National Astronomical Observatory of Japan

NAOJ Statement on the Potential Impairment of Astronomical Observations by Satellite Mega-Constellations

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Thanks to communication and broadcasting satellites, we can enjoy fulfilling lives in modern society. For example, we can view satellite television programs all over the country and our cellphones can tell us our exact location on the globe by receiving signals from the U.S. Global Positioning System (GPS) and Japan’s Quasi-Zenith Satellite System (QZSS) “Michibiki.”

On the other hand, because these satellites reflect sunlight optical/infrared telescopes for astronomy recognize them as “artificial stars.” Also, radiocommunications between satellites and the ground can impair radio astronomy observations. Given this situation, we have been striving to protect and preserve the environment for astronomy observations and established the Spectrum Management Office on April 1, 2019.

SpaceX, a U.S.-based private space company, started launching Starlink satellites on May 24, 2019, aiming to provide global internet access through satellite communications. This first batch of the satellites numbered only 60, but SpaceX plans to establish a mega-constellation network eventually consisting of nearly 12,000 satellites. It is expected that once the satellite constellation is completed, approximately 200 satellites (or artificial stars) will always be visible in the sky. In fact, the Lowell Observatory in Arizona has already had an image it was taking of galaxies streaked by a number of diagonal trails left by light reflected from the Starlink satellites.

In response to this, the International Astronomical Union (IAU) issued a statement on June 3, 2019, expressing concern about the impairments that mega-constellations like Starlink can cause for astronomy observations. The concerns expressed in this statement included not only the potential impairment of optical observations, but also the possible effects from radiocommunications between satellites and the ground on radio astronomy observations.

As the central organization for astronomy in Japan, the National Astronomical Observatory of Japan (NAOJ) develops and operates research facilities including the Subaru Telescope and ALMA, and has achieved a number of outstanding results. The Universe and the starry heavens are invaluable treasures for all of humanity. In order for us to better understand the Universe, we need to keep our “sky” transparent to a wide range of electromagnetic wavelengths. Therefore, we believe that our primary mission is to work side-by-side with the IAU and other astronomical observatories around the world, in asking for the cooperation of satellite-related businesses to seek possible solutions.

We ask for your understanding and support as we address this issue.

(English translation of a statement first issued in Japanese on July 9, 2019.)

Starlink trains observed on 21:52 JST, May 25, 2019. (Credit: Hiratsuka City Museum)

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