A big aspect of this proposal *not* mentioned in the BBC article is the importance of metallicity on star formation - in other words, what star environments (old vs. young) form more planets.
You can argue all you please about how Hubble is out-of-date and needs cancellation, but the real experts will disagree with you. Astronomers are quite irate about the Hubble's cancellation, and rightly so. Politicians should not dictate how NASA spends its paltry budget - and doubly so in an election year when your poll numbers are looking grim.
Sean O'Keefe was picked for the head of NASA precisely because he has a reputation as a budget cutter. The man knows *nothing* about space science.
But don't take my word for this. The American Astronomical Society - an organization that includes essentially all the professional astronomers in America, and rarely if ever takes a political stand - released a statement pleading to reconsider the cancellation:
the oil layer can be adusted within microns of a desired setting. No other type of lens element approaches such accuracy
Sounds like someone needs a good class in optics.
In order to create a lens that meets the *bare minimum* of optical quality - i.e. no destructive interference between different areas of the lens - you need to have your wavefront accurate to within one-quarter of the wavelength you're trying to focus.
Since your average visible photon is in the 500 nanometer range (turquoise light, roughly), you need a lens that produces wavefront accuracy at least to within 125 nanometers (that's.125 microns for the non-metrically inclined).
A lens that's only accurate to within a micron wouldn't be worth its weight in turnips.
Actually, painting the entire rock a brighter or darker color significantly different from it's current color would work - if you have enough time, it's the best possible solution, as it's a passive one.
I'm not sure why people seem to think that you only need to paint half. I'm also not sure why other people think that because asteroids rotate this doesn't work - it is actually *because* the rock rotates that it does work.
This relies on a phenomenon called the Yarkovsky effect. It can be thought of this way: Imagine you're standing on the asteroid where it's "asteroid high noon". Light is being absorbed throughout the "asteroid day" and heats the surface, particularly if the asteroid is darkly colored (e.g. a carbonaceous asteroid). After a while, the asteroid rotates and the sun sets. The asteroid then reradiates this heat in the direction of "asteroid evening". As it rotates more, by the time "asteroid morning" rolls around, the area your standing on has cooled down enough to radiate much less. Ergo, there is a differential radiation pressure on either side of the asteroid, which results in a net force over time. If it rotates with the same spin orientation as its orbit, its orbit will get wider. If it rotates with the opposite spin as its orbit, its orbit will get smaller.
By painting the rock, you change this force - the brighter the paint, the more light is reflected, the less thrust, thereby changing the path.
One last comment - the effect is subtle, so it would need to be applied early. It also preferentially favors diversion for small asteroids, since the Yarkovsky effect is a surface phenomena. The larger the asteroid, the smaller the surface-area-to-volume ratio, and the less deflection this thrust will do.
Interesting...very interesting. As someone who has built their own newtonian, I feel obliged to comment...
One thing that's important to realize is that any telescope is a compromise. However, this design makes some compromises that I don't know I would be willing to make.
The obvious benefit of such a design is to get a large aperture and a long focal-length without having to balance on a ladder. In general, if you want an 18" newtonian scope, you'd have to go down to a focal ratio of 4.25 or less to stay on the ground (that corresponds to a focal length of (4.25 x 18") = 76.5"). The problem with short focal length scopes is that they have to be much more accurate for their aperture...basically, it's easier to get a really good figure for a long focal length mirror. Long focal length scopes also have less coma (a certain kind of aberration), so kudos to him for this design with a focal ratio of 8.
However, I see three serious problems with this design:
1) Secondary size. In order to pack a greater percentage of that long focal length into the beam after reflection from the secondary, you have to make your secondary significantly bigger. This, to me, is unacceptable. He's using a 6" secondary, which is covering fully 33% of the main mirror's aperture. Not only does this cut down on the total light you see, but also reduces the minimum angular resolution...as long focal length scopes excel at high-res viewing, you're essentially shooting yourself in the foot right after you bought a really excellent foot. To give you a basis for comparison, my scope has only 21.6% of the primary covered by the secondary (mine also has a focal ratio of 7.5).
2) That 15 degree angle has got to be killer. When constructing scopes, it's plenty easy (er, well, easier, anyway) to make a perpendicular angle from your secondary. It seems like lining up that 15 degree angle correctly (known as collimation) every time you set up the scope is going to be difficult at best, especially when you have to line the "eyepiece tube" up at a 30 degree angle every time, as well. A couple degrees off and you're already introducing significant aberration.
3) Viewing angle. How do I look through an eyepiece that's only 30 degrees off the optical axis? With difficulty, at best. One of the main purposes of the scope - viewing comfort - is compromised by this. The obvious solution is to use a mirror diagonal, but that, again, is then only cutting more into the amount of light you see (no surface reflects 100% of the light), as well as presenting the potential for more surface defects.
This confusing concept is only further obfuscated by shockingly poor science writing. For example:
"Black holes were conceived during World War 1 by the German astronomer Karl Schwarzschild, who while serving in the war was scratching solutions to Einstein's theories...Einstein first thought the idea was nuts."
Wrong, black holes were first conceived by Laplace back in 1798. Moreover, no one thought it was nuts - it was a natural consequence of orbit theory coupled with a finite speed of light.
Umm, No. Let's do a couple back-of-the-envelope calculations, shall we?
OK, assuming the Sun has a density of 1 (which is actually fairly close overall) and a radius of 350,000,000 m:
Mass = Density * Volume = (1000kg/meter-cubed) * (4/3*Pi*(r-cubed)) = 1000kg * 3.14159 * 1.333 * (350,000,000m)^3 = 1.8 x 10^29 kg
Now, I'm not sure which ton they're using, but since this is a BBC article, I'm assuming they mean a megagram.
So, losing a billion tons (a trillion kg) would be about: 10^12kg/3.8 x 10^20 kg = 5.6 x 10^-18 solar masses =.000000000000000056% of its mass
Not a whole lot, really.
Of course, all this is moot, since the actual rate of fusion is actually *governed* by the amount of gravity. The less mass, the less gravity pushes in on the fusion core, the less heat, the slower fusion actually occurs. It all balances out.
In fact, the life of the sun would be lengthened by removing mass, as smaller cooler stars (red dwarfs) burn much, much longer than larger ones. Think slowly smoldering cinder versus raging bonfire - which uses up its fuel quicker?
This is a suprisingly common phenomenon, which many people have tried to explain to some avail.
The key lies in noticing that the sounds are, as you mention, timed perfectly with the visuals. As the aurora occurs about 60 miles up, if this were really the sound of the aurora itself it would come at least 5 minutes later. (5 secs per mile, at least at STP, which it isn't that high up).
So...current theory has it that the aurora is producing radio waves which travel the speed of light, which produce electric fields at ground level. The same way that static electricity will cause things to move and crackle, so too this happens when the local electric field is altered. Usually anything really dryed-out will work - pine needles, leaves, even dry hair.
One thing that might confirm this - the sounds that you have heard - did they occur on very dry nights, e.g. when it's extremely cold out?
Slashdot Mirror
In case anyone's interested and prefers a little more science in their science reporting, here's the original proposal (it's a text file):
. pro
http://www.stsci.edu/observing/phase2-public/9750
A big aspect of this proposal *not* mentioned in the BBC article is the importance of metallicity on star formation - in other words, what star environments (old vs. young) form more planets.
You can argue all you please about how Hubble is out-of-date and needs cancellation, but the real experts will disagree with you. Astronomers are quite irate about the Hubble's cancellation, and rightly so. Politicians should not dictate how NASA spends its paltry budget - and doubly so in an election year when your poll numbers are looking grim.
Sean O'Keefe was picked for the head of NASA precisely because he has a reputation as a budget cutter. The man knows *nothing* about space science.
But don't take my word for this. The American Astronomical Society - an organization that includes essentially all the professional astronomers in America, and rarely if ever takes a political stand - released a statement pleading to reconsider the cancellation:
AAS's cancellation statement
I believe there's a statement from the UK's Royal Astronomical Society there, too.
the oil layer can be adusted within microns of a desired setting. No other type of lens element approaches such accuracy
.125 microns for the non-metrically inclined).
Sounds like someone needs a good class in optics.
In order to create a lens that meets the *bare minimum* of optical quality - i.e. no destructive interference between different areas of the lens - you need to have your wavefront accurate to within one-quarter of the wavelength you're trying to focus.
Since your average visible photon is in the 500 nanometer range (turquoise light, roughly), you need a lens that produces wavefront accuracy at least to within 125 nanometers (that's
A lens that's only accurate to within a micron wouldn't be worth its weight in turnips.
Actually, painting the entire rock a brighter or darker color significantly different from it's current color would work - if you have enough time, it's the best possible solution, as it's a passive one.
I'm not sure why people seem to think that you only need to paint half. I'm also not sure why other people think that because asteroids rotate this doesn't work - it is actually *because* the rock rotates that it does work.
This relies on a phenomenon called the Yarkovsky effect. It can be thought of this way: Imagine you're standing on the asteroid where it's "asteroid high noon". Light is being absorbed throughout the "asteroid day" and heats the surface, particularly if the asteroid is darkly colored (e.g. a carbonaceous asteroid). After a while, the asteroid rotates and the sun sets. The asteroid then reradiates this heat in the direction of "asteroid evening". As it rotates more, by the time "asteroid morning" rolls around, the area your standing on has cooled down enough to radiate much less. Ergo, there is a differential radiation pressure on either side of the asteroid, which results in a net force over time. If it rotates with the same spin orientation as its orbit, its orbit will get wider. If it rotates with the opposite spin as its orbit, its orbit will get smaller.
By painting the rock, you change this force - the brighter the paint, the more light is reflected, the less thrust, thereby changing the path.
One last comment - the effect is subtle, so it would need to be applied early. It also preferentially favors diversion for small asteroids, since the Yarkovsky effect is a surface phenomena. The larger the asteroid, the smaller the surface-area-to-volume ratio, and the less deflection this thrust will do.
Interesting...very interesting. As someone who has built their own newtonian, I feel obliged to comment...
One thing that's important to realize is that any telescope is a compromise. However, this design makes some compromises that I don't know I would be willing to make.
The obvious benefit of such a design is to get a large aperture and a long focal-length without having to balance on a ladder. In general, if you want an 18" newtonian scope, you'd have to go down to a focal ratio of 4.25 or less to stay on the ground (that corresponds to a focal length of (4.25 x 18") = 76.5"). The problem with short focal length scopes is that they have to be much more accurate for their aperture...basically, it's easier to get a really good figure for a long focal length mirror. Long focal length scopes also have less coma (a certain kind of aberration), so kudos to him for this design with a focal ratio of 8.
However, I see three serious problems with this design:
1) Secondary size. In order to pack a greater percentage of that long focal length into the beam after reflection from the secondary, you have to make your secondary significantly bigger. This, to me, is unacceptable. He's using a 6" secondary, which is covering fully 33% of the main mirror's aperture. Not only does this cut down on the total light you see, but also reduces the minimum angular resolution...as long focal length scopes excel at high-res viewing, you're essentially shooting yourself in the foot right after you bought a really excellent foot. To give you a basis for comparison, my scope has only 21.6% of the primary covered by the secondary (mine also has a focal ratio of 7.5).
2) That 15 degree angle has got to be killer. When constructing scopes, it's plenty easy (er, well, easier, anyway) to make a perpendicular angle from your secondary. It seems like lining up that 15 degree angle correctly (known as collimation) every time you set up the scope is going to be difficult at best, especially when you have to line the "eyepiece tube" up at a 30 degree angle every time, as well. A couple degrees off and you're already introducing significant aberration.
3) Viewing angle. How do I look through an eyepiece that's only 30 degrees off the optical axis? With difficulty, at best. One of the main purposes of the scope - viewing comfort - is compromised by this. The obvious solution is to use a mirror diagonal, but that, again, is then only cutting more into the amount of light you see (no surface reflects 100% of the light), as well as presenting the potential for more surface defects.
This confusing concept is only further obfuscated by shockingly poor science writing. For example:
"Black holes were conceived during World War 1 by the German astronomer Karl Schwarzschild, who while serving in the war was scratching solutions to Einstein's theories...Einstein first thought the idea was nuts."
Wrong, black holes were first conceived by Laplace back in 1798. Moreover, no one thought it was nuts - it was a natural consequence of orbit theory coupled with a finite speed of light.
Umm, No. Let's do a couple back-of-the-envelope calculations, shall we?
.000000000000000056% of its mass
OK, assuming the Sun has a density of 1 (which is actually fairly close overall) and a radius of 350,000,000 m:
Mass = Density * Volume
= (1000kg/meter-cubed) * (4/3*Pi*(r-cubed))
= 1000kg * 3.14159 * 1.333 * (350,000,000m)^3
= 1.8 x 10^29 kg
Now, I'm not sure which ton they're using, but since this is a BBC article, I'm assuming they mean a megagram.
So, losing a billion tons (a trillion kg) would be about:
10^12kg/3.8 x 10^20 kg = 5.6 x 10^-18 solar masses
=
Not a whole lot, really.
Of course, all this is moot, since the actual rate of fusion is actually *governed* by the amount of gravity. The less mass, the less gravity pushes in on the fusion core, the less heat, the slower fusion actually occurs. It all balances out.
In fact, the life of the sun would be lengthened by removing mass, as smaller cooler stars (red dwarfs) burn much, much longer than larger ones. Think slowly smoldering cinder versus raging bonfire - which uses up its fuel quicker?
This is a suprisingly common phenomenon, which many people have tried to explain to some avail.
The key lies in noticing that the sounds are, as you mention, timed perfectly with the visuals. As the aurora occurs about 60 miles up, if this were really the sound of the aurora itself it would come at least 5 minutes later. (5 secs per mile, at least at STP, which it isn't that high up).
So...current theory has it that the aurora is producing radio waves which travel the speed of light, which produce electric fields at ground level. The same way that static electricity will cause things to move and crackle, so too this happens when the local electric field is altered. Usually anything really dryed-out will work - pine needles, leaves, even dry hair.
One thing that might confirm this - the sounds that you have heard - did they occur on very dry nights, e.g. when it's extremely cold out?