The Tour Guide’s Cheat Sheet
Mount Pleasant Observatory
The 26m diameter radio telescope was originally located at Orroral Valley (ACT), forming part of NASAís Spacecraft Tracking and Data Acquisition Network where it operated from 1965 to 1984 In that time it tracked numerous unmanned science missions that focused on Earth observation and astronomy. The 26m telescope also supported two significant manned programs: the Apollo-Soyuz Test Project (1975) and the Space Shuttle, including itís first launch in 1981. Following the closure of the Orroral Valley tracking station, NASA donated the telescope to the University of Tasmania. It was moved to Mount Pleasant, where it was opened in 1986. The telescope is now used for a wide range of research projects including the study of massive star formation, pulsars and active galactic nuclei. It also participates in regular observations with other radio telescopes in Australia and overseas using the technique of Very Long Baseline Interferometry (VLBI) to synthesize a telescope as large as the Earth.
26m telescope factiods:
The 14m antenna was built by the Universityís Physics Department in 1981 for the purpose of dedicated observations of the Vela Pulsar, a bright neutron star rotating at 11 times per second. The 14m antenna has caught Vela glitching (undergoing a sudden and unpredictable increase in rotation rate) on 5 occasions. The cause of these glitches is unknown but is thought to be related to the interaction between the crust of the star and itís superfluid core.
The 12m antenna is the newest addition to the Observatory and was opened in 2010. It forms part of the three-telescope AuScope VLBI Array, the other two telescopes located in Katherine (NT) and Yarragadee (WA). The array carries out geodetic VLBI observations to measure and monitor the orientation of the Earth in space, the length of the day, and the structure and movement of the Australian continent.
Active Galactic Nuclei
There are millions of galaxies in the Universe. All the big ones - including our own Milky Way - have huge black holes at their centres. These are between a million and a billion times heavier than the Sun, which itself weighs 2 million million million million million kilograms! Black holes are supposed to be black, but actually regions immediately surrounding them are the brightest things in the Universe. Black holes suck matter up (physicists call this “accretion”), and the friction during this accretion process makes regions just outside the black hole event horizon glow white hot. We call these regions Active Galactic Nuclei (AGN).
During the accretion, AGN also eject jets of plasma (which consists of electrons moving at close to the speed of light, spiralling around magnetic field lines). These jets are the most powerful outbursts in the Universe, and we can see them with radio telescopes. Because they are so bright, we can observe AGN to huge cosmic distances and use them to study how the Universe has evolved. AGN also allow us to probe extreme physics - for example, whether the laws of physics as we know them still work in regions of really strong gravity or magnetic fields. Often this work is done using the technique of very long baseline interferometry, where signals from telescopes separated by thousands of kilometres are combined to create a much larger virtual telescope; this huge virtual telescope can then peer into the very inner regions of AGN, where the strongest gravity and magnetic fields are found.
Quasars used for geodesy are a type of AGN; they are used because AGN can be seen to such huge distances across the cosmos that they are effectively fixed reference points on the sky.
The Earth appears to be fixed, but it’s not.
Did you know that the pull of gravity by the Moon and Sun not only makes the sea go up and down to make tides, but also squeezes and stretches the land? The ground you’re on now is changing constantly in height, moving up and down by up to 40 centimetres every day! But the ground is also moving over hundreds and millions of years. Our land sits on enormous plates which can be bigger than the biggest countries. They constantly move around at speeds of up to a few centimetres per year without us noticing. They press against each other pushing up mountains, or they move apart making the oceans bigger, so much so that over millions of years new mountains and oceans are formed. In some places, earthquakes happen frequently and then the Earth moves very quickly in a very short time.
The Earth itself doesn’t stand still either.
The Earth moves around the Sun at a speed of about 30 km every second. The Earth spins on its axis once every 24 hours, which is why our days are that long. But a day is not exactly 24 hours and things like the wind pushing on mountain ranges can change it. The Earth also wobbles as it spins. The Earthís pole is also moving a few metres per year.
So if everything is moving, how do we know where we are?
To measure where we are, we need to compare to things far away from the Earth that don’t move. Those things are called quasars and are located at the edge of the universe. They are so far away that the signal that comes from them takes billions of years to get to us even though it’s travelling at 300,000 km a second. Quasars are powered by black holes and appear only as a very small point when observed from Earth. Thatís why they form an ideal frame to hold on to.
Radio telescopes are really good at observing quasars. If you have two radio telescopes you can measure how long it takes for the quasar signal to reach one telescope compared to the other. This difference in time tells you how far apart the telescopes are. By making lots of these measurements with lots of telescopes you can find out their positions to better than a centimetre and see how their positions change. You can use this information to measure the shape and size of the Earth, see how it’s wobbling and measure the length of the day. This information is used to tell satellites where they are. If radio telescopes didn’t make these measurements your smart phone wouldn’t be able to tell you where you are!
And who does all those measurements for us?
Scientists such as geodesists and astronomers provide us with all the information we need. They organize the observation of quasars with radio telescopes and determine the positions on Earth and in space. The technique for doing this has become known as Very Long Baseline Interferometry, or VLBI for short. Geodesy is the science of measuring the surface of the Earth and changes on it.
VLBI experts are now working to improve how well we measure positions, and hope to see in the next few years how the Earth is changing at millimetre scales. This will let us measure things like the effect of the melting of glaciers on sea level rise. In a way, we’ll be using black holes to measure Climate Change!
All of this is done by hundreds of scientists and engineers from more than 20 countries working together and organized by the International VLBI Service for Geodesy and Astrometry (IVS). Australiaís contribution to the global VLBI network includes three radio telescopes across the continent, at Yarragadee (WA), Katherine (NT) and Hobart (TAS). The Australian VLBI network is operated by the University of Tasmania as part of AuScope, a diverse framework of infrastructure for research in geological, geochemical, geophysical, and geospatial subjects.