Keep in mind that the orbital solution is based
on only a short arc: only 28 days, about one twelfth of a complete revolution. Our estimates of the orbital parameters -- and behavior --
could change quite a bit over the next few months.
What is the
difference if someone learns something by reading online documents or by going to hear some
windbag talk about it for 50 minutes? There isn't....
I couldn't recommend it to anyone with the
intelligence to learn things on their own.
People can read material in books just as well as they can read them on-line. Libraries have existed for centuries. If your argument is correct, universities should ALREADY be obsolete.
No one should need to go to college, because everyone can just read books and gain all the skills and knowledge he needs.
And, yes, I not only went through college, but I now work at one. I'm one of the windbags that GigsVT mentioned. Would you like me to poll the students in my class? "Okay, guys, I'll just stop coming to class, preparing lectures and readings, giving you homework, and answering your questions. Instead, I'll just wait until the quarter ends and give you the final exam."
Care to wager how many of those students would jump at the chance to avoid this old windbag?
"Flybys like this happen every 50 years or so," says
Don Yeomans, the manager of NASA's
Near-Earth Object Program office at JPL. The last
time (that we know of) was August 31, 1925, when
another 800-meter asteroid passed by just outside
the Moon's orbit.
Actually, asteroids pass even closer to the Earth every year; most of them are just smaller than 800 meters. In many cases, we don't detect the objects until after they've gone past.
Here's a list of objects which have come closer to the Earth than 2002 NY40 in the past decade or so.
The final column shows the closest approach in terms of the Lunar Distance (between Earth and Moon). For 2002 NY40, that's about 1.3.
Name or Nominal Date +/- Nominal Designation YYYY-mmm-DD HH:MM D_HH:MM (LD/AU)
apparantly Pioneer 10's power system is going
to run out of juice in a few years
(solar powered I guess - the W/m^2 will
probably be too low to power the probe
at that point).
Pioneer 10 is powered by a device called an "RTG", which stands for "radioisotopic thermoelectric generator." A chunk of Plutonium-238 heats up one side of a thermocouple, generating electricity. Since the Pu-238 has a half-life of 88 years, the power supplied by the RTG decreases over decades. At this point, there is barely enough power to run one or two particle detectors or send back a message to Earth.
Tom Droege, an engineer at Fermilab, liked to build electronic projects as a hobby. In the mid-nineties, he became interested in astronomy, and decided to build electronic cameras and attach them to small telescopes in his backyard. He started simple, with a 1-D FAX chip, but has worked his way up to 2048x2048 CCDs. You can read a bit about the evolution of his cameras,
or see some pictures of the
construction of a Mark IV .
He started a group known as
The Amateur Sky Survey, which has been working on software for analyzing the images from his cameras. After three years of scanning the celestial equator, we published a paper containing over 10 million measurements of stars in several passbands. You can read
a preprint or
the paper itself if you subscribe to PASP.
Based on our experience, I'd say that one of the hardest things about turning a backyard observatory into a serious scientific instrument is the bookkeeping: carefully recording all the necessary information and calibrating your results against the standard catalogs is a real pain, and doesn't have the same sex appeal as building the hardware or the software. But it's just as necessary.
Other books which mix chemistry with biography
on
Nature's Building Blocks
·
· Score: 3, Informative
I enjoyed reading two other books which blend heavy doses of chemistry with the story of a boy's journey through adolescence:
"The Chemical Elements", by Primo Levi, describes his experiences as a young Jew in Nazi Germany. I especially like his struggle when asked by the authorities to figure out how to improve the processing of some sort of metallic ore: he was fascinated by the intellectual puzzle, but, of course, determined not to help the enemy. The fact that he was essentially a prisoner of the German army at the time adds an extra element of suspense.
"Uncle Tungsten", by Oliver Sacks, follows an English boy through roughly the same period of time.
Both are chock full of the sort of fascinating chemical facts described in this review, but they feature compelling human stories as well. It doesn't hurt that Levi and Sacks are damn good writers:-)
I'm an astronomer. I study supernovae. A number of years ago, I crunched the numbers on the various types of hazards posed by nearby supernovae. You can find the work at
The bottom line is: no need to worry for anything more than about 50 parsecs = 160 light years away from us. There are zero known stars within that radius which could become supernovae, so there's no need to worry about this right now. In a few tens of millions of years, the Sun might move closer to some possible SN progenitor, but I'm not holding my breath.
The stars WERE hot and blue when the emitted
the light we are now seeing; if you had looked
at the spectrum of the starlight back then
(because you were floating in space close to
the stars), it would have peaked in the
ultraviolet.
However, the light has travelled a long way
to reach us, and the universe has been expanding
since then. The redshift of these objects is
around z=5.58, which means that we observe photons
to have a wavelength (z+1) = 6.58 times longer
than their rest wavelength. The peak of the
spectrum has moved from the near UV to the near
infrared. Hence, the stars would appear red
if viewed by a person.
The pictures were formed by combining images
taken through several different filters with
HST. Each filter was in the visible range.
The astronomers who made the picture set the
Red plane of the image to correspond to the
picture taken in the reddest filter,
the Green plane to the filter of intermediate
wavelength, and the Blue plane to the bluest
filter. It's false color, but reasonably
like a person would see.
Well, ok, camera resolution might not be so important in most research, but I would imagine
that doing the Palomar sky survey (hundreds of
huge plates) with CCDs would be impossible
(it would probably require trillions of pictures).
The Sloan Digital Sky Survey is using CCDs to map one quarter of the entire sky, in five passbands. Its main camera uses a mosaic of 30 2048x2048 CCDs to cover an area about 2.5 degrees across (although there are gaps between the chips). Other mosaic cameras have even more pixels.
Future ground-based surveys will use electronic detectors, not photographic plates. The increased sensitivity and linearity of electronic detectors, plus their inherent digital output, make them far superior to plates.
I was surprised to read a blurb from TransOrbital which claims that
The photos from lunar orbit will be very high resolution, utilizing a telescope with an HDTV camera. "We expect to be able to see the tire tracks from the Apollo-era rovers."
The laws of physics state that the smallest angular detail visible to a system is 1.22 times (lambda/diam), where "lambda" is the wavelength of the light and "diam" is the diameter of the lens. This limit is set by diffraction. Now, if the lens is 10 cm in diameter, and the light is red light of 600 nm wavelength, then the limiting resolution is about 7.3e-6 radians, or 1.5 arcseconds.
In order to see details of linear size "L", a camera with resolution "theta" radians must be closer than D = L/theta. Suppose the tire tracks are 20 cm wide each. Then the spacecraft must have an orbit of about (0.2m)/7.3e-6 = 27 km or lower to resolve them. That's quite a bit lower than the Lunar Orbiter spacecraft...
Now, it's true that the long, long tracks of the lunar rovers might make a high-contrast feature over a large area; and that feature might show up in pictures, even if its width is smaller than the limiting resolution. In fact, I suspect that this is why the advertising mentions the rover tracks: because compact items like the rovers themselves, or the remaining sections of the Lunar Module spacecrafts, will NOT show up in the pictures.
If the spacecraft has a safer orbit, more than 27 km above the lunar surface, or it has a camera lens less than 10 cm in diameter, then the limiting resolution decreases, and the smallest object which can be discerned is larger than 20 cm. I wouldn't get too excited, yet.
I'm a member of the Sloan Digital Sky Survey, and this is the first I've heard of this idea. I guess I'm not surprised to hear it, since the SDSS has always been at a loss to explain just how it would make information available to the public at large (a requirement put upon it by NASA and the NSF for certain funding).
Let me give you some idea for the current state of the survey: we're taking a number of "test" strip scans of portions of the sky, and have perhaps 2 or 3 out of roughly 50 or 60 scans done so far. There's still an issue with calibrating the data, but we're working on it. The data is put on tape at the mountain, shipped by FedEx to Fermilab, and they reduce the heck out of it with pipelines specially designed for the survey. The data goes into a database at FNAL, and a copy is sent to JHU. I believe that Microsoft would work with a copy of the JHU database. Some of the JHU astronomers are building a friendly querying system so that people can ask questions like:
Give me info on all the stellar objects in this tiny area of the sky, with colors (g-r) 2.0, and with no close companions
The database will also allow people to download little "postage-stamp" sized pictures of the sky which are cut out around all detected objects.
You can see some examples of pictures (and detected objects) at:
As another poster stated, we look at each piece of the sky only once (well, small sections twice), so finding motions or variability from this data alone won't be easy.
The survey won't be finished, in my opinion, until sometime around 2003 or so (for the imaging half of the survey -- the spectroscopic section of the survey will take another few years after that). There is some period of a year or so -- it's rather vague at this point -- before data is released to the public. I'm not sure if it's a year or two after the photons are collected, or a year or two after they have been calibrated and placed into the database. It's possible that a small subset of the commissioning data might be made available sometime before then, but I wouldn't hold my breath.
I'd be happy to answer questions about the Sloan Digital Sky Survey, if someone wants to set up an interview mechanism (hint, hint).
As another poster has already stated, most astronomers doubted the claim that this object was actually a planet. The evidence was skimpy:
it was close to a close binary star
it was dimmer than the stars
some claimed to see a "filament" joining the object to the binary
Astronomers have had a number of bad experiences based on "filaments" which appear to connect two objects -- which are actually at very different distances from us. There was a heavily publicized case a few years back, in which Halton Arp claimed that such a "filament" joined a quasar and a nearby galaxy, thereby "proving" that the quasar was much closer than its redshift would indicate. Sigh.
Anyway, back to TMR-1C. I remember talking to other astronomers at the summer meeting of the American Astronomical Society in 1997, in San Diego, and most of them agreed with me that this was just a chance superposition of a background star with the binary. We thought that the discoverers should have waited for some additional evidence:
did the "planet" share a common motion in space with the binary star (we call this "proper motion"); it would take a few years to confirm this, since one has to wait for the stars to move a perceptable amount
did the "planet" have the proper colors? A planet in this system would have a particular ratio of visible to near-infrared to far-infrared radiation, whereas a background star would have very different ratios. Again, this would take time to confirm, since one would need to apply for telescope time at observatories with the proper equipment.
My guess is that when the researchers (who work for NASA) started talking about their work with their colleagues, word reached the upper echelons of administrators, who probably ordered the press releases. I am speculating that it might have been hard for one of the astronomers on the team, if he or she had serious doubts about the claim; it's not easy to tell your boss to shut up.
But a scientist is supposed to do this...
Oh, and the poster who claims that astronomers have not detected ANY extra-solar planets is dead wrong. The radial velocity measurements he interprets as "changes in stellar shape" are really due to the motions of stars in orbits around their center of mass with bona-fide planets. Check out
Physicists seem to have taken on some of the heaviest questions of human existence: " Why are we here? Why is the world the way it is? Where have all the Gods gone?"
Well, most physicists haven't, actually; and those who do, cease to be physicists and become philosophers... and, in general, annoy greatly those physicists who refrain from abusing their credentials to take money from a public desperate for reassurance.
The images produced by Pogge and Martini show material in the inner spiral arms of the galaxies. It's a stretch to refer to this as material "being sucked into gigantic black holes." Note the scale of the images: the resolution is a few hundred light years. The accretion disk around the black hole is less than one light year in radius; it is completely unresolved in thes pictures.
The material shown in these images MAY be spiralling gradually in towards the center of the galaxies, but it may also be in relatively stable orbits around the center. Suppose that a small component of the total velocity -- which is several hundred km/sec -- is radially inwards. It would take tens of millions of years for the material to reach the black hole.
Writing that these pictures show gas which is "being sucked into a gigantic black hole" is about as accurate as writing "and here's a picture of Angeline Jolie growing old and wrinkled at the Academy Awards ceremony." Sure, technically, she is growing oldER and adding a micro-wrinkle or two as she sits in the audience... but it's not really relevant under the circumstances.
By a curious coincidence, I just wrote up a lecture on black holes at the centers of galaxies for the introductor astro course I'm teaching. Check out http://spiff.rit.edu/richmond/classes/phys240/le ctures/blackholes/blackholes.html.
Many schools are rushing to distance learning and web-based courses, in order to attract a new set of students and in order to cut costs. While it may be possible to create a good web-based course, which challenges students and allows them to interact with each other and with the teacher, it is also possible to create poor web-based courses.
In the worst cases, web-based courses are just books: "here, read these pages, then take a test." They may be worse than books, since the standards of publishing on the web are much lower than they are in print.
I do teach at a university, and I'm still struggling to figure out how to do a good job. One of the important things, I think, is to force students to do something in class -- not simply listen passively to what I say. Another important thing is for me to listen carefully to student questions, answer them -- and figure out how to present the material more clearly next time.
It may be possible for a professor to interact in similar ways with students over a bulletin-board; but not if the class contains 300 or 500 students. We can't put up web pages and then expect to serve triple the number of students we serve in a regular course.
Oh, and while web-based courses may make sense for some of the introductory courses, I agree with many posters that upper-level classes and graduate courses should be taught in person. In those classes, the primary mode of learning is by asking questions -- really detailed questions -- and having discussions. Face-to-face is much better for that sort of in-depth interaction than E-mail.
This is the most distant quasar, but not by any means the most distant object we've seen so far. Astronomers have found a galaxy which is probably at redshift 6.68 (although this is based on a single emission line), and other galaxies definitely at redshifts larger than this new quasar. There are also hints that some of the galaxies visible in the Hubble Deep Field are at much greater redshift, perhaps z > 10, but that needs to be confirmed with spectroscopic observations.
> Scientists are indeed open to a great deal, so > long as you presume a materialist > universe which is empirically knowable,
Well, yes. Science is a way to study a universe which is empirically knowable. It does not address ideas which are empirically unknowable... like religion.
Science cannot address questions which do not, even in theory, imply observable results.
Posters have asked "Could the 'dark matter' be made up of these distant galaxies, just detected in X-rays by Chandra? Or could it be made up by MACHOs?" There is a very strong reason to believe that the answer to both these possibilites is "no." Here's why:
One of the strongest pieces of evidence in support of the Big Bang theory is the very good match between the abundance of light elements (hydrogen, deuterium, helium, lithium and beryllium) predicted by the BB, and actually observed by us. The BB theory places some limits on the amount of the "critical mass density" of the universe which can be made up of ordinary baryonic matter. That limit is much less than 1.0, closer to about 0.1. What that means is that _if_ the BB is correct, and _if_ the universe contains the critical mass density, _then_ most of that mass density must be non-baryonic matter.
Now, baryonic matter is good old protons, electrons, and neutrons: we and most of what we can see in the current universe (stars, planets, galaxies, etc.) are made of baryons. The galaxies just discovered by Chandra are undoubtedly made of stars (baryonic). Black holes are made of baryons, under most scenarios in the literature. MACHOs are just low-mass stars or high-mass planets, and they, too, are baryons.
So what the heck _isn't_ baryonic? Well, neutrinos aren't. There was a hope about twenty years ago that most of the mass of the universe might consist of neutrinos -- but recent experiments indicate weakly that the neutrino mass is too small to do the job. A universe of neutrinos would also lead to large-scale structure of galaxies and galaxy clusters very different than that which we observe. So, neutrinos are probably out. That leaves exotic stuff: wierd particles called "axions" or "WIMPs", or "strange matter"; all of these are theoretical, not experimentally confirmed (as far as I know)
In short, _if_ the density of the universe is even close to the critical density, it means that a) some exotic sort of matter dominates or b) the current theory of BB nucleosynthesis is wrong.
If we discover that some asteroid may hit the earth after some reasonably long time interval -- say, 5 to 15 years -- then there is indeed something we can to do prevent it; or, at least, try to prevent it. We could launch a rocket armed with nuclear bomb(s) to intercept the asteroid when it is still far, far, far away. Exploding the bomb(s) near the asteroid will alter its orbit by some small amount... but if the asteroid is far enough away, that small amount may prevent the collision.
There have been many studies of the technical feasibility of this idea. A good place to start is http://impact.arc.nasa.gov/
I don't understand the physics... but I find the idea that local dark matter (yes, within our own galaxy) may be remnants of stars from a far-future universe very unlikely.
The URL above gives the abstract in ASCII, but the article itself is in Postscript. If you look at the main article, pay special attention to the figure which shows the REAL "signal" of reflected light from the planet, and the signal from a fake planet inserted into the data. The fake signal is clearly there, but I'm not confident that the claimed signal is.
How did they do it? The basic idea is: they took spectra of the star with very high resolving power, which spread out light into different wavelengths; or, equivalently, spread out light at different velocities. They knew when the planet ought to be coming towards us, and going away from us, in its orbit around tau Bootis, and with what speed. That meant that they could examine _very carefully_ spectra to find hints of spectral features which were shifted -- ever so slightly -- from their ordinary positions. They found weak evidence that some spectral features were shifted to the blue when the planet was coming towards us, and to the red when the planet was going away from us.
But, if you ask me, it's a two-sigma result. Needs more observation.
As for the claims of specific elements... well, my guess is that the authors saw the weak, time-varying features in spectral lines produced by some element, and the press misinterpreted this to mean that that element was present in/on the planet. If the planet is simply reflecting light like a perfect mirror, it will produce these weak, time-varying features for ALL lines of ALL elements. Given the signal-to-noise ratio in the spectra I saw in their paper, I don't think that the authors are really advocating the presence of any specific elements in/on the planet.
And if they _were_ (which I emphasize is unlikely), it would be elemental oxygen, not atomic oxygen.
A good idea, certainly, but _really_ tough technically. I think that the press is running away with the story.
I am a college professor, so this issue is pretty important to me. I'm still trying to make up my mind... I do agree with one poster that there _is_ a worry about schools using online course materials to teach classes (with or without adjunct professors). Distance learning is a really hot topic at my school; the administration wants to move in that direction.
Some of us really do put a lot of work into our courses, and, while it is a nice ego-boo to hear that students elsewhere may use our materials to help themselves learn, it would annoy me greatly to learn that someone may be making money off notes that I made (or verbatim copies).
I think that if someone approached me about using notes derived from my lectures, I'd be happy to work with him -- perhaps we could improve the quality if we worked together. Perhaps it boils down to an issue of courtesy.
> I know of a few large databases out there using > PostgreSQL, but one I have access to is > the TASS project (http://www.tass-survey.org), > which currently has about 28Gb of > astronomical data.
Actually, it's only about 5 GB on our main site. But the next generation of our cameras will easily generate many GB per year, so we'll reach that 28 GB limit pretty soon...
Permit me to clear up a few questions and misconceptions. Interested readers can read the technical details for themselves in preprints on the LANL server:
A good summary: http://xxx.lanl.gov/abs/astro-ph/990819
The event MACHO-97-BLG-41 http://xxx.lanl.gov/abs/astro-ph/9908038
The event MACHO-98-BLG-35 (to which this Slashdot article refers indirectly) http://xxx.lanl.gov/abs/astro-ph/9812252
Okay, now for my comments:
1. Contrary to "cemerson"'s post (which should have been moderated to "MisInformative":-), the work _was_ done in with optical telescopes; in fact, small ones, only a meter or so in diameter (rather than the 8-meter or 10-meter behemoths like Keck). The basic method is to take pictures of the same field of stars over and over and over, and look for variations in the brightness of any star with time. The technique works best if one can point at a large number of stars at once; the two best sources for crowded fields are the Bulge of the Milky Way and our nearest neighboring galaxy, the Large Magellanic Cloud. Both are best viewed from the southern hemisphere, and the data described in the recent press releases comes from Chile, South Africa, and New Zealand.
2. The Bulge of the Milky Way is about 8,000 parsecs (about 25,000 light years) away from us. The LMC is about 50,000 parsecs away. These are the "background" stars. A star roughly halfway between us and the "background" will cause the greatest lensing effect as it passes between us and the "background" star.
3. When such an event occurs, the "background" star becomes brighter. Now, here's the key: if the "foreground" object is a lone star, then one can predict theoretically the shape of light curve: the background star brightens slowly at first, reaches a somewhat sharp peak in brightness, and then fades exactly as it brightened: the rising and falling phases look exactly the same, symmetric. And, in fact, most of the observed microlensing events (there have been over 100 followed in the past decade) follow this predicted, symmetric curve very closely.
4. But, if the "foreground" object is not a lone star, but a binary star, or a star with a planet, the light curve will depart from its theoretical, symmetric shape. If there's a planet around the foreground star, and it passes in front of the background star, it can cause a distinctive "spike" in the light curve: a short, sudden, very brief rise and fall. The event MACHO-98-BLG-35 shows a LITTLE bit of evidence for such a spike: see Figure 9 in the paper by Yock: http://xxx.lanl.gov/abs/astro-ph/9908198
5. There are several efforts underway to detect planets around other stars by searching for the tiny 'eclipses' caused as a planet passes in front of its star in its orbit, but no solid detections yet. This is very difficult, because even a big planet like Jupiter causes only a (roughly) one-percent dip in the light of its star -- and many stars vary by more than one percent. Planets like the earth decrease the light by even smaller amounts, maybe one-hundredth of one percent. At that level, _most_ stars are variable. So, one must disentangle the intrinsic variation of the star from the brief dip caused by the planet -- and that means waiting months/years for the planet to come around in its orbit again. You can find information on one such search, Kepler, at this site: http://web99.arc.nasa.gov/~mars/vulcan/
According to the articles referenced for this story, the system requires "a few kilowatts" to produce a magnetic field of the required strength. That's a lot of power. If one uses solar panels to provide, they must be big.
The amount of power in sunlight is roughly 1400 Watts per square meter, divided by the square of the distance from the sun (in AU). Thus, at Jupiter's distance, the power is down to about 50 Watts per square meter. If the panels are 100% efficient, they must be about 4.5 meters on a side to produce 1 kiloWatt. Real panels are more likely to be about 25% efficient; thus, one needs panels about 9 meters on a side to provide a single kiloWatt. If the "few" kilowatts mentioned is really 4 kiloWatts, the panels would need to be about 18 meters on a side. That's getting pretty darn big -- and, of course, more massive, decreasing the acceleration of the craft.
At the distance of Saturn, about 10 AU, the panels need to be twice as long on each side to provide the same amount of power.
Solar panels + magnetic fields might work in the inner solar system, but it won't provide much oomph in the outer solar system. A ship could accelerate to a high speed before reaching Jupiter, say, but it would be unable to use its magnetic system to slow down as it passed Neptune or Pluto.
Slashdot Mirror
JPL has a very nice tool for looking at the orbits of asteroids. Go to
http://neo.jpl.nasa.gov/orbits/
for the general case. For 2002AA29 in particular, you can use
http://neo.jpl.nasa.gov/cgi-bin/db?name=2002AA29&g roup=all&search=Search
Keep in mind that the orbital solution is based on only a short arc: only 28 days, about one twelfth of a complete revolution. Our estimates of the orbital parameters -- and behavior -- could change quite a bit over the next few months.
People can read material in books just as well as they can read them on-line. Libraries have existed for centuries. If your argument is correct, universities should ALREADY be obsolete. No one should need to go to college, because everyone can just read books and gain all the skills and knowledge he needs.
And, yes, I not only went through college, but I now work at one. I'm one of the windbags that GigsVT mentioned. Would you like me to poll the students in my class? "Okay, guys, I'll just stop coming to class, preparing lectures and readings, giving you homework, and answering your questions. Instead, I'll just wait until the quarter ends and give you the final exam."
Care to wager how many of those students would jump at the chance to avoid this old windbag?
Actually, asteroids pass even closer to the Earth every year; most of them are just smaller than 800 meters. In many cases, we don't detect the objects until after they've gone past.
Here's a list of objects which have come closer to the Earth than 2002 NY40 in the past decade or so. The final column shows the closest approach in terms of the Lunar Distance (between Earth and Moon). For 2002 NY40, that's about 1.3.
You can generate such lists yourself at The NEO Program's list of Near Earth Objects.
Pioneer 10 is powered by a device called an "RTG", which stands for "radioisotopic thermoelectric generator." A chunk of Plutonium-238 heats up one side of a thermocouple, generating electricity. Since the Pu-238 has a half-life of 88 years, the power supplied by the RTG decreases over decades. At this point, there is barely enough power to run one or two particle detectors or send back a message to Earth.
For a detailed history of RTGs, check out this Miamisburg Environmental Management Project report.
Current solar panels are pretty much useless beyond the orbit of Jupiter.
He started a group known as The Amateur Sky Survey, which has been working on software for analyzing the images from his cameras. After three years of scanning the celestial equator, we published a paper containing over 10 million measurements of stars in several passbands. You can read a preprint or the paper itself if you subscribe to PASP.
Based on our experience, I'd say that one of the hardest things about turning a backyard observatory into a serious scientific instrument is the bookkeeping: carefully recording all the necessary information and calibrating your results against the standard catalogs is a real pain, and doesn't have the same sex appeal as building the hardware or the software. But it's just as necessary.
I enjoyed reading two other books which blend heavy doses of chemistry with the story of a boy's journey through adolescence:
:-)
"The Chemical Elements", by Primo Levi, describes his experiences as a young Jew in Nazi Germany. I especially like his struggle when asked by the authorities to figure out how to improve the processing of some sort of metallic ore: he was fascinated by the intellectual puzzle, but, of course, determined not to help the enemy. The fact that he was essentially a prisoner of the German army at the time adds an extra element of suspense.
"Uncle Tungsten", by Oliver Sacks, follows an English boy through roughly the same period of time.
Both are chock full of the sort of fascinating chemical facts described in this review, but they feature compelling human stories as well. It doesn't hurt that Levi and Sacks are damn good writers
I'm an astronomer. I study supernovae. A number of years ago, I crunched the numbers on the various types of hazards posed by nearby supernovae. You can find the work at
http://a188-l009.rit.edu/richmond/answers/snrisks. txt
The bottom line is: no need to worry for anything more than about 50 parsecs = 160 light years away from us. There are zero known stars within that radius which could become supernovae, so there's no need to worry about this right now. In a few tens of millions of years, the Sun might move closer to some possible SN progenitor, but I'm not holding my breath.
The stars WERE hot and blue when the emitted
the light we are now seeing; if you had looked
at the spectrum of the starlight back then
(because you were floating in space close to
the stars), it would have peaked in the
ultraviolet.
However, the light has travelled a long way
to reach us, and the universe has been expanding
since then. The redshift of these objects is
around z=5.58, which means that we observe photons
to have a wavelength (z+1) = 6.58 times longer
than their rest wavelength. The peak of the
spectrum has moved from the near UV to the near
infrared. Hence, the stars would appear red
if viewed by a person.
The pictures were formed by combining images
taken through several different filters with
HST. Each filter was in the visible range.
The astronomers who made the picture set the
Red plane of the image to correspond to the
picture taken in the reddest filter,
the Green plane to the filter of intermediate
wavelength, and the Blue plane to the bluest
filter. It's false color, but reasonably
like a person would see.
The Sloan Digital Sky Survey is using CCDs to map one quarter of the entire sky, in five passbands. Its main camera uses a mosaic of 30 2048x2048 CCDs to cover an area about 2.5 degrees across (although there are gaps between the chips). Other mosaic cameras have even more pixels.
Future ground-based surveys will use electronic detectors, not photographic plates. The increased sensitivity and linearity of electronic detectors, plus their inherent digital output, make them far superior to plates.
The laws of physics state that the smallest angular detail visible to a system is
1.22 times (lambda/diam), where "lambda" is the wavelength of the light and "diam" is the diameter of the lens. This limit is set by diffraction. Now, if the lens is 10 cm in diameter, and the light is red light of 600 nm wavelength, then the limiting resolution is about 7.3e-6 radians, or 1.5 arcseconds.
In order to see details of linear size "L", a camera with resolution "theta" radians must be closer than D = L/theta. Suppose the tire tracks are 20 cm wide each. Then the spacecraft must have an orbit of about (0.2m)/7.3e-6 = 27 km or
lower to resolve them. That's quite a bit lower than the Lunar Orbiter spacecraft
Now, it's true that the long, long tracks of the lunar rovers might make a high-contrast feature over a large area; and that feature might show up in pictures, even if its width is smaller than the limiting resolution. In fact, I suspect that this is why the advertising mentions the rover tracks: because compact items like the rovers themselves, or the remaining sections of the Lunar Module spacecrafts, will NOT show up in the pictures.
If the spacecraft has a safer orbit, more than 27 km above the lunar surface, or it has a camera lens less than 10 cm in diameter, then the limiting resolution decreases, and the smallest object which can be discerned is larger than 20 cm. I wouldn't get too excited, yet.
Let me give you some idea for the current state of the survey: we're taking a number of "test" strip scans of portions of the sky, and have perhaps 2 or 3 out of roughly 50 or 60 scans done so far. There's still an issue with calibrating the data, but we're working on it. The data is put on tape at the mountain, shipped by FedEx to Fermilab, and they reduce the heck out of it with pipelines specially designed for the survey. The data goes into a database at FNAL, and a copy is sent to JHU. I believe that Microsoft would work with a copy of the JHU database. Some of the JHU astronomers are building a friendly querying system so that people can ask questions like:
Give me info on all the stellar objects in this tiny area of the sky, with colors (g-r) 2.0, and with no close companions
The database will also allow people to download little "postage-stamp" sized pictures of the sky which are cut out around all detected objects.
You can see some examples of pictures (and detected objects) at:
http://a188-l009.rit.edu/richmond/sdss/showtell
As another poster stated, we look at each piece of the sky only once (well, small sections twice), so finding motions or variability from this data alone won't be easy.
The survey won't be finished, in my opinion, until sometime around 2003 or so (for the imaging half of the survey -- the spectroscopic section of the survey will take another few years after that). There is some period of a year or so -- it's rather vague at this point -- before data is released to the public. I'm not sure if it's a year or two after the photons are collected, or a year or two after they have been calibrated and placed into the database. It's possible that a small subset of the commissioning data might be made available sometime before then, but I wouldn't hold my breath.
I'd be happy to answer questions about the Sloan Digital Sky Survey, if someone wants to set up an
interview mechanism (hint, hint).
Astronomers have had a number of bad experiences based on "filaments" which appear to connect two objects -- which are actually at very different distances from us. There was a heavily publicized case a few years back, in which Halton Arp claimed that such a "filament" joined a quasar and a nearby galaxy, thereby "proving" that the quasar was much closer than its redshift would indicate. Sigh.
Anyway, back to TMR-1C. I remember talking to other astronomers at the summer meeting of the American Astronomical Society in 1997, in San Diego, and most of them agreed with me that this was just a chance superposition of a background star with the binary. We thought that the discoverers should have waited for some additional evidence:
My guess is that when the researchers (who work for NASA) started talking about their work with their colleagues, word reached the upper echelons of administrators, who probably ordered the press releases. I am speculating that it might have been hard for one of the astronomers on the team, if he or she had serious doubts about the claim;
it's not easy to tell your boss to shut up.
But a scientist is supposed to do this
Oh, and the poster who claims that astronomers have not detected ANY extra-solar planets is dead wrong. The radial velocity measurements he interprets as "changes in stellar shape" are really due to the motions of stars in orbits around their center of mass with bona-fide planets. Check out
http://cannon.sfsu.ed u/~gmarcy/planetsearch/planetsearch.html
and
http://www.obspm.fr/encycl/encycl.html
Well, most physicists haven't, actually;
and those who do, cease to be physicists and become philosophers
In this opinion of this physicist.
The images produced by Pogge and Martini show material in the inner spiral arms of the galaxies. It's a stretch to refer to this as material "being sucked into gigantic black holes." Note the scale of the images: the resolution is a few hundred light years. The accretion disk around the black hole is less than one light year in radius; it is completely unresolved in thes pictures.
... but it's not really relevant under the circumstances.
e ctures/blackholes/blackholes.html.
The material shown in these images MAY be spiralling gradually in towards the center of the galaxies, but it may also be in relatively stable orbits around the center. Suppose that a small component of the total velocity -- which is several hundred km/sec -- is radially inwards. It would take tens of millions of years for the material to reach the black hole.
Writing that these pictures show gas which is
"being sucked into a gigantic black hole" is about as accurate as writing "and here's a picture of Angeline Jolie growing old and wrinkled at the Academy Awards ceremony." Sure, technically, she is growing oldER and adding a micro-wrinkle or two as she sits in the audience
By a curious coincidence, I just wrote up a lecture on black holes at the centers of galaxies
for the introductor astro course I'm teaching. Check out
http://spiff.rit.edu/richmond/classes/phys240/l
In the worst cases, web-based courses are just books: "here, read these pages, then take a test." They may be worse than books, since the standards of publishing on the web are much lower than they are in print.
I do teach at a university, and I'm still struggling to figure out how to do a good job. One of the important things, I think, is to force students to do something in class -- not simply listen passively to what I say. Another important thing is for me to listen carefully to student questions, answer them -- and figure out how to present the material more clearly next time.
It may be possible for a professor to interact in similar ways with students over a bulletin-board; but not if the class contains 300 or 500 students. We can't put up web pages and then expect to serve triple the number of students we serve in a regular course.
Oh, and while web-based courses may make sense for some of the introductory courses, I agree with many posters that upper-level classes and graduate courses should be taught in person. In those classes, the primary mode of learning is by asking questions -- really detailed questions -- and having discussions. Face-to-face is much better for that sort of in-depth interaction than E-mail.
This is the most distant quasar, but not by any means the most distant object we've seen so far. Astronomers have found a galaxy which is probably at redshift 6.68 (although this is based on a single emission line), and other galaxies definitely at redshifts larger than this new quasar. There are also hints that some of the galaxies visible in the Hubble Deep Field are at much greater redshift, perhaps z > 10, but that needs to be confirmed with spectroscopic observations.
For more details on some of the other, distant celestial objects, see
Ned Wright's Cosmology Tutorial.
> long as you presume a materialist
> universe which is empirically knowable,
Well, yes. Science is a way to study a universe which is empirically knowable. It does not address ideas which are empirically unknowable
Science cannot address questions which do not, even in theory, imply observable results.
One of the strongest pieces of evidence in support of the Big Bang theory is the very good match between the abundance of light elements (hydrogen, deuterium, helium, lithium and beryllium) predicted by the BB, and actually observed by us. The BB theory places some limits on the amount of the "critical mass density" of the universe which can be made up of ordinary baryonic matter. That limit is much less than 1.0, closer to about 0.1. What that means is that _if_ the BB is correct, and _if_ the universe contains the critical mass density, _then_ most of that mass density must be non-baryonic matter.
Now, baryonic matter is good old protons, electrons, and neutrons: we and most of what we can see in the current universe (stars, planets, galaxies, etc.) are made of baryons. The galaxies just discovered by Chandra are undoubtedly made of stars (baryonic). Black holes are made of baryons, under most scenarios in the literature. MACHOs are just low-mass stars or high-mass planets, and they, too, are baryons.
So what the heck _isn't_ baryonic? Well, neutrinos aren't. There was a hope about twenty years ago that most of the mass of the universe might consist of neutrinos -- but recent experiments indicate weakly that the neutrino mass is too small to do the job. A universe of neutrinos would also lead to large-scale structure of galaxies and galaxy clusters very different than that which we observe. So, neutrinos are probably out. That leaves exotic stuff: wierd particles called "axions" or "WIMPs", or "strange matter"; all of these are theoretical, not experimentally confirmed (as far as I know)
In short, _if_ the density of the universe is even close to the critical density, it means that a) some exotic sort of matter dominates or b) the current theory of BB nucleosynthesis is wrong.
There have been many studies of the technical feasibility of this idea. A good place to start is
http://impact.arc.nasa.gov/
http://xxx.lanl.gov/abs/cond-mat/9911101
I don't understand the physics ... but I find the idea that local dark matter (yes, within our own galaxy) may be remnants of stars from a far-future universe very unlikely.
http://xxx.lanl.gov/ps/astro-ph/9911314
The URL above gives the abstract in ASCII, but the article itself is in Postscript. If you look at the main article, pay special attention to the figure which shows the REAL "signal" of reflected light from the planet, and the signal from a fake planet inserted into the data. The fake signal is clearly there, but I'm not confident that the claimed signal is.
How did they do it? The basic idea is: they took spectra of the star with very high resolving power, which spread out light into different wavelengths; or, equivalently, spread out light at different velocities. They knew when the planet ought to be coming towards us, and going away from us, in its orbit around tau Bootis, and with what speed. That meant that they could examine _very carefully_ spectra to find hints of spectral features which were shifted -- ever so slightly -- from their ordinary positions. They found weak evidence that some spectral features were shifted to the blue when the planet was coming towards us, and to the red when the planet was going away from us.
But, if you ask me, it's a two-sigma result. Needs more observation.
As for the claims of specific elements ... well, my guess is that the authors saw the weak, time-varying features in spectral lines produced by some element, and the press misinterpreted this to mean that that element was present in/on the planet. If the planet is simply reflecting light like a perfect mirror, it will produce these weak, time-varying features for ALL lines of ALL elements. Given the signal-to-noise ratio in the spectra I saw in their paper, I don't think that the authors are really advocating the presence of any specific elements in/on the planet.
And if they _were_ (which I emphasize is unlikely), it would be elemental oxygen, not atomic oxygen.
A good idea, certainly, but _really_ tough technically. I think that the press is running away with the story.
Michael
Some of us really do put a lot of work into our courses, and, while it is a nice ego-boo to hear that students elsewhere may use our materials to help themselves learn, it would annoy me greatly to learn that someone may be making money off notes that I made (or verbatim copies).
For an example of the material I put online for my students (before each lecture), see stupendous.rit.edu/classes/p hys212/phys212.html
I think that if someone approached me about using notes derived from my lectures, I'd be happy to work with him -- perhaps we could improve the quality if we worked together. Perhaps it boils down to an issue of courtesy.
> I know of a few large databases out there using
...
> PostgreSQL, but one I have access to is
> the TASS project (http://www.tass-survey.org),
> which currently has about 28Gb of
> astronomical data.
Actually, it's only about 5 GB on our main site. But the next generation of our cameras will easily generate many GB per year, so we'll reach that 28 GB limit pretty soon
Permit me to clear up a few questions and misconceptions. Interested readers can read the technical details for themselves in preprints on the LANL server:
:-), the work _was_ done in with optical telescopes; in fact, small ones, only a meter or so in diameter (rather than the 8-meter or 10-meter behemoths like Keck). The basic method is to take pictures of the same field of stars over and over and over, and look for variations in the brightness of any star with time. The technique works best if one can point at a large number of stars at once; the two best sources for crowded fields are the Bulge of the Milky Way and our nearest neighboring galaxy, the Large Magellanic Cloud. Both are best viewed from the southern hemisphere, and the data described in the recent press releases comes from Chile, South Africa, and New Zealand.
A good summary:
http://xxx.lanl.gov/abs/astro-ph/990819
The event MACHO-97-BLG-41
http://xxx.lanl.gov/abs/astro-ph/9908038
The event MACHO-98-BLG-35 (to which this Slashdot article refers indirectly)
http://xxx.lanl.gov/abs/astro-ph/9812252
Okay, now for my comments:
1. Contrary to "cemerson"'s post (which should have been moderated to "MisInformative"
2. The Bulge of the Milky Way is about 8,000 parsecs (about 25,000 light years) away from us. The LMC is about 50,000 parsecs away. These are the "background" stars. A star roughly halfway between us and the "background" will cause the greatest lensing effect as it passes between us and the "background" star.
3. When such an event occurs, the "background" star becomes brighter. Now, here's the key: if the "foreground" object is a lone star, then one can predict theoretically the shape of light curve: the background star brightens slowly at first, reaches a somewhat sharp peak in brightness, and then fades exactly as it brightened: the rising and falling phases look exactly the same, symmetric. And, in fact, most of the observed microlensing events (there have been over 100 followed in the past decade) follow this predicted, symmetric curve very closely.
4. But, if the "foreground" object is not a lone star, but a binary star, or a star with a planet, the light curve will depart from its theoretical, symmetric shape. If there's a planet around the foreground star, and it passes in front of the background star, it can cause a distinctive "spike" in the light curve: a short, sudden, very brief rise and fall. The event MACHO-98-BLG-35 shows a LITTLE bit of evidence for such a spike: see Figure 9 in the paper by Yock:
http://xxx.lanl.gov/abs/astro-ph/9908198
5. There are several efforts underway to detect planets around other stars by searching for the tiny 'eclipses' caused as a planet passes in front of its star in its orbit, but no solid detections yet. This is very difficult, because even a big planet like Jupiter causes only a (roughly) one-percent dip in the light of its star -- and many stars vary by more than one percent. Planets like the earth decrease the light by even smaller amounts, maybe one-hundredth of one percent. At that level, _most_ stars are variable. So, one must disentangle the intrinsic variation of the star from the brief dip caused by the planet -- and that means waiting months/years for the planet to come around in its orbit again. You can find information on one such search, Kepler, at this site:
http://web99.arc.nasa.gov/~mars/vulcan/
According to the articles referenced for this story, the system requires "a few kilowatts" to produce a magnetic field of the required strength. That's a lot of power. If one uses solar panels to provide, they must be big.
The amount of power in sunlight is roughly 1400 Watts per square meter, divided by the square of the distance from the sun (in AU). Thus, at Jupiter's distance, the power is down to about 50 Watts per square meter. If the panels are 100% efficient, they must be about 4.5 meters on a side to produce 1 kiloWatt. Real panels are more likely to be about 25% efficient; thus, one needs panels about 9 meters on a side to provide a single kiloWatt. If the "few" kilowatts mentioned is really 4 kiloWatts, the panels would need to be about 18 meters on a side. That's getting pretty darn big -- and, of course, more massive, decreasing the acceleration of the craft.
At the distance of Saturn, about 10 AU, the panels need to be twice as long on each side to provide the same amount of power.
Solar panels + magnetic fields might work in the inner solar system, but it won't provide much oomph in the outer solar system. A ship could accelerate to a high speed before reaching Jupiter, say, but it would be unable to use its magnetic system to slow down as it passed Neptune or Pluto.