The most distant stars for which we can measure distances with stellar parallax are of light-years away. (Note: Assume the parallax measurements are those possible with the GAIA spacecraft.)

Wave functions describe orbitals in a hydrogen atom. each function is characterized by 3 quantum numbers: n, l, and ml. if the value of n = 2: the quantum number l can have values from to . the total number of orbitals possible at the n = 2 energy level is .