Results of Massive Satellite tv for pc Constellations on Astronomy – Explaining Science


Lots of you should have seen the pictures again in 2019 which confirmed  lengthy ‘trains’ composed of as much as sixty SpaceX Starlink satellites crossing the sky in a straight line. These photos hit the headlines not solely due to the variety of satellites, however due to their brightness.

A ‘practice’ of SpaceX Starlink satellites, the satellites are round 300 km in altitude. Within the days after launch these trains break up because the satellites place themselves into their ultimate orbits at round 550 km altitude.

The satellites are nonetheless being launched in batches of sixty at a time and their objective  is to supply worldwide quick web protection. Conventional satellite tv for pc web operators have a small variety of satellites in geostationary orbit (GEO), 35 800 km above the  Earth’s floor. This limits response instances, protection and bandwidth. It takes round 0.12 seconds for radio-waves to journey between the satellite tv for pc and the Earth.

SpaceX’s plan is to encompass the Earth with numerous satellites in Low Earth Orbit (LEO). This presents significantly better response instances and larger capability than GEO satellites. The plan is that the community of Starlink satellites will develop over the subsequent few years forming a ‘floating web spine’, offering a sooner various to the fibreoptic cables that span the world.

Satellite constellations Rebuilding internet

At time of scripting this publish,  SpaceX have launched 2282 Starlink satellites, all in orbits round 550 km above the Earth.  2062 of those satellites are nonetheless in orbit. (A lot of the satellites launched in 2019 had been check satellites which have been deliberately deorbited.)  They’ve been given approval by the U.S. Federal Communications Fee (FCC) to launch as much as 12000 satellites  and  are in search of permission to place a further 30 000 Starlink satellites into orbit.  To place these numbers into perspective, within the sixty 5 years for the reason that launch of Sputnik-1 again in 1957, almost 13 000 satellites have been positioned into Earth orbit, of which 5300 are nonetheless working. So round 40% of  functioning satellites are SpaceX Starlinks!

Satellite constellations satellites in orbit

Supply  ESA

Different Operators

Excessive pace satellite tv for pc broadband is prone to be an enormous progress space sooner or later, as a result of it presents entry to web with out want for an costly mounted line infrastructure, which could be troublesome and really expensive to construct in distant areas.   By 2040, it might be value in extra of 400 billion {dollars} every year. So, it’s not stunning that different corporations are planning comparable massive LEO satellite tv for pc constellations. Though none of those corporations appear to have plans as bold as SpaceX or have launched as many satellites.


OneWeb are British firm partially owned by the UK authorities. They’ve constructed an preliminary constellation of 428 satellites, which can be expanded as demand for his or her service grows.

Satellite constellations OneWeb2

In contrast to SpaceX Starlink, OneWeb are aiming their service to companies, governments  departments, telephone community operators and different organisations slightly then particular person shoppers.

Amazon – Undertaking Kuiper

Amazon plan to launch  a constellation of 3236 satellites. A growth referred to as undertaking Kuiper. As but no satellites have been launched, the primary launches are deliberate this yr (2022). So they’re just a few years behind SpaceX, however they intend to be an enormous participant in a rising market and Amazon have huge monetary muscle.  By way of turnover Amazon is among the largest corporations on our planet (2021 turnover was $470 billion) and in 2020 it was reported that Amazon would make investments $10 billion in Undertaking Kuiper.

Satellite constellations Amazon


The Canadian firm Telesat have a constellation of 298 LEO satellite tv for pc, which it plans to increase to round 1700 satellites within the close to future.

Satellite constellations Telesat

Impression on astronomy

There was a lot written within the press in the previous few years concerning the influence of those satellite tv for pc constellations on astronomy (not all of  these studies have been correct). In comparison with astronomical objects and satellites in larger orbits, LEO Satellites transfer quickly throughout the sky and are on the whole brighter than different satellites as a result of they’re nearer to Earth.

Nonetheless LEO satellites spend a lot of the evening within the Earth’s shadow and are solely seen within the twilight hours. That is described additional within the video on the finish of this publish.

Satellite constellations LEO

A satellite tv for pc in a Low Earth orbit will spent roughly half of its orbit within the Earth’s shadow when will probably be invisible to an observer as a result of it’s not illuminated by the Solar

House X have been partaking with the astronomical neighborhood to scale back the brightness of the Starlink satellites. The  lengthy trains of satellites seen simply after launch are a brief formation, which break up because the satellites disperse and transfer to their larger orbits 550 km above the Earth. All Starlink satellites launched since August 2020 have a visor fitted which reduces the quantity of daylight mirrored again to Earth by an element of three. A latest examine discovered that the typical magnitude of Starlink satellite tv for pc fitted with the visor was +5.92 – making them solely simply seen to the bare eye, when considered by somebody with good eyesight at a location with out vital mild air pollution.

In uncooked astronomical photos satellites are generally captured once they transfer throughout a telescope’s subject of view. They seem as streaks, wanting a bit like meteor trails. Nonetheless, picture processing software program utilized by astronomers (together with amateurs) can determine satellite tv for pc tracks and strip them out of the ultimate photos.

This would possibly current extra of a difficulty if the variety of LEO satellites had been to extend twenty-fold within the subsequent 15 years. Somewhat than a picture containing a single satellite tv for pc path, a typical picture taken within the twilight hours would include a number of trails, as quite a few satellites crossed the sphere of view.

The big telescope being constructed on the Vera Rubin observatory could also be notably badly affected. It has an 8.4 metre major mirror (giving it a really excessive sensitivity) and likewise a really massive detector giving it a really massive of view – so many satellites shall be captured in its photos. It is a subject I mentioned in a earlier publish. 

LSST Rubin Observatory

Impression on radio astronomy

Radio astronomy is allotted protected bands during which radio transmitters, together with these on satellites, are forbidden to function. Examples of protected bands are

  • the area round 1.420 MHz referred to as ‘the 21-cm hydrogen line’
  • the area round 1.660 GHz the OH-line
  • the area round 22.235 GHz,  which is a frequency at which interstellar water vapour clouds emit radio waves.

Nonetheless, radio astronomers generally take observations outdoors the protected bands. They will do that as a result of massive radio telescope are sometimes located in radio quiet zones, usually in distant areas, the place there may be  very low amount of artifical radio transmissions. If, within the coming many years, there are tens of 1000’s of LEO satellites beaming highly effective radio transmission in any respect areas on Earth, then in future there could also be no radio quiet zones anyplace and lots of frequencies outdoors the protected bands shall be closed to radio astronomy. It is a subject about which I may write an ideal deal about however, within the pursuits of preserving this publish at an inexpensive size ;-),  I’ll go away the ultimate phrase to Tony Beasley, director of the Nationwide Radio Astronomy Observatory,  who stated in 2020.

SpaceX is legally transmitting inside one in every of their [allocated] bands and there are going to be impacts for anybody making an attempt to do radio astronomy,” ….”These spectrum allocations signify the targets and intent of society. We make [them] to allow commerce and to allow protection and all types of actions. We have now to return to an answer that satisfies all these to some extent

And Lastly……

Will probably be fascinating to see how issues develop over the subsequent decade and the way huge the influence on ground-based astronomy seems to be. Rather a lot will rely on willingness of the satellite tv for pc broadband corporations to interact with the astronomical neighborhood. What is obvious to me is that satellite tv for pc broadband  is prone to change into increasingly more necessary over the subsequent decade.

For these reader who need a bit extra data I’ve made this video on the Explaining Science YouTube channel which expands a few of these subjects additional


When measuring the brightness of objects within the sky, astronomers use the magnitude scale the place the decrease the magnitude worth the brighter the article.  The dimensions was invented by the traditional Greek astronomers who categorized all the celebrities seen to the bare eye into six magnitudes. The brightest stars got a  magnitude of 1, the subsequent brightest magnitude 2 and so forth. The faintest stars seen to the naked-eye by somebody with good eyesight got a  magnitude of 6.

Values within the magnitude scale had been standardised  by nineteenth century astronomers  to make an enhance in magnitude of 5 a lower in luminosity of issue of 100. So for instance, a star of magnitude 6 seems 100 instances fainter than one in every of magnitude 1.  The brightest star within the  sky Sirius has magnitude -1.4. The primary synthetic satellite tv for pc Sputnik had a magnitude of round 6 – making it nearly seen to the bare eye when considered at a location with out vital mild air pollution

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