binary star - Is the angular resolution of a telescope irrespective of used eye-piece?

The Raleigh criterion is the maximum theoretical limit that ignores the architecture, quality, and state of maintenance of optics. It basically says "assuming the optics in this instrument are PERFECT, this is the resolution you could get out of it". It's a calculation that looks only at the diameter and ignores everything else. In other words, no matter how good the instrument, you cannot beat Raleigh - but you could make things worse.

In practice, of course things are worse. Take a parabolic mirror, as used in many telescope architectures, such as the newtonian. All parabolic mirrors generate perfect images only in the center of the field of view. Anything off-center is subject to coma, an aberration that even "perfect" paraboloids will exhibit. So the real resolving power gets worse as you move towards the edge of the field.

On top of that, you have to add real-world manufacturing imperfections that any mirror will have. Also add distortions caused by temperature differences, etc.

All these contribute to distort the image formed in the focal plane of the primary mirror. The eyepiece's role is to examine and magnify that image, for you to see. That's how telescopes work - primary optics form an image in the primary focal plane, which is then examined with the eyepiece.

Of course the quality of the eyepiece will contribute to further degradation of what you actually see. Even with "magic" primary optics, if you had a "perfect" image in prime focus, a bad eyepiece will blur it. In real life, most eyepieces are at least half-decent in the center of the field (some are not), but quality degrades towards the edge. High quality eyepieces will not introduce visible degradation in the center and over most of the field. Top of the line eyepieces will not degrade the image visibly anywhere.

meteorite - Blowing up an asteroid/comet really potentially worse?

Well there are some things to consider. Initially if you could make sure that after you blow up an asteroid you will end up with numerous but small enough pieces so that they will either: one, burn up in the atmosphere or two, be headed away from Earth (and not hitting us five years later) then we are OK, and blowing up the asteroid with a missile would be a fair solution.

The problem here lies in the fact that we know little about the internal composition of asteroids in general, and presumably even less about a particular one, so it is very hard to predict exactly where the pieces of the asteroid generated by an impact are or aren't going to end up or, be headed towards or even its size.

Another scenario could be that if you effectively smashed the asteroid into small pieces that could then burn into the atmosphere, and if those pieces were coincidentally to end up being consumed by Earth's atmosphere, it would heat up provoking presumably an unpleasant day on Earth of course depending on the mass of the object.

But there is a much better solution than that Armageddon-Hollywood inspired one. It is call gravitational tethering. There is something we know, and we know very well about asteroids, and that would be their trajectory paths or orbits. Even when a new asteroid is discovered, its orbit can be computed pretty quick and with great accuracy (because we know the solar system's gravity very well). So if an asteroid is to impact Earth, it is likely that we will know with years, probably decades in advance. And so we can just send a space vehicle (called gravity tractor), with enough mass and time in advance, and place it just beside the asteroid, hence allowing us to tilt its orbit by just a tiny amount, due to the gravitational pull between the two objects. Now when you consider the effect of that tiny amount in the long run, it effectively deflects the path of the given asteroid from that of the Earth so that it won't hit us 20 or 30 years later.

And this is something we have control over, and something we can predict with great accuracy. It is the (safe) way to go.

If you are still not happy with my answer, you can listen to Neil de Grasse Tyson himself explaining it in this 5 min video.

Also check out this talk from the American Museum of Natural History on "Defending Earth from Asteroids" LINK

Further reference here.

biochemistry - Does GFAJ-1 use Adenosine triarsenate as its energy currency?

This is a cool topic/question.

To answer your question. The hypothesis was based on the conjecture that there was so little phosphorus in the culture medium that phosphorous would have been replaced by arsenic in all its roles in the cell. IF they had found arsenate DNA, it would have been derived from NTAs (nucleotide tri-arsenates) or a hybrid Phosphorous/Arsenic analog of the compound as DNA polymerase consumes NTPs to create DNA. If there were only NTAs to drive DNA biosynthesis, then the cell's energy cycle would also have had to use ATA.

BUT

The primary evidence was that the mono lake strain grew in a fermentor (culture) with lots of arsenic (which is impressive) and very little phosphorous. how little? 3 micromolar. The investigators say that they did add a little phosphorus (3-5 micromolar), which, after some more careful accounting, appears to be enough to keep the bacteria growing at the observed rate without using arsenate nucleotides (submitted to Science).

This is not completely surprising as the original publication in 2010 of a preliminary finding in Science Express which only had x-ray abosorbtion fine edge spectroscopy work consistant with an arsenate like that found in a phosphorus backbone. Given that they did not produce a more direct reading of the compounds such as mass spec or an NMR experiment, this looked pretty iffy in the first place.

You an see why arsenic life was so improbable - a dozen (or more) vital pathways in the cell would have to adapt to use NTAs - pretty much all at once. If they had I suspect Mono lake would be full of those suckers.

Its sort of a bummer, for those of us who want to discover new forms of life, but you can't find what isn't there.

If we built one hundred 3m telescopes and point them to a single star what would be the final resolution?

We'll mount all of them in a same location and connect them to each other (like VLT) so they will combined all the results and will produce some staggering images however my question is, would they be able to produce an image close to the resolution of a 300m optical telescope?

light - Longest and shortest wavelength

Well, I don't think this question is entirely answerable. The true answer, I think, is that there really are no limits, as Rob Jeffries commented.

However, using Wikipedia as my only source, the crab pulsar holds the current record for most energetic gamma ray emissions at 80 TeV (wavelength of about $1.5times10^{-11}$nm).

Whereas the longest detected wavelength would surely only be limited by our detector sensitivity. Any imaginable wavelength could be lengthened further by an arbitrary factor via, for example, scattering.

EDIT: Source: Gamma-ray Astronomy (Wikipedia)

What happens to the information on the event horizons of two merging black holes?

Not every scientist agrees that information is "encoded" on the surface of a black hole. Many scientists believe black holes actually destroy information. In fact, Stephen Hawking and Kip Thorne made a famous wager against John Preskill about whether information is destroyed by black hole.

The simplest (and in my opinion, most likely) answer to your question is that black hole event horizons don't encode any information at all. The black destroys it. Which is why we say "black holes have no hair". Once you make a black hole out of any material, you can no longer tell what went into it. If you make one of photons or neutrinos or neutrons or whatever, all you know after the black hole forms is the amount of mass/energy it contains.

So when two black holes collide, their event horizons still contain zero information. Zero from the first black hole plus zero from the second.

human biology - What are differences between formation of embryonic disc in chick and mammal embryo?

Embryonic disc forms on top of yolk during cleavage on chicken embryo, while between amniotic sac and yolk sac inside blastocyst after implantation on human embryo.

---

Some further processes take place on and in the embryonic disc: specifically these here during the week 3.

Embryonic disc formation includes still during the 3rd week of development:

1. Formation of the primitive streak


2. Genesis of the germ layers


3. Genesis of the notochord

Formation of the primitive streak: The process of primary neurulation appears to be similar in chick and mammalian. The embryonic disc becomes oval and then pear-shaped, the wider end being directed forward. Near the narrow, posterior end, the primitive streak makes its appearance and extends along the middle of the disc for about one-half of its length from migrated ectoderm cells.

Genesis of the notochord: “The notochord extends beneath the neural tube from the base of the head into the tail.” - As the mesoderm develops between the ectoderm and endoderm it is separated into lateral halves by the neural tube and notochord.

Figure 2: Neurulation. NB the use of neural groove is correct. Notochord is below neural groove. - Genesis of germ layers here: from a flat thing to a developed one.

Figure 3: Genesis of notochord and primitive streak. Yolk-sac surrounds notochord and primitive streak.