Flashcards

Roland Schenkel
Flashcards 101 Flashcards
Students 12 Students
Language English
Level University
Created / Updated 17.01.2012 / 23.01.2021
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0 Exact answers 89 Text answers 12 Multiple-choice answers
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Principle of the correlation of the two signals from the two telescopes

crosscorelation: shift one data series to the other until the best match is found.

Signal to Noise Ratio very bad => long observation (up to 10’)

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What do you see? (Fig. 2.3)

Map of known and used (ICRF) Quasars

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Wie funktioniert VLBI?

Minddestens zwei Radioteleskope messen die Signale, welche von eine Quasar ausgesendet werden. Dabei werden die Daten mit einem Zeitstempel versehen um sie danach korrelieren zu können. So können danach die Laufzeitunterschiede vom Quasar zum einen oder anderen Teleskop ermittelt werden.

Daraus können Positionen abgeleitet werden.

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How big are Quasars?

Quasars are cores of galaxies. Seen from Earth they have often a complex structure and an extension of up to 60''.

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Where in de Observation Equation of VLBI do you find the coordinates of the Quasars?

In the unit vector (e) poiting to the Quasars (barrycentric coordinate system)

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What is a barycentric intertial system?

Static coordinate sysstem with origin in the barycenter of the solar-system (or Earth-Moon-System)

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Transformation from barycentric to earth fixed system? Parameters?

Lorentz-Transformation, Speed is the only parameter

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What is that strange PNUXY?

Transformation from Earth-fixed to space-fixed, P: Precession, N: Nutation, U: Rotation matrix with Greenwich sidereal time as argument, X,Y: Polar motion