  According to the cosmological principle, the Universe should appear
isotropic, without any preferred directions, to an observer whom we may
consider to be fixed in the co-moving co-ordinate system of the expanding
Universe. Such an observer is stationary with respect to the average
distribution of the matter in the Universe and the sky brightness at any
frequency should appear uniform in all directions to such an observer. However
a peculiar motion of such an observer, due to a combined effect of Doppler
boosting and aberration, will introduce a dipole anisotropy in the observed sky
brightness; in reverse an observed dipole anisotropy in the sky brightness
could be used to infer the peculiar velocity of the observer with respect to
the average Universe. We determine the peculiar velocity of the solar system
relative to the frame of distant radio sources, by studying the anisotropy in
the sky brightness from discrete radio sources, i.e., an integrated emission
from discrete sources per unit solid angle. Our results give a direction of the
velocity vector in agreement with the Cosmic Microwave Background Radiation
(CMBR) value, but the magnitude ($\sim 1600\pm 400$ km/s) is $\sim 4$ times the
CMBR value ($369\pm 1$ km/s) at a statistically significant ($\sim 3\sigma$)
level. A genuine difference between the two dipoles would imply anisotropic
Universe, with the anisotropy changing with the epoch. This would violate the
cosmological principle where the isotropy of the Universe is assumed for all
epochs, and on which the whole modern cosmology is based upon.

Cosmology and Nongalactic Astrophysics;Space Physics