Eight cores, working hard:
orbits, orbits…
more orbits.

Suki is cold.
Laptop is warm.
Suki sits on keyboard.

Machine vexation,


(click to embiggen)

Zodiacal Light West of Flagstaff, Feb. 2015

U.S. Naval Observatory - Flagstaff Station (click to enlarge)
U.S. Naval Observatory – Flagstaff Station (click to enlarge)

The zodiacal light at 7:51 pm (MST) on February 10, 2015, as seen from the west parking lot of the U.S. Naval Observatory near Flagstaff. If you’re wondering where the Observatory is, it’s about five miles west of downtown (Google maps link).

Below are two versions of a stack of eight 30-second exposures taken with a ZWO ASI120MM camera mounted on a camera tripod. This was 1h 47m after sunset (6:04 pm), and 21 minutes after the end of astronomical twilight (7:30 pm). You can see several naked-eye astronomical wonders, which are marked on the annotated version:

Zodiacal light from NOFS, 2015-02-11 (click to enlarge)
Zodiacal light from NOFS, 2015-02-11 (click to enlarge)
Zodiacal light from NOFS, 2015-02-11, with annotations (click to enlarge)
Zodiacal light from NOFS, 2015-02-11, with annotations (click to enlarge)


Sense and Sensibility and the American Gun Culture

Sense and Sensibility.

Jane Austen put these two words together for a specific reason.

Sense: meaning, understanding, prudence, sound judgement.

Sensibility: sensitivity, awareness, empathy.

She didn’t have to worry about guns the way we do, the way America does today. But if she had I think she likely might have said something worth our while to contemplate. Sense. Sensibility.

We have yet another senseless shooting, this time too close to my home in Flagstaff. At Northern Arizona University, where a close family member teaches, a student retrieved a gun from his car and shot four students, murdering one. (One is still in the ICU.) Over a simple fist fight, hurt feelings, wounded pride — a child lies dead and many lives destroyed.

A spat quickly broke out online over whether or not to call this one (there are so very many) a “mass murder.” The NAU police reassured the public, saying that this was not like another mass shooting that had just happened at a college in Oregon. Others were not buying it. Perhaps because of the shock and cognitive dissonance that comes with a shooting that is too close, too personal, they are missing the point.

A common (sadly — shamefully — this is all too common) behavior can stem from a myriad of complex generators, complicated motivations, because human psychology is, in the now, a complex miasma of innate character, upbringing, experience, and happenstance — nature and nurture and randomness. Yet, dead people on the ground are dead people on the ground: mass shooting, mass murder.

What is the point?

Ask yourself: what is the most common denominator in each one of these mass shootings, this endless succession of mass murders, this underbelly of America’s prolonged spiral to suicide? The answer is readily apparent to anyone not blinkered by stubborn ignorance or mindless fear: the uniquely sick American obsession with weaponry, in concert with the rigidly immoral, ignorant, selfish, counterfactual, antifactual, infantile, long-bankrupt ideology of the right wing, one consequence of which — just one of innumerable repercussions from a depraved world view — is a near-complete absence of meaningful gun regulation.

To choose slaughter (intended or not) over minor inconvenience to the sensible — which is really what we are talking about with effective regulation of firearms — is not an act that comes from moral or ethical values; it is sick and depraved.

You may be thinking, “but this does not apply to me.” Do you choose to stand by and do nothing? Are you silent? Then you, too, have opted for preserving our awful status quo, for senseless bloodshed, shattered bodies, ruined lives, devastated families. Inaction is a choice.

Silence is a choice.

To choose instead reason, and sense, in light of overwhelming evidence; to proactively choose responsibility to the people around you, and empathy for those not in your shoes, and good governance in public policy — these come from ethical, moral values. Reasonable values. Wouldn’t this be better than continuing to tacitly approve senseless carnage?

That is the point.

It is time we start acting like adults, you and I — own up to our responsibility. It is up to you, and me, and you and you and you. The nature of this monster, this beast that we have allowed other monsters to create and nurture while you and I were distracted, is that none of us gets to opt out; you cannot not play.

So which do you choose? Continuance of our national blood bath? Or sense and sensibility?

Fun with Python

Draw your own conclusions:

Grammar vs. politics. Or, education vs. ideology.
Grammar vs. politics. Or, education vs. ideology. (click to embiggen)

The red points are data from a grammar.com analysis of nonnegative Facebook comments on the pages of these presidential candidates. The black curve is the most-optimal least-squares fit of a polynomial (fourth-order, in this case) that, among the polynomials tested (orders zero through eight), minimizes the information loss of that model representation of the data. This information loss minimization is called the Akaike Information Criterion.



Fast hairy monsters high up on a wall, incognizant of their fortune, being as they are—at least on occasion—and in more than one sense of the word, ascendant, beyond the ken of three prowling, ever-watchful, and even faster (as if that were imaginable, but imagination, I have noticed, often wears the Emperor’s illusory purple), hungry—or so they yowl at me, incessantly—feline beasts known throughout the land, their domain, not just for their sleek and deadly elegance but for torturing, and in turns dismembering, in that horrifying, playful, pure-sociopath way unique (one hopes) to their species—these nimble piliferous octopeds would be glad, if they but had the ganglions for it, that I spy them, at least some of them, first.

Protected: Why doesn’t everything mix into everything else?

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Is Trump’s Lead Significant?

Snapshot of polling results among Republican voters over the past three months [click to embiggen]
Snapshot of polling results among Republican voters over the past three months [click to embiggen]
At the moment, The Donald leads nationally among Republicans, with 29.8% favorability. Roughly 30% of polled Republicans currently favor Trump over the rest of the Republican Field of Clowns. People argue that 30 percent is not terribly impressive. Are they right?

You have to interpret more carefully than that. Roughly 30% of polled Republicans prefer Trump over the others. That last bit is important: that many other Clowns are vying for the prize matters in the interpretation of Trump’s 29.8 percent.

Since there are fifteen Clowns in this poll, an even distribution of favorability would be 6.7% per Clown. So Trump’s 29.8% is a pretty big outlier. How big? The mean of this favorability distribution is $\mu = 6.1$%, pretty close to the 6.7% expectation. The standard deviation of this distribution of Clown favorability ratings is $\sigma = 7.4$%. Trump’s $p = 29.8$% therefore is a $\Delta = \dfrac{\left|p\, – \mu\right|}{\sigma} = 3.2$-sigma outlier, which is statistically significant. What this means is that the chance of that being just a statistical fluke (i.e., the likelihood that a random choice from among a Gaussian distribution with $\mu = 6.1$% and $\sigma = 7.4$% would land you at 29.8% or higher) is $1 – \mathrm{erf} \left(\dfrac{\Delta}{\sqrt{2}}\right) = 0.0014 = 0.14$ percent.

In the physical sciences, a result lying three or more standard deviations away from the null hypothesis value is the typical bar for publishable significance. $\mathrm{erf}$ is the error function:

$$\mathrm{erf}(z) = \dfrac{1}{\sqrt{\pi}} \int_{-z}^z e^{-t^2} dt$$

and is the probability of a random variate lying between $-z$ and $+z$ in a distribution with zero mean and standard deviation $\frac 12$. Now, the 0.14% result above would hold if the favorability distribution were a normal (i.e., Gaussian) distribution, which it certainly is not. But the conclusions should correspond closely enough to reality to use as an approximate guide.

The next candidate down is Carson at 16.0%, and Bush is third at 8.3%. Carson is only 1.3 sigma out from the mean (Bush: $0.3\,\sigma$), which corresponds to the likelihood of his favorability rating being where it is or higher due to random chance is 18 percent (Bush: 77%).

Conclusion: Trump’s and Carson’s leads above the rest of this particular Republican Field of Clowns are currently significant, while for the rest it’s a coin toss in terms of preference — even for Bush.

Update 9/10: Numbers and graphic updated from original to reflect values current as of 10 September.

Hotel Balcony

Open the sliding glass door

to a wall of humidity.


The Scorpion—

its supergiant heart Antares

reaching further than Mars—

an unaccustomed ten degrees higher

in the evening sky.


Antares, the Sun, and the orbit of Mars ("Redgiants" by Sakurambo at English Wikipedia - Transferred from en.wikipedia to Commons.. Licensed under Public Domain via Wikimedia Commons)
Antares, the Sun, Arcturus, and the orbit of Mars
(click to embiggen)
(“Redgiants” by Sakurambo at English Wikipedia. Licensed under Public Domain via Wikimedia Commons.)



Prevailing Wind

Kalaeloa runway 22L

from seven thousand feet:

one end is heavier

in skid marks.

30,000 feet over the Pacific

Cauliflower and gossamer,

red-tinged clouds—

we chase a bloody Sun.

A Bookmans Lament

One hundred nine dollars of credit on the ledger,

A hundred nine dollars of glee.

I look around.

The aisles, I walk down.

Twenty-seven dollars of credit for me…

Nutballs and the Mode

Atheist Republic's Kaaba: Love Wins
A stylized Kaaba (click to embiggen).

Recently, Atheist Republic (AR) posted this image (⇒) in response to the Supreme Court’s decision (pdf) that legalizes marriage in the U.S. It is a Photoshopped image of the Kaaba in Mecca. The reaction from noisome elements of the Muslim community has been, predictably, swift, violent, and largely incoherent (cf. the Facebook post or AR’s original Twitter post for a sampling). AR’s post is fine; I think it is timely, in good taste, and makes a good point. However, I think AR made a mistake.

AR responded to the growing shit storm in a subsequent post on their web site (WARNING: one image, about ¾ of the way into the post, is deeply disturbing), electing to show a number of select examples of the insults and threats they’ve received to make a point:

Please keep in mind that these aren’t members of ISIS or Al-Qaeda making these statements, but rather are your everyday average Muslim.


…these aren’t extremists or jihadists, they’re just average Muslims. These are the ones who call themselves “moderate”.

And, if you are feeling particularly thick-headed:

To make it clear that these are supposed “moderate” Muslims, I’d like to point out that we know for a fact that one of these men is a US citizen. This particular commenter has specifically asked for information from one of our admins that he suspects lives in his area, and threatened said admin with physical violence against this admin and their family.

A skewed distribution (click to embiggen). Where do you think IPLs reside?

One thought kept nagging me as I read AR’s response: AR furnishes no valid evidence or argument to support the all-too-common claim that these select nutballs are “your everyday average Muslim” (as opposed to the crazies that carry out terrorist attacks in the name of their religion or, more accurately, their ignorant, deranged ideology). It seems likely to me that the cretinous whackjobs sprinkling AR’s posts with turds are neither average nor representative of Muslims in general. These whackjobs are—like our own noisome right-wing nutballs—an abnormally incoherent, ignorant, and vocal minority. I’ve no doubt average Muslims are as willingly delusion-controlled as our average Christians here in the U.S., but I have to question that the infantile profane loudmouths of either organized delusion system lie anywhere near the peaks (i.e., the modes) of their respective population distributions.

The excerpts above—and, indeed, AR’s entire argument—illustrate several common logical fallacies. In the first two excerpts, the author is arguing by assertion. This is a counterproductive rhetorical tactic. It raises people’s hackles, to your disadvantage.

The third excerpt is somewhat more interesting. First, it cherry-picks an anecdotal example. (The example itself also seems hardly relevant—a red herring.) This is a surprising mistake, since cherry-picking is perhaps the most common logical fallacy for which rationalists such as AR criticize religionists and the right-wing.

In this excerpt the author also equates being a U.S. citizen with being “moderate”, with no supporting argument or evidence. As recent events in the U.S. have shown repeatedly, there is nothing moderate about the beliefs of U.S. terrorists, Muslim or not. This is  a false equivalence, perhaps the second most common logical fallacy employed by the right (or maybe the third, behind strawman argument).

This is not an apology for “average” adherents to horrifically damaging organized delusion systems. From all that I’ve seen, Western religions are among the most senseless and destructive invented concepts in the history of humankind. But accuracy, precision, and validity in our claims and arguments, whatever the context, matter.

We rationalists are—or should be—better than this.


Seriously, you do not need to see this image—it cannot be unseen.

 Speaking of crazies, is there much, if any, difference between a Muslim terrorist who slaughters innocents in a medical treatment building and, say, a Christian terrorist who slaughters innocents in an African American church? Or between that (or any other) Muslim terrorist and a Christian terrorist who shoots dead a medical doctor during church services?

Why I Use Python (part 1)

PHP needs a semicolon at the end of every statement. So does C. So does C++. So does Java. Why? So far as I can tell, for no other reason than laziness on the part of language designers.

(Note: stuffthathappens is no more.)




DDA 2015 – Constraints on Titan’s rotation from Cassini mission radar data

This is one of a series of notes taken during the 2015 meeting of the AAS Division on Dynamical Astronomy, 3-7 May, at CalTech. An index to this series (all the papers presented at the meeting) is here.

Bruce Bills (JPL)


We present results of a new analysis of the rotational kinematics of Titan, as constrained by Cassini radar data, extending over the entire currently available set of flyby encounters. Our analysis provides a good constraint on the current orientation of the spin pole, but does not have sufficient accuracy and duration to clearly see the expected spin pole precession. In contrast, we do clearly see temporal variations in the spin rate, which are driven by gravitational torques which attempt to keep the prime meridian oriented toward Saturn.

Titan is a synchronous rotator. At lowest order, that means that the rotational and orbital motions are synchronized. At the level of accuracy required to fit the Cassini radar data, we can see that synchronous rotation and uniform rotation are not quite the same thing. Our best fibng model has a fixed pole, and a rotation rate which varies with time, so as to keep Titan’s prime meridian oriented towards Saturn, as the orbit varies.

A gravitational torque on the tri-axial figure of Titan attempts to keep the axis of least inertia oriented toward Saturn. The main effect is to synchronize the orbit and rotation periods, as seen in inertial space. The response of the rotation angle, to periodic changes in orbital mean longitude, is modeled as a damped, forced harmonic oscillator. This acts as a low-pass filter. The rotation angle accurately tracks orbital variations at periods longer than the free libration period, but is unable to follow higher frequency variations.

The mean longitude of Titan’s orbit varies on a wide range of time scales. The largest variations are at Saturn’s orbital period (29.46 years), and are due to solar torques. There are also variations at periods of 640 and 5800 days, due to resonant interaction with Hyperion.

For a rigid body, with moments of inertia estimated from observed gravity, the free libration period for Titan would be 850 days. The best fit to the radar data is obtained with a libration period of 645 days, and a damping time of 1000 years.

The principal deviation of Titan’s rotation from uniform angular rate, as seen in the Cassini radar data, is a periodic signal resonantly forced by Hyperion.


  • Titan:
    • hard to see surface
    • Cassini’s radar intended for mapping surface
      • didn’t get much by way of repeat observations (“tie points”), which are needed to constrain rotation
      • most data near poles — not terribly helpful
  • Rotation model from tie-point observations
    • Stiles et al. 2008: 50 tie points over 2.8 yr
    • Now: 2602 tie points over 10 yr
    • solve for 3 params (RA & DEC of spin pole, angular rate)
    • $P = 15.94547727 \pm 6.03 \times 10^{-7}$ d
    • spin pole precession
      • gravity model: ~250 yr
      • not clearly seen in data
    • spin rate variations
      • seen in data
      • dynamical model
        • assume Titan in synch. rotation
        • gravity torque
        • dissipation
        • $\rightarrow$ libration period ~850 d
        • Hyperion has nontrivial influence
    • fit: libration period = 645.4 d, damping time = 430 yr, rotation period slightly changed

DDA 2015 – Recent Formation of Saturnian Moons: Constraints from Their Cratering Records

This is one of a series of notes taken during the 2015 meeting of the AAS Division on Dynamical Astronomy, 3-7 May, at CalTech. An index to this series (all the papers presented at the meeting) is here.

Session: Moon Formation and Dynamics I

Henry C. (Luke) Dones (SWRI)


Charnoz et al. (2010) proposed that Saturn’s small “ring moons” out to Janus and Epimetheus consist of ring material that viscously spread beyond the Roche limit and coagulated into moonlets. The moonlets evolve outward due to the torques they exert at resonances in the rings. More massive moonlets migrate faster; orbits can cross and bodies can merge, resulting in a steep trend of mass vs. distance from the planet. Canup (2010) theorized that Saturn’s rings are primordial and originated when a differentiated, Titan-like moon migrated inward when the planet was still surrounded by a gas disk. The satellite’s icy shell could have been tidally stripped, and would have given rise to today’s rings and the mid-sized moons out to Tethys. Charnoz et al. (2011) investigated the formation of satellites out to Rhea from a spreading massive ring, and Crida and Charnoz (2012) extended this scenario to other planets. Once the mid-sized moons recede far from the rings, tidal interaction with the planet determines the rate at which the satellites migrate. Charnoz et al. (2011) found that Mimas would have formed about 1 billion years more recently than Rhea. The cratering records of these moons (Kirchoff and Schenk 2010; Robbins et al. 2015) provide a test of this scenario. If the mid-sized moons are primordial, most of their craters were created through hypervelocity impacts by ecliptic comets from the Kuiper Belt/Scattered Disk (Zahnle et al. 2003; Dones et al. 2009). In the Charnoz et al. scenario, the oldest craters on the moons would result from low-speed accretionary impacts. We thank the Cassini Data Analysis program for support.

Canup, R. M. (2010). Nature 468, 943
Charnoz, S.; Salmon, J., Crida, A. (2010). Nature 465, 752
Charnoz, S., et al. (2011). Icarus 216, 535
Crida, A.; Charnoz, S. (2012). Science 338, 1196
Dones, L., et al. (2009). In Saturn from Cassini-Huygens, p. 613
Kirchoff, M. R.; Schenk, P. (2010). Icarus 206, 485
Robbins, S. J.; Bierhaus, E. B.; Dones, L. (2015). Lunar and Planetary Science Conference 46, abstract 1654
Zahnle, K.; Schenk, P.; Levison, H.; Dones, L. (2003). Icarus 163, 263


  • Can cratering records constrain moon ages?
    • see http://space.jpl.nasa.gov
    • small inner moons (and Mimas) interact strongly with rings — the so-called “ring moons”
      • migrated from outer edge of rings ~100 Myr
    • regular moons (Mimas-Iapetus) are (assumed?) primordial
    • transition is abrupt where tidal forces prevent formation
    • formation of moons from spreading rings:Charnoz et al. 2010,Canup 2010,Charnoz et al. 2011,Crida &Charnoz 2012
      • ring spreads viscously
      • outside Roche limit, formation
    • Lainey et al. 2012: dissipation stronger than thought
      • decreases timescale considerably
  • Impact rates
    • $R_{moon} = R_J \dfrac{R_S}{R_J} \dfrac{R_{moon}}{R_S}$
    • Crater scaling: diameter vs. velocity
    • impacts/$10^9$ yr: Mimas 8.5, Rhea 48
    • Mimas & Rhea counts: Robbins et al. 2015 (LPSC)
    • plot: #craters larger than D vs. D
    • Mimas: saturated up to $D \sim 20-45$ km
    • Rhea: saturated up to $D \sim 25$ km
  • Summary
    • Mimas: Craters are near saturation for diameters < 20 km
    • Rhea: saturation < 25 km
    • Ages may be underestimated