by Duncan Lunan

With the evening sky becoming darker as the year goes on, the brighter stars are becoming more prominent and the constellation figures are coming back – see ‘The Autumn Stars’, ON August 28^th, 2022.  The Autumn equinox is on September 23^rd, and if weather permits, I shall be trying to photograph the sunrise and sunset at the Sighthill stone circle in Glasgow, now that there’s open access to it at last.  Unlike the situation at the summer solstice, where the position of the Sun is virtually unchanged for at least two weeks either side of the event, at the equinox the position of the Sun changes rapidly from day to day and catching it really does depend on the weather.  (See ‘Solstices, Equinoxes and Sighthill’, ON September 19^th, 2021.)  Immediately after the success of its lunar lander  (see below), the Indian space agency ISRO has announced its intention to send an observatory named Aditya ‘Sun’ to the Earth-Sun L1 point, taking four months to get there after launch planned for September 2^nd.

The Moon will be New on September 15^th, and Full on September 29^th, passing Jupiter on the 4^th, and Venus on the 11^th and 12^th.

After making 5 orbits of the Earth, working outwards, India’s Chandrayaan-3 moonprobe transferred to the Moon’s sphere of influence on 1^st August, and the first approach photographs were released on August 7^th.  After 5 braking burns to lower the orbit, circular orbit around the Moon was achieved on August 16^th.  Separation of the Vikram lander from the propulsion module occurred on August 17^th, before descent from a height of 100 km over the south pole on August 23^rd, deploying the Pragyaan  (Sanskrit for wisdom)  rover on the 24^th.  This time the propulsion module carried only one scientific instrument, for measurements in transit between Earth and Moon;  Chandrayaan 2’s had nine instruments and is still working well in lunar orbit, two years later.

STOP PRESS news, 9.30 p.m., 29^th August:  the Pragyaan lander has detected a wide range of metallic elements, as was to be expected in a lunar highland region, but has also found and definitely confirmed the presence of sulphur, the first example of the volatile elements which the various probes are going to the south pole of the Moon in hopes to find.

India might have been pipped at the post for the honour of being the fourth nation to land a spacecraft on the Moon.  After years of delay, with a launch originally scheduled for 2016, Russia launched Luna 25, its first moonprobe since Luna 24 in 1976, on August 11^th.  It was the first moonprobe of their own because the first 24 were Soviet, as they insisted at the time.  It came despite the withdrawal of international cooperation following the invasion of Ukraine, and that included a precision guidance system for landing, developed by the European Space Agency.  Luna 25 also entered close orbit around the Moon on August 16^th, with a landing attempt expected on the 21^st or 22^nd.  However, a braking manoeuvre on August 19^th went wrong and it crashed into the Moon, as apparently happened with Luna 15 in 1969  (see ‘Lost on the Moon’, ON August 20^th 2023.)  

No sooner had that happened, though, before Japan announced its next attempt, ‘Smart Lander for Investigating Moon’  (SLIM), to land in a crater called Shioli in Mare Nectaris.  SLIM is aiming for a pinpoint landing  (not previously achieved except on manned landings), to study specific rocks within a 100-metre range.  Itself only 2.4 metres by 1.7 by 2.7, it carries a small Lunar Exploration Vehicle and still smaller ‘transformable robots’ made by a toy company.  SLIM was scheduled for launch on August 25^th, along with an advanced x-ray telescope to remain in Earth orbit, but has been postponed due to high winds in the upper atmosphere – the launch window remains open until September 15^th.  The launch will be broadcast live by JAXA, Japan’s national space agency, when it happens.  Like the Indian lander, SLIM will follow a slow trajectory, reaching the Moon 3-4 months after launch and attempting to land a month later.  (Zulfikar Abbany, ‘Moon Sniper:  Japan Aims Anew at a Lunar Landing’, www.dw.com, online, 26^th August 2023.)

In the Journal of Geophysical Research:  Planets on August 7^th, Chinese scientists, and others including a team at the University of Aberdeen, announced a major discovery by the Deep Penetrating Radar on the Yutu-2 rover, in the crater Van de Graaf, one of the deepest on the lunar Farside.  Below 300 metres of regolith  (broken rock), there is a smaller, buried crater, and below that seven layers of lava, getting progressively thicker with depth.  (Isobel Whitcomb, ‘China’s rover maps 1,000 feet of hidden ‘structures’ deep below the dark side of the moon’, Space.com, August 19^th 2023.)  That supports the idea that the Farside was originally much more like the Nearside with its dark lava ‘seas’, which were buried by ejecta from the big Nearside impacts, leaving only isolated dark spots like the Sea of Moscow and the crater Tsiolkovsky.  Similar scanning over a range of Farside sites will be needed to confirm that fully, if it is the explanation.

After inferior conjunction with the Sun on September 6^th, the planet Mercury returns to the morning sky, near the Moon on September 13^th, rising at 5 a.m. by the 20^th, below and to the left of Venus, and is at maximum elongation from the Sun on the 22^nd. 

Venus returns to maximum brightness in the morning sky in Cancer on the 18^th, pulling ahead of us after inferior conjunction, is passed by the Moon on the 11^th and 12^th, and rises at 3 a.m. by the end of September.  On August 21^st the Parker Solar Probe made its 6^th flyby of Venus, which will take it to 4.5 million miles from the Sun on September 27^th, with one more Venus pass on Christmas Eve, 2024, and a still closer approach to the Sun at 3.9 million miles in 2025.   

Mars is out of sight beyond the Sun, in Virgo, and is passed by the Moon on September 16^th, when neither will be visible.  The Curiosity rover has now bypassed a difficult sandy slope about 1000 feet up Mount Sharp, after repeated unsuccessful attempts to scale it, and has begun sending pictures of a small field of craters, caused by the breakup of a meteoroid above the mountain, billions of years ago.  It’s expected that the field will yield new data about the successive episodes of flooding, in the remote past when Mars still had water.  Analysis of data obtained by Curiosity in 2021 has now revealed that there were seasonal variations in the rate of deposition on the mountain, back then  (‘Did Mars Have Seasonal Weather Patterns?’, ON 11^th August 2023).

In a much-anticipated event, the return capsule from NASA’s OSIRIS-Rex spacecraft will land in the USA on September 24^th, bringing back samples from the asteroid Bennu.  Japan’s Hyabusa 1 & 2 spacecraft have previously returned asteroid samples to Earth, but have succeeded only in returning dust grains, where OSIRIS-Rex is bringing back an overflowing hopper full of dust and fragments.  Bennu is designated a Potentially Hazardous Asteroid, though it’s not currently on a collision course with Earth, and to everyone’s surprise it turned out be a ‘junk pile’ of loosely bound fragments rather than solid rock.  NASA’s next asteroid mission launch, on October 5^th, could hardly have a more different target:  the metallic asteroid Psyche, which may turn out to be a solid chunk of nickel-iron, 130 miles across.  Last year it seemed some of the instruments might not be ready in time, but those problems have been overcome, and on June 26^th the spacecraft was ready to have its foil insulation installed before launch.  Meanwhile on November 1^st the Lucy mission, on its way to Jupiter’s Trojan asteroids, is by chance going to pass close to asteroid (152830) 1999 VD57, now named Dinkinesh, and although that’s only 0.4 miles across, who knows what surprises it will have for us?

Jupiter rises about 9.00 p.m. in Aries, coming back to where it was in the evening sky in summer last year, and begins to move backwards against the stars as the Earth overtakes it.  The Moon is nearby on September 4^th, passing below the Pleiades the following night.  The volcanic moon Io and its shadow cross Jupiter’s disc on the night of September 21^st-22^nd.  The September issue of Astronomy Now predicts that Io may also transit the Great Red Spot, though it’s not absolutely certain due to the varying speeds of Jupiter’s cloud formations.

Saturn in central Aquarius is visible all night, still moving westward after opposition, at its closest to us, on August 27^th.  The Moon is near Saturn on 26^th September.  

Uranus in Aries rises at 9.00 p.m., about the same time as Jupiter, and is near the Moon on September 5^th.

Neptune is in the sky all night, in Pisces, closest to us at opposition on September 19^th, when it will be south-southeast of the distinctive feature of Pisces known as ‘the Circlet’  (see map).  Neptune is near the Moon on September 1^st and 28^th, and on the 1^st it will be occulted by it as seen from Antarctica and South Georgia.  On the 28^th there will be a similar event, visible only from the extreme south of New Zealand.

After successful photography of Uranus and Neptune from angles that can’t be seen from here, by the New Horizon spacecraft, now 8 billion kilometres from Earth, NASA has announced a new programme to study them with the probe while they’re near opposition, backed up by terrestrial observations.  Amateur astronomers are invited to participate, as long as they have telescopes with apertures greater than 16 inches.  (Keith Cooper, ‘NASA’s New Horizons will investigate Uranus from the rear (Neptune, too). Here’s how you can help’, Space.com, 16^th August 2023.)  I don’t know what the current situation is, but when I was taken to see one in 1984 at Juniper Lake in California, there were only three 16-inch reflectors in private hands in the UK, all of them hand-built by their owners along with the two-storey buildings needed to house them.  Harry Clough in South Ayrshire was one of those three, in the mid-1970s.  Braithwaite Telescopes, the last telescope maker in Scotland, subsequently offered one as the top of their range, with the option of acquiring it mounted on a trailer for movement between observing sites.  I don’t know how many were sold  (at least one as I recall), but such is the difference in purchasing power in the USA that the Juniper Lake telescope had been bought commercially, by three ordinary chaps  (one was a policeman and another a fireman).  Even now, I suspect there may not be many UK participants – though I do know of one 20-inch Dobsonian telescope in private hands.

Duncan Lunan’s recent books are available through Amazon.  For more information see Duncan’s website, www.duncanlunan.com.

You can download a copy of the Sky Map for September here: