Note added June 9, 2005: This entry was featured in the 10th Skeptics’ Circle hosted by Skeptico. As usual, there’s great stuff there.

So I’m sitting in my home office at night, slogging away at my blog (hmm… “blogslogging”? I may have coined a new word here). Even though it is fully dark outside, the window shade is up because earlier I wanted to let in the dying sunlight and cool twilight air, and I simply hadn’t gotten up to close it yet. My wife is in the living room reading, and the Little Astronomer is asleep, so I have a sense of being alone. Then, out of the corner of my eye, I see something move outside.

I hate that feeling. The cold wave that goes through me, the feeling of being, well, almost naked, defenseless. I move just my eyes to the window, and see the fence, the neighbor’s house (too damn close, I hate California sometimes), the front left corner of my recycling bin, the top of a snapdragon growing in a pot along the fence. I also see the reflection of my office in the darkened window, a Universe where in-and-out is reversed. But in both realities everything is static. There is no motion, no hint of anything having changed position.

I turn my eyes again to my lovely prose, and just as I start to type, I see motion again. This time I move my head, and this time, as before, there’s nothing there.

As a kid, my brain went through many years of training as a creduloid, someone who believes just about anything, simply because someone told me so. UFOs, astral projection, the Bermuda Triangle– at some point, I believed in it. Over time I figured out how to ask for evidence, how to evaluate it, and how to form an opinion based on that evaluation. I’ve had a long time to make that procedure second nature.

So my skeptical brain kicks into gear easily and smoothly. Nothing’s moving out there, my brain reasons. So either something moved in here (unlikely; there is nothing in here that can move), or it’s an illusion (likely; I’ve been fooled before). OK, assume it’s an illusion. Can I test it? I need to try to repeat it.

I position myself just as I was when I saw the apparition, and start typing. Suddenly, I see it again! A motion, out of the corner of my right eye. This time, though, I don’t move. I sit very still, and then slowly start moving my head, left to right, up and down, just a little bit.

Sure enough, after a few seconds, I know exactly what has happened. The ceiling light above and behind me reflects in my glasses. The light bounces off my glasses and illuminates my right eye. My eye reflects in my glasses and then back into my own right eye. In other words, the motion I see is the motion of my own eye, as seen by my own eye. My glasses act as a mirror, but not a very good one, so the outlines of my pupil and iris are not terribly distinct. And the geometry of the situation is pretty finicky; if I move my eye even a little bit the reflection disappears.

That’s why I see nothing when I turn my head, and even when I just move my eyes. If the angles aren’t just so, the reflection doesn’t manifest itself.

I laugh. My immediate thought, skeptic that I am, is to wonder if this accounts for some sightings of ghosts. I know for a cold, hard, fact that most people are not trained to think critically. Polls show a lot of people believe in ghosts. And a lot of people wear glasses. What is the size of the population who live in the intersection of those three characteristics?

I’d love to see statistics. Have any ghost researchers done that study? It’s easy enough: take the number of people who have seen ghosts, and get the ratio of those who wear glasses to those who don’t. If that ratio is significantly higher than for the rest of the population, then I think we can explain quite a few “ghost sightings”.

But having seen the quality of a lot of ghost hunters on TV, in magazines, and from reading about paranormal/psychic fairs, I can just guess they probably have little or no interest in finding out that ratio. Boo hoo.

It’s a mystery. I don’t like mysteries! They give me a bellyache, and I’ve got a beauty right now.

-Captain James T Kirk, “Man Trap”

Starship captains may not like mysteries, but scientists do.

Back in the 1990s I had my teeth sunk into a big one. I was studying a ring of gas a light year across, centered on a star that had exploded in 1987 [note: that link will take you to a series of essays I wrote on this star and the ring, and is a good preliminary read to get more details on what I'm talking about here]. I was a graduate student working on a team led by Bob Kirshner, and we had many observations of this object using Hubble Space Telescope. The exploded star, called Supernova 1987a, had been studied for years by people all over the globe, but the ring was seen best in our Hubble images. My job was to analyze the data and figure out what was going on with it.

I was able to find out quite a bit about it: how big it was, how much gas was in it, how dense it was, and by really pushing the data to its limit I was able to get an educated guess at the cross-sectional shape of it (like slicing a ball in half shows it has a cross-section of a circle, or cutting a piece of wood shows it has a rectangular cross-section; bizarrely, the ring appeared to have the cross section of a crescent, so it was shaped like the metal rim of a bicycle wheel).

What we couldn’t figure out, to be blunt, was what it was doing there. It didn’t make sense that such a dense doughnut of gas would encircle a star like that. We had ideas, and we knew they were the right track, but the devil is in the details, and the details are what kept us up late at night. Worse, the star had two other rings around it, offset from it, like the two bulbs in an hourglass. What the heck were they? We’d seen them around other stars, but again, the specifics of this case made it hard to understand what they were doing there.

Things got weirder. In the middle of the ring, the exploding star was expanding (you can see that debris as the elongated nearly-vertical stuff in the middle of the ring in the images above) . Eventually, after more than 10 years, that debris started hitting that inner ring. We expected to see the ring light up again starting in the lower part then moving around in both directions, like a circular fuse lit at one spot. That didn’t happen; we got a single bright blob for a while, with no other action. Finally, months later, we started seeing more blobs.

And yet, after all that, this weird structure had (at least!) one more surprise waiting for us.

When a star like this detonates, only the outer layers explode outward. The inner part, the core, collapses down, and you get either a black hole or a weird dense object called a neutron star. Everyone expects this event to have formed a neutron star, but no one can find it. There were early reports it had been seen in the late 1980s, but they turned out to be false alarms.

But now, 18 years after the event, we really should be seeing it. But recent observations show it just ain’t there, or, if it is, it’s much, much fainter than expected. The team tried everything they could to find it, and came up blank. Generally, a young neutron star is bright because gas and junk left over from the explosion fall onto it. So maybe there is some reason that the junk was cleared away by the blast. Or maybe there is more dust blocking the view than expected. Or maybe it formed a black hole, or maybe the magnetic field of the neutron star is too weak, or maybe maybe maybe. There are lots of maybes to go around.

But no matter how you slice it, Supernova 1987a is a weird object, and probably always will be. There may be other objects similar to it out there, but 87a was the first we ever discovered, and is the best studied. And yet, for all we know about it, there are still mysteries to be found.

Personally, I like things that way. I enjoy finding things out. If we knew everything, what fun would that be?

I get questions about Stephen Hawking quite a bit. This irritates me, for two reasons:

1) His biggest contribution to physics is probably his idea that black holes can leak radiation, a hypothesis that marries General Relativity to Quantum Mechanics, and is therefore nearly impenetrable, and

2) He is smarter than I am, and more famous, so I hate him.

So there you go. But I was surprised, when researching him some years ago, to find out that besides a brilliant scientist, Hawking is actually an accomplished gangsta rapper. This may surprise you too, but as they say, if it’s on the Internets it must be true:

MC Hawking chilling with Coolio while they go over the Theory of Relative Hammer Time

Still don’t believe me? Then check out MC Hawking’s crib.

As Dr. Hawking himself says, "I ain’t Thomas Dolby, science don’t blind me."

Last year, on March 7, the Mars rover Sprit took an image of a streak in the martian sky. It looked like a meteor trail, but it might also have been an older probe like Viking still orbiting the Red Planet. Scientists weren’t sure.

Now they are. The streak was the trail from a meteor burning up in the thin martian atmosphere. It was probably originally part of the comet Wiseman–Skiff, which takes about 6 years to orbit the Sun. Comets are big chunks of frozen gas and rock, and when they get near the Sun the frozen gas sublimates, or goes right from a solid to a gas. The little bits of rock frozen in the matrix then work their way free, and follow in roughly the same orbit. When a planet plows through the debris, you get a meteor shower.

Evidently Mars had a shower of its own in March, and Opportunity just happened to catch one of those bits of rock as it made its last hurrah.

Sometimes, those bits of jetsam make their way to the ground. They’re called “meteorites” then… and Mars has one of them too! Opportunity found a meteorite on Mars in January 2005, though that one is probably made of iron, and so it came from a denser asteroid, not a comet. Still, that’s cool. Opportunity found small craters, too. And the rovers are still going! I wonder what else we’ll see in the coming weeks and months.