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# What is the VLBI technique?

## What is the VLBI technique?

VLBI is a geometric technique: it measures the time difference between the arrival at two Earth-based antennas of a radio wavefront emitted by a distant quasar. Since the antennas are fixed to the Earth, their locations track the instantaneous orientation of the Earth in the inertial reference frame.

Why is VLBI important?

VLBI produces very precise distance measurements on the Earth’s surface, allowing us to learn about the Earth’s size, its shape, variations in its spin rate, changes in the orientation of its polar axis—all by observing quasi-stellar objects (quasars) and other natural radio sources.

### How precise is VLBI?

VLBI Love number determinations have been shown to have a precision of better than a centimeter in terms of equivalent displacement (Herring et al., 1983, Carter et al., 1985).

What is a baseline astronomy?

There are several definitions of baseline in astronomy: In radio astronomy a baseline is the vector connecting two radio telescopes that is used in interferometry to determine the fringe rate of a source at the nominal “phase centre” of an observation.

## What is the Very Long Baseline Interferometry VLBI and why is it important?

Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.

What is a baseline in astronomy?

### What is the baseline of a telescope?

In radio astronomy a baseline is the vector connecting two radio telescopes that is used in interferometry to determine the fringe rate of a source at the nominal “phase centre” of an observation.

What are the two most important properties of a telescope?

The two most important properties of a telescope are:

• Light gathering ability – The better a telescope can gather light, the better you will be able to see far away stars and faint objects in the night sky.
• Magnification – The magnification of a telescope describes how much larger the telescope can make objects appear.

## How do interferometric telescopes work?

So, how does interferometry work? An interferometer combines the light from two or more telescopes, allowing astronomers to pick out the details of an object as though they are being observed using mirrors or antennas measuring hundreds of metres in diameter.

What are the two most important properties of a telescope Choose 2 answers?

The two most important properties of a telescope are its light-collecting area and its angular resolution. A telescopes light-collecting area tells us how much total light it can collect at one time.

### What is the most important part of the telescope?

The most important aspect of any telescope is its aperture, the diameter of its main optical component, which can be either a lens or a mirror. A scope’s aperture determines both its light-gathering ability (how bright the image appears) and its resolving power (how sharp the image appears).

Who built the first practical reflecting telescope?

Isaac Newton
In late 1668 Isaac Newton built his first reflecting telescope. He chose an alloy (speculum metal) of tin and copper as the most suitable material for his objective mirror. He later devised means for shaping and grinding the mirror and may have been the first to use a pitch lap to polish the optical surface.

## How is the VLBI IVs used in geodesy?

The IVS contributes to geodesy via measurements used in geodetic VLBI, an extremely accurate technique for making high-precision global measurements of the speed and angle of the Earth’s rotation to millimeter accuracy. VLBI also allows measurement of tectonic plate movement. VLBI is also important in astronomy and astrometry.

How is VLBI used to measure the movement of tectonic plates?

Geodetic VLBI also allows scientists to measure the movement of the Earth’s tectonic plates extremely accurately. VLBI measurements of the distance between the radio antennas at Westford, Massachusetts, and Wettzell, Germany, show that North America and Europe are separating at a steady rate of about 17 millimeters per year.

### How is VLBI used to measure the San Andreas Fault?

Scientists also use geodetic VLBI to measure changes in the position of the San Andreas fault in California, as the Pacific plate slips past the North American plate at the rate of about 5 centimeters per year. Visit these other excellent sites to learn more about VLBI and many of its implementations, as well as groups related to the IVS: