This is what it is really like to be married to an astro-dweeb. Weird nerdy things turn up on the dining room table.
This was our table the week before last
These are Iodine absorption cells attached to temperature controllers.
They are pyrex cylinders about 4 inches long by 2 inches diameter. The ends of the cells are pyrex optical flats which are glass welded to the body by a glass blower.
A crystal of molecular Iodine is placed in the cell and then a vacuum is pumped so that ideally the cell contains nothing but Iodine. Heating the cell above 38 degrees C causes the crystal to evaporate into purple Iodine gas.
There is a thermocouple along the outside of each cell and the cell is wrapped in electrical heating tape. The tape & thermocouple are attached to a temperature controller which runs at a temperature of 50C or 60C.
At the telescope the Iodine cell is mounted directly in front of the entrance slit to a spectrometer. The telescope “collects” light from stars which passes through the cell and enters the spectrometer. Starlight passing through the gas has its spectrum modified. This `reference' spectrum is then compared with unmodified starlight.
So ….. light leaves a stellar surface and travels for many years & decades dodging interstellar clouds and dust until it enters the Solar System where it goes about dodging Solar System dust and asteroids, etc until it enters the earth’s atmosphere.
Finally, if the weather is nice and the telescope pointed in its direction, the light hits the telescope primary mirror which focuses it on the entry slit of the spectrometer. The Iodine cell is mounted directly in front of the spectrometer so that the starlight passes through it before entering the spectrometer. In passing through the Iodine cell, the starlight has the Iodine spectrum “impressed” onto itself. The spectrometer disperses the starlight into its component colours - since the starlight has first passed through the Iodine absorption cell, the dispersed spectrum includes both the stellar spectrum and the Iodine spectrum.
At the end of all this the iodine spectrum is basically a measuring stick whereby they can measure tiny shifts in the stellar spectrum caused by the Doppler effect and can calculate changes in the velocity of the star, allowing them to infer if the star has any planets.
These cells were about to join some others for a week at the US National Institute of Standards and Technology (NIST) to determine the true underlying spectrum & wavelength scale of each cell. This is just a section of the Fourier Spectrometer (FTS) at NIST which was used to do this.