Stars, Galaxies, and Fiber Optics

The first time I remember learning about fiber optics was in a behind-the-scenes article published in 1980 or so about the making of Star Trek: The Motion Picture. The article talked about how they got light to all the buttons on the bridge set and showed them illuminated with bundles of optical fiber. Nowadays, as I’ve mentioned in several earlier posts, I work with instruments that use optical fiber to carry light collected by each of the telescopes I work with to the instrumentation where its analyzed.

On the telescope side, those fibers are attached to an optical assembly that must be placed at just the right spot to catch focused light. If the star or galaxy is out of focus, not all the light goes down the optical fiber. We also have guider cameras that work to keep the object precisely aligned on the fiber so all the light gets to the spectrograph. It’s a lot of complex hardware to work right to precisely measure the the redshift of distant galaxies or look at a star and determine whether or not it has planets in orbit. This past week, we’ve been commissioning both the DESI spectrograph at the Mayall 4-meter and the NEID spectrograph at the WIYN 3.5-meter. One of the most important milestones is to get light from the object you want to measure to the spectrograph and see if you get the flux you expect. Here’s the NEID team at WIYN looking at early test results.

Yes, light leaves a star dozens of light years away, enters our telescope, goes down the optical fiber and is photographed with the spectroscope, then all that data can be viewed and analyzed on a laptop computer. When I filmed the trailer for The Astronomer’s Crypt a couple of years ago, I was asked why we didn’t use a room full of fancy computers and monitors. We just had a couple of computers, one of which was a laptop. The reason is that I’ve seen a lot of control rooms where simple computers are the only ones present!

As you can imagine, it’s quite a relief to see all the work pay off in a spectrum that shows the flux level you expect. All of this is pretty exciting stuff and, as it turns out, my birthday fell during this past week’s tests. Seeing NEID as it nears readiness for scientific use is pretty exciting in its own right, but we had another surprise on the day of my birthday. Ethan Peck, who plays Spock on Star Trek Discovery, was on a road trip and decided to visit the observatory. A tour was arranged and he spent the beginning of the night at the WIYN telescope. For me, it was quite a thrill to have Spock, of all people, wish me a happy birthday! He brought a Polaroid camera with him and we snapped a photo of us standing by my control station. Here we are at WIYN. Ethan Peck is in the center (in white) and I’m to the left.

Meanwhile, across the mountain at the Mayall 4-meter, commissioning has continued on the DESI instrument. The instrument had its official “first light” a couple of weeks ago and a wonderful image was released that, I think, really illustrates the power of DESI.

Image credit: DESI Collaboration, Legacy Surveys; NSF’s National Optical-Infrared Astronomy Research Laboratory/NSF/AURA

Here you see an image of all 5000 DESI fibers superimposed on the sky. At the bottom of the fiber array is M33, the Triangulum Galaxy. Below that is a view of the spectrum from just one of the 5000 fibers showing the light from that little piece of the galaxy. In it, you can see the lines labeled that denote the presence of hydrogen, oxygen, nitrogen, and even sulfur. Now remember that each fiber in that picture gives the same kind of data for the piece of sky its on. You can read the full press release about DESI’s first light at: https://nationalastro.org/news/desis-5000-eyes-open-as-kitt-peak-telescope-prepares-to-map-space-and-time/

All of the robotic positioners moving those fibers at the top of the Mayall telescope get hot and there’s a chiller system to keep them cool. This week, that chiller system will be automated, but last week, we had to monitor it by eye and it requires a person to turn the system on and off by hand. The person doing that remarked how spooky it is to be in the depths of the Mayall with all the lights out and remarked how she kept looking over her shoulder, wondering if someone was there. This is another aspect of my job that definitely helped to inspire The Astronomer’s Crypt. You can learn more about the novel and see the trailer I mentioned earlier at http://www.davidleesummers/Astronomers-Crypt.html.

Cable Wrangling

In previous posts about the DESI spectrograph being installed at Kitt Peak’s Mayall 4-meter telescope, I’ve focused on the 5000 robotic positioners at the telescope’s focal plane, which is up at the top of the telescope, and the ten spectrographs located in a climate controlled room at the telescope’s base. However, I haven’t talked a lot about how the light from the 5000 positioners gets down to those spectrographs. The light travels along optical fibers that run from the telescope’s focal plane down to the room with the spectrographs. The whole distance is roughly 40-meters (or a little less than the length of half a football field).

In the photo to the left, you can see the cables running along the front of the telescope at this angle. They’re draped over the blue horseshoe structure in the foreground. Several of the cables are draped down in the lower left-hand side of the photo. There are ten cables that run from the top of the telescope to the room with the spectrographs. Each cable contains 500 individual optical fibers. Each of these cable bundles feeds one of the spectrographs at the telescope’s base. Since each cable contains 500 optical fibers, they are heavy cables. They’re also very fragile. It would be challenging enough to run these fibers from one point to another if they could be locked down in one position. However, the telescope actually has to move, so we can look at different parts of the sky. This means these heavy, fragile cable bundles have to move too.

Before construction even began on the DESI spectrograph, engineers spent time figuring out the best way to run the cables that minimized how much they had to move. Also, there are devices called e-chains that help assure cables stay nice and neat as the telescope moves. This past week, one of the engineers snapped a photo of me helping to prepare one of the e-chains for installation. He was in a lift up near the telescope’s top and looked down at me and another one of the telescope engineers hard at work. I’m the one in the yellow hard hat.

As I mentioned earlier, these cables are both heavy and fragile. That means there’s been a lot of heavy lifting that requires a great deal of care about where we step and place the cables. We don’t want to bend them too tightly, or they could break. The upshot is that this has been exhausting work. Everyone feels wiped out at the end of the day.

Still, we see the proverbial light at the end of the tunnel, or perhaps that should be the light at the end of the fiber! Once the cables are run, we only need to install the last three spectrographs, then the system will be complete. How soon we’ll start observing with the DESI spectrograph will depend on the results of preliminary testing which has already commenced and will be finished soon after the installation is complete. That said, I am told there’s a very good chance we’ll be pointing DESI at targets on the sky in less than a month. At that point, we may start to understand more about this mysterious thing that astronomers have dubbed dark energy.

DESI Naked!

This weekend finds me at Bubonicon 51 in Albuquerque, New Mexico. I’m moderating panels about space cowboys and large scale scientific surveys. If you’re in town, click the link to get the details and drop by. I’d love to see you there. Of course, part of my interest in large scale scientific surveys has to do with the work I’ve been helping with over the last year and a half, installing the DESI Spectrograph at the Mayall 4-meter telescope at Kitt Peak National Observatory. During my my recent shift at the observatory, I got a rare look at the new instrument not just “under the hood” but before the hood even went on.

In the photo above, you see DESI on the left, just over the orange platform. Standing on the ground floor in the foreground are just a few of the telescope engineers and technicians who have been installing this new, innovative instrument which will be used to make a 3D map of about a third of the known universe. DESI itself is an array of 5000 fibers mounted on robot positioners that can be precisely centered on targets each time the telescope moves. The light from those objects then travels down fibers two stories below. The fiber bundles are ready to be run along the telescope. You see them coiled up on the white carts to the lower right of the photo above. Each black cable contains 500 fibers. One of my jobs this week was labeling those cables so people can keep it straight which cable is which as they run them along the telescope.

Here are all the DESI fiber positioners mounted to the telescope. You can see each of the ten cables coming up into ten sets of fiber positioner “petals.” Each of these petals was installed into the telescope with great care about a month ago. Light was placed on all the fibers and it was confirmed that in all the transportation and installation, none of the fibers were broken. All of them transmit light as expected! This week, the control electronics are being wired up and routed through the telescope. Once this chore is complete, more testing will happen to assure that the fibers still transmit light and each of the robot positioners moves as expected using the electronics routed through the telescope.

All of those fibers will eventually come into a clean room downstairs to a series of ten spectrographs. Do you begin to sense a pattern? Ten petals, ten cables, ten spectrographs. As it turns out, another job of mine this week was helping to install the seventh spectrograph, which you see in the lower right of the photo above. Western fan that I am, I feel like you can now cue Elmer Bernstein’s score for The Magnificent Seven. Of course, that won’t last long. soon we’ll have an eighth, ninth, and tenth spectrograph.

Each of those spectrographs will be used to examine the light from 500 fibers. To make the map, we’ll be using these spectrographs to see how far characteristic chemical lines in spectra have shifted from where they normally sit within the rainbow toward the red end, which is one measure of how far away those objects are. We’ll compare that to statistics of how far apart they are, which turns out to be another measure of how far away they are. That said, just because we’re mostly looking for the redshifts, there will be all kinds of other spectral data available that can tell astronomers all kinds of information about properties of galaxies all over the sky. One of the most exciting things about the DESI program is that this data will be available to all. In this post, I may be laying DESI bare for all to see, but the whole project will be laying much of the universe bare, and in the process expanding the body of astronomical knowledge.

  • For a fictional and frightening look behind the scenes at an astronomical observatory, read The Astronomer’s Crypt.
  • To take a tour through the wonders of the solar system, read The Solar Sea.
  • To travel back in time to the Old West, check out Owl Dance!

Practice Makes Perfect

I spent last week at Kitt Peak National Observatory assisting with the installation of the Dark Energy Spectrographic Instrument on the Mayall 4-meter Telescope. We spent a couple of months running the refurbished telescope through its paces on the sky with a simple commissioning camera and now it’s time to finish installing the complete instrument. As we get ready to install this complex array of 5000 robot-positioned fibers that feed ten spectrographs, I find myself thinking of the old saw “practice makes perfect.” Well, how exactly do you practice building and installing an instrument no one has built and installed before? As it turns out, there are ways to do this.

One of the major tasks this week has been “dummy” petal installation. The photo above shows a view of the 4-meter telescope from the top. We’re facing the primary mirror (which is covered with white covers that say “Danger: No Step”). In front of that, and right in front of the camera is the prime focus assembly. The 4-meter mirror focuses light into the prime focus assembly. In the old days, a camera sat there. Now there will be 5000-optical fibers aligned with objects on the sky by robot positioners. Those robot positioners are quite delicate and take up a lot of room, so a test petal has been created. The petals fit in the pie-shaped wedges you see in the photo. The dummy petal is the one with Swiss cheese, like holes. It’s carefully guided into position by the red mechanical assembly. Lasers are used to make sure the petal is positioned very carefully and put in at just the right place. Here’s what one of the real petals looks like.

The entire fiber petal sits in the silver box. The black structure on the right is the same size and shape as the Swiss cheese dummy petal. Behind that is a tightly packed array of delicate fibers. The real petal above will have to be placed precisely without breaking anything. So, in this case, we practice by creating a mockup to try out all the procedures and check that we know what we’re doing before we start installing all the really delicate, expensive instrumentation. There will be ten petals like the one in the photo above and light from their fibers will go down to ten spectrographs two floors below the telescope. We currently have six of those spectrographs installed in a clean room.

Currently, three of the spectrographs are in the lower layer of racks. Three are in the upper layer of racks. The spectrographs are where the real science happens. Light that comes down the fibers is spread apart into a literal rainbow and we can see the characteristic fingerprint of the chemical elements of the objects that each fiber in the spectrograph is pointed to.

The spectrographs and the petals remind us that practice makes perfect when you do things repeated times. We’re practicing with the dummy petal, but then we’ll install ten real petals. We’ve installed six spectrographs and we have four more to go. Each time we take another step forward, the easier the process becomes.

Of course, practice made perfect on our way to building these spectrographs in the first place. We built other, smaller fiber spectrographs and learned lessons from their construction. We’ve learned about robotics and we’ve learned lessons from other people who also work in the field by following their work.

Writing is much like this. You practice by doing. You might start with some short stories to get the hang of writing. Then you might try your hand at a novel chapter, then you’ll write another. All the while, you should keep reading to see what others are doing and have done. You’ll learn techniques as you try them out. You will likely encounter difficulties, but as you keep reading, you’ll be sensitive to those difficulties and you’ll see how others have solved them. This is just one of the ways that science has taught me to be a better writer and being a writer has taught me to be better at the science work I do.

You can learn more about my writing at http://www.davidleesummers.com

The Backbeat of the Universe

This past week, I’ve been helping to re-commission the Mayall 4-meter telescope at Kitt Peak National Observatory and commission the first components of the new DESI spectrograph that we’ve been installing. In nautical terms, you can think of this as being like a shakedown cruise. We’re making sure the telescope is primed for taking scientific data and we want to assure we’ve worked out all the kinks from the telescope sitting idle for a year while it was rebuilt. We’re also making sure the components of the new instrument work as expected.

I have mentioned in previous posts that DESI is a spectrograph fed by 5000 optical fibers, each of which can be positioned to sit on a specific target in the sky. Those 5000 fibers have not yet been installed. What we have now is more of an optical camera installed at the top of the telescope in the black “can” at the top of the picture in this post. That allows us to evaluate the image quality through the telescope and make sure the light from objects on the sky will actually fall on those 5000 fibers when they’re installed.

We also have the guider that will be used with DESI. A telescope like the 4-meter is designed to track the sky with great precision, but because it’s such a large real-world machine, imperfections always creep in, so we have a camera that watches the sky and makes fine corrections to the telescope’s pointing as it tracks the sky. The commissioning instrument we have on now, will let us put the guider through its paces.

The goal of the DESI’s five-year mission is to make a three-dimensional map of about one-third of the entire sky, by giving us not only precise positions of every object we can see in that area, but by giving us distance as well. So, how can DESI do this? It takes advantage of something cool that happened in the early universe.

Everywhere you look in the sky, as far away as we can see, which also means as far back in time as we can look, is something called the cosmic microwave background. This is the universe as it looked about 400,000 years after the Big Bang. Given that the universe is 14 billion years old, that’s a long time ago! Before the epoch of the cosmic microwave background, light was bound up and couldn’t escape. At 400,000 years, the universe had expanded enough that that light and heat could escape, but there was enough gravity to try to keep that from happening. These competing forces set up acoustic waves throughout the universe. These acoustic waves were everywhere and they collided, setting up beat frequencies. These beat frequencies helped to set up localized points of gravity which drew material inwards. In the fullness of times, those localized points would become galaxies. Here’s what the universe looked like at that time.

Image courtesy WMAP Science Team

Now here’s the cool part, because we understand acoustic theory, we can predict how far apart these localized points will be and we can look to see if galaxies tend to be distributed as you would predict from looking at these acoustic waves. In fact, they are. Galaxies today tend to be separated by factors of about 500 million light years. Statistically, they’re much more likely to be at some factor of that than say, 400 or 600 million light years.

If you know how far apart galaxies are today and you know how far apart the acoustic beats were in the primordial universe, you can use geometry to look at more distant galaxies. We used to use how far a galaxy’s chemical fingerprint was shifted toward the red end of the spectrum as a way to measure distance to those galaxies. However, that assumes you understand the rate the universe is expanding. The separation between galaxies at the same redshift, will tell you how far away they actually are without making assumptions about the way the universe expands.

I will be speaking more about this and the DESI project at two astronomy club meetings in the next month. The first presentation will be for the Astronomical Society of Las Cruces on Friday, April 26 at 7pm. The meetings are held at the Good Samaritan Village in Las Cruces, New Mexico. More information about the location is available at: https://aslc-nm.org/MonthlyMeeting.html.

My other presentation will be given to the Phoenix Astronomical Society in Phoenix, Arizona on May 9 at 7:30pm. You can find more details about the location at: http://www.pasaz.org/index.php?pageid=meetings.

Lasers on Telescopes

For me, the phrase “lasers on telescopes” brings to mind super villains capturing top secret astronomical facilities in order to execute a nefarious plan. I think of Mr. Freeze capturing Gotham Observatory to build a giant freeze ray in the movie Batman and Robin. Perhaps a funnier and better example is Chairface Chippendale using a laser in a telescope to deface the moon with his name in the TV series The Tick.

Laser measuring tool (on yellow arm between black mirror covers) over the Mayall primary mirror.

In fact, lasers are used on telescopes. Perhaps the best known real-world examples are telescopes that use laser guide stars. This is a technique where astronomers fire a laser mounted on the telescope into the sky. The laser light is scattered by the atmosphere, but optics in the telescope correct that light back into the proper size beam and also correct the stars seen at the same time. We had a system like that at the 2.1-meter telescope at Kitt Peak run by CalTech. There was also a system like that at the 3.5-meter telescope at New Mexico’s Apache Point Observatory.

Now, these lasers are not ones that are likely to be co-opted for nefarious purposes by super villains. Lasers used for guide stars just aren’t that powerful. That said, they can’t be used with impunity. The artificial guide star laser at Kitt Peak was visible in the ultraviolet band and would interfere with optical telescopes also observing in that band. What’s more, I’ve been told Apache Point Observatory had to clear laser firings with the Air Force, who had a base nearby. The observatory’s laser wasn’t likely to shoot down planes, but we could imagine tragic results if a pilot happened to fly through a laser’s line of sight only to be blinded.

This past week, while working at the Mayall 4-meter telescope, we were also using a laser. In this case, it wasn’t fired at the sky, but the laser was mounted on the telescope’s mirror cell and fired at different surfaces on the telescope to get precise measurements. Now that the refit for DESI is nearing completion, the engineers need to make sure everything went back together as it was designed. They need to make sure all the new parts are placed in just the right place. If not, this is the time to make adjustments. Measurements of telescopes are important because they help to assure that astronomers can focus the telescope properly. Precise measurements are also critical to determine the proper weight distribution of the telescope, which in turn helps it track the sky precisely.

As it turns out, I also spent part of this past week working on an adaptive optics system a little like those laser systems I mentioned. However, the WIYN Tip-Tilt Module doesn’t actually use a laser. Instead, it takes precision measurements of an actual star and uses optics within the instrument to bring that star as close as possible to a precise point. I’ve seen it used to deliver incredible image quality with stars only 0.3 arcsecs across. To put that in perspective, star images with WIYN are typically more like 0.8 arcsec across. The size difference is the result of atmospheric blurring.

This all echoes something I’ve been saying in the past few blog posts. If something isn’t quite right, there are ways to fix it, even when its a multi-million dollar scientific project. By comparison, books are much easier to fix. It’s why beta readers and editors are so important to the writing process. They help us see places where we didn’t express ourselves clearly, made something work in an artificial way, or simply used the wrong word. It’s part of why reviews are so important. Reviews help customers, but they also help writers because they tell them what worked and didn’t work.

Over the years, reviews helped me refine my craft until I could write books like Owl Riders and Firebrandt’s Legacy. And yes, reviews are helping me shape the 25th anniversary edition of The Pirates of Sufiro, which I’m working on right now. I hope you’ll join me on a journey to one of the worlds I’ve created and, if you do, please leave a review to let me and others know what you thought. The titles in this paragraph are links where you can get more information about the books.

Reassembling the Mayall

Back in July, I discussed some of the different components that had come in for the DESI instrument being installed at Kitt Peak National Observatory’s Mayall 4-meter telescope. You can read about them in the post, Assembling the Puzzle. The corrector optics and hexapod alignment system have been installed into the telescope’s top end. Here I am, hard at work torquing the bolts that hold it all together.

If all goes according to schedule, the new top end will be lifted to the top of the telescope next week. At that point, the telescope will look more like itself again. Control cables and network boxes for the top end assembly will then be assembled so astronomers working in the control room can talk to the instrument. At that point, the work platforms that are visible in the older post will be disassembled. Here’s a look at the top end, almost ready to lift up to the top of the top of the telescope.

Once the top end is back on the telescope, the primary mirror, which is currently out of the telescope, will need to be re-aluminized. Telescope mirrors are finely polished, curved glass. Over the top surface is a very thin layer of aluminum which is applied in a vacuum chamber. The vacuum chamber for this process is the biggest one in the southwestern United States. I describe a scary scene involving such a chamber in my novel The Astronomer’s Crypt. Fortunately, care is taken to operate the chamber very safely in real life.

One thing to note about the top end in the photos above is that there is no actual instrument mounted yet. Astronomers rarely sit at an eyepiece actually looking through a telescope anymore. Most of the time, there’s a high precision digital camera looking through the telescope. Sometimes that high precision camera is designed to look at a specific wavelength region, such as optical light or infrared light. Sometimes that camera doesn’t look at the sky directly, but at light that’s been reflected off a grating. A grating is just a reflecting surface that breaks up light like a prism. The advantage to a grating is that you lose less light than you do when you shoot it through a chunk of glass. Breaking up light then allows you to see lines in spectra that tell you about the chemistry of the object you’re looking at.

In a nutshell, that’s the kind of instrument DESI is. Astronomers are interested in the chemistry of the objects they’re looking at. However, there’s one other feature you get by studying these spectral lines. When an object moves, the lines shift toward the blue end of the spectrum if the object is moving toward the observer or toward the red end of the spectrum if the object is moving away. That’s what we mean when we talk about blue shift and red shift. What’s more, how far the chemical lines have shifted is a measure of the object’s velocity through space. The goal of DESI is to measure the velocity of some 5000 objects every time the telescope points to a new target. That said, this data will be available to everyone and it contains all the fundamental chemical information about the objects the telescope is pointing at.

Before the final DESI instrument goes on, there will be a commissioning instrument. That will be more like a regular camera—more like looking through an eyepiece. The goal of the commissioning instrument will be to align the telescope on the sky after all this work has been done and assure that the telescope has good pointing so that we can get the best data when we’re using the spectrographs later.

Once the commissioning instrument goes on the telescope, I’ll return to my regular nighttime duties at the Mayall, shaking down the rebuilt telescope and getting it ready for its next five year mission. My novel, The Astronomer’s Crypt, which I mentioned in passing, is not just a horror novel, but it provides a look behind the scenes at an observatory. If you’re interested in seeing what goes on at night at a facility like Kitt Peak, or one of the other observatories where I’ve worked over the years, it’s a great place to start. Just be warned, not only will you encounter astronomers, engineers and technicians, but some ghosts, a monster from Apache lore, and a few other surprises as well. You can get more information about the novel at: http://www.davidleesummers.com/Astronomers-Crypt.html