On 11/7/2011 1:14 AM, Szczepan Bialek wrote:
"The first observations of cosmic radio emission were made by the American
engineer Karl G. Jansky in 1932, while studying thunderstorm radio
disturbances at a frequency of 20.5 MHz (14.6 m). He discovered radio
emission of unknown origin, which varied within a 24-hour period. Later he
identified the source of this radiation to be in the direction of the centre
of our Galaxy. From: http://encyclozine.com/science/astronomy/radio

I understand that the frequency "varied within a 24-hour period". It is the
"diurnal effect".
And what about the 365 days period (annual effect)?
S*



You mean when earth is generally heading "towards" the galactic center
vs when earth is heading "away" from the galactic center?

People doing deep space navigation deal with this all the time, since
navigation is done by measuring the frequency of the received signal
from the spacecraft. There's nothing special about it. spacecraft on
some heliocentric trajectory, Earth on a different heliocentric
trajectory. Measure frequency shift, they use to determine spacecraft
trajectory by applying (mostly) Newtonian physics (you do have to use
relativistic corrections to get the last gnat's eyelash of precision).

Since you only get to measure in one direction, you have to make
assumptions about what's going on in the other directions, (e.g. cross
range), which can lead to disasters (Mars Climate Orbiter, most recently).

You can do various forms of VLBI and DeltaDOR to get some cross range
information, but nothing as good as what you're getting for range (where
velocity and range are measured to mm/s and cm sorts of accuracy)