The Orbit of Sirius A and B
Sirius is orbited by a small white dwarf, Sirius B,
some ten magnitudes fainter than Sirius itself. The period of the orbit is very close to 50 years.
Sirius B, discovered in 1862, remains a popular challenge
to double star observers. There
have been nearly 2000 recorded positions for Sirius during the last 150 years made
by over 125 astronomers, professionals and amateurs alike. In the image at the
left the locations of the visual observations are plotted in green while the
photographic observations are orange.
The
distribution of all Sirius observations, as a function of time, are shown in
the figure below. The maximum
separation of the two stars is 11 seconds of arc and occurred in 1979. Sirius B
passed closest to Sirius in 1994 and is now separating from Sirius A. The
presence of the companion was first suspected by the German astronomer,
Friedrich Wilhelm Bessel, in 1844.
He deduced that an unseen body was producing a periodic irregularity of
in the proper motion of Sirius as it moved relative to other stars in the sky. The plot below illustrates the
intertwined sinuous paths of Sirius A (dark curve) and Sirius B (dotted
curve). The straight dashed line
is the path of the center of mass of the Sirius System.
The paths of Sirius A and B in the Sky
Chapter
4 – A Dark Star Prophesied in
Sirius: The Brightest
Diamond in the Night Sky
Chapter
5 – A Dark Star Revealed in
Sirius: The Brightest
Diamond in the Night Sky