Wednesday, August 30, 2006
Thursday, August 24, 2006
Poor Pluto has suffered a couple of weeks of highs and lows, but this morning astronomers at the 2006 General Assembly of the International Astronomical Union defrocked Pluto, removing it from our list of planets in the Solar System.
Some astronomers are happy, some are mad, and some are ambivalent. But I promise that if you call Pluto a "planet," I will not call the IAU Police and have you arrested.
The passed definitions of planets are (copied shamelessly from the IAU):
- A "planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.
- A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape , (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
- All other objects except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".
- The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
- An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
- "Small Solar-System Bodies" currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
Note one glaring omission -- this definition of the word "planet" means that planets orbit the sun. So what are the objects the size of Jupiter and Saturn circling other stars? I think those are planets, but why they are excluded from this definition, I don't know.
Tuesday, August 22, 2006
While astronomers continue an emotional debate over the definition of a planet, real science goes on. One of my friends, Doug Clowe, has headed an investigation into the dark matter content of a cluster of galaxies. What Doug and his collaborators found was that, in one cluster, the dark matter doesn't line up with the visible matter. This is solid evidence that dark matter is some strange, exotic thing and not just ordinary matter or a misunderstanding of our theory of gravity.
In the picture above, there are really three bits of information. The white and yellow are pictures of galaxies taken with an ordinary telescope. The pink "glow" is extremely hot gas, so hot it glows only in X-rays. And the blue is a map of the gravitational force, made by careful analysis of how that gravity bends and distorts light from more distant galaxies.
The amount of gas glowing in the X-rays is quite ordinary matter -- hydrogen, helium, iron, carbon, etc., -- heated to 10 million degrees. In fact, the amount of matter in the pink glow is much more than the amount of matter in the visible galaxies. So the pink glow really traces out the "ordinary" matter in the picture. The pull of gravity, which comes from a combination of dark matter and "ordinary" matter, will be strongest where there is the most matter. So, since the blue and pink do not line up, the matter that causes the gravity is NOT the "ordinary" matter that causes the X-rays. So it must be dark matter! This marks a new, independent confirmation of dark matter.
What is this dark matter? Astronomers and physicists have some ideas, but we have never directly detected dark matter in a laboratory. Such a detection would prove beyond any doubt that dark matter exists (and would win the team a Nobel prize). But, for now, astronomers can rest comfortably that dark matter actually exists.
Friday, August 18, 2006
So the big news from the 26th General Assembly of the International Astronomical Union is the pending definition of the term "planet," which, if passed, means the Solar System will have 12 or more planets. But, believe it or not, when 2500 astronomers get together, there is much more to talk about than how many planets can dance on the head of a pin.
In fact, there is so much going on that it is impossible for one person to see it all. Part of the General Assembly is that a dozen or more simultaneous, smaller meetings take place during the meeting.
In order to keep attendees updated on everything that is going on, a small daily newspaper, the Dissertatio com Nuncio Sidereo III, or "Conversations with the Sidereal (stellar) Messenger." The name is Latin and taken from the title of a book written by one of the first great astronomers, Johannes Kepler, in 1610. Putting together the Nuncius every day is hard work, especially since the editors are clearly non-native English speakers. So kudos to the editors! If you would like to read the Nuncius, keep in mind that it was written by astronomers for astronomers. But you are more than welcome to read PDF versions of it at this web site.
Wednesday, August 16, 2006
This news release from the General Assembly of the International Astronomical Union surprised me in some ways. It is the official proposal on the definition of a "planet." Instead of demoting Pluto to a "minor planet," it actually saves Pluto and re-promotes the asteroid Ceres to planet status (see my last post for that story).
The proposed definition actually makes some sense, scientifically. It is a definition based on measurable properties -- the shape of an object and its "dynamical state," (e.g., does it orbit another, much larger planet?).
In other ways, this definition is lacking. It says that planets are "not stars," which just means that the group did not want to develop a definition for separating stars, brown dwarfs, and planets. It also ignores the fact that, while Ceres and Pluto may be round, there are many, many non-round objects that are extremely similar (asteroids and the icy Kuiper belt objects). However, this definition may be the best possible one.
The new definition is not yet "accepted." That requires a vote of the full assembly of the IAU, which will not happen for a couple of weeks yet.
Monday, August 14, 2006
On Wednesday, the 2006 meeting of the International Astronomical Union begins in Prague. I will NOT be there, as I have to leave for the telescopes in Chile tomorrow, and a week after that I am moving from Arizona to Texas. But several thousand astronomers will be in Prague over the next two weeks to talk about research and discuss important scientific and procedural issues.
One of the biggest topics that will come up is the definition of a planet. The issue of whether Pluto will continue to be called a planet has captured the public's attention, but this will also deal with what to call objects the size of Jupiter floating through space, and what to call objects ten times the size of Jupiter orbiting other stars.
The gossip I've heard (which may be wrong) is that there is no good definition of a planet. Many of us would claim to know a planet if we saw it, but crafting a working definition is hard! Perhaps the best definition would include how planets are formed, but we can't be certain how any specific object formed.
As for Pluto, it has historically been called a planet, but now we know of dozens of objects that are very similar to Pluto in almost every way -- size, shape, where they are in the Solar System, what they are made of, having moons, and so on, and so on. So, if you want to keep calling Pluto a planet, we will end up with a couple of dozen planets in our Solar System. Or, we could set a size limit, and then we would have 8 planets in the solar system (but what about planet moons that are larger than Mercury?). And what is the rational for a size criterion?
In 1801, astronomer Giuseppe Piazzi discovered a moving object in the sky. It's orbit was between Mars and Jupiter, and it was thought this could be a new planet. The object was named Ceres, and for almost a year was known as the 8th planet (Neptune and Pluto were still unknown). Then, another, almost identical object was found between Mars and Jupiter. Within a few years, several of these were known. They were much smaller than the other planets, and so soon became known as "asteroids," and Ceres was demoted from planetary status.
Pluto has been a planet for over 70 years, but my hunch is that soon it, too, will have to be demoted to the king (or maybe just prince) of the "Kuiper Belt Objects." (Kuiper is pronounced KOI-pur).
My other hunch is that, no matter what the definition of a planet is, many people will be unhappy.
Sunday, August 13, 2006
A cousin of mine forwarded me an email with the above picture and the following text:
This photo is a very rare one, taken by NASA. This kind of event occurs once in 3000 years. This photo has done miracles in many lives. Make a wish .. you have looked at the eye of God. Surely you will see the changes in your life within a day. Whether you believe it or not, don't keep this mail with you. Pass this at least to 7 persons. This is a picture NASA took with the Hubbell telescope. Called "The Eye of God."
First, this is not a once-in-3000-year occurrence. This is a picture of the Helix Nebula, which was discovered sometime before 1825 and has been visible ever since. The nebula is what is known as a "planetary nebula," and is formed when a star like the sun runs out of nuclear fuel and sheds its outer layers. The hot furnace of the dying star lights up the shed gas, producing a planetary nebula. Other famous planetary nebula include the Ring Nebula, the dumbbell Nebula, and the Cat's Eye Nebula.
And, as far as I can tell, no astronomer has ever referred to this as the "Eye of God." Everyone I know calls this the "Helix Nebula," it's proper name. In fact, if you do a search for images of the "Eye of God," several different planetary nebulae show up.
This is just further evidence that you need to be careful when someone asks you to forward an email to everybody you know -- I'm glad my cousin asked before forwarding it to her whole email list. Likewise, if you ever have a question about an email you've received talking about something astronomical, feel free to ask!
Friday, August 11, 2006
Our conference in Leicester, England, is continuing. Most of the talks are on more specialized projects, and it can be hard to stay awake. But there are nuggets of science important for my work hidden among the rest.
The biggest topic is the terror alert due to the foiling of a plot to bomb airplanes bound for the US. As someone who will be on a flight from the UK to the US on Saturday, I am quite happy they caught the plotters. But it does mean that travel will be even less fun, as we cannot bring anything on board beyond essential medicines -- not books, soduku puzzles, iPods, etc. So, I will be forced to watch the airplane movie (probably Ishtar 2, with by luck).
The above picture, taken from the Sydney Herald web site, is Heathrow Airport yesterday. We'll see what it is like at Gatwick tomorrow.
Wednesday, August 09, 2006
All week I am at a conference in Leicester, England. We have talks all day long, and enjoy ourselves at night. (The above picture is renowned astronomer James Liebert participating in "Morris Dancing", a traditional English folk dance).
Of course, we are learning a lot, too. I've learned that several white dwarfs (dead stars with the mass if the sun but only the size of the Earth) have "rings," just like Saturn. In fact, the size and mass of the rings are very similar. We've also learned about stars that have escaped from star clusters, large numbers of white dwarfs in globular star clusters, and many very specialized topics.
Friday, August 04, 2006
After a busy week of getting ready, I am at the airport and ready to go to the United Kingdom for our white dwarf conference in Leicester (rhymes with "Lester". I think.)
In addition to talks and posters and meetings with friends and collaborators, we get to have some fun, too. After all, what is the point of travelling a third of the way around the globe to sit in a classroom all day? We have a visit Sunday to Warwick Castle, a conference dinner complete with Morris dancing astronomers, and a few other special treats.
I will try to blog if I can; I'm unsure how easy it will be to get internet access.
Wednesday, August 02, 2006
The above picture was taken by scientists in Antarctica, who are starting to see hints of the sun for the first time in months as the Antarctic winter begins to wind down. The story from CNN can be found here.
These clouds are known as "nacreous" clouds, and also are known as "mother of pearl" clouds. These clouds form in the stratosphere (higher than almost all other clouds) and have shapes dominated by wave-like motions in the stratosphere.
For those interested, "nacreous" means something possesing the qualities of mother-of-pearl, or iridescent.