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.

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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


Ramping up the Refit

This past week, I’ve continued my work supporting the refit of the Mayall 4-meter telescope for the upcoming DESI spectrograph. DESI is the Dark Energy Spectroscopic Instrument and it will be capable of measuring of the spectra of 5000 objects at a time. Its mission objective is to collect data to help us understand the nature of Dark Energy in the universe. We don’t yet know what Dark Energy is, all we really know is that appears to make the expansion of the universe accelerate with time. To be able to collect these 5000 spectra, the telescope needs a new top end. Indeed, the first thing I saw when I came to work on Monday morning was the old top end sitting on a flatbed trailer outside the telescope being ready to go into storage.

The Mayall 4-meter is a reflecting telescope and the primary optical component is a big 4-meter diameter mirror at the bottom. The light from that mirror is then focused at that top end and either collected by a camera sitting there at “prime focus” or a sent down to an instrument underneath the telescope using a secondary mirror. The top end held both the prime focus and the secondary mirror and could be flipped end-for-end to allow either to happen. DESI will have its 5000 fibers in a new top end and indeed, part of the reason for selecting the Mayall was to have a telescope sturdy enough to handle that large an instrument. At the moment, the telescope is missing its top end, but the new one will be installed soon. There are work platforms, which enabled people to loosen the old top end so it could be lifted out with a crane. The work platforms also keep the telescope structurally stable while there’s no top end in place.

The top end only holds part of the instrument. It will have 5000 optical fibers which may be precisely positioned onto target objects. The light from those fibers is sent along the fibers to spectrographs in an environmentally controlled room where the light will be spread out and photographed so it can be analyzed. In the dark energy survey itself, most people will be looking at the so-called redshift—how far the characteristic spectral “fingerprint” of certain chemicals shifts to the red as a result of its velocity away from us. However, those same chemical fingerprints may be used to understand properties of the objects being looked at and this data will be available to anyone who wants to use it.

Because dark energy is an exciting topic in its own right, but also because this project will be generating so much raw data that’s useful to so many astronomers, it’s a major worldwide undertaking. To break the light from the fibers into spectra will require ten spectrographs which will reside in a carefully climate-controlled room. An exciting milestone I got to watch this week, was unpacking the first of those spectrographs when it arrived from France. Below, you can see the engineers inspecting the optical elements. Note the rainbow visible on the corrector plate of the right-most optical element. That’s exactly what this device is built to do! Break the light into rainbows.

Today finds me in Phoenix, Arizona for Leprecon 44. If you’re in town, I hope you’ll drop by and check out some of the panels and workshops.

Refitting the Mayall: Teardown

I was in 8th grade when Star Trek: The Motion Picture came out. One of the things that fascinated me in that movie was the refit of the Starship Enterprise. I was captivated by how the ship looked at once much the same and yet completely different. It looked sleeker and more powerful and familiar space on the ship such as the bridge, sickbay, and the transporter room had all been updated. I’m getting to experience something much like the Enterprise refit in real life. In this case, I’m involved in refitting the Mayall 4-meter telescope at Kitt Peak National Observatory.

Like the Starship Enterprise, the Mayall has a forty-five year history of discovery. Originally built to use photographic plates, the telescope has played an important role in such discoveries as establishing the role of dark matter in the Universe from measurements of galaxy rotation, and determining the scale and structure of the Universe. Over the years, new instrumentation has been added to the telescope including advanced digital cameras and spectrographs.

The purpose of the refit is to install a new instrument called DESI, which stands for Dark Energy Spectroscopic Instrument. 5000 optical fibers will be installed at the telescope’s prime focus (the top end of the telescope) and run to cameras in another room. The goal is to observe tens of millions of galaxies and quasars, constructing a three-dimensional map spanning the nearby universe to 10 billion light years.

In order to achieve this goal, the entire top end of the telescope has to be replaced and much of the control software and electronics are being redone so that it’s truly state of the art. To achieve this goal, we literally have to gut the telescope and install new components from the inside out. During my most recent shifts at the telescope, I’ve been involved in just that. In the photo to the right, you can see that the bottom of the telescope is missing and replaced with scaffolding. That’s because the large 4-meter mirror is out for recoating. Also, all the optics are missing from the secondary mirror assembly at the top of the telescope. Ultimately, that will be removed completely and replaced with a new secondary ring. The men in the photo are removing a counterweight assembly used to precisely balance the telescope when instruments are added and removed. Electrical panels are open on the side of the telescope where control cabling going back to the photographic days will be removed and replaced with new control cabling. Modern electronics mean the telescope will have about 10% of the cables as it did when originally built!

The refit has also allowed me a rare opportunity to see parts of the telescope I’ve never been to before, even after operating it for some thirteen years. Earlier this week I got to help the electronics technicians work on some cabling in the “horseshoe.” That’s the big, blue horseshoe-shaped mount you see in the photos above. We actually ended up working down in the broad, blue, oval-shaped tube you see in the photo just above. I dubbed it the sinking submarine, because it’s a cramped space and we were standing at a 32-degree angle relative to the ground!

It’s going to be exciting to watch the telescope take shape again after the teardown process. New parts will be arriving in the coming months. A large crane will be deployed outside the 4-meter to lift out the old secondary ring and bring in the new one. The plan is to be back on sky to test components of the new instrument later this year. Once those tests are completed, other components will be finished, revised if needed and then installed. At that point, the Mayall’s new five-year mission to map the universe will begin.


Finder Scopes

One of the things I like about working at Kitt Peak National Observatory is that my job has a lot of variety. I contribute to important science projects and I help with engineering that helps to achieve the observatory’s science goals. Sometimes I act as something of a councilor, commiserating with observers during inclement weather. I even get to employ my writing skills when documenting tasks for our operations manuals.

This past week, one project I helped with was testing a new finder scope for the 4-meter telescope. Finder scopes don’t often get a lot of attention, but they serve an important function. Telescopes often give you such an enhanced view of the sky that it’s difficult to know exactly where you’re pointed. A finder scope is simply a smaller telescope mounted to the bigger telescope that lets you see a wide swath of the sky and confirm that you’re looking where you think you should be. Even my 90mm telescope has a finder scope on it. It’s the little tiny telescope piggybacked on the bigger telescope.

Here’s a view of the finder scope mounted to the top of the 4-meter telescope at Kitt Peak. Note that it’s basically just a camera lens directing light into a little digital camera.

This will prove vitally important when we start using the DESI spectrograph on the 4-meter. With that instrument, we’ll have fibers directing most of the light to spectrographs instead of a direct view of the sky. We will have a guide camera, but if, for some reason, the telescope pointing is off, it may be hard to find where we are. Because of that, it’s nice to have a widefield view of the sky. The images taken with the finder scope won’t be the ones you see in most magazines, but still, we played a little while testing and took a nice photo of the Andromeda Galaxy, M31 and it’s companion, M110.

We also took an image of the Pleiades, which is a nearby open cluster visible with the naked eye. These are young stars with nebulosity still around them. Even with our small telescope, it only took 30 seconds to see some of the nebular clouds.

Speaking of variety, another job I did this week was help an astronomer monitor a Jupiter-sized planet as it transited its star. This planet had a rotational period of only 1.6 days and we monitored it with the WIYN telescope at the same time the Kepler Space Telescope monitored it. Having two telescopes monitoring it at the same time allows for scientists to confirm and double check results. The system we were watching is very much like system I wrote about in the anthology A Kepler’s Dozen. You can learn more about the book and find places to order at http://www.davidleesummers.com/Keplers-Dozen.html. The book gives a unique look at the types of worlds discovered by the Kepler Space Telescope. My co-editor on the project was Dr. Steve B. Howell, head of the Astronomy and Astrobiology Division at NASA’s Ames Research Center.