1. The Black Hole at the Centre of the Milky Way
As part of her talk at last Thursday's Girls in Physics Breakfast, Prof Rachel Webster showed a short video produced by the European Space Observatory (ESO).  The video assembled images of the Milky Way to slowly zoom in on the Black Hole at the centre of the Galaxy, Sagittarius A* (Sgr A*).  The ESO also has an extensive video catalogue.
The video starts with a field of view of 10 light years and slowly zooms down to 1 light day.  As you pass 1 light year, you see stars moving in a curved paths, then the elliptical paths are traced out.  At a distance on 1 light day, the names of each star can be read, with stars on eccentric orbits speeding through their closest approach.
Like planets around the sun, these stars around the black hole can be used to determine the mass of the black hole.  This is the  wikipedia page for Sagittarius A*   The figure on the right from that webpage shows a small selection of some of the stars.  The little ellipse in the bottom right corner shows the orbits of Pluto and Neptune on the same scale, the red line is Sedna, a dwarf planet with a period of 11,400 years.
The webpage includes a table of data for several of these stars with data values for: period (years), semi-major axis (secs of arc), closest approach (AU), eccentricity and speed at closest approach as a percentage of the speed of light.
For example S2 has a period on 16.2 years, an e value of 0.88 and a speed at closest approach of 2.56% of c.  The current record is S4714 with a max speed of 8% of c.
If you wish to use the data to determine the mass of the black hole, you will need an estimate of the average radius.  This can be obtained from the average of the semi-major and semi-minor axes, whose values in metres can be obtained from the values for the closest approach and the eccentricity.

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2. Enrolments in VCE Physics
VCAA has released the 2022 enrolment data for VCE subjects.  These have been incorporated into the ongoing analysis by Vicphysics.. Below are some observations of the data and trends.

• VCE Physics: A reduction in student numbers, mainly male, combined with a larger age cohort produced a significant drop in the participation (that is, Year 12 enrolments as a percentage of the age cohort as measured when they were in Year 7). Chemistry had a comparable increase in male numbers, bringing their male numbers to about 50 less than physics, whereas historically they are about 500 less than Physics.  This increase in the number of male Chemistry students is a consequence of the large male enrolment in Unit 1 Chemistry in 2021, which was not continued for Unit 1 in 2022.  The female numbers for both Physics and Chemistry decreased slightly.
• Retention from Unit 2 to Unit 3.  For the last decade or more, Unit 3 enrolments as a percentage of the number doing Unit 2 the year before has been steadily increasing, particularly for girls. In recent years it has seemed to plateau, last year there was a slight drop. The data values are two percentage points higher than those for Chemistry.
• Retention from Year 10 to Unit 1 Physics. The Unit 1 enrolments as a percentage of the Year 10 population the year before have been steadily falling since the mid 1990's.  For Chemistry, the value for both males and female students is about 20% and reasonably steady.
• Specialist Maths. Since 2003 the participation has been steadily decreasing, there was a momentary pause in 2013 and 2014 and since then the decrease has continued, albeit at a slower rate. Last year 5.5% of the age cohort did Specialist Maths.
• Year 12 numbers. The Year 12 student population as a percentage of the age cohort (based on the numbers when they were in Year 7), have been steadily increasing for the last few decades.  However the value peaked in 2010 at 90.0% and has dropped back significantly for the last two years (2022: 85.6%), no doubt due to COVID.

These graphs and those for other VCE Science and Maths subjects plus analysis are available here. 
Just a note in passing, when last year's Year 12 students were in Year 7 in 2017 was when the Year 7 student numbers statewide were beginning to increase.  The 2022 Year 7 numbers are 12.5% greater than those of 2017, with larger numbers still coming through the primary schools.

2. Geothermal Energy in Gippsland

• ABC Science Show interview (15 min interview with Prof Webster)
• Website of Vic Government's Department of Energy, Environment and Climate Action. The webpage on Geothermal Exploration in Victoria
• Australian Geothermal Association: Article on the use of geothermal energy to heat the aquatic centre in Traralgon. It includes a link to a more detailed article co-written by Prof Webster on the performance of the aquatic centre.

3. Datalogging and Flight
Kelvin Barraclough, formerly of Gisborne Secondary College, has been recording data on flight for many years and used the data in his classroom.  He has presented on this at past conferences and his extensive material is on our website.  It includes:

• Powerpoint presentation plus support notes
• Excel files on aircraft takeoff and manoeuvres at Point Cook as well as helicopters, train rides and simple walking.

These can be found on the vicphysics website at this webpage.

Kelvin has now provided an extra 10 data files on commercial flights.  They include take offs and landings of an A380, an A350 and an A321. 
The data collected in these Excel files includes acceleration (x, y and z), orientation (azimuth, pitch and roll), latitude and longitude and time.  There are also two files showing the analysis that is possible from the data.

These extra files along with hi original files have been added to a new webpage on our website titled 'Teachers' Websites', it can be found under the 'Teachers' heading below 'Course Planning'. 4. Events for Students

Girls in Physics Breakfasts in 2023
A breakfast at Monash University has been confirmed for Friday, 21st July. Details and flyers are available
The Girls in Physics Breakfasts program starts this term.  Below are the dates and venues that are open for bookings with the speakers and their topics.  

• 21st July, Monash University.  Speaker: Dr Karen Livesey, University of Newcastle.  The AIP Women in Physics Lecturer for 2023. Topic: Nanomagnets: New materials to address biomedical and technological problems
• 2nd August, Geelong. Speaker: A/Prof Elizabeth Hinde, Melbourne University, Topic: Glow in the dark – Using fluorescence to observe DNA in a living cell
• 11th August, Wodonga. Speaker: Emma Dyce, Medical radiation physicist, Topic: Treating skin cancer with radiotherapy
• 16th August, Traralgon. Speaker: Prof Rachel Webster, Melbourne University, Topic: Geothermal: vast energy reserves beneath our feet
• 25th August, Ballarat. Speaker: Dr Taissa Danilovich, Monash University, Topic: Molecules in Space
• 1st September, Bendigo. Speaker: Dr Amanda Karakas, Monash University Topic: Stars as chemical element factories

The cost this year is $20 per student, the first teacher attends for free.  There is a discount to $5 for low ICSEA schools, you need to contact Vicphysics to request the discount.
For more details and to book go to the Vicphysics website.
Flyers for Term 3 events will be up in coming weeks.

International Lepton Photon Conference. Public Lecture, Convention Centre, 6pm, 20th July.
The Conference runs from 17th to 21st July.  The public lecture on Thursday, 20th July will feature Suzie Sheehy (University of Melbourne and Oxford University) and Alan Duffy (Swinburne University of Technology) in a talk titled 'How to Discover a Universe'.

It will be held in the Clarendon Auditorium at MCEC from 6pm until 7pm.

Cost: $15. Click here to book.

Bios: Dr  Sheehy is a physicist, science communicator and academic who divides her time between her research groups at the University of Oxford and University of Melbourne. Her research addresses both curiosity-driven and applied areas and is currently focused on developing new particle accelerators for applications in medicine. An award-winning public speaker, presenter and science communicator, Suzie is dedicated to sharing science beyond the academic community. Her 2018 TED talk has been viewed over 1.8M times and she has been an expert TV presenter for a number of Discovery Channel shows including four seasons of Impossible Engineering. In her talks and shows, Sheehy loves to bring real-life demonstrations and experiments, and she has shared these with hundreds of thousands of audience members. 'The Matter of Everything' is her first book.
  5. Events for Teachers 

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8.   Physics News from the Web
Items selected from the bulletin of the Institute of Physics (UK).
Each item below includes the introductory paragraphs and a web link to the rest of the article.

a) Gravitational lensing of supernova yields new value for Hubble constant
Astronomers have measured the Hubble constant using light from a supernova that exploded 9.34 billion years ago. On its way to Earth, the light passed through a galaxy cluster and was deflected by the cluster’s immense gravitational field, which focused the light towards Earth. This effect is called gravitational lensing.

The lumpy distribution of mass in the cluster created a complex gravitational field that sent the supernova’s light along several different paths towards Earth. When the supernova was first observed in 2014, it appeared as four points of light. As the four points faded, a fifth appeared 376 days later. This light was delayed by the longer path it had taken through the cluster.

During those 376 days the universe had expanded, which means that the wavelength of the late arriving light was redshifted. By measuring this extra redshift, the team was able to calculate the Hubble constant. Using several different mass distributions models for the clusters, the team came up with values for the constant of either 64.8 km/s/Mpc or 66.6 km/s/Mpc
.
b) Swallowable X-ray dosimeter monitors radiotherapy in real time
Researchers from Singapore and China have developed a swallowable X-ray dosimeter the size of a large pill capsule that can monitor gastrointestinal radiotherapy in real time. In proof-of-concept tests on irradiated rabbits, their prototype proved approximately five times more accurate than current standard measures for monitoring the delivered dose.
c) Concentrated solar reactor generates unprecedented amounts of hydrogen
A new solar-radiation-concentrating device produces “green” hydrogen at a rate of more than 2 kilowatts while maintaining efficiencies above 20% .
The system consists of a parabolic dish seven metres in diameter. This dish collects sunlight over a total area of 38.5 m², concentrates it by a factor of about 1000 and directs it onto a reactor that comprises both photovoltaic and electrolysis components. Energy from the concentrated sunlight generates electron-hole pairs in the photovoltaic material, which the system then separates and transports to the integrated electrolysis system. Here, the energy is used to “split” water that is pumped through the system at an optimal rate, producing both oxygen and hydrogen.

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