Every once in a while, the stars (or, in this case, satellites) align, and keen observers can receive an unexpected light show. That happened a few weeks ago at the Subaru telescope in Hawai’i. An eerie green laser seemingly appeared out of nowhere, as captured in a YouTube video uploaded to the telescope channel. Luckily, their source was no more ominous than a passing satellite, and with its video posted publicly, now everyone could enjoy the light show.
The most likely cause of the lasers from space is the Daqi-1(or Atmospheric Environment Monitoring) satellite, which contains an Aerosol Carbon Detection Lidar (ACDL) that emits a green laser at the 572nm wavelength. At that frequency, it can determine how much carbon dioxide is in the particular region of space that it’s traversing – a helpful data point for an environmental satellite.
Daqi-1 only launched in April of 2022 and will eventually make up a suite of networked satellites intended to monitor greenhouse gas emissions. It just so happened to be passing above the Subaru telescope that day, and there also happened to be a cloud formation that allowed the lasers to be much more visible than they would be otherwise.
Daqi-1 also isn’t the only satellite that could have made such a display. Originally the NASA satellite ICESat-2 was thought to be the culprit, as it also has a green laser operating at 532 nm. However, it was intended to measure ice sheet elevation and land topography, so not quite the same use case as Daqi-1. Also, the satellite didn’t appear to be over the island at the time.
Overall, this harmless display resulted in a pretty spectacular light show. However, there is a growing chorus among ground-based telescope operators about the increasing number of satellites impinging on their ability to do good science by interrupting long exposure times by passing overhead. We’ve written plenty of articles explaining that elsewhere, but for now, it seems we can expect more unplanned laser light shows to crop up worldwide.
Image of the Daq-1 satellite before launch.
Credit – CNSA
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Composite image from the Subaru telescope video showing a series of green lasers passing above it.
Credit – Subaru Telescope Starcam YouTube Channel