HartRAO Home

HartRAO Home > news > NASSP and Rhodes University Students Radio Astronomy Practical 2004/09/03-9


NASSP and Rhodes University Students Radio Astronomy Practical 2004/09/03-9


Students of South Africa's National Astrophysics and Space Science Programme arrived at HartRAO on 2004 September 3 to start their radio astronomy practical. A total of fifteen NASSP students participated, and were joined by three Physics Hons students from Rhodes University, making this the biggest RA practical held at HartRAO (and making use of every available bed on site!)

group
Click on image for large version

The combined group of NASSP and Rhodes students, with Director Justin Jonas on the left.

Justin started the students off with measuring the noise figure of a microwave receiver, of the type installed on the radio telescope. This was followed by calibrating the receivers on the telescope by means of drift scans through standard radio sources, and then deriving the aperture efficency of the telescope in each receiver band.

Having calibrated the telescope, the students observed some objects with "unknown" radio characteristics - the planets Jupiter and Venus, the prototype quasar 3C273, and the well-known Orion Nebula.

On Monday Mike Gaylard introduced the students to spectroscopy at radio frequencies. The photographs below capture some of the action.

Mike
Click on image for large version
Mike started with a discussion of the types of spectra we can observe at optical wavelengths, and asked the students to predict what we should see from an incandescent lamp and from a fluorescent light.

incandescent lamp
Click on image for large version
The students used Project STAR spectrometers to test their predictions, and are seen here using them on an incandescent lamp.

fluorescent lights
Click on image for large version
The overhead fluorescent lights were the next target.

PC screen
Click on image for large version
The next challenge was predicting the spectrum of light from PC screen showing a predominantly white image. Rhodes University PhD student Adrian Tiplady found his PC was the centre of attraction.

Sun
Click on image for large version
The last test was the spectrum of the Sun, observed by looking at the sunlight scattered by the blue sky.

For most of the students, this was the first time that they had used a spectrometer.

Orion nebula spectrum
Click on image for large version
The students then moved on to radio spectroscopy, and as an example, the spectrum of the radio emission from a gaseous nebula (HII region). These produce both broadband continuum emission and line emission at discrete frequencies from the ionised hydrogen gas. After an introduction to the theory, the Orion nebula was used as a target for spectroscopy of a recombination line from its ionised hydrogen. The brightness temperature of the radio continuum emission at 5 GHz was measured by means of a drift scan across the nebula, and the autocorrelation spectrometer was then used to observe the H100alpha emission line. Here Mike shows how instrumental effects are minimised by combining an on-source spectrum and an off-source spectrum.

reducing data
Click on image for large version
The students at work obtaining the temperature of the Orion nebula from their data.

microwave amp
Click on image for large version
Justin explains how we measure the performance of a microwave amplifier.

microwave performance
Click on image for large version
Getting down to the measurements - attaching the cold load, housed in a bath of liquid nitrogen, to the input of the microwave amplifier.

drift scans
Click on image for large version
Students measuring the antenna temperature in left- and right-circular polarization from a drift scan through a calibrator radio source, having imported the data into a spreadsheet.

sun map 1
Click on image for large version
Sarah Buchner sets up an input file on the control computer for making a map of the Sun.

sun map 2
Click on image for large version
Sarah explains how to map the radio emission from the Sun by making a raster map of scans across it.