Here you will find monthly updates on some of the most interesting research the Epoch of Reionisation group at Curtin University are up to. Not only will there be awesome pictures and/or videos, but details on the science behind them and links to the published (or soon to be published) research papers that back it up.
Monthly media will be updated on the first of each month. Within the week before the new month this site may not be accessible as the site is being updated.
The “Fighter Jet” of the Ionosphere
January 2019’s “Monthly Media” is a series of observations from Dr Chris Jordan that he has affectionately named “The Fighter Jet”, showing the positional offset due to the ionosphere of known radio sources as they pass overhead of the Murchison Widefield Array using techniques detailed in this paper.
Radio sources (such as distant galaxies) can appear to be shifted from their expected position in observations due to density lumps in the Earth’s ionosphere.
These density lumps refract light, causing the sources to appear shifted from where they would have been in an image if the ionosphere were not there, and are more common when the ionosphere is behaving “poorly”.
A “poorly behaved” ionosphere can be thought of like ripples on the surface of water – when you want to image something underneath, the ripples confuse things.
In the below video, you can see the radio sources (the dots) passing overhead through the course of the observations.
The colours of the radio sources indicate which direction the source has been shifted from where it should be in the image.
The background waves passing through the observations are reconstructed from the source offsets, following the method published in this paper, in order to better visualise the ionospheric disturbances being observed.
While most of the MWA observations made on the offsets of radio sources fall into the previously understood types of ionospheric disturbances, observations such as the “Fighter Jet” do not fall neatly into those categories.
Understanding how the ionosphere shifts the apparent position of distant radio sources can also be used to understand how it shifts the apparent position of GPS satellites, which gives us more reliable measurements for GPS applications, and a better understanding of space weather.
Past Monthly Media
The expected window through which the Murchison Widefield Array sees the Universe, as simulated by M. Sokolowski et al 2017, paper available at doi.org/10.1017/pasa.2017.54
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.
December 2018’s “Monthly Media” is a series of images from Dr Jack Line‘s upcoming paper showing how observations of satellites passing over the Murchison Widefield Array (MWA) telescope can be used to understand the MWA’s ‘window’, through which it sees the Universe.
This window, which is called the primary beam, can be a complicated affair for a radio telescope such as the 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 this video, 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.
A simulation of how the Moon reflects the radio waves of the Milky Way.
Just like the back of a spoon reflects visible light, appearing to curve straight lines, so too does the Moon reflect the otherwise straight line of our Milky Way galaxy into a circle when at the right angle.
As time passes, the position of the reflected galaxy changes on the Moon, as shown in this video.