Telescopes give us a ‘window’ to peer out into the Universe from, but before we even try and understand what’s outside, we need to be sure we know what the window itself looks like. This Monthly Media is from Dr Jack Line, who shows us how he builds up the image of the ‘window’ into the Universe.

This window, which is called the primary beam, can be a complicated affair for a radio telescope such as the Murchison Widefield Array (MWA), because the telescope is made up of many antennas.

We can test the shape of the primary beam of a single antenna in the lab, but for the whole MWA, with thousands of these antennas spread over 6 kilometres in the Australian outback, it’s not so easy.

A single satellite being simultaneously observed by a single MWA antenna and by 16 of them (otherwise known as a tile). These observations are then compared to understand the complexities of observing with multiple antennas.

Luckily, GPS and communications satellites whose orbits take them into the line of sight of the MWA can be used to measure the shape of the primary beam.

By using a single reference antenna with its known beam shape, and simultaneously watching satellites pass overhead with the reference antenna and a tile of antennas (16 antennas linked together in a square grid), the power both detectors observe can be compared, and the primary beam shape of the MWA tile can be inferred.

In the video below, each satellite passing overhead can be seen tracing out a path of the primary beam pattern, and over time each pass builds up a complete picture of the ‘window’ through which the MWA telescope views the Universe.

The shape of the ‘window’ (primary beam) through which the Murchison Widefield Array sees the Universe, slowly being built up as satellites pass overhead.

Now all we need to do is understand what’s on the other side of that window!