Mike Brown's Planets: May 2008

Circular arguments

When something exciting was happening and astronomers wanted other astronomers around the world to know, they used to send a telegram to one central location from which subsequent telegrams were then exploded to observatories around the world. The CBAT --Central Bureau for Astronomical Telegrams -- still exists today to provide the same service, except that it is all done by email today. The CBAT issues International Astronomical Union Circulars, which used to be, in fact, rectangular, approximately the size of an index card, on which new exciting information was mailed. Again, today, it is all email. The switch from telegrams arriving at observatories to emails arriving in everyones already overstuffed in box is another sign of the quaintness being snuffed out of astronomy in favor of efficiency. And I, for one, say thank goodness for efficiency.

Today, we are issuing our IAU Circular describing the moon shadows. It will read something like this:

Mutual Events of 2003 EL 61 and its Inner Satellite

Daniel Fabrycky (Harvard University), Darin Ragozzine & Michael Brown (California Institute of Technology) and Matthew Holman (Smithsonian Astrophysical Observatory)

Orbital fits to the relative astrometric positions of dwarf planet 2003 EL61 (IAUC 8577) and its inner satellite, S/2005 (2003 EL_61) 2 (IAUC 8636), have revealed a near edge-on orbit, implying likely mutual events. The orbital model was based on images from HST (WFPC2) and Keck (LGS-AO). Due to the changing orientation of the Earth-EL_61 line of sight, the orbit is moving closer to edge-on until August 2008, after which the orbit will open up again. The current distance of closest projected approach is ~500 km, nearly the same as the semi-minor axis of the triaxial primary (Rabinowitz et al. 2005, ApJ, 639, 1238), so events will likely be grazing. Shadows of the satellite and EL_61 will likely miss each other. The unocculted lightcurve has double-peaked rotational modulation of full amplitude 0.25 mag and period 3.9 hours; template lightcurves of this variation are available from Holman. The duration of the events will be between 0 and ~6 hours; ingress and egress will consist of ~0.03 magnitude changes on a timescale of ~10 minutes. Telescopes distributed in longitude are needed to follow events as the orbital period is 18.36 d. The main body is rather faint (V~17.4 mag), so high-precision photometry requires moderate (~1 m) collecting area.

Due to orbital eccentricity, events in which the main body occults the satellite are more likely to occur than events in which the satellite occults the main body. Our orbital model predicts mid-event times as follows (add or subtract up to 3 hours for ingress or egress times).

For the satellite occulting the main body:

HJD 2454617.58 +/- 0.07 = 5/31 01:50+/-1:40 UT

HJD 2454635.84 +/- 0.07

HJD 2454654.11 +/- 0.07

HJD 2454672.48 +/- 0.08

For the main body occulting the satellite:

HJD 2454625.22 +/- 0.07 = 6/07 17:10+/-1:40 UT

HJD 2454643.45 +/- 0.07

HJD 2454661.79 +/- 0.1

-------

What does all of this mean? First, a little sadness. We missed most of the shadows by a few years. There is only a chance to observe about 3 more this year, and then not again for 130 years.

The next event is visible over Asian/Europe, but we think it is likely to just be a graze, so nothing will be clear. After that we are on to Hawaii and Japan again for June 7th.

Honestly, I think we're too late. But what a great project it will be for our great-great-great-grandkids.

Moon shadow Monday

On Friday morning, my graduate student, Darin Ragozzine, sent email around to the whole group with the subject "Can I borrow the Keck telescope on Monday night?"
On Thursday night Darin had gotten the third of five pictures from the Hubble Space Telescope of 2003 EL61, aka Santa, and its two moons (rudolph and blitzen). With this third picture Darin could final put together the orbit and Blitzen to see if, as we hoped, Blitzen is currently passing directly in front of and behind Santa. And it is!
Here's what we now known. Blitzen takes about 18 days to go around Santa, so once every 9 days it either passes directly in front or behind. Measuring the precise times of these events would lead us to an exquisite knowledge about Santa and its moons.
But there is bad news, too. This series of events doesn't last forever. As Santa orbits the sun our viewing angle changes, and an orbit that is currently edge on opens up so there are no more events. As far as we can currently tell, these events will only be observable for a little more than a month, and then not again for 130 years. We have about five events left in our lifetimes.
Yikes!
The first one occurs this Monday night/Tuesday morning, and it is only observable for eastern Asia and Hawaii. Hawaii! At this point Darin wisely remembered that on Monday night another member of our group -- Emily Schaller (that is Dr. Emily after her successful Ph.D. thesis defense 2 weeks ago) -- is already scheduled to be at the Keck telescope (the biggest telescope in the world) on Monday night. We'll be looking from there!
The fact that Emily is at Keck that night is just good luck; we were scheduled 6 months ago to do something else entirely. At a telescope like Keck once you're on the schedule the night is yours to do what you want. It had just better be good. This will definitely be good.
Unfortunately the event starts a little late in the night. By the time Blizten goes behind Santa it will already be nearing morning in Hawaii. By the time Blitzen reemerges the sun will be up. Emily will miss it.
Late Friday afternoon I pulled out a map of the earth and drew a huge circle around the places where it will be dark when Santa reemerges. India. Japan. China. Korea. Far eastern Russia. I then got my list of world wide observatories to see what was there. The largest telescope and best chance is in India. Other good ones are in Japan and Taiwan.
How do you get someone half a world away to try to observe something like this in two days? I don't know anyone at any of these observatories. I resorted to google searching to find any email addresses I could for each place and blindly sending email out. Next, I thought: who do I know that might know someone? I contaced an Indian astronomer at Caltech. I then suddenly remembered that one of my own graduate students, Meg Schwamb, worked for a while at an observatory in Taiwan. She had some good thoughts about who to contact, and she started emailing.
By the end of the night last night we had emailed dozens of people across eastern Asia. We're waiting to see who, if anyone, will respond.
Assuming all goes well and we can confirm this event Monday night, we will publicly announce the next one that happens about 9 days later so we can get everyone possible involved. Based on our current data, we think the next one occurs over Europe and the eastern United States. Stay tuned.
In the meantime, here is the pleading email that I sent halfway around the world last night:
>Dear Colleagues:
>We have just determined that one of the satellites of 2003 EL61, the 4th
>largest known Kuiper belt object, is currently in a perfectly edge-on
>orbit and is undergoing mutual eclipses and occultations for the next
>few months. After this year it appears the next such events will not
>occur for the next 130 years.
>
>Study of these events yields an incredible bonanza of scientific results
>(part of a popular article describing results from the recnt
>Pluto-Charon mutual events can be read at
>http://books.google.com/books?id=G7UtYkLQoYoC&pg=PA545&lpg=PA545&dq=mutual+event+pluto&source=web&ots=jDOfb3sWHL&sig=jjLkVTF21FuL-8TiGUT0gy7X5nQ&hl=en
>
>These events give similar exquisite geometric constraints as transits of
>extra-solar planets.
>
>We just found out that mutual events are currently occurring, and it
>appears that only 5 more events will occur this century. The next one is
>this Tuesday night at ~16:00 UT. This event can only be observed from
>~India, China, Taiwan, Japan. We are currently trying to enlist as many
>observatories as possible to obtain several hours of photometry of this
>event. Currently the uncertainty in the timing is a few hours, but over
>the weekend we will get one more astrometric point from HST which should
>allow us to predict the time to about ± 1 hour.
>
>2003 EL61 is approximately 17th magnitude. The occulatation will
>diminish the total brightness by approximately 1%. We thus think that
>only ~1-meter telescopes or larger will have a chance of being able to
>obtain an accurate time for the event. The diminishing will occur over
>~20 minutes. 2003 El61 varies in magnitude by ~.2 mags over a 2 hour
>period, so it will also be important to obtain photometry during the
>same phase for comparison. We also have some extremely accurate HST
>photometry over the entire rotation period to which any ground-based
>photometry could be compared.
>
>We are attempting to alert all major observatories which might be able
>to observe this event in the hopes that each of these 5 events can be
>thoroughly studied. We are happy to coordinate analysis of these
>observations, but we are equally happy for people to perform their own
>analyses of these exciting events. If anyone does observe, however, we
>would greatly appreciate a report of either success or lack of success
>of observing the dimming due to the occultation. Any timing that can be
>provided provides a better prediction for the [small number of]
>remaining events.
>
>We apologize for the short notice; we were not anticipating that these
>events were occurring right now. Because of the short notice, I
>personally will not be available for the next 2 days to help coordinate
>(I am taking my geology class on a trip to the mountains where I have no
>email contact), but my student Megan Schwamb (mschwamb@caltech.edu) will
>be coordinating events in my absence and will be happy to answer any
>questions in my absence.
>
>Thank you for your consideration and I look forward to working with you,
>if possible, on these extremely exciting observations.
>
>Sincerely,
>
>Mike Brown
>
>
>
>
>
>

How not to, um, be too bad

One of the main things that you might convince yourself of if you walked around classrooms at almost any high powered research institution – including my own institution – is that the ability to do something well and the ability to teach that thing well are totally unrelated. It’s not that there are not good teachers in these places – every place has some outstanding teachers – but you would never be able to predict who is going to be one of the good ones by looking at a CV or noting how famous the person is as an academic.

We all know this to be true.

So I was particularly amused the other day when I got an invitation to give a talk about how to be an effective teacher.

“I have no idea how to tell someone how to be an effective teacher,” I protested.

“But you’re such a good teacher you must know how,” I was told.

First rule of effective teaching: don’t assume that someone who is good at something knows how to teach it. Particularly if that thing is teaching.

I couldn’t really get out of it. Last year I won Caltech’s Richard Feynman Prize for Outstanding Teaching, which is a flattering shot of confidence that perhaps I am doing something right in my classroom, but along with the prize comes some responsibilities. Last fall I had to talk to a group of graduate students about how to be an effective teaching assistant (“Don’t overestimate how organized your professor is”) and I had to give a talk at a graduation lunch on a topic of my choosing (“Why it’s OK to feel like an impostor”). I have to speak at the big dinner before graduation this year (haven’t started thinking about that one).Talking about effective teaching was one of the things I had to do.

Three weeks before the talk I was asked for a title. I had not, of course, even begun to think about what I was going to say (Second rule of effective teaching: know what you intend to say). Jokingly, I suggested “Teaching: How not to suck,” knowing that they would not actually use such a rude title. So, of course, they did. And then they plastered signs with the title all around campus.

Such a shockingly rude title led to a higher-than-usual interest in hearing what I had to say. Plus there was free food. The lecture hall was relatively full. Sadly, though the talk itself kind of sucked (Third rule for effective teaching: don’t raise expectations unrealistically).

I did end up with a few things to say; I just didn’t say them in an organized coherent enough way to have it be useful to anybody who was in the audience. But being forced to think about how to describe effective teaching did give me time to come up with a few general principles, of which some have already been stated. Here are a few more:

Fourth rule for effective teaching: have a thin skin. Students always like professors who care, but they rarely understand exactly what that caring really means. Yes, it is important to me that I teach effectively and students learn what I think they are supposed to be learning and they’re not bored. But I also have a very thin skin. To be short (and rude): I hate to suck. I really really hate to suck. And, believe me, sometimes I do. Students out in the audience of large lecture halls think they are very clever about surreptitiously falling asleep without being noticed. I always notice. There are days when I lecture and I simply know it is not going well. I am not clear; I ramble; I say things in the wrong order. And when I leave the lecture hall I feel simply awful. And I go back to my office and think “I do not want this to ever happen again” and I work hard on the next lecture. But not really because I am a magnanimously caring, but because my skin is too thin to have this happen too many times.

Fifth rule of effective teaching: lecturing is bad. I am fairly convinced that lecturing is one of the least effective ways of transmitting information ever invented. We lecture because that is what the monks did in the medieval times before they had books or computers or videos, and no one seems to have really thought very hard about whether or not this makes any sense anymore. So why do it? I challenged my audience during my talk to come up with any reasons they could think of for why lecturing might be useful. They had three thoughts: (1) It might be entertaining; (2) It might aid memory; and (3) It might aid comprehension.

Is any of this true? Who knows! But simply asking them the question totally changed the dynamic of the lecture. They were no longer passive recipients of wisdom from me, but active participants in trying to figure out what was going on. The change in the room was obvious. People sat up in their chairs; eyes were opened; hands were raised. And all of this means, I think, that brains were engaged. They will remember this part of the lecture more than any other part, and when they stand up in their own classes to give lectures perhaps they will think to themselves “why am I lecturing” and they will at least be thoughtful about what they are doing.

The point, of course, was to demonstrate that lecturing is bad. Engaging is good. I do think that a classroom section can be entertaining and aid memory and aid comprehension, but I think that this rarely happens when I stand and deliver a one-way lecture. If it’s one way it might as well be a video, which is significantly more efficient.

Sixth rule of effective teaching: humbly remember your days of ignorance. I teach a class on geology. Conveniently, I know very little geology. I thus relate quite strongly to my students who are seeing these concepts for the first time. I actually think that it would be very clever to require that introductory classes are taught by relative outsiders to the field.

Seventh rule of effective teaching: never ever go late. All students will hate you even if you are the most informative and entertaining person in the world. Fifty minutes after the start, not a single person still wants to be around. The same is true here, thus I end.

Nervous gyrations

On Sunday May 11^th, at 6:53 PM, looking from my backyard, the sun will still be appealingly gleaming above the western horizon, with almost an hour to go before it sets. Almost straight overhead the almost-first quarter moon will be waiting to steal the show as soon as the sun is gone. But I won’t be looking at either one. My eyes will be focused just above the eastern horizon where my current favorite outer solar system object – 2003 EL61, better known as Santa – will just be rising. OK, so I won’t see anything but blue sky; even at night Santa is about 10,000 times too faint to see with the naked eye. But I’ll be looking that direction thinking about the fact that at that moment the Hubble Space Telescope will be joining our hunt for moon shadows. On May 11^th and then four other days over the following two week period, the telescope will come around the earth, swing towards Santa, and snap a quartet of pictures to help us determine precisely where the small satellite (aka Blitzen) is.

This is good news! Without the Hubble we feared that it would be another year or two before we figured out the orbit well, and in that time it was quite possible that shadows of Blitzen would no longer be falling on Santa. The case that we made in our emergency plea to use the telescope must have been compelling; within two days of sending in the proposal we had heard back that we had been approved. But there was some bad news, too. Hubble is approaching two decades in space, so things sometimes fail. Visits by the space shuttle continually fix the Hubble back up and add new capabilities, but with the space shuttle fleet itself barely limping along, Hubble has gone without a visit now for more than six years (a new visit is scheduled for late summer). In that time some of its gyroscopes have failed.

Gyroscopes are critical on a spacecraft like the Hubble, because they keep track of which direction is which. They work just like a spinning top works. As long as the top stays spinning fast it stays pointed in the same direction (in the case of a top that would be up); as the spinning slows the top starts to wobble and finally falls down. In space, with no gravity, the top would just keep spinning in whichever direction it was originally pointed. If the spacecraft does some maneuver to point in a different direction, the top still stays fixed pointing in whatever direction it started. Tops – which is all that gyroscopes really are – are great for space, because, with no gravity and no compass, there are not many other ways to figure out which direction you’re pointing.

If the Hubble had no gyroscopes left it couldn’t do anything. Luckily, three still survive. With three gyroscopes you can point anywhere in space at anytime. Wisely, though, the people who run Hubble decided that it was better to keep one in reserve in case one of these last three fails. So Hubble operates with two gyros. With only two you can still point to anywhere in the sky, but not at anytime. And this where the bad news comes in. After about noon on May 24^th Hubble can’t observe Santa again for a few months.

The people at Hubble wanted to know: was it still worth doing the observations? We had to ponder. We think Blitzen takes about 19 days to go around Santa. From May 11^th (which was the soonest we could get on the telescope) until May 24^th is only 13 days. So we won’t see the complete orbit, but we think we’ll see enough to be able to calculate where Blitzen is the rest of the time. “Proceed!” we said.

But then there was worse news. Hubble uses the gyros for course pointing, but for keeping the telescope absolutely still during the course of the observations it also tracks a pair of bright stars close to the target. And, by bad luck, there aren’t enough of them close to Santa. A single star is available up until the 19^th, and then absolutely nothing. We can do the observations, slightly degraded, with a single guide star, but there is nothing to be done after the 19^th. So now we were crammed into May 11^th through the 19^th, an eight day window, when we really had hoped for a full nineteen day window. They asked again: is it still worth it?

By luck, if you only had eight days out of nineteen, these might be precisely the eight days you would want. They are when Blitzen is closest to Santa, which is the part of the orbit we need to know best. But still, it’s going to make our lives even harder than before. Will it still work? We did some quick calculations and decided, once again, we could do it. So we’re on for our eight days in May.

Now I’m nervous. We promised a pretty spectacular result to the people at Hubble. We need to deliver. There is always the chance that the new data will show that the shadows just finished happening and we’re too late. That would be bad luck, but we could at least hold our heads high and say we figured it out, just a little late. No, what makes me nervous is the possibility that we will get the data and still not be able to figure it out. People will say: OK, what’s the answer? And we will have to say. Well, um, we still can’t quite calculate the orbit. We can’t tell you when there will be moon shadows. Wait until next year.

I don’t think this will happen, so mostly it’s just paranoia. And I always have it. Every single evening when I am sitting at big telescope and the sun goes down and the dome shutters open I get similarly nervous. What if we did something wrong and all of our careful calculations about what we are going to look at and what we might discover were wrong? What if we forgot to take something into account? What if there is a better way to be using the telescope? What if…

And then the sky darkens and our first targets appear on the screen and I forget all of the nervousness and worry and get to work.

The same thing will happen, I hope, with this project. I won’t be at the telescope this time. I’ll be sitting at my desk sometime a few days after May 11^th, when the data finally get transmitted and processed and downloaded onto my computer, and I’ll pull up the first image and forget all of the nervousness and worry and get to work.

Pages

Circular arguments

Moon shadow Monday

How not to, um, be too bad

Nervous gyrations