Southern SERENDIP


Southern SERENDIP was first connected to the Parkes Radio Telescope on 20 March, 1998 with the ability to scan eight million channels at once. This has now been upgraded to 58 million channels. The instrument 'piggybacks' onto surveys of the sky that the telescope is currently carrying out.

The bottom two graphs on the right are show the preliminary data from Southern SERENDIP sprctometer in its eight million channel mode.

The first graph is called a "waterfall" plot. Along the horizontal axis is the frequency range we are examining. In our case it is from just over 1420.5 MHz (MegaHertz) to 1418.0 MHz. This frequency covers the neutral hydrogen line, which on Earth is at 1420.40575168460 MHz.

Hydrogen is the most abundant element in the universe and this spectral line comes from a rare transition in neutral hydrogen. What is important is that this line is universal and allows us to study the mass distribution in the universe. Its very universality also means that we can mount a *speculative* argument that any other intelligent civilisation might attempt to transmit radio frequencies with an artificial signature near to this spectral line in the hope of being seen. Of course, this is a guess and may not be right - but it is a guess which a number of groups around the world are examining closely just because the neutral hydrogen frequency is so pervasive and travels well.

The vertical axis is made up pancake layer fashion, starting from the bottom up, of "hit" data. Each layer represents the frequency range chopped up into approximately 4.2 million channels each 0.6Hz wide (if you multiply 0.6 x 4.2 million you get approximately 2.5 MHz).

Not all 4.2 million channels in each layer are shown but only those in which are called "hits". A "hit" is a channel which has a signal strength greater than at least 12 times the mean of 8,000 or so channels which surround it. The final graph shows these hits layer upon layer and looks like a waterfall.

Each layer is expected to have some 25 hits alone just from the statistical noise received in the 4.2 million channels. The whole graph represents about 2,000 scan layers or just over an hour in time.

Were we to have a candidate ExtraTerrestrial Intelligence (ETI) signal we would expect a narrow but sloped line on the waterfall plot. It would be sloping because it is moving relative to us and narrow because that is sufficiently different from astronomical objects to be noticed. This would indicate something intentional. So far the only such intentional signals which have been found have come from satellites launched by an intelligent race on a planet called Earth.

The waterfall plot on the right are results for scans Southern SERENDIP took when pointed at three regions of the sky as described below. The strong vertical lines are radio frequency interference (RFI) and this is with us whether we like it or not. On the top of the graph are a couple of greenish patches. This is red-shifted neutral hydrogen and we got these "hits" as the telescope crossed our galactic plane. Red-shifted simply means that the neutral hydrogen frequency is less than it is here on Earth because it is moving away from us. This is caused by relative motion between us and the external hydrogen.


Where the telescope was pointing


The second graph goes together with the waterfall plot. It shows where the telescope was pointing in celestial co-ordinates. Celestial co-ordinates are measured in Right Ascension (RA) (the position of the lines radiating from the South celestial pole marked SCP around the celestial equator which is the outermost circle) and Declination (the circles around the SCP). RA is measured in hours (shown on outside of graph in blue numbers) Dec is measured from -90 at the SCP to 0 at the equator.

In short, celestial co-ordinates are fixed to the stars and independent of Earth's motion (well this is almost true to a high degree of accuracy!)

The yellow "worm-like" marks are where the telescope took data in the sky. The purple lines indicate telescope travel to new pointing positions.

The graph also contains a dotted yellow line with yellow numbers. This marks our own galactic plane and the longitude on this plane. One of the "worm-like" scan patterns crosses this plane and it is this which generates the greenish marks on the waterfall plot described above.

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Dr Frank Stootman
Dr Frank Stootman with one of the 14 sheets of engineered silicon that are behind the Southern SERENDIP experiment


Parkes Radio Telescope
CSIRO's 64 metre radio telescope at Parkes, New South Wales, Australia, which houses SETI Australia's Southern SERENDIP project.


Waterfall plot
Waterfall plot - Click on image for detail


Aiming of Parkes during data collection on 15/6/00
Where the Parkes radio telescope was aiming during data collection on 15 June, 2000: