Our Radio Telescope

Our radio telescope

	The University of York's radio telescope was built by technicians in the workshop here. The telescope, seen under construction in the workshop on the left, was designed and built (with associated electronics) entirely at the University...
	...and here is the 3m diameter dish on the roof, ready for use by students and staff.
	These pictures show the drive mechanism for the telescope fitted with the brake on. This brake is used when the weather gets nasty and there is a danger of high winds damaging the telescope. Whilst this brake is on, the telescope is locked in position to prevent strain on the drive mechanism.

How to operate the telescope

The two sets of controls which are used to manoeuvre the telescope are in altitude and azimuth coordinates. The control box itself (as seen to the right of the picture below) consists of a brake system and a drive system. In order for the drive system to work in either the altitude or azimuth directions, you must first release the brake by holding down the brake switch, then holding down the drive switch. Thus as a safety measure, if the break switch is let go, the telescope will no longer turn.

1 Monitor for visual checking of telescope orientation and movement. 2 21cm Hydrogen line spectrometer. 3 Altitude indicator. 4 Azimuth indicator. 5 Altitude drive controls (up/down). 6 Azimuth drive controls (CW/CCW). 7 Drive unit power switch. 8 Altitude brake release switch. 9 Azimuth brake release switch. 10 Brake unit power switch.

Important safety information for students using the radio telescope

Whereas actually operating the equipment present little risk to yourself, there are risks to the equipment. To ensure that the telescope remains in good working order, all students must follow the following guidelines.

Wind

• It is highly important that when moving the telescope, you check that the winds outside are not too strong. To determine if it is safe to move the telescope, there is a wind sock near to the telescope which will give an indication as to whether it is safe to move the dish. If you are in any doubt, ask a technician. This is important, as if the telescope is moved in high winds, it will put strain on the gears and you may break it.
• If at any point you notice that the winds are getting strong, you must cease the experiment you are doing and return the telescope to the 'parked' position (altitude 90 degrees, azimuth 90 degrees), i.e. it should be aligned vertically to minimise the surface area of the dish exposed to the wind.
• Prior to any forecasted strong winds, it is likely that technicians will have locked the telescope in the 'parked' position manually. If not and you are using the equipment and believe there to be a danger to the telescope from winds, please contact a technician so that they can access the roof and lock the telescope manually.
• When leaving the controls for any significant length of time, please put the telescope in the parked position. The same goes for when you finish using the equipment for the day, the telescope should always be placed in the parked position.

Stuck gears

• It is often the case that when you are moving the telescope, the drive mechanism seems to become stuck and the telescope will move no further. This is probably due to dust and other debris becoming stuck in the gears and stopping them from turning. If this happens, simply attempt to move the telescope in the opposite direction and then back again. Do not rapidly press and release the drive controls as this could damage the motors.
• If the problem persists, contact a technician and they will access the telescope and assess the problem.

Choosing your radio source and making an observation

The radio waves that students predominantly observe with this telescope come from hydrogen clouds throughout the galaxy (or even in nearby galaxies). The system is thus set up to look at the 21cm (1420MHz) hydrogen spectral line. It is this specific wavelength which forms the basis of the radio telescope laboratory experiment, as this experiment involves looking at various regions in the plane of the Milky Way.

As it is most likely that students will be observing gas clouds within the Milky Way (although, as previously stated, it is possible to look at nearby galaxies), here is a rough guide to making observations:

• Decide where in the Milky Way you want look. The laboratory experiment will involve looking at a wide range of galactic coordinates, and to obtain the most useful information, you will usually be looking in the galactic plane (galactic latitude 0,0,0). For example, galactic longitude (0,0,0) with galactic latitude (0,0,0) will have you looking straight through the centre of the galaxy.
• You will next have to convert the galactic coordinates you have chosen into figures of altitude/azimuth coordinates so you will be able to point the telescope (controlled in alt/az coordinates) to the correct point in the sky. To do this, you will need to use the coordinate conversion program, located via the MS Quickbasic link on the desktop.
• Once you have the telescope pointed in the correct direction, to obtain the most accurate scans, it is also possible to make a correction for the Earth's relative motion towards/away from the source. This relative velocity can be calculate by going to "Velocity Line of Sight.exe" on the desktop and choosing the "vel" command. Help on this command is given in the program. However, how you choose to handle this information is completely up to you; whether you attempt to input this figure into the scanning program (discussed below) or you simply make a qualitative discussion on the effect it has.
• SpectraCyber is the program that is used for making the scans. There are many different features which can be adjusted to make the best scans, so it isn't practical to go through them all here. However, the program is fairly self explanatory and students will be given a brief introduction on the use of all programs before they start using the equipment. When you start the scanning process, you will see your data being plotted on a graph of volts (i.e. intensity) against Doppler shift (viewable in figures of Km/s or KHz). It is then up to yourself to determine what the data that you have collected means and how you can use it to build up a picture of the structure of the Milky Way.
• It is then possible to save the scan that you have taken, before opening up this data in a program such as EasyPlot for further analysis on the key features of the graph and the peaks on it (such as gas cloud temperature).

So how do you get a 'good' scan?

Well, depending on what you hope to gain out of the observations you are making (be it a qualitative discussion or a rigorous quantitative investigation of the your chosen source), there are several steps that you can take to make sure you are obtaining the best quality data that you possibly can.

• Repeat readings - Take as many repeat scans of the same part of the galaxy as you can. The more repeat scans you do, the less electronic noise becomes a problem since this becomes averaged out. You should aim to do a minimum of 3 scans of each part of the sky.
• Clear sky readings - You may also find it prudent to take what is known as a clear sky reading (i.e. pointing the telescope completely out of the plane of the galaxy and taking a scan of "free space"). Doing this will ensure that earth-based sources are not interfering with your scans of the Milky Way.
• The Earth's relative motion to source - As mentioned previously, it is possible to make an adjustment for the relative motion of the Earth towards your source. This relative motion will obviously have an effect on the Doppler shift readings that you obtain.
• Inside the SpectraCyber programme - There are also things within the scan programme that you can do to gain the best scans. Adjusting a fairly wide range of settings will give you a better quality scan. For instance, you can adjust the scan rate, time/step and spectral gain amongst others.

Click here to read about an experiment with the radio telescope.