BAA Ordinary Meeting, 2021 January 23 : ZOOM

2021 July 31

Alan Dowdell

This meeting was held as a webinar using Zoom and YouTube, due to the continued restrictions caused by COVID-19.

Alan Lorrain opened the meeting at 2.30 p.m. and said that there had been a Council meeting that morning, at which the likelihood of starting traditional face-to-face meetings again was discussed. It was thought the earliest this could be was in the autumn of the year.

He then welcomed the afternoon’s speaker, Dr Ann Bonell. Dr Bonell is the president of Leicester Astronomical Society.

‘Now you see it, now you don’t’

Dr Bonell explained that this talk would be a review of some supposed astronomical bodies which have turned out not to exist.

She started by discussing the hypothetical planet Vulcan. People believed that such an object existed between Mercury and the Sun because Mercury does not move as according to Newtonian laws; its orbit is ‘wrong’ by 43 arcseconds per century.

The mathematician Le Verrier, at the suggestion of François Arago, published a report in 1843 on the orbit of Mercury. In 1845, observations were made during a transit of this planet across the Sun, which showed that Le Verrier’s prediction was wrong and needed more work. His calculations were, however, used in the discovery of Neptune. In 1859, he did a particularly in-depth study of Mercury’s orbit, which still did not match observations. He then proposed the existence of a new planet or multiple smaller bodies inside the orbit of Mercury. This had been suggested before, but he was the first to give a mathematical justification. It is unclear who suggested the name of Vulcan, which entered general usage.

Edmond Modeste Lescarbault, a doctor and amateur astronomer, recorded a slow-moving object transiting the Sun, lasting for 1h 17min 9s on 1859 Mar 26. He wrote to Le Verrier on 1859 Dec 22, after hearing about the announcement of a possible new planet. Le Verrier was excited but suspicious, and made an unannounced visit to Lescarbault on Dec 31, accompanied by a witness. Le Verrier was informed of how Lescarbault used a simple clock to make these observations, and a homemade pendulum for timing. It was also revealed that he often recorded his observations by writing them on a plank of wood. Despite this, Le Verrier became satisfied that the observation was correct and proceeded to announce this to the world. Lescarbault was awarded Légion d’honneur for his observation.

Not everybody was convinced. Emmanuel Liais reported that he had observed the Sun at the same time as this supposed discovery and that he had not seen Vulcan.

Le Verrier produced orbital predictions for Vulcan based on the observations, giving it a period of 19d 17h and a distance of 0.14au from the Sun. Prediction times for future transits were produced. These transits were looked for but with no success.

The well-known astronomer, James Craig Watson, and the comet discoverer Lewis Swift made independent observations of a Vulcan-like object during the total eclipse of 1878. However, neither of these observations matched predicted Vulcan positions.

With the death of Le Verrier in 1877, the interest in Vulcan waned and finally died following new predictions of Mercury’s orbit using Einstein’s equations instead of Newton’s. However, following the 1970 solar eclipse, Henry Courten reported several objects near the Sun. This led him to propose the existence of an asteroid belt between Mercury and the Sun, since named the Vulcanoids, but this was never confirmed.

Modern observations using the SOHO and MESSENGER spacecraft were made, but no objects resembling Vulcanoids were found.

The search for Vulcan did lead to another discovery, however. The 19th-century German astronomer Heinrich Schwabe observed the Sun for 17 years, looking for planets. He did not find any planets, but he noted a regular variation in sunspot numbers, with a period of approximately 10 years.

It was suspected for a short period that Mercury had a moon. On 1974 Mar 27, Mariner 10 went past Mercury and detected strong UV radiation which then disappeared, only to return three days later. The source appeared to have moved at 4km/s, the sort of speed expected for a moon. The object was finally identified as the hot star 31 Crateris. This made astronomers realise that UV radiation can penetrate the interstellar medium further than had been thought.

For a while it was also thought that Venus had a moon, called Neith(e). In 1672, Giovanni Domenico Cassini noted a companion while observing the planet, but did not report it. In 1686 he saw it again, and word started to spread. He estimated that the object had the same phase as Venus and about a quarter of its diameter. Apparently, this object was observed 18 times by a total of five observers during 1761. During the transit of Venus in 1671, some observers claimed to see a dot following the planet, but others did not. Then in 1766, Father Hell of Vienna published a report stating that all these observations were optical illusions. Not everyone, however, was convinced.

In 1884, Jean-Charles Houzeau said this object was not a moon but another planet, which orbits the Sun every 283 days and comes in conjunction with Venus every 1,080 days. The skilled observer Edward Emerson Barnard saw a proposed satellite in 1892 at 7th magnitude. It has since been suggested that this observation could have been of a nova.

In 1846, Frédéric Petit thought that the Earth had another moon, with a period of 2h 44min and an elliptical orbit, at a distance of between 3,570 and 11.4km. Le Verrier heard this report and was dismissive of it. However, Petit’s proposal received more widespread awareness as it was referred to in Jules Verne’s book From the Earth to the Moon. We do of course have a temporary moon called Cruithne, which orbits the Sun but interacts with the Earth’s orbit at times.

The hypothetical gas giant Tyche was proposed to be located in the Oort Cloud by John Matese in 1999. This unseen object was an explanation for the orbital behaviour of long-period comets. The WISE space telescope did not find it which, if it exists, puts a limit on its possible size.

Themis is the name given to the tenth satellite of Saturn, which was ‘discovered’ by William Henry Pickering on 1905 Apr 28. However, it did not exist. Pickering had already discovered the ninth satellite, so he had some credibility for his observations. He even got awarded the Lalande Prize for this discovery, and that of the non-existent tenth satellite.

Planet X was the label for a proposed planet affecting the orbits of Uranus and Neptune. The work on this by Percival Lowell led to the discovery of Pluto.

Nemesis is a hypothetical star proposed in 1984, which could be a red or brown dwarf. It would be close to our solar system, orbiting the Sun at a distance of 1.5ly. Its existence could explain the 30-million-year cycles of mass extinctions on Earth; its interactions with the Ort Cloud would result in comets being sent Earthwards. Unfortunately, this object has not been found.

Does Planet Nine exist in our solar system? It could be causing manipulation of minor planets’ orbits. Its proposed orbit takes it out to 400–800au, with a period of between 10,000 to 200,000 years. There are surveys looking for it to the east of Orion.

It is interesting to speculate what other theories could one day be abandoned. Patrick Moore, who had plenty of alternative proposals sent to him, referred to their proponents as ‘independent thinkers’.

Mr Wilson thanked Dr Bonell for her interesting talk and, after a few questions, continued by introducing Dr David Arditti for the Sky Notes.

Sky Notes

Dr Arditti commenced by saying he had just finished doing a Zoom talk for the Society for Popular Astronomy, which was on the subject of music and astronomy and is available on the SPA Facebook page. This talk was an example of the cooperation between the two societies.

The first subject for the Sky Notes was variable stars – making a change from the habit of saving them till last, almost as a footnote. Recent observations show that alpha Orionis is now back up to magnitude 0.6. Dr Mark Kidger’s paper in the Journal about its fade [130(6), 342–348 (2020)] proposed that a dimming may happen again; his prediction was for Apr 12 of 2021. A comparison star chart is available via the Variable Star Section web page. Another easy variable to monitor is Algol, and a time for mid-eclipse was predicted for 2021 Jan 26. Dr Arditti encouraged new observers to have a go and monitor these events.

A new nova had recently been discovered, called Nova Persei, or V1112 Per. Mike Harlow obtained a spectrum of this nova using an old BAA objective prism. The supernova SN 2021aai, discovered on 2021 Jan 12, was imaged by Nick James soon after its discovery. The variable deep-sky object Hubble’s Variable Nebula was imaged by Richard Sargent.

Dr Arditti showed the approaching lunar phases at the time of this meeting. The first-quarter Moon was to be very high in the evening sky on 2021 Mar 21.

The planets Jupiter and Saturn had been in close conjunction, and were imaged together by Dr Arditti alongside the Moon on 2020 Dec 17. Unfortunately, Dr Arditti missed when the two were at their closest, on Dec 21, due to the sky being clouded out. However, an image taken by Martin Lewis on Dec 20 clearly shows them within the same telescopic field of view. An image of this event taken by Eric Sussenbach was also shown. Peter Anderson from Queensland imaged the two planets in the same field on Jan 21. He also photographed a similar image of the pair 60 years previously, on 1961 Feb 20.

An image of Mercury in the evening sky taken by Peter Lawrence on 2021 Jan 21 was shown, as was an image of the planet obtained by Luigi Morrone on 2020 Nov 11. This image was compared with one generated using the program WinJUPOS, which showed close correspondences.

Images of Mars taken on 2021 Jan 9 by Dr Arditti and on 2021 Jan 15 by Martin Lewis showed how much the northern polar cap had shrunk. In Mr Lewis’ image the planet has a size of nine arcseconds. Mr Lewis also created a very detailed albedo map of Mars.

A map of Jupiter was presented, showing the planet as it appeared in November. It was prepared by Andy Casely, Clyde Foster, and Eric Sussenbach. An image by Mr Foster was shown, taken in South Africa on Dec 26, which showed Clyde’s Spot.

Images by Mr Lewis taken on 2020 Nov 5 showed Neptune and Triton, and Uranus with its moons. He took these using a 444mm Dobsonian. A composite image, also taken by Mr Lewis and titled ‘Parade of the planets’, was shown.

There was a lack of prominent comets, but 2021 A1 (Leonard) was possibly getting brighter. It was at 19th magnitude at the time of the meeting, but Dr Arditti noted that by 2021 December it could be at 4th magnitude. It was to be in the northern sky for a long time. An image taken on 2021 Jan 1 showed 2021 A1 as a very faint object.

An image of the comet 2020 M3 (ATLAS) taken by Peter Carson on 2020 Nov 7 was shown, as was an image of 156P/Russell-LINEAR taken by Martin Mobberley on 2020 Nov 15.

The near-Earth object 1999 RM45 was to have a close approach of 7.6 lunar distances on 2021 Mar 2–3, and would be at its brightest, magnitude 13.4, on 2021 Mar 1.

The Quadrantids were generally clouded out for most observers in the UK, but David Talabér made radio observations using GRAVES radar to detect its activity on 2021 Jan 2.

A stunning image of the total eclipse of the Sun on 2020 Dec 14, taken in Argentina by Andreas Möller and Miloslav Druckmüller, was shown. Nick James and Mike Frost were on the same expedition to see this event, organised by Astro Trails, and Mr James captured two comets in the same field: C/2020 X3 SOHO and C/2020 S3 ERASMUS.

The Sun’s activity was picking up. An image of it, taken on Jan 21 by Gary Palmer, was shown.

Dr Arditti then showed a non-BAA image, but a stunning one, taken by NASA of M51 using the Stratospheric Observatory for Infrared Astronomy (SOFIA), showing the magnetic field of this galaxy. An artist’s impression of quasar J0313-1806 was also shown. This is the most distant quasar found to date and is powered by the earliest-known supermassive black hole.

Finally, Dr Arditti reminded members to look at the Association’s web page, as some new features had been added.

Mr Wilson thanked Dr Arditti for his talk and the meeting was closed.

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Alan Dowdell, Meetings Recorder