SRT
Learning to use the Small Radio Telescope (SRT)
Objective: Students
will learn the basic functions of the SRT interface, and some basic terms of
radio astronomy.
The small radio telescope comes with a software controller
written in the JAVA computer language. This tutorial is to help you get started
with the software and the telescope. Start up the program in either the simulation mode or the normal
(telescope controlling) mode.
1.
A map of the sky.
Standing on the earth’s surface,
you can see approximately half of the sky. The other half you could see if the earth was not there! Maybe you can see less than half, if your
view is obstructed by trees or buildings. On your screen is a map of the sky.
The numbers on the axes are the
coordinates of points in the sky in the reference frame of your telescope. Azimuth,
on the x-axis, tells you the direction on a compass in degrees relative to
north. Elevation, on the y-axis is the angle of the object above the
horizon. Your computer already knows
the location of some objects in the sky.
2. Moving the
telescope to point at an object.
To point the telescope at one of the objects, click
on the object on the map. Then click
“track” at the top of the screen. The
telescope will move to point at the object.
3.
Moving the telescope to point at any point in the sky.
You can send the azimuth and
elevation of any point in the sky directly to the SRT. To do this, click on the “azel” button at
the top of the screen. Then click in
the text field at the bottom left of the screen. Type the azimuth in degrees, followed by a space, followed by the
elevation in degrees. Then hit
enter. The telescope should begin to
move.
4.
Making a frequency plot for a source.
A radio source is an object in the sky that emits
radio waves. One thing we are
interested in is the frequency of the radio waves that these sources emit. Click the “freq” button at the top of the
screen. Then type in the text box: “1420.4 51”. This tells the telescope to take readings in 51 bins centered at
1420.4 MHz. The default width of a bin
is 0.04 MHz. When you point the
telescope at a source or point in the sky, the frequency vs. temperature
(intensity) plot will be displayed in the upper right portion of the
screen. The plot on the right is
updated each time the intensity is measured at each frequency, while the plot
on the left is a time average of all the measurements.
5.
Doing a “25 point plot” of the sun.
We can see if the telescope is
pointing in the correct direction by making a 25 point scan of the sun. Choose the sun as the source and point the
telescope there. Click “freq” and type
“1419 1”. You want only one
frequency. Click “npoint”, and
wait. The telescope should now scan the
area around the sun. When the telescope
is finsihed, it will make a plot of the sun in a small window next to the
frequency plot window. If the sun is
centered on the plot, the telescope is pointing correctly. If it is not, you can enter corrections
using the “offset” button. Click the
offset button and enter azimuth <space> elevation of the correction in
the text box.