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The casual observer

December brings us into the season of Birak, the first summer. The silver lining of the hot dry days is the clear night skies great for stargazing. Earth’s position in its orbit during summer faces us towards the outer parts of the Milky Way galaxy dominated by Orion and its neighbouring constellations, which have firmly established their presence in the eastern sky during the evening.  

Image: Several prominent constellations visible in the east this month. 

Credit: Stellarium 

December 22 brings us the summer solstice. If you make a note of where the Sun is every day, up to the summer solstice the Sun rises slightly higher in the sky each day, and on the day of the solstice it reaches its highest point in the sky. This is the day of the year with the longest amount of daylight and the shortest night. People living on the tropic of Capricorn will see the Sun pass exactly overhead on this day. 

Image: The tilt of the Earth faces the southern hemisphere towards the Sun during summer, and the Sun reaches its highest point in the sky on the day of the solstice. 

Credit: Bureau of Meteorology 

The Geminids meteor shower peaks on Dec 14, conveniently around the New Moon. You do not want to miss this prolific shower, and in good conditions you may see dozens of meteors per hour emanating from the constellation of Gemini. The best time to see this shower is late evening of Dec 14 and into the early morning of Dec 15, looking to the north with a clear view of the horizon. In good conditions you may see dozens of meteors per hour. Well worth staying up for. 

December 25th is an important day in the scientific calendar as we celebrate the birthday of the most influential person in history. Happy birthday Isaac Newton. 

 

ISS sightings from Perth 

The International Space Station passes overhead multiple times a day. Most of these passes are too faint to see but a couple of notable sightings are: 

Date, time  Appears  Max Height  Disappears  Magnitude  Duration 
9 Dec 8:58 PM  10° above NW  90°  10° above SE  -3.9  6.5 min 
10 Dec 8:10 PM  10° above NNW  42°  10° above ESE  -3.4  6 min 

Table: Times and dates to spot the ISS from Perth 

Source: Heavens above, Spot the Station 

*Note: These predictions are only accurate a few days in advance. Check the sources linked for more precise predictions on the day of your observations. 

Phases of the Moon

Last Quarter

December 5

New Moon

December 13

First Quarter

December 20

Full Moon

December 27

Last Quarter

December 5

Dates of interest

  1. Geminids peak

    December 14

  2. Moon near Saturn

    December 17

  3. Summer solstice

    December 22

  4. Potential first launch of the Vulcan Centaur rocket

    December 24

  5. Isaac Newton’s birthday

    December 25

Planets to look for

Jupiter and Saturn continue to make for excellent viewing in the north and northwest respectively after sunset. Mercury joins the evening planet show for the first half of the month, visible low on the western horizon. 

Image: Mercury, Saturn and Jupiter after sunset, joined by the Moon on Dec 14. 

Credit: Stellarium 

Venus is still looming above the eastern horizon before sunrise, as it has been for the past few months. It has overtaken Earth it its orbit and because it is leading our planet it will continue to be visible in the morning sky before sunrise for some months yet.  

Mars is still lost in the glare of the Sun. It is almost exactly on the opposite side of the Sun from Earth right now. We won’t be getting any good views of this planet for a while. 

Constellation of the month

Tucana the Toucan 

Tucana is a medium sized constellation located far in the southern sky. It is one of the constellations that make up the Southern Birds, along with Pavo, Phoenix and Grus. 

The brightest star in the constellation, Alpha Tucanae, is an orange subgiant star about 200 light years away and is generally associated with the head or beak of the bird. 

Image: Tunaca, with Alpha Tucanae marking the hanging leaf.  

Credit: Stellarium 

Beta Tucanae, representing the tail of the bird in the above image, is an interesting six-star system consisting of a triple system of binary stars. 

Tucana is home to the notable globular clusters 47 Tucanae and NGC 362. Globular clusters contain many thousands of stars tightly compacted within a few dozen light years. 47 Tucanae is the second brightest globular cluster in the sky, making it a popular target for stargazers. NGC 362 is notable for its highly eccentric orbit that brings it to within only a few thousand lightyears of the Milky Way at its closest approach. 

Most of the Small Magellanic Cloud (SMC) lies within Tucana. The SMC is an irregular dwarf galaxy that is a satellite of the Milky Way, orbiting our galaxy much like a moon orbits a planet. Containing several hundred million stars and located about 200 000 light years away, the SMC is easily bright enough to be seen with the naked eye in a sky free of light pollution. 

Image: The Small Magellanic Cloud, with 47 Tucanae (right) and NGC 362 (top, left of centre). Despite their apparent visual closeness, the two globular clusters and SMC are all unrelated to each other. If you look hard enough you can see a smiley face.  

Credit: ESO/VISTA VMC 

Object for the small telescope

47 Tucana 

With more than half a million stars compacted into a region only 150 light years across, 47 Tucana makes for a rich stargazing experience.  

Image: 47 Tucana 

Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration Acknowledgment: J. Mack (STScI) and G. Piotto (University of Padova, Italy) 

47 Tucana has been the subject of several studies by the Hubble Space telescope. One study showed white dwarf stars migrating from the centre of the cluster to the outer edges. This confirmed what astronomers had predicted to be a general behaviour in globular clusters, that the heavier stars ‘sink’ towards the centre of the cluster, but as these heavy stars age and turn into white dwarfs – losing a lot of mass in the process – they are displaced from the centre of the cluster by the remaining heavy stars.  

Another Hubble study failed to detect any exoplanets inside the cluster. This is consistent with planet formation being correlated with higher metallicity stars. The 13-billion-year age of 47 Tucana indicates it contains many first- or second-generation stars, low in metals and less likely to form planets. 

There’s a lot of science to be done in this fascinating ball of light. 

Feature Article 

Starship Integrated Flight Test 2 – More of a success than a failure. 

On Nov 18 the SpaceX Starship roared to life for the second time ever on Integrated Flight Test 2 (IFT2). For a quick recap: Starship consists of the first stage Superheavy booster and the second stage Starship. Note that the word ‘Starship’ does double duty here referring to the entire stack as well as the second stage. 

Image: Starship, labelled. 

Credit: SpaceX, labels added by Smith/Scitech. 

If everything went perfectly, the plan was for the rocket to launch from Starbase in Texas and perform stage separation, with the Superheavy booster performing a soft landing in the ocean, while Starship would accelerate to nearly orbital speed and travel around the world once before re-entering the atmosphere and splashing down near Hawaii. What ended up happening during IFT2 is that Starship cleared the launch tower with all engines working and completed stage separation successfully. The Superheavy booster soon thereafter experienced a rapid unscheduled disassembly, while the Starship vehicle continued on for another few minutes, almost making it to orbit before unintentionally dismantling itself.  

 

Video: Starship Integrated Flight Test 2. Skip to 38:45 for launch

Credit: SpaceX 

Why not experience that again in 360? 

Tunnel visioned armchair commentators were quick to call this launch a failure, but compared to the first test flight in April 2023, Integrated Flight Test 1 (IFT1), it was significantly more successful. It is worth looking at what modifications were made to Starship between IFT1 and IFT2 to understand why SpaceX call the launch a success. 

A lot of criticism of IFT1 was of the launch pad itself, ‘Stage Zero’ as SpaceX calls it. During IFT1, Starship almost completely destroyed the launch pad, gouging hundreds of tons of concrete out of the ground and flinging debris everywhere.  

To remedy this serious shortcoming, SpaceX installed an enormous water deluge system, essentially a giant sprinkler head, intended to torrent water into the hot exhaust and dampen the shock from the booster as the rocket launches.  

Video: Water deluge flame deflector 

Credit: SpaceX 

Comparing imagery of the launch pad after IFT2 and IFT2 speaks for itself.  

Image: Launchpad viewed after IFT1 (left) and IFT2 (right).  

Credit: RGV Aerial Photography  

Mostly hidden from view but of critical importance is the replacement of hydraulic thrust vectoring with electric thrust vectoring. Thrust vectoring refers to steering the rocket by pointing its engines in different directions. The Superheavy booster contains 33 engines: twenty of them are fixed in place around the outside of the booster, while the inner 13 can orient – or gimbal, as it is called – to point in different directions and steer the rocket.  

Elon Musk on X: “Starship Super Heavy engine steering test https://t.co/VG4RQAGuyk” / X (twitter.com) 

Video: Gimbaling the centre engines. Note this is an older booster with only 9 centre engines instead of 13. 

Credit: Elon Musk, SpaceX 

In IFT1, these engines were gimbaled hydraulically. That is, they used high pressure fluids to drive pistons to steer them, somewhat like a power steering system in a car. During IFT1, a number of failures of the hydraulic system occurred, ultimately causing some engines to shut down, and eventually hydraulic pressure was lost entirely, and SpaceX completely lost control of the vehicle, causing it to tumble out of control.  

To this end, the hydraulic system was replaced with electric actuators to control thrust vectoring. This means these are no longer points of failure in the event of hydraulic pressure being lost. The result was all 33 booster engines successfully igniting and operating for the full 2:45 minute duration of the booster flight up until stage separation. 

Image: All 33 raptor engines operating in unison during IFT2. 

Credit: SpaceX 

Perhaps the most spectacular change is the introduction of hot staging. Many rocket designs will shut down the booster stage completely and separate the second stage before igniting it. Hot staging refers to lighting the second stage while the booster is still firing. This has the advantage of keeping all the fuel flowing in the right direction but requires the booster to be designed to withstand literally another rocket launching from on top of it. 

Video: If you only watch one video today, make it this one. Hot staging of Starship in IFT2. Note that several booster engines are still running while Starship ignites its engines. This is to keep the fuel in the booster and Starhship settled at the bottom of their tanks. 

Credit: SpaceX 

Ultimately there seems to be some problems introduced by the hot staging, as shortly after staging the booster exploded. Some speculations suggest that the booster flip manoeuvre may have still caused problems with the fuel feeding into the booster engines. Others suspect oxygen leaks. Whatever the cause, the booster entered the next life.  

Image: Superheavy booster (left) and Superheavy booster 1/10th of a second later (right). It was at this point we suspected that there was a bad problem and we would not go to space today. 

Credit: SpaceX 

The Starship second stage continued on for several more minutes and very nearly made it to orbit. Based on telemetry data it reached an altitude of 148 km, well into space, and maxed out at a speed of 24124 km/h, only slightly short of the 27500 km/h needed to stay in orbit. Video footage is hard to interpret but it there seems to be a large puff of gas given off by Starship shortly before it too underwent a rapid unscheduled disassembly and telemetry went dead. 

Observers from the National Oceanic and Atmospheric Administration tracked a debris cloud raining back to Earth shortly thereafter. 

Image: Debris field of Starship detected by NOAA. Pour one out for the big rocket that couldn’t.  

Credit: NOAA, Howard, McDowell 

While the complete Starship stack was destroyed, the 8-minute flight of IFT2, complete with successful hot staging, getting into space and very nearly making it to orbit, was significantly more successful than the 4-minute IFT1, complete with its failure of stage separation, not getting to space and not getting anywhere close to orbital velocity. SpaceX already has a number of additional Starships at various levels of completion, with various levels of improvement over the vehicles used in IFT1 and IFT2, so it is only a matter of time before IFT3.  

Third time is the charm? 

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