  The famous three-body problem can be traced back to Isaac Newton in 1680s. In
the 300 years since this "three-body problem" was first recognized, only three
families of periodic solutions had been found, until 2013 when \v{S}uvakov and
Dmitra\v{s}inovi\'c [Phys. Rev. Lett. 110, 114301 (2013)] made a breakthrough
to numerically find 13 new distinct periodic orbits, which belong to 11 new
families of Newtonian planar three-body problem with equal mass and zero
angular momentum. In this paper, we numerically obtain 695 families of
Newtonian periodic planar collisionless orbits of three-body system with equal
mass and zero angular momentum in case of initial conditions with isosceles
collinear configuration, including the well-known Figure-eight family found by
Moore in 1993, the 11 families found by \v{S}uvakov and Dmitra\v{s}inovi\'c in
2013, and more than 600 new families that have been never reported, to the best
of our knowledge. With the definition of the average period $\bar{T} = T/L_f$,
where $L_f$ is the length of the so-called "free group element", these 695
families suggest that there should exist the quasi Kepler's third law $
\bar{T}^* \approx 2.433 \pm 0.075$ for the considered case, where $\bar{T}^*=
\bar{T} |E|^{3/2}$ is the scale-invariant average period and $E$ is its total
kinetic and potential energy, respectively. The movies of these 695 periodic
orbits in the real space and the corresponding close curves on the "shape
sphere" can be found via the website:
http://numericaltank.sjtu.edu.cn/three-body/three-body.htm
