According to Colwell

This year was my first exposure to what is apparently an annual e-mail hoax regarding Mars appearing to be as large as the Moon in the sky. Since I’m teaching an introductory astronomy course this semester it might make for a good teaching moment. One student received the e-mail from her mother, and my wife got it from a friend. Physically, Mars is about twice as large as the Moon and a whole heck of a lot further away. Rather than looking up numbers in a textbook (or wikipedia), the layperson can figure this out with simple quantitative reasoning. The Moon orbits the Earth and Mars orbits the Sun. This tells us that Mars must be much further from the Earth. Earth’s gravity keeps the Moon in orbit because it is close enough to the Earth for Earth’s gravity to be more important than the Sun’s. For Mars to appear as large as the Moon, it would need to be as close to the Earth as the Moon. The timescale for the motion of Mars is roughly a year (a martian year is about two Earth years, but we don’t need to worry about precision to a factor of two, or even a factor of ten, for this exercise). Thus, the idea that one day Mars is its normal pinpoint size and the next day it is huge contradicts the actual time it takes for Mars and the Earth to move relative to each other. On the one hand I find it discouraging that people are unfamiliar enough with the appearance of the sky to give hoaxes like this any credibility. On the other, maybe there is some value in it: if it makes someone look up at night for a few minutes, then next time they’ll know to send this and similar e-mails straight to the junk folder.

There is an astronomical event worth noting this week, however. In the early hours of Tuesday there will be a total lunar eclipse. It will be more easily visible from the western United States than the in the East. This chart gives a map of the times and how much is visible from different parts of the world. A lunar eclipse occurs when the Moon passes through the shadow of the Earth. Because the Earth has an atmosphere, the Moon does not become completely dark: sunlight is refracted through the Earth’s atmosphere causing it to be deflected and still strike the Moon. Red light is more strongly refracted than blue, so the full Moon becomes reddish in color during the eclipse. Lunar eclipses are one way that the ancients knew the Earth was round: they realized they were seeing the shadow of the Earth, and the shadow had a round edge. The only object that always casts a round shadow is a sphere. Lunar eclipses occur about every six months instead of every month because the Moon’s orbit is not in the same plane as the Earth’s orbit around the Sun, so only twice each year do the three objects roughly line up.

It was thirty years ago today that the Voyager 2 spacecraft was launched from Florida for a grand tour of the outer solar system. (Voyager 1 was launched two weeks later; the details of their trajectories led Voyager 2 on a slower path to the outer solar system, so while launching later, Voyager 1 actually got to Jupiter and Saturn first.) At the time of launch it was not known if there would be funding for Voyager 2 to continue to Uranus and Neptune and become the only spacecraft (still) to explore those planets at close range. I have a special fondness for the mission because the data returned from the flyby of the outermost two planets in the solar system formed the core of my Ph.D. dissertation.

Voyager 2 is about 12 light-hours from Earth and is operating with about 300 Watts of power from its radio-isotope thermoelectric generators (RTGs). Its scientific mission continues with measurements of the magnetic field and charged particle densities as the spacecraft drifts across the boundary between the heliosphere and interstellar space. This is as good a definition as any for the edge of the solar system - the location where the background plasma is no longer dominated by streaming solar wind electrons and protons from the Sun but by the interstellar medium. There are comets gravitationally bound to the Sun much further away than Voyager 2 right now, but you’d have to go a fair way toward the nearest star to pass the Oort cloud of comets.

Unlike the Harry Potter movies, Stardust is a movie filled with magic that follows rules unknown to us in the audience. So while we have become used to what witches can do in the world of Harry Potter, we really don’t know what to expect in the magical world of Stardust. Charlie Cox plays Tristan who journeys into the magical kingdom hidden in the heart of England in order to retrieve a fallen star to win the heart of the town beauty. The star in question turns out to be a beauty too, Yvaine (Claire Danes). She is sought by the very old and very ugly witch played by the very beautiful Michelle Pfeiffer because witches get a good long dose of youth from drinking from the heart of a star. Meanwhile each son of the dead king is searching for the ruby he cast into the sky so he can claim the throne. Robert DeNiro has a show-stealing turn as a take-no-prisoners captain of a flying boat that catches lightning so he can sell it to Ricky Gervais (creator of the BBC The Office).

It’s an enjoyable fantasy romp, and refreshingly original, and the tone set by director and co-screenwriter Matthew Vaughn remains lighthearted and upbeat even as likable characters are killed. That’s a bit of a double-edged sword because it shows how little emotional investment I had in the characters, but at the same time kept a smile on my face for nearly the whole movie.

Beyond knowing that Jane Austen died at a young age and never married, I don’t know much about her life. After seeing Becoming Jane I probably still don’t. It is easy to imagine that the dramatic romantic turns presented in the movie were extrapolated from sparse evidence. So it is probably better to think of this movie as a Jane Austen novel brought to film, rather than a Jane Austen biography. And it succeeds, though of course with the caveat that unlike in her novels, this time the smart and attractive independent-thinking woman does not get happily hitched to the perfect man.

Anne Hathaway plays Austen, and while I am always initially distracted by her strikingly pronounced eyes and mouth, she did a good job and eventually (for me) disappeared into the role. The movie is populated by characters that are clearly meant to be the real-life inspiration for some of Austen’s most memorable fictional characters, primarily those in Pride and Prejudice. Happily, here they are rarely as absurd, with the possible exception of Maggie Smith’s meddling wealthy Aunt. Jane has two suitors that don’t suit her, but neither is as repugnant as Mr. Collins from Pride and Prejudice. Her mother is much more practical and reasonable than Elizabeth Bennett’s mother, and her father is not as dryly inspiring as his fictional counterpart. All this is to the better, so that while the passionate and ill-fated romance between Jane and Tom Lefroy (imagined here to be her real-life Mr. Darcy) feels fictional, the rest of the characters and the overall presentation of Austen’s life as she enters adulthood are a believable representation of what her life and world might have been like.

I confess to some mixed emotions (pride and envy, neither particularly virtuous, and seemingly incompatible, I admit) upon discovering from friend and fellow Cassini Ring-er John Weiss that someone has taken my two false-color renderings of Saturn’s rings from UVIS observations and used them to make custom ties. See here for my original A ring image tie, and here for (in my opinion) a much more interesting tie with the “CAT Scan” image from earlier this year. Should I buy moxieann’s creations? I suppose so. After all, the reason moxieann got those tie designs up on the internet instead of me is that I’m too lazy and completely incompetent when it comes to making money. And moxieann isn’t. She (I’m guessing) has also used other Cassini images for ties as well as mugs. I’m drowning in mugs (and I think I could make one cheaper at cafepress.com), and I almost never wear a tie, but I confess to being tempted. That purple and yellow one looks great.

Here is the manatee that paid us a visit after the shuttle launch.

Attempting to take advantage of our proximity to the nation’s spaceport, we ventured east to the coast to see the recent launch of the Phoenix mission to Mars’s north polar region. The launch was scheduled for 5:26 a.m. local time. Confident that I could get to Cocoa Beach in 45 minutes, and that we were going to a spot slightly closer (Jetty Park), I planned to leave at 4:30. We missed our target departure time by only 2 minutes, but I was sadly mistaken on the time it takes to get Jetty Park. With almost no margin for error, we ended up scrambling to get to a viewing spot on the side of the road a scant 3 minutes before launch. This made for a stressful rather than anticipatory pre-launch wait, but the Delta 2 rocket made a spectacular and rapid ascent through a clear Florida sky, leaving behind enough exhaust at high altitudes to generate a colorful and ring-shaped high altitude noctilucent cloud.

Having learned from our experience of not leaving early enough for a launch, today we set out to Titusville to see the launch of Endeavour to the International Space Station two hours before launch, with a driving estimate to the viewing site of 30 minutes in normal conditions. We had not prepared, however, for the normal driving conditions just to get the five miles from our house to the road that leads to Titusville. Forty-five minutes later, we were still stuck in bumper-to-bumper traffic and had traveled about four miles. This is the kind of thing that will eventually drive me insane. Amazingly, ten minutes and one mile later the traffic opened up suddenly and we were speeding to the private dock where our gracious host, UCF student Nate Lust, was waiting with reserved parking spaces on the edge of the Indian River (the name for the stretch of the Atlantic Intercoastal Waterway between Titusville and Kennedy Space Center). Still, I had not totally exhausted my means of messing things up. There are two shuttle launch pads, 39-A and 39-B. Both are visible from the shore in Titusville, but I could not visually tell which one actually had the shuttle on it. Opinion on the dock was mixed, and I confidently convinced myself (and anyone who cared to listen) that the shuttle was on the pad on the left from our vantage point. Thus, I happily trained my video camera and binoculars on this empty launch pad while the shuttle soared skyward completely out of my field of view. Of course, I quickly turned my gaze, but I missed that exciting first couple of seconds as the steam cloud first erupts and the shuttle with its bright solid rocket motor glare emerges from behind it.

Any disappointment was more than compensated for by the friendly visit of a manatee a few minutes later as we prepared to leave the dock. Anne-Marie’s eagle eyes spotted the manatee, and Nate simply turned on a hose, and the manatee appeared shortly, attracted by the fresh water. Very cool. I’ll post pictures of the manatee and crappy video of the shuttle launch shortly.

Cassini colleague Matt Hedman and other members of the imaging team have published a paper identifying an intriguing arc in Saturn’s G ring as the source of the particles in the rest of this faint dusty ring. Most dust rings in the solar system are associated with small moons. Enceladus’s geysers are responsible for most of the particles in the E ring. There are faint dust rings at Jupiter where the dust particles have orbits that clearly link them to individual moons. The moons produce the rings not through geologic activity like Enceladus, but as giant cosmic targets for interplanetary micrometeoroids which constantly pepper the moons at high speeds and knock off tiny bits of ice and rock. In the case of the G ring, Hedman found that there was a significantly brighter arc within the ring that is locked in a 7:6 corotation resonance with the moon Mimas. Apparently the particles in this G ring arc are knocking into each other and also being bombarded by meteoroids to act as a swarm of so-called “parent bodies” for the rest of the G ring (try calling your own parents that - it’s fun!), rather than an individual large satellite parent body. There’s even the chance that some of these mini-moonlets in the arc might be observed when Cassini flies particularly close to the G ring arc during Cassini’s extended mission, now in full-scale planning. I have a special interest in this study because I developed models of dust-ring production from swarms of parent bodies in the ring systems of Uranus and Neptune for my Ph.D. dissertation. The G ring appears to be similar, now, to the Adams ring of Neptune, the first ring known to have a distinct and long-lived arc, though the G ring is far fainter overall than the Adams ring.