In positron emission tomography (pet), a positron collides with an electron and the two particles disappear in a burst of a) an alpha particle and a gamma ray. b) two beta particles. c) a neutron and an alpha particle. d) two gamma rays

The largest observatory complex in the world is on mauna kea, the tallest mountain on earth. what are some factors astronomers consider when selecting an observatory site? don’t forget practical ones. should astronomers, for example, consider building an observatory on denali (mount mckinley) or mount everest?