Leonid meteor shower

The Leonid meteor show peaks on the night of the 17th/18th November this year. There will be no Moon to spoil the view and hopefully no clouds either! The radiant will clear the horizon about 10:30UT, but The actual peak in activity is expected around 05:00UT of the 18th (see the chart below). Observed rates are in the region of 10 to 15 per hour.

The position of the radiant on the morning of the 18th November.

Clear skies.

September’s talk: ‘Lady Pioneers of the BAA’

Given by Mike Frost (Director of the historical section of the BAA), this was a first for Abas, as it was our first online talk. 

Mike has collected information on a  remarkable catalogue of women who were involved in the earliest years of the British Astronomical Association (and its forerunners, the Liverpool and Leeds Astronomical Societies), and managed to reel off a lot of information in just an hour.

Mary Acworth Evershed (maiden name M.A. Orr, 1867-1949) was the first director of the BAA Historical Section and she produced the first popular guide to the southern stars.  Her husband John ran an observatory in southern India (Kodaikanal).  Mary became a keen solar observer and they later moved to Australia.  She also wrote a who’s who on those people who had had lunar craters named after them.  Her astronomical knowledge also enabled her to identify many astronomical allusions in Dante’s inferno, long overlooked or just forgotten.  Tracy Dougherty has written a biography about her.

Elizabeth Brown (1830-1899) was a solar specialist who had her own private observatory in Gloucestershire.  She was a member of the Liverpool AS even though she did not live there.  She was a keen umbraphile; she chased total solar eclipses in Russia, Trinidad and Norway, and wrote travelogues thereof.

Lady Huggins (née Margaret Lindsay Murray, 1848-1915) was into photography and spectrography and met her future husband William in the 1870s.  Their shared interest in spectrography brought them together, as they discovered that some stars shared the same spectrum as our Sun, and that some nebulae were emission nebulae like M42.  Prior to her adding her photographic skills to the mix, he had been hand-drawing the spectra.  They co-authored an atlas of spectrography.

Agnes Clerke (1842-1907) was an inaugural council member of the BAA.  She hailed from Cork and wrote  ‘A Popular History of Astronomy during the 19th Century’. She spent several months in South Africa also.

Annie Scott Dill Maunder (née Annie Russell, 1868-1947) reminds us of how limited the prospects were for women in that time.  She was able to study maths at Cambridge but was not allowed to graduate.  She worked as a ‘computer’ at the Royal Greenwich Observatory but lost her job when she married her boss Walter, who was widowed with five children.  Married women were not allowed jobs.  She loved astronomy and joined the BAA as soon as she could and continued to work as her husband’s assistant.  She specialised in solar observing.  She plotted sunspots through two solar cycles and was the first to identify the pattern we call the butterfly diagram, where sunspots early in the solar cycle form nearer the poles, but they form nearer and nearer to the equator as the cycle progresses..  She too, produced a popular book: ‘The Heavens and their Story’.

Alice Everett (1865-1949) was another to become a ‘computer’ at Greenwich after studying maths at Cambridge, but also failed to further her career through being a woman.  She worked at the ‘Carte du Ciel’ star atlas project in Potsdam (Germany) then tried to get observatory jobs in the USA.  She came back to the UK, left astronomy, although she remained a kingpin of the BAA, and she became very involved in optics, electrical engineering and the fledgling days of TV design.  She worked for the Baird company.  She had familial links with Scotland and Ireland.

Mary Adela Blagg (1858-1944) came from Cheadle (Staffordshire) and there is a statue of her there.  She came from a large, wealthy family and was educated at home.  In those days scientists would often supplement their wages by touring the country and giving talks, and this was how Mary became interested in astronomy.  She got hooked on variable stars, and mapped their luminosities, cleverly extrapolating the bits of a cycle that got missed.  She also standardised the lists of named lunar craters, fixing those names that could no longer be attached to craters because of old ambiguous recordings.  She provided this information for the IAU, and did nearly all of this by correspondence.

Fiammetta Wilson (1864-1920) seems to have been a real character.  Born Helen Worthington in Lowestoft, married, moved to Canada, came back to the UK and was co-director of the BAA meteor section.  She got into trouble when trying to observe during the blackouts of WW I.  Mike described her as a bit of a fanatical observer and may have suffered burnout.

Grace Cook (1877-1958) was another co-director of the BAA meteor section.  She came from a wealthy family, had her own observatory, and when her family business began to fail she continued her astronomy and was the first Briton to observe Nova Aquilae in November 1918.

Catherine Octavia Stevens (1864-1959) was another who became director of the BAA meteor section.  She observed the three total solar eclipses of 1900, 1905 and 1932.  She was particularly interested in observing the shadow bands which can usually be seen briefly in the very final stages just before and after totality.

Gertrude Bacon (1874-1949) was a founder member of the BAA and apparently another character.  She was able to see the eclipse of 1896 (Norway) then used a hot air balloon to try to observe the Leonids in 1899 above the clouds.  Unable to see the land below, and after pulling the wrong string, she and her fellows nearly ended up in the Bristol Channel but luckily came down in Neath in the morning.  They had not flown in the dark before.

Mike wound down his talk by mentioning other women briefly, some of whom may be worth looking up:

Dorothea Klumpke Roberts, born in San Francisco also observed the 1899 Leonids from a balloon.  By that time she had moved to Paris to be head of the observatory and had joined the BAA.

Agnes Giberne (1845-1939), a BAA founder member who wrote children’s books on astronomy.

Irene Elizabeth Toye Warner, who wrote about ancient history and the worship of the planet Venus, before becoming involved in spiritualism.

The RAS charter of 1820 did not recognise women directly but gave them honorary fellowships.  Notable among them were Caroline Herschel, Mary Somerville, Agnes Clerke, Margaret Huggins and Annie Jump Cannon. When the RAS charter was amended in 1915 so that women could be members in their own right, five women joined, and they were already BAA members.  Among them was Annie Maunder.

I’m glad our first online speaker was a polished Zoom talker.  A good subject and a good start to our season.  I have left some of the women’s names out, but am happy to pass them on to anyone interested.

March’s talk: Studies of nearby star clusters with the Gaia data

March 2020, and luckily our early end to our season came with a very mind-expanding talk came from Dr Floor van Leeuwen from the institute of Astronomy in Cambridge.  He worked on the Hipparcos star position data and his talk was “the nearby Open Clusters as observed in the Second Gaia data release”.

The Gaia satellite continues to make very accurate observations of star positions and uses the Earth’s orbit as a baseline so that it can record their parallaxes.  By recording star positions over six month intervals over time it can also record stars’ proper motions across the sky.  Its optics have a folded focal length of 35m and has two mirror units separated by 106° whose images are projected onto the same focal plane.  All this provides excellent triangulations and very accurate stellar parallaxes down to ten micro-arcseconds.

The detectors are 100CCDs which are elongated; this enables them to scan to a high or a low resolution depending on the direction of scan.

They need to be kept to a very accurate temperature and cannot scan in the plane of the ecliptic for fear of looking at the Sun and being fried.  In practice Gaia is kept facing 45° from the Sun so the best coverage is of the zone within 45° of the poles although all sky coverage has been completed.

The positions of around 1.7 billion stars was released on 25/4/18.  This was the second data release after the first one in 2016.

The data contained positions of open clusters and he has based his research on those clusters within 240 parsec of us.  These include our familiar friends the Hyades, the Alpha Persei group, Pleiades, Praesepe and less familiar ones such as Blanco 1.  It is able to detect stars down to magnitude 20.

In the case of the Hyades, 480 stars have been found to be part of the group and their average distance is 47.6pc.  Van Leeuwen used data from 300 of the stars.  They appear to be moving away from us towards a converging point.  They display a proper motion, especially those nearer to us.  There are also stars moving through the cluster but their proper motions don’t fit.  There are also stars that are right on the converging point so they don’t have a proper motion, just a parallax (line of sight effect), as they move directly away from us.  Using the data he was able to construct a 3D view of the cluster, and that it appears flattened along the plane of the Milky Way.

Gathering data depends on the distance.  Anything beyond 250pc is hard to see.  If the cluster members are not moving quickly through space that also makes movement harder to detect.  Praesepe is such an example.

Coming back to the Hyades, he placed its members onto the HR diagram and they produce a lovely main sequence line with a thin second line running along just above it.  These are double stars so their combined light makes them appear .75 of a magnitude brighter.  There are already some white dwarfs.  The Hyades are only about 790 million years old.

When van Leeuwen plotted Praesepe along with the Hyades he found their velocities suggested they were of the same origin.  Praesepe’s distance averages 186pc and its age is around 710 million years.  It contains at least 771 stars.  Unfortunately a lot of the stars are too faint for Gaia to obtain enough data.

In the case of the Pleiades and Blanco 1 their double stars also follow the main sequence line on the HR diagram, slightly above the main line.

In total, van Leeuwen used nine clusters in his study, and he combined them all onto the HR diagram. Although these clusters are all quite young, you can see the big stars have already been leaving the main sequence and turning into white dwarfs (at the bottom left) but on the bottom right are small stars that haven’t yet evolved onto the main sequence line.

Other findings are that the Pleiades members are spread out to 11° in diameter.  All we see from the ground is about 6°.

Sizes of globular clusters can also be scanned out to be much bigger than first thought: Omega Centauri is 3—4° and 47 Tucanae is much bigger than the Moon in our sky.

The Gaia mission is hoping to continue up to 2025, with two more data releases in the pipeline.  The longer we can observe these local clusters, the clearer the proper motions of their stars will become.

Bear in mind that these data releases will be made available to citizen science, and that you can access these archives yourself should you wish.  You just have to register.  Beware though that there is so much stuff that you would take a day to download it and your computer would need to have petabytes of capacity.  The best Gaia website is www.gaia.ac.uk

(The nine star clusters used in the study are: Hyades, Pleiades, Praesepe, Alpha Persei group, Coma Berenices, NGC 2451, Blanco 1, IC 2602, IC 2391)

Our after tea talk was Dan Larkins who informed us of various websites where you can have free access to astronomy books and magazines.

The best links are epubBoooks, project Gutenberg and Internet Archive.