Astronomers observe dramatic changes in the system during the months before and after periastron
The epicyclic frequencies are related to the oscillations frequencies of the periastron
and orbital plane of a circular orbit when we apply a slightly radial and vertical perturbations to it.
In 2009 they motivated amateurs to visit Tenerife to observe the periastron
of the ultra-hot binary WR 140, the best-studied member of a class of objects called colliding-wind binaries (S&T: April 2011, page 28).
General relativity predicts that, like the precession of the perihelion of Mercury, the periastron
of the pulsar (the point of its closest approach to the black hole) will precess in the plane of its orbit, at rates that are highly sensitive to the orbital parameters, from more than 4 degrees per year for an eccentricity of 0.
The original idea was for a small workshop for researchers involved in the observations for the 2011 delta Sco periastron
campaign, but it grew into a conference that drew scientists from around the world and generated 56 papers for the proceedings.
In July of 2011, the highly-eccentric Be star system Delta Scorpius was predicted to have an interaction between its companion star and its circumstellar disk during its periastron
passage which takes place every eleven years.
The paper includes four other bright southern systems including Beta Phoenicis which has now apparently passed unobserved through periastron
In planets the latter motion is called precession of perihelion; in stars it is either precession of periastron
or precession of apsides.
The orbit of 70 Ophiuchi continued to confound observers until remarkably recently; even the 1984 periastron
(when the two stars passed closest to each other in space) occurred much later than expected.