Skynotes: October 2024
Upcoming events
Comet in our skies!
Comet C/2023 A3 (Tsuchinshan-ATLAS) is in our pre-dawn skies low in the east. A visitor from the far away Oort Cloud on a million-years orbit of the Sun, this comet was jointly discovered by China’s Purple Mountain Observatory and the asteroid alert telescope ATLAS in South Africa. By 27 September it had reached perihelion (closest to the Sun) and became visible. If it survives its path around the Sun, it should be visible again in the early evening in the west from October 9. See the article by Professor Jonti Horner in The Conversation, and also pictures and information on EarthSky and ABC News.
Discoveries near and far
Crystal clear Mercury
After an eight-year journey and during its fourth of six passes by Mercury – each one reducing its speed to allow orbits from next year – the JAXA-ESA BepiColombo probe has transmitted sharp images of the solar system’s innermost planet. This time its closest approach on September 4th was a mere 165km and gave the probe a superb look at the little planet’s south pole region. Included were views of several double-walled or “peak ring” basins which are primary objectives for the mission. These are large smooth-floored craters with inner circular ranges of peaks surrounding a smooth centre. Are these inner peaks the result of a rebound effect after a major impact?
Enjoy this BepiColombo fly-by video accompanied by Vivaldi’s Four Seasons.
Explore:
ESA BepiColombo Fourth Fly-By Space.com
Free-floating worlds
In the star cluster in the nebula NGC1333 some 960 light years away the James Webb Space Telescope (JWST) has discovered six free-floating planetary-mass objects (FFPMOs) - brown dwarfs - with masses of 5 to 15 Jupiters. Only one of them appears to have a proto-planetary disc. How do such bodies form in isolation? Does current theory of star and planet formation need adjustment? It is estimated that about 10% of the objects in the cluster are likely isolated and not bound to other stars while elsewhere in the nebula larger massive stars with attendant protoplanets are forming from discs of gas and dust.
These free floaters have such low mass they cannot reach the high core temperatures needed for nuclear fusion of hydrogen. Instead the best they can manage is initial low-level deuterium fusion and slow gravitational contraction which produces infrared energy (heat). JWST was able to detect their faint warm glows in the nebula. The discovery raises the question whether we can draw clear distinctions between massive planet and brown dwarf. Within a dust cloud is it simply the available supply of material or other factors that determine if a planet, brown dwarf or a star forms?
One of the free-floating objects is visible in this JWST image. It is the small orange dot in the top left corner.
Discover more:
ESA Peeking into Perseus
Space.com JWST finds 6 wandering ‘rogues’
Chandra Brown Dwarfs
Melbourne Sun times
| Date | Rise | Set | Day length | Solar noon* |
|---|---|---|---|---|
| Tuesday 1st | 5:55am | 6:24pm | 12:28hours | 12:09pm |
| Friday 11th | 6:40am | 7:33pm | 12:53hours | 1:06pm |
| Monday 21st | 6:26am | 7:42pm | 13:16hours | 1:04pm |
| Thursday 31st | 6:14am | 7:53pm | 13:39hours | 1:03pm |
*When the sun is at its highest, crossing the meridian or local longitude.
Australian Eastern Daylight Time (AEDT) begins on Sunday 6th at 2am when clocks move forward 1 hour.
Moon phases
| Phase | Date |
|---|---|
| New Moon | Thursday 3rd |
| First Quarter | Friday 11th |
| Full Moon | Thursday 17th |
| Third Quarter | Thursday 23rd |
Moon distances
Lunar apogee (furthest from Earth) is on Thursday 3rd at 406,161 km.
Lunar perigee (closest to Earth) is on Thursday 17th at 357,175 km.
Planets
Mercury is not visible this month as it is too close to the Sun after its passage behind our star.
Venus is now the ‘evening star’ seen from 7:50pm low in the west at dusk before setting about 10:30pm.
Mars can be seen in the east from 2:30am and before fading from view in the morning light by 6am.
Jupiter is visible from 1am in the north-east after which it will be lost to view in the north by 4am in early dawn light.
Saturn can be seen from around 8:15pm in the north-east and as it traverses to the north it will disappear by 6:15am.
Meteors
The Orionids appear from the 15th-29th but peak on the 21st-22nd with perhaps 30 meteors per hour from midnight until dawn. Centred on Orion near the red supergiant star Betelgeuse, they are typically very fast and bright entering the atmosphere at 66 km per second and vaporising 100 km above the surface leaving persistent trails. Dr Tanya Hill and Professor Jonti Horner explains the meteor shower in The Conversation.
The Orionids shower was first recorded by the Chinese in 288 AD and is associated with Comet Halley. In 1705, Edmund Halley after studying records of some comets that seemed to re-occur, used Isaac Newton’s new laws of motion to calculate the comet’s orbit predicting a return in 1758 (which he did not live to see). Every 75 years Comet Halley passes through the inner solar system leaving a trail of particles for Earth to intersect twice a year - the April/May Eta Aquarids and the October Orionids.
Stars and constellations
In the north
As the year progresses we see Aquila (the Eagle) and its principal star Altair (Alpha Aquilae) directly north but Lyra (the Lyre) and its bright star Vega (Alpha Lyrae) have left our northern skies this month.
In the west
Scorpius is now moving down to the west with the red-giant star Antares the middle of three stars that mark the scorpion’s body. High above following the scorpion is the asterism ‘the teapot’ which gives you the position of the bow and arrow held by the centaur Sagittarius.
In the east
Formalhaut in Piscis Austrinus (Southern Fish) is the bright evening star in the east this month. But as spring ends and we move towards summer we will progressively begin to see from the north-east to the south-east a rich collection of night sky objects:
- The beautiful Pleiades cluster (also known as the Seven Sisters).
- Taurus the bull with red giant star Aldebaran.
- The inverted Orion the hunter with the right way up ‘Saucepan’ and red supergiant Betelgeuse.
- Canis Major and the brightest night-time star Sirius (also known as The Dog Star).
In the south
In a dark sky in the south-east are the isolated Large and Small Clouds of Magellan (our galaxy’s nearest neighbours) as well as the vast band of billions of stars and dark dust clouds that make up what we can see of our own galaxy, the Milky Way. In the evenings this month it runs in a broad arc from south to north. From our location about 28,000 light years from the centre of our disc shaped galaxy we have an edge-on view along the plane of the galaxy where the density of stars is greatest. As you look away from the Milky Way to either side of the sky you see far fewer stars. In those directions you are peering through only a thousand or so light years out into intergalactic space, to the north or to the south of the galactic plane. We are still trying to fully understand the size and shape the Milky Way.
Low in the south-west are the Pointers, Alpha and Beta Centauri, in the constellation of Centaurus (the other centaur in our night skies). Following the line of the two bright Pointers leads to the Crux (Southern Cross).
Explore:
International Space Station
At a distance of about 400km the ISS completes an orbit every 90 minutes and appears as a bright point slowly moving across the night sky. Here are some of the brightest passes expected this month over Melbourne:
Morning
Tuesday 8th 5:45am to 5:52am West-South-West to North-East
Wednesday 9th 5:00am to 5:04am South-South-West to North-East
Evening
Sunday 13th 8:02pm to 8:09pm North-West to South-East
Sunday 27th 9:43pm to 9:46pm South-West to West-South-West
Heavens Above gives predictions for visible passes of space stations and major satellites, live sky views and 3D visualisations. Be sure to first enter your location under ‘Configuration’.
On this day
1942, first object to reach space, the experimental V2 (‘Vengeance’) rocket, was launched from Peenemünde, Germany in a brief flight over the Baltic.
4th 1957, Sputnik (USSR) was launched to become the first artificial satellite.
4th 2004, SpaceShipOne was launched as the first private spacecraft into space.
5th 1923, Edwin Hubble (USA) established that M31, the Andromeda Galaxy, is separate to our own Milky Way Galaxy.
7th 1959, first photos of the moon’s far side are taken by Luna 3 (USSR).
9th 1604, a Type1A supernova 20,000 light years away in constellation Ophiucus is visible from Earth, and on 17th Johannes Kepler observes and publishes his account of the new star. It is the most recent supernova visible to the naked eye in our galaxy.
10th 1967, the United Nations’ Outer Space Treaty on the peaceful exploration and use of space was established. By now 109 nations are signatories and several other agreements and conventions have been created to cover space law.
11th 1958, Pioneer 1 (USA), a battery- powered probe aiming for lunar orbit, fails to reach escape velocity and burns up.
11th 1968, first crewed Apollo mission, Apollo 7 (USA), launched into Earth orbit in test of Saturn V rocket and Command and Service Module (CSM).
12th 1964, USSR’s Voskhod 1 (‘Sunrise’) was the first spacecraft with a crew of more than one. In this case, three cosmonauts who orbited for 41 hours.
13th 1773, the Whirlpool Galaxy M51a, 31 million light years away in constellation of Canes Venatica, is discovered by astronomer Charles Messier.
18th 1967, Venera 4 (USSR) is the first probe to analyse the atmosphere of another planet when it does so at Venus.
19th 1910, birth of Subrahmanyan Chandrasekhar who had major insights into stellar evolution and black holes.
24th 1998, Deep Space 1 (USA) probe was launched to test innovative technologies, including an ion engine, while visiting Asteroid Braille and Comet Borrelly.
27th 1994, first sub-stellar object orbiting a star is found, a brown dwarf at Gliese 229.
29th 1991, Galileo probe (USA) is the first to visit an asteroid, Gaspra 951, on its way to Jupiter.
31st 2000, Expedition 1, first resident crew of the International Space Station, arrived by a Russian Soyuz craft for a 136 day stay lasting until March 2001. The three-person crew (one American and two Russians) made the station fully operational, hosted three visiting US Space Shuttles, and received two Russian Progress supply vehicles.