Light Curves for Binaries
identify a binary star from the light curve and deduce its
period
explain the causes of
variability in the light curve of a binary star
The brightness of some objects in the sky does not remain constant over a measurable period of time. There are a number of possible reasons why.
Variable stars
The absolute magnitude of some stars changes over a period of days because
of the physics of what is actually happening inside the star. One such type of
star is called a Cepheid variable (because the first example was found in the
constellation of Cephius).
Why its brightness varies is to do with the balance between the nuclear and gravitational forces inside the star.
Binary stars
Imagine a pair of stars in orbit around each other in the plane lined up
with our line of sight. As they eclipse each other the amount of light we see
falls.
The actual shape of the light curve will depend on the relative size and shape of the stars and on how much they eclipse each other. If their plane of rotation is parallel to our line of sight then the larger star will completely eclipse smaller one.
Supernovae
When a giant star collapses it does so spectacularly with an explosion. The shock wave may stimulate the production of new stars in nebulae by causing regions of gas and dust to collapse. Depending on how massive the star was we may end up with a neutron star or possibly even a black hole. A supernova explosion is seen as a big increase in brightness which lasts for just a few days before it fades. In 1054 Chinese and Arab astronomers observed a supernova in Taurus. A supernova remnant, the Crab Nebula, is now observed in the same place.