Still calling, ET?

In 1960, radio astronomer Frank Drake carried out a pioneering attempt to pick up radio signals from intelligent beings on planets orbiting other stars. He used a 26-metre dish and observed at a wavelength of 21 cm. He pointed the antenna at two nearby sun-like stars, Tau Ceti and Epsilon Eridani. He failed to pick up anything that was obviously of extraterrestrial origin, but because of the number of things working against him it is not surprising. These searches for extra-terrestrial intelligence (SETI) are not trivial things.
The antenna used by Drake was typical of the larger radio telescopes at that time. Dish antennas are convenient to engineer, and can be made large, up to 100 metres or so, to collect lots of those weak, cosmic signals.

However, the downside is the bigger the dish compared with the observing wavelength, the smaller the patch of sky it can "see." At the wavelength Drake used, that patch of sky was only the size of the full moon. Typically, big dish radio telescopes see even smaller patches of sky. For example, the 46-metre radio telescope at the Algonquin Radio observatory, at a typical observing wavelength of 2.8 cm would see only about 1% of the area of the lunar disc. So Drake was stuck with pointing the radio telescope at single stars, one at a time. It is true that countless more distant stars were in the field of view of the antenna, but they were so far away there was little chance of any radio transmissions from their planets being detectable.
Problem number two is what radio frequency we should choose. For example, when we listen to an FM radio station, we can hear it without hearing other radio stations. This is because all these stations are allocated their own frequencies. Unless we tune to the frequency of any given radio station, we are not going to hear it. Drake had a bigger problem; he had no idea what frequency he should tune to. Just tuning around and listening would not be any good. The signals would almost certainly be so weak you would have to stay at that frequency for a long time to build up a detectable signal. There are billions of viable frequencies and Drake could only monitor one at a time.

Then there are the questions: "Does that star have planets?", "Could any of them support life?",  "Does it have life?", "Is that life intelligent?", "Has it developed radio technology?", "Is it transmitting now?" 

In an attempt to understand the odds, Drake formulated the "Drake Equation," which enables us to estimate our chance of receiving a signal from intelligent aliens. Of course, when Drake did his landmark investigation, he did not know whether other stars have planets, and most of the numbers he put into the Drake Equation were not much better than guesses. Today we know stars generally have planets and we are even finding earth-like ones. We have a better idea of what to look at. Our observing hardware has immensely improved. We now have receivers that can observe over most of the radio spectrum simultaneously, and are building radio telescopes that can see a lot more sky while achieving high sensitivities, such as CHIME. This instrument consists of four huge cylindrical antennas, which can see simultaneously most of the sky. We also have sophisticated signal searching software, using artificial intelligence in some cases, which should be more effective at finding signals, and which will never get bored or tired. In addition, these searches can now piggyback on other observing programmes. We are now well equipped for our search. Of course, if those aliens have detected our TV signals, they may well have decided it is better not to attract our attention.

  • Venus remains prominent in the west after sunset.
  • Before dawn, going right to left, Mars, Jupiter and Saturn lie low in the southeast, and Mercury very low in the dawn glow. The moon will reach last quarter on the 16th. 

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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