On June 23, the Vera Rubin Observatory telescope, also known as the Simonyi Survey Telescope, will see its first light. This unique instrument has the largest field of view of any large professional instrument. It will detect many objects in the Solar System and beyond.
Starry sky surveys
The Vera Rubin Observatory is a giant telescope that is set to start operating this summer. To be more precise, it should see its first light on June 23, and its full-fledged operation will begin on September 16, 2025.
Many large telescopes in the world have been built and are being built. And some of them are much larger than this astronomical instrument. For example, the mirrors of the Giant Magellan Telescope have a total diameter of 24.5 meters. So why is everyone paying so much attention to a much more modest telescope?
Modern astronomy follows two parallel paths. One of them involves increasing the field of view of the instrument to cover as many objects and phenomena as possible at the same time. The other is the detailed study of individual objects, which requires a large aperture (mirror diameter) that can collect many photons in a short time.
The problem is that telescopes with a wide field of view are usually small, and thus will not show astronomers faint objects. At the same time, large telescopes almost always cover only a tiny area of the sky and can only see the immediate surroundings of an object of interest to scientists. This fundamental discrepancy raises an important question: how can we get both wide and deep views of the sky in a short time?
Compiling catalogs of stars, comets, asteroids, or exoplanets has never ceased to be one of the main tasks of astronomy. This is evidenced by the Gaia space telescope, which has already completed its work, but the data obtained from it will be published for many more years, and discoveries based on it will last for decades.
Historically, the same telescopes were used to survey the starry sky in search of new and interesting things as were used to study specific objects in it. However, after the Second World War, it gradually became clear that the increase in magnification capabilities led to the fact that telescopes collect information from a very small piece of the sky, i.e., they have a very narrow field of view. As a result, it would take too long to survey the entire celestial sphere with their help.
That is why, in the mid-1990s, the concept of the Large Synoptic Survey Telescope, which was later renamed the Simonyi Survey Telescope, emerged. It would combine high magnification with a very wide field of view, allowing it to quickly survey the entire sky and detect new objects.
However, there was not enough money for all the projects. Therefore, there was talk about the importance of such a tool, but funding was allocated mainly to those projects that were of interest to astrophysicists who wanted to unravel the secrets of the Universe.
The case got off the ground only in 2008 after billionaires Bill Gates and Charles Simonyi donated a huge amount of money for the construction. A few years later, the US government joined them. In 2014, the construction of the telescope finally started, and now, a decade later, it is getting ready to start working.
Telescope design
Optical telescopes are based on two basic principles: refraction, i.e., the deflection of rays by lenses, and their reflection by mirrors. The creation of this type of instrument began with lenses, so people think of them mainly in this way. However, mirrors are lighter and easier to manufacture in reality, so for many years, all large telescopes have been built as reflectors.
This works well when looking closely at one small area of the sky. However, if you need to look at a large portion of the sky, spherical mirror systems begin to exhibit a flaw called spherical aberration. Simply put, the parts of the reflective surface that are far from the center distort the light too much, and nothing can be done about it.
That is why the Simonyi Survey Telescope is based on the rather exotic Paul-Baker scheme, which is based on three mirrors as close to flat as possible.
The largest of them has the shape of a wide ring with a diameter of 8.36 meters, it reflects light onto a secondary mirror, also ring-shaped, but with a diameter of 3.6 meters, and it directs it to the third, which is located inside and slightly behind the first and has a diameter of 5 meters.
Thus, the light inside the telescope is reflected not twice, as usual, but three times. However, this is not the end of its journey. Next, it is sent to the camera, where it passes through a system of three lenses, the largest of which has a diameter of 1.55 m, and only then gets to the 3.2 gigapixel light-sensitive matrix, i.e., the number of dots is a hundred times higher than on a professional camera.
All this is done to provide a field of view of 3.5°. For comparison, the cross-section of the Sun and Moon in the sky is only 0.5°. At the same time, the telescope will be moving all the time, making 15-second exposures every 20 seconds. It is expected that in this way it will be able to take up to 200 thousand images annually.
Who is Vera Rubin?
In June 2019, it was announced that the observatory that will house the new telescope will be named after Vera Rubin. The instrument itself retained the name associated with Charles and Lisa Simonyi. This is how they honored the memory of the prominent American scientist. Vera Rubin was one of those astronomers who looked at the universe from a broad perspective.
As early as her doctoral dissertation in 1954, she discovered that most galaxies in the Universe are not scattered randomly but clustered together. Later, she studied the Andromeda Galaxy and other spiral galaxies and found that the motion of the stars in them did not correspond to the predictions of Newtonian gravity.
The analysis of these two facts led her to believe that somewhere in space, there must be a hidden mass, predicted by Fritz Zwicky and later called dark matter.
Rubin herself was not happy about this fact. According to the scientist, it would be better to explain all the discrepancies found by an alternative theory – modified Newtonian dynamics –but her further research refuted this assumption. So the fact that much of the work of scientists is devoted to the search for something they have no idea about, and which hardly manifests itself, is largely to her credit.
What will the new telescope look for?
The tasks facing the Vera Rubin Observatory are in the spirit of the work of the scientist who gave it its name. The first is to find 90% of near-Earth asteroids. Everyone is afraid of stones falling from the sky, but the probability that an asteroid with a diameter of one kilometer will reach us from the outskirts of the Solar System and collide with the Earth over a period commensurate with the duration of civilization is extremely small.
But there are plenty of small fragments of several tens or even hundreds of meters in size, even inside the orbit of Mars. The task of finding most of them was set before American scientists 20 years ago, but since then, it has become clear how difficult it is.
All of these stones are here, close by. But they are too numerous and too small to be caught by conventional methods. And each of them can destroy an entire city if it hits the Earth. And it is the Simonyi Survey Telescope with its wide field of view that can catch them.
Another task that the new telescope will face is the detection of transneptunian objects. Probably everyone has heard about the search for the ninth major planet in the Solar System. Most likely, there is no such planet beyond Neptune, although this is not known for certain.
But there are many bodies with diameters of several hundred kilometers. And astronomers have not yet discovered most of them. But it may be thanks to the new telescope that we will finally map the outskirts of the Solar System properly.
In addition, it is expected to help find many comets and asteroids in other parts of the Galaxy. Another task will be to map the Galaxy. These studies will complement the data obtained from the Gaia space telescope.
Another important task for the Vera Rubin Observatory will be the study of new and supernova stars. On the scale of the Universe, they flash extremely frequently and at the same time have a brightness comparable to globular clusters, or even entire galaxies. Some of them are Type Ia and can be used as “standard candles” for distance measurements.
Modern telescopes could have seen them a long time ago in numbers much larger than they are now. But we simply do not have that many telescopes. And this is also a problem that the new survey telescope should solve.
Finally, the Vera Rubin Observatory will search for evidence of the existence of dark matter. To do this, it will monitor the phenomenon of gravitational lensing, which occurs when a massive object is located between us and a more distant source, and the image of the latter is distorted due to the curvature of space-time by the massive object.
It is expected that all this data will come from the telescope in such large quantities that the team of scientists will simply not have time to process it manually. Therefore, this observatory is also likely to become a testbed for artificial intelligence systems.
