Tag Archives: Jupiter

Cosmos 6: Travellers’ Tales

by Shane L. Larson

Sitting at the gate at Chicago’s O’Hare International Airport, staring at the thousands of other people around me, I am struck by how remarkably connected the modern world is.  I’m not thinking about smartphones and instant personal communication; rather I’m staring out the window at a Boeing 777 and thinking that I can go travelling virtually anywhere on the Earth, in just a day or so, by walking down the jetway.  And we all do it in a blink of an eye.  Sometimes we go for work, to exotic places like Dallas or Albuquerque.  Sometimes we go to visit family, like grandma in Mobile, or Aunt Becky and Uncle Bob in Bemidji.  But sometimes, we jet off across the world, just to go exploring.  We go to see the grand Buddha of Leshan, or the primeval rain forests of the Amazon, or the volcanoes near Reykjavik, or Gaudi’s Sagrada Familia in Barcelona.

(L) The Grand Buddha of Leshan. (R) Sagrada Familia. [Photos by S. Larson]

(L) The Grand Buddha of Leshan. (R) Sagrada Familia. [Photos by S. Larson]

While on our adventure, we take selfies, we send text messages that say “Guess where I am?”, and we wonder at the marvels of the world. When we return home, we may bring a few trinkets — a silk shirt, a wall hanging, a journal embossed with foreign words and images.  But the things we return to time and again, years after our voyage, either in idle strolls down memory lane or to show family and friends, are our pictures.  Pictures are the single most common and important thing brought back from adventure voyages, as they alone have the magic to transport us  back to those far away lands, with our friends alongside us.

Text messages and selfies, some of the most common travellers' tales of the modern age.

Text messages and selfies, some of the most common travellers’ tales of the modern age.

There was a time when our world was not so easily accessible, when the far corners of the Earth had not yet been discovered, and adventurers didn’t know what they would find on a long voyage of discovery. In the 1700’s, Captain James Cook made three epic voyages around the world, aboard ships whose names have become synonymous with exploration and discovery: HMS Endeavour (a name latter passed onto a United States space shuttle orbiter), and HMS Resolution. Cook’s papers and journals of those voyages were collected and studied for many years after his death, but one of the greatest treasures returned from the voyages were images of far away lands. In those days of exploration, every ship was crewed not just by sailors, but by professionals.  Some were scientists tasked with observing and recording discoveries along the voyage, and others were artists tasked with capturing images of the voyage to record and relay the adventure to those left behind. Without those artists eyes, we would never know what Cook saw on those first, epic voyages.

Images by artist William Hodges, who accompanied James Cook on his second voyage. (L) The HMS Resolution near Antarctica, and (R) HMS Resolution in Matavai Bay, Tahiti.

Images by artist William Hodges, who accompanied James Cook on his second voyage. (L) The HMS Resolution near Antarctica, and (R) HMS Resolution in Matavai Bay, Tahiti.

Today, the world is completely mapped, cultures (for the most part) have been found and documented, and there are precious few places humans have not yet tread.  Voyages of new discovery come more rarely, and people like you and me have adventures that begin with airplane rides and are documented through the lenses of smartphones.  While you and I have set our sights on worldly adventures like visiting Mammoth Cave in Kentucky, or picnicking in the shadow of Moai on Easter Island, our species’ thirst for adventure has grown beyond the Earth.  We have embarked on a new adventure to seek out new horizons and unknown landscapes far out into the Cosmos. The primary commodity of these new adventures are pictures — thousands and thousands of stunning pictures of cosmic vistas that move our spirits in ways we could have never imagined.

I often dream of being able to visit the Moai of Easter Island. [Illustration by S. Larson]

I often dream of being able to visit the Moai of Easter Island. [Illustration by S. Larson]

The sky has always compelled us to look up.  Even were we not fascinated with the strange and unearthly things we have found in the sky, the sky presents events that compel us to look up.  Consider the case of eclipses.  The Sun is the most brilliant source of light in the solar system, and every object it shines on casts a shadow, including the Earth. The Moon, on its rounds about the Earth, sometimes fleets through the shadow of the Earth.  As it passes into the shadow, it begins to disappear, an ever growing curve of shadow slowly eating the bright disk of the Moon. When it reaches the center of the shadow, the Moon takes on a deep reddish hue, cast in scarlet tones by the sunlight streaming around the Earth and through its atmosphere — an Earth sunset on our closest neighbor in the Cosmos.  This event is called a lunar eclipse.

(L) The geometry of a lunar eclipse. (R) iPhone image of the total lunar eclipse on 10 Dec 2011. [images by S. Larson]

(L) The geometry of a lunar eclipse. (R) iPhone image of the total lunar eclipse on 10 Dec 2011. [images by S. Larson]

The Moon also casts a shadow, and sometimes that shadow falls on the surface of the Earth, casting a fleeting moment of darkness wherever it falls.  Seen from the Earth, the Moon creeps across the Sun, an ever growing curve as the Moon blocks the brilliant solar disk.  At the center of the eclipse, the Moon covers the Sun and those standing in the center of the shadow are treated to a rare sight — the blazing corona of the Sun.  This event is called a solar eclipse.  Eclipses in our ancient past were unexpected and likely inspired fear and superstition.  Today, we can predict when they occur and where to stand to see them. People from all over the world step onto airplanes, and fly to stand in the shadow of the Moon.  They take their cameras with them, and capture images of the event to share with friends and family when they return from their travels.

(L) The geometry of a solar eclipse. (C) Image of total solar eclipse taken by Arthur Eddington in 1919. (R) Hydrogen alpha image of the annular solar eclipse on 20 May 2012 in Cedar City, Utah. [by S. Larson]

(L) The geometry of a solar eclipse. (C) Image of total solar eclipse taken by Arthur Eddington in 1919. (R) Hydrogen alpha image of the annular solar eclipse on 20 May 2012 in Cedar City, Utah. [by S. Larson]

Another, rare kind of eclipse is called a Transit of Venus, when Venus passes between us and the Sun, appearing as a small black dot traversing the solar disk. Beautiful and inspiring to see, observing a transit of Venus was one of the first ways that people figured out to measure the distance from the Earth to the Sun. Transits can be seen in pairs roughly every 121 or 105 years (a 243 year pattern), when the orbits of Earth and Venus are aligned just right. The most recent pair of transits was in 2004 and 2012. Two scientists, Charles Green and Daniel Solander, accompanied James Cook on his first voyage, tasked with observing a transit of Venus, which they did from Tahiti on 3 June 1769.

Transit of Venus seen from Wasilla, Alaska on 5 June 2012 [by S. Larson]

Transit of Venus seen from Wasilla, Alaska on 5 June 2012 [iPhone photo, through a solar telescope, by S. Larson]

While one could spend a lifetime standing on the surface of the Earth looking up into the Cosmos, some part of us knows that we could learn so much more if we just go up there.  And so we have.  For the most part, our emissaries beyond the Earth have been robots — machines of human design, supremely instrumented and exquisitely engineered to make interplanetary voyages that we cannot. Our robots have sailed the interplanetary sea and visited every major world in the solar system, providing tantalizing and brief glimpses of alien shores through pictures radioed back to their creators on faint radio links.  Travellers’ tales, recorded through the electronic eyes of semi-intelligent robots, are the principal commodity of the age of space exploration. Tales that paint a tapestry of wonders brilliant and evocative, tempting us with the promise of what we might discover if we were to dig deeper, push farther, and continue the exploration.

Of all the many worlds in the solar system of which we are aware, there are only five on which we have landed and returned images from the surface: the Moon, Venus, Mars, Saturn’s moon Titan, and the asteroid Eros. These are the only worlds beyond the Earth whose surfaces we have tread upon, and only on the Moon and Mars have we ventured away from the landing site (using rovers). At all of the sites, we have tantalizing pictures of alien shores that sing a siren song of adventure when we look out across them. 

(A) Surface of Eros by NEAR-Shoemaker. (B) Surface of Titan by Huygens. (C) Surface of Venus by Venera 14. (D) Apollo 15, station 9 on Hadley Rille. (E) Surface of Mars, near Bonneville Crater by the Spirit Rover.

(A) Surface of Eros by NEAR-Shoemaker. (B) Surface of Titan by Huygens. (C) Surface of Venus by Venera 14. (D) Apollo 15, station 9 on Hadley Rille. (E) Surface of Mars, near Bonneville Crater by the Spirit Rover.

But most of our probes are not landers — they are semi-intelligent cans of electronics, wires, metal and composites that we have hucked out into the Cosmic sea, leaving them destined to drift forever in the sky.  Most of the images they return are all taken from orbit or on a one chance “flyby.”  The stories they tell are a bit like describing a state by looking out the window of a plane as it passes overhead, but the tales are riveting mysteries of the past, present and future of the worlds in our solar system. 

On Mercury, we’ve found a vast impact basin, just discovered in 2008 by the MESSENGER spacecraft. The basin is more than 700 kilometers across; if it were on Earth it would stretch from San Francisco to Seattle.  A vast circular hollow excavated in the early days of the solar system, the central plains are a vast expanse of ancient lavas criss-crossed with ridges and troughs that have been frozen into the landscape since their formation — there is no weather on Mercury to weather and fade the scars of ancient geologic trauma.  We’ve named it Rembrandt after the famous Dutch painter — a fitting name for such a picturesque place.

(L) Rembrandt, on Mercury. (R) Saturn by Cassini.

(L) Rembrandt, on Mercury. (R) Saturn by Cassini.

At Saturn, Cassini has radioed back exquisite images of the subtle tawny clouds of Saturn, always framed by the brilliant arc of the great rings.  But on its way to Saturn, Cassini did a little sight-seeing, and as it sailed past Jupiter toward Saturn, recorded a mesmerizing movie of that planet’s banded clouds. The clouds swirl and rotate as they are pressed before winds blowing as fast as 500 kilometers per hour, nearly twice as fast as the strongest winds ever seen on Earth.  

Jupiter's cloud bands, as seen by Cassini.

Jupiter’s cloud bands, as seen by Cassini (click to animate).

Among all the space probes we have set adrift, five hold a special place of honor.  They are Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, and New Horizons.  These are the only probes we’ve built that are destined for interstellar space after their reconnaissance of the solar system.  Thousands of years from now, their creators long forgotten and returned to dust, these spacecraft will sail on into the interstellar void of the galaxy.

Now fallen silent, their energy reserves exhausted, the Pioneers no longer send tales home to Earth. But each carries a story with it, in the form of a small plaque telling the tale of the probes’ origins, should any intelligent being find it in the distant future.  A bottle cast into the Cosmic Ocean, I often wonder about those who might one day stumble on Pioneer 10 and 11.  Will they be alien intelligences?  Or perhaps will they be some impossibly distant descendant of humans, stumbling on a forgotten remnant of their past? Will they understand the message, and understand what Pioneer was doing in a long forgotten epoch of time?

(L) The Pioneer plaque, amidships on Pioneer 10. (R) The two sides of the Voyager record.

(L) The Pioneer plaque, amidships on Pioneer 10. (R) The two sides of the Voyager record. You can explore the Voyager record online (at the JPL Voyager site, or at a complete online archive), or in the (now out of print) book Murmurs of Earth.

Both Voyager spacecraft also carry a message in the form of a Golden Record. The record contains instructions for use, a map pointing back toward Voyager’s origin, and its own set of travellers’ tales: a set of 55 greetings in different languages of Earth, 116 images of life on Earth, and 90 minutes of music from around the world ranging from masterpieces by Mozart, to Chuck Berry’s Johnny B. Goode, to a traditional Peruvian wedding song.  The record bears one final message, inscribed on its inner edge, a handwritten message: “To the makers of music — all worlds, all times” (etched by Timothy Ferris, the producer, when the record was completed).

The ADS All Sky Survey, a rotatable interactive map showing where we've taken pictures of the sky.

The ADS All Sky Survey, a rotatable interactive map showing where we’ve taken pictures of the sky.

The principal commodity of science, and astronomy in particular, is knowledge. The tangible evidence of that knowledge is pictures.  Images capture both scientific knowledge and cultural aesthetic; they can be appreciated by everyone for the wonder they evoke and the questions they provoke.  At a recent gathering of the American Astronomical Society, some of my colleagues showed a new kind of astronomical map.  It is a map of the entire sky, but instead of showing us the secrets veiled away in the deep Cosmos, the map shows us how often we have looked at or studied — taken a picture of — a particular place in the sky. To the trained eye, you can see the Andromeda Galaxy, the Large and Small Magellanic Clouds, the plane of the Milky Way, the plane of the Solar System, and the area covered by the Sloan Digital Sky Survey.  But what amazes me most about this picture is how LITTLE of the sky we have seen — most of the map is  black, meaning no picture has been taken there.  That is a staggering shame, since as the Hubble Deep Field as shown (and its successors, the Ultra Deep Field, and the Extreme Deep Field), even the most remote, dark and (we thought) empty places in the sky are filled with uncountable mysteries.  The sky is a BIG place, and we are far from having seen it all.

And so we continue to stare, we continue to take pictures, and we continue to spin travellers’ tales about what we’ve seen, what we know, and what we still would like to discover.

The Hubble Ultra Deep Field (UDF), showing what is unseen but can be found if you stare at an empty part of the sky for long enough.

The Hubble Ultra Deep Field (UDF), showing what is unseen but can be found if you stare at an empty part of the sky for long enough.

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This post is part of an ongoing series, celebrating the forthcoming science series, Cosmos: A Spacetime Odyssey by revisiting the themes of Carl Sagan’s classic series, Cosmos: A Personal Voyage.  The introductory post of the series, with links to all other posts may be found here:  http://wp.me/p19G0g-dE

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The Size of the Cosmos

by Shane L. Larson

As many of you know, I ascribe much of my aspirations in life as a scientist to being exposed to Cosmos at a very early age.  Within the first five minutes of the first episode, Carl said a very big thought: “The size and scale of the Cosmos are beyond ordinary human comprehension.”

As I have grown into my career in science, I have lost sight of this simple fact. I’ve learned to write big numbers. I’ve learned to convert between meters and kilometers and lightyears when needed. I’ve even learned to use “crazy relativist units” and measure distance, time, energy and mass all in meters (something that confounds my students, my parents, and many of my astronomer friends!). I’ve done this enough now that when I calculate numbers, I know if they sound right.  Two million lightyears to a galaxy in the Local Group? Sure that sounds fine.  750 Megaparsecs to a quasar? Sure, I’m down with that.  1.3 billion kilometers to Saturn?  Word.

Developing a sense for big (and small!) numbers and whether they “sound right” is an essential skill for scientists, and we spend inordinate amounts of time training ourselves and our students to be facile with them.  But that completely bypasses Carl’s point — these numbers are HUGE.  They encode how utterly small we are on the grand scale of the Cosmos!

One of my hobbies is walking Solar System Walks when I encounter them (here is a long list at Wikipedia; another list at Air & Space).  These scale models lay out the Solar System, marking the location of planets at the appropriate spatial scale to give you a sense of how large the Solar System is (forget the Universe itself).  My favorite is one in Anchorage, Alaska, known as the “Lightspeed Planet Walk”  — if you walk at normal speed, the time it takes you to reach each planet is the same time it would take light to make the journey you made.  That is awesome.  Start at Earth, and shine a laser pointer at Neptune the moment you start walking; you’ll reach Neptune at the same time your feeble green laser beam reaches the real planet Neptune!

The center of the Lightspeed Planet Walk in Anchorage, Alaska, with a scale model of the Sun.

The center of the Lightspeed Planet Walk in Anchorage, Alaska, with a scale model of the Sun.

Despite the large physical scale of these walking models, I still often feel like they don’t capture the immensity in a way that really shocks my brain. I’ve thought about this fact a lot, and suspect it is because when I’m walking the model, it feels quite ordinary.  As I’m meandering from Mars to Jupiter, I’m not really thinking about how far I’m walking. I’m distracted by my daughter prattling about why Pluto should still be a planet, and watching ducks eat algae, and avoiding speeding mountain bikers.

But a couple of weeks ago, one of my astronomy friends showed me something that blew my socks off.  It’s a very simple demonstration you can do right at home that captures how messed up my mental picture (and I’ll bet yours!) of the solar system is!  I think my mental pictures are messed up because we often show the family of the Sun all together, to better show the relative size of the planets, like the image below.

A typical representation of the Solar System, often used in books, online references, and mass media.

A typical representation of the Solar System, often used in books, online references, and mass media.

What this image fails to show, is the spacing between the worlds.  We’ve known the relative spacing of the planets for some time, the distances having been worked out using basic geometry together with clever observations (many of which can easily be done in your own backyard), and through application of the laws of physics (notably Kepler’s Laws of Motion, and Newton’s Universal Law of Gravitation).

Folding pattern to make a reasonably spaced representation of the planetary orbits in the Solar System on a long strip of paper.

Folding pattern to make a reasonably spaced representation of the planetary orbits in the Solar System on a long strip of paper.

Let me teach you the trick my friend showed me.  Get a long strip of paper (adding machine paper, or other strip paper works well), about 1 meter long.  On one end, write the word SUN and on the other end write PLUTO.  Now fold the strip in half, and unfold it again.  What object in the solar system lies halfway between the Sun and Pluto?  It is the planet Uranus; write this on the fold.  Now fold the end marked Pluto down to Uranus.  Label this as the location of the orbit of Neptune.  What does this show us?  There isn’t  much in the way of planets in the outer half of the solar system!

Now fold the end marked Sun down to Uranus.  On  this new fold write Saturn.  Fold the Sun down to  Saturn and label the new fold Jupiter.  Fold the  Sun to Jupiter and label the new fold  Asteroids.  At this point, about 93% of your strip is  between the asteroids and Pluto.  This is the part of the solar  system that is euphemistically called “The Outer Solar  System.”  Fully half of the known planets in the solar  system are still to be squeezed between the Asteroids and  the Sun!  Let’s do that next.

Fold the Sun to Asteroids, and label this fold  Mars.  The last part is two folds before labeling: fold the Sun to Mars, then fold the end over to Mars again.  The result is three folds.  Starting at the  Sun, label them Mercury, Venus and Earth.  The entire procedure creates a map with amazingly accurate spacing between the worlds (yes! I calculated the errors; I was curious!).

The results of all your folding endeavours!

The results of all your folding endeavours!

Now stare at your model for a moment.  The solar system is a lot of empty space!  The places that are easiest to get to are close to Earth, but are still very far away.  The distance to the Moon is about the width of a pencil line, and it took Apollo astronauts 4 days to cross that gulf.  Mars is six to eight months away by rocket.  Look how close it is to Earth!  It took the Cassini spacecraft almost seven years to get to Saturn.   When the New Horizons spacecraft flies by Pluto in 2015, it  will be have been outbound for almost nine-and-a-half years!  The  solar system is a big place. And the Cosmos is far vaster.

I think what amazes me the most about this model is that places I normally think of as very far away are much closer to Earth than my brain normally thinks of them.  Consider Jupiter; it is in the Outer Solar System.  But on the map, it is only 1/8th the distance between the Sun and Pluto!  Wow.

“The size and scale of the Cosmos are beyond ordinary human comprehension.”  Perhaps; certainly outside the realm of our everyday experiences. But our ingenuity gives us ways to push our brains to try to understand, and clever demonstrations like this one give you ways to ponder and think.  So get out your scissors, and start folding.

(L) The full length of the Solar System model. (R) My own version of this model, shown next to a typical Earthling.

(L) The full length of the Solar System model. (R) My own version of this model, shown next to a typical Earthling.