You repeated the same question twice but the answer is hypothesis.
Answer:
Spectroscopy
Explanation:
Spectroscopy is a tool that scientists typically use to determine the mass, structur and the temperature of stars or other objects within the observable universe.
In general, scientists take a spectrum of the object they observe using a spectrograph. It is based on the theory that the lines of absorption at a given wavelength are special for each element.
Hence, the correct answer is spectroscopy or spectrograph.
Rhenium is the very dangerous (hazard wise) it should be handled carefully and you should understand that THIS should not be taken lightly I hope this helps!:)
Gravity can be such a tricky subject to talk about I wish I could answer this I need to study more
