Bright BlueWalker 3 satellite concerns astronomers

Telescope dome with Milky Way in background and long bright line of BlueWalker 3 in front.
BlueWalker 3 (BW3) leaves trails in the night sky. The breaks in the trail are from the breaks in the 4 20-second exposures used to create this image. The Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona stands in the foreground. Image via KPNO/ NOIRLab/ IAU/ SKAO/ NSF/ AURA/ R. Sparks.

New satellite raises concerns

BlueWalker 3 (BW3), a new communications satellite from AST SpaceMobile, is raising worries within the world’s community of professional astronomers. The International Astronomical Union (IAU) issued an announcement on November 28, 2022, voicing its concerns. AST SpaceMobile launched the massive satellite in September 2022. Unfurled, it’s now more than 26 feet per side (about 8 meters per side) and can be as bright as the brightest stars (around first magnitude), according to the IAU. BW3 is currently the largest commercial communications satellite in low-Earth orbit, and the company has plans to eventually launch six of these satellites per month, with possibly more than 100 in total.

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The IAU on BlueWalker 3

The IAU said that BW3 has become one of the brightest objects in the night sky. At times, it is as bright as magnitude 1, which is on par with some of the brightest stars in the sky, such as Antares or Spica (the 15th and 16th brightest stars in the night sky).

It’s not just the visible brightness that astronomers find concerning. It’s also the strong radio waves that BW3 and its successors will emit. These radio waves will interfere with the work of astronomers. The director-general of the Square Kilometer Array Observatory, Philip Diamond, said:

Astronomers build radio telescopes as far away as possible from human activity, looking for places on the planet where there is limited or no cell phone coverage. Frequencies allocated to cell phones are already challenging to observe even in radio quiet zones we have created for our facilities. New satellites such as BW3 have the potential to worsen this situation and compromise our ability to do science if not properly mitigated.

Piero Benvenuti, director of the IAU Center for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS), said:

BlueWalker 3 is a big shift in the constellation satellite issue and should give us all reason to pause.

The announcement stated:

The IAU and CPS partners recognize that the new satellite constellations have an important role in improving worldwide communications. However, their interference with astronomical observations could severely hamper progress in our understanding of the cosmos. Their deployment should therefore be conducted with due consideration of their side effects and with efforts made to minimize their impact on astronomy.

How to see BlueWalker 3

People have reported seeing BW3 pass overhead in dark skies, comparing it to some of the brightest stars. In the tweet below, you can see the satellite passing through the bowl of the Big Dipper. The short streak of light that is BW3 looks every bit as bright as the second magnitude stars in the bowl.

If you want to see for yourself just how bright BW3 is in your skies, visit to find when it will pass over your area. Satellites shine due to reflecting sunlight from high over Earth, so when they fall completely in Earth’s shadow, they disappear from view. Therefore, the couple of hours after sunset and before sunrise are when you’ll have an opportunity to see BW3.

Originally, had question marks in the boxes for magnitude. But now that the satellite has an established orbit with many sightings, the magnitude boxes have numbers. For my location, the brightest pass in the next week will be magnitude 2.4, similar in brightness to Phecda, the bottom star in the Big Dipper’s bowl. Check the site to see if the satellite will be close to magnitude 1 from your location.

The IAU would like you to submit your observations of BW3 to better understand the effects of the new satellite.

Personal observations of the new satellite

I observed BW3 for three nights in a row in late November. On all three nights (November 20, 21 and 22), the satellite took a similar path across the sky and appeared close to third magnitude. Each time it cut across the sky near Jupiter. When it was lower near the horizon, I was unable to spot it due to light pollution. Not until it was closer to 25 degrees high in the sky could I spot it from the background murk. Below are some of the simple, handheld iPhone videos I took of the passes.

In this first video, you can spot the dim light (similar in brightness to other satellites) passing just below Jupiter:

In the second, shorter video, you’ll want to look straight above Jupiter for the little light moving off to the upper left.

What is BlueWalker 3?

AST SpaceMobile described BW3 in relation to its milestone of unfurling:

BW3 is the largest-ever commercial communications array deployed in low-Earth orbit and is designed to communicate directly with cellular devices via 3GPP standard frequencies at 5G speeds. Now that it has been unfolded, the satellite spans 693 square feet [64 square meters] in size, a design feature critical to support a space-based cellular broadband network. The satellite is expected to have a field of view of over 300,000 square miles [777,000 square kilometers] on the surface of the Earth.

Abel Avellan, Chairman and Chief Executive Officer of AST SpaceMobile, said:

The successful unfolding of BlueWalker 3 is a major step forward for our patented space-based cellular broadband technology and paves the way for the ongoing production of our BlueBird satellites.

A statement from AST SpaceMobile

Dave Mosher from AST SpaceMobile reached out to EarthSky with the following statement:

AST SpaceMobile’s mission is to help solve the major global problem of lack of connectivity, which affects billions of people around the world. We are building the first and only space-based cellular broadband network — one that is designed to provide coverage to areas currently beyond the reach of today’s networks.

Our planned network aims to connect devices around the world and support a universal good. Cellular broadband for more people globally would help ease poverty, support economic development, build a more equitable and diverse digital society, and save lives.

We are eager to use the newest technologies and strategies to mitigate possible impacts to astronomy. We are actively working with industry experts on the latest innovations, including next-generation anti-reflective materials. We are also engaged with NASA and certain working groups within the astronomy community to participate in advanced industry solutions, including potential operational interventions.

As part of this work, AST SpaceMobile is committed to avoiding broadcasts inside or adjacent to the National Radio Quiet Zone (NRQZ) in the US and additional radioastronomy locations that are not officially recognized, as required or needed. We also plan to place gateway antennas far away from the NRQZ and other radio-quiet zones that are important to astronomy.

While other constellations may require thousands of satellites — there could be as many as 58,000 in orbit by 2030, according to a recent US government report — we plan to provide substantial global coverage with a network of 168 or fewer satellites.

Increasingly crowded skies

The issue of increasing satellites in our skies is becoming a familiar complaint. How can humans balance the racing technological advances but still preserve our dark skies?

Astronomers are trying to work with the satellite companies such as SpaceX with its burgeoning Starlink satellites to find some kind of compromise. You can read more in How satellites harm astronomy: what’s being done.

Bottom line: BlueWalker 3 is a bright new satellite in our skies. The IAU has raised the alarm over this satellite and others like it, which could interfere with astronomical research.

November 29, 2022

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