It was early Thursday morning when astronomer Matt Muterspaugh noticed something strange with the star he had been observing for the last year and a half. Telescope data taken from the night before showed that the brightness of the star had dipped significantly. He contacted other astronomers who had also been observing the same star, to let them know what he had seen and to keep an eye on it for any more changes. Then by the following morning, the star had dimmed even more.

That’s when he and the others knew it was time to signal the alarm: the weirdest star in our galaxy was acting weird again. And it was time for everyone to look at this distant celestial body — to figure out what the hell is going on. “As far as I can tell, every telescope that can look at it right now is looking at it right now,” Muterspaugh, a professor at Tennessee State University, tells The Verge.

“As far as I can tell, every telescope that can look at it right now is looking at it right now.”

The star Muterspaugh has been looking at is KIC 8462852, though it’s also known as Tabby’s Star. That’s because Tabetha Boyajian, an astronomer at Louisiana State University, first noticed this strange star a couple years ago after looking through archive data from Kepler — a NASA spacecraft that’s been hunting for planets that exist outside of our Solar System. Boyajian was part of a citizen science project called Planet Hunters, where volunteers can analyze Kepler data to look for planets, and they alerted her to the wonky star. “Our users flagged it to be something really interesting,” Boyajian tells The Verge. “They came to the science team and asked, ‘What is this? That’s not a planet clearly.’”

The data showed that KIC 8462852 experienced some extreme fluctuations in brightness, way more than what a passing planet would cause. At one point, the star’s light dimmed by up to 20 percent. It was a huge dip, like nothing that had ever been seen before, indicating something big and irregular may be orbiting around the star.

Then in late 2015, astronomer Jason Wright from Penn State suggested a tantalizing scenario for the dips. Perhaps large megastructures created by an alien civilization were orbiting around the star, explaining the weird changes. “Aliens should always be the very last hypothesis you consider,” Wright told The Atlantic at the time, “but this looked like something you would expect an alien civilization to build.” That’s when Tabby’s Star became popularly known as the “alien megastructure” star.

Of course, astronomers are more focused on a natural explanation: perhaps a huge swarm of giant comets periodically orbits the star. The only way to narrow down the possibilities is to observe the star in real time as the dimming is happening. And all we had were past observations of the fluctuations caught by Kepler. “We were kind of stuck in a spot where we couldn’t do anything,” says Boyajian. “We had all the data we could and to learn anything more we needed to catch it in action again.” The problem, though, is that Tabby’s star is unpredictable. The fluctuations aren’t exactly repetitive and don’t seem to follow any known pattern — making it hard to know when the strange star will be strange again. “Things that change the brightness of a star happen in a very regular pattern,” says Muterspaugh. “And from what we can tell so far, [this star] is not periodic. We cannot predict when it happens, and that makes it very weird.”

astronomers have been observing the star basically around the clock

That’s why astronomers have been observing the star basically around the clock since they first learned of its dimming behavior. To do this, Boyajian started a Kickstarter campaign called “Where’s the Flux?” to secure funding for enough telescope time to continuously monitor the star. The campaign successfully raised more than $100,000, which helped Boyajian and others set up a year-long observation program through the Las Cumbres Observatory, which has telescopes stationed throughout the world. At the same time, Muterspaugh independently set up an observation campaign with the robotic telescopes at the Fairborn Observatory in Arizona. These telescopes are essentially automatic, observing certain targets in the sky on their own when the rest of us are sleeping. Muterspaugh had programmed one of these telescopes to constantly keep an eye on Tabby’s Star. And for the most part, the star has been quiet, behaving more or less like normal.

Then on April 24th, data from Fairborn indicated that the star had dimmed ever so slightly. It wasn’t enough of a change for astronomers to think the star was acting up again, but everyone was still on their guard. There was an idea that this small dip could be a preliminary event before the real thing. And sure enough, nearly a month later, the huge dimming that Kepler saw seems to be happening again.

ALERT:@tsboyajian's star is dipping



This is not a drill.



Astro tweeps on telescopes in the next 48 hours: spectra please! — Jason Wright (@Astro_Wright) May 19, 2017

And it’s really the moment that everyone has been waiting for with Tabby’s Star. It gives astronomers the opportunity to use their entire arsenal of telescopes to observe these fluctuations as they occur. Kepler only observed the light fluctuations in just one broad range of light colors. Now, we can use telescopes to observe the star’s light in numerous colors and light spectrums, and that can give us a better idea of the types of chemicals that are present when these changes occur or the properties of the objects that are blocking the light. For instance, if it is just a bunch of comets, then they’re going to be very close to the star and super hot, according to Jason Wright, and that’s something we can pick up by observing in the infrared spectrum.

If it’s the other theory — the alien one — then it’s unclear what we’ll see. Maybe we’ll see some kind of artificial element associated with the blockage. No one is making any definitive statements just yet, since now is the time to simply observe, and it’s going to be a while before astronomers decode what they see this weekend. So all the theories are still on the table — including the alien megastructures. “That theory is still a valid one,” says Muterspaugh. “We would really hate to go to that, because that’s a pretty major thing. It’d be awesome of course, but as scientists we’re hoping there’s a natural explanation.”

But the good news is we’re going to get a lot of data. Boyajian says the response from the science community has been overwhelming, and everyone who can help right now is doing their best to watch and document changes. “It’s neat to see it turn full circle from citizen scientists who discovered the star and then an opportunity for folks interested in science to follow up and learn more about what this star is,” Boyajian says. “It’s really humbling to work with all these science enthusiasts and have this support for this really interesting star.”

Update May 20th, 11:30AM ET: This post was updated to include quotes and information from Tabetha Boyajian.