Saturday, January 24, 2015

The Fallen Gods of the Celestial Spheres

Owen Gingerich, Cambridge, MA (May 27, 2009)

How many planets are there in the Solar System? Cinques stellas errantes, noted the german naturalist Alexander von Humboldt, drawing from the ancient greek tradition of the ἀστέρες πλανῆται. Six, would say Copernicus; do not forget the one you are standing upon. Seven, added Herschel, as this bluish comet he was observing was definitely failing to develop a tail, and could only be Uranus, the father of Saturn, in turn father of Jupiter, ruler of the gods and father of everybody else. 

Wes Traub
That was however not to last. Take a large piece of paper and plot the distance of each planet with respect to the solar system center. A XVII century astronomer will notice that the space between the planets is somewhat regular, doubling as you go from Mercury to the farthest globe revolving around the Sun. With one exception: there is a large gap between Earth and Mars, a missing planet to hop through on your way to the red demon of war. Giuseppe Piazzi found it, Cerere Ferdinandea, Ceres for the ages. It was not alone: Pallas was found next, and then Juno, and finally Vesta, all sharing the same gap between Earth and Mars in such close orbital proximity that repulsed reason. "Two stars keep not their motion in one sphere", chimed in King Henry in Shakespeare. But they kept coming, the small planets and a new large one, found on the opposite end of this magic number sequence. Neptune god of the sea, the farthest of them all. Eleven planets and counting, but as small ones kept being discovered, inexorably crowding this oasis-belt separating us from the parched canal-builder martians, a reform was in order. Herschel himself proposed to call these solar system gnomes as asteroids, "star-like" wandering objects. Ceres and company were demoted, and the asteroid belt was born. It is estimated to contain almost 2 million bodies, of which Ceres is the largest member. The number of planets regressed back to eight, with great relief of all schoolchildren around the world, saved from having to memorize an ever increasing list of orbs with funny mythological names.

Menkind proposes but nature disposes... and in 1930 Clyde W. Tombaugh, "astronomer, teacher, punster and friend" discovered a new planet, farther away than even lonesome Neptune. He called it Pluto, after the suggestion of 11 years old Venetia Burney that decided that the roman god of the underworld would not mind to roam at such distance from the Sun. The nine planets were born, as well as a yellow canine, pet of a famous mouse and his goofy doglike friend (a Disney marvel of a dog which is pet of another dog).

Everybody knows that this was not the end of the story. Pluto is distant, but not alone. Chiron was discovered next, and then Pholus, and then others occupying the empty space just inside the orbit of Neptune. They were named Centaurs and nobody dared to call them planets in fear to upset once more the celestial spheres. But then come the cubewanos (after 1992 QB1, left nameless for having exhausted the greek Olympus) just outside Pluto, and then the plutinos (sharing orbits with Pluto), and the twotinos even beyond the cubewanos... The whole Kuiper belt, 20 times as wide and 200 times heavier than the asteroid belt, came into existence, debris of an inchoate solar system that never coalesced into proper planets. Some Kuiper belt body are large: Eris even larger than Pluto, with Makemake, Sedna, 2007 OR10, Quaoar and Orcus following suit. Eris is the goddess of chaos, strife and discord, and true to her name immediately plotted to unset the smaller Pluto from its undeserved planetary status.

David Charbonneau
And so it was. On August 24, 2006 the International Astronomical Union (IAU) voted to formulate a revised definition of planet, trying to limit this status to the larger bodies in the solar system. The winning proposal defined a planet as a spherical body orbiting the Sun, having sufficient mass to clear its orbits from other objects. Ceres in the middle of the populous asteroid belt, and Pluto as just one of many Kuiper belt objects, were not satisfying this definition, and were demoted once and for all to the class of dwarf planet. This somehow caused consternation for multitudes of school children around the world, that started to send hate-mail to the poor astronomers involved in the decision. The state legislature of Illinois even voted for Pluto to remain a planet, albeit to the same effect of the state of North Carolina when it voted global warming out of existence by legislative decree. If you read this, please don't be nasty, astronomers are nice people too and Pluto likes to be the king of the Kuiper belt, rather than the runt of the solar system. 

Pluto will be visited by the New Horizons spacecraft later this year. Launched on January 19, 2006, the probe has just been roused from hibernation as it approaches Pluto, for a two-weeks data-gathering flyby at the end of a 9 years trip. After Pluto, New Horizons will continue its voyage through the Kuiper belt, visiting another of its inhabitants, if one will be found within reach of the path that can be accessed with the remaining fuel onboard the spacecraft. New Horizons carries a few ounces of the ashes of Clyde Tombaugh, that died 10 years before the spacecraft launch, when Pluto was still a planet, and the goddess of discord had yet to uphend the orders in the celestial spheres.

The photo above shows Owen Gingerich, Chairman of the International Astronomical Union's Planet Definition Committee, at the time of the Pluto discussion. I took the photo during the same event I describe in the previous post. The two smaller photos show Wes Traub and David Charbonneau, hunters of extrasolar planets. On this respect, if you think that 8 planets in the solar system are not enough, console yourself with almost 2,000 planets already discovered orbiting over 1,000 stars other than the Sun: these are big objects and are not at risk to be demoted by a hasty IAU. Their names are kind of boring (resembling more a telephone number than a deity) but this will also change soon: the IAU decided to delegate the naming of extrasolar planets to the public. Despite the competition being open to amateur astronomers from the whole world, it appears that japanese groups were very efficient in registering for this task, and secured over one third of the total naming rights. Fortunately Japan has thousands of gods in its Olympus, so we should not run out of names, at least for a while! 

Not just planets: the arrow points to comet Lovejoy, promise (Ames, IA, Jan 23, 2015)

Sunday, January 4, 2015

Photographing Astronomers

Giovanni talking at his 50th anniversary celebration, Cambridge, MA (May 28, 2009)

From time to time I am asked to take pictures at astronomy meetings. It is not an easy task for me, since I don't have any formal training to cover events and my equipment is not ideal for low light. I also lack the confidence to position myself where I should be for composing the best images, being afraid of distracting the speaker or the audience with my wandering around. So I generally sit in the front row near the podium, with a fast prime lens trying to capture as much natural light as possible. It doesn't make for the sharpest pictures, but the lectern light (or laptop screen) often provides an interesting illumination. Plus I have the advantage, with respect to professional photographers, to understand what's going on in the talk, predicting in advance when the good moments are coming and when I can expect an interesting expression from the speaker. The last time I wore my photographer's hat at an astronomy meeting was last spring, for the retirement celebration of a faculty member in my department. I am still working on the photos; today's post is from a previous event, celebrating the 50th anniversary of science of one of my mentors, Giovanni Fazio.

Giovanni talking with Mike Warner
Giovanni is the person that made it possible for me to work in the US. It was him, almost 20 years ago, that suggested I should apply for a fellowship from the Smithsonian Institution to complete my Ph.D. at the Harvard-Smithsonian Center for Astrophysics, where he is based. I was supposed to stay there for one year, but then I stayed the whole 3 years necessary to complete my program. After that I found a postdoc in the same institution, until I was hired by Giovanni as staff scientist to work on the infrared camera he was building for NASA's Spitzer Space Telescope. I worked with Giovanni for the whole cryogenic mission of Spitzer (that is, until the camera consumed its refrigerant and the program was scaled back). I am still collaborating with him, from Iowa where I moved after I left the Spitzer group. Giovanni is the best boss anybody could hope to work for; in many years of working together, I never heard him raising his voice even once, or order somebody to do something; when a task needed to be done, it was just enough that he mentioned it in our group meetings: somebody would volunteer to do it, with everybody's help, just out of Giovanni's charisma. This is how it is working with Giovanni.

Frank Licata
Despite his italian name, Giovanni was born in San Antonio Texas and does not speak italian. His parents emigrated from different parts of Italy (I believe Tuscany and Sicily) and met when they were already in the US. Their respective dialects were so different that English was their only common language. Giovanni grew up at a time when it was easier for talented kids to go to top schools regardless of their family's economic conditions: after completing his undergraduate studies at a liberal arts Catholic school in Texas he went-on to do its Ph.D. in Physics at MIT. Giovanni background was particle physics; the poster held by Frank Licata in the photo at the right shows a young Giovanni looking at a gamma ray detector that he flew in the 1960s with a balloon, to measure cosmic radiation hitting the stratosphere. These were pioneering years for science: Giovanni is fond to tell the story of how, early in his career, he was tasked to manually insert the target for an experiment at the Brookhaven accelerator. The way you would do it now would be to shut down the accelerator, make a gazillion radiation check, then walk-in with some protective equipment and replace the target: safe, but requiring days of downtime between pulses. The way they did it then was more efficient: replace the target between one pulse and the next, avoiding to be fried by the "beam-of-death" by calculating the exact interval in which the accelerator was down between pulses. Apparently this technique was not recommended even at the time, and the horrified management tried to discourage the exercise by surrounding the target area with a tall fence (to no avail, as they only had to factor-in the fence climbing time as part of the target replacement procedure). This technique was not perfect: Giovanni jokes that they knew the cross section (how much of the beam was absorbed) of everybody in the lab.

Jeffrey Hoffmann
From particle physics Giovanni moved to particle astrophysics (pioneering telescopes lifted by balloon flights to allow detection of radiation otherwise absorbed by the thick lower atmosphere) and was one of the founders of gamma ray and x-ray astronomy. He then moved further down the energy spectrum, and become one of the pioneers of infrared astronomy (this is how I met him). Giovanni was one of the proposers of the NASA space infrared great observatory, the one that would later become the Spitzer Space Telescope. Spitzer was originally meant to fly with the Shuttle, the same as the Hubble Space Telescope, and Giovanni was the principal investigator of an early prototype that flew with the Shuttle during the Spacelab 2 mission (STS-51-F, in 1985). The small photo on the left shows NASA astronaut Jeffrey Hoffmann, toasting to Giovanni during the celebration dinner. Hoffmann was one of the Shuttle mission specialists working on NASA astronomy experiments; while not involved with Giovanni's Shuttle infrared telescope he was part of the STS-61 crew that refurbished the Hubble telescope by fixing its "blurred" optics.

Spitzer was finally launched with a Delta II "Heavy" in 2003, almost 25 years after being initially proposed. It carried the camera designed by Giovanni and his group, which is still taking images well after its designed operational time (the telescope primary mission ended in 2009 when the liquid helium coolant was exhausted). Spitzer is still the source of the largest fraction of the data I use in my research. Giovanni is also still going strong, working towards the next mission that will carry one of his instruments to space into the next decade.

Irwing Shapiro (former CfA director) telling some animated story about Giovanni

Friday, January 2, 2015

One Year plus 0.242190 Days

Moore's Memorial Park, Ames, IA (January 10, 2014)

New year, new post, the first update of this blog since the last summer. The fall has come and gone: a cold November spell, with the only snow we got so far in this season, and an unusually warm December with autumnal weather through the solstice into the new year. The photo above? A snowfall from last year. This year's weather looks more like the small iphone photo below on the left.

January 1st, 2015
It is customary at the beginning of a new year to look back at the 364.242190 spins that the planet did in its last revolution around the Sun. I will refrain from that... you are welcome to go to +Massimo Marengo and read all my rants about the never ending (but very much enjoyed) new course I had to teach this semester (in summary: lots of work to prepare new classes, and not much sleep to recover between one lecture and the next), discovering how I live in the only populated place on earth that is seemingly cooling as a consequence of climate change, the continuing disappointment of a society that for each step forward in equality seems to make three step backwards in racial and economic inequality. Let's talk instead about the calendar itself, and the consequence of these 0.242190 extra days at the end of each year. 

Wishful thinking
Unless you live on a celestial body that is locked in some period resonance with some larger mass (e.g. the moon always shows the same face to Earth, hence the duration of its day is the same as the length of a month; Mercury rotates three times every two of its years), the length of the day and the length of the year are totally random. So it happens that if you want to have a calendar with an exact number of days for each year you are pretty much out of luck, because the seasons would drift by one day every fourth year, and you would soon be celebrating harvest in the middle of spring. That was the situation in antiquity, at the time Julius Cesar went to Egypt to biblically meet the queen Cleopatra. Egypt at the time was the cultural center of the Mediterranean, thanks to the famous library in Alexandria where the summa of all knowledge was kept. It was in Alexandria that Cesar consulted with the local astronomer Sosigenes, and figured out the need to add one extra day every four years to take into account the extra time that kept accumulating at the end of each year. This is how the leap years were born.

More like it
The celestial spheres, however, are indifferent to the desires of humankind, and 0.25 (one day every four year) is not the same as 0.242190. The seasons kept shifting, albeit more slowly and in the opposite way, even after the Julian calendar correction. So was the situation in the middle ages, when the calendar was again out of sync by 10 days. This was not good for the Church, since it completely messed up the complicated calculations that were used to determine the calendar date of Easter. As a result, Pope Gregorius XIII decreed that the day following October 4, 1582 was to be October 15, 1582, obliterating from existence 10 full days from the history of the world, and removing one leap year every century (but not if the century was divisible by 400). With these changes the calendar was forced to sync again with the seasons, with an accuracy better than 0.002%. Not all countries, however, adopted the Gregorian calendar right away: not everybody was very keen to follow the dictates of a Catholic pope. The orthodox Russia, for example, didn't fix their calendar until 1918: as a result, the October bolshevik revolution actually happened in November!

Moore's Memorial Park, Ames, IA (January 10, 2014)


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