steuard: (physics)
Saturday, May 24th, 2014 04:19 am
We live in a remarkable era. If you brought an ancient Greek astronomer to the present day and dropped him off in a field somewhere, he would be awestruck, and maybe terrified. (Heck, it probably wouldn't even need to be an astronomer: I think that most people were quite familiar with the night sky until recent times.)

The meteor shower was pretty much a bust: I was outside for a decent stretch and only saw two for sure, plus a couple more "maybes" that were too brief and dim for me to judge whether they came from the expected radiant point. (To be fair, from where I was in our backyard I was seeing far less than the full sky.)

But in the same time, I saw at least half a dozen satellites, ranging from "almost too dim to see" to "easily the brightest object in the sky". It's obviously been too long since I just lay back to watch the stars: those things are now a near-constant presence. So I really do wonder how that Greek time traveler would react to the modern sky: what would those swift-moving, variable brightness points of light mean to him? What would Plato make of it? What stories would Homer tell?

For that matter, I'm sure that there are still plenty of societies and communities today that have little knowledge of high technology, from isolated tribes to rural villages. What do *they* make of the satellites that now pass constantly over their heads? This is a recent phenomenon: its origin is easily within living memory, and it has only gradually become as frequent as it is today. What stories do those people tell? Do they know or guess that these are the work of human beings? Do they fear that the newly mobile stars are an omen of some approaching doom?

And what stories might we tell about ourselves, as we alter the face of the heavens so deeply without ever pausing to think what an astounding achievement that is?
steuard: (physics)
Monday, September 2nd, 2013 10:02 pm
You've probably heard at some point that tides on Earth are mostly caused by the moon, along with some smaller but still noticeable effects from the sun. In other words, the two objects' tidal forces are comparably strong (rather than being many orders of magnitude different: Uranus doesn't appreciably affect our tides!). You've probably also heard (or seen, during an eclipse) that the moon and the sun appear to be about the same size in the sky, even though the sun is vastly larger (but farther away). Remarkably, it turns out that these two facts are directly related.

Here's the idea. Let's say that the distance from Earth to some distant object is D, the radius of that distant object is R, and its density is p (I won't bother typing the usual "rho"). Ignoring constant numerical factors that would be the same for every (spherical) object, the mass of that distant object is proportional to p R3. The gravitational acceleration due to that distant object is proportional to M/D2 = (p R3)/D2, but if you're experienced in the math of Netwon's gravity it's fairly straightforward to show that tidal forces are instead proportional to M/D3 = (p R3)/D3. (Tidal forces refer to the difference in gravitational force on opposite sides of the earth, and that extra power of 1/D essentially comes from a linear approximation of the changing force that's proportional to REarth/D.) Factoring that a little differently, that means that tidal forces are proportional to p (R/D)3. But using a little trig, R/D is just the tangent of (half of) the angular size of the object in the sky, and for small angles that equals the angular size.

In other words, the tidal force exerted on the Earth by a distant object is proportional to the density times the cube of its angular size. Since the moon and the sun have about the same angular size, it's only the sun's lower density that makes its effects on our tides less significant. And as expected, planets like Uranus have a much less significant effect, since their angular size is tiny by comparison (and their density is in the same ballpark).

Neat, huh?
steuard: (physics)
Monday, August 6th, 2012 01:12 pm
This is an absolutely stunning image: the Curiosity rover spotted while descending to the Martian surface, dangling under its parachute. It took some tremendously careful calculations by the Mars Reconnaissance Orbiter team (and some good luck) to snap this shot of a fast-moving object in the few moments available (they had to aim the camera in advance, tell it when to take the shot, and hope). The Bad Astronomer gives a bit more detail. (Click the image for a larger version.)


(Image via NASA/JPL/University of Arizona )

I honestly yelped out loud with glee when this image showed up on my screen. (Good thing my office door was closed.)

I'm still in awe that this insanely complicated landing scheme worked; for once, the reality of space exploration turned out to be just as awesome as what science fiction promised us fifty years ago. I mean, heat shields and parachutes are old hat, sure, but to follow those up by setting the one-ton rover gently on the ground using a crane suspended from a hovering rocket platform? That's just crazy talk. (Here's a nice video summary, for those just catching up.) And it worked. IT WORKED. (Sorry... I seem to have something in my eye.) Now we get to find out what remarkable science we can do.

EDIT: For those who aren't following all this on their own, a couple of followups. First, it turns out that the same (large) image by the MRO also includes the heat shield that had separated from Curiosity a minute earlier, still falling toward the ground. And second, there's already a rough video of the landing as seen from a camera on the bottom of Curiosity itself. (It sounds like they'll eventually have the whole thing in high definition, too!) This just keeps getting cooler.
steuard: (Default)
Sunday, July 15th, 2012 11:31 am
Charged particles released after the big solar flare last week have been reaching the Earth all weekend, and there's a good chance of an impressive aurora tonight! (I probably ought to have said something yesterday...) There's a good Aurora Forecast page from the University of Alaska that will show you what to expect where. In fact, if it weren't sunny right now, their Short Term forecast map seems to imply that auroral activity would likely be happening right over Michigan (and Montana and Maine and possibly even farther south than that) and that it might even be visible on the horizon as far south as New Orleans. Who knows whether it will be anything like that tonight, but try to have a look!
steuard: (physics)
Sunday, July 8th, 2012 08:24 am
I've finally finished mucking with my poster of the solar system!

I made some last minor adjustments to the look of it (the black goes all the way to the edge, now, as does a "throwaway" portion of the Sun image), I clarified the license terms (with explicit permission to pay someone to print a copy of your own), and I put up a link to buy the poster on Zazzle. (I don't see much need to also list at CafePress... right?)

I still don't know for sure whether the college will actually decide to print a bunch of these for marketing in August or September. If they do, I might be able to buy a few from them at cost for anyone who'd like to have a copy, which would presumably be cheaper than what you'd get from Zazzle. But you're obviously welcome to just buy the things online, too, and that would give you more flexibility about the size you want. (If you do, let me know how Zazzle's quality is!) If you have any suggestions on making the interface at Zazzle a little easier to use, I'm all ears: it's a bit annoying that I can't specify a minimum size, for instance (and that the "this aspect ratio only" option is more trouble than it's worth).

This'll be my last post about the poster for a while, honest! (Kim will no doubt be glad to hear that.)
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Wednesday, June 20th, 2012 10:01 pm
When our college president sent out his monthly campus update, I was pleasantly surprised to see my picture: he was happy about the very successful public viewing event that another professor and I arranged for the transit of Venus on June 5. (I'm up for tenure this fall, so the recognition is good!) We got an article on the front page of the local paper that morning, and between that and a campus email we wound up sharing the event with something like 150-200 people over the course of the evening.

It was a lot of fun. We gave people three ways to view the transit. They could stand in line to look through our good telescope (with its solar filter). (That's what's pictured above, though this was just my attempt at a hasty, imperfectly-focused shot right before I had to leave. You can barely even make out the cool sunspots in my picture.) They could look at a fairly large image projected on the wall (pictured below), which wasn't as clear but allowed lots of people to look at once. And finally, they could use my Harvey Mudd solar viewing glasses (thanks, HMC!): it was just possible to make out the round black disk of Venus blocking the sun without magnification, but that was one of the coolest parts of the experience for me.

I won't clutter up everyone's friends pages with pictures... )

That last picture shows an impromptu scale model of the inner solar system that I set up on the football field (right next to the telescopes). I put a picture of the Sun on the 25 yard line, with the right scale to match Earth right on the goal line. Venus then wound up on the 7 yard line. If you click to zoom in on this photo, you might just be able to spot the tiny picture of Earth printed there (which is also to scale, along with the Moon and the distance between them). The solar system is big, and it's something of a miracle that these tiny little planets with their differently-tilted orbits ever manage to line up enough for transits at all. In fact, I got rather excited talking about all this to the crowd: a friend took a video of me giving my last "welcome chatter" of the night, after the crowd had thinned out a lot. (The college made its own video of the event, too. But it doesn't look like anyone thought to take pictures of the long line that we had for the first hour or so.)

Finally, the fun of the event and of tracking down pictures of the sun and planets for my scale model got me interested in making a poster of the planets to put up outside our planetarium. I spent a block of time hunting around NASA websites for big chunks of a weekend and a few evenings, and assembled this:

The full-resolution PDF will print 4'x3' with a resolution of at least 120dpi (and considerably more for many objects); I'll eventually be sharing it under a Creative Commons license. I'm pretty proud of it: you can't read them on this little picture, but each planet and moon comes with some interesting fact about the object. (There are very few posters like this based on real images, and too many of those obsess over dull numerical data instead of remarkable things like Mars's seasonal dry ice caps or Triton's probable geysers of liquid nitrogen.)
steuard: (Default)
Monday, June 4th, 2012 06:48 pm
Tomorrow (Tuesday, June 5) starting at about 6:04 Eastern time, the planet Venus will pass directly between the Earth and the Sun. This is a Rare Thing: the next time will be in 2117. There's been a lot of good science done using these transits in the past (like the first good estimates of the size of the solar system) and they still provide neat science opportunities today (like the plan to refine exoplanet detection by looking at the moon that I wrote about previously).

So look around locally for a chance to view the transit in person! Lots of observatories and planetariums and other groups will be organizing viewing events, which is probably your best bet. If you want to view it yourself, you can look at the official Transit of Venus site for some suggestions. (Don't look directly at the sun! Don't point an ordinary telescope at the sun!) Or look for some of the many webcasts out there: the Bad Astronomy site is planning what sounds like a good one, and there are others from NASA and other places. But you should really try to have a look: it won't look awe inspiring, but watching this sort of thing as it happens and thinking about the vast celestial objects in play can inspire great thoughts on astronomy and our place in the universe. Good stuff!
steuard: (physics)
Sunday, May 20th, 2012 10:54 pm
When we realized that our trip to see family in Los Angeles was going to line up with the (partial) solar eclipse, Kim and I made sure to bring a pair of the solar viewing glasses that Harvey Mudd sent out to alumni a few weeks ago. We were on our way to dinner when it started (after showing off the baby to a bunch of thrilled relatives all afternoon), and Kim's mom and I got to watch it begin from the car. (We politely declined to pass the glasses to Kim in the driver's seat when she asked for a turn.)

When we got to dinner, it was about halfway to maximum, and we all popped outside in turns occasionally to have a look. I was just about done with dinner when it reached maximum coverage (about 85% here), so I went outside to look. It was great, and when some people nearby looked at me curiously I got all excited and showed them, too. That drew more attention, and more and more people were drawn in by all the ooohs and ahhhs. (There were even a bunch of servers and staff from the restaurant.)

All in all, I probably shared the event with two or three dozen people. It was a fantastic science outreach experience, and I think Kim and her mom mostly forgave me for abandoning them in the restaurant with the baby for 15 minutes or so. (My only disappointment was that with the sun so low in the sky, there wasn't a good view of the crescent shadows under the tree leaves: that's one of the most awesome sights during an eclipse.) I hope Alma's public viewing of the transit of Venus in a few weeks goes as well!
steuard: (physics)
Sunday, May 6th, 2012 10:30 pm
One of the things that still blows my mind about our studies of planets around other stars (beyond the simple fact that we can see them at all) is that astronomers are actually able to figure out the composition of their atmospheres. That's possible when a planet passes between us and its star: it creates a tiny shadow that dims the star's light ever so slightly, and an even tinier fraction of that light passes through the planet's atmosphere. So if the spectral pattern of the star's light changes when the planet is in the way, we can analyze the changes to tell us what's its air is made of.

We think we understand the technique pretty well, but it would be great if we could test it out on a planet whose atmosphere we already understand. If only there were some known planet expected to pass between us and its star, we could point the Hubble at it and check this calculation against the known result. Well, hey! The planet Venus is going to transit across the sun on June 5th (the next time will be in 2117: watch it (carefully), and take your kids!). Only one problem: pointing the Hubble straight at the sun would destroy its sensitive optics (much like staring at it with unprotected eyes: be careful!).

So what are they going to do instead? Point the Hubble at the moon. The idea is that studying the much weaker reflected light of the sun (and briefly, of a tiny bit of the atmosphere of Venus) will be a decent test of those models. As long as they take a careful sample of the reflected spectrum for many hours before the transit, they can get an accurate baseline reading. Then by taking equally careful (and lengthy) measurements during the transit, they can measure the difference when Venus is present. If all goes well, the measurements will yield the same "no life on this planet!" signal that we've already established by looking straight at it.

Studying Venus by staring at the moon: crazy, but awesome. (Here's the original article: Hubble to Use Moon as Mirror to See Venus Transit.)
steuard: (physics)
Tuesday, April 24th, 2012 09:19 am
I am really excited by what I've heard about Planetary Resources, a private company that has just announced plans to mine near-earth asteroids for precious metals and other resources. Here's a write-up from the Bad Astronomy blog that goes into details: it sounds like these folks have a plausible business plan (as well as the necessary level of patience, and a dedication to the underlying cause of advancing humanity in space that will be an important complement to their profit motive).

Maybe it's just too much science fiction in my youth, but I've always felt that it will be important for humanity to Get Out: to avoid having all our eggs in this one basket called Earth. There are a whole lot of reasons for that (more of them than I had as a youthful sci-fi reader), and I won't go into them now. But it's been clear to me for a long time that while governments were the obvious choice to take the first steps into the solar system, we won't really be a spacefaring species until private industry and even private individuals are able to go there on their own. Asteroid mining seems like a really good stepping stone in that direction: small and close enough to be achievable, and with enough potential profit to make it appealing to investors. As soon as one of these ventures pays off, dozens more will spring up overnight, and space industry will go from being an epic project to a commodity. I don't know if we'll ever get out of our own solar system, but I look forward to the day when we can at least use more of it than we do today.


Meanwhile, in other news (only tangentially space related), it's possible that the Fermi gamma ray telescope satellite has seen a direct hint of the long-sought dark matter particle! There's a full write-up at the R├ęsonaances blog, but the gist is that if you look straight at the galactic core (where dark matter should be most concentrated) the telescope sees an excess of photons with a very specific energy, as if there were some unknown source at that energy on top of the known gamma ray sources (which are all spread out over a range of energies). The only model in the literature that could explain such a pattern is the decay of a dark matter particle with that same energy (or something close to it). The most likely particle mass that would explain this data is about 130 GeV: that's 130 times the mass of an entire proton (and, by an odd coincidence that might not be a coincidence, just 5 GeV or so above the current best estimate of the Higgs boson mass).

This will be a big deal if it turns out to be true: the first direct evidence of particle physics beyond the 30-year-old "standard model" (and the first concrete reason to believe that particle physics won't be dead as a practical matter after the LHC). It's thrilling stuff. The one thing that's puzzling to me about this is that I saw this news a week ago on that one blog, and I haven't heard anything else about it since. (I talked to an Alma graduate who studies experimental cosmology while he was back for graduation, and he said he'd heard about it but didn't know enough to comment beyond that.) Is there some reason for skepticism that has kept all of my other physics/astronomy blogs silent on the story thus far? Only time will tell. But it will be a lot of fun to watch.
steuard: (Default)
Sunday, March 20th, 2011 01:20 pm
LJ doesn't seem to want me to embed the video, so I'll just give a link to the original site; it's worth watching full screen.

The movie there was assembled from a huge number of still photos of Saturn taken by the Cassini probe, and it's absolutely fantastic. The best part is the full-color section, which starts a little before the one minute mark. I continue to find it amazing that we live in an era when we can actually see these sights "for real" like this... and I hope that one day, we human beings will be able to see it in person.
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Wednesday, September 22nd, 2010 10:59 pm
Here's what I want as my computer desktop image, or maybe as a screensaver:

I want a pretty landscape, maybe a mountain lake with some nearby woods. I want the lighting of the scene to follow a more or less real time 24-hour day/night cycle (including shadows, appropriate tints for dawn and dusk, things like illumination by moonlight, and stars in the sky at night). If possible, I want the appearance to adjust to follow the seasons in real time, too. (Including a bit of variation in weather or at least clouds would be interesting as well, though I'd want to be able to forbid completely overcast skies.) Something like this may exist: anyone know?

But... I want this simulated landscape to be located on a habitable, Earthlike moon of a gas giant planet. (Rings? Maybe.) The scene's lighting should be based on not just the sun but also light reflected from the sunlit parts of the central planet (and perhaps on any other moons that pass nearby in their own orbits), and the planet's appearance in the sky should be scientifically accurate. The seasonal cycle should be based at least generally on some calculation of solar heating based on the orbits involved. (That might not be much different than what we're familiar with, but I'd want to check. Would there be any significant monthly cycle on top of the annual one?) It might even be fun to include some mildly spectacular feature somewhere in the night sky, too: a nearby nebula or cluster, maybe. Bonus points if there is a practical orbit for another inhabited moon of the gas giant to occasionally come close enough to see continents and weather patterns (and city lights at night).

I'd be amazed if anyone had actually written a program encompassing this whole idea, but I think it should be possible today. If it were done well (with good attention to both art and science, and with configurable details if possible), I'd be willing to pay a fairly substantial price for it.