Alert!

The night sky is full of objects that change in brightness or move through our Solar System, but if we're not looking in the right place at the right time we'll miss them — especially if they’re far away or don’t give off much light. Rubin Observatory was designed specifically to detect changes in the sky on a broad scale and to alert us to each one. Rubin automatically compares new images to older images to detect changes in an object's position or brightness, and it generates an alert for each change it observes. If a star explodes or an asteroid moves across the sky, Rubin will catch it in the act.

There are a couple of reasons Rubin Observatory is particularly good at detecting changes. First, the telescope moves so quickly that it revisits the same area of sky every few nights, which means it can frequently capture images of the same objects. Second, Rubin Observatory's light-collecting power and sensitive camera ensure that even faint or faraway objects that change will trigger an alert. Rubin's combination of speed and imaging power helps it detect a lot of action — about ten million alerts are generated every single night! This constant series of alerts is called the "alert stream."

But can you imagine getting ten million alerts on your computer or your phone? To deal with this potentially-overwhelming alert stream, Rubin Observatory alerts will be directed to “community brokers” — software systems that ingest, process, and serve astronomical alerts from Rubin and other surveys to the broader scientific community. The brokers add additional contextual data to each alert, which might include light curve analysis and/or classification into types using machine learning. This information allows scientists to identify and prioritize objects for follow-up observations.

Rubin’s alerts are world-public; anyone can access them by visiting the website of one of Rubin’s alert brokers. Scientists filter these alerts according to their research interest — for example, a scientist studying near-Earth asteroids can use a broker’s dashboard tools to identify and focus on alerts related to these asteroids. Meanwhile, Rubin keeps searching the sky for more action.