Why do the moon and earth have shadows? how much of the sun would you see if you were standing in the umbra?
how much of the sun would you see if you were standing in the penumbra?

Asingle-molecule microscopy experiment is performed on a slide containing 1000 molecules each of green, red, cyan, and yellow fluorescent proteins (gfp, rfp, cfp, and yfp, respectively). the experiment measures the number of antibodies bound to each type of protein, finding that 900 molecules of gfp, 10 of rfp, 1 of cfp, and 3 of yfp are bound at 1 nm concentration of antibody. a. what is the specificity of the antibody for gfp? b. what is the kd of the gfp–antibody interaction?