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Rubin Observatory

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The Vera C. Rubin Observatory is the new name for the Large Synoptic Survey Telescope (LSST) currently being constructed in Chile.

The Objective

When it becomes fully operational in October 2022, the observatory will take ten years to photograph all of The Universe it can see. With a field of view of 4° (or about eight times the width of a full moon, it will use a 3.2gigapixel CCD imaging camera – the largest ever constructed – to photograph the entire sky (18,000 sq.°) every three or four nights.

Post processing will compare those photographs with ones already taken, identify what has moved and by how much, and make that information available to astronomers worldwide within 60 seconds. It will map the movement of galaxies in space over time and make it possible to calculate and catalog their masses and observe how they distort space-time. We will better understand the Universe.

The observatory’s job description also includes: [*]

Case Studies

The LSST is the first astronomical observatory to be built for this purpose so any survey of existing facilities will reveal only general characteristics.

Nice Observatory, Nice, France (1886)

The building was designed by Charles Garnier and the dome by Gustave Eiffel*. The dome opening is covered by a panel that retracts, creating the profile we associate with observatories. The interior image shows what was the largest refracting (i.e. glass) telescope at the time. It also shows how Eiffel’s dome rests on a circular drum inside Garnier’s rectilinear building.

Palomar Observatory, California, USA (1928)

Instead of a retractable dome covering, California’s Palomar Observatory has a split sliding arrangement. Assuming similar levels of weatherproofing and mechanical complexity, this double sliding arrangement should require less time to fully open and close.

Sphinx Observatory, Switzerland (since 1937)

The Sphinx Observatorium is built on the ridge between the Swiss peaks of Mönch (left, below) and Jungfrau (right). It is 3,571m above sea level and an astronomical dome and a meteorological dome allow research into meteorology, astronomy, glaciology, physiology, radiation, and cosmic rays.

The observatory now includes four laboratories, a pavilion for cosmic ray research, a library, mechanical workshop, and living quarters for ten. The scientific area includes two large laboratories, a workshop, a weather observation station plus two terraces for experiments.

As the highest man-made structure in Europe, it has viewing decks open to the public. The observatory is reached by elevator shaft trough the mountain.

Indian Astronomical Observatory (IAO), India

Located in Ladakh near the Indian border with China, IAO is one of the world’s highest observatories at 4,500 metres asl. A drum supports a rotatable dome housing the telescope and an attached building houses support facilities.

Caltech Submillimeter Observatory on Mauna Kea, Hawaii, U.S. (1985)

This has an integrated rotating mechanism that doesn’t require a drum for stability. The telescope is exposed when the roof retracts along the circular side rails. Built in an ecologically sensitive part of Hawaii, it is currently decommissioned prior to dismantling.

Extremely Large Telescope, Chile

The ELT is designed to search for Earth-like planets around other stars in the “habitable zones” where life might exist. It has a double-sliding canopy and no drum.

Site Selection

Many astronomical observatories were built in places where atmospheric conditions are no longer suitable for observational astronomy. Newer observatories are typically located in remote areas at high altitude, with little or no precipitation, low temperatures, low humidity, and low levels of atmospheric and light pollution. All these factors result in a high number of clear nights per year and for high-quality images, and occur together in the Chilean mountain range of Cerro Pachón where the the Gemini South (left, below) and Southern Astrophysical Research telescopes (right, below) are already located. The initial construction cost of Rubin Observatory was reduced by sharing their base facilities 100km away at La Serena, as well as their fibre-optic link to relay the 30 terabytes of data the observatory will produce each night.

Site Analysis

The design for the Rubin Observatory summit facility takes advantage of the natural topography of the El Peñón summit on Cerro Pachón. The main telescope enclosure occupies the highest and largest peak, and the attached service and operations building steps down into a saddle area to the southeast.The specific orientation of the summit facility was selected after extensive weather testing and a computational fluid dynamics (CFD) analysis of the site verified that it provided the best seeing environment, or the least air disturbance, for the telescope. Geotechnical studies of the natural rock at the site have shown that it is strong and erosion-resistant. []

28/07/2020 Thanks to Roger who pointed me towards this document  that’s a construction progress report for the summit facilities. Section 2.1.2 contains the following explanation for the  general layout of the summit facility. “One clear implication from the first documentation of environmental conditions was that the prevailing steady wind would be a major factor in shaping the buildings and their relationship to the dome and telescope. Keeping the buildings low and providing turbulence-suppressing treatment on any large structures adjacent to the telescope would help avoid ground-heated air being pushed up into the observing path of the telescope. Also affecting building layout and massing was the available area on the selected site. El Peñón peak is a relatively narrow ridge which is steeply sloped on the approach side. These factors logically favored a multi-level facility stepping down into the saddle between the main peak and a small adjacent hill, which was a convenient location for the smaller calibration telescope facility”. Nice work, Roger!

Technical Solutions

The camera will take a 15-second exposure every 20 seconds. This time is a compromise between a long exposure that would allow faint sources to be spotted and a short exposure that would clearly capture the motion of faster-moving objects. Each field is photographed twice in case one is rendered unusable because of cosmic rays hitting the camera. Repositioning the telescope within five seconds requires a very short and rigid structure but, even so, realigning the mirrors and instruments takes one second and the other four are reserved for the structure to settle down. This short structure means a very small f-number [the ratio of the system’s focal length to the diameter of the lens opening] and that the camera must be focussed with extreme precision.

SLAC National Accelerator Laboratory –, CC BY-SA 4.0,
Todd Mason, Mason Productions Inc. / LSST Corporation., CC BY-SA 4.0,
By Todd Mason, Mason Productions Inc. / LSST Corporation –, CC BY-SA 4.0,

The exceptionally heavy telescope is mounted on a concrete drum for added stability. On top of the drum is the azimuth assembly which is basically a giant motor to realign the telescope. “Magnet motors” are said to allow fast, smooth, and quiet transitions but accuracy of repositioning can’t not be important when distant galaxies are being photographed in order to check if they’ve moved.

This shows the “elevation drive arc” after it was test fitted (in Spain) with aluminum surrogate motor magnets. The motor magnets have been installed in the azimuth track and covered with plywood to keep them from attracting metal fragments during the assembly process.


Concrete base with steel-frame structure and sheet metal cladding. It’s a shed.

This photo of LSST at sunset was taken by Gemini South observer Gianluca Lombardi.

Architectural Solutions

So then, why does the Rubin Observatory look the way it is? Is there any part of it that can’t be justified by function or performance? We find it difficult not to anthropomorphize something that has its highest part concerned with looking and observing even though this is just how visibility works. (Animals may turn their heads but no animal can freely rotate its head through 360°.) But what’s with the body-like shape attached to it? It’s like no other astronomical observatory.

Here’s what.

The telescope enclosure and service and operations building (above) have a stepped-down layout. This design provides a contiguous protected environment for transporting and maintaining the camera and mirrors. The mirrors of LSST are exposed to the night sky and, over the course of the 10-year survey, the mirrors will become dusty and their coatings will develop imperfections that will affect the telescope’s performance. This side facility is for equipment to transport, wash and re-coat the mirrors.

This will happen every two years for the primary mirror and every five for the secondary mirror and will occur in a temperature-controlled space distant from the observatory itself. These heated operations spaces are below the service level with the heat-generating equipment located below that, and farthest from the telescope. An 80-ton platform lift will carry the mirrors and camera between the telescope and maintenance levels as necessary. It’s a bit more complicated than cleaning your glasses.

November 11, 2018 – The Coating Chamber for the Large Synoptic Survey Telescope (LSST) arrived on the summit of Cerro Pachón, safely completing a 15 week journey from Deggendorf, Germany, where it was constructed. The 128-ton Coating Chamber is the largest single piece of equipment to arrive at the LSST observatory site to date, and will soon be joined by the Telescope Mount Assembly (TMA), from Spain, and the 8.4-meter Primary/Tertiary (M1M3) Mirror, from the United States, which are expected to arrive in 2019.
Submitted by LSST Coating Chamber Engineer Tomislav Vucina: Photos of construction of the coating chamber, where LSST’s mirrors will be recoated every few years. We anticipate M1M3 (coated with aluminum) will be cleaned and recoated every 2 years, and M2 (coated with protective silver) every 5 years. Reflectance monitoring will allow us to predict when this more time-intensive work is necessary, and it will likely be coordinated with other scheduled downtime. More information on the washing and coating process can be found at has many more photographs showing all aspects of facility construction from 2015 through to May this year. It’s a brilliant resource.

The construction and operation of the ventilation louvres suggest they’re no more than simple openings to provide ventilation and indirect illumination. It’s unlikely they would all be open at the same time. Any building free to rotate 360° would need openings on all sides if some of them are to always face the optimal direction or directions. The only clue I found on the website was the sentence “Light baffles, wind protection, and thermal controls with natural ventilation and daytime cooling mitigate environmental issues such as ambient light, wind, and large variations in temperature, which can all affect image quality.” Moreover, opening and closing these baffles isn’t dependent on human comfort or judgment as “The Rubin Observatory telescope and facility are designed to be highly automated, requiring little human intervention”.

The folded structure of the washing and re-coating facility is less easy to explain. The high-level windows are definitely well shaded but there are easier ways of achieving this.

This next photograph shows some serious air handling on the lowest level so my guess is that whatever load there is, is reduced by having the shape provide a degree of self-shading at the middle of the day.

28/07/2020 Rather than their primary purpose being self-shading, the folded side surfaces are an example of the previously mentioned “turbulence-suppressing treatment” [provided to] “any large structures adjacent to the telescope [so as to] avoid ground-heated air being pushed up into the observing path of the telescope.”

It’s very difficult to find any information on the design of the observatory or even who or what firm designed it. I could find out about control software architecture and active optics system software architecture but not about architecture. I did find a photograph of representatives from eight US and Chilean Architectural and Engineering companies visiting the site in 2009 but nothing about who was eventually awarded the job. It’s not important we know but, all the same, it suggests that this building designed to assist advancing our understanding of The Universe is not Architecture. I’m good with that.

The closest the Vera C. Rubin Observatory comes to being Architecture is visualizations that render it with

  • no materiality whatsoever
  • disregard for the Sun
    • curious shadows emphasizing the play of light upon volumes in space
    • an improbable position (for 30° 40 14 Slet alone at night)
  • ignorance of the building’s purpose
    • telescope cover open during daytime
    • sunlight hitting the exact place it’s least wanted
  • anthropomophicization
    • emphasis on the “body” with a “head” turning at some “inquisivite” angle
    • ventilation louvres expressively open as if “gills” for “respiration”
  • vehicles and people pointlessly indicating “human scale”
  • an overly dramatic sky

The Vera C. Rubin Observatory

Vera Rubin worked in many fields of observational astronomy but her most important contribution was measuring the discrepancy between the observed rotational rates of galaxies and their predicted rates of rotation. Her work provided strong evidence for the existence of dark matter that Swiss astrophysicist Fritz Zwicky first proposed in 1933 and, by showing that they form inside dark matter, advanced our understanding of galaxies.


*27/07/2020 I corrected the name of the designer of the dome of Nice Observatory to Gustave Eiffel. Thanks to Roger for letting me know.

**28/07/2020 There’s lots of interesting information in this Project Report. Thanks again Roger!


  • A great article, but I think you’ve got your Eiffels mixed up. The Nice Observatory dome was designed by Gustave Eiffel …

    • says:

      Dear Roger,

      Hello again Roger! My emails to your address were returned, but I wanted to thank you for that extra information. It seems that the triple folded roof/walls to the low structure would help to suppress turbulence pushing “ground-heated air up into the observing path of the telescope.” That seems more likely than my self-shading theory, although that would be a bonus if avoiding heat being generated from anywhere is the overriding principle. I’ve updated the post with this new information.

      And thank you for recommending that book about Palomar. I’ll start tracking it down. I’m excited about the title. I think in my googletravels I may have even seen an image of the cover. Palomar is a very handsome observatory.

      And also thanks for sending that construction site report. I’ll definitely go through it. My days are also rather unstructured at present.

      All the best, and thanks again,