Guest post: Smaller than a dust mote

Today we're fortunate to feature a guest post by my friend, fellow blogger, and twin-separated-at-birth, Andrew Butters, whose blog Potato Chip Math is a must-read.  Like myself, Andrew is a devotee of astronomy, and here he'll take us on a voyage into deep space -- and give you a change of perspective you might never have considered.

Enjoy!

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I'll admit it, I'm a space nerd. I have been since high school and only got more intense when I started studying Applied Physics at university. There is a lot of weird science at the astronomical level and to comprehend it you have to wrap your head around concepts that you won't ever encounter in your daily life and then understand how to measure them. The two measurements that trip up just about everyone who hasn't studied them are time and distance. At an astronomical level those two things are astonishingly gigantic, so much so that to the average person they might as well have no meaning at all.

This is why, when I read a recent article on space.com, my mind, which studied this at a university level for several years, was sufficiently blown. Space.com does a decent job putting in lay terms what authors Linhua Jiang, Nobunari Kashikawa, Shu Wang, Gregory Walth, Luis C. Ho1, Zheng Cai, Eiichi Egami, Xiaohui Fan, Kei Ito, Yongming Liang, Daniel Schaerer, and Daniel P. Stark of the published article, "Evidence for GN-z11 as a luminous galaxy at redshift 10.957," explained in painstaking mathematical and scientific detail for the journal Nature Astronomy. I'll summarize it even further: space is fucking huge.

In the article, the authors prove rather conclusively that the farthest observable galaxy to date is a whopping 13.4 billion light years away. Don't let the word "years" in there fool you. A light year is a measure of distance and 13.4 billion of them are the equivalent of 127 nonillion kilometers (127,000,000,000,000,000,000,000,000,000,000 km). To put that into a different perspective, there are 3600 seconds in an hour, a million seconds is a little over 11.5 days, and a billion seconds is 31.7 years. What about 127 nonillion seconds? That's 4.25 x 10^22 centuries or roughly five orders of magnitude longer than the age of the Universe itself.

So, space is huge. So what? Well, for me, it puts my existence on this third rock spinning in circles around a rather average sun as part of a rather average galaxy into perspective. As with any good conversation on this topic, it’s probably a good idea to lead with a little Carl Sagan. Many of you have seen this picture before:

[NASA – Image in the public domain]

It was taken in 1990 by the Voyager I probe on February 14 at the request of Carl Sagan. It took a decade for the request to come to fruition, but after it did here’s what he had to say about it:

"We succeeded in taking that picture [from deep space], and, if you look at it, you see a dot. That’s here. That’s home. That’s us. On it, everyone you ever heard of, every human being who ever lived, lived out their lives. The aggregate of all our joys and sufferings, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there on a mote of dust, suspended in a sunbeam.

"The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that in glory and in triumph they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of the dot on scarcely distinguishable inhabitants of some other corner of the dot. How frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light.

"Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves. It is up to us. It’s been said that astronomy is a humbling, and I might add, a character-building experience. To my mind, there is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly and compassionately with one another and to preserve and cherish that pale blue dot, the only home we’ve ever known." — Carl Sagan, speech at Cornell University, October 13, 1994

To give you an idea of exactly how far away Voyager I was when it took that photograph, here’s a picture, though it’s not to scale. As we’ll see in a bit the scale of the Solar System, and indeed the Universe, is staggeringly massive.

Joe Haythornthwaite and Tom Ruen [CC BY-SA 4.0], from Wikimedia Commons

How far away is that? It’s far. I mean, really far. The Pale Blue Dot photograph was taken 6 billion kilometers away. Voyager 1 launched in September 1977 and traveled at an average speed of roughly 60,000 km/h, and it still took thirteen years for it to get that far away. Neptune, the most distant planet in the Solar System takes 165 years to make a single trip around the Sun. When Neptunians say, “Winter is coming,” and have a look of concern on their faces it’s for good reason.

What if the Moon were the size of a single pixel on your screen right now? It’s a cool exercise to ponder and it gives us a real sense of the vastness of our surroundings. In fact, someone thought it was so cool that they created a model for it. Spend a few minutes scrolling (and scrolling and scrolling and scrolling) through it.

If the Moon Were 1-Pixel

This is all well and good, but what about beyond our Solar System? We orbit but one star out of hundreds of billions in our galaxy alone and our galaxy is but one of trillions in the observable Universe. To get a sense of what lies immediately beyond our Sun there are a couple of really cool, interactive sites you can visit Our Stellar Neighborhood, http://stars.chromeexperiments.com/, which allows you to zoom and pan and view 100,000 of the nearest stars. Solar System Model, https://www.solarsystemscope.com/, is a similar tool, but this one has more features and also includes options to show spacecraft, constellations, dwarf planets, comets, and a lot more. Still, nothing we’ve seen so far gets us out of our galaxy, the Milky Way, at the center of which is a black hole.

What about beyond our galaxy? A few years ago, while pondering the vastness of the Universe, some smart person at NASA decided that they would take the Hubble Telescope and point it at a small square of nothingness to see what they could see. Suffice it to say they were not disappointed.

https://www.nasa.gov/mission_pages/hubble/science/xdf.html

Every bit of light you see in that picture is a galaxy. In each galaxy are hundreds of billions of stars. This picture represents only a fraction of a fraction of a fraction of the sphere of our night sky. To photograph the rest of it you would need to take another 12,913,983 pictures.

Which is all fine and dandy, but again, people have a hard time comprehending the scale. All of our reference points are too small and too slow. Fortunately, someone at NASA put together something that shows that even if you travel at the upper limit for speed – the speed of light – it takes a really long time to get anywhere. One could say that the speed of light in that respect is rather slow. Put another way, space is huge.

How long it takes for light to travel between the Earth and the Moon

How long it takes for light to travel between the Earth and Mars 

Finally, for anyone wondering where God and religion fit in, I will leave you with this (enlarge the photo when it loads and scroll): 

[Source link]

~ Andrew


Other Important and Interesting Links:

Ten Female Astronomers

Ten Inspiring Women in Science

Eight Free Science Resources

Levels of Infinity

Space Missions

Two Trillion Galaxies

LA to New York Earth Timeline

Exoplanet Orbits

A Virtual Universe

Daylight Map

ISS Payload Camera

Scale of Solar System & Universe

Black Hole Size Comparison

How Big is the Universe?

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This week's Skeptophilia book recommendation is apt given our recent focus on all things astronomical: Edward Brooke-Hitching's amazing The Sky Atlas.

This lovely book describes our history of trying to map out the heavens, from the earliest Chinese, Babylonian, and Native American drawings of planetary positions, constellations, and eclipses, to the modern mapping techniques that pinpoint the location of stars far too faint to see with the naked eye -- and objects that can't be seen directly at all, such as intergalactic dust clouds and black holes.  I've always loved maps, and this book combines that with my passion for astronomy into one brilliant volume.

It's also full of gorgeous illustrations showing not only the maps themselves but the astronomers who made them.  If you love looking up at the sky, or love maps, or both -- this one should be on your list for sure.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Seeing the light

Picture this: you're walking down a road on a dark, moonless night.  In the distance, you see a light.  How far away is the light?

The problem is obvious.  You can only make a good guess about the distance between you and the light source if you know how bright the light actually is.  A close-by dim light will have the same apparent brightness as a faraway bright light.  (The opposite would be true, too, of course.  You could only estimate the light source's intrinsic brightness if you knew how far away it was.)

That, in a nutshell, is the difficulty with making distance measurements of astronomical objects.  There are three tools, though, that can help to get around this problem.

The first only works for relatively nearby objects.  It's called parallax, and it has to do with the apparent motion of objects when you are actually what's moving.  You've all seen this; when you're driving down the freeway, nearby objects (such as the fence running along the side of the road) seem to zoom past a lot faster than distant ones (such as the mountain in the distance).  To figure out something's distance using parallax, you need two measurements of its apparent position relative to the unmoving background.  Then, using the distance you know that you have traveled, it's a matter of simple trigonometry to figure out how far away the object is.

Even nearby stars, though, exhibit such a tiny parallax that it requires a very long baseline -- such as the position of the Earth between June 21 and December 21.  By that time, it's halfway around its orbit, and the baseline is the orbit's circumference -- about three hundred million kilometers.  However, objects farther away than about ten light years have such a minuscule parallax that it's effectively undetectable.

The second, discovered by astronomer Henrietta Swan Leavitt in the early twentieth century, is a peculiarity of a type of variable star called a Cepheid variable.  Cepheid variables have a regular rise and fall in brightness, and Leavitt discovered (using fairly nearby ones) that their pulsation rate is directly proportional to how bright they actually are.  And, as I pointed out above, once you know how bright a light source is, you can estimate how far away it is.  (Making Cepheids one of the most commonly used "standard candles" in astronomy.)

The third sprang right from Leavitt's discovery.  When the light from distant galaxies was analyzed, astronomer Edwin Hubble observed something strange; it was red shifted.  Red shift is the electromagnetic version of the Doppler effect -- the wavelengths of light get stretched out (move toward the red end of the spectrum) if an object is moving away from you.  The more the shift, the greater the velocity.  But the kicker occurred when Hubble used  Leavitt's discovery of the relationship between a Cepheid variable's pulsation rate and intrinsic brightness to figure out how far away these galaxies were, and found another interesting correlation; the farther away the galaxy was, the greater the red shift -- and therefore, the faster it was moving away from us.  This led directly to the Big Bang/expanding universe model, and marks the origin of modern cosmology.

There's a fourth method, though, only recently discovered, but which was the technique used in a study that appeared last week in the Astrophysical Journal to determine the distance to five hundred distant galaxies.  It's called echo mapping, and it works like this.

Many, if not all, galaxies have a massive black hole at the center.  Black holes are not amenable to any of the standard methods of distance calculation.  They don't emit light, so even the red shift method won't work.  But one feature of most massive black holes is that they are surrounded by a torus-shaped dust cloud of debris.  The intense gravitational pull of the black hole draws matter into it, heats it up, and causes it to emit radiation in sudden bursts.  That radiation flashes outward and is absorbed by the inner surface of the dust cloud, warming it and creating an infrared signal that is detectable by telescopes on Earth.

Well, we know that light travels at three hundred thousand kilometers per second, and also that light's intensity drops off as a function of the inverse square of the distance from the source (twice as far means four times dimmer, three times as far means nine times dimmer, and so on).  Dust only forms if the temperature is below twelve hundred degrees Celsius -- any hotter and the molecules are torn apart by the thermal energy.  So a large black hole, with a large radiation output, would generate a dust cloud with a larger inner radius -- just as campers sitting around a campfire need to be closer to a smaller fire to be as warm as someone farther from a bigger fire.

So that's all the pieces.  If you know the time between the initial flash of radiation from the black hole and the subsequent infrared signal emitted by the dust cloud, you can figure out the circumference of the dust cloud.  Knowing the circumference tells you how intense the radiation source is (bigger circumference = more intense radiation source).  This gives you the actual luminosity of the accretion disc around the black hole -- and therefore how far away it is.

What never fails to impress me about scientists, and science in general, is the cleverness with which problems are approached.  Some of the best solutions to scientific questions have come from completely out-of-the-box ideas, or (as in the case of Henrietta Swan Leavitt's discovery about Cepheid variables) using something that at first appears to be a trivial factoid to illuminate something truly enormous.

I don't know about you, but whenever I see stuff like this, I always think, "I would never have thought of doing that."  I know that part of it is that, being a non-scientist, I haven't been steeped in one subject for years.  But I think the really successful scientists, the ones who make the major breakthroughs, are the ones whose brains are able to bring together what initially appear to be entirely disparate bits of information, and generate a synthesis that is way bigger than the sum of the parts.

In other words, science is primarily a creative act.

A fitting way to end this post is a quote from the brilliant Austrian physicist Lise Meitner:

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One of my favorite TED talks is by the neurophysiologist David Eagleman, who combines two things that don't always show up together; intelligence and scientific insight, and the ability to explain complex ideas in a way that a layperson can understand and appreciate.

His first book, Incognito, was a wonderful introduction to the workings of the human brain, and in my opinion is one of the best books out there on the subject.  So I was thrilled to see he had a new book out -- and this one is the Skeptophilia book recommendation of the week.

In Livewired: The Inside Story of the Ever-Changing Brain, Eagleman looks at the brain in a new way; not as a static bunch of parts that work together to power your mind and your body, but as a dynamic network that is constantly shifting to maximize its efficiency.  What you probably learned in high school biology -- that your brain never regenerates lost neurons -- is misleading.  It may be true that you don't grow any new neural cells, but you're always adding new connections and new pathways.

Understanding how this happens is the key to figuring out how we learn.

In his usual fascinating fashion, Eagleman lays out the frontiers of neuroscience, giving you a glimpse of what's going on inside your skull as you read his book -- which is not only amusingly self-referential, but is kind of mind-blowing.  I can't recommend his book highly enough.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]