August 2017: Summer Patchwork

In the show this time, we talk to Dr. Caitriona Jackman about adventures in the outer Solar System, Josh Hayes rounds up the latest news, and we find out what we can see in the August night sky from Ian Morison and Claire Bretherton.

The News

Last month marked 10 years since the launch of Galaxy Zoo, a project which invites members of the public to classify galaxies in images taken by robotic telescopes across the world.
The project was launched on 11th July 2007 and had immediate success through the discovery of a new type of object called a quasar ionisation echo. Named Hanny's Voorwerp after its discoverer Hanny van Arkel, a Dutch primary school teacher, this was the first of many objects identified by the project. The count now stands at over 125 million galaxies identified, with a huge range of characteristics being seen. This output is far greater than any identification algorithm could produce and the introductory paper has had over 750 citations. Among many interesting studies conducted by Galaxy Zoo was one in galaxy rotation. Participants were asked to say whether face on galaxies were rotating clockwise or anti-clockwise. Assuming that galaxy alignment was random, the researchers were expecting roughly equal numbers of each, but found an excess of anti-clockwise rotation. The researchers investigated to see if there was a bias by showing participants the same images, but mirrored and found that there was still a bias towards (incorrect) anti-clockwise identification! When correcting for this, it was found that spiral galaxies which are near to each other have a tendency to rotate inexoplanets and discover new pulsars. They have even branched out beyond astrophysics and the power of the public is now being used to to count giraffes and elephants, transcribe Shakespeare's handwritten documents and identify parts of cells. Here's to another, even more successful decade of citizen science!

Measurements from an Indian lunar orbiter have suggested that the levels of water ice below the Moon's crust are much higher than previously thought. Launched in 2008 and operated until 2009, the Chandrayaan I spacecraft has revealed that whilst the majority of the lunar surface has only background levels of water, there are some regions with an excess when compared to this background. Further study of these areas shows that all of them are associated with material ejected from below the surface by a volcano, known as pyroclastic deposits. Since these rocks were formed below the surface, they can be used to infer the composition of the lunar mantle without having to drill down through the crust. The high level of water seen in these pyroclastic rocks is thought to mean that there is more water under the surface of the moon than previously thought. This has led to some discussion of further manned missions to the moon to collect samples from the pyroclastic deposits or extract water from below the lunar surface. (Item contributed by Antonia Newell.)

A team of Japanese scientists have completed an investigation into the effects of gravity on plant growth by successfully growing cucumbers on board the ISS. The experiment was designed to discover if gravity or water has a greater impact on root growth. On Earth, there are two effects which govern root growth: hydrotropism, where roots grow towards high concentrations of water; and gravitropism, where the roots grow in the direction of the pull of gravity. By growing cucumbers on the ISS, the effects of microgravity could beinvestigated. The experiments showed that hydrotropism has a greater influence in controlling root growth. This could have interesting impacts on long distance space travel, as it would appear that in order to grow plants well, we only need to use water concentration gradients and can manage without strong gravity. This discovery is an important one in the steps towards long-term space habitation.

Interview with Dr. Caitriona Jackman

Monique interviews Dr. Caitriona Jackman from the University of Southampton about her extensive involvement with both the Juno and Cassini missions, active around the giant planets Jupiter and Saturn respectively. Among the discussion are UV aurorae, the perils of space weather, the mystery of what Jupiter's core is like and the correct way to sniff a Saturnian moon.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during August 2017.

The Planets

• Jupiter Now four months after opposition, Jupiter can still be seen low in the southwestern sky after nightfall. It sets at about 1 am BST as July begin. As the month progresses its brightness falls from -1.9 to -1.7 magnitudes as its angular size falls from 34 to 32 arc seconds. It lies in Virgo, initially some 8 degrees to the west of Spica, reducing to 4 degrees as the month progresses and will pass Spica on September 11th on its journey towards the lower parts of the ecliptic. Next year it will only reach an elevation of some 25 degrees when due south and, in the following two years, just 18 degrees before it moves back towards the more northerly parts of the ecliptic. Even so, with a small telescope one should easily be able to see the equatorial bands in the atmosphere, sometimes the Great Red Spot and up to four of the Gallilean moons as they weave their way around it.
  
  
• Saturn came into opposition on June 11th and so will be at its highest elevation due south as darkness falls. It shines initially at magnitude +0.3 falling to +0.4 during the month and has an angular size of ~17 arc seconds. With an angle of 26.8 degrees inclination to the line of sight, the rings are virtually as open as they ever can be. Their maximum tilt, at 27 degrees, will come in October - the first time since 2002. Saturn ceases its westwards, retrograde, motion on August 25th. It is sad that Saturn, now lying in the southern part of Ophiuchus between Sagittarius and Scorpius, only reaches an elevation of ~17 degrees above the horizon when due south so hindering our view of this most beautiful planet. If imaging Saturn (or Jupiter), Registax 6 has a tool to align the red, green and blue colour images to largely remove atmospheric dispersion from the image. At somewhat over £100 one can purchase the ZWO atmospheric dispersion corrector which uses two, contra rotating, prisms to carry out an even better correction - and which can also be used for visual observing.
  
  
• Mercury Given a very low western horizon, Mercury, showing an 8 arc second disk and shining at magnitude +0.4 might just be seen after sunset at the beginning of August. Binoculars may well be needed but please do not use them until after the Sun has set. It passes between the Earth and the Sun (inferior conjunction) on August 26th.
  
  
• Mars passed behind the Sun in July, but will be hidden in the Sun's glare all month so cannot be observed.
  
  
• Venus is visible in the east before dawn this month, rising around 3 hours before sunrise. Its magnitude dims slightly during the month from -4 to -3.9 as its angular diameter shrinks from 14.5 to 12.5 arc seconds. However, at the same time, its illuminated phase increases from 74 to 83% which explains why the magnitude does not drop too much. Its elevation before sunrise is greatest on August 2nd when Venus lies close to the open cluster M35 in Gemini.
  
  

Highlights of the Month

August - Find the globular cluster in Hercules and spot the 'Double-double' in Lyra. Just to the left of the bright star Vega in Lyra is the multiple star system Epsilon Lyrae, often called the double-double. With binoculars a binary star is seen but, when observed with a telescope, each of these two stars is revealed to be a double star - hence the name!

August - A good month to observe Neptune with a small telescope. Neptune comes into opposition - when it is nearest the Earth - on the 2nd of September, so will be well placed both this month and next. Its magnitude is +7.9 so Neptune, with a disk just 3.7 arc seconds across, is easily spotted in binoculars lying in the constellation Aquarius as shown on the chart. It rises to an elevation of ~27 degrees when due south. Given a telescope of 8 inches or greater aperture and a dark transparent night it should even be possible to spot its moon Triton. (This is my objective around the end of the month!)

The Moon and Saturn - Late evening on the 2nd of August, the waxing Moon will be seen to the upper right of Saturn. Antares lies down to its lower right.

The mornings of August 12th and 13th: midnight to dawn - look out for the Perseid meteor shower. If clear, these mornings should give us a chance of observing the Perseid meteor shower - produced by debris from the comet Swift-Tuttle. The early morning of the 12th August will give us the best chance, if clear, of viewing the shower, but the peak is quite broad and so it is well worth observing on the nights before and after. Most meteors are seen looking about 50 degrees from the 'radiant' which lies between Perseus and Cassiopeia. This year a gibbous Moon rises before midnight so will be low in the sky for some time the early hours of the 12th so it will be best to observe them as soon as it is really dark. Moonlight will hinder our view, but it should still be possible to spot many meteors. NB: As we need to view a very wide area of sky, normal binoculars would be of no use, but the Vixen SG 2.1 x 42 that I have just reviewed in the Astronomy Digest, could be useful as they will darken skylight from the Moon somewhat and enable fainter meteors to be seen - albeit over a smaller field of view.

16th August 07:40 - 08:40 BST: A daylight Occultation of Aldebaran - In the early morning of the 16th, Aldebaran will be occulted by the Moon - visible with a telescope (but keep it well away from the Sun). The times are for London and will vary somewhat across the country. In a line from Leverburgh on the Isle of Harris across to Wick, a grazing occultation will be seen at 8:01 BST.

19th August - before dawn: Venus and a thin crescent Moon - Before dawn on the 19th, if clear, Venus will be seen just 2 degrees above a very thin waning crescent Moon.

25th August - after sunset: Jupiter below a thin crescent Moon - After sunset on the 25th, if clear, Venus will be seen below a thin waxing crescent Moon.

August 14th and 30th: The Straight Wall - The Straight Wall, or Rupes Recta, is best observed either 1 or 2 days after First Quarter (30th August: evening best) or a day or so before Third Quarter (evening of the 14th August best). To honest, it is not really a wall but a gentle scarp - as Sir Patrick has said "neither is it a wall nor is it straight"!

Southern Hemisphere

Claire Bretherton tells us what we can see in the southern hemisphere night sky during August 2017.

Kia ora and welcome to the August Jodcast from Space Place at Carter Observatory in Wellington, New Zealand.

The Planets

• Mercury finishes its best evening appearance of the year this month. At the beginning of August it sits low in the west after dark, just above Regulus, the brightest star in Leo, setting around 7:45. By mid month it will disappear from view, lost in the evening twilight as it heads back towards the Sun in our skies. Jupiter is a little further north, midway up our northwestern skies. It is slowly moving below and towards the right of Spica over the course of the month. Both are quickly dropping down our evening skies, with Jupiter setting at around 11pm at the beginning of August, but by around 9:30 at the end.
  
  
• Saturn - Further around still, Saturn is high in the northeast after dark, with Antares above and to the left, and remains in our sky for most of the night. A waxing gibbous moon passes close to Saturn on the 3rd and 31st of the month, whilst on the evening of the 25th, a thin 3 day old crescent Moon will sit just below Jupiter.
  
  
• The Moon - On the 22nd of August the Moon will pass directly between the Earth and the Sun, causing a total Solar eclipse. The eclipse path will run across the United States, but unfortunately no part of it will be visible from New Zealand. The next total Solar eclipse visible from our shores won't be until July 2028.
  
  

Constellations

Last month we looked at some of the amazing objects in Scorpius and Sagittarius, towards the centre of the Milky Way. This month we'll move along a little from our Galaxy's bright centre to where it passes overhead through Centaurus, Crux, the Southern Cross, and the constellations of Carina, Vela and Puppis that make up the great ship Argo Navis.

Crux - Crux, the Southern Cross lies on its side after sunset in the south western sky, with the Diamond Cross and false cross below. Above Crux are Alpha and Beta Centauri, the brightest stars in the constellation of Centaurus. Known as the pointers, they guide our eye to Gamma Crucis, the star at the top of Crux, and help us identify the true Southern Cross.

Omega Centauri - To the right of the pointers, and just outside the main band of the Milky Way is the spectacular globular cluster Omega Centauri. This is by far the largest and brightest globular cluster in the Milky Way appearing as a fuzzy star to the naked eye. With binoculars it is an even more stunning sight, spanning almost a full degree of the sky, twice that of the full moon, whilst a small telescope will show a shimmering ball of stars, with many individual stars visible towards the outskirts.

The Jewel Box - Close to Beta Crucis, in the Southern Cross, is a different type of star cluster. NGC 4755, also known the "Jewel Box", is an open cluster about 6,500 light years away. It is rich and bright with the stars showing an array of different colours, highlighted by an orange-red supergiant. At magnitude 4.2, the Jewel Box can easily be seen with the naked eye. It is dominated by an A-shaped asterism of bright stars, which is observable with binoculars, whilst even a small telescope will reveal a stunning sight. The name comes from Sir John Herschel's vivid description of the cluster as a "casket of variously coloured precious stones".

The colours of these stars tell us how hot they are. The red stars are the coolest, with temperatures around 3000K, yellow stars like our Sun are closer to 6000K, whilst the hottest, bluest stars reach temperatures of 30,000 Kelvin or more. In order to get this hot these stars have to use a huge amount of fuel very quickly, so they don't live very long - they live fast and die young. The most massive live for just a few million years. The fact that NGC4755 still contains a number of these hot blue stars tells us that it is relatively young, in fact it is one of the youngest star clusters known, with an estimated age of just 14 million years.

Coal Sack - Just to the left is a dark patch known as the Coal Sack nebula. This is a huge cloud of interstellar dust and gas some 700 light years away. It is so thick and dense that it obscures the light from more distant stars, appearing as a darkened area against the bright backdrop of the Milky Way. Aboriginal astronomers have observed the Coalsack for at least 40,000 years, whilst to Māori here in New Zealand it is known as te Patiki or the flounder.

Carinae Cluster - Below the Coalsack, at the tip of the Diamond Cross asterism in Carina is the Theta Carinae cluster, or IC 2602, an open cluster containing around 60 individual stars. At magnitude 1.9 it is the third brightest open cluster in the sky and is often known as the Southern Pleiades, although it is still much fainter than its northern counterpart. The cluster spans around 50 arcminutes, over 1.5 full moon diameters, so it is best viewed with binoculars or a low powered telescope giving a wide field of view.

Carinae Nebula - Around 4 degrees to the right of Theta Carinae is the famous NGC 3372, the Eta Carina nebula, a huge cloud of glowing gas estimated to be around 7500 ly away. At 4 times the size of the Orion Nebula, it is one of the largest nebulae of its type in our skies. With the naked eye you'll be able to pick out the brightest central areas, but with binoculars you should be able to see Eta Carinae itself as a golden star within the nebula. Eta Carinae is actually a system of at least two stars, which combined are around 5 million times more luminous than our Sun. The largest has around 90 times the Sun's mass and is so bright that the radiation pressure it produces is almost too strong for the gravity holding it together, causing a constant stream of material out into space.

Highlights of the Month

Venus - In the morning skies, Venus is now rising around 5am. The Moon will pass nearby on the 19th, sitting just above Venus in the north east at sunrise. The two will move towards the north by midmorning, providing a perfect opportunity to try and spot Venus in the daylight, with Venus sat just to the right of a thin waning crescent Moon.

Wishing you clear skies from the team here at Space Place at Carter Observatory.

Odds and Ends

This month in the Odds and Ends we discuss a recent paper which points out some potential errors in the LIGO collaboration's data analysis of their gravitational wave detections, which were announced last year.

The paper, which has become colloquially known as 'The Danish Paper' appeared on the arXiv on the 13th of June and set off an interesting chain of events, both from a scientific and sociological perspective. A blog post on the Forbes news website by Sabine Hossenfelder created a large amount of interest in the paper, and the potential that it was calling into question a Nobel Prize-worthy finding in astrophysics. However, a rejoinder from a member of the LIGO collaboration in another blog post pointed out a number of issues with the Danish Paper itself, with the detailed fallout still continuing.

Ian, Monique and Charlie discuss the content of the Danish Paper and it's rebuttal, and the impacts it may have on how science is communicated with the public.

Additional Caveat from Ian: This was recorded on the 20th of July. There has been subsequent revision of 'The Danish Paper' by the authors, taking into account comments from journal referees. The situation is still evolving (along with our understanding and opinions!) and it is left to the listener to judge whether we are too quickly jumping to conclusions in our discussion, we apologise if this seems so.

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