Beamwidth of the SRT
Objective: Students will measure the beamwidth of the
Small Radio Telescope and compare with the diffraction limit for the telescope
and wavelength.
Introduction: Students should have completed the
“Beamwidth of the Eye” activity or should at least read the introduction to
that activity.
1.
Open your data in a spreadsheet. One column should be Azimuth and the other should be
Temperature.
2.
Correct your angle for elevation. A degree of azimuth at a high elevation is smaller than a degree
of azimuth at low elevation. Make an
angle column using the formula: angle = azimuth * cos(elevation).
3.
Plot the angle (x-axis) vs the temperature (y-axis), and
print the graph (full page). Draw a
smooth curve of the data. (Don’t
connect-the-dots).
4.
Draw a horizontal line at the minimum temperature you
measured.
5.
Draw a horizontal line at the maximum temperature you
measured.
6.
Draw a horizontal line at the average of the maximum and
minimum temperatures.
7.
Find the two angles where the temperature curve intersects
the average temperature line.
8.
The difference between these two angles is the beamwidth of
the SRT.
9.
Find the diffraction limit of beamwidth for a telescope the
same size as the SRT at 1419 MHz.
2.
What factors other than diffraction could affect the
beamwidth of the SRT?
3.
How large would a radio telescope at 1419 MHz have to be to
have approximately the same beamwidth as your eye?
Things to
Try:
2.
Radio astronomers are interested not just in the beamwidth
but in the shape of the beam. Measure
the shape of the SRT beam by writing an appropriate command file and making a
surface plot of the results. (This is
not a small project).
3.
Could you measure the beamwidth of the SRT using something a
source other than the sun? Try and see.