wthomp

For those wondering if we could get sharper images with JWST, here’s the previously imaged black hole (same angular size as our own) compared to a single pixel from Hubble’s wide field camera 3:

https://twitter.com/alex_parker/status/1116070667068170240?s...

JWST will have smaller “pixels” but is in the same ballpark.

Unfortunately JWST won’t come close to being able to resolve Sgr A*. They measured its diameter in micro-arcseconds, whereas JWST’s limiting resolution will be measured in 10s-100s of milli-arcseconds.

For mercury, the L1 and L2 points would be closer to the planet.

Many circumstellar disks have been detected, but this is the first unambiguous detection of a circumplanetary disk. This is believed to be material swirling around a protoplanet, accreting on to it, and perhaps, forming moons. The actual processes of how planets form out of protoplanetary disks are still not well understood, so observations like this will help narrow things down. Quite impressive that they were able to resolve it with ALMA.

The diffraction limit is the fundamental resolution limit of a telescope. This is the size of "spot" that will be created on the camera sensor for a single point of light like a star [1].

Its easy to calculate, just take the wavelength of the of light you want to observe and divide it by the diameter of the primary mirror (and multiply by ~1.2).

For example, for JWST observing in the mid-infrared, say 4micron, with a 6.5 meter diameter mirror, has a resolution limit of: 4e-6 / 6.5 = 6.15e-7 Or about 0.6 micro-radians (astronomers would normally use arcseconds but leaving in radians for clarity).

This is just the theoretical limit though, it's reduced by any imperfections in the optics, and for telescopes on the ground, it's limited by the blurring of the Earth's atmosphere to about 4 micro-radians.

For narrow fields of view, however, ground-based telescopes can use adaptive optics to compensate for this shimmering/blurring in real time and reach close to their theoretical diffraction limit. Plus, they can be much bigger since we don't have to launch them into space. I'm not familiar with the MGT but this might be how it will surpass JWST in terms of resolution (which again also depends on the wavelength).

For infrared observations though, a huge effect that can't be compensated for is sensitivity. At mid-infrared wavelengths, the Earth's atmosphere actually glows and makes it much harder to see faint sources. This is one of the ways JWST will really shine.

[1] Note however that you can still do things like measure the position of an object to less than the diffraction limit using e.g. centroiding. But you can't tell if there are two objects or one below this limit.

This related blog post also talks about the history of the symbol and programming:

https://cormullion.github.io/pages/2020-10-09-asterisk/