Hubble Accuracy Surpassed By Earthbound Telescope 87
randuev writes "A high-speed adaptive optics system helped the Large Binocular Telescope (on Earth) to beat the accuracy of the Hubble Space Telescope's observations. 'A special sensor detects atmospheric distortions in real time and controls the mirror to adjust its position to compensate, effectively canceling out the blurring. The mirror can make adjustments every one-thousandth of a second, with accuracy to better than ten nanometers.' Now, that's what I call real-time. This nifty trick multiplied the Strehl ratio (optical quality) of the LBT by about 80 times. The new system was tested in May and June, so hopefully we'll soon see more space around us in higher resolution on Google Sky."
Re:Sounds good (Score:5, Informative)
While this does mean that it could possibly make some Deep Field images. There is still another problem that makes this possibly intractable. The atmospheric absorption of some wavelengths means that it might still not be able to see certain areas in the spectrum effectively; this could prevent it from being able to produce nice deep field images like the hubble. However this ability to resolve objects that much better means that it could most certainly be effective at searching for planets.
Re:More please!!! (Score:5, Informative)
Alas, there's no way around the Rayleigh criterion: http://en.wikipedia.org/wiki/Angular_resolution [wikipedia.org]
We're not going to construct one-hundred-kilometer size telescopes any time soon.
Sarcasm, right? (Score:3, Informative)
In case my sarcasm detector is giving a false positive, the answer is you don't need adaptive optics for a mirror diameter of 30 cm or less, because at those sizes you get more blurring from diffraction than from atmospheric effects.
Re:More please!!! (Score:3, Informative)
There's no particular barrier to the construction of interferometers of such aperature in space, especially at longer wavelengths. You don't actually need to control the separation precisely: just measure it.
Comment removed (Score:2, Informative)
Re:What a testament to the HST... (Score:2, Informative)
Re:Sounds good (Score:4, Informative)
it's resolution that's better, not accuracy (Score:4, Informative)
The adaptive optics increases the resolution of the telescope by eliminating the refractive errors caused by atmospheric turbulence. And the basic resolution of the LBT is better because its 8.4m mirrors are over 3 times the diameter of the 2.4m Hubble mirror.
The ideal would be a larger mirror in space, such as the James Webb telescope is to be if it works.
[Disclaimer: I eat lunch with LBT engineers, so I know way too much about the gory details of getting 600 magnetic actuators to work together without breaking glass.]
Watch the documentary (Score:3, Informative)
not in the IR though (Score:4, Informative)
Much of astronomy is being pushed by the need to image deeply in the infrared. For example, to discover the most distant objects in the universe, you need to use near- and mid-infrared wavelengths (because objects that are far away are receeding rapidly, hence redshifted). And for this, mostly what you want is raw photon count, not sharpness (although that would be a "nice-to-have" someday).
Unfortunately (for astronomy), the atmosphere absorbs heavily in the infrared wavelengths (aside from a few windows, which give us our passpands), and as a result, a 1 meter telescope in space still beats an 8 meter on the ground, in almost every respect (putting cost aside for a moment...).
At least for infrared work...
Re:Sounds good (Score:3, Informative)
The big difference between ground-based telescopes using active optics or adaptive optics to obtain diffraction-limited images, and the Hubble taking advantage of the lack of an atmosphere to obtain diffraction-limited images is that Hubble can do this over a large field of view whereas ground-based telescopes can only do this for extremely small fields. This is because the coherence length of the turbulence cells in the atmosphere that are responsible for atmospheric blurring (called seeing) are very small, and the active optics (or adaptive optics) can only correct over areas that are about the same size as the coherence length. So, ground-based telescopes are not going to be replacing space-based telescopes for research that requires fields of view larger than about 10 arcsecond square.
Re:Several limitations to Adaptive Optics (Score:4, Informative)
So the answer to the first question is, infrared and near infrared are the wavelengths most useful for meaningful astronomy, because they allow astronomers and cosmologists to see through clouds of interstellar dust and gas to the interesting stuff in the clouds, and the interesting stuff hidden behind those clouds. That's why Hubble has both visual and infrared technology on-board. As well, infrared spectroscopy will tell us which nearby planets have the kind of chemistry that indicates the possibility of life. Due to water vapor, the atmosphere is virtually opaque to these frequencies so they must be viewed either from extreme altitude (balloon or very high flying jets), or space.
The color images that Hubble produces from visual light are in fact heavily altered and do not reflect what the human eye would perceive. Typically the colors being recorded are from the light emitted by Hydrogen, Sulfur, and Oxygen. Hydrogen and Sulfur both emit light in the Red optical spectrum, and if they were presented as the color the human eye perceives would blur together. Instead, the Hubble images view Hydrogen as Red, and Sulfur as Green with Oxygen providing the blue. This gives rich full color images rich in detail and visually stunning color. Images from infrared telescopes are used in exactly the same way, you just can't see those colors. So the representation in either case is not "real".