The Voyagers were launched in 1977 (I remember the hoopla), so that makes their current age around 33 years. They are wonderful devices, but they can't warp time:-/
I teach astronomy courses to university students.
The best object by far to look at is the Moon, as
others have said.
it's big and bright, so you can't miss it
students can compare the view through the
telescope to the view with their naked eyes
students can compare the view through the
telescope to the view through binoculars
I've written a number of outdoor lab exercises
for introductory astro students which would
be perfectly appropriate for your students.
You can read
one on the Moon, in particular. Or you can
look at the lists of exercises in
this class
or
this other class for more ideas.
I'd recommend the "Limiting Magnitude" exercise
as one which you can do when the Moon isn't up.
It will help if you have several pairs of binoculars
in addition to the telescope.
Astronomers have measured transmission spectra of a planet circling the star HD 209458 and a planet circling the star HD 189733 (and probably others). The first successful measurements, which found sodium in the spectrum of HD 209458b, were published by Charbonneau et al. in 2002. See ApJ 568, 377 (2002).
Here's the way things work right now in my field, astrophysics: a scientist has an idea. He writes a grant proposal to the NSF and receives money. He uses the money to (hire a grad student, travel to telescope, build an instrument, etc.). He writes a paper on the results. In order to have the paper published in one of the big journals -- which is necessary to gain credit for tenure, promotion, reputation among peers -- he PAYS THE JOURNAL ~$110 PER PAGE. The journal makes the information available only to subscribers, who pay around $50-$100 for individuals or $1500-$3000 for institutions.
If you don't publish in the big peer-reviewed journals, you don't get recognition.
So, suppose that the government changes things: now the journals must make government-funded research available to the public without charge. The journals will lose money from their subscriber base; after all, who would bother to pay for the articles when they are free? Where do the journals make up the money? My guess: they increase the page charges. Now it might cost $200 or $250 per page to publish an article in a journal. Whence comes that extra money? From the government grant.
Result: the scientific papers are now available freely to the public, but scientists must ask for more money from the NSF in order to pay the higher page charges.
Disclaimer: I teach physics at an American university.
When you switch from a big lecture class to small, "workshop"
rooms which use computer-based sensors, you raise the cost of
the class by factors of many.
it now takes six professors to teach the class instead
of one
the computers and sensors are now used almost every day,
instead of once a week or so, which means that if
they break, they halt a class dead in the water.
That means you need more spares, and you need to
upgrade computers more frequently.
Smaller classes are good -- of course. I am much more
effective in smaller classes than in a big lecture.
But do students want to pay 4-7 times more for the
privilege of having small classes?
I'm teaching a "workshop" class in which I can't depend
on the computers at all. It doesn't bother me --
I have exercises which use metersticks and stopwatches.
But it does cause problems for professors who have
become used to using the nice computer-based sensors.
Our department/university just can't afford to replace
the computers right now.
I'm just trying to point out that changing the
way some courses are taught may lead to increased
costs. That's all.
... but "the age at which researchers have built
up large research teams to carry out projects for
which they (for the most part) acquire funding."
In other words, eighty years ago, a 30-year old
physicist and a technician or two could build
a device to study the absorption of X-rays by
various elements. The resulting publications
might win a Nobel Prize.
These days, a 30-year old physicist is working
as a post-doc in someone else's lab. He won't
by the leading author on the grant proposal to
design a new detector for CERN -- some 50-year
old with an established track record will be.
That 50-year old guy will probably still be
alive when the detector is finally built and
goes into action. He MIGHT still be alive when
the Nobel Prize committee gets around to
considering the results of the research.
If you think this is lamentable, ask yourself
about bridges. How many people design and
build large highway bridges BY THEMSELVES
these days? None. Do you long for the days,
millenia ago, when a single man, or perhaps
a man and his brothers, might construct a
bridge to span the local creek?
Practical architecture has become too big
for one man to do all by himself. The
items of interest just cannot be built by
a single person in a human lifetime.
The same is true in SOME spheres of the
sciences, but not all.
So the announcement about the discovery of a planet not capable of supporting life... is proof that Hubble's replacement will be able to find planets that will support life?
Kepler will be a small telescope (about 1 meter) in orbit, with the sole
mission of looking at a few fixed areas on the sky and
searching for planets by the transit method: take thousands
of pictures and look for stars which become dimmer for
a few hours due to a planet crossing their disks. This small
mission will launch in spring 2009 and is NOT a replacement
for HST.
The James Webb Space Telescope (JWST) is Hubble's replacement.
It will be much larger (with a mirror around 6.5 meters in diameter)
and carry out many, many different types of observations.
This mission will launch, uh, some time around 2013, if all
goes well.
The National Astronomical Observatory of Japan, in Mitaka, has a system called "4D2U" set up in a small building. It features dome about 20 meters wide with (if I recall correctly from my visit in the spring) 11 or 13 projectors. Most of the projectors face in one particular direction, the same direction which the seats face, so that the resolution and color balance are highest where people are looking. The team at Mitaka has written their own software to do real-time motion through space and time; it looks a lot like Celestia, and may be based in part on it.
You can see details and download code for your own use by going to
Read it yourself at mobileread.com.
I made the cardboard version myself -- works fine after a little fiddling,
as long as you don't need to copy hundreds of pages.
The distance to the event can be estimated using its redshift; the redshift of the supernova itself, and/or the redshift of its host galaxy. For objects which are more distant than the Virgo Cluster (roughly), the redshift and Hubble's Law provide a very good _relative_ distance estimate. Using the redshift of this event, and the redshifts of other supernovae, we can see very clearly that this event is more luminous than the usual supernova, even if we don't have the _absolute_ distance.
You _can_ argue that this event has the usual luminosity of a Type Ia supernova, and that its distance is much smaller than inferred from its redshift; but that turns out to make the galaxy and its surroundings appear very peculiar, in several different ways. It is simpler to conclude that the supernova is the only unusual phenomenon in this case.
The basic idea is that the astronomers used an infrared space telescope to take very deep images. They then tried to remove all the obvious sources of light, and examined the resulting "blank" images very carefully. They claim that there are very faint sources of infrared radiation which remain, and that the spatial correlation of these sources is roughly what one would expect if they were young galaxies in the very early universe.
There are limited opportunities for other astronomers to examine the same regions with other telescopes and at other wavelengths; that could provide evidence that might support the claim, or weaken it (if, for example, radio telescopes detect some of these sources and show that they are ordinary galaxies in the relatively nearby universe, that would weaken the claim in the press release).
We can also just wait a decade or so for JWST, a more powerful infrared space telescope, to observe the same field.
I'm not sure of your point here. My understanding is that "for profit" journals don't pay for peer review or referee. They charge a page fee. However, they keep the copyright.
Correct. The parent poster claimed that "the public" should have free access to all scientific research, the copyrights to which are largely owned by a few journals. I was trying to say that if "the public" wants to own the copyright to this material, then "the public" ought to pay for all the expenses involved in refereeing, editing, typesetting, publishing, and distributing the journals.
If it weren't for the huge federal investment in research, you probably wouldn't be getting your $110 per page fee.
Strike 1. You don't understand how the refereed astronomical journals work. I pay THEM $110 per page so that they will publish my paper; they do not pay me.
Your RIT paycheck may not have a federal imprimatur on it but without federal funding, RIT wouldn't be able to pay you squat.
Strike 2. RIT has a long history of teaching and has only recently -- in the past 5 or 7 years -- started heading in the direction of research. The school has a very detailed breakdown of income from tuition and expenses on items such as faculty salaries. Most of the money spent on my salary comes from tuition.
Would you care to try for a third statement illustrating your ignorance of this topic?
All scientific works ever written. This is work done by scientists for the betterment of mankind and to have it locked away from the public behind electronic library access fees is absurd. The public has a right to academic works, not just academics.
When "the public" pays me to referee papers by other astronomers, and "the public" pays the page charges for the papers I write ($110 per page, by the way), and "the public" pays the editors and typesetters of the journals, then "the public" might assert a right to those papers.
Just to forestall the inevitable responses, no, the federal government is not paying my salary, and no, it hasn't paid for the page charges of my most recent publications. The NSF and NASA do support a great deal of research in astronomy, of course, and grants from those agencies do pay for good fraction of the publications in this area.
On second thought, almost all recent work in astronomy and physics is freely available to public at the LANL preprint archive site, so maybe this whole discussion is moot....
These Type 1a Supernova are used as one step on the distance ladder, correct?
Type Ia supernovae are indeed one of the last rungs on the distance ladder; they can be used to estimate distances to very distant galaxies.
So if we no longer believe they all have the same brightness, that means the distance we have on record for many objects is now wrong?
No, that's an overstatement. Type Ia supernovae are one of several different indicators used to estimate distances to very distant galaxies -- not the only one. _If_ we suddenly thought that the luminosity of _all_ Type Ia supernovae was significantly higher, _then_ we would have to re-examine the agreement between distances derived from Type Ia supernovae and other methods. The net effect might be a slight shift in the value of the Hubble constant, which is used to estimate distances to really, really distant objects.
However, if only 1 in 100 or fewer Type Ia supernovae are more luminous than expected, it won't make any significant difference in studies which use lots of supernovae.
The Nature paper in which this work is published has a figure showing all the measurements of this supernova's brightness; you can see it on Nature's web site at
There are four measurements near time of maximum light, in the red (r) and near-infrared (i) passbands. There are many more measurements starting about 15 days after maximum light in the rest frame, including some in a blue-green (g) passband. Here's what the researchers did to find the maximum brightness of this supernova, so that they could compare it to others:
a) fit models based on the light curves of other supernovae to the r and i measurements,
and the late-time g measurements
b) choose a different passband -- the greenish V passband of the Johnson-Cousins system,
which is closest to their own g passband (the one with no data at max light)
c) use their models to estimate what the light curve in the V filter would have been
This can be a tricky business. Their major conclusion, that this supernova was more luminous than typical ones, is probably correct, but their claim that they can measure the peak magnitude in the V-band to an uncertainty of 6 percent seems a bit bold.
As the press release states, if atypical SNe are very rare, then this probably doesn't have any major impact on the use of Type Ia SNe in cosmology.
Further aggravating is that every time a book comes out with a new edition (yearly in many cases) the instructor puts the new edition in as a required text. The "old" text are removed from bookstore circulation. Does a physics book for a second or third semester class change that much in the course of a year?
Publishers are constantly changing the web sites which are associated with their introductory physics textbooks. If a professor chooses to use the material on the web site -- often homework problems -- then he is almost forced to adopt the new text.
I am a university professor. I don't require my students to purchase textbooks for the introductory physics courses I teach. I provide my complete lecture notes online, and permit students to use older textbooks if they wish; after all, the material we're covering hasn't changed in the past few hundred years, so _any_ textbook they can find will serve as a useful reference.
I write my own homework problems so that my students won't have to purchase a textbook simply for that purpose.
The bookstore hasn't broken my hands, nor has the university reprimanded me. We've just started a new fall quarter this week, and I'm still teaching.
So, in brief, your statement is not correct.
Re:The new result, in a nutshell thanks
on
Dark Matter Exists
·
· Score: 2, Informative
Can you comment on whether the data support a candidate such as wimps, machos, etc ? (or am I betraying my ignorance with these acronyms
This data provides no evidence for the makeup of the dark matter.
Other observations suggest that the dark matter is not Massive Compact (Halo) Objects, or MACHOs.
The idea that dark matter might be composed of some sort of Weaking Interacting Massive Particle, or WIMP,
is a bit out of fashion these days, but still a possibility, as far as I know.
The new result, in a nutshell
on
Dark Matter Exists
·
· Score: 5, Informative
Astronomers observed a distant cluster of galaxies in optical light, with ordinary telescopes, and in X-ray light, with a telescope in space. This is an unusual cluster of galaxies, since there is clear evidence that one small group of galaxies are "interlopers:" members of a smaller cluster which fell into a larger one some time ago. Members of this interloping group are all bunched together at one side of the main cluster.
The visible light image shows the galaxies within the cluster. It also shows, much fainter and much smaller, a very large number of BACKGROUND galaxies -- these are objects way, way farther away than the big cluster. As the light from these background galaxies passes through the big cluster, it is bent very slightly by the gravitational field of the cluster. This gravitational lensing distorts the shapes of the faint, little background galaxies just a bit, but with care, we can measure the effect. We learn from the lensing where the matter is in the cluster: that is, we can figure out where the stuff which produces gravitational effects is distributed. That's part one: a map of the matter within the cluster, based on gravitional lensing.
The X-ray image shows emission from hot gas within the cluster. We have known for several decades now that large clusters of galaxies are immersed in giant clouds of very hot gas, at temperatures of millions of degrees. The gas emits copious amounts of X-rays. In most clusters, the amount of this hot gas -- its total mass -- is much larger than the amount of mass we can see in stars. That is, counting the stars in the galaxies suggests a total amount of mass-in-stars M, but computing the amount of hot gas necessary to emit all the observed X-rays yields a mass-in-hot-gas of around 10*M, ten times as much.
On the other hand, the amount of mass derived from the gravitational lensing of background galaxies is about 10 times larger still, or about 100*M. The stuff which produces the gravitational lensing does not emit visible light, nor X-ray light, nor, as far as we can tell, any electromagnetic radiation. Therefore, we call it "dark matter". It produces a gravitational force, but that's about all we know about it. (There are additional reasons for believing that this mysterious stuff is not made up of electrons, protons and neutrons, but that's another story).
This new result is interesting for this reason: the X-rays appear on one region of the cluster of galaxies, telling us that the bulk of the ordinary matter is RIGHT HERE. The map of total mass we can make from gravitational lensing appears in a different region of the cluster, telling us that the bulk of the dark matter is OVER THERE. It is very clear that the dark matter and ordinary matter are distributed in different places. This isn't too surprising, perhaps, if one small group of galaxies rammed into a big cluster -- the gas ram pressure might push on the ordinary hot gas in a different way than on the dark matter (which wouldn't feel any ram pressure at all, actually).
As Martin Hardcastle pointed out to me in a Google newsgroup a few days ago (thanks, Martin!), this is certainly not the first evidence for dark matter -- we have a number of examples in which gravitational forces are larger than the amount of visible matter would suggest -- but it is the first good case in which the distribution of the dark and ordinary matters are so clearly displaced.
Astronomers were debating Pluto's status back in the early 90's.
No, the overwhelming majority of astronomers were not.
We don't care. Really. The issue "what is a planet?"
has for most of us the same urgency and relevance that
"what is a continent?" has for geologists.
No, the scientific community is in a constant state of polarization, between the old guard, wary of new things and ideas, and the new breed, mainly young researchers thinking outside the box.
There certainly _are_ topics on which there is vigorous
debate in the astronomical community -- for example,
the nature of gamma-ray bursts, or the accuracy and precision
of the cosmological distance scale, or the physics of
supernova explosions. But this isn't one of them.
The issue exists solely because a very few people who
(for some reason) are seeking publicity go to the
media periodically with a "new twist" on this question.
Adding the question "is Pluto a planet" to the list
of serious astronomical questions of the day does a
disservice to those other questions.
Why not fix the "official" number of planets at nine, including the largest, nearest, and most well-known of the Kuyper Belt Objects, and leave it at that?
Because there's nothing the scientific community loves more than controversy
No, actually, I (and most of the astronomers in my
peer group) do NOT enjoy the ongoing saga. We would
like the whole matter to go away.
The real answer is
Because there's nothing the media
loves more than controversy
Editors know that "telling people that stuff they learned in
elementary school is wrong" can pull emotional
strings and get a rise out of some people... and
that leads to profit.
This whole article is misleading. The new research has very little
to do with our knowledge of the size and age of the universe.
(And, yes, I am an astronomer).
Stanek and company have used measurements of one eclipsing binary system to determine the distance to M33. This is a good way to measure distances, as it avoids the perils of even a short "ladder" of methods. They find a distance modulus of 24.92 +/- 0.12 mag to the binary. You can read their paper on astro-ph at
Go to Table 7 of their paper, in which they compare their distance to previous measurements. There are 12 previous values, measured by several techniques (only 2 of the papers use Cepheids). The range of those previous values is 24.32 +/- 0.45 to 24.86 +0.07/-0.11. Their new distance is inconsistent, at the 1-sigma level, with 6 of the 12 others; thus, it is consistent with 6 of the 12 others.
Yes, it's true that the HST Key Project distance to M33, computed using Cepheids, is smaller than the new distance by an amount well outside the quoted uncertainties. But that's not a big deal, by itself. M33 is only one of a number of galaxies which serves to calibrate secondary distance indicators, which may in turn be used to find the Hubble constant. A small change in the distance to M33, even if true, would not make any major change to H-nought.
Recall that M33 is close enough to us that its radial velocity is NOT caused by the expansion of the universe, but instead by the gravitational forces of the galaxies in the Local Group. The press release's statement
The team's results suggested that the stars were about 3 million light-years from Earth--or about half-a-million light-years farther than would be expected using the commonly accepted Hubble constant value.
is absolute nonsense. One cannot USE the Hubble constant and radial velocity of M33 to calculate its distance. The radial velocity of M33 is -179 km/sec, so "using" the Hubble costant to determine its distance would yield a negative distance. Phht.
This is a very nice, and very very worthwhile scientific project -- I have followed the DIRECT team's efforts for years, and encourage them to keep going! -- but the press release tries too hard to make it into some sort of breakthrough with profound immediate results.
[a spectrum] obtained with Gemini-South telescope (+ GMOS) on
Feb. 21.024 UT, shows that underlying a power-law continuum are
features consistent with a broad-lined type-Ib/c supernova
(designated 2006aj) near maximum light, confirming the findings of
Masetti et al. (GCN 4803).
It appears to be a Type Ib/c supernova --
meaning a massive star, which has lost most
of its hydrogen envelope, running out of
fuel in its core and exploding -- in a
relatively nearby galaxy. By "nearby",
I mean "at a redshift of z=0.033",
which is still much farther away than
the Virgo or Coma clusters of galaxies.
It is currently around magnitude 18, and may
brighten by a magnitude or so, but will still
require a pretty big telescope and sensitive
camera to detect.
Re:For the rocket scientists out there....
on
Pluto Probe Delayed
·
· Score: 3, Informative
Quoth the parent:
> is the energy requirement to enter orbit rather than just flyby that large?
In order to reach Pluto in a reasonable
number of years, the probe must move very fast. Let's see...
very roughly, it goes 40 AU in nine years. That's about
4.5 AU per year, or a cruising speed of about 21,000 m/s.
If you wanted to put it in orbit around Pluto, you'd have
to decrease its speed to the orbital speed of Pluto, which
would be a few hundred m/s. That means you'd have to
decrease the speed by roughly 20,000 m/s... or, to a good
approximation, you'd have to remove all the velocity you
had added to the probe in the first place. The mass of
the probe is roughly 1,000 kg, so its momentum must
be decreased from about (20,000 m/s) * (1,000 kg) = about
20 million kg*m/s to zero.
To reduce the momentum, you fire an engine pointing
backwards: the engine throws exhaust products forward
at some speed, and the momentum they carry away reduces
the remaining momentum of the probe. Chemical rockets
have typical exhaust speeds of around 2,000 m/s, so
to remove 20 million kg*m/s, you'd have to throw
around 10,000 kg of mass out of your engine.
(Yes, yes, it's more complicated than this, but for
the purpose of illustration, it's close enough).
But, wait a minute: the probe's mass is only
1,000 kg. It can't carry 10,000 kg of fuel and
oxidizer, too. So it cannot slow itself down
enough to enter orbit around Pluto. If you wanted
to design a probe which could enter orbit, you'd
have to make it carry huge amounts of fuel
for this burn when it reaches Pluto... but then
you'd need an enormous rocket to accelerate the
fuel and probe to 20,000 m/s in the first place.
Slashdot Mirror
The Voyagers were launched in 1977 (I remember the hoopla), so that makes their current age around 33 years. They are wonderful devices, but they can't warp time :-/
I teach astronomy courses to university students. The best object by far to look at is the Moon, as others have said.
I've written a number of outdoor lab exercises for introductory astro students which would be perfectly appropriate for your students. You can read one on the Moon, in particular. Or you can look at the lists of exercises in this class or this other class for more ideas.
I'd recommend the "Limiting Magnitude" exercise as one which you can do when the Moon isn't up. It will help if you have several pairs of binoculars in addition to the telescope.
Good luck!
Astronomers have measured transmission spectra of a planet circling the star HD 209458 and a planet circling the star HD 189733 (and probably others). The first successful measurements, which found sodium in the spectrum of HD 209458b, were published by Charbonneau et al. in 2002. See ApJ 568, 377 (2002).
Here's the way things work right now in my field, astrophysics: a scientist has an idea. He writes a grant proposal to the NSF and receives money. He uses the money to (hire a grad student, travel to telescope, build an instrument, etc.). He writes a paper on the results. In order to have the paper published in one of the big journals -- which is necessary to gain credit for tenure, promotion, reputation among peers -- he PAYS THE JOURNAL ~$110 PER PAGE. The journal makes the information available only to subscribers, who pay around $50-$100 for individuals or $1500-$3000 for institutions.
If you don't publish in the big peer-reviewed journals, you don't get recognition.
So, suppose that the government changes things: now the journals must make government-funded research available to the public without charge. The journals will lose money from their subscriber base; after all, who would bother to pay for the articles when they are free? Where do the journals make up the money? My guess: they increase the page charges. Now it might cost $200 or $250 per page to publish an article in a journal. Whence comes that extra money? From the government grant.
Result: the scientific papers are now available freely to the public, but scientists must ask for more money from the NSF in order to pay the higher page charges.
Disclaimer: I teach physics at an American university.
When you switch from a big lecture class to small, "workshop" rooms which use computer-based sensors, you raise the cost of the class by factors of many.
Smaller classes are good -- of course. I am much more effective in smaller classes than in a big lecture. But do students want to pay 4-7 times more for the privilege of having small classes?
I'm teaching a "workshop" class in which I can't depend on the computers at all. It doesn't bother me -- I have exercises which use metersticks and stopwatches. But it does cause problems for professors who have become used to using the nice computer-based sensors. Our department/university just can't afford to replace the computers right now.
I'm just trying to point out that changing the way some courses are taught may lead to increased costs. That's all.
In other words, eighty years ago, a 30-year old physicist and a technician or two could build a device to study the absorption of X-rays by various elements. The resulting publications might win a Nobel Prize.
These days, a 30-year old physicist is working as a post-doc in someone else's lab. He won't by the leading author on the grant proposal to design a new detector for CERN -- some 50-year old with an established track record will be. That 50-year old guy will probably still be alive when the detector is finally built and goes into action. He MIGHT still be alive when the Nobel Prize committee gets around to considering the results of the research.
If you think this is lamentable, ask yourself about bridges. How many people design and build large highway bridges BY THEMSELVES these days? None. Do you long for the days, millenia ago, when a single man, or perhaps a man and his brothers, might construct a bridge to span the local creek?
Practical architecture has become too big for one man to do all by himself. The items of interest just cannot be built by a single person in a human lifetime. The same is true in SOME spheres of the sciences, but not all.
Kepler will be a small telescope (about 1 meter) in orbit, with the sole mission of looking at a few fixed areas on the sky and searching for planets by the transit method: take thousands of pictures and look for stars which become dimmer for a few hours due to a planet crossing their disks. This small mission will launch in spring 2009 and is NOT a replacement for HST.
The James Webb Space Telescope (JWST) is Hubble's replacement. It will be much larger (with a mirror around 6.5 meters in diameter) and carry out many, many different types of observations. This mission will launch, uh, some time around 2013, if all goes well.
The National Astronomical Observatory of Japan, in Mitaka, has a system called "4D2U" set up in a small building. It features dome about 20 meters wide with (if I recall correctly from my visit in the spring) 11 or 13 projectors. Most of the projectors face in one particular direction, the same direction which the seats face, so that the resolution and color balance are highest where people are looking. The team at Mitaka has written their own software to do real-time motion through space and time; it looks a lot like Celestia, and may be based in part on it.
You can see details and download code for your own use by going to
http://4d2u.nao.ac.jp/index_E.html
Read it yourself at mobileread.com. I made the cardboard version myself -- works fine after a little fiddling, as long as you don't need to copy hundreds of pages.
The distance to the event can be estimated using its redshift; the redshift of the supernova itself, and/or the redshift of its host galaxy. For objects which are more distant than the Virgo Cluster (roughly), the redshift and Hubble's Law provide a very good _relative_ distance estimate. Using the redshift of this event, and the redshifts of other supernovae, we can see very clearly that this event is more luminous than the usual supernova, even if we don't have the _absolute_ distance.
You _can_ argue that this event has the usual luminosity of a Type Ia supernova, and that its distance is much smaller than inferred from its redshift; but that turns out to make the galaxy and its surroundings appear very peculiar, in several different ways. It is simpler to conclude that the supernova is the only unusual phenomenon in this case.
You can read the technical papers on which this press release is based:
http://arxiv.org/abs/astro-ph/0612445
http://arxiv.org/abs/astro-ph/0612447
The basic idea is that the astronomers used an infrared
space telescope to take very deep images. They then tried
to remove all the obvious sources of light, and examined
the resulting "blank" images very carefully. They claim that
there are very faint sources of infrared radiation which
remain, and that the spatial correlation of these sources
is roughly what one would expect if they were young galaxies
in the very early universe.
There are limited opportunities for other astronomers
to examine the same regions with other telescopes and
at other wavelengths; that could provide evidence that
might support the claim, or weaken it (if, for example,
radio telescopes detect some of these sources and
show that they are ordinary galaxies in the relatively
nearby universe, that would weaken the claim in
the press release).
We can also just wait a decade or so for JWST, a more
powerful infrared space telescope, to observe the same
field.
Correct. The parent poster claimed that "the public" should have free access to all scientific research, the copyrights to which are largely owned by a few journals. I was trying to say that if "the public" wants to own the copyright to this material, then "the public" ought to pay for all the expenses involved in refereeing, editing, typesetting, publishing, and distributing the journals.
Strike 1. You don't understand how the refereed astronomical journals work. I pay THEM $110 per page so that they will publish my paper; they do not pay me.
Strike 2. RIT has a long history of teaching and has only recently -- in the past 5 or 7 years -- started heading in the direction of research. The school has a very detailed breakdown of income from tuition and expenses on items such as faculty salaries. Most of the money spent on my salary comes from tuition.
Would you care to try for a third statement illustrating your ignorance of this topic?
When "the public" pays me to referee papers by other astronomers, and "the public" pays the page charges for the papers I write ($110 per page, by the way), and "the public" pays the editors and typesetters of the journals, then "the public" might assert a right to those papers.
Just to forestall the inevitable responses, no, the federal government is not paying my salary, and no, it hasn't paid for the page charges of my most recent publications. The NSF and NASA do support a great deal of research in astronomy, of course, and grants from those agencies do pay for good fraction of the publications in this area.
On second thought, almost all recent work in astronomy and physics is freely available to public at the LANL preprint archive site, so maybe this whole discussion is moot....
Type Ia supernovae are indeed one of the last rungs on the distance ladder; they can be used to estimate distances to very distant galaxies.
No, that's an overstatement. Type Ia supernovae are one of several different indicators used to estimate distances to very distant galaxies -- not the only one. _If_ we suddenly thought that the luminosity of _all_ Type Ia supernovae was significantly higher, _then_ we would have to re-examine the agreement between distances derived from Type Ia supernovae and other methods. The net effect might be a slight shift in the value of the Hubble constant, which is used to estimate distances to really, really distant objects.
However, if only 1 in 100 or fewer Type Ia supernovae are more luminous than expected, it won't make any significant difference in studies which use lots of supernovae.
I study supernovae for a living.
i g_tab/nature05103_F1.html
The Nature paper in which this work is published has a figure showing all the measurements of this supernova's brightness; you can see it on Nature's web site at
http://www.nature.com/nature/journal/v443/n7109/f
There are four measurements near time of maximum light, in the red (r) and near-infrared (i) passbands. There are many more measurements starting about 15 days after maximum light in the rest frame, including some in a blue-green (g) passband. Here's what the researchers did to find the maximum brightness of this supernova, so that they could compare it to others:
a) fit models based on the light curves of other supernovae to the r and i measurements,
and the late-time g measurements
b) choose a different passband -- the greenish V passband of the Johnson-Cousins system,
which is closest to their own g passband (the one with no data at max light)
c) use their models to estimate what the light curve in the V filter would have been
This can be a tricky business. Their major conclusion, that this supernova was more luminous than typical ones, is probably correct, but their claim that they can measure the peak magnitude in the V-band to an uncertainty of 6 percent seems a bit bold.
As the press release states, if atypical SNe are very rare, then this probably doesn't have any major impact on the use of Type Ia SNe in cosmology.
Publishers are constantly changing the web sites which are associated with their introductory physics textbooks. If a professor chooses to use the material on the web site -- often homework problems -- then he is almost forced to adopt the new text.
I am a university professor. I don't require my students to purchase textbooks for the introductory physics courses I teach. I provide my complete lecture notes online, and permit students to use older textbooks if they wish; after all, the material we're covering hasn't changed in the past few hundred years, so _any_ textbook they can find will serve as a useful reference.
I write my own homework problems so that my students won't have to purchase a textbook simply for that purpose.
The bookstore hasn't broken my hands, nor has the university reprimanded me. We've just started a new fall quarter this week, and I'm still teaching.
So, in brief, your statement is not correct.
This data provides no evidence for the makeup of the dark matter.
Other observations suggest that the dark matter is not Massive Compact (Halo) Objects, or MACHOs. The idea that dark matter might be composed of some sort of Weaking Interacting Massive Particle, or WIMP, is a bit out of fashion these days, but still a possibility, as far as I know.
Astronomers observed a distant cluster of galaxies in optical light, with ordinary telescopes, and in X-ray light, with a telescope in space. This is an unusual cluster of galaxies, since there is clear evidence that one small group of galaxies are "interlopers:" members of a smaller cluster which fell into a larger one some time ago. Members of this interloping group are all bunched together at one side of the main cluster.
The visible light image shows the galaxies within the cluster. It also shows, much fainter and much smaller, a very large number of BACKGROUND galaxies -- these are objects way, way farther away than the big cluster. As the light from these background galaxies passes through the big cluster, it is bent very slightly by the gravitational field of the cluster. This gravitational lensing distorts the shapes of the faint, little background galaxies just a bit, but with care, we can measure the effect. We learn from the lensing where the matter is in the cluster: that is, we can figure out where the stuff which produces gravitational effects is distributed. That's part one: a map of the matter within the cluster, based on gravitional lensing.
The X-ray image shows emission from hot gas within the cluster. We have known for several decades now that large clusters of galaxies are immersed in giant clouds of very hot gas, at temperatures of millions of degrees. The gas emits copious amounts of X-rays. In most clusters, the amount of this hot gas -- its total mass -- is much larger than the amount of mass we can see in stars. That is, counting the stars in the galaxies suggests a total amount of mass-in-stars M, but computing the amount of hot gas necessary to emit all the observed X-rays yields a mass-in-hot-gas of around 10*M, ten times as much.
On the other hand, the amount of mass derived from the gravitational lensing of background galaxies is about 10 times larger still, or about 100*M. The stuff which produces the gravitational lensing does not emit visible light, nor X-ray light, nor, as far as we can tell, any electromagnetic radiation. Therefore, we call it "dark matter". It produces a gravitational force, but that's about all we know about it. (There are additional reasons for believing that this mysterious stuff is not made up of electrons, protons and neutrons, but that's another story).
This new result is interesting for this reason: the X-rays appear on one region of the cluster of galaxies, telling us that the bulk of the ordinary matter is RIGHT HERE. The map of total mass we can make from gravitational lensing appears in a different region of the cluster, telling us that the bulk of the dark matter is OVER THERE. It is very clear that the dark matter and ordinary matter are distributed in different places. This isn't too surprising, perhaps, if one small group of galaxies rammed into a big cluster -- the gas ram pressure might push on the ordinary hot gas in a different way than on the dark matter (which wouldn't feel any ram pressure at all, actually).
As Martin Hardcastle pointed out to me in a Google newsgroup a few days ago (thanks, Martin!), this is certainly not the first evidence for dark matter -- we have a number of examples in which gravitational forces are larger than the amount of visible matter would suggest -- but it is the first good case in which the distribution of the dark and ordinary matters are so clearly displaced.
No, the overwhelming majority of astronomers were not. We don't care. Really. The issue "what is a planet?" has for most of us the same urgency and relevance that "what is a continent?" has for geologists.
There certainly _are_ topics on which there is vigorous debate in the astronomical community -- for example, the nature of gamma-ray bursts, or the accuracy and precision of the cosmological distance scale, or the physics of supernova explosions. But this isn't one of them. The issue exists solely because a very few people who (for some reason) are seeking publicity go to the media periodically with a "new twist" on this question.
Adding the question "is Pluto a planet" to the list of serious astronomical questions of the day does a disservice to those other questions.
No, actually, I (and most of the astronomers in my peer group) do NOT enjoy the ongoing saga. We would like the whole matter to go away.
The real answer is
Editors know that "telling people that stuff they learned in elementary school is wrong" can pull emotional strings and get a rise out of some people ... and
that leads to profit.
Sigh.
This whole article is misleading. The new research has very little to do with our knowledge of the size and age of the universe.
(And, yes, I am an astronomer).
Stanek and company have used measurements of one eclipsing binary system to determine the distance to M33. This is a good way to measure distances, as it avoids the perils of even a short "ladder" of methods. They find a distance modulus of 24.92 +/- 0.12 mag to the binary. You can read their paper on astro-ph at
http://xxx.lanl.gov/abs/astro-ph?papernum=0606279
Go to Table 7 of their paper, in which they compare their distance to previous measurements. There are 12 previous values, measured by several techniques (only 2 of the papers use Cepheids). The range of those previous values is 24.32 +/- 0.45 to 24.86 +0.07/-0.11. Their new distance is inconsistent, at the 1-sigma level, with 6 of the 12 others; thus, it is consistent with 6 of the 12 others.
Yes, it's true that the HST Key Project distance to M33, computed using Cepheids, is smaller than the new distance by an amount well outside the quoted uncertainties. But that's not a big deal, by itself. M33 is only one of a number of galaxies which serves to calibrate secondary distance indicators, which may in turn be used to find the Hubble constant. A small change in the distance to M33, even if true, would not make any major change to H-nought.
Recall that M33 is close enough to us that its radial velocity is NOT caused by the expansion of the universe, but instead by the gravitational forces of the galaxies in the Local Group. The press release's statement
is absolute nonsense. One cannot USE the Hubble constant and radial velocity of M33 to calculate its distance. The radial velocity of M33 is -179 km/sec, so "using" the Hubble costant to determine its distance would yield a negative distance. Phht.
This is a very nice, and very very worthwhile scientific project -- I have followed the DIRECT team's efforts for years, and encourage them to keep going! -- but the press release tries too hard to make it into some sort of breakthrough with profound immediate results.
Sigh.
IAU Circular 8674, which states in part
There is a good deal of news in the GRBLog:
http://grad40.as.utexas.edu/grblog.php
Just search for "GRB 060218".
It appears to be a Type Ib/c supernova -- meaning a massive star, which has lost most of its hydrogen envelope, running out of fuel in its core and exploding -- in a relatively nearby galaxy. By "nearby", I mean "at a redshift of z=0.033", which is still much farther away than the Virgo or Coma clusters of galaxies.
It is currently around magnitude 18, and may brighten by a magnitude or so, but will still require a pretty big telescope and sensitive camera to detect.
Quoth the parent:
In brief, yes.
(Warning: back-of-the-envelope calculations follow)
In order to reach Pluto in a reasonable number of years, the probe must move very fast. Let's see ...
very roughly, it goes 40 AU in nine years. That's about
4.5 AU per year, or a cruising speed of about 21,000 m/s.
If you wanted to put it in orbit around Pluto, you'd have to decrease its speed to the orbital speed of Pluto, which would be a few hundred m/s. That means you'd have to decrease the speed by roughly 20,000 m/s ... or, to a good
approximation, you'd have to remove all the velocity you
had added to the probe in the first place. The mass of
the probe is roughly 1,000 kg, so its momentum must
be decreased from about (20,000 m/s) * (1,000 kg) = about
20 million kg*m/s to zero.
To reduce the momentum, you fire an engine pointing backwards: the engine throws exhaust products forward at some speed, and the momentum they carry away reduces the remaining momentum of the probe. Chemical rockets have typical exhaust speeds of around 2,000 m/s, so to remove 20 million kg*m/s, you'd have to throw around 10,000 kg of mass out of your engine. (Yes, yes, it's more complicated than this, but for the purpose of illustration, it's close enough).
But, wait a minute: the probe's mass is only 1,000 kg. It can't carry 10,000 kg of fuel and oxidizer, too. So it cannot slow itself down enough to enter orbit around Pluto. If you wanted to design a probe which could enter orbit, you'd have to make it carry huge amounts of fuel for this burn when it reaches Pluto ... but then
you'd need an enormous rocket to accelerate the
fuel and probe to 20,000 m/s in the first place.
It just isn't practical. Sorry.