Advances in technology help us see more in the sky

Photo: DRAO

The Canadian Hydrogen Intensity Mapping Experiment at the National Research Council's Dominion Radio Astrophysical Observatory near Penticton is a revolutionary new Canadian radio telescope designed to answer major questions in astrophysics and cosmology.

The radio telescope at the Algonquin Radio Observatory, located in Algonquin Park, Ontario, is typical of the radio telescopes built around the world in the 1960s.

It is a spectacular instrument with a 46-metre dish. At an operating wavelength of 2.8 centimetres it can "see" a patch of sky about one tenth the diameter of the Moon in the sky.

That means that pointing the instrument at known cosmic sources of radio waves and measuring the strength and other properties of their radio emissions is quite easy. However, using it to map a large area of sky involves scanning the region of interest, measuring the radio brightness one "pixel" at a time.

Searching the sky for unknown, new objects would also be a very tedious process. The operating cost of large telescopes like that one does not encourage large-field mapping projects because of the time involved and largely rules out more speculative searches, making purely serendipitous discoveries rare.

There is always strong competition for observing time on the larger astronomical instruments and in general the proposals with the highest probability of getting results are the ones most likely to be accepted. Moreover, large, single-dish telescopes can usually be used for only one project at a time. In addition, until recently, the data obtained usually went home with the astronomer and after he or she was done with it, ended up stored on a shelf in their office. Back in the 1960s, that was usually in the form of stacked reels of magnetic tape.

Things are very different now. Let's look at the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope, now operating at the National Research Council's Dominion Radio Astrophysical Observatory near Penticton, and the CHORD (Canadian Hydrogen Observatory and Radio transient Detector) radio telescope currently under construction. Both have a huge field of view—most of the sky over the observatory. Secondly, despite the very focussed-sounding names for these instruments, they can be used for many different experiments, often at the same time.

Whereas older radio telescopes could only accept a narrow band of wavelengths at a time, these instruments can grab a substantial chunk of the radio spectrum and digitize it. Once that is done, the data can be split among multiple channels of signal processing, each set up for a different experiment. It is possible to image different areas of sky and search for fast radio bursts and other things at the same time.

Another big difference is in the data that is recorded. In the past, due to the limited capacity of digital data handling and storage media, astronomers took home data that was mostly, or completely processed, which meant it was of limited use for any other projects. Today, we can handle almost unprocessed data, so after the intended information has been extracted, it is possible to search that data for other things.

Finally, the data is stored in large repositories, such as the Canadian Astronomy Data Centre, where it is available for use by other researchers. In some cases the data is private for a year or so, giving the astronomers who obtained it a chance to analyze it and to get their results into print first.

One possible downside in the new style of radio astronomy is we don't need to travel at those instruments, which are usually at exotic locations, to make the observations. However, the new form of astronomy provides much more efficient use of the money spent on building and operating observatories, and makes their scientific productivity higher than ever. That is exciting.

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• Venus now lies very low in the east before dawn. After dark Jupiter shines yellowish-white high in the west and red Mars is high in the southwest.

• The Moon will reach last quarter on April 20.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.