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Simons Observatory @simonsobservatory.org · 20/07/2026

Time for our annual meeting at U Toronto! Do you have any questions for the astrophysicists there? #astronomy

A phototgraph of people seated in a lecture theater with laptops in front of some of them while a few people are on the stage showing a video projected on a screen.

Simons Observatory @simonsobservatory.org · 13/05/2026

Happy 60th birthday to physicist Uroš Seljak, born on 13 May 1966 in Slovenia, who coined the term "B-mode" and figured out with others that we could probe the era of inflation with the Cosmic Microwave Background in 1996-1997. 30 years later, we (and others) are on the hunt for them!

A series of swirly black lines are overlaid on a blue-green background with a yellow band in the middle, distorting it. This image won a 2019 wikimedia competition for science images. Uros' explanation:

"Scientists believe our Universe started with a rapid expansion, during which tiny quantum seeds were imprinted into the fabric of spacetime, leading in time to creation of galaxies, stars and planets, including the Earth. To prove this theory scientists are searching for B-modes, a spiral type of polarization imprinted in the microwave sky. However, Milky Way emits dust, which is also polarized, and scientists must learn how to distinguish the two signals.

This image was created by taking dust emission as measured from the Planck satellite and converting its intensity into a polarization pattern. The bright yellow band is Milky Way as seen in the microwave sky. A B-mode was imprinted into a single spot by locally rotating the dust polarization pattern by 45 degrees. A hilly landscape was added at the bottom to represent that many of the B-mode experiments are ground based, in places from Antarctica to Atacama desert in Chile.

This picture is a great example of a teamwork in science and could not have been made without the input of numerous people. Special thanks to the Planck satellite team who observed and made public the data this is based on, Susan Clark for the original inspiration, Yu Feng for the data processing and Andrej Berlot for the post-processing. "

A photograph, seen from behind and under, an SO Small Aperture Telescope (SAT) is pointing at the night sky. It is a white cylinder attached to a mount and partly covered by a tarp. A large vertical jackscrew controls the elevation orientation of the telescope. Thick red cables can be seen exiting from the side of the telescope at the edge of the image.

Uros Seljak, standing behind a podium speaking into a microphone. He is a White man with brown hair and greying temples wearing a dark grey suit, a white shirt and a blue-grey tie. Behind him are three flags: EU, Slovenian, and the University of Ljubljana.

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Simons Observatory @simonsobservatory.org · 21/04/2026

Congrats to Simons Observatory members Colin Hill and @msyriac.bsky.social for receiving the Breakthrough New Horizons Prize in Physics for work on CMB lensing! Our LAT is raring to go and image the gravitational lensing of the CMB deeper than ever before! (Credit: SO/O. Kusiak/K. Perez Sarmiento)

A map of blobs in grayscale, that correspond to the gravitational lensing measured by the SO LAT in a small part of the sky (the edges of the image give the dimensions in degrees. The whole patch is roughly 15x45 degrees

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Simons Observatory @simonsobservatory.org · 10/03/2026

POV: You're an observatory 🔭 in a remote part of the world but somehow aren't worried about this whole "oil price spike" thing. An important part of our Advanced Simons Observatory grant was to make our observatory mostly #SolarPowered Image credit: Dr Benjamin Schmitt, U Penn

The photovoltaïc array of the Simons Observatory nearly complete in the Atacama Desert. Mountains are visible in the distance of the earthy landscape, small clouds drift in the blue sky above.

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Simons Observatory @simonsobservatory.org · 26/02/2026

Our Large Aperture Telescope making friends last December.🧪🔭 Nuestro Telescopio de Gran Apertura haciendo un amigo el pasado diciembre. Image Credit: Federico Nati

A yellow-orange vicuna (kind of looks like a miniature lama) stands in the foreground of a white structure in a rocky landscape. The structure has two parts: a U-shaped part, to which is attached a rectangular box with one side open. The box part looks like it can rotate on its attachement axis.

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Simons Observatory @simonsobservatory.org · 26/02/2026

The Northeastern US wasn't the only place with snowfall last weekend... It also snowed at our site, nestled at 5200m above sea level in the Atacama desert! ¡El fin de semana pasado nevó en nuestro observatorio, situado a 5200 m sobre el nivel del mar en el desierto de Atacama!🔭 Image: Niklas Tampier

Steps in the snow. In the background, some funnel-like structures can be seen set against a blue sky.

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Simons Observatory @simonsobservatory.org · 19/12/2025

On the sixth day of CMBmas my telescope gave to me: Six SATs a-funding FIVE SCORE PAPERS Four parts of Stokes Three fine SATs 🔭 Two optics designs and a low PWV We have a new paper out, presenting how we are expanding the SAT side of SO, to detect B-modes ever better. arxiv.org/abs/2512.15833

A timeline of the SAT construction and operations. A box reads: "SAT science: Searching for the signature of primordial gravitational waves generated in the early Universe"
The timeline indicates 3 SATS/36000 detectors observing from 2024 to 2027, and 6 SATs/62000 detectors from 2027 to 2035. Four of the SATs are labelled 90/145GHz, one is labelled 225/280GHz, one 27/39GHz. The uncertainty on r (sigma r) drops to 0.001 in 2035, compared to 0.003 in 2028.

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Simons Observatory @simonsobservatory.org · 18/12/2025

On the fourth day of CMBmas, my telescope gave to me: Four Stokes components Three working SATs 🔭 Two optics designs and a low PWV Any light can be decomposed into the four so-called Stokes parameters: total intensity I, two linear polarizations Q and U, and circular V. SO measures I, Q and U.

A diagram illustrating the three possible polarizations of light. The x and y axes of an electrical field are labelled in black. For light coming out of the screen towards you, the linear polarization Q, in red, makes a + cross shape along those x and y axes, U, in blue, is rotated by 45° and makes an x shape. A green circle with two arrows on it attempts to represent circular polarization V.

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Simons Observatory @simonsobservatory.org · 17/12/2025

On the third day of CMBmas, my telescope gave to me: Three working SATs 🔭 Two optical designs and a low PWV Last winter, we fixed a cracked lens in one of our Small Aperture Telescopes. We put it back on its' platform and it's now scanning the sky again. (Timelapse made by Josh Borrow, UPenn)

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Simons Observatory @simonsobservatory.org · 15/12/2025

On the second day of CMBmas, my telescope gave to me: Two optical designs 🔭🧪 and a low PWV We are fielding both refractors and a reflector in the Atacama Desert, (see our two previous threads for explainers!) bsky.app/profile/simo... bsky.app/profile/simo... Image credit: Elle Shaw

A view of the Atacama desert on the shoulder of a mountain. In the foreground, the SO LAT stands, like a 10m tall searchlight painted white. In the background, on the left, some big upturned funnels can be seen: they shield our delicate SATs from having to see the mountain.

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Simons Observatory @simonsobservatory.org · 15/12/2025

On the first day of CMBmas, the observatory Had a low PWV Telescopes like us are inconvenienced by water in the atmosphere emitting/blocking microwaves (same reason why a microwave heats food well). Luckily, the #Atacama desert has one of the lowest Precipitable Water Vapour amounts Earth.

A Mercator map of the world with the countries outlined. The map is mostly white, but Greenland, Tibet, the Andean Plateau and Antarctica are colored in various shades of blue. The legend indicates this means lower amounts of precipitable water vapor. The color scale goes from 0 to 5, with antarcitca the closest to 0, Greenland , Chile and Tibet sit between 1 and 2.5

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Simons Observatory @simonsobservatory.org · 24/07/2025

We're having our collaboration meeting this week! Many of our members went to the University of Manchester, many more are online. Kudos to the local team for an adorable logo (with a pun in it of course) 🐝-modes are the sweetest honey! #AstroSci

A group of about a hundred people arrayed outdoors on a lawn in front of a multi-story brick building detailed with oxidized copper panels. The sky is grey but they are smiling

A roundel with written "Simons Observatory" on top and "Face-2-face Manchester 2025" at the bottom. The roundel shows the Manchester skyline in grey on a black background. A stylized telescope at the bottom left shines a light at a white and orange pixel-art bee.

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Simons Observatory @simonsobservatory.org · 26/06/2025

Cool results from our cousins at the South Pole Telescope! 🔭 With our Large Aperture Telescope, we hope to reach a similarly exquisite sensitivity as they do on their green patch over a large sky area (that I crudely outlined in blue).

An oval projection of the full night sky, with the galaxy forming a wispy horseshoe figure through it. several trapezoids of color cover different parts of it. The original caption reads:
"FIG. 3. Footprints of the SPT-3G surveys—Main (green filled area), Summer (orange filled area), and Wide (red filled area)—shown alongside the ACT DR6 survey mask (blue solid line). We show Galactic dust as measured by Planck in the background [45] and indicate the most contaminated region with the Planck GAL080 mask as shown in gray shading with a white border. This work is based on observations of the SPT-3G Main field. The combination of the SPT-3G Main, SPT-3G
Summer, and SPT-3G Wide fields will constitute the Ext-10k field, which will probe 25% of the sky with low noise and high resolution."

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Simons Observatory @simonsobservatory.org · 06/05/2025

OK, who was throwing a rave inside the Large Aperture Telescope 🔭? (Image credit: Prof. Suzanne Staggs, Princeton)

A night photo of a large building-sized telescope. The building is in two parts: a big u-shaped structure is mounted on a pivot, and itself ensnares a smaller brick-shaped box that can swivel with a hole in it. Some rocks in the background are visible in yellow, illuminated by an unseen source. Red safety lights at the bottom of the U element and ice blue light from within the telescope's opening complete the scene

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Simons Observatory @simonsobservatory.org · 28/04/2025

We had snow last week at our site! Our telescopes 🔭 like being cold, our teams not so much. Here you are looking inside the sun-shield of one of the SO SATs, the actual lenses and the focal plane sit beneath that shiny cover, cooled to cryogenic temperatures. Image credit: Dr Elle Shaw, UT Austin

A front view of one of the SO Small aperture telescopes from up close. The top half of the image is filled by a conical structure we are looking into: its inside is covered with a white, wallpaper looking structure. There is snow piled up on the bottom lip of the cone. At the end of the cone is an aluminium foil cover.
Beneath and behind the cone you can see a white metal platform that holds the rest of the telescope, including its mount. Various surfaces are covered in snow, black cables meander around the scene.
In the background, a deep blue sky and a shiny screen that provides additional sun and terrain shielding.

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Simons Observatory @simonsobservatory.org · 10/04/2025

This week, we are trying to assess performance of our Large Aperture Telescope by looking at the planet Mars. For our telescope, it appears as a point, so we can understand our optical response and pointing by observing it. Image credit: Mark Devlin. ☄️🔭

The Simons Observatory LAT with its aperture open, looking at the sky at night. Red safety lights illuminate the bottom of the telescope structure, while a few stars shine in the background.

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Simons Observatory @simonsobservatory.org · 17/03/2025

We have first light on our Large Aperture Telescope! www.simonsfoundation.org/2025/03/17/s... After installing our mirrors over the last few weeks, we have started looking at the sky. We are still tuning the telescope, but we can already make maps of objects in the sky, like Mars. ☄️🔭🧪

A green dot (Mars) surrounded by a white ring on a purple background. A faint white x pattern is visible

One of the mirrors being lowered by crane inside the white box that constitutes the LAT housing. Behind it is the barren landscape of the Atacama desert

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Simons Observatory @simonsobservatory.org · 13/03/2025

We have a brand new website! simonsobservatory.org Go check it out for information on what we do, recent publications, and cool images. 🧪🔭

A drone view of the Atacama desert on a clear day with the SO site in the foreground.

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Simons Observatory @simonsobservatory.org · 04/03/2025

The second preprint is about our small aperture telescopes. We ran simulations to forecast how much of a problem shifts in the shape of our beam within a band (color corrections/chromaticity) would be for our cosmological analysis. arxiv.org/abs/2503.01791 This project was led by Nadia Dachlythra.🔭☄️

$A figure with four panels showing oscillating, roughly exponential lines in different colors between blue and yellow. The caption reads: Figure 1. Logarithmic profiles of five monochromatic co-polar beam maps generated for each of the 93 (top left), 145 (top right), 225 (bottom left), and 280 GHz bands (bottom right), using TICRA TOOLS software. Each set of (five) maps is produced at frequencies of uniform spacing across the full frequency range of the corresponding band. All bands are assumed to have 25% fractional width, and all beam maps are generated for a detector on the center of the focal plane of a simulated three-lens refracting telescope.$

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Simons Observatory @simonsobservatory.org · 04/03/2025

We have two preprints out on the arXiv today 🔭☄️! The first one is about an #NSFFunded upgrade to our Large Aperture Telescope, roughly doubling the number of detectors in it: arxiv.org/abs/2503.00636 enabling us to probe the sky deeper than ever. The paper was led by Susan Clark and Colin Hill.

A timeline of the LAT's status between 2020 and 2034. Construction lasts until 2025, the LAT gets upgraded sometimes in 2028, sensitivity raises with time to 2.5 microK/arcmin over 20000 square degrees. 3d renders show the LAT and the focal plane getting filled up

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Simons Observatory @simonsobservatory.org · 21/02/2025

P.S. At this point, since @evevavagiakis.bsky.social is not writing this post, I can mention her children's book with adorable little neutrinos if you want to learn more about them. www.penguinrandomhouse.com/books/706338... 9/8

Cover of an MIT Kids Press book called "I'm a neutrino - Tiny particles in a big Universe." Some doodly neutrinos are tumbling in front of a pastel spiral galaxy

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Simons Observatory @simonsobservatory.org · 21/02/2025

This is a scale-dependent effect, so we know how to identify it. It is also sensitive to the mass of the relativistic particles zipping through. That includes neutrinos! (Image from the CMB-S4 science book arxiv.org/abs/1610.02743) 7/8

A series of curves of the CMB lensing power spectrum with changing colors matching to specific sums of neutrino masses.
The caption below it says: The effect of massive neutrinos on the matter power spectrum and CMB lensing power spectrum. Top Left: The effect of neutrino mass on the matter power spectrum. Top Right: The change to the matter power spectrum relative to the case with massless neutrinos. Bottom Left: The projected matter power spectrum observed through CMB lensing shows the same suppression with neutrino mass. Bottom Right: The relative change to the lensing potential power spectrum.

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Simons Observatory @simonsobservatory.org · 21/02/2025

Because the LAT has a much larger mirror, it can resolve finer details on the sky. The resolution is roughly 1/40th of a degree, about the same as someone with a 6/10-7/10 vision. This makes us able to see the small deflection of CMB light by matter's gravity. (Image credit: ESA/Planck) 3/8

An illustration of gravitational lensing by large scale structure. We are viewing a brick-shaped slice of the Universe in perspective. At the far end, the blue-orange Planck map emits some rays. Those wind through a purple haze that represents the matter of the universe organizing into filaments, walls and voids. at the front of the brick the haze has condensed into a web-like structure.

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Simons Observatory @simonsobservatory.org · 21/02/2025

As we are putting the finishing touches on our Large Aperture Telescope 🔭, now might be a good time to explain what science goals it serves. The problem is that there are many to choose from! (Image credit: Mark Devlin) 1/8

A large aluminium mirror made of square panels is being attached to a metallic truss structure inside a housing by several people. The people are less than a third the size of the mirror. The top of the mirror is attached to a wooden beam that is itself attached to some ropes that disappear towards what we assume to be a crane beyond the top of the image.

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Simons Observatory @simonsobservatory.org · 15/02/2025

Fog can't stop us from installing our last mirror 🔭 Image credit: Toby Satterthwaite

A large aluminium mirror made of square panels is being lifted by a crane on a foggy day. Many ropes are connected to it to control the hoist

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Simons Observatory @simonsobservatory.org · 14/02/2025

Do not flip 6m secondary mirrors without experienced PI supervision and heavy duty equipment. Do not try this at home. 🔭 Image credit: Mark Devlin

A crane is lifting one end of a big rectangular trussed structure that contains the LAT secondary mirror covered by a tarp. The structure is therefore pivoting around one of its corners, the large edge is ~30º off the ground already. In the background is a foggy mountain.

The crate is now more vertical, maybe flipped 70º towards its short base.

A shot from further away. The structure is now resting on its narrow face. Two persons in a cherry picker inspect the tarp. The structure is anchored in place with big ropes. In the background the LAT awaits.

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Simons Observatory @simonsobservatory.org · 10/02/2025

Big day! The primary mirror is in the LAT! Credit: Elle Shaw

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Simons Observatory @simonsobservatory.org · 06/02/2025

PSA: Lift 6m mirrors with your crane, not with your back

A view of the SO site in the Atacama desert. A crane is lifting a large wooden box in front of the Large Aperture Telescope building.

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Simons Observatory @simonsobservatory.org · 04/02/2025

SATs and stars 📸 Elle Shaw, Felipe Carrero

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Simons Observatory @simonsobservatory.org · 30/01/2025

Sneak peek at one of our LAT mirrors in its crate. Everything appears to go ok. Image credit: Mark Devlin

A view inside a big wooden crate. On the left are wooden slats, on which a mirror made of square panels rests. The mirror extends diagonally towards the top right of the image, its other end fading in darkness. At the top of the image is a tarp deformed by the water accumulated in it. At the bottom, the edge of the mirror can be seen, resting on its back structure.

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Simons Observatory @simonsobservatory.org · 30/01/2025

No, it's because all smurfs are blue.

A blue panel with three ports, two of which are connected by a bright blue cable. To the left of the image is the name of the contraption: a SMuRF

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Simons Observatory @simonsobservatory.org · 29/01/2025

Happy Lunar New Year! Common snakes in the Atacama desert include the cabling that links the detectors in our telescopes 🔭 to the readout system. The readout was designed at SLAC (cmb.sites.stanford.edu/slac-microre...), can you guess why it is painted blue? Image credit: Nick Galitzki

A mass of blue cables link a panel on the left of the image to a server-rack looking contraption on the right. The panel on the left is affixed to a larger metal structure with tubes running along it. The server-contraption is sitting on a table, twice as tall as a thermos in the foreground.

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Simons Observatory @simonsobservatory.org · 24/01/2025

We're at the site! Who's ready for a craning montage? #astronomy

A very large wooden box (approx 2.5x8x8m) being hoisted by an erector crane in front of the SImons Observatory LAT building. Several people are in the foreground, almost toy figurines compared to the scale of the box and the telescope.

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Simons Observatory @simonsobservatory.org · 22/01/2025

The mirrors for our Large Aperture Telescope are on their way to our site! 🔭

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Simons Observatory @simonsobservatory.org · 21/01/2025

This is the main job of our small aperture telescopes (the SATs). We have three so far (funded by @simonsfoundation.org), but got funding to add three more thanks to some of our members in Japan and the UK! Next time, I'll talk about the LAT and how it will help us achieve our science goals. 8/8

An SO SAT is in the foreground. It looks like a big funnel mounted on a swivel pivot, surrounded by various boxes that hold parts of the telescope's controls. In the background is the ground screen, a tall circular wall that stops the telescope from seeing the terrain around.
At the top is an evening sky with faint pink and orange clouds.

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Simons Observatory @simonsobservatory.org · 21/01/2025

We are searching in the polarization of the CMB for a pattern called B-modes that can only be generated by primordial gravitational waves, which are a generic prediction of inflation models. (Image credit: Lucy Reading-Ikkanda/Simons Foundation) 7/8

A poster made by the Simons foundation explaining SO's search for the B-modes.

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Simons Observatory @simonsobservatory.org · 21/01/2025

Our main tool is a family of telescopes we assemble and operate in the Atacama desert in Chile. (Image credit: Hovercal/polocalc teams) 2/8

A view of the SO site from a drone. In the center of a desolate mountain landscape, the SO site is visible. The one "Large Aperture Telescope", several stories tall, on its mount, is in front. A little distance from it are three round enclosures that contain the "Small Aperture Telescopes". In the background other CMB telescopes are visible: the ground shield of the defunct Atacama Cosmology Telescope, the CLASS telescopes, and the Simons Array.

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Simons Observatory @simonsobservatory.org · 21/01/2025

Hello everyone! As an introduction: we are a global collaboration dedicated to exploring the microwave sky with members based on every continent except Antarctica (although some of us go there on occasion). 1/8

More than a hundred people standing in a plaza in rows on a summer day. Behind them are some trees and a glass facade.

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