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Comment by sandworm101 | Hacker News Reader

Can webb even point at tabby's? Ive never seen a strait answer on this, but i think webb's sunshield arrangement limits it to objects away from the ecliptic, which is fine if you are looking at stuff outside our galaxy.

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I've been curious about this as well and decided to look it up; there's a nice video that shows it off fairly well[1]. The sunshield is perpendicular to the light coming from the sun, as is the view from the telescope, though the sunshield is large enough that it can be off several degrees and still keep the telescope in shadow. You can rotate the telescope about that axis and remain perpendicular to the sun allowing a 360 degree view forming a plane. As it orbits around the sun that plane is hitting a different slice of the sky so over the course of 6 months you can view everything.

[1] https://webbtelescope.org/contents/media/videos/1157-Video

That explains the contradictory statements I've seen over the years. The program can view the entire sphere over a period of a year, but at any one moment the telescope only has access to see stars within a particular plane. So it isn't available for ad hoc targeting of interesting things as they happen (nova, transits etc) unless they are in the plane of available options at that moment.

That also meshes with the cultural issued behind the scenes. JWST has always been more of an stellar astronomy and cosmology instrument. It won't be much use in looking at closer/moving things like Oumuamua or phenomena like Tabby's star transits that occur at very particular times. So it isn't an instrument for so-called "planetologists", which is the hot field in modern astronomy but was barely a thing when JWST began.

Of course JWST is an instrument for studying exoplanets (among other things). Something like 24% of the first year’s approved observing proposals are for doing just that. There are coronagraphs in two of the main instruments, all specifically meant for exoplanet observations.

https://eos.org/features/overture-to-exoplanets

Exoplanets are one type of planet and their detection is really just a subset of stellar astronomy in that it relies on stellar instrumentation. The hot stuff these days is within the solar system, especially since since the Pluto flyby. Minor plants, planet X, extra-solar objects (Oumuamua) and the hunt for life within our solar system ... these are the big areas of public interest in the next decade and will be the focus for planetology (I still cannot say that without thinking of Herbert).

OK, you're really not making much sense. I mentioned exoplanets because that was a (barely) plausible interpretation of something that was a "hot field in modern astronomy but was barely a thing when JWST began", since the preliminary studies for JWST did happen in the mid-1990s, when exoplanets were first beginning to be found. The actual serious design work, though, was in the early 2000s, when exoplanets were definitely a hot topic.

But if what you really mean is "within the solar system" (which, um, excludes "Tabby's star"), well... "barely a thing when JWST began" is complete nonsense. I mean, studying things within the solar system is something astronomy has been doing for literally thousands of years. (And, no, it hasn't suddenly become "the hot field" in any sense, leaving aside the point that there are multiple things that might be considered "hot fields" at the moment, and that there's never a single "hot field" anyway.)

JWST is perfectly useful for solar-system science: there are about 22 approved Cycle 1 General Observer proposals in that field, including one specifically meant for any "interstellar object" (like 1I/'Oumuamua or 2I/Borisov) that might show up during the first year: https://www.stsci.edu/jwst/phase2-public/2337.pdf

And the second-largest set of Guaranteed Time Observation proposals (proposals from "scientists who helped develop the key hardware and software components or technical and inter-disciplinary knowledge for the observatory"), after "Extra-solar Planets", is "Solar System": https://www.stsci.edu/jwst/science-execution/approved-progra...

Webb can 'see' everything but objects between Webb's location and the sun. At each moment, it's limited to part of the sky, but over a whole year, it can observe in all directions.

It's constrained to about 10 degrees in the roll axis, 50 degrees in pitch (-5 to +45), 360 in yaw. At any given moment, it can point anywhere in about 39% of the full sky (inner solar system excluded of course), but can access the entire sky over a period of 6 months.

see: https://jwst-docs.stsci.edu/jwst-observatory-characteristics...

Or in video form: https://www.youtube.com/watch?v=y0bOi3kVIBs

Perspective is funny. When I think of it hanging out there in space I think of it as having 360 in roll. But I guess if you were facing in the direction of the mirror that would be 360 in yaw.

yeah, really depends on the coordinate system you use but to me it's like a square-rigged ship with the sunshade as the hull, the tower as mast, and the main mirror as sail.

And it's consistent with the terminology used to describe parts of the sunshade during deployment -- fore/aft sunshield pallets, port/starboard sunshield booms..

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