So you have what, like one day left to buy presents. You’re panicked, and you’re not sure what to do. Run to the bookstore for a gift certificate? Hope the local superbox has more cartons of electric toothbrushes? Just panic?

There are some things you still can do. They may not be the latest video game or a big plasma TV, but there are some things you can do to get gifts, and maybe do a good deed at the same time:

1) Donate to JREF: The James Randi Educational Foundation (full disclosure: I’m President of the JREF) is trying to make the world a better place by promoting critical thinking. The JREF provides local and national media a rational viewpoint if they need it (and boy, do they need it), and is currently in a phase of expansion that, frankly, costs money. Donating to the JREF will help it achieve its goal of a planet filled with skeptical people. You can become a member, too, for buy a membership for a friend or loved one. It’s tax-deductible, and the end of the year is coming…

2) Buy my book: ’nuff said.

3) Skepchick: The Skepchicks posted a skeptical holiday gift guide. It’s a bit late to get things shipped, but they have some cool ideas.

4) Skeptical charities: Both TechSkeptic and The Friendly Atheist have posted lists of non-religious charities, should you choose to remain secular but still be able to do good things.

The holidays are for everyone, even skeptics. Have fun, enjoy friends and family, and maybe you can even make the world a better place at the same time.

Richard and Tiffany.

I just heard the new episode of the Australian podcast Skeptic Zone with the charming and dashing Richard Saunders — this one has a wonderful interview with the totally awesome Pamela Gay, who talks up astronomy and the International Year of Astronomy 2009.

Right after that, at about 25 minutes in, first year University astronomy student and Aussie skeptic Tiffany Day reviews my book Death from the Skies! I won’t give away what she says, but I will mention that she is an unusually intelligent and perceptive person.

If you’re in the Iowa area, and you aren’t frozen in a block of ice, I’ll be on KDTH radio for a (taped) interview with Tom Berryman on Friday at 12:30 central time (and for those of you not in the central plains, it will be archived eventually on their site). We talked various topics, including the book of course, as well as aliens and movies. Being topical, I used Dubuque as an example of a city being hit by an asteroid. I hope they don’t mind.

… I think some might want to build this.

I think this money would be better spent building a giant magnifying glass we can launch into orbit to simulate a gamma-ray burst’s effect on Earth. But that’s just me.

Tip o’ the cibolla to … my sister.

What the heck is dark energy?

We still don’t know. We’re pretty sure it exists; several independent observations indicate that the expansion of the Universe is accelerating. We’ve known for almost a century that the Universe is getting bigger, but in 1998 it was discovered that the rate at which it expands is itself getting bigger every day. Whatever is behind this is acting almost like anti-gravity, or more accurately a pressure that is making the Universe inflate faster every second of every day.

The galaxy cluster Abell 85 (optical image on left) is infused with million degree gas that gives off X-rays (right). By measuring the amount of this gas, astronomers have determined that dark energy exists and that it’s a constant throughout the cosmos. Not bad from a pink blob. Credit: NASA/CXC/SAO

But we don’t know what the heck this stuff is. We’ve hung the name "dark energy" on it, but we know very little about it. For example, is it a constant across space, with a strength that never changes with distance or time? Or is it a function of space itself? If it’s the latter, that means it gets stronger as space itself expands. That is, if there is some amount of dark energy in every cubic centimeter of space, and there are more cubic centimeters of space as the Universe expands, then dark energy will get stronger as time goes on. That means the acceleration will accelerate, growing ever-more until the Universe tears itself apart!

We’re talking here about determining the eventual fate of the entire Universe. Obviously, there’s some interest in this topic.

And now astronomers have found a new way to measure dark energy that may be able to differentiate between the two contenders. When the Universe was young, matter started to coalesce by gravity, forming huge structures millions of light years across. These collapsed to form galaxies and clusters of galaxies, like cities composed of thousands of smaller towns.

If the Universe were not expanding, forming clusters would be easy. As time went on, more matter could fall in to the cluster, forming more galaxies and making the cluster bigger. But since the Universe was expanding, there was a limit to how big the clusters could get; the outermost fringes would be moving away from the central regions, and that limited the amount of raw material available to make galaxies. It’s like going to the grocery store and trying to fill your cart with cans of spaghetti sauce, only to find workers removing the cans from the shelf at the same time. The number of cans you wind up with depends on how quickly the grocery store clerks are unshelving them.

So the sizes of clusters today depends on how quickly the Universe expands, and this cosmic expansion depends on the amount and flavor of dark energy infusing it. Aha! If we carefully study the sizes of clusters in the near and distant Universe, we can get a handle on dark energy!

That’s just what Alexey Vikhlinin of the Smithsonian Astrophysical Observatory and his team did. They examined the hot gas in more than a dozen clusters with the Chandra X-ray Observatory. The gas is the raw building material of clusters, and can be used as a tracer for how the clusters formed and how big and massive they are now.

What they found is, to me, something of a relief. First, they confirmed that the growth of clusters is consistent with the presence of dark energy in the first place (some people still doubt that dark energy exists, but this is another nail in the coffin of any alternative hypotheses). Second, they found that their results indicate that dark energy is a constant throughout the Universe. That is, it is not growing in strength with time, and the Universe won’t rip itself to shreds in the dim future.

Phew!

I’m impressed with this work. One good thing about it is that it’s independent of any other measurements of dark energy that have gone on before. We’ve been using things like distant supernovae to measure how fast the Universe is expanding; that’s how dark energy was discovered in the first place. Other studies have looked at the pervasive microwave glow of the Universe, and other indicators have been used as well. This is the first to use the hot gas in clusters, and it doesn’t rely on these other methods. That makes scientists more confident the result is correct.

Not that we really understand dark energy yet. We can measure its effects, but we don’t know what the heck it is. The most recent work is also bothersome: it indicates that the amount of dark energy in the cosmos we measure is 10¹²⁰ times smaller than it should be. That’s a bit off! Obviously, there is something we’re missing, and many people suspect that there are extra dimensions to the Universe that we cannot see, and this may be the problem (it may also explain why gravity is so much weaker than the other three fundamental forces, but that’s another story…).

The good news is that this new work with clusters may shed some light on dark energy, and on the very nature of the Universe itself. But to me, there is more good news… What all of this is telling us is that the Universe is even more complex than we thought. That makes it more interesting, more cool, and more fun! There’s so much more left to learn, and the path to that knowledge is where the adventure lies.

[Note: If you want to Digg this article, please go to here and not to the link in the button above. While I'm glad someone else submitted this to Digg, there was no specific information posted on that link. And if none of this makes sense to you, don't sweat it. Just enjoy the article below. ]

In Auckland, New Zealand recently a warehouse was set ablaze. It was quite the inferno, needing a huge effort to quell it.

No one knows what started it… but rumors are spreading that it was a meteorite that did the damage. Several people saw a fireball in the sky, and it happened around 10:00, around the time the fire started.

Case closed, right?

Bzzzzt. Nope. I will almost guarantee a meteorite did not start this fire! Why not?

Meteors are chunks of rock or debris that enter the Earth’s atmosphere. They violently compress the air, heating it up — it’s not friction that does the heating, contrary to common belief. But common wisdom also says that meteorites would hit the ground still burning hot, and cause fires wherever they land. And after all, we’ve seen it in countless movies!

However, there’s a piece of info you should remember here: that’s in the movies. In real life, meteorites don’t work that way. A small meteoroid (the solid part of the glowing meteor) will burn up rapidly, leaving nothing to hit the ground. If it’s somewhat bigger, like the size of a car, it’ll explode high in the atmosphere, and then pieces of it will rain down. However, those smaller pieces fall relatively slowly, and have plenty of time to cool down before they hit. The recent fireball over Canada shows that, as did a rain of meteorites that hit Chicago a few years ago did too. No fires were caused by those rains of rocks from space, because they were cold when they hit.

A piece of rock or metal large enough to retain its heat when it impacts the ground would be pretty big, like over 100 meters across. Those tend to be a bit more obvious when they impact, since they explode with a yield equal to that of a 15 megaton blast.

That might do a bit more damage than start a warehouse fire. Had something like that been the cause of the Auckland warehouse fire, there wouldn’t be anyone left in the city to report it. There would be a smoking hole a mile across.

I’ve heard reports like this one many times. They always — always — turn out to be non-extraterrestrial in origin. Just because a bright meteor was seen does not mean it caused the fire! That’s a logical fallacy: post hoc ergo propter hoc, "after this therefore because of this." There’s a reason that’s called a fallacy.

So that’s why I think a meteorite didn’t cause this fire, and I’m pretty sure there’s a more down-to-Earth explanation here… at least one that started off down-to-Earth and didn’t just end up that way.

Tip o’ the Whipple Shield to BABloggee Bret Hall.

Well, I’m back from my excursion to Phoenix, which was totally fun; I was part of a TV documentary shoot and I’ll be posting videos and pix eventually. The only bad parts were not getting a chance to hang out with my friends Evo and Sheila (wrapping the shoot at 8:30 p.m. and having a 6:40 a.m. call time for the next morning puts a damper on the carousing), and the horrendous turbulence on the way home. I have been in bad turbulence before, but this was the first time I was seriously wondering if this Might Be It. We dive bombed a half dozen times, and got seriously tossed around.

But I made it. I’m home, there’s a beautiful coating of delicate snow on the ground, the Sun is struggling to break through, and I have a bazillion things to get done today. So I’ll leave you for now with the podcast of the interview I did with Little Atoms. Here’s the web page, and here’s the direct link to the MP3 download.