Professional astronomers don’t make discoveries by looking through an eyepiece like you might with a backyard telescope. Instead, they collect digital images in massive cameras attached to large telescopes.
Just as you might have an endless library of digital photos stored in your cellphone, many astronomers collect more photos than they would ever have the time to look at. Instead, astronomers like me look at some of the images, then build algorithms and later use computers to combine and analyze the rest.
But how can we know that the algorithms we write will work, when we don’t even have time to look at all the images? We can practice on some of the images, but one new way to build the best algorithms is to simulate some fake images as accurately as possible.
With fake images, we can customize the exact properties of the objects in the image. That way, we can see if the algorithms we’re training can uncover those properties correctly.
My research group and collaborators have found that the best way to create fake but realistic astronomical images is to painstakingly simulate light and its interaction with everything it encounters. Light is composed of particles called photons, and we can simulate each photon. We wrote a publicly available code to do this called the photon simulator, or PhoSim.
The goal of the PhoSim project is to create realistic fake images that help us understand where distortions in images from real telescopes come from. The fake images help us train programs that sort through images from real telescopes. And the results from studies using PhoSim can also help astronomers correct distortions and defects in their real telescope images.
The data deluge
But first, why is there so much astronomy data in the first place? This is primarily due to the rise of dedicated survey telescopes. A survey telescope maps out a region on the sky rather than just pointing at specific objects.
These observatories all have a large collecting area, a large field of view and a dedicated survey mode to collect as much light over a period of time as possible. Major surveys from the past two decades include the SDSS, Kepler, Blanco-DECam, Subaru HSC, TESS, ZTF and Euclid.
The Vera Rubin Observatory in Chile has recently finished construction and will soon join those. Its survey begins soon after its official “first look” event on June 23, 2025. It will have a particularly strong set of survey capabilities.
The Rubin observatory can look at a region of the sky all at once that is several times larger than the full Moon, and it can survey the entire southern celestial hemisphere every few nights.
The Vera Rubin Observatory will take in lots of light to construct maps of the sky.
Rubin Observatory/NSF/AURA/B. Quint, CC BY-SA
A survey can shed light on practically every topic in astronomy.
Some of the ambitious research questions include: making measurements about dark matter and
