a measure of the total amount of matter contained in an object
a system that consist of two stars in orbit about there common center of mass, held together by their mutual gravitiational attraction. most stars.
2 stars appear close together, but very seperated in reality
can be viewed from earth
the time it takes to complete one full orbit
orbit not directly on, see its projection onto the plane the sky
kepler's 3rd law
the distance between the two stars is the semi-major axis of the orbit
one-half of the major axis of an elipse, the way in which the size of an elipse is usually quantified
the average distance of eaurth from the sum=1
center of mass
the "average" position in space of a collection of massive bodies, weighted by their masses. For an isolated system this point moves with constance velocity, according to Newtonian mechanics.
double-line spectroscopic binary
binary system in which spectral lines of both stars can be distinguished and seen to shift back and forth as the stars orbit one another