Diffraction spikes

The colorful lines emanating from some of the bright stars in Rubin images are called diffraction spikes. They happen when a bright star’s light bends around support structures as it travels through the telescope’s optical system — primarily the struts holding Rubin’s secondary mirror and camera in place. Light from the brightest stars can bounce around inside the telescope optics, creating a faint halo around the star as well:

Other reflecting telescopes produce diffraction spikes as well, and they each have slightly different diffraction patterns depending on how they’re built and how they operate. Because a telescope always produces the same diffraction spike pattern, you can think of it as a telescope’s fingerprint.

Rubin Observatory’s unique diffraction pattern comes from the specific design of its optics and the supports that hold its secondary mirror and camera in place. Because Rubin’s camera rotates between one exposure and the next, the pattern rotates relative to the sky. When many exposures taken through different filters are combined into a single image, the diffraction spikes can appear as colorful pinwheels around bright stars. Once you know what to look for, you can often recognize a Rubin image on social media or in a news article before you even read where it came from.

Further exploration:

• Learn more about Rubin’s optics on the Rubin technology web page

• Explore Rubin’s Ocean of Stars image in Skyviewer on your own, or take a guided tour