The Doppelgänger Distance

In the latest American Scientist, I came across a book review of Paul Davies’ new book The Eerie Silence. It’s another take on the old Fermi Paradox that bedevils the SETI crowd. Very briefly, it goes like this: if aliens exist, where are they? It sounds flip, but the more you pick at it, the more you realize it’s a significant puzzle. Shouldn’t we at least be able to detect other civilizations, since they’ve had ten billion years or so to get busy? You’d have to guess that we’re arriving late to the party. Only… where is everybody?

In this context, Davies touches on the concept of the Great Filter (which I’ve discussed before). The idea here is that, gosh darn it, intelligent life IS rare. And why? Here’s a quote from the review:

… given that we don’t see any evidence that other intelligent creatures have taken over big chunks of the cosmos, some Great Filter must be operating to prevent life from evolving to the point of colonizing our galaxy. […] Perhaps we’ve already made it through the Great Filter and will go on to colonize the visible universe ourselves. But it may be the case that civilizations as advanced as ours typically go on to destroy themselves before they reach the star-hopping phase, and that we have a Great Filter in our future.

This is why I’m interested in the the Doppelgänger Distance. It’s the distance from earth at which, given our current technology, we could hear the noise made by an exact copy of the current earth, assuming this noise was arriving right now (i.e. don’t worry about the time of transit). The Doppelgänger Distance could grow with either the sensitivity of our ears or the noise of our voices. Assume the listener knows where to listen, but the speaker is making no special attempt to be heard.

As the Doppelgänger Distance gets larger, we can feel better and better about having passed through the Great Filter. This is because, even if we are eventually so foolish as to do ourselves in, at least we will have rocked the neighborhood (which neighborhood being our Twin-o-Sphere, or the spherical volume for which the the Doppelgänger Distance is the radius). Someone clever in the vicinity will have heard us. And more importantly, we will have heard them. So: if we don’t hear anybody at all, then maybe we’re the first. Which would place the Great Filter behind us (in all likelihood).

If we make it this far and then wipe ourselves out, that would totally suck.

Saturn in the Big Picture

I remember, as a kid, being mesmerized by these cheesy old sci-fi paintings of the frozen surface of a moon IX around Tau Ceti 4, or some such thing. Frosty rocks in the foreground, a gas giant looming large above, and maybe a space ship for good measure. I was aware of how speculative these paintings were, but they could still get you to ask the question “What would it be like to be there?”

The Boston Globe’s Big Picture has a new entry on Cassini’s latest adventures around Saturn, and the amazing thing is how much these honest-to-goodness photographs resemble those old sci-fi paintings. For instance:

I half expect to see a busty astronaut in a tight-fitting space suit floating nearby, a disintegrator pistol at her side. If one of those shows up the next set of pictures, man, I will be impressed.

Alan Taylor, the editor of The Big Picture, is a Saturn-o-phile from way back. Here’s a Cassini Flickr set from his pre-Globe days.

In other planetary exploration news, I regret to inform you that your little Mars lander Phoenix did’t make it through the winter. A noble spaceship among the frosty rocks and under pink skies, Phoenix, may you rest in peace.

Dan’s latest: Yet Another Planetarium Simulation

Great news! Dan Schroeder, the physics professor whom some of you will remember from his excellent reviews of iPhone astronomy apps, has written his own astronomy applet. Give it a look.

Why write another astronomy program? Here’s Dan’s answer.

To be useful to most of my students, a simulation program has to be (a) free; (b) delivered through a web browser, with nothing to download or install; (c) easy for beginners to understand; and (d) convenient for showing the motions of the stars and other objects with respect to earth’s horizon.

It’s a lot of fun to play with, and I like how Dan notes that his UI was partially inspired by H.A. Rey’s stargazing books, of which I too was, and remain, a loyal fan.

The High-Water Mark of Winter

I have wonderful news: the days will not, in fact, keep getting shorter and shorter until inky blackness is total and the sun is forever blotted from the sky. Maybe you are cleverer than I am, but I have my doubts every year. In my corner of the northern hemisphere, yesterday was the day with earliest sunset. Although the day as measured from sunrise to sunset will keep shrinking for a few more weeks, the sunset has done its worst and must now spend six months in retreat. Get her running and keep the skeer up! There’s better days ahead, boys.

When I mentioned the significance of this day to my wife, she asked me just how much later the sun will set today. With the help of a handy spreadsheet from the NOAA, I can now tell you the answer. And the answer is… three seconds. Say what you will, but that’s three more seconds of sunlight where I come from.

Here’s a screenshot from an iPhone app that I recommend (as does Dan) called Star Walk. It shows the sun crossing the horizon on its way to bed.


And finally, while we are on our way to the winter solstice here, Saturn has been experiencing its equinox. Check out these Big Picture views of Saturn at equinox. That Cassini machine is a wonder.

Dan’s iPhone Astronomy

Here’s the setup for a joke: once there was a mathematician, a physicist, and an engineer, and… Oh, wait, that’s not the setup for a joke. That’s a description of my house in grad school. Okay, it was actually a trailer, not a house, but that’s not important. For the purposes of today’s story, what you need to know is that I was the engineer in the trio, and Dan was the physicist. Dan is now on the faculty at Weber State in Ogden, Utah. He has a blog that I enjoy reading, and as an iPhone owner I was especially pleased to come across his very thorough review of iPhone star charting applications.

I always liked looking over Dan’s shoulder when he was evaluating products he was considering buying (camera lenses, star charts, baking supplies), because Dan is the most thorough evaluator I know. Go look at his star chart reviews and you’ll see what I mean. He’s a one-man Consumer Reports! Read what he has to say and buy one of the recommended apps. It’s a good thing to know the stars in your neighborhood.

Thanks Dan!

Galaxy on the rise

Once on a camping trip in Utah, I took a picture of our group late at night. I had a tripod and used a long exposure, but not being a very skilled photographer, I wasn’t sure how it was going to turn out. When the pictures came back from the lab, I was in for a surprise (historical footnote: in ancient times, photographs were “developed” at remote mountaintop “laboratories” and returned to you on the backs of fast-trotting donkeys). I couldn’t find my night-time snapshot. It was a while before I realized what looked like a mid-day shot was actually taken at midnight. The sky was bright blue and the colors were vibrant. Only the tiny traces of stars in the sky and our blurry faces gave it away. It was hard to believe my little camera could see such a different world.

On Kevin Kelly’s sprawling site I came across this lovely time-lapse animation taken at a star party in Texas. Amazingly, it was taken with an SLR camera on tripod. Put on your slow eyes and watch the earth turn.

Galactic Center of Milky Way Rises over Texas Star Party from William Castleman on Vimeo.

I’m familiar with what the Milky Way looks like in dark skies, so I was watching this video thinking “It’s going to be subtle… is that it? No… is THAT it? No.” But that camera has better eyes than you or I do. When the galaxy comes up, trust me, it’s not subtle.

Galileo’s telescope

It’s been a big year for anniversaries. First we have Abraham Lincoln and Charles Darwin blowing out 200 candles apiece (were they jealous of each other?), and now comes a Galileo event at twice that span: 400 years. When you put it that way, it’s interesting to consider that Darwin gets you halfway to Galileo. Quick question: if two Darwins buys a Galileo, what can you buy with two Galileos (800 years)? Answer: Cambridge University, which was founded in 1209. So it goes.

But back to Galileo. In fairness, we are talking not about his birth year (1564), but the first year in which he turned his famous telescope upon the heavens. A curious historical footnote is that Galileo did not invent the telescope, but he does seem to have been the first to think to point it straight up. In honor of the events of 1609, this year is to be an International Year of Astronomy. Last weekend witnessed the 100 Hours of Astronomy celebration. Visit their web site to see some fun short videos from observatories around the world in Around the World in 80 Telescopes.

But what about Galileo’s original telescope? You can still find it (or one of its early siblings anyway) at the Istituto e Museo di Storia della Scienza in Florence. I’ve been there, and let me tell you it is worth the visit.

As you enter the museum, you see part of an enormous marble dial for a barometer and thermometer that used to sit in the Loggia dei Lanzi in the famous Piazza della Signoria. But, this being Florence, public displays of science gave way to public displays of art, and so the instrument was banished to the museum. On the second floor you can find not only Galileo’s old telescopes, but also, bizarrely, his old finger. It is, in fact, his middle finger, and although Galileo was pardoned by Pope John Paul II in 1992, I would have to guess that it still points at Rome.

Pictures of the Sun

It’s fun to look at pictures of planets taken by our robotic eyeball extenders. We get to see things that are too darn far away to see with even the biggest earthbound telescope.

But there’s another kind of treat when we look at our own sun with new eyes from here on earth. We’re used to seeing marvelous detail in the moon’s changeless cratered face, but the sun is just a blinding fireball to our eyes.

When I look at a planet, I think “That’s a place.” I can imagine flying over it, or even stepping out of my little tin spaceship onto its surface. But the sun is always just the sun. Not really a place, just a white hole in the sky. My imaginary spaceship never goes there.

New telescopes (and a few space probes) are changing that. The featureless sun is really a charismatic world of curdling fire, boiling magnetic storms, and vast billowing exhalations of solar steam.

These pictures (from the Boston Globe’s Big Picture series) prove that the sun is a place jammed with personality: The Sun – The Big Picture. And if you want to know why they call it “solar wind”, be sure and look at the animation where a strong gust from the sun whips the tail off a comet

False equinox and the refraction bonus

The autumnal equinox is nearly upon us. Or is it?

Equi + Nox, which comes from the Latin for “noxious horse”, or more generally “nightmare” … oh I’m sorry … wrong book. Here it is: equinox means the length of the night should equal the length of the day. Theoretically.

But someone’s been lying to you. Here’s an article that blows the top off this seasonal myth: The Equinox Error: The Fallacy of Fall’s Arrival.

If you look at the sunrise tables in your local paper, you’ll see this first day of Fall is longer than the first night. Can nothing be trusted? First Lehman Brothers, now this!

The discrepancy is due to the refraction bonus. Mr. Atmosphere bends Mr. Sunbeam over his knee so that by the time you see the Sun kissing the horizon, it’s actually been out of the building for some time. That is: the Sun’s light gets bent in such a way that its apparent position is lower than its actual position.


I think this phenomenon actually may be due to an expensive government bailout intended to stabilize the public markets. “Give them more daylight, for God’s sake!” said Ben Bernanke, “They need to buy!”

How do you plan to spend your refraction bonus?

Astronomical crowdsourcing and Hanny’s Voorwerp

I once heard an interesting story about a group of scientists that had written some improbably small thing on a metal platter, something like the IBM logo written in individual xenon atoms. And here’s what they learned: it was easy enough to write something tiny, but having written it, it took them several hours to find it again so they could image it for their press release. I love the idea of something being lost at the nano scale. It may be just at the tip of my tongue, but if it’s only a few angstroms wide, it’s as good as gone.

There’s a similar problem with astronomy research. We have, via programs like the Sloan Digital Sky Survey, imagery that packs 120 megapixels into 1.5 square degrees of sky. How do you find the good stuff? If you can teach a computer to find good stuff, that’s great, but if not, you’ve got a real problem. That’s where the Galaxy Zoo project comes in. Web-organized volunteers are helping to classify galaxies, something that is, apparently, still very difficult for computers to get right. And every now and then people like the Dutch schoolteacher Hanny van Arkel find weird stuff that you can’t tell a computer to look for anyway, precisely because it’s unexpected. This is Hanny’s Voorwerp

I love the fact that there’s a green goblin in the sky named after a Dutch schoolteacher and volunteer astronomer. Also, it’s fun to learn what voorwerp means in Dutch.