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Comment by petschge | Hacker News Reader

The limit in some sense is the size of the Earth. This picture is from an interferometer observing at very high radio frequencies (wavelength of 1.3 mm) using telescope around the Earth. To improve resolution you would either have to go to even higher frequencies (we have a very hard time doing interferometry there) or find baselines larger than what fits on Earth. And you don't just need a long baseline, but need to keep the baseline constant to within a fraction of the wavelength. So if you want to use satellites to get longer baselines you would have to know their orbit to within a tenth of a millimeter.

As an aside: that image is basically black and white. The intensity is just mapped to black -> orange -> white instead of black -> gray -> white.

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I wonder how important time is in collecting these data? Because if 6 months isn’t an issue, then the array size could be expanded in one axis to the diameter of Earth’s orbit around the sun, no?

The collecting time is important, but mainly to 1) sample the rotation of the Earth in the Fourier space for better angular resolution and 2) for raising your overall signal-to-noise ratio is the image (but the one released is already pretty good, so not much improvement can be done there unless you're trying to go for the faint features in the image).

Unfortunately, you can only do interferometry with simultaneous measurements (we need information about the difference in the phase of light hitting the receiving antennas), so the motion of Earth around the Sun is largely irrelevant, unless you can park another antenna at a trailing orbit (see space VLBI for that).

What you're thinking of is probably parallax measurements of distance - that's how missions like Gaia can pinpoint distances to stars in Milky Way (and some in its satellites as well).

Thanks.

We seem to need a big radiotelescope on the moon then? That should give simultaneous measurement on a much larger baseline?

I doesn't even need to be that big. A 60 meter dish would do nicely.

Problem is, you would want to have several Gigahertz of (radio) bandwidth. You are not going to down link that raw, but rather as a number of channels, integrated over a number of microseconds and digitized at something between 4 and 64 samples per bit, but we are still talking a down link data rate of gigabits per second.

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