius A only $\endgroup$
    – pol0
    Oct 17 '18 at 0:40
  • $\begingroup$ Sirius B has a wider orbit $\endgroup$
    – pol0
    Oct 17 '18 at 0:40
  • $\begingroup$ looking at the link you included, as.utexas.edu/white_dwarfs/wkshp_05/SiriusAB.pdf, it looks like Sirius A has an orbit of 12 arc seconds in total, is that correct? $\endgroup$
    – pol0
    Oct 17 '18 at 1:22
  • $\begingroup$ It looks like so. I think this source is slightly outdated, so I'm not putting too much reliance on it. $\endgroup$
    – MystaryPi
    Oct 17 '18 at 2:21
  • $\begingroup$ I read it wrong actually, it only goes to -0.5, so around 6.5 arc seconds. $\endgroup$
    – pol0
    Oct 17 '18 at 2:23

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