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The casual observer

June brings us into the season of Makuru, a time for rainy weather and colder temperatures. It also brings the bright central parts of the Milky Way into better view at reasonable time. Winter is the best time of year to view the Milky Way, with Sagittarius and Ophiuchus being flags marking the central regions of the galaxy.  

Image: Ophiuchus and Sagittarius surrounding the centre of the galaxy.  

Credit: Stellarium 

Venus is still hanging there in the western sky after sunset, orders of magnitude brighter than nearby Mars. 

The winter solstice happens on the Jun 21. For people in the Southern Hemisphere this is the shortest day of the year, and for people in the Northern Hemisphere it is the longest. People living on the tropic of cancer (23.5 degrees north) will see the Sun pass directly overhead. Functionally, this is the point in Earth’s orbit where the Sun appears to stop drifting north in the sky and starts moving south. This is what ‘solstice’ means after all: Sol-sun, sistere-stands still.  

The best way to get a feel for this is to make a note of where the Sun sets each day against the horizon. From Jun 21 onwards you will see the apparent position of the sunset against the horizon start to move south. The southerly motion of the Sun will continue until the occurrence of the summer solstice in December and the process reverses. 


Image: Viewed from space, Earth’s Northern Hemisphere will reach its maximum solar coverage on this day, while the Southern Hemisphere will reach its least. 

Image Copyright: 2017 EUMETSAT 


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 Jun 6:05 AM  27° above WSW  51°  10° above NNE  -3.5  5 min 
16 Jun 6:34 PM  10° above NW  73°  41° above ESE  -3.8  4.5 min 

Table: Times and dates to spot the ISS from Perth 

Source: Heavens above, Spot the Station 

Phases of the Moon

Full Moon

June 4

Last Quarter

June 11

New Moon

June 18

First Quarter

June 26

Full Moon

June 4

Dates of interest

  1. Moon near Saturn

    June 10

  2. Moon near Jupiter

    June 14

  3. Possible final launch of Ariane V rocket. This will be to launch the Syracuse 4B and Heinrich Hertz communication satellites.

    June 16

  4. Winter solstice

    June 21

  5. Moon, Venus and Mars together in the west after sunset

    June 22

Planets to look for

Venus continues to dominate the western sky in the evenings. Look for the bright thing in the west around and after sunset, that’s Venus. 

Mars is technically there in the northwest after sunset as well but is getting noticeable fainter as it gets further away. In their orbits around the Sun, Earth overtook Mars in December 2022, when the red planet appeared brightest in the night sky, and we are now nearly on the other side of the Sun from it making it appear very faint. By the end of the month, it’s brightness will have dropped to magnitude 1.7 by end of the month. 

The Moon joins Venus and Mars after sunset on June 22 for a nice trio to look at. 

Image: Venus, Mars and the Moon on the evening of Jun 22 

Credit: Stellarium 

Saturn is rising about midnight. The best time to catch it is high in the sky before sunrise. It is distinctly more yellow than any surrounding stars so is reasonably easy to spot. If you’re out before sunrise you will also be able to see Jupiter low on the eastern horizon as well. 

Mercury will also be visible in the hour before sunrise for the first half of the month. 

Constellation of the month

Ophiuchus the Serpent Bearer 

Ophiuchus is a large constellation located roughly toward the centre of the galaxy. The name Ophiuchus translates from Greek as ‘snake bearer’ and so the constellation is often shown as exactly that. The snake in question is fittingly associated with the constellation Serpens, which borders Ophiuchus on either side as Serpens Caput (the head) and Serpens Cauda (the tail). 

Observationally, Ophiuchus is represented by a ‘pointed rectangle’ pattern of stars, with the brightest star Alpha Ophiuchi marking the tip of the point. This star is more commonly known as Rasalhague, meaning ‘Head of the Serpent Charmer’ 

 Image: Ophiuchus and Serpens together in the sky. Note that Serpens is separated into two regions. 

Ophichus crosses the celestial equator – the imaginary projection of Earth’s equator into space, so is equally visible to people in the Northern and Southern Hemisphere. Interestingly, the ecliptic also passes through Ophiuchis, meaning the apparent path of the Sun and planets through the sky passes through the constellation, making Ophiuchus a zodiacal constellation as well. 

Being close to the plane of the Milky Way, Ophiuchus contains many star fields and clusters, including the globular clusters M9, M10 and M12 and the open cluster  

Of historical importance, Ophiuchus was the location of Kepler’s Supernova – a supernova event in 1604 that was observed and described in detail by Johannes Kepler in his book “De Stella Nova in Pede Serpentarii” (On the New Star in the Foot of the Serpent Handler). This supernova is the most recent supernova to be observed in the Milky Way and for a short period was brighter than any star in the night sky, with a magnitude of about –2.5. These observations were later used by Galileo to challenge the Arisotelean dogma asserting that the heavens were eternal and unchanging. 

Image: The remnant of Kepler’s Supernova 

Credit: NASA 

Modern analysis of the supernova remnant has identified Kepler’s Supernova as a type 1a event, a special type of supernova where a white dwarf star strips matter off a nearby companion star until it gets so heavy it collapses and explodes. 

The same scenario can be observed playing out in the nearby object RS Ophiuchi, a binary system consisting of a white dwarf star and a red giant companion that will eventually undergo a type 1a supernova event. As the white dwarf strips material from the red giant companion, this material accumulates on the surface of the dead dwarf star and every now and then, when enough material has built up, conditions are perfect for a brief and intense period of fusion on the surface of the white dwarf.  

Image: Artist impression of a white dwarf stripping matter from a red giant companion. 

Credie: NASA/CXC/M.Weiss 

This brief, intense period of activity makes the otherwise dim white dwarf star hundreds of times brighter, often making it visible in the night sky. Historical astronomers called these ‘nova’, meaning ‘new’ stars. If the same star undergoes this behaviour more than once it is called a repeating nova.  


Image: Brightness of RS Ophiuchi over time with distinct nova events standing out. 

White dwarfs can only exist up to a certain mass called the Chandrasekhar Limit, a mass of about 1.4 solar masses. As a white dwarf continues to strip matter from its companion star, getting heavier and heavier and occasionally flaring up in a nova, eventually its mass will reach the Chandrasekhar Limit. Once this happens the electron degeneracy that holds the star together fails, and the star collapses and explodes in a supernova. This will be the fate of RS Ophiuchi sometime in the future. 

Object for the small telescope

Barnards Star – The second closest star system to us. 

We all know Alpha Centauri is closest star system to the Sun, with Proxima Centauri specifically the closest star, but Barnard’s Star, located in the constellation of Ophiuchus, slips under the radar because it is far too faint to be seen by eye.  

Like Proxima Centauri, Barnards star is a red dwarf star, requiring a telescope to observe. Unlike Proxima Centauri, Barnard’s star has no bright companions and so wasn’t properly studied until the early 20th century when it’s extreme angular velocity of 10.3 arc seconds per year indicated that it was very nearby. Its measured distance of 5.29 light years places it as the second closes star system, and the fourth closes star to the Sun after the Alpha Centauri trio. 

Image: Barnards Star circled against neighbouring stars 

Credit: Stellarium 

Barnards Star is moving at about 142km/s in the general direction of the solar system and will make its closes approach in about 9000 years where it will almost, but not quite, become the closest star to the Sun. It will still just be edged out of that title by Alpha Centauri which is also getting closer to the Sun. 

Image: Nearby stars to the Sun over time 

Credit: FrancescoA 

The star is notable for its age, estimate to be at least 7 billion years old. There have been several claims of evidence for planets orbiting it, but these have all been ruled out and currently it is unknown if the star has any planets. 

Feature Article

JUICE – the Jupiter Icy Moon Explorer 

On Apr 14 the European Space Agency launched the Jupiter Icy Moon Explorer (JUICE) on a one-way trip to Jupiter. Launching atop the ever-reliable Ariane V, the same rocket that launched the James Webb Space Telescope in 2021, JUICE will take 8 years to reach Jupiter on an orbit that includes flybys of Earth and Venus. 

Image: The second last launch ever of the Ariane V rocket takes flight with JUICE on board. 

Credit: ESA 

As the name suggests, JUICE’s mission is to explore the moons of Jupiter, specifically focusing on three of the Galilean moons: Ganymede, Callisto and Europa. Upon arriving in the Jovian system in July 2031, JUICE will complete 35 orbits of Jupiter, passing by the Galilean moons on each orbit, before eventually entering orbit around Ganymede in 2035.  

Image: Timeline of milestones for JUICE 

Credit: ESA 

These three moons are of intense interest to scientists because they are all known to contain vast subsurface oceans. Europa is the most obvious ocean world, with a highly reflective surface of ice crisscrossed by cracks. In the same way Earth’s crust is cracked because the continents are drifting around on a bed of molten rock, you can quickly conclude that the surface of Europa is cracked because it is floating on a bed of molten ice, AKA liquid water. 

Subtle clues about the unusually low densities of Ganymede and Callisto, about 30% the density of Earth, the behaviour of Ganymedes magnetic field and auroras, and the interaction of Jupiter’s magnetic field with Callisto, led astronomers to conclude that these moons also harbour deep subsurface oceans, likely containing more water than all the oceans on Earth.   

Image: Europa’s icy surface crisscrossed by cracks. 

Credit: NASA/JPL-Caltech/SwRI/MSSS 

The search for liquid water is one of the key flags when looking for signs of life in the universe. Our understanding of life on Earth suggests that liquid water above all else is a vital ingredient, and this is why water worlds are of such great interest to scientists. 

JUICE will also conduct important studies of the environment around Jupiter. Scientists are curious about the relationship between the planet and its moons, and how the magnetic field, radiation and plasma environment around Jupiter interacts with the moons. This is significant because the results can be used to provide context and hints to what circumstances might be like around gas giants that are known to orbit other stars, a great number of which have already been discovered.  

Image: Jupiter and several moons. A potential archetype for gas giant planets in the universe. 

After JUICE’s launch, there appeared to be a problem with the deployment of the Radar for Ice Moon Exploration (RIME). This instrument is designed to used ground penetrating radar to study the moons to a depth of about 9km. The 16m long antenna was folded up for launch but failed to unfold after launch as expected. After several weeks of tweaking, including firing the spacecraft’s main engine and rotating the craft to face the radar towards the Sun to warm it up, engineers were finally able dislodge a tiny pin that was preventing the radar from deploying, and the unit is now fully operational. 

GIF: The RIME antenna finally deploys. 

Credit: ESA 

Jupiter is currently orbited by NASA’s Juno spacecraft, which is intensely focused on studying the planet itself rather than its moons. Like Juno, JUICE is solar powered, with 85 square metres of solar panels delivering just under 1kW of power at Jupiter’s distance from the sun. Jupiter really is at the limit of solar powered spacecraft. Missions that have travelled beyond Jupiter have all used radioisotope thermoelectric generators to provide power. 

Image: Artist impression of JUICE near Jupiter with its large solar panels deployed. 

Credie: ESA 

JUICE carries with it a commemorative plaque for Galileo. It was Galileo’s observations of the moons of Jupiter in 1610 that provided the first evidence that Earth was not the direct centre of universe. The plaque contains replicas of several pages of Galileo’s book, Siderius Nuncius, where he published his observations of the moons. 

Image: The plaque on JUICE containing replicas of several pages of Siderius Nuncius 

Credit: ESA 

It is expected that JUICE will reach Jupiter in 2030, long after the Juno mission comes to an end in 2025. However, it will be joined shortly thereafter by NASA’s Europa Clipper mission, a spacecraft expected to launch in 2024 and designed to go into orbit around Europa. The two missions will complement each other in the study of the Jovian system. 


Meanwhile in the Scitech Planetarium 

Coming soon… Pink Floyd “The Dark Side of the Moon” Planetarium event. Learn more.


Other space news 

The Webb telescope finds water in the asteroid belt. 

SpaceX achieved a chamber pressure of 350 bars in the new raptor 3 engine. 

Environment groups sue the Federal Aviation Authority over the Starship launch 

SpaceX shared video footage of a faring from the Falcon Heavy re-entering the atmosphere 

The Webb telescope discovers asteroid belts around the star Fomalhaut. 

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