A thoroughly sporadic column from astronomer Mike Brown on space and science, planets and dwarf planets, the sun, the moon, the stars, and the joys and frustrations of search, discovery, and life. With a family in tow. Or towing. Or perhaps in mutual orbit.

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.
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
>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.
>Mike Brown

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