To calculate the dashed orbits from the stellar positions, astronomers had to assume that

a. if they observed for many more years, the dots would trace out ellipses
b. the stars are all main-sequence stars
c. if they observed for many more years, the dots would trace out parabolas
d. the central object has a mass of about 4 million solar masses

Need in all of themmm only answer if you know plsssss

What is friction? how does it affect the motion of an object?

Light from two different sources are incident upon the same side of a polarizing filter. light from one source is polarized with total intensity ip, while light from the other source is unpolarized with total intensity iu. as you rotate the polarizing filter through 360 degrees, the intensity of the transmitted light on the other side varies by a factor of 9. what is the relative intensity of the initial polarized source to the unpolarized source, or ip/iu?