September 2020: A Pair of Planets

In the show this time, we talk to Andrew Tkachenko about Stellar astrophysics in the era of big data, Fiona Porter rounds up the latest news, and we find out what we can see in the September night sky from Ian Morison, Haritina Mogosanu and Samuel Leske.

The News

In the news this month: intermediate mass mergers, telescope troubles, and a sighting of a much younger solar system.

First up, LIGO and VIRGO have spotted the gravitational waves of an unusual black hole merger. Since gravitational waves were first detected in 2015, a variety of astrophysical mergers have been seen between black holes and neutron stars. The most recent detection is unusual in the mass of the black holes involved – the pair were around 66 and 85 times the mass of the Sun, merging to form a black hole of around 142 solar masses.Next, some less good news – the Arecibo radio telescope in Puerto Rico is no longer able to operate as a result of recent damage. A steel cable that was used to support part of the telescope's structure snapped, breaking an antenna and tearing a 30-metre hole in the telescope's 302-metre dish.Finally, the Very Large Telescope in Chile has produced the first image of a pair of exoplanets around a Sun-like star. The star seen is very young – only about seventeen million years old – but is otherwise very similar to the Sun, with a comparable mass. The planets, however, are quite different to those in our own solar system: the inner planet weighs in at around fourteen times the mass of Jupiter, orbiting at 160 AU from its parent star, while the outer one is around six Jupiter masses and orbits at 320 AU. For comparison, 1 AU is the distance between the Earth and the Sun, and Pluto orbits at an average of 40 AU.Very few exoplanets have been directly imaged like this; the first one, also by the Very Large Telescope, was in 2004, and there are still less than 50 images total. Only two other systems with multiple planets have been imaged, and neither had a Sun-like star, so this is makes for a very interesting look at something like a much younger version of our solar system.

Interview with Andrew Tkachenko

Dr Andrew Tkachenko talks about his work on astroseismology and the use of machine learning for classifying groups of stars. In particular he discusses the TESS and Kepler missions and using light curves (plots of brightness against time) to classify stars with machine learning. He also introduces the planned PLATO mission as a future experiment this method will be useful on. Andrew also talks about what led him to Manchester and how the work he has been doing could be useful for a ground based survey that Manchester researchers Mark Kennedy and Rene Breton are involved in.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the Northern Hemisphere night sky during September 2020.

Southern Hemisphere

Haritina Mogosanu and Samuel Leske from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during September 2020.

• The First point of Libra

  These fancy words are naming the point on the celestial map where from Earth it looks like the Sun shifts celestial hemispheres. As the Sun is changing its position in relation to the background stars every day, the two main lines you will find on a celestial map, the celestial equator (see above) and the ecliptic cross over at equinoxes. 2000 years ago the September crossover occurred in the constellation Libra. Due to Earth’s wobble, which has a spinning top movement, the crossover happens now in Virgo. Astronomers however kept the First point in Libra as the name for the September equinox. In 400 years from now it will be in Leo. (by the way this is the same reason why the time when the Sun is in any particular zodiacal constellation shifted back with almost a month too. The equinox is only a moment in time as Earth continuously moves as it orbits around the Sun.

• What’s the Sun up to?

  According to TimeandDate.com, September Equinox in Wellington, New Zealand is on Wednesday, 23 September 2020 at 1:30 a.m. NZST. As the month goes, the days will be longer than the nights until we reach Summer Solstice. Since the equinoxes only occur twice per year they are very special astronomical events.

• Spring begins on the 1st of SeptemberSince 1870s New Zealand used the meteorological dates to mark the beginning of spring, thus spring here begins on the 1st of September! People who come here from the Northern Hemisphere usually think that spring begins at the autumnal equinox- which by the way is on the 23rd. But just for the sake of the argument, according to WeatherWatch Managing Director Philip Duncan, there are actually four ways to start a season (1) looking at astronomical dates, which would place the date on September 22 or 23, based on the equinox, (2) by meteorological dates – which is a three-month division of the year into seasons, thus Spring starts on September 1, (3) observing the solar winter, which is the three “darkest” months with the June 21-22 winter solstice in the middle, which shifts the beginning of spring to August 8 and (4) looking at what nature does, which in New Zealand is hard to pin down.

• The Milky Way and Zodiacal Light

  In September, the asterism of Scorpius is at this time of the year the Fishhook of Maui that drags the Milky Way down from the sky. We get to admire the amazing galactic centre and the Milky-Way.kiwi inside it which is fantastic. Enjoy it while it lasts!

  In addition to the Milky Way, if you are stargazing from somewhere with very dark skies, you can spot what is called the “Zodiacal Light”. It's a cone-shaped light that stretches from low on the horizon along the ecliptic. Yes, it is the ecliptic again!! The zodiacal light is the light we see reflected from dust and ice particles in the plane of our own solar system! How cool is that? So in the sky we can see both the galaxy that we inhabit and the solar system. Two objects at two completely different scales! And in different parts of the sky as well. But the part of the sky where we observe the Zodiacal Light, is where the ecliptic would be. Once you;ve learned where that is you will see it is very useful, especially at figuring out where the planets are in the sky, as they orbit around the Sun in the same path, you’ve guessed it on the ecliptic. But because some of their orbit planes are ever so slightly on an angle compared to Earth’s plane, they don't match perfectly so that’s why the Zodiacal band is a band of stars about 8 degrees each side of the ecliptic as that’s where the planets are visible.

• Scorpius, Centaurus and Southern Cross

  After sunset, you can see the fish hook at Zenith and then falling down towards the western part of the sky. Scorpius Te Matau a Maui has a magnificent red supergiant star Antares, Maori call it Rehua. It is the Summer wife of the Sun. In a telescope it looks like a beautiful ruby and is impossible to miss on a clear night. It looks quite reddish, just like planet Mars! The name Antares is the rival of Mars, as planet Mars sometimes gets very close to Antares, because Antares is one of those stars on the Zodiacal Band. When this happens the two of them rival in redness and brightness. I believe Mars wins but that’s just because is made of iron. We took a lot of images of Antares recently with our new fantastic project the Slooh Telescopes and it’s a really big star.

  Scorpius has some fabulous deep sky objects. Also with Slooh, we took a heap of them over the last month.Cat Paw’s nebula this one is a good astrophotography target, The Butterfly Cluster, or M6 which you can also see in a telescope, it’s an open cluster of stars, M7 also known as Ptolemy’s cluster is also an open cluster M4, the globular cluster near Antares. NGC 6231 or Melotte 153 is a beautiful open cluster as well which was discovered as far back as 1654 by Giovanni Hodierna, who listed it as “luminosae” in his catalogue. South of Scorpius you can find the constellation of Centaurus, a creature that is half-human and half-horse in Greek mythology, home of Alpha, Beta and Omega Centauri.This time of the year it is very high in the sky so in a good position to observe.

• Circumpolar objects to New Zealand

  In September, in the evenings, you will find the Southern Cross in the south western part of the sky. So just after sunset is at the 3 o’clock position heading down followed by the pointers. Canopus would be at the same time grazing the southern horizon so hard to see from hilly Wellington. Achernar and the two Magellanic Clouds would be in the south eastern part of the sky.Some other bright stars Just after sunset, Virgo will be on the western horizon, very close to the Sun. It will be visible only in the first part of the month, with the beautiful star Spica sinking beyond the horizon by the middle of the month. In Libra, Zubenelgenubi and Zubeneschamali are the former claws of scorpius, now the scales of justice. Some sources say that they have been chopped from Scorpius and recreated into a scale of justice at the time when the First Point of Libra was in Libra, which is why Libra was created by our ancestors, not because they noticed that people born that time of the year were indecisive, or always tried to get revenge or where weighing their arguments carefully, but to mark one of the two equinoxes. Sagittarius has many beautiful bright stars, and I love the particular teapot shape it has which now can be seen as the constellation is at Zenith. Nunki is our favourite star this month also because we took a picture of it recently.

• Oldies but Goldies – famous in the North

  In the north, we can see the bright star Altair in Aquila, the constellation of the eagle, a triangle-shaped constellation in north-eastern skies. Lower on the northern horizon, mirroring somewhat Canopus, the second brightest star in the sky which is lower on the southern horizon, is Vega, nicknamed Antopus by the awesome Ian Cooper. This is a play of words with Antares, which means the rival of Mars, Ian says that Vega rises low in the north when Canopus is low in the south and they are like two rivals eyeing each other up. Another beautiful star is Albireo, in Cygnus. It is a spectacular blue and red giant double. Only about 10 degrees above the horizon, the stars of Lyra, where Vega lays, also host a fabulous Messier object, which is really easy to see in a telescope, that is M57 the Ring Nebula, the remnants of a star. In astronomical terms it is a planetary nebula. Nearby, another one of its kind, remnants of another star that died is in Vulpecula, M 27 – Dumbbell Nebula is another good target. As they are not so good to photograph from Wellington, we've just been using the telescopes from Slooh which have prime views of these amazing objects. Probably the best star and one of my favourite objects in the night sky is Albireo, which we also view with Slooh, just because it is too low to photograph.

• Dark patches

  The Milky Way Kiwi is really well visible at this time of the year, you’ll need a very dark sy to see it though. The lines of dust that go through the centre of the Milky Way are striking and they are the neck of a gigantic emu bird for our neighbours, the aboriginal people in Australia. The other famous dark patch here is the Coalsack, near the Southern Cross. The coalsack is also known as the flounder, which is the Māori name for it. In deed, if you find a truly dark sky, you will see the resemblance. The Coalsack is an appropriate name, as diamonds are sometimes found in the coal, inside the dark patch, made of interstellar dust matter is the Jewel Box, or the Kappa Crucis Cluster, NGC 4755.

• The Moon and the Planets in September 2020

  Full Moon is on September 2nd, Last quarter on September 10, New Moon on September 17, and First Quarter on September 24. Jupiter and Saturn are in the sky. Mars is catching up and will soon be at opposition and Venus is in the morning sky, at the beginning of the month is rising around 4:30 AM.

Odds and Ends

George is organizing a professional workshop for UK postgraduate students who will be working with data from the Atacama Large Millimeter/submillimeter Array (ALMA). While George has organized workshops before, what makes this one different is that it will be virtual, which is a first for George. The advantages are that people can attend the workshop while staying home, so they do not need to take any health risks when travelling and also do not need to spend any money on train fare or hotel rooms. However, people will need to set up the data processing software CASA on their own computers as well as download the ALMA data that will be used for demonstration purposes during the workshop, and that could be more challenging if George and other ALMA staff are not physically present to help. The workshop will be sometime in the fall. Hopefully, it will go well.

Michael describes the QUBIC mission, one of many attempts to hunt for B-mode polarisation of the CMB. The collaboration has been working on a number of articles over the last few months. In particular a test of the prototype instrument in Paris was discussed. The preprint (as yet unpublished) version of that can be found here .

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