Ashok Gupta
Next year, the world of astronomy is about to get even bigger with the first operational launch of the Vera C. Rubin Observatory. This massive observatory is currently under construction on the summit of Cerro Pachón, a mountain nearly 9,000 feet high in Chile.
The observatory will feature an 8.4-meter telescope that will capture light from distant galaxies and channel it into the world’s largest digital camera, producing incredibly deep images of the entire southern sky.
If you’ve ever wondered how engineers scale digital camera technology from something small enough to fit inside your phone to something big enough to capture entire galaxies, we turned to Rubin Observatory to find out about this unique piece of kit. WebMD spoke to scientist Kevin Reel. It could help uncover some of astronomy’s biggest mysteries.
world’s largest digital camera
On a basic level, the Rubin camera works just like a commercial digital camera in your cell phone – although its technology is actually closer to cell phone cameras from five years ago, as it uses a sensor technology called a CCD. Instead of CMOS, because observatory camera manufacturing started 10 years earlier. The biggest difference is in terms of scale: the resolution of your phone camera can be 10 megapixels, but the Rubin camera has a mind-bending 3,200 megapixels.
To give you a more concrete idea of what 3,200 megapixels would look like, a 378 4K TV screen would be needed to display an image at full size, According to SLAC National Accelerator Laboratory, which is building the camera. With this kind of resolution you can see a golf ball from 15 miles away.
To achieve this type of resolution, every element of the camera hardware needs to be designed and manufactured with extreme precision. One component of a camera that requires particularly careful manufacturing is the lens. There are three lenses to help correct any aberrations in incoming signals, and each should have a completely blemish-free surface.
This is even more difficult to achieve than the precision required for telescope mirrors, as both sides of the lens need to be polished equally. “The challenge is, now, instead of one surface for a mirror, you have two surfaces that have to be perfect,” Reel explained. “All the optics of this observatory — the lenses and the mirrors — they’re the kind of thing that takes years to build.”
Getting the right lenses in the kind of kit needed for this type of telescope isn’t even the hardest part. “It’s a known technique,” Reel said. “It’s tough, but there are companies that know how to make these lenses.”
Where Rubin is pushing the camera with its sensor into rarely trodden ground. With such an insanely high resolution of 3,200 megapixels, the camera’s 189 sensors need to be arranged in an array and tweaked until the exact specifications are reached. Each of these sensors has 16 channels, so that’s a total of 3,024 channels.
“For me personally, the biggest challenge has been the sensors,” Reel said. “To have 16 readout channels and 189 sensors, and read them all at the same time. So data acquisition, and really meet the sensor requirements.”
Those requirements for the sensor are for things like a very low level of read noise – that grainy texture you’ll see when you take a picture in the dark using your cell phone. To reduce this noise, which would interfere with astronomical observations, the sensor is cooled to minus 150 degrees Fahrenheit. But even that can only help so much, so the sensor has to be manufactured very carefully to reduce reading noise – something only a handful of companies in the world can do.
Another issue is with the focal plane of the camera, which has to do with how the camera focuses. To keep this plane perfectly flat, within a few microns, the sensor is mounted on a raft made of silicon carbide, then mounted in the camera.
One important way the camera on a telescope differs from a typical digital camera is in the use of filters. Instead of capturing color images, telescope cameras actually take black-and-white images at different wavelengths. These images can be combined in different ways to select different astronomical features.
To do this, the Rubin camera is equipped with six filters, each of which separates different wavelengths of the electromagnetic spectrum – from ultraviolet, through the visible light spectrum and into the infrared. these are filters large round pieces of glass Those need to be physically moved in front of the camera, so there’s a mechanism attached to the camera to swap them in and out as needed. A wheel spins around the camera body, bringing the needed filter to the top, then a hand takes the filter and slides it into the space between the lenses.
Finally, there’s the shutter. It consists of a two-blade system that slides over the face of the lens and then back to capture an image. “It’s extremely accurate,” said Reel. “The distance between those moving blades and lens number three is very, very close.” This requires careful engineering to ensure that the spacing is exactly right.
looking at the big picture
All of this precision engineering will enable Rubin to be an extremely powerful astronomical instrument. But it’s not as powerful as instruments like the Hubble Space Telescope or the James Webb Space Telescope, which are designed to look at very distant objects. Instead, Rubin will look at entire vast swathes of the sky, surveying the entire sky very quickly.
It will survey the entire southern sky once per week, repeating this task over and over again and collecting approximately 14 terabytes of data each night. By having regularly updated images like this one, astronomers can compare what happened in a given patch of sky last week and what’s there this week – and that helps them catch fast-evolving events like supernovae. It helps to see how they change over time.
So it’s not only using the camera hardware to collect all that data that is a challenge, but also processing it fast enough to make it available to astronomers in time so they can see new events as they happen .
And the data will also be made publicly available. You will be able to select any object in the southern sky and pull up images of that object, or browse through survey data showing the sky in astonishing detail,
a deep, big sky survey
As well as being a resource for astronomers looking to see how a particular object changes over time, the Rubin Observatory will also be important for identifying near-Earth objects. These are asteroids or comets that come close to Earth and could potentially threaten our planet, but which can be difficult to detect because they move across the sky so fast.
With its large mirror and field of view, the Rubin observatory will be able to identify objects that come particularly close to Earth and are called potentially hazardous objects. And because this data is refreshed frequently, it should be able to flag objects that require further study for other telescopes to spot.
But the observatory’s greatest contribution may be in the study of dark matter and dark energy. In fact, the observatory is named after American astronomer Vera C. Rubin, who discovered the first evidence of dark matter through her observations of galaxies in the 1960s and 1970s.
The Rubin Observatory will be able to probe the mysterious substance of dark matter by observing the universe on a very large scale.
“To actually see dark matter – well, you can’t,” explained Reel. “But to really study dark matter, you have to look at the scale of the galaxy.”
By looking at how fast the stars around the edge of the galaxy are spinning, you can work out how much mass must be between those stars and the galactic center. When we do, the mass we can see isn’t enough to explain those rotations — “not even close to enough,” Reel said. So there is a lack of mass that we need to explain. “That’s dark matter,” he says.
The same principle applies to entire clusters of galaxies. By observing the orbits of galaxies within the clusters that Rubin will be able to see with its wider field of view, the observations gain a new level of statistical power. And to study the related phenomenon of dark energy, a hypothetical type of energy that explains the rate of expansion of the universe, astronomers can compare the calculated masses of large objects with their observed masses.
“You get to see every galaxy cluster, and you can’t get much data from the whole sky,” Reel said. “There are real benefits to having a smaller field of view versus all the data available on the subject.”
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