During the 12-hour period centered on
source transit, the interferometer traces out a complete elllipse on
the $(u,v)$ plane. The maximum value of $u$ equals the actual
antenna
separation in wavelengths, and the maximum value of $v$ is smaller by
the projection
factor $\cos\delta$, where $\delta$ is the source declination. If
the interferometer has more than two elements, or if the spacing of the
two elements is changed daily, the $(u,v)$ coverage will become a
number of
concentric ellipses having the same shape. Thus the synthesized
beam obtained by east-west Earth-rotation aperture synthesis can
approach an elliptical Gaussian. The synthesized beamwidth is
$\approx u^{-1}$ radians east-west and $\approx u^{-1} \sec\delta$
radians in
the north-south direction. The synthesized beam is circular
for a source near the celestial pole, but the north-south resolution is
very poor for a source near the celestial equator.
The
Australia Telescope Compact Array (ATCA) of six 22 m
telescopes on an east-west baseline located about 500 km northwest of
Sydney, Australia.
Image
credit