Uhm, during a solar eclipse, the moon only blocks the sun in a spot a few tens to a few hundreds of km in size. So he's right, you're wrong...
And for your satellite example, if your satellite is a couple of meters in diameter, all you need to do to "unblock" the star is to move a few meters to the side.
You're right, bit of a mess-up there. Still, 20cm thick over a diameter of 8.4 meters is still pretty thin, although it's indeed honeycombed, so the actual thickness is higher, but only partially filled.
A telescope mirror needs a number of special properties, from rigidity and weight, but also thermal stability and the ability to polish it efficiently.
For nearly 50 years the largest mirror was the 5 meter Hale telescope, but in the late '80s materials science and casting techniques had evolved to the point where we could reliably cast larger, lighter telescope mirrors, and computing power to the point where active suspension of thinner mirrors is possible.
However, this doesn't mean we can create weightless mirrors, and an 8.4m mirror with a short focal length and two different surfaces still requires quite a bit of internal strength. Glass still has a higher density than water.
An 8.4m mirror has a surface area of 220 square meters, even assuming the density of water (1000 kg/m3) 25 tons corresponds to a thickness of only about 12 cm, or less than 5 inches, which is very very thin, and as I said, glass has a density higher than water, so the actual thickness would be substantially less.
Yes, it's the same.
A shorter focal ratio ("fast") allows for a larger field of view with the same size CCD-chip. The "side-effect" of this is that a larger bit of sky falls onto the individual pixels, which means you sacrifice resolving power for sensitivity.
And any estimate that can range between 380 and 5 is not an estimate. It more closely resembles a wild guess than an educated one.
If it stays around 5 Earth masses for a couple decades, I may start to respect it.
Actually, the estimate doesn't range between 380 and 5, 380 earth masses was an early estimate of the upper limit, more recent study points to 5 earth masses as being the likely upper limit.
At any rate, since a solar mass is about 334000 earth masses, the range from 380-->5 isn't quite so huge as to include another thousandfold increase as a likely possibility. And like I said, the trend has been down, not up...
Oh, and I'm sure the scientific community cares a whole lot about your "respect"...
Only, the odds of this happening are quite spectacularly small.
Small is not nonexistent. I wasn't attempting to mislead - I was just wrong. Being wrong in this one case does take away from the message that I'm trying to keep in front of people: Astronomers and earth scientists believe that global cataclysm has occurred on Earth in the past, and will occur in the future. Although that outcome is unlikely today and tomorrow, even this century, in the fullness of time it's not just likely - it's certain. If we don't get humanity established on some other place in the mean time, it's game over for our species. There isn't any credible disagreement on this issue.
Basically, estimates of the Oort Cloud mass can be made based on the size & distribution of long-period and non-periodic comets. These estimates have actually decreased in recent years, and range from a total mass of 380x Earth to (more recently) no more than 5x Earh.
You could call that an "educated guess" if you want, but it's one based on more science than your Solar Mass estimate. (Besides, isn't "estimate" just an other word for "educated guess", and infinitely preferrable above "number pulled out of my ass to scare the folks at Slashdot with" ? )
It's a bit like we can be pretty much 100% certain that there are no 1000km sized asteroids waiting to be discovered in the Asteroid belt between Mars & Jupiter. If such an object did exist, we would have seen it by now because we've checked the sky with sufficient detail that any object that size would already have been discovered.
It is true that theoretically a huge, massive, Nemesis-like object could exist and be undetected, but that object would then not be a red or brown dwarf, or even a black hole, because by now we know enough about the physical properties of such objects that we know our current surveys would have spotted it by now.
Of course, something more exotic might be lurking out there, but that is pure conjecture, and besides, the main reason "Nemesis" was invented (to explain periodic extinctions) has vanished because we now know those extinctions are far less "periodic" than we originally assumed.
Indeed, it is still Popular, but not among serious scientists.
Until about a decade ago, we could say "we don't know", with the IR surveys made since IRAS, we can actually put upper limits on objects out there which are below the threshold where such an object could have a "Nemesis" like effect.
Also, our knowledge of the fossil record and extinction events has advanced significantly since the theory was first posited, and the supposed "regularity" of the Extinctions has vanished, knocking out the main other argument for such an object.
I took exception to your estimation of the total mass of the Oort cloud, it is indeed quite conceivable that Mercury sized objects exist in the Oort cloud and haven't been detected yet, and they could be sent into the inner Solar System and collide with Earth. Only, the odds of this happening are quite spectacularly small. Except if you claim that there are a huge number of mercury-sized objects out there, in which case you'll also need to explain why we're not seeing their larger siblings, which we would statistically expect to be out there too. Unless there's a physical reason objects in the cloud top out at a size below our current detection limit
Actually, there is a physical reason for this: there isn't enough matter in the Oort cloud for really large objects to be likely there. Certainly not a Solar mass.
Things like the Oort cloud tend to follow some kind of statistical distribution in the size of their constituent particles. If there really was a Solar mass worth of matter out there, the odds are extremely high that some of that matter would be in the form of Jupiter sized objects.
Actually, the total mass is not "probably much larger than the mass of its larger objects".
A few comparable examples:
50% of the total mass of the asteroid belt resides in the 4 largest asteroids.
70% of the total mass of the known solar system outside the sun resides in one object, Jupiter.
And the original author claimed that the Oort cloud is more massive than the sun and all the planets. I could probably acknowledge that, in theory, the mass of the Oort cloud could be on the same scale as the mass of all the planets, though this is extremely unlikely, but an extra solar mass of matter in the cloud? Not a chance. If this were the case, we would be capable of detecting the Oort clouds around other stars easily, which we cannot.
Space is big, but the Sun contains a LOT of matter.
Yes, this is the "Nemesis" theory, which was popular in the '70s and '80s for explaining "regular" extinction events. However, the events are less "regular" than suggested by proponents of the theory, and if such a star really existed, Infrared All Sky Surveys would have detected it by now. They haven't, so it doesn't exist.
Incorrect, the sum of the mass of the Oort cloud objects *might* be larger than the Earth's mass, maybe even a few Earth masses, but it is certainly not "far more than the mass of the sun and all the planets".
While an Earth sized planet might exist in the Oort cloud and not be detected, it is essentially impossible for anything Jupiter-sized to exist there, for two reasons: (a) Infrared all-sky surveys would have detected it by now and (b) a massive object like that would cause a significant detectable influx of smaller objects (comets) from the region where it exists. No such "preferred" direction is detected in long-period comets, and the number of long-period comets we find is at least an order of magnitude lower than we would see if there really was such a massive object out there.
I copied the Garland theme into a custom "Mira" theme and modified it there, I did code the javascript directly into the custom theme, this seemed the most convenient way of doing it, since I've also customized other aspects of the Garland theme (not many, but enough to make it worthwile to separate the theme out from Garland.)
On a site I manage, Mira Public Observatory (Belgian Dutch site), I've used IE6-only conditional commenting of some javascript and a class attribute to replace the transparant PNG's with less attractive GIF's on IE6 browsers. On all other browsers, the script isn't run, so the images aren't replaced.
This doesn't actually slow down the site in any really noticeable manner for IE6-users, and not at all for anyone else (admittedly, I simply ignore IE5.5 and older, but by now that's less than 0.2% of my visiting audience). I've found this a good compromise, the IE6 users get a slightly slower and less pretty site, but the difference isn't huge and I expect them to die out in a few years anyway...
I'm sorry if I came of a bit too offensive, it's not specifically aimed at you, but every time Lotus Notes is mentioned on Slashdot, a lot of people start complaining about it, usually referring to problems in earlier versions of Notes (At least, by this time, the "Interface Hall of Shame" meme seems to be dying out...). Notes is far from a perfect piece of software, and has a considerable number of quirks, but it is by no means as bad as some make it out to be, and there is no other single application/platform which does all that it is capable of and IBM is trying (and succeeding) in improving many of the more criticized aspects.
Actually, they just announced at Lotussphere that for Notes 8.5, they are working on an Eclipse-based Designer, which then would be quite simple to also make available on other platforms than Windows... So it's very likely going to happen.
In the mean time, as far as I know, it's possible to run Designer under Wine.
Well that is hardly helpful to those who wish to use a Lotus Notes client on a non-Microsoft platform.
Where Lotus Notes actually uses the Mozilla rendering engine, as anyone who knows something about the more recent Notes-versions knows. But please, don't let facts come in the way of decade old prejudices...
Actually, while the measurement of the extrasolar planets with "known" masses is likely to be considerably less precise than the mass measurements of Eris & Pluto, it is by no means as "based on models" as you imply.
Those planets for which actual density has been determined are in a special class (or at least, special from our viewpoint): These are planets which (a) pass in front of their star as seen from earth, thereby causing a slight dimming of the starlight seen from here, and (b) have sufficient mass to cause a measurable red/blueshift in the spectrum of their parent star.
The dimming of the light gives us their apparent diameter relative to their parent star, the duration of the dimming gives us a pretty accurate idea of the diameter of the star, the red/blueshift gives us their mass relative to their parent star and the orbital period gives us, to a considerable degree of accuracy, the mass of their parent star.
These four parameters are actual measurements, so since we can derive the actual mass & diameter of the planet from these four parameters quite easily, the average density value we derive is as close to a direct measurement as we'll get.
For planets which do not eclips their star as seen from earth, only lower limits to their mass can be determined (so the planet has to be "at least x earth masses") and even those do indeed depend on stellar modelling to determine the mass of the star, but since without the eclipses, there is currently no way to determine the diameter of said planet, there is no realistic way to determine the actual density of the planet anyway.
Yes, current stars are considered to have a limit of 100-150 solar masses, but this is in large part because of "pollution" due to heavy elements (anything heavier than Helium)
The first generation of stars (called Population III stars had essentially no heavier elements, because they did not exist at the time, and models suggest that such "metal-free" stars could have been much heavier than current stars.
Trouble is, if they were really that heavy, they would have burned through their fuel at an extremely rapid rate, exploded, spreading heavier atoms everywhere and preventing any future generations of stars from become as heavy as them. Because of their very short lifespan, no population III stars would survive until now, and indeed while we do see Population II stars (old, metal-poor stars) and Population I stars (newer, metal-rich stars like our sun), no population III stars are actually known.
The interesting thing here is that we can now see so far back, that we might be looking at the light from that first generation of stars.
Slashdot Mirror
Uhm, during a solar eclipse, the moon only blocks the sun in a spot a few tens to a few hundreds of km in size. So he's right, you're wrong...
And for your satellite example, if your satellite is a couple of meters in diameter, all you need to do to "unblock" the star is to move a few meters to the side.
You're right, bit of a mess-up there. Still, 20cm thick over a diameter of 8.4 meters is still pretty thin, although it's indeed honeycombed, so the actual thickness is higher, but only partially filled.
A telescope mirror needs a number of special properties, from rigidity and weight, but also thermal stability and the ability to polish it efficiently.
For nearly 50 years the largest mirror was the 5 meter Hale telescope, but in the late '80s materials science and casting techniques had evolved to the point where we could reliably cast larger, lighter telescope mirrors, and computing power to the point where active suspension of thinner mirrors is possible.
However, this doesn't mean we can create weightless mirrors, and an 8.4m mirror with a short focal length and two different surfaces still requires quite a bit of internal strength. Glass still has a higher density than water.
An 8.4m mirror has a surface area of 220 square meters, even assuming the density of water (1000 kg/m3) 25 tons corresponds to a thickness of only about 12 cm, or less than 5 inches, which is very very thin, and as I said, glass has a density higher than water, so the actual thickness would be substantially less.
Yes, it's the same. A shorter focal ratio ("fast") allows for a larger field of view with the same size CCD-chip. The "side-effect" of this is that a larger bit of sky falls onto the individual pixels, which means you sacrifice resolving power for sensitivity.
Like I said, we will know in a couple decades.
And any estimate that can range between 380 and 5 is not an estimate. It more closely resembles a wild guess than an educated one.
If it stays around 5 Earth masses for a couple decades, I may start to respect it.
Actually, the estimate doesn't range between 380 and 5, 380 earth masses was an early estimate of the upper limit, more recent study points to 5 earth masses as being the likely upper limit. At any rate, since a solar mass is about 334000 earth masses, the range from 380-->5 isn't quite so huge as to include another thousandfold increase as a likely possibility. And like I said, the trend has been down, not up... Oh, and I'm sure the scientific community cares a whole lot about your "respect"...
Small is not nonexistent. I wasn't attempting to mislead - I was just wrong. Being wrong in this one case does take away from the message that I'm trying to keep in front of people: Astronomers and earth scientists believe that global cataclysm has occurred on Earth in the past, and will occur in the future. Although that outcome is unlikely today and tomorrow, even this century, in the fullness of time it's not just likely - it's certain. If we don't get humanity established on some other place in the mean time, it's game over for our species. There isn't any credible disagreement on this issue.
No disagreement from me there!
Small addition: Wikipedia has a good overview (with scientific references) of the Oort Cloud mass (look at "Structure and Composition")
Basically, estimates of the Oort Cloud mass can be made based on the size & distribution of long-period and non-periodic comets. These estimates have actually decreased in recent years, and range from a total mass of 380x Earth to (more recently) no more than 5x Earh.
You could call that an "educated guess" if you want, but it's one based on more science than your Solar Mass estimate. (Besides, isn't "estimate" just an other word for "educated guess", and infinitely preferrable above "number pulled out of my ass to scare the folks at Slashdot with" ? )
Uhm, no...
It's a bit like we can be pretty much 100% certain that there are no 1000km sized asteroids waiting to be discovered in the Asteroid belt between Mars & Jupiter. If such an object did exist, we would have seen it by now because we've checked the sky with sufficient detail that any object that size would already have been discovered.
It is true that theoretically a huge, massive, Nemesis-like object could exist and be undetected, but that object would then not be a red or brown dwarf, or even a black hole, because by now we know enough about the physical properties of such objects that we know our current surveys would have spotted it by now.
Of course, something more exotic might be lurking out there, but that is pure conjecture, and besides, the main reason "Nemesis" was invented (to explain periodic extinctions) has vanished because we now know those extinctions are far less "periodic" than we originally assumed.
Indeed, it is still Popular, but not among serious scientists.
Until about a decade ago, we could say "we don't know", with the IR surveys made since IRAS, we can actually put upper limits on objects out there which are below the threshold where such an object could have a "Nemesis" like effect.
Also, our knowledge of the fossil record and extinction events has advanced significantly since the theory was first posited, and the supposed "regularity" of the Extinctions has vanished, knocking out the main other argument for such an object.
I took exception to your estimation of the total mass of the Oort cloud, it is indeed quite conceivable that Mercury sized objects exist in the Oort cloud and haven't been detected yet, and they could be sent into the inner Solar System and collide with Earth. Only, the odds of this happening are quite spectacularly small. Except if you claim that there are a huge number of mercury-sized objects out there, in which case you'll also need to explain why we're not seeing their larger siblings, which we would statistically expect to be out there too. Unless there's a physical reason objects in the cloud top out at a size below our current detection limit
Actually, there is a physical reason for this: there isn't enough matter in the Oort cloud for really large objects to be likely there. Certainly not a Solar mass.
Things like the Oort cloud tend to follow some kind of statistical distribution in the size of their constituent particles. If there really was a Solar mass worth of matter out there, the odds are extremely high that some of that matter would be in the form of Jupiter sized objects.
Actually, the total mass is not "probably much larger than the mass of its larger objects".
A few comparable examples:
50% of the total mass of the asteroid belt resides in the 4 largest asteroids.
70% of the total mass of the known solar system outside the sun resides in one object, Jupiter.
And the original author claimed that the Oort cloud is more massive than the sun and all the planets. I could probably acknowledge that, in theory, the mass of the Oort cloud could be on the same scale as the mass of all the planets, though this is extremely unlikely, but an extra solar mass of matter in the cloud? Not a chance. If this were the case, we would be capable of detecting the Oort clouds around other stars easily, which we cannot.
Space is big, but the Sun contains a LOT of matter.
Yes, this is the "Nemesis" theory, which was popular in the '70s and '80s for explaining "regular" extinction events. However, the events are less "regular" than suggested by proponents of the theory, and if such a star really existed, Infrared All Sky Surveys would have detected it by now. They haven't, so it doesn't exist.
Incorrect, the sum of the mass of the Oort cloud objects *might* be larger than the Earth's mass, maybe even a few Earth masses, but it is certainly not "far more than the mass of the sun and all the planets".
While an Earth sized planet might exist in the Oort cloud and not be detected, it is essentially impossible for anything Jupiter-sized to exist there, for two reasons: (a) Infrared all-sky surveys would have detected it by now and (b) a massive object like that would cause a significant detectable influx of smaller objects (comets) from the region where it exists. No such "preferred" direction is detected in long-period comets, and the number of long-period comets we find is at least an order of magnitude lower than we would see if there really was such a massive object out there.
Okay, all of Behe's examples of irreducible complexity have by now been so thoroughly refuted that it's really sad some people still cling to them.
See http://www.talkorigins.org/indexcc/CB/CB200_1.html
For this one.
I copied the Garland theme into a custom "Mira" theme and modified it there, I did code the javascript directly into the custom theme, this seemed the most convenient way of doing it, since I've also customized other aspects of the Garland theme (not many, but enough to make it worthwile to separate the theme out from Garland.)
On a site I manage, Mira Public Observatory (Belgian Dutch site), I've used IE6-only conditional commenting of some javascript and a class attribute to replace the transparant PNG's with less attractive GIF's on IE6 browsers. On all other browsers, the script isn't run, so the images aren't replaced.
This doesn't actually slow down the site in any really noticeable manner for IE6-users, and not at all for anyone else (admittedly, I simply ignore IE5.5 and older, but by now that's less than 0.2% of my visiting audience). I've found this a good compromise, the IE6 users get a slightly slower and less pretty site, but the difference isn't huge and I expect them to die out in a few years anyway...
I'm sorry if I came of a bit too offensive, it's not specifically aimed at you, but every time Lotus Notes is mentioned on Slashdot, a lot of people start complaining about it, usually referring to problems in earlier versions of Notes (At least, by this time, the "Interface Hall of Shame" meme seems to be dying out...).
Notes is far from a perfect piece of software, and has a considerable number of quirks, but it is by no means as bad as some make it out to be, and there is no other single application/platform which does all that it is capable of and IBM is trying (and succeeding) in improving many of the more criticized aspects.
Actually, they just announced at Lotussphere that for Notes 8.5, they are working on an Eclipse-based Designer, which then would be quite simple to also make available on other platforms than Windows... So it's very likely going to happen.
In the mean time, as far as I know, it's possible to run Designer under Wine.
Are you using Gmail? Ever since gmail v2 I'm getting very regular crashes when navigating *away* from gmail, this on FFox 2
Actually, while the measurement of the extrasolar planets with "known" masses is likely to be considerably less precise than the mass measurements of Eris & Pluto, it is by no means as "based on models" as you imply.
Those planets for which actual density has been determined are in a special class (or at least, special from our viewpoint):
These are planets which (a) pass in front of their star as seen from earth, thereby causing a slight dimming of the starlight seen from here, and (b) have sufficient mass to cause a measurable red/blueshift in the spectrum of their parent star.
The dimming of the light gives us their apparent diameter relative to their parent star, the duration of the dimming gives us a pretty accurate idea of the diameter of the star, the red/blueshift gives us their mass relative to their parent star and the orbital period gives us, to a considerable degree of accuracy, the mass of their parent star.
These four parameters are actual measurements, so since we can derive the actual mass & diameter of the planet from these four parameters quite easily, the average density value we derive is as close to a direct measurement as we'll get.
For planets which do not eclips their star as seen from earth, only lower limits to their mass can be determined (so the planet has to be "at least x earth masses") and even those do indeed depend on stellar modelling to determine the mass of the star, but since without the eclipses, there is currently no way to determine the diameter of said planet, there is no realistic way to determine the actual density of the planet anyway.
Yes, current stars are considered to have a limit of 100-150 solar masses, but this is in large part because of "pollution" due to heavy elements (anything heavier than Helium)
The first generation of stars (called Population III stars had essentially no heavier elements, because they did not exist at the time, and models suggest that such "metal-free" stars could have been much heavier than current stars.
Trouble is, if they were really that heavy, they would have burned through their fuel at an extremely rapid rate, exploded, spreading heavier atoms everywhere and preventing any future generations of stars from become as heavy as them. Because of their very short lifespan, no population III stars would survive until now, and indeed while we do see Population II stars (old, metal-poor stars) and Population I stars (newer, metal-rich stars like our sun), no population III stars are actually known.
The interesting thing here is that we can now see so far back, that we might be looking at the light from that first generation of stars.