Iodine for dinner?


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.

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50 responses

  1. I love the idea of measuring and analyzing starlight. It sounds lovely.
    Also scientifically, this was a very interesting post, although all of the new terms made my head hurt a little.

  2. All the terms made my head hurt a lot. Then I made the mistake of following up with an in-office review of the eye, structure, surgeries, and complications…. I barely passed the test! (stoma, epithelial tear, DLK, myopia, hyperopia, presbyopia… BLEH!)

  3. Sweet mechanical things to play with I know it is a guy thing! But it looks like a fun thing to play with, I can not tell you about the items like that I have bought just to play with also the fun I have had repairing items like those! But again that is what they used to call a guy thing now it is a nerdy or mechanical inclined person and women are getting into it more and more now a days, But to some people work is work and home is home separating them is always a good thing!But I bet he is in his element enjoying playing with this stuff no matter where he is!

  4. Cool, alot of jargon I recognize. I seen Spectrographs. I know the
    Doppler effect. Light is amazing that it is
    both a wave and a particle.
    And then there's gravitational lensing.
    Your astro dweeb must have his own telescopes, what kind are they Emjay?
    I built a 10'' Dobsonian Reflector. Miss it. Someday I would like to build a 16"

    Inferences can be misleading inho.Thanks for the Astro tech stuff!

  5. Well done, Emjay! If you wrote the descriptive text yourself it sounds like a bit o' the "Dweeb" is rubbing off on you. Is the coffee can version of the device going in for calibration at the NIST? Not only a money-saver but a touch of fun in that one! Will these devices go on research outings with him? By the way, ever hear of the magazine "Make"? They usually don't describe creation of high-level scientific instrumentation but certainly the kitchen table construction and scrounged parts fit in with the Maker philosophy. Now, if I can convince my mate to allow me to disassemble and clean my thrft store discovery –a comptometer– on the kitchen table… nah, that won't happen! — JG

  6. I must admit that I started to have that "zoning-out" look on my face when I continued reading. I guess this is a little too technical for me. I just re-read the whole thing again, and finally got to the end of it. Now I see why I liked chemistry more in school. Did you happen to teach Mr. Emjay all these things? 🙂 You can surely teach me, if I were a more obedient student.

  7. Ha! I'm with an audio engineering guy so tons of cables / wires and carp make for a huge storage challenge. But astrodweeb – that's really cool. I like it.

  8. The iodine adsorption cells requires a high resolution echelle spectrometer to be able to work properly so they usually use them on a 3 metre plus telescope (a little big for our backyard LOL). He did build a telescope when he was younger but we do not have one now.

  9. I'm sure to him it is not like a "real" job. The best ones never are; you always feel a little guilty that they are paying you to have all this fun.Seriously cool post and toys. Now if we could just get more folks to understand how the science works! (Including some in the geology community, sad to say…)How many exoplanets has your hubby found? Does he also analyze the light for planetary/stellar composition? Is he looking for newer solar systems or old, established firms?John

  10. I thought it was extremely fascinating. I read it reallllly late last night….early in the morning this morning and I'm fairly sure I understood the concepts. I totally enjoy learning new things.

  11. LOL – after 9 years of marriage (and 3 of dating prior to that) a little of it is rubbing off. I did have to get some help though to make sure it was factual. Yes the coffee can went to NIST – it is almost whimsical – it is going on a telescope in Chile. The cells that were measured are used in telescopes in Australia (AAT), Hawaii (Keck) and Chile.I will have a look for "Make" – I have not heard of it. LOL – the first real job I had was in a finance department, pre-computer, and there was a whole group of comptometrists pounding away on those funky machines! They were incredibly fast with their fingers.

  12. That is oh so cool: the coffee can filter attached to a world-class telescope! All I can say is WOW. The URL for Make is: I understand it, Comptometers were used by engineers in designing the Apollo spacecraft for lunar missions and, as you know, were used well into the 1990s. Great machines, can outperform electronic calculators when under the fingers of a good operator since multiple numbers are entered at once. — JG

  13. LOL – it's all good stuff and you just never know when it will come up in conversation ……(and I'm sure there is still some free space in your brain for a bit more).

  14. LOL – I imagine it is hard to store that sort of "stuff". My ex husband was an Actuary and I laugh now to think that I complained about papers and files being everywhere!

  15. lol, yeah I would think so. No back yard astronomy huh.I used to always go to the Reuben H. Fleet Science Center in SD. Every first Teus of the Mnth, Amateur Astronomers would bring their scopes down for viewing. One night, there was a cool meteor! A bollide.

  16. He and his collaborators have found many extrasolar planets now – I think he has given up counting. It is pretty crowded out there! This technique is suitable for discovering planets orbiting mature, middle aged stars – like the sun. Others use the spectra to measure the chemical composition of nearby sun-like stars.

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