For almost all of human history, the night sky has guided us across continents,
illuminating our path forward. The stars are as entwined with our civilisation as
are the land and the sea. But, that sky is changing; while the stars,
nebula and supernova remnants are as brilliant as ever, few of us will ever get the chance to
see them as they once were — even though all it would take to do so is a flick of a switch.
I’m Alex McColgan and you are watching Astrum. Join me today as we explore how the night sky
has changed in our own lifetimes, and uncover the drastic effects that artificial light,
both visible and invisible, has had on us, on crucial ecosystems and on
important scientific research. We will see how a well-intentioned ‘green' revolution made it worse,
how we’ve put artificial constellations of our own into orbit, and how even the natural
constellations themselves are changing. That’s right, we’re going to see how our
sky will change in 1,000, 1,000,000, and even billions of years into the future.
As it is with anything that changes gradually over time, we rarely realise what is happening. But,
every once in a while that gradual change can be laid bare, as it was during the ’94
earthquake in Los Angeles. A large part of the city’s electrical grid was knocked out in
the early hours of January 17th, revealing the effect of decades of increased light pollution
in an instant. So shocked were residents by what they saw as they evacuated their homes,
that some stopped to look up in awe of what had always been there, hidden by the city lights.
One even phoned the observatory to ask what the “giant silvery cloud” was that they were seeing.
Sadly, even the sky you saw when you first looked to the stars as a child is not how it is now. From
2011 to 2022 the average light pollution increased by 10% a year, meaning that it
has more than doubled over that time. So let’s travel to a dark sky location on a clear night,
far away from the sky-glow of towns and cities and look up,
to understand what we’ve lost, before we learn how we might get it back.
There is a useful measure used to rate the quality
of the night sky by eye called the Bortle Scale, which ranges from 1-9.
In a city, under the brightest of skies you may only be able to count a hundred stars,
this is a 9 on the Bortle scale; but as you travel away from the lights,
the sky reveals more until it becomes nearly unrecognisable.
As you drive out to the surrounding urban area the night sky darkens to Bortle 7,
here on a clear night you might get to see a hint of the Orion Nebula,
visible only as a diffuse-looking star. Clouds under these skies will be very well lit. Once
you’re out past the city limits into the rural countryside, you’re now under Bortle 3 skies,
and much more is revealed. Messier objects 15, 4, 5, and 22, all star clusters, are now naked-eye
objects. Andromeda is clearly visible, and, if you look carefully, you’ll glimpse the Triangulum
Galaxy. These two galaxies at 2.5-2.7 million lightyears away are the furthest objects we can
see with the naked-eye. And what about that ‘giant silvery cloud’ they saw in Los Angeles? That’s
our Milky Way, a diffuse band that arcs across the sky, which contains over 100 billion stars.
Finally, after a few hours of driving you’re now under Bortle 1 skies. A true dark sky site
with a pristine view. When we set out from the city you could only see a hundred stars, here,
you will see thousands. It may even take you some time to notice the constellations that
you thought you knew, lost as they are in the awesome detail of this dark sky.
If you’re lucky enough to live in the Southern Hemisphere you’ll be looking
towards the galactic centre and you may even notice that it casts shadows onto the
ground.My friends in the Northern Hemisphere, no need to be envious, our fortunes will be
reversed as we orbit to the opposite side of the galaxy… in a mere 120 million years.
Elements of the beautiful Orion Complex are visible in both hemispheres;
a 1200 lightyear-wide star forming region containing the Horsehead,
Flame and Orion nebulae, though binoculars are strongly advised!
The closest object that is fully revealed in such a dark sky produces no light of its own:
interplanetary dust. This dust is illuminated by the sun and forms a band of light known as the
Zodiacal light, which spans from horizon to horizon featuring a central focus
called the gegenschein, appearing directly opposite the sun’s position over Virgo.
Sadly, those of us who live in cities never experience a genuine night sky at all,
and are effectively stuck in an artificial twilight.
This can have unexpected effects on us as well as the night sky.
So how do a few lightbulbs block out an entire galaxy? In a word: skyglow. Any light that is
emitted upwards will pass through the atmosphere where it can be scattered in any direction. The
light that is reflected back towards the ground to our eyes or telescopes is seen as skyglow,
which has the effect of drastically reducing the signal to noise ratio
of incoming light from space, affecting our ability to see it and to study it.
You may have experienced something similar on a dark foggy drive. Perhaps in an attempt to
see more of the road, you’ve turned on your full beams. The slight upward angle of these
lights reflects light up illuminating the fog in front of you, which has the opposite
effect of what you intended: It bleaches the field of view and obscures the road ahead.
To make things worse, it’s not just that the sky is now brighter,
tragically, our eyes are now also less able to see in the dark when we do go outside. Human
eyes have the incredible natural ability to detect brightness across a full 9 orders of magnitude. We
are able to do this because we have two types of vision. The first is known as photopic vision and
it’s the one you’re using now, it’s our daytime colour vision recorded by our eye’s cone cells.
The second is scotopic vision, an ultra-sensitive monochrome night vision, recorded by our eye’s
rod cells. It is this scotopic vision that allows us to see the faintest details in the night sky.
Modern lighting is reducing our access to our scotopic vision, because, to the human eye,
all light is not equal. In the past 10-15 years a movement towards more energy-efficient LED lights
has shifted the spectrum of light pollution from the orange hues of the sodium lamps to blue/green
frequencies of LEDs, which we are more sensitive to. These blue-green frequencies slow down dark
adaptation, or worse, can fully reverse it in minutes, which is why you’ll often see
astronomers and night-time pilots using red lights or red goggles to ensure the scotopic
vision is maintained. To access full scotopic vision, we require a near absence of short
frequency light for at least 30 minutes, and it can continue to improve for up to 2 hours.
So, you may be wondering, if we are so sensitive to the blue frequencies of typical LED lights,
why can’t we use less of it and reduce overall light pollution? And you’d be right, we could!
The reality is though, that we don’t. LEDs are so efficient compared to sodium and filament lights,
that we save energy and money even when they’re run much brighter. So,
that’s what we so often do: we run them brighter because we all feel safer in a well-lit area,
even if we are statistically no more likely to be the victim of crime.
Our eyes also contain retinal cells that are not involved with seeing and instead help to
regulate our body clock. These cells are particularly sensitive to shorter
wavelengths, too. So artificial light, and LEDs in particular, don’t just affect our
ability to see the night sky, they affect us in other more severe ways too. The disruption of
our circadian rhythms by light disrupts the production of several key hormones,
including melatonin. Incredibly, this can affect our body through a dramatic cascade
that can lead to metabolic and mood disorders, and most severely: cancer.
While for us humans, there is at least some upside in extending the length of the day artificially,
for the rest of nature there is almost nothing but downside. Lights interfere with the circadian
rhythms of wildlife, too; disrupting how and when they sleep, migrate, reproduce,
hunt and evolve. Almost every species studied to date is negatively affected by lighting,
at the level of both the individual animals and their populations. Scientists have studied fishes,
birds, amphibians, insects, invertebrates, ecosystems hundreds of meters below the surface
of the sea and even trees. Deciduous trees, which regrow their leaves each year, can be tricked
into maintaining their foliage all year round; causing stress that can eventually kill the tree.
There are simple things we can each do that manage that rare combination of saving us
money and improving our health! The best, of course, is to turn off unwanted lights,
particularly outdoor lighting and uplighting. When installing new or replacing new lights,
look to install low-power LEDs with a lower colour temperature of say 3000K
instead of 5000K. Well-designed lighting will have shielding to focus the light
to where it needs to be and minimise excess light shone into the atmosphere.
But away from ground-based artificial lights,
we are now facing a significant increase of light pollution coming to us from space.
On the 4th October 1957 the Soviet Union launched Sputnik 1: the first satellite to venture into
space. In the decades that followed there was a steady increase in the number of active
satellites; increasing by 30 a year on average in the 60 years to 2017. But, from 2018 onwards
Elon Musk’s SpaceX has been doing something unprecedented. But before we get to that, with
this many eyes in the sky,Your data, which may contain everything someone may wish to know about
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Since 2018, SpaceX has launched nearly 7000 satellites into space. Oh, and 1
Tesla Roadster. As it stands SpaceX have twice as many active satellites in low earth orbit,
as every other company and country on Earth combined. I’ve seen some hockey-stick-shaped
graphs in my time, but this one is stratospheric. The vast majority of these new satellites have
gone into low-Earth orbit (LEO) at an altitude of only 550km. The United Nations Office for
Outer Space Affairs UNOOSA have speculated that 100,000 more satellites could be launched in the
next decade. There are no regulations that limit the number of satellites that can be launched,
and many agreements and understandings around reducing the potential for light
pollution are informal. These satellites in LEO are particularly bad for light pollution,
contributing to skyglow and producing trails in amateur astrophotography and research images
that can render them unusable. Astrophotography can require long exposures of several minutes
and it’s likely that these exposures will capture the trails of satellites in that time.
This is an image of the Horsehead Nebula, and there are three trails in this image!
And even I myself have seen it in my own shot of the Orion Nebula!
We can easily see the effect satellites have on visual astronomy, we can even watch them
trail across the sky in real-time. But these man-made constellations that deliver GPS, mobile
communications & satellite internet all operate in the radio wave spectrum, too, spanning MHz and GHz
frequencies, which can potentially interfere with scientific observations. Radio signals
easily pass through galaxies, solar systems, interstellar gas clouds and Earth’s atmosphere
revealing secrets of our universe that would otherwise be hidden. All the more incredible,
then, that the radio signals from my wi-fi router can barely make it through a few stud walls!
Radio astronomy was key in establishing the shape and rotation of the Milky Way,
discovering quasars and pulsars, and detecting organic molecular species like cyanide,
ammonia, water and amino acids in interstellar molecular gas clouds.
It was a radio telescope in Ohio that received the famous “Wow!” signal in
1977. It was detected at 1420 MHz, a value believed to be the frequency of
choice that an alien civilisation would attempt to communicate over,
and it is protected from commercial use to keep it quiet. It is, though, still
debated whether the “Wow” signal was terrestrial interference… or an extraterrestrial phenomenon.
But while we are talking about how communications interfere with astronomy, astronomy can also
interfere with communications. In 1978 Arno Penzias and Robert Wilson were awarded the
Nobel Prize in physics for discovering that the interference in their antenna wasn’t pigeons,
it was the cosmic microwave background - the cooled remnants of the universe’s first light.
The detection of this low-level hum in their Bell Labs antenna,
and understanding its cause, all but proved the Big Bang hypothesis.
In another happy accident, the radio waves emitted by the black hole at the centre of our galaxy,
Sagittarius A*, were detected because of its interference with transoceanic phone calls!
I love these two stories as it highlights humanity at its best,
at its most inventive and at its most curious. Pausing in the hustle
of developing new technologies to remark “Huh, that’s odd” led to two incredible discoveries.
So much has been discovered in the radio wave spectrum, yet there are deeper mysteries that
cannot go unsolved. That's why the Square Kilometre Array Observatory is being built
in radio quiet zones — the most ambitious radio observatory project of all time. I
don’t say that lightly — it is. Its stated aims are to probe the cosmic dawn and the emergence
of the first stars and galaxies; to challenge Einstein’s General Theory by indirectly observing
gravitational waves; to seek the origin of life; to look for aliens; and, to understand
how our galaxy and universe are changing due to pressures like entropy, gravity & dark energy.
But what does that change look like to us, from Earth?
If we look up to the stars through a light polluted sky, space appears stagnant and it
can be easier to believe that we are instead on a Truman Show-like film set with fixed stage lights
for stars, than on a rock in motion through our galaxy. But under a dark sky, nothing feels still
as we get a sense of our voyage through space and time. Earth is orbiting the black hole at
the centre of our galaxy at 828 000 km/h; we are heading away from the galactic plane and hurtling
in towards the centre. Our perspective and every object we can see, is moving. In this video by
the ESA from data captured by the Gaia telescope we can see how our night sky really is changing.
In 1000 years time, only the keenest astronomers would notice a difference from today’s
constellations, though we may be lucky enough to witness Betelgeuse going supernova.
But in around 10,000 years, we will have a new north star. Polaris will have moved away from the
celestial pole, and it will have been replaced by the brighter Vega. And let’s take a closer
look at the constellation of Orion and the stars around it, they will change dramatically over the
next 450,000 thousand years: Orion’s sword will shatter and his bow will disintegrate.
Zooming out to the entire night sky let’s watch our galaxy evolve over 4.5 million
years - Orion is in the bottom right. What we can’t know with this data though are how many
more stars will go supernova, and how many more will be born. We’ll just have to wait
and see! And that’s going to be a heck of a lot easier if you would just turn off those uplights!
But over the next few billion years, the sky will begin to look so unrecognisable that you could
be forgiven for thinking we were in a different galaxy altogether… because we would be. Andromeda
currently takes up 3º of our sky, about SIX moon widths. It is accelerating towards us and is
expected to reach us in 5 billion years, by which point it will be the sky. Galaxies are so diffuse,
that Andromeda and the Milky Way would pass through each other almost without impact. But,
it’s what we can’t see that is all around us that will seal our fate - gravity. Over the next
5-10 billion years, our two galaxies will yo-yo and rip each other apart, with a huge burst of
star formation from the mixing gases, turning two spiral galaxies into one elliptical blob.
Unfortunately, you would be unlikely to see this from Earth because of the extreme natural light
pollution caused by the sky literally being on fire. Our sun will have become a red giant.
In 1 trillion years the last star will be born. There is nothing but decay left for
the universe. The galaxies we can see outside of our extended galaxy will
become faint and they dim and move beyond our observable universe. In 120 trillion years,
all stars will be extinguished, and the night sky will fade to black.
As is so often the case in our complex world, there are unexpected outcomes from our behaviours.
Our night sky is changing in many ways; it has been obscured, but it is not lost. Towns,
cities and governments all over the World are beginning to understand the issues and
are making changes in ordinances and in law to protect our skies and the wildlife underneath it.
So … If this video has inspired you to visit a dark sky or reduce your impact,
head to darksky.org to find out more, and to https://www.lightpollutionmap.info if you’re
curious about the light pollution in your area.
Thanks for watching making this video required some long-term planning and work which we were
only able to do thanks to the consistency and sustainability of your memberships as
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meanwhile click the link to this playlist for more astrum content I'll see you next time.