November 2023

Planets to look for

Jupiter is the attention grabber this month as it reaches opposition on Nov 3. It will dominate the eastern sky all evening and is a great target for a telescope or even binoculars. 

Saturn continues its leisurely march across the sky. It is visible directly north at sunset as a yellowish object that stands out amongst the fainter stars that make up Capricornus. From here it will hang out in the northwestern sky until it sets around midnight.  

Image: Jupiter and Saturn joined by the Moon on Nov 22 

Credit: Stellarium

Venus continues to greet early risers, appearing in the eastern sky from about 3:30AM to be joined by the sunrise a couple of hours later.  

In the second half of the month, Mercury appears out of the glare of the Sun and can be seen in the western sky at sunset. It will be joined by the crescent Moon on Nov 14. 

Perhaps lost in the glory of Jupiter, Uranus is at opposition on Nov 14. This presents an excellent target for the more experienced stargazer. 

Constellation of the month

Grus the Crane 

Grus (pronounced either “Groose” or “Gruss”) is a middle sized constellation located in the southern sky. Its name deriving from the Latin word for ‘crane’, Grus is one of four constellations that make up the Southern Birds, which also include Pavo, Phoenix and Toucana. (You can read more about Pavo in this edition of The Sky Tonight) 

Image: Grus and nearby Pisces Austrinus 

Credit: Stellarium 

Unlike many constellation artworks, Grus looks kind of like its namesake. 

Some of the stars in Grus had originally been included in nearby Pisces Austrinus – the Southern Fish – but the constellation came into its own in the 16th century based on observations from Dutch navigators.  

Grus is home to a number of easily visible optical binaries, stars that look close together from our line of site but in reality are separated by significant distances. Delta Grus and Mu Grus, which respectively mark the body and neck of the crane, visible in the above image are two such examples.  

Image: Delta Grus (top left) and Mu Grus (middle top). 

Delta 1 Grus is a yellow star about 410 lightyears away, while Delta 2 Grus is a slightly fainter red giant star 425 lightyears away. The two are separated on the sky by only 45 arc seconds, making it easy to think they are related. 

Grus is also home to the Spare Tyre planetary nebula. With a name that elegant, you know this nebula was discovered by an Australian (Walter Gale in 1894, if you’re wondering). 

Image: The Spare Tyre planetary nebula. 

Credit: ESO 

Planetary nebulae are misleadingly named. Far from being the birthplace of planets, they are the dying cries of low mass stars. As the star at the centre of the Spare Tyre Nebula reaches the end of its life, it throws its outer layers off into space. The intense radiation coming from the now exposed inner layers of the star ionises the ejected outer layers of material, causing the whole thing to glow. 

Classy people refer to this nebula as IC 5148.  

Jupiter 

The king of the planets is deservedly titled. Jupiter will make for excellent viewing for the next couple of months, so even if you don’t catch it at opposition on Nov 3 you will have plenty of opportunity later. 

Through even a cheap telescope you should easily be able to see the planet resolved into a disk, and even its largest moons, the Galilean satellites.  

Image: Simulated view of Jupiter and the Galilean moons on Nov 3. 

Credit: Stellarium 

Uranus 

For a more challenging target, the greenish blue disk of Uranus will also make for good observing for the next couple of months. 

A more modest telescope will definitely give you better results, and the best time to go looking is in the late evening in the first half of the month, before the light of the Waxing Moon starts to interfere with observations. 

Image: Uranus in a decent amateur telescope. 

Credit: Martin Lewis 

Feature Article 

The Most Extreme Fast Radio Burst (yet) 

An Australian led team of scientists has used CSIRO’s Australian Square Kilometre Array Pathfinder telescope to discover the most distant fast radio burst ever. 

Since that sentence is quite a mouthful, let’s wind back a step. A Fast Radio Burst (FRB) is a millisecond long burst of radio waves that comes from space. First discovered in 2007 based on data collected by the Parkes Radio Telescope (The Dish!) in 2001, FRBs are almost always extragalactic in origin, which means that for us to notice them at all they must be enormously powerful. 

Image: Artist impression showing the extragalactic origin of FRB’s. 

Credit: ESO/M. Kormesser 

These can’t be seen by our eyes, but they can be detected by very sensitive radio telescopes, like the Australian Square Kilometre Array Pathfinder (ASKAP), located on Wajarri Yamaji country in Murchison, Western Australia. ASKAP consists of 36 dishes, each 12m across and spread out over an area about 6km on a side, that combine their observations in a process called interferometry to produce extremely detailed and precise radio images of the sky.   

Image: ASKAP dish with more in the background.  

Credit: CSIRO/A. Cherney 

Easily detected by ASKAP on June 6 2022, the burst now known as FRB 20220610A, has a redshift 1.016 meaning it happened about 8 billion years ago, when the universe was less than half its present age. ASKAP has the sensitivity and resolution to pinpoint exactly where in the sky this burst came from 

Precise location known, the scientists then used the Very Large Telescope (VLT) in Chile to collect follow up observations in optical light, the same that our eyes can see. This technique of multi wavelength observations is typical of modern astronomy: why use one set of data when you can use more? The VLT observations show that the burst came from two interacting galaxies, or possibly one large lumpy galaxy. 

Image: Optical imagery shows interacting galaxy sized objects with the location of the FRB circled.  

Credit: Ryder Et. al 

Huge amounts of energy are released in FRBs. In this case the burst released as much energy in a millisecond as the Sun releases in 30 years. For those of you playing along at home, that’s a power of about 4 billion billion billion billion billion Watts.  

Interestingly, scientists currently don’t know the cause of FRBs, however their exceedingly short duration of about 1ms does provide clues. In 1ms, light travels 300km, which means that the source of FRB’s must be extremely small, yet their enormous energies imply some extreme physics is going on. There are numerous ideas ranging from black hole-neutron star mergers to exotic ‘starquakes’ on magnetars. 

FRBs are exciting for astronomers because they can be used to probe the early universe and the intergalactic medium. We usually think of the universe as containing stars and galaxies; it’s easy to forget the space in between. Cosmological models of universal evolution predict there should be significant amounts of matter located between galaxies in the form of extremely tenuous plasma. Even though it is tenuous, space is big, so there’s a lot of stuff there. This ‘stuff’ is collectively called the intergalactic medium (IGM) 

Image: Computer simulations of the universe’s evolution predict filaments of galaxy clusters, shown as white dots on blue strands, interspersed with the hot gas of the intergalactic medium, red.  

Credit: Illustris Collaboration 

Crucially, FRBs can and do interact with the IGM. A FRB consists of many different radio frequencies all bundled together, think of it a bit like a broadcasting station that gives off a lot of different channels. As the FRB travels through the IGM, the lower frequencies get slowed down because of their interactions with the matter in the IGM, a process called dispersion. This means that the burst physically stretches out, so when it arrives at Earth, the high frequency waves are detected first, followed by a long “tail” of decreasing frequencies. Astronomers can use the duration of this tail to infer how much ‘stuff’ the FRB has interacted with, and in doing so they can estimate the amount of matter in the IGM. It’s as simple as it is complicated.  

Image: FRB 20220610A, with the distinctive tail easily discernible.  

Credit: Ryder Et. al 

In 2020, Australian scientists applied this logic to a collection of distant FRBs and concluded that about 50% of the mass of the universe is located in the intergalactic medium. Read that sentence again. Half of the stuff in the universe is located as hot plasma in between galaxies. Every time you look at an impressive picture of a galaxy containing hundreds of billions of stars, countless planets and gas clouds etc, just remember that there’s at least that much extra stuff outside the galaxy. 

Image: There’s more where that came from.  

Credit: 2002 R. Gendler, Photo by R. Gendler 

It is worth clarifying, this is not including Dark Matter and Dark Energy, which seem to make up about 95% of the matter and energy of the universe. What we’re talking about here is that of the remaining 5%, half of it is stars and galaxies, and the other half is the IGM. 

Data from FRB 20220610A is consistent with the burst interacting with large amounts of ionised material in the IGM, with the scientists reporting “The relationship between its redshift and dispersion confirm that the bulk of the baryonic matter was ionized and in the intergalactic medium when the universe was almost half its present age.” 

The universe is a wonderful place.