23 years since Mum died (Aug 17 2025)

August 29, 2025

Sometimes life has a way of moving you beyond wants and hopes. (Flynn, Tron Legacy)

August 17 2025 (17 days ago) marks 23 years since my Mum died.

Dad’s birthday was 95 days earlier (17+30+31+17) on May 14. He died on January 7 2020.

Karen and I visited my mother’s and father’s plot at Centennial Park, Adelaide, on the afternoon of August 17.

What’s in a number?

7, 17, 23, 31. Four prime numbers.

17+30+31+17. An almost palindrome.

A universe. A life.

Am I just hallucinating?

Am I just an hallucination?

Who can tell.

Still miss them. Of course.

A Tale of 3 Novae

July 3, 2025

A couple of months ago I was asked to give an update at the July 2 2025 ASSA general meeting about T CrB, the binary star system that is anticipated to reach magnitude 2 or 3 when it goes into outburst as a recurrent nova (one of only 10 known), which it has done a few times before at roughly 80 year intervals.

In the meantime, we had two bright southern hemisphere novae (around magnitude 5) in June, so my T CrB talk turned into an update about 3 novae: T CrB, V462 Lup, and V572 Vel. The second and third were the subject of my last two posts.

My update was followed by a great talk about variable star photometry with the Seestar S50 by a former colleague, Andrew Murphy. The slides for his talk (and a course project) are here, as of 20 July 2025.

Here’s the PDF for the talk I gave, with thanks to Kym Thalassoudis for allowing me to include his images of V462 Lup and V572 Vel:

Here are the Powerpoint slides as well:

Another bright southern nova!

June 28, 2025

We may still be waiting for T CrB, but within less than a month we’ve seen 2 bright southern hemisphere novae: V462 Lup and now PNV J10251200-5331109 (aka V572 Vel)!

Technically it’s still classed as a possible nova (PNV) before spectroscopic confirmation, although there was a positive Gamma-ray Space Telescope observation overnight while I was sleeping.

Australian John Seach (NSW) discovered this (at magnitude 5.7), and Andrew Pearce (WA) independently found it (magnitude 5.5) on June 25 .

This object has eta Carina at its upper left in this Stellarium screenshot, and below it the “false cross” which consists of stars from Carina and Vela.

This smaller field of view provides more detail with 3 stars at the upper left of the false cross asterism (if the cross was standing upright) at bottom of the picture.

The observing campaign for PNV J10251200-5331109 (aka V0572 Vel) reports the progenitor star as likely being a 22.2 blue star with large amplitude variability.

The sky conditions were not great last night, but I estimated the nova candidate at 4.8 through 15×70 binoculars, through gaps in cloud with DSLR photometry pending.

Rotate this 20 degree FOV AAVSO finder chart 90 degrees right to get the false cross asterism in the same orientation as the screenshots above.

This 8 degree FOV finder chart provides the comparison stars of interest at the moment within a binocular field or two.

As I write this there have been less than 40 observations submitted to the AAVSO International Database.

After being away for a couple of days, I read an email yesterday from Andrew Wendelborn (ASSA) before seeing the official announcements, so thanks for the early heads-up Andrew! The timing worked out well in general.

Nova in Lupus

June 21, 2025

A nova, now designated V462 Lup, was discovered on June 12 by the ASAS-SN survey at magnitude 8.7 and has since risen to around magnitude 5.5. It has apparently not yet peaked. The progenitor star is thought to have been around magnitude 22, and as with all novae, the rapid brightness increase over a few days is impressive (although not as rapid as some).

Lupus, and the nova, are high in the evening sky as shown in this Stellarium screenshot:

The orientation here is at around midnight on June 21 2025 but Lupus is visible from early evening. This Stellarium screenshot shows the region around the nova corresponding to the image at top.

With the help of this AAVSO finder chart I have made a few visual estimates and there is some DSLR photometry pending. The visual light curve as of the early hours of June 21 is shown below with two of my binocular visual estimates in purple, the last one just a few hours ago:

Meanwhile, T CrB is still quiet.

Another T CrB update (still waiting)

April 22, 2025

I’ve been observing the constellation Corona Borealis (CrB) as often as possible since late February at around 5 or 6am. Daylight Saving Time ended here just over a week ago. With CrB gradually becoming observable earlier, if I’m still awake at 1am (fairly often), I can observe it (with binoculars) before I go to bed now.

In an October 2024 article in the Research Notes of the American Astronomical Society, When will the Next T CrB Eruption Occur? by Jean Schneider, the author writes:

By going more carefully into the dates of occurrence of the past eruptions, one finds that the successive events date separations are an integer multiple of the orbital revolution period.

…

In summary, the eruptions are not strictly periodic, but the eruptions were all separated by an integer multiple of the orbital period 227.5687 days.

From that, I tentatively infer that the eruption date after 1946 February 9 should be 2431861 + N*227.5687 where N is an integer close to 128, if the orbital period remains constant.

The upshot was predictions for the T CrB eruption of March 27 2025, Nov 10 2025 or June 25 2026. The popular press latched onto this article and suggested a greater certainty than was warranted. It’s now a few weeks after the first of these dates and no nova eruption has occurred yet.

We will see about November. In the meantime, we wait.

Observing T CrB again

February 22, 2025

I started observing the constellation of Corona Borealis (CrB) again this week, in preparation for the recurrent nova T CrB (aka The Blaze Star) to erupt. This was the first time I’ve done so since early October 2024, when the constellation left Adelaide’s evening sky.

On February 20th from around 5:15am, I spent 45 minutes or so reacquainting myself with the region through hand-held 7×50 binoculars, reminding myself of the comparison stars I’ll use to estimate the change in brightness of the nova, and the asterisms that will help me remember where they are.

Even pre-eruption, T CrB is observable in a small telescope at around magnitude 10, but from suburban skies, anything fainter than magnitude 6.5 or 7 is difficult through 7×50 binoculars, especially when twilight approaches. Still, it’s perfectly good enough to be able to say whether the nova event has happened.

As a reminder, the nova was anticipated before the end of 2024, but nature doesn’t always cooperate with our expectations. When the eruption does happen, T CrB will be visible without the aid of binoculars or telescopes, as bright as alpha CrB aka Alphecca (see the image below).

Why start observing it again now? For two reasons.

  • That part of the sky is observable from here again, even if at 5am.
  • There is recent evidence from spectroscopic observations that the rate of accretion of material around the white dwarf from the “donor” star in the pair that makes up T CrB (or any nova system) is significantly increasing. Such an increase, if it’s happening, may be a sign that the thermonuclear runaway is close.

Even so, there is not universal agreement that this result implies the nova is imminent.

Given Murphy’s Law, it will be entirely possible to miss the initial brightening, since observing 2 or 3 times a night (as I was doing last year for awhile) is not so easy in the wee hours, given the need to sleep and work, not to mention that some nights/mornings will be cloudy!

Still, it won’t stop me, and many others, from trying and in any case, the nova will be easily observable for several days either to the naked eye or with binoculars.

Here’s hoping we’ll have a bright nova (the brightest of all known recurrent novae) sometime in 2025!

On the N Days Of Christmas, part 8

January 12, 2025

My last post ended with the strong hint that I may not have been finished with this topic.

In part 4, triangular numbers were used as a first simplification to computing the total number of gifts for the 12 days of Christmas by eliminating some additions.

It turns out that the polynomial from part 5 is the equation for the class of tetrahedral numbers.

I wanted to determine the optimal solution from first principles and experimentation. The triangular numbers link was found through serendipity (listening to an unrelated podcast). I learned about tetrahedral numbers through further reading after finishing part 7.

In a Wikipedia article about the 12 days of Christmas song, Donald Knuth’s analysis of computational complexity is mentioned and then as an afterthought:

Incidentally, it is also observed that the total number of gifts after m days equals m3 / 6 + m2 / 2 + m / 3.

which is the polynomial we saw from part 5.

One thing led to another and I came across another Wikipedia page about tetrahedral numbers that are computed with this function. The name of the class of numbers arises from the fact that such numbers can be modelled by stacking spherical balls into a tetrahedron, as illustrated with this nice 3D graphic:

The number of balls in each layer is a triangular number. The number of balls in the tetrahedron is the nth tetrahedral number, and also the number of gifts for the nth day of Christmas.

gifts-for-day-of-xmasn = 1 ball in layer1 + 3 balls in layer2 + 6 balls in layer3 + … + n(n+1)/2 balls in layern

There is also a relationship to the problem of finding the optimal way to stack canon balls worked on by Johannes Kepler (one of my heroes, who realised that planetary orbits are elliptical, not circular), but that’s a different post.

Here are some other interesting things I found along the way:

  • The year that most of the thought went into my posts was 2024, which turns out to be the 22nd tetrahedral number.
  • Ian Phillipps won an Obfuscated C competition in 1988 with a C program that generates the text of the 12 days of Christmas song. The code was described by the judges as “…like what you would get by pounding on the keys of an old typewriter at random”, and as the same Wikipedia article goes on to say: “…takes advantage of the recursive structure of the song to print its lyrics with code that is shorter than the lyrics themselves.”
  • There’s a proof by induction for the tetrahedral numbers for all n that uses the equation for triangular numbers in the inductive step. This deserves further discussion, and perhaps I will return to this from another viewpoint in future.
  • The nth tetrahedral number is represented by the 3rd rising factorial of n divided by the factorial of 3. This yields a slightly more compact equation than the polynomial, but is just another way of expressing it, so is no better computationally. The equality-related expressions below partially recapitulate the explorations throughout this series of posts, with the rising factorial form at right (source: Wikipedia).
  • The 4th diagonal of Pascal’s triangle (built from binomial coefficients) contains the tetrahedral numbers (from left or right). The triangular numbers are in the 3rd diagonal, and the counting numbers are in the 2nd diagonal.

source: https://sahilmohnani.wordpress.com/2013/02/23/pascals-triangle-cubic-quartic-and-sextic-numbers/

It seems that the avenues down which one could stroll in relation to this topic are never-ending.

I can’t promise not to ever return to it, but it’s time to move on I think, at least for now.

Photometry of SX Phoenicis

October 4, 2024

I recently carried out photometry of the short period pulsating variable star SX Phoenicis.

This star has a very short period of 79 minutes over which it ranges between around magnitude 6.8 and 7.5! Contrast this with a Cepheid variable whose period is measured in many days or weeks and Miras with pulsation periods of many months.

The light curve above was derived from photometry of more than 400 images, using median stacking to group images close in time in order to reduce the scatter between datapoints. Almost two cycles were captured here. There are not many observations of SX Phoenicis in the AAVSO International Database, so I will very likely contribute more.

SX Phoenicis is the prototype (the first example) of a class of variable stars which has two pulsation modes, one with a period of around 79 minutes (as shown in my light curve above), the other around 62 minutes. The temperature of the star varies between 7,230 and 8,170 degrees Kelvin at minimum and maximum brightness, smallest and largest radius, respectively.

The origin of this kind of star is unclear but one possibility is that it comes from the merger of two stars, creating a single star that is more luminous and more blue than expected of the older galactic halo population in which it resides, a so-called blue straggler.

The Eagle Nebula

October 4, 2024

I recently took an image of the Eagle Nebula (Messier 16) in the constellation Serpens with my Seestar. This object is around 6000 light years distant from us.

M 16: The Eagle Nebula (20 minute exposure, f/5)

The nebula takes its name from imagined outstretched wings. I agree with Karen that a small dark region near the centre of the nebula also bears an eagle-like (possibly even moreso) semblance.

M 16 (region imaged by Hubble and James Webb Space Telescopes)

The Hubble Space Telescope (HST) imaged this region in 1995 with the result dubbed The Pillars of Creation (credit: NASA):

The tips of the finger-like structures glow with stars forming within. The arrowed region in my image is rotated 180 degrees from HST’s.

The James Webb Space Telescope has taken even more impressive images of The Pillars, such as this one:

Stop native extinction. Sure. But at what cost?

September 29, 2024

n30_w1150
n30_w1150 by BioDivLibrary is licensed under CC-PDM 1.0

A recent (23 September 2024) ABC 7:30 Report story, Back from Extinction, gave an interesting account of the Wild Deserts program that is aiming to reverse the trend toward native animal extinction in Australia. Fair enough. We don’t have a great record.

Bilbies, bandicoots, bettongs and quolls, once thought extinct in New South Wales for over a hundred years, are reclaiming parts of an outback NSW desert. (source: ABC 7:30 Report)

This seems to be a positive thing for the species and the ecosystem in which they once thrived.

About 6 minutes into the 7 minute clip, the discussion turns to controlling the causes of extinction, including feral animals, in particular cats. The method of control discussed in the program is a device that attracts a cat into a confined area such that a dose of 1080 poison is applied to its fur, which it then licks, ingests, so is poisoned and dies.

Sometimes, 1080 finds its way near locations in which pets live.

People described the death of their “loved one” from 1080 baiting as one of the most horrific experiences of their lives. Symptoms of 1080 poisoning included … vomiting, defecating, urinating, frenzied running … “screaming”, convulsions, confusion, fear, coma and finally, death. The Conversation

So, the suffering of a non-native animal doesn’t matter? Just collateral damage?

Of course the native species has to fight for survival in the ecosystem into which they’re introduced, but at least they have a fighting chance to live as opposed to being murdered for being the wrong species, in the wrong place (Australia), at the wrong time.

But, are they being reintroduced to “rebalance” or “re-engineer” the ecosystem or from which they were removed by us, or for their own “right” to live? Or both?

There is an idea, often unspoken, that native species have more value than non-native. Cats, dogs, livestock etc are not native to Australia. Neither are humans. Livestock are not native, but they are favoured by farmers over dingoes which have been here for thousands of years.

Being cute and cuddly shouldn’t be an important factor either but you would be forgiven for thinking so sometimes.

To be honest, I’m left with the feeling that both native and non-native feral species are often seen as a means to an end. That’s obviously true in the case of livestock.

As it turns out, I do not think that cats (for example) should be allowed to roam unsupervised in backyards or elsewhere, where that would result in harm to native animals whose species is in threat of extinction. Limiting freedom in this case seems to be a necessity, but that doesn’t mean it’s fair, and it doesn’t mean the pet should suffer.

It would seem that animals can go from being considered as a pet to a pest, depending upon location and negative impact in their environment, e.g. cat-as-pet vs cat-in-backyard-eating-birds or cat-as-feral. I’ve written elsewhere about another mammal that’s mostly considered a pest but that like most of us, is just trying to get on with its life.

Of course, all animals can be viewed as pests from the right point of view, all carry disease, all can do damage to ecosystems. Not to downplay the importance of the work being done by researchers in the Wild Deserts program, but it’s just interesting, and at times disturbing, to see the various ways in which we think we “know best”.