<p>I'm not asking about the astronomical equipment itself. I'm asking about the auxiliary equipment and modeling needed to enable the primary astronomical equipment to work properly at the sub-milliarcsecond level. Things such as clocks, software models of the Earth's rotation, etc. How accurate does the timing need to be? How accurate does the modeling of the Earth's rotation need to be? Do Earth tides need to be taken into account?</p>
<p>Some astronomers are claiming to perform microarcsecond astronomy. I would assume that that is even more stringent than milliarcsecond astronomy. How much more stringent?</p>
<p><a href="https://astronomy.stackexchange.com/a/50412/2618">This answer</a> suggests timing accuracy (UT1) needs to be in the tens of milliseconds for arcsecond astronomy. That suggests tens of microseconds accuracy for milliarcsecond astronomy, and tens of nanoseconds accuracy for microarcsecond astronomy.</p>

CC BY-SA 4.0
2022-11-02T12:45:59.493Z
Cool question; is it wavelength agnostic? Does "sub-milliarcsecond" apply to both resolving power and astrometric position measurements?
uhoh
CC BY-SA 4.0
2022-11-02T12:48:00.503Z
@uhoh I think sub-milliarcsecond astronomy (and finer) is typically in the realm of radio astronomy. I don't think visible wavelength astronomy is up to the task. At least not yet.
David Hammen
CC BY-SA 4.0
2022-11-02T12:48:20.710Z
potentially helpful: [Will the Magdalena Ridge Optical Interferometer be able to image extended objects like the surface of the Moon?](https://astronomy.stackexchange.com/q/33914/7982)  0.5 mas (potentially) and its predecessor, the [Navy Precision Optical Interferometer](https://lowell.edu/research/telescopes-and-facilities/npoi/)
uhoh
CC BY-SA 4.0
2022-11-02T12:48:39.037Z
Related: [What programs do astronomers use to ensure their observatory control computer has accurate time?](https://astronomy.stackexchange.com/questions/50365)
David Hammen
CC BY-SA 4.0
2022-11-02T16:48:48.007Z
As an example, the ESO Very Large Telescope Interferometer instrument [GRAVITY](https://www.eso.org/sci/facilities/paranal/instruments/gravity/inst.html), operating in the near infrared at K band (2.2 microns), has 10-100 microarcsecond astrometric precision with 3 milliarcsecond resolution. This implies centroiding to 1/30th of a resolution element/pixel which has bearing on the achieved astrometric accuracy - non adaptive optics ground-based images will have a pixel scale at best of ~0.2-0.4"  so 1/30th pixel centroiding gives ~10mas precision at best
astrosnapper
<observational-astronomy>
What special auxiliary equipment / modeling are needed for ground-based sub-milliarcsecond astronomy?
David Hammen
# What special auxiliary equipment / modeling are needed for ground-based sub-milliarcsecond astronomy?

(Asked by: username_0 on 2022-11-02)

I'm not asking about the astronomical equipment itself. I'm asking about the auxiliary equipment and modeling needed to enable the primary astronomical equipment to work properly at the sub-milliarcsecond level. Things such as clocks, software models of the Earth's rotation, etc. How accurate does the timing need to be? How accurate does the modeling of the Earth's rotation need to be? Do Earth tides need to be taken into account?

Some astronomers are claiming to perform microarcsecond astronomy. I would assume that that is even more stringent than milliarcsecond astronomy. How much more stringent?

[This answer](https://astronomy.stackexchange.com/a/50412/2618) suggests timing accuracy (UT1) needs to be in the tens of milliseconds for arcsecond astronomy. That suggests tens of microseconds accuracy for milliarcsecond astronomy, and tens of nanoseconds accuracy for microarcsecond astronomy.

**Tags:** observational-astronomy

> **Comments:**
> **username_1**: Cool question; is it wavelength agnostic? Does "sub-milliarcsecond" apply to both resolving power and astrometric position measurements?  
> **username_0**: @username_1 I think sub-milliarcsecond astronomy (and finer) is typically in the realm of radio astronomy. I don't think visible wavelength astronomy is up to the task. At least not yet.  
> **username_1**: potentially helpful: [Will the Magdalena Ridge Optical Interferometer be able to image extended objects like the surface of the Moon?](https://astronomy.stackexchange.com/q/33914/7982)  0.5 mas (potentially) and its predecessor, the [Navy Precision Optical Interferometer](https://lowell.edu/research/telescopes-and-facilities/npoi/)  
> **username_0**: Related: [What programs do astronomers use to ensure their observatory control computer has accurate time?](https://astronomy.stackexchange.com/questions/50365)  
> **username_2**: As an example, the ESO Very Large Telescope Interferometer instrument [GRAVITY](https://www.eso.org/sci/facilities/paranal/instruments/gravity/inst.html), operating in the near infrared at K band (2.2 microns), has 10-100 microarcsecond astrometric precision with 3 milliarcsecond resolution. This implies centroiding to 1/30th of a resolution element/pixel which has bearing on the achieved astrometric accuracy - non adaptive optics ground-based images will have a pixel scale at best of ~0.2-0.4"  so 1/30th pixel centroiding gives ~10mas precision at best  

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