We ve all used thermometers to measure temperature but sometimes we need to measure temperature in places you (1) __ can t put a thermometer -- for example, inside a rocket engine. One of the best methods for those really hard-to-get-to place is based on laser spectroscopy. Light from a laser point- (2) __ ing at the region of interest is absorbed by molecules and some (3) __ of it are re-emitted back towards the source where it can be (4) __ measured. The re-emitted fight is shifted in frequency (changed in wavelength) by amounts that depend on the molecule and also the temperature and pressure of the surrounding gas be- (5) __ cause of collisions among the molecules. The single, sharp frequency from the laser is thus smeared out into a whole spectrum of frequency whose shape can be used to determine (6) __ the temperature provided so that the molecular transitions and (7) __ line shapes are known. Because it is the main component of the air, it is convenient to use nitrogen since its molecular (8) __ properties are known from room temperature to temperature of about 1,200 degree Celsius from experimental measurements. (9) Although this is a large range, it is far short of what it is needed (10) __ for, some applications.