In various places on my site and in this blog, I have mentioned centrifugal force. Invariably when I do so, someone pedantically comes along and says "That’s not a real force! It’s fictional! It’s really just centripetal force".

Let me clear and blunt here: that’s wrong. Centrifugal force is every bit as real as centripetal force. It’s just in a different frame. "Centripetal" means "center-seeking", and "centrifugal" means "outwards-seeking" or, more literally, "center-fleeing". You’d think these are opposites, but they are in fact the same thing! It just depends on your point of view.

If you are standing outside a spinning object, and then draw a diagram of the forces, yes, you’re better off using centripetal force. The math works out more easily. But if you’re on that spinning object, then the forces are easier to draw assuming a centrifugal force. Really!

Think of it this way: watch a car make a right turn. The people inside have inertia, and they "want" to stay moving forward. The car pushes them to the right, toward the center of the circle it is making. Centripetal.

Now sit inside that car. When the car turns right, which way do you feel yourself leaning? Toward the left, away from the center. You feel a force towards the outside of the circle.

Tadaaa! Same thing, different viewpoints.

Centripetal = centrifugal. Got it? They’re the same thing. If one is real, then so’s the other. Once more, just to make sure:

Centripetal = centrifugal.

Cripes, I hope I don’t ever have to explain that again. If I run across this non-issue again, I will link the perpetrator to this page and make them read it three times.

And if you don’t get it, don’t feel bad. James Bond didn’t either.

You knew Skepticality, the skeptical podcast, was back, right? Of course you did.

Today they posted a new podcast featuring, ahem, me! You can download it here, or go to the main Skepticality site to see what’s what. We talked about Pluto, and DragonCon, and dark matter, and underpants mice gnomes, and some salacious stuff because I can’t help myself when I talk to Swoopy (mmmm, Swoopy), and somewhere in all that there’s probably something that might be interesting.

Given that August 27th was when Mars was supposed to be as big as the Moon, my old buddy Rob Sparks let me know that even cartoonists are in on the joke.

Tip o’ the cartoonist’s beret to Rob Sparks, duh.

It’s pretty obvious I love astronomy. It inspires us, and I think in many cases brings out the best in humanity: the wonder, the curiosity, and the desire to explore.

That’s why I get more than a little upset when someone twists astronomy, misusing it to further their own ends. You can find any number of people who do that; check the main site for names if you care to. But just about the worst thing that can be done to astronomy is for it to be used to scare people. There are scary things in space, sure, but it’s easy for these things to get amplified beyond what they deserve. And amplified they are, in many cases so that money can be made.

Enter ABC television.

They have a show coming out tonight (Wednesday, Aug 30 at 9:00 p.m.) about doomsday scenarios. Several friends of mine, scientists, were interviewed for it, and it looks like it will be an interesting and fun show. I think this is a great hook to get people interested in astronomy, but only if it’s done right. A lot of people don’t understand the science involved, and so you have to tread carefully lest you scare them needlessly. The show may very well balance things, giving a fair picture of dangers from space. Unfortunately, the same cannot be said of their advertising for it.

ABC has been promoting the show online, and their advertising department went out of its way to scare people needlessly. Here’s the opening line from the promotional article (which, incidentally, is billed as a science news article):

Imagine a black hole swallowing Earth, ending life in an instant. It’s not only the stuff of pulp sci-fi novels but, scientists say, a looming possibility.

Not to be too subtle here, but that’s a load of crap. It’s not "looming" at all. I found a paper that showed that the odds of even a normal star getting anywhere near us are only one in 100,000, and that’s over the next 3.5 billion years. The odds of a black hole getting that close are much smaller. I’ll be clear: there is nothing to worry about. Black holes are really far away, and pose no danger to the Earth.

Later they quote physicist Michio Kaku as saying,

“Then, in the year 2000, all hell broke loose,” Kaku says. “At that point, we had conclusive evidence that there are wandering black holes — nomads, renegades — right next to us in our own backyard of a galaxy.”

When he says "right next to us" he is not being literal. The nearest known black hole is 1600 light years away, or about a quadrillion miles. I feel pretty safe about that.

It isn’t until the next paragraph, almost all the way down the first page of the article, that they ease this up somewhat:

Fortunately, scientists say the probability of a black hole heading straight toward Earth and swallowing us whole is highly unlikely.

No kidding. That would have been a nice thing to say up front… along with numbers to back it up.

This is fear-mongering, pure and simple, and it’s loathsome. I am particularly sensitive to this after the scare-tactic garbage spewed by such people as Nancy Lieder and Mark Hazlewood. It’s truly awful behavior.

Mind you, I participated in a show on the SciFi channel about doomsday scenarios as well, but I was careful to talk about how long the odds are of any of them actually doing any damage (though most of that was cut out, of course). I also wrote an article for Sky and Telescope magazine that appeared in June about this exact topic, and again I was careful to say that the odds are long indeed; I’d worry more about an iceberg hitting a cruise ship in Bermuda.

The scientists interviewed were trying to provide fun quotes, so I don’t blame Kaku (much– I do think he should have been more circumspect with his comments, but for all I know he was quoted out of context, and may have put things in perspective but wasn’t quoted doing so), or any of the other scientists in the article (or in the ABC show so far as the previews available let me see them). I blame ABC for promoting this like it’s an imminent threat.

And while I’m at it, I’ll poke an accusatory finger at The Huffington Post, who linked to this story with the headline "Scientists Worry “Wandering Black Holes” Could Approach Earth…". That’s just so much eyewash as well.

I’ll watch the show tonight if I can, but I’m leaving extremely early in the morning for Dragon*Con, so I doubt I’ll be able to write up anything until later Thursday, if at all. The show may be pretty good; they did get some good people in it. So don’t get me wrong, I’m not saying anything about the show… until I see it. It’s ABC’s advertising department I hold in contempt.

Earlier, I blogged about the Cas A supernova explosion. I noticed an interesting thing in the images just released by Hubble, but the original post was getting too long, and my "discovery" deserves its own post.

Looking at the image, you can see that Cas A isn’t perfectly spherical (hardly anything really is). Look at the upper left side: it looks a little like a freeze frame of a popping balloon, doesn’t it? Here’s a closeup:

It may have been that the explosion was not perfectly spherical, that the actual supernova may have been a little off-center. It’s also possible that the explosion was fairly symmetric, but the gas outside it was slightly less dense in one direction, so the expanding supernova blast wave could move more quickly in that direction. However it happened, that upper-left structure is a blow-out, where the blast wave burst through the surrounding material (you can see it better in the super high-res version which is 4000×2900 pixels). It left behind those long fingers, those tendrils of gas. They stretch all the way to the edge of the frame.

You can see that structure in radio waves and X-rays, but I’ve never seen it so clearly in optical light before. That’s part of the power of Hubble, to be able to trace faint fuzzy stuff due to its higher resolution. Even more interesting is the separation of color in the "jet": in the high-res version you can see how the material closer in to the center of the explosion is green, and the material farther out is purple. In this image, purple is from sulphur, while green is from oxygen. Sulphur is heavier than oxygen, which is funny; you’d expect the lighter stuff to be outside the heavier stuff (lighter stuff would be moving faster). But here it’s the opposite. Why?

On Earth, heavy stuff sinks, right? Gravity is a downward force, and the heavy stuff feels a greater force in that direction than light stuff does, so it sinks. A similar thing is happening in the Cas A blowout. The material ejected from the supernova is accelerated outward by forces in the explosion. Heavy stuff (like sulphur) flows toward the direction of the force, so the heavy stuff "sinks" outward, passing the lighter stuff. Another way to think of it is that the acceleration is outward, opposite the direction of gravity, so the heavy stuff will sink in the direction opposite the way it does on Earth. Heavier stuff here sinks downward, so heavier stuff in the explosion sank outward. Weird, huh? It’s the same thing as when a helium balloon moves backward when you hit the brakes in a car.

Sometimes things happen the opposite way than you expect. The Universe is subtle, but there’s always a reason for things to happen the way they do. It’s like there is a higher force at work here… and there is. It’s called science.

Image credit: Robert A. Fesen (Dartmouth College, USA) and James
Long (ESA/Hubble), NASA, ESA, and the Hubble Heritage (STScI/AURA)-
ESA/Hubble Collaboration

In the year 1680, a star in our Galaxy blew up. It wasn’t noticed on Earth, because even though it’s relatively close as these events go — 10,000 light years away — it was behind a thick layer of gas and dust, so its light was dimmed (see the footnote).

But now, 300+ years later, the expanding debris from the explosion is visible. It was first seen as a radio source, and was named Cas A, the first radio source detected in the constellation Cassiopeia. It’s now been observed across the electromagnetic spectrum, and is a pretty cool object. The image displayed here was from Hubble, and was just released today.

We think the star that blew up was about 40 times the mass of the Sun. It lived a violent life, shedding most of its outer layers before it finally exploded. All that sloughed-off gas expanded outward, and when the core exploded the ejecta screamed outward much faster, slamming into the gas, ramming it, making it glow. It’s now a roughly spherical shell of material expanding at tens of millions of kilometers per hour.

As it happens, Cas A was the subject of an educational activity I developed with the help of a team of other folks, both at my home school of Sonoma State University and at Gettysburg College. While developing the activity I calculated some amazing things about the nebula.

The amount of iron in the nebula — just the iron — is over 1000 times the mass of the Earth. That iron was created in the blast, alchemically converted from lighter elements. In fact it’s thought that all the iron in the Universe was made in such explosions. The supernova that made Cas A also created more than enough iron to account for all the iron in a star like the Sun. In the long run, over the lifetime of the the Galaxy, these explosions (which occur roughly once or twice per century) generated enough iron to make 300 million stars like the Sun!

Calcium (as well as a slew of other elements) was created as well. The mass of the calcium in Cas A is very roughly 10²⁹ grams, enough to make 10²⁸ gallons of milk! If you’re curious, there are about 5 grams of calcium in a gallon of milk (I’m rounding the big numbers here pretty severely).

I think that’s all pretty amazing. The iron in your blood and the calcium in your bones were forged in the fires of the death throes of some unknown massive star billions of years ago. The matter was ejected, shot into the Galaxy, where it slammed into and merged with a cloud of gas and dust. That floating junk — the "ash", essentially, from a tremendous explosion — formed the Sun, the planets, and eventually… you.

Footnote: Yes, I know– some of you will think that it didn’t blow up in 1680, that’s just when the light reached us, and it really blew up 10,000 years ago. I disagree. We cannot say anything about that event until the light reaches us, and in a real sense that event has not happened until the light reaches us. Time flows like light, I sometimes say, meaning that the event itself happens when the light reaches us. So it is acceptable to say that the explosion actually happened in 1680.

Image credit: Robert A. Fesen (Dartmouth College, USA) and James
Long (ESA/Hubble), NASA, ESA, and the Hubble Heritage (STScI/AURA)-
ESA/Hubble Collaboration

Check this out: a flight simulator using Google maps!

You can even trick it into starting at your house, or anyplace where you have the latitude and longitude. The Little Astronomer and I flew a plane from our house to the Golden Gate Bridge. Top speed is like 40 mph, so it takes a while to actually get anywhere. But it’s fun, and I can see this being able to be expanded to do lots of other fun things, too.

Tip o’ the aviator goggles to Angela Gunn, who is "endlessly fond" of me.