The Herschel Telescope Close To Blast Off

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.'"

Comments

Cant wait

[dilvish_the_damned]

till they first post the images from this baby.

Re:Cant wait

[Chris Burke]

Given the additional 1m on the reflector, it'd be safe to assume a far better performance than Hubble.

Yep. Meters matter. A lot. The summary says the mirror is 1.5 times as big (3.5m/2.4m), but really area and thus quantity of incident light is what matters so it's more like 210% as big as Hubble (3.5^2)/(2.4^2). This is a big space telescope. All else being the same, I'd expect this to show a good deal more distant/faint objects.

It says it's infrared, so this may be more comparable to Spitzer than Hubble. Spitzer is only 0.85m. This beast is 17 times the light bucket Spitzer is.

Re:Cant wait

[mcgrew]

gaze at really cold places and objects in the Universe

I would think a stethoscope would be a better instrument for examining my ex-wife's heart!

Re:Cant wait

[MBGMorden]

Due note too, that the James Webb Space Telescope (the US's next telescope slated to launch in 2013, assuming funding doesn't dry up) is slated to have a 6.5m mirror, which should produce some REALLY nice results.

Re:Cant wait

[Anonymous Coward]

In addition to that, the JWST will feature a micro-shutter array, composed of over 62,000 individual shutters in the area of a postage stamp. The idea is that each shutter can be independently opened and closed so visible light from near, bright objects can be blocked out making it easier to view objects that are further away.

I had the opportunity to tour the clean room at Goddard Space Flight Center where the array is being fabricated. The techniques used seemed to mirror the techniques used to manufacture modern microprocessors. It was very interesting to be guided through the process, there are definitely some incredibly smart people at Goddard.

Here is some more information and pictures of the array.

Re:Cant wait

[Nyeerrmm]

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.

not about imaging

[Anonymous Coward]

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.

It will be intresting for sure

[SGDarkKnight]

As for all the new discoverys i'm sure these new telescopes will find, i'm curious if they will do the same thing with these as they did with the hubble, by pointing it at a "black" region of space and leaving it there for a while gathering exposures, only to discover that the region wasn't "black" at all, it was completely filled with all sorts of different galaxies, and this was only a small point in space they were looking.

Here is the link for the Hubble info in case you're intrested.

http://hubblesite.org/newscenter/archive/releases/1996/01/text/

Re:It will be intresting for sure

[ceoyoyo]

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:It will be intresting for sure

[physburn]

Being infrared means it will much better good chance to find exo-planet and asteroid belts. Wonder which of the Herschel or Kepler missions will find more planets.

Extra Solar Planets Feed, Astronomy Feed

Re:It will be intresting for sure

[Anonymous Coward]

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:It will be intresting for sure

[ceoyoyo]

Kepler. Kepler is designed to find lots and lots of planets.

Herschel is general purpose, so it will spend a lot of it's time looking outside the galaxy. But it should be very useful for looking in more detail at the planets Kepler finds.

Re:It will be intresting for sure

[James Youngman]

This is somewhat ironic considering that William Herschel discovered a planet (Uranus) while Kepler did not.

Re:It will be intresting for sure

[ceoyoyo]

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 for the Hubble deep field, and the original paper (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.

Infrared?

[oneiros27]

If it's in infrared, then it's NOT a Hubble replacement, it's a Spitzer replacement.

Re:Why not visible light?

[StaticEngine]

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?

[mjaga]

It's because it makes sense to use space telescopes to look at radiation that can't be observed with ground based telescopes, because the Earth's atmosphere absorbs all of it. Herschel with its three instruments (HIFI, PACS and SPIRE) operates in the submm and far infrared, a part of the spectrum inaccessible from ground, and will spend a lot of observing time e.g. to look at interstellar water, a molecule believed to play an important role for the cooling of star forming clouds.

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[account_deleted]

Comment removed based on user account deletion

Re:hubble mistakes?

[sidyan]

As described in here, the point of putting the observatory in a Lissajous orbit around the Earth-Sun L2 Lagrange point is to have the three nearest and largest sources of infrared light pollution (the earth, the moon, and the sun) sufficiently far away and in the same hemisphere relative to the observatory, allowing for a clear viewing angle anywhere in the other hemisphere.