Observing Pulsars and Dark Matter

In a meeting today about the upcoming Square-Kilometer Array, I got to learn a little bit about pulsars and cosmology. Or at least, about what a radio telescope can do to observe pulsars and the earliest origins of the universe.

It turns out that pulsars, at least distant ones, do not manifest themselves as a blink of bright light (radiation). While presumably the signal starts out at a single frequency, over long distances it suffers dispersion that smears the pulse out over a range of frequencies. Even worse, the arrival time also gets smeared, so the higher frequencies arrive first and then “slide” down towards the lower ones (see example at right, taken from this handy explanation of pulsar dispersion). This means that if you aren’t sweeping frequencies at just the right time, you might totally miss a pulsar signal. The SKA will be hunting for these. Astronomers are particularly eager to find pulsars close to black holes, because pulsars are extremely reliable clocks and you should be able to test some interesting relativity hypotheses with a pulsar that’s within the black hole’s distortion field. (Related: see this ultra-cool animation of a recently discovered pulsar pair.)

Even more intriguingly, the SKA will be looking deep into the earliest evidence of the universe’s existence. Light takes time to travel, so the further away a source is, the farther back in time we are seeing it. If we look far enough, we can see back to when clouds of neutral hydrogen (a proton plus an electron) roamed the universe, before stars were created. At that time, we believe that clumps of dark matter formed. These aren’t directly observable, but they attracted the neutral hydrogen (which is observable and opaque). The hydrogen acts as a “tracer” for dark matter. Once stars formed, the radiation they gave off ionized the hydrogen (stripped off the electrons), and it became transparent… so dark matter once again could only be observed indirectly (e.g., through gravitational lensing). Yet due to distance and the limitation of light speed, we can still see back to the time of neutral hydrogen and record the shapes of dark matter then in existence.

On a lighter note: The History of the Universe in 200 Words or Less.

The Reverse Corte in Waltz

This step recently came up in a waltz class I am taking with the Caltech Ballroom Dance Club. It’s a really lovely and simple step that ends in the unusual position (for waltz) of the follower outside partner.

  1. Leader (backing): right foot back, begin to turn to the left
    Follower: left foot forward, turning to the left
  2. Leader: close left foot to right, continuing to complete 3/8 turn to the left
    Follower: right foot to side, continuing to turn and rise
  3. Leader: shift weight to right, lowering at the end of the beat
    Follower: close right foot to left, lowering at the end of the beat (outside partner)

(More nitty-gritty details for those so inclined.)
Other than in step one, there isn’t very much actual motion. (In fact, it’s almost more of a hesitation with turn, in my opinion.) But that lack of progression leaves a lot of room for some beautiful swaying and shaping. The first step can have some contra-body movement, in which the couple’s upper bodies turn slightly to the left (against the natural slight motion to the right otherwise implied by this step). Then steps 2 and 3 can be stretched out, with a slow, lovely rotation (of the upper bodies) to the left as the couple floats upward and then settles (late) on the end of 3.

It turns out that this step is part of the Bronze syllabus for International Waltz. Despite, well, fifteen years of dancing, I don’t consciously remember ever encountering it before. I’m very glad to add it to my repertoire!

Note: in my opinion, while following this step is a breeze (and great fun!), leading it is significantly more difficult. The leader’s first step backward and then closing while rotating 3/8 and leading the follower’s rotation is a challenge to both balance and coordination. However, it’s a beautiful, compact yet (optionally) showy step, and it flows very nicely into a back whisk. Enjoy!

P.S. Art by Parviz Yashar.

Learning to Teach to Learn

I’ve been making steady progress with my Italian podcasts: please (per piacere or per favore) and thank you (grazie), days of the week (oggi è giovedì!), numbers (up to 100), Merry Christmas (Buon Natale! Clearly I’m still working my way towards the present in podcast-land). I’ve also been picking up more vocabulary through livemocha.com‘s Rosetta-Stone-like lessons. They step you through six phases, in increasing difficulty: learn (look at pictures, read the caption, listen to it spoken), reading (match pictures to text), listening (see picture and match audio to text), magnet (drag and drop word tiles in the right order to form a correct caption for a picture), writing (compose your own sentences based on the new vocab), and speaking (record yourself reading a passage aloud).

I finished the first six-part lesson and ran straight into a huge potential time trap. You see, once you submit your writing and speaking “lessons”, they are posted for others to comment on. This is absolutely fantastic, as you can get feedback (for free) from other users of the site, and generally from those who have more expertise in the language you are studying than you do. But once you submit a lesson, the site lists for you the last few entries other people have made on that same lesson. And since it’s fresh in your mind, of course you might click through… and then you might start spotting small mistakes… and writing little helpful comments. And then the teacher in you roars to life and you start clicking through all of these entries, because, well, you can’t let this happen. Not only that, but you get “mochapoints” for commenting on others’ submissions, and extra points for being the “first to review” anything. (Mochapoints aren’t worth anything, they’re just a status marker indicating your level of activity on the site. But apparently this is still motivating on its own.)

An hour later, you realize that you’ve just spent an hour grading other people’s rudimentary Italian essays (e.g., “The woman is tall. The boy is fat. You are rich. I am poor.”). While this is undoubtedly yet another useful way to reinforce your language learning (you end up checking extra-carefully before posting a correction for anyone else!), it’s not clear that this is overall the best use of your time. You step gingerly away from the site, but not after listening to (and commenting helpfully on) one of Vitor-from-Brazil’s spoken English submissions. Sigh.

P.S. Vitor later “friended” me, apparently in gratitude for my comments. Awwww.

Reverse the Flow of Time on your iPod Shuffle

I’ve been enjoying a variety of podcasts on my iPod Shuffle, from knitting to Sandra Tsing Loh to Italian language lessons. One thing that’s been driving me batty is that when I drop new podcasts onto the iPod, they end up in reverse chronological order (newest first), which is almost always not the order I want them in. Any changes I make to the order (sorting by column or moving podcasts around) are mysteriously lost when I undock the iPod. To judge from the Web, I’m not the only one with this vexation.

Thankfully, Stephen Mielnicki posted the solution (buried in this thread): go into your Podcasts (not on the iPod) and click the “Release Date” column to order them in ascending order, rather than the default descending order. This order will propagate to the iPod, even for podcasts you previously copied over. Useful to know—but unintuitive; the obvious metaphor for the iPod is to treat it like another playlist, and in this case it definitely doesn’t behave like one.

Another thing I learned about the iPod Shuffle while googling is that when you put it in “random play” mode, it deliberately skips over podcasts and audio books. I’d noticed that it never played these things, but figured it was just because they were such a small fraction of the iPod’s contents and therefore had a low probability of being chosen. But this is a nice feature. (Of course, it seems to achieve it merely by looking at file extensions.)

Italian Greetings

I listened to a few more lessons from learnitalianpod.com. I like the dialogue, but the female speaker is much clearer than the male speaker so I tend to prefer listening to her. Also, three (slow) repetitions of everything is about one more than I need at this point (this may change as we move away from cognates :) ). And finally, I really wish that the transcripts of the dialogues were freely available; to get access to them, you have to pay a monthly fee. This means I (instead) end up digging around to find how to spell everything, since I’m definitely a visual learner and I don’t remember things well unless I know how they are spelled. That isn’t necessarily bad, since the extra searching provides additional reinforcement. However, it did lead to a mistake I made in my last post: “Pleased to meet you” should have been “Piacere di conoscerti” (the informal version), not “Piacere di conoscerla” (the formal version). This explains the apparent inconsistency in the level of formality. Personally, I’d rather learn the formal since it is more likely to be useful. But I’ll try to be patient and wait for it. :)

New phrases today include:

  • Buon giorno! Good day!
  • Arrivederci! Goodbye!
  • Come ti chiami? What is your name?
  • Io mi chiamo Kiri. My name is Kiri.
  • Così e così. So-so. (Response to “come stai?”)
  • Io sono ocupado. I’m busy.
  • Io sono felice, perché mia mama è a Venezia. I’m happy, because my mother is in Venice. (That’ll be handy!)

I also got the full “to be” conjugation:

io sono noi siamo
tu sei / Lei è (formal) voi siete / Loro sono (formal)
lui/lei è loro sono

Michelle’s comments on my previous post now make more sense. :) Interestingly, capitalization matters here — the formal “you” pronouns get capitalized regardless of sentence position. (That way you can tell them from the third person pronouns, presumably.)

Another useful resource: italianlanguageguide.com.

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