In 1968 NH3 molecules were discovered in gas clouds near the center of our Galaxy. The NH3 molecules showed emission lines in transitions arising from metastable J = K rotational states. NH3 has many transitions at about 1.25 cm; hence, a great deal can be learned about the gas clouds. In particular, 1-1, 2-2, 3-3, 4-4 have excitation temperatures of 24K, 65K, 125K, 203K respectively. Thus, one can determine temperatures very accurately by comparing line strengths to statistical theory. NH3 is particularly useful as an interstellar thermometer since all of these lines can be detected by a single radio telescope with essentially the same beam size. Generally, a telescope measures the antenna temperature TA of an object which is related to the brightness temperature TB of an object by TA=Ωs/ΩA TBj; Ωs/ΩA≤1. TA = TB when Ωs≥ΩA where ΩA is the solid angle of the antenna pattern and Ωs, is the solid angle of the source as seen from the antenna. If measurements can be made with the same telescope, TB for different spectral lines will be simply related to the TA for the lines and one does not have the complication of source size and geometry.