Questions tagged [vlbi]

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4 votes
2 answers

How is Earth's Rotation Angle (ERA) defined and measured

UTC typically ticks with TAI. But to keep UTC from drifting far from the rotation angle of the Earth we occasionally add leap seconds to ensure that UTC does not drift too far from the UT1 timescale. ...
13 votes
2 answers

Why hasn't VLBI been used to try and image giant exoplanets?

A Jupiter-sized object at 10 pc subtends an angle of 0.0001 arcseconds (100 micro-arcsec) at the Earth. The Event Horizon Telescope interferometry network is capable of a (demonstrated) angular ...
3 votes
0 answers

Mark 6 VLBI Recorder 32Gpbs, 2 bit sampling

I was reading the paper about the first M87 EHT Results, part 3 (link to article PDF), where the data processing pipeline is explained. The recording system used was a Mark 6 recorder with 32Gbps and ...
1 vote
1 answer

Why space-based VLBI scattering sub-structure is "Hopefully, a new promising tool to reconstruct the true image of observed background target(s)"?

@HDE226868 mentioned in the observatory that the GBT@20 – The Celebration; Twenty Years of Innovation and Discovery was going on. There are plenty of YouTube videos and slide sets available as links. ...
0 votes
1 answer

Did the Spectr-R space-based radio telescope use on-board accelerometer to measure non-gravitational acceleration for baseline correction?

This answer to Why is space-based VLBI scattering sub-structure "Hopefully, a new promising tool to reconstruct the true image of observed background target(s)"? summarizes the contribution ...
17 votes
2 answers

Is Optical VLBI theoretically feasible? If not why not?

There are plenty of optical interferometers in use with baselines of up to maybe 1km. As far as I can find out, they all work by directly collecting the light at all the telescopes, using mirrors to ...
9 votes
2 answers

How are the atomic clocks synchronised between worldwide VLBI telescopes?

I know that VLBI needs precise synchronised atomic clocks to calculate the baseline distance between the radio telescopes at cm level. But i cant´t find any information how the atomic clocks are kept ...
4 votes
1 answer

Why don't we build an interferometer between Earth and the Moon?

The Event Horizon Telescope (EHT) does interferometry from an array of telescopes spread all across Earth. The data is locally stored on a hard drive and shipped to a central location, so the ...
8 votes
1 answer

Why aren't GPS clocks sufficient to synchronize VLBI observations?

In very long baseline interferometry, it is typical to use a hydrogen maser atomic clock to sample data. However, given how expensive these atomic clocks are, it seems surprising that more ...
6 votes
0 answers

Did the Juno mission locate Jupiter at the same precision as Saturn (4 km)?

Juno's low perijove should be great for measuring Jupiter's gravitational effect on Juno's orbit. Cassini together with VLBI has measured Saturn's location to within 4 km. Will Was Juno be able to ...
7 votes
1 answer

Exactly what in Saturn has been located to within 4 km precision?

Saturn has been located with fantastic precision thanks to Cassini and VLBI. The location of the 120,000 km diameter giant planet (when defining the 1 bar pressure level as its surface) is known to ...