Bluewalker-3 satellite was brighter than almost all stars

 Can you still study the stars if they’re drowned out behind bright objects much closer to Earth?

That’s the question that optical astronomers are currently asking, and a new study has looked into the impact that one mega satellite called BlueWalker-3 has had on astronomy.

“The interference of satellites in astronomy has become an increasingly pressing issue over the last few years,” commented first author Sangeetha Nandakumar from the Instituto de Astronomía y Ciencias Planetarias, Universidad de Atacama, Chile.

The research – which was undertaken by an international team of astronomers including those in New Zealand – has been published in Nature.

Bluewalker-3 is an apartment-sized satellite prototype from American company AST SpaceMobile, which is one of many companies looking to low-Earth orbit for creating an internet network.

The satellite is the largest commercial antenna system ever deployed into low-Earth orbit.

“The night sky is a unique laboratory that allows scientists to conduct experiments that cannot be done in terrestrial laboratories. Astronomical observations have provided insights into fundamental physics and other research at the boundaries of our knowledge and changed humanity’s view of our place in the cosmos,” says Imperial College astronomer Dr Dave Clements.

“The pristine night sky is also an important part of humanity’s shared cultural heritage and should be protected for society at large and for future generations.”

Astronomers had first sounded the alarm in September 2022 just after Bluewalker-3 launched. Once it had unfurled, they discovered that it was approximately in the range of the top 50 brightest stars – a magnitude 2.

Now, the research in Nature has looked at Bluewalker-3’s brightness over 130 days, and they confirmed that the peak brightness was a magnitude 0.4 in April earlier this year. This is brighter than the magnitude 2 that they thought, as in this system, the brighter the object, the lower the rating.

This would have made Bluewalker-3 one of the brightest objects in the sky, but still less than Sirius – the brightest star. 

“Optical observations confirm that Bluewalker-3 increases in brightness when Bluewalker-3 is at a higher elevation above the horizon, and indicate that the range between the observer and Bluewalker-3 is a primary contributor to the apparent/observed magnitude,” the researchers wrote in their new paper.  

The researchers also noted that the adaptor that attached BlueWalker-3 to the rocket that took it into orbit had broken away from the satellite. This piece of the satellite exceeded the maximum brightness from the International Astronomical Union and wasn’t added to the public catalogue for four days, which meant that astronomers couldn’t track if the satellite would be above the patch of the night sky they’re imaging.

The team and others in the astronomical community are calling for impact assessments for satellite operators and better data on orbits on all satellites and pieces of satellites to ensure researchers can avoid the worst of the effects.