The Herschel Telescope Close To Blast Off 136
pha7boy writes "The Herschel space observatory, the European Space Agency's answer to the Hubble Telescope, is about to be sent into orbit. With a mirror 1.5 times the size of the Hubble mirror, the Herschel will look at the universe in the infrared and sub-millimeter range. This 'will permit Herschel to see past the dust that scatters Hubble's visible wavelengths, and to gaze at really cold places and objects in the Universe — from the birthing clouds of new stars to the icy comets that live far out in the Solar System.'"
not about imaging (Score:5, Informative)
This instrument is capable of great science, but spatial resolving power is not it's strong suit. Since it is measuring at wavelenghts much greater than hubble (100-1000x), the 3.5 meter mirror doesn't give you anything like hubble.
Infrared == looks far away (Score:4, Informative)
A telescope with a bigger mirror can concentrate more light, therefore it sees fainter, more distant, objects. And the further away things are in the universe, the more red-shifted their light is. It really makes sense a space telescope being designed for infrared light, rather than visible.
Re:It will be intresting for sure (Score:5, Informative)
I'm sure they'll do many deep fields.
Astronomers were well aware that the region of sky used for the Hubble deep field was full of distant objects. It was chosen because the lack of bright, close objects makes it simpler to do really long exposures of the distant, dim ones.
One of the stated goals of the Herschel is to look back to the beginnings of the universe. The best way to do that is by choosing a dark area of the sky and exposing as long as you can.
Re:Why not visible light? (Score:5, Informative)
Redshift, probably.
When you're looking at things really really far away, the frequencies shift towards the red end of the spectrum due to the doppler effect of the Hubble Expansion. If we only looked in the visible spectrum, we wouldn't see anything, because the light had already shifted out of the proper range. Thus, but looking towards the infrared and longer wavelengths, we can actually detect things that originally light emitted in the visible spectrum but are reaching us in a heavily stretched state.
Re:Why not visible light? (Score:3, Informative)
I wasn't exactly sure myself until this comment [slashdot.org] and this wiki entry [wikipedia.org]. If we focused them on visible spectrums, we'd not notice the most distant emissions. Since attempting to detect obejects that are extremely distant is the apparently the whole bit with the Herschel telescope it starts to make sense.
Re:Why not visible light? (Score:4, Informative)
I'm only an amateur astronomer but... With adaptive optics we can get better visible light images with ground based telescopes like Keck than with any orbiting telecope that could be launched any time soon. However, infrared is blocked by the atmosphere so an observatory without an atmosphere is required.
Re:It will be intresting for sure (Score:5, Informative)
In fact, there is no case for very long exposures like the Hubble Deep Field or the Chandra Deep Fields (X-rays) with infrared telescopes, because the maximum depth reachable is not limited by sensitivity (exposure time) but by confusion (resolving power).
The confusion limit is reached when you can not detect any more sources because the field is so crowded that they start overlapping with each other. This limit is usually reached in infrared telescopes long before the detection limit (a few minutes), because the wavelength of the light in this spectral range is so big that the resolving power is very poor.
Note that resolving power is proportional to the diameter of the main mirror and inversely proportional to the observing wavelength, so a ~4.5m telescope like Herschel operating at 100 microns has aproximately half resolving power of an amateur 6cm telescope operating in visible light.
This also implies that the "ESA response to Hubble" statement is absurd and misleading
Re:Why not visible light? (Score:4, Informative)
Yup. I don't know that I'd even call myself an amatuer astronomer but I remember being fascinated by a Nova episode about IRAS ages ago.
This is a very poorly explored region of the spectrum, hence the interest. I think the issue with sending up another Hubble is that it just isn't as much bang for buck.
Don't get me wrong - it seems silly not to have ONE visual spectrum space telescope, but looking into different wavelengths is far more likely to turn up revolutionary results and advance the field.
Here's an analogy. We discover a planet on a distant star. Which is more likely to turn up new results - a detailed observation of that distant planet, or a careful high-resolution analysis of craters on the Earth's moon? Sure, the latter might be good science, and turn up results, but it just isn't going to be as likely to change how we think about everything.
Re:Why not visible light? (Score:3, Informative)
Comment removed (Score:5, Informative)
Re:To Be Announced... (Score:3, Informative)
Not to be outdone by Europe, the US plan to launch the next generation follow-up to the Hubble Telescope!
That would be the James Webb Space Telescope [wikipedia.org], and it's been in the works for quite a while.
Re:Infrared == looks far away (Score:3, Informative)
That's correct, but the more distant objects are moving away faster than the nearest ones.
Re:hubble mistakes? (Score:5, Informative)
Launch Date: April 16 (Score:4, Informative)
April 16 Ariane 5 Herschel & Planck
Launch time: approx. 1230 GMT (8:30 a.m. EDT)
Launch site: ELA-3, Kourou, French Guiana
Arianespace Flight 188 will use an Ariane 5 rocket with an ECA upper stage to launch the European Space Agency's Herschel and Planck observatories. The Herschel infrared telescope will study the evolution of stars and galaxies and the Planck spacecraft will observe the cosmic background radiation left over from the Big Bang. [Jan. 14]
http://www.spaceflightnow.com/tracking/index.html [spaceflightnow.com]
Re:Infrared == looks far away (Score:2, Informative)
Thanks for the info. One thing that confuses me about that is assuming everything is moving away from the origin of the universe, wouldn't all galaxies always move away from each other.
On large scales yes that is correct...
I recall reading that in some many billions of years, another galaxy will collide with ours. Wouldn't these 2 outcomes be mutually exclusive? Genuinely curious about this.
...but not on local scales, where the gravitational effects are larger. The Mily Way is gravitationally bound in the Local Group (see Wikipedia).
Re:Infrared == looks far away (Score:1, Informative)
Gravity acts on irregularities in the expanding matter to form clumps which continue to move outward from the center. Otherwise, nothing larger than hydrogen atoms would exist.
Isn't this similar to Spitzer Space Telescope? (Score:2, Informative)
This is same idea, but a much larger mirror, as the Spitzer Space Telescope:
http://www.spitzer.caltech.edu/about/index.shtml [caltech.edu]
The ESA, NASA and JPL have collaborated on this project since this appears to scaled up version of Spitzer Space Telescope with 6 years of advanced technology and lesson learned from Spitzer Space Telescope.
Good luck ESA with sending Herschel and Planck in space.
Re:It will be intresting for sure (Score:2, Informative)
Wow, what a bunch of historical revisionism. How, exactly, were astronomers supposed to be 'well aware' that that pointing Hubble at a patch of sky where all previous surveys had shown nothing at all, would produce such interesting results?
What actually happened was that the director of the observatory has some 'discretionary' observing time on the telescope, that he/she is completely free to do what they want with, without the usual procedure of submitting an application for approval (a process that is quite competitive). Most likely, a normal application to observe in the deep field would have been rejected, on the grounds that there is insufficient justification and it could easily have ended up as a waste of time. Imagine submitting an application saying "we propose to point this multi-billion dollar instrument at a region of sky that is completely black and as far as we know, contains nothing" ? But Robert Williams, the then-director, decided to devote a large proportion of his discretionary time in 1995 to deep field imaging. The rest is history. And pretty pictures.
Re:Cant wait (Score:3, Informative)
I thought focal length was the biggest factor in resolution?
Diffraction limit is set by lambda/diameter -- the longer the wavelength to larger the mirror required to get the same limit.
But then again all I know about telescopes comes from hobbyist visible light scopes.
On the ground you're almost always resolution limited by the atmospheric seeing, as long as your aperture is over ~10cm or so. Anything larger form there is going to help with collecting more light (i.e. detecting fainter objects with shorter exposures) but not with resolution any more.
Re:Cant wait (Score:5, Informative)
In a certain respect, it is related to the focal length, if you consider the eyepiece or sensor fixed. If you have a fixed pixel size on your CCD, then changing the focal length will change the angular size of each pixel, and thus change the resolution, although I think this kind of result is usually called magnification. Similarly, when using an eyepiece, the magnification is related to the ratio of the focal lengths, so a longer focal length will change the magnification
When the CCD pixels get small enough though, that size is no longer the limit on the resolution. Instead (neglecting atmospheric effects) you run into the fact that photon impacts are defined by probability densities that behave like waves, and you get a certain 'spreading' around the nominal impact location. The diameter of this spreading (the Airy disk) means that two sources that are too close together cannot be distinguished from each other, and this is called the diffraction limit. (There are other equally valid explanations for this effect, particularly coming from a wave perspective, this is just the one that I started typing.)
Now, in order to reduce this you want to bring in more photons from further seperated distances, meaning you want a larger aperture in order to improve the diffraction limited resolution. Generally the limiting angular resolution is given by theta_r = 1.4 lambda/D. Of course, if you have too strong of aberrations in the optical system, have to deal with atmospheric 'seeing' effects, the system is not diffraction limited, and the point spread function spreads out more.
Of course, its dangerous to compare the capabilities of telescopes at different wavelengths (Hubble is visible, Herschel is infrared to millimeter wave), because the total amount of light available changes, the angular resolution changes, and the engineering requirements change. Really, Hubble is about the maximum size optical space telescope you can make with current launch vehicles without moving to a completely new kind of telescope (active feedback with wavefront sensing like JWST). Herschel is able to be bigger easily because it requires significantly lower precision, due to the larger wavelengths.
Re:It will be intresting for sure (Score:5, Informative)
Bravo. The post full of true but irrelevant detail, the tone of righteous indignation... excellent troll.
Just in case you were serious, have a read through the wikipedia entry [wikipedia.org] for the Hubble deep field, and the original paper [harvard.edu] (PDF link).
Pay particular attention to the "Field Selection" section of the paper. Note that both the Wikipedia article and the introduction to the paper talk about how the project was designed to image a "typical" field, with the intention of studying (among other things) galaxy morphology in the very early universe. Also, the introduction to the paper outlines several other preceding medium and deep field studies that provided the motivation for the Hubble deep field project (goes to how the astronomers knew they were likely to find galaxies - previous studies did NOT show nothing at all).
Now, moving on to the field selection part of the paper, note how the target field was chosen because of the absence of nearby sources, and upper limits on the strength of the sources present (not NO sources present, but rather no STRONG, CLOSE sources present).
The kicker of course, is this quote: "Eisenhardt (1995) kindly provided KPNO 4m R-band CCD images (2x300 second exposures) as further verification that the fields were typical in terms of source counts..." (emphasis mine). A truly empty portion of the sky, with no observable signal sources would be VERY atypical.
Taking a quick tour through the source table in the paper, I noticed a source at around magnitude 17. The tables later in the paper suggested that there are sources present up to magnitude 15. That's pretty faint, but magnitude 15 is reachable by moderate amateur telescopes and the naked eye. Considerably better can be done with amateur CCD equipment and long exposures.
One of the fundamental assumptions of cosmology is that, on the large scale, the universe is pretty much the same no matter what direction you look. A totally blank area back as far as Hubble can see would be very unusual.
Again, I'm sorry to ruin your beautiful troll with actual references, but it was so well done someone might believe you!
PS: the "a normal application... would have been rejected" claim doesn't seem to be nearly as iron-clad as your tone implied.
Re:Why not visible light? (Score:3, Informative)
True. But the oldest galaxies (what Herschel is mainly designed to look at) don't emit in the visible, even in their own (rest) frame. That's because the earliest galaxies are very dusty, and all this dust is opaque to the visible light. The stars are still there, glowing away, but their light is absorbed by this dust. This absorption heats the dust, warming it to 35K (give or take), which, as all things with non-zero temperature do, emits radiation like a blackbody. This light is then redshifted such that it's blackbody spectrum peaks in the submillimeter, which is what Herschel looks at.
Disclaimer: I work on BLAST [blastexperiment.info], a balloon-borne experiment (cheaper than a satellite) which has detectors nearly identical to the ones of the SPIRE (main) instrument on Herschel.
This just in! Slashdot editors are Math Retards! (Score:2, Informative)
With a mirror 1.5 times the size of the Hubble mirror....
No, it's 2.3 times the size.
It's 1.5 times the diameter of the Hubble mirror. That equals 2.3 times the size.
Some days, you just gotta wonder about the /. editors' intelligence....