In the show this time, we talk to Dr. Amanda Karakas about star evolution, Ian rounds up the latest news, and we find out what we can see in the August night sky from Ian Morison and Claire Bretherton.
This month in the News: Pluto flyby, Earthiest planet yet and Buckyballs in space.
The dwarf planet Pluto received a visit this month from NASA's New Horizons space probe, revealing spectacular features of colour, atmosphere and geology on the Solar System's ninth most-massive object. As described on last month's Jodcast, New Horizons has carried an array of instruments towards Pluto since 2006, but has only just flown by the dwarf planet, lingering long enough to capture images of Pluto and it's largest moon, Kharon, which have greatly changed our view of them. Amongst the spectacular discoveries was the apparent variety of Pluto's surface textures. Whilst it was expected that Pluto would be inert and pock-marked by billions of years of impacts from smaller lumps of ice and rock, the data received from New Horizons showed a relatively fresh and clean looking surface, indicating that either the rate of bombardment is much lower than thought in this part of the Solar System, or that geological activity on Pluto re-configures its crust and smooths away the impact craters. Initial guesses from astronomers are that this indicates the surface is only around a hundred million years old, a compartively short span in the few billion years since Pluto's formation. Further evidence of geological activity was also seen in other features. Huge mountains appear to rise three and a half kilometres up, comparable to the Canadian Rockies here on Earth, but apparently made of water ice --the only ice strong enough at minus two hundred and thirty five celcius to be capable of supporting such large structures. Away from the mountains and at the edge of the prominent heart-shaped region named the Tombaugh region, after Pluto's discoverer, there are also apparent glaciers of frozen Nitrogen flowing and merging around more solid features. What is creating the warmth causing these glaciers to move is so far unknown, but could be radioactive processes within the rocky core of the dwarf planet. New Horizon's view of Pluto's companion Kharon also provided surprises, with the moon showing huge canyons kilometres long, possibly casued by tidal forces from Pluto, and a dark polar region christened 'Mordor'. Further information on Pluto and Kharon will come in a torrent over the next sixteen months -- the time it will take to download all that which has already been taken by New Horizon's instruments. Before turning its attention away from Pluto New Horizons also took measurements of Pluto's atmosphere. As well as a spectacular image showing the sun lighting up the haze around the dwarf planet, the probe also measured the deflection of radio waves sent from Earth in order to measure the density of the atmosphere, showing it to have around half the mass inferred from previous measurements. As well as the wealth of data still to be downloaded from this month's observations, New Horizons will now travel on towards the Kuiper belt of small objects which encircles the Solar System, where it plans to rendezvous with one or two of the larger, fifty mile wide objects in around five years time.
Also this month, much excitement was generated by the latest release of information on extra-solar planets (that is, planets outside our solar system) from the Kepler satellite. Of particular interest of the twelve was the planet known as Kepler 452b, as it is one of the most Earth-like so far discovered, even if there is some way to go before any true Earth analogues are confirmed. Kepler 452b has around five times the mass, one and a half times the radius and twice Earth's gravity, meaning that it doesn't score as highly on the Earth Similarity Index (ESI) used to rank exoplanets as some of those previously discovered. It does however exist in orbit around a G-class star very similar in attributes to our own Sun, at a distance putting it in the 'habitable zone', where estimated temperatures and atmospheric pressures may be able to support the formation of liquid water. Much else remains unknown about the planet, with the technical paper describing its discovery giving only around a 50/50 chance of it being a rocky terrestrial planet rather than a small gas planet. Travel times would also be long; Kepler 452b is fourteen hundred light years away in Cygnus, meaning it would take the New Horizons probe some twenty-six million years to get there at its current speed. It is however further evidence of the richness of variety of exoplanets which exist and a fantastic demonstration of astronomers' ability to discover and learn about such tiny, faint and distant objects.
Finally, a research problem dating back nearly a century was given a probable solution this month by the discovery of some unique properties of bucky balls in space. Buckminsterfullernes, to give the full name to the football-shaped constructions of sixty carbon atoms, have been known to exist in space since 2010, when the Spitzer infra-red satellite observed them in the remnants of a white dwarf star. This month a team of chemists at the University of Basel in Switzerland managed to create a cold, high vacuum environment approximating interstellar space and measured the spectra of bucky balls (that is, how they absorb and emit different colours of light) trapped there by electric fields. The spectra appeared consistent with so-called 'Diffuse Interstellar Bands' observed in interstellar gas both inside and outside our own galaxy. These Diffuse Interstellar Bands were first observed by University of California graduate student Mary Lea Heger in 1919 and have had multiple suggested explanations since, with some even proposing they could be from free floating deep-space bacteria. The discovered match with the properties of bucky balls appears to be a very good one, however, showing how technically challenging chemistry work -- it took the team in Basel nearly 20 years to achieve -- can shed light on astronomical problems.
Interview with Dr. Amanda Karakas
Dr. Amanda Karakas from Mt. Stromlo Observatory, ANU is currently studying the evolution of stars similar to our own Sun, and how they create elements using theoretical modelling techniques. In this interview, she discusses the methods used to model a star from birth to death, and the intricacies of modelling the part of the star where the most violent reactions take place: the core. She also tells us about the problems involved with simulating such complicated systems, and about how we can test our models by using spectral observations of stars or by analysing the chemical composition of meteorites we can find right here on Earth. Finally she gives us a glimpse into the future the Solar Sytem as our own Sun ages.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during August 2015.
The nights are slowly lengthening, giving us more time to enjoy the views this month will bring, including the main highlight of the month: The Perseid Meteor Shower.
As sunset begins to fade Arcturis, the brightest star in Botes, sets on the western horizon. High in the south the Milky Way cuts through the Summer Triangle formed by the stars Vega of Lyra, Deneb of Cygnus, and Altair of Aquila. The dark and dusty region of the Milky Way known as the Cygnus Rift lies a third of the way between Altair and Vega. Within the Cygnus Rift is Brocchi's Cluster, the asterism resembling an upside-down coathanger. Rising from the southeast is the Great Square of Pegasus. Follow Alpheratz, the Great Square's top left corner, to see the Andromeda Galaxy, our nearest major neighbour, visible as a faint and fuzzy glow.
- Jupiter will be visible low and in the west during the twilight hours early in the month before it passes behind the Sun on August 26th.Venus passed 6° below Jupiter on July 31st, and remains close to it, but both will quickly become difficult to spot as the month progresses.
- Saturn is the sole bright planet visible outside twilight hours. It lies in Libre near the double star Alpha Librae, and falls in brightness from +0.4 to +0.5 magnitudes. On August 2nd it ceases retrograde (westward) motion and begins its journey eastward toward Scorpius. One hour after sunset it will lie 20° above the horizon with a 17" disk. On August 21st Saturn reaches Eastern Quadrature. The shadow on its rings will reach maximum extent, giving a fantastic 3D view of our Solar System's crown jewel.
- Mercury rises slightly higher in the twilight sky this month, but will be hidden after twilight hours.
- Mars rises in the east 70 minutes before the sun as August begins, shining at magnitude +1.7. By month's end Mars will rise 2 hours before the sun, at +1.8 magnitudes. On August 8th at 5° it will lie below Castor and Pollux in Gemeni about 45 minutes before sunrise. On August 20th and 21st it will lie close to M44, the Beehive Cluster.
- Venus lies too close to the Sun to observe safely after sunrise this month, but will gradually rise earlier than the sun throughout the month; by month's end it will be visible for 90 minutes before the sun rises at a brightness of -4.5 magnitudes, an angular brightness of 52", and a phase of 9%
- Two thirds of the way up the right hand side of the Keystone of Hercules is M13, the brightest globular cluster visible in the northern sky. To the east, 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!
- Neptune passes closest to the Earth during opposition on August 31st and will be easy to spot at a magnitude of +7.9 near the constellation of Acquarius. With a telescope of 8 inches or greater aperture it should be possible to spot its moon Triton as well.
- August 7th is one of the last chances to see Jupiter this apparition. Given clear skies and a low western horizon it should be possible to spot Jupiter and Mercury and the star Regulus within a one-degree diameter circle.
- The main highlight of this month comes in the form of the Perseid Meteor Shower, visible between midnight and dawn on August 12th-14th. The peak of the shower comes after sunrise on the morning of August 13th, so before sunrise that morning will be the best chance to spot the shower. Most meteors will be seen 50° from the radiant between Perseus and Cassiopeia. With the New Moon on the 14th, there will be no moonlight to hinder our view during the peak, when one might expect to see 50 to 70 meteors per hour.
- Looking west on August 22nd an hour after sunset Saturn will be close to a first quarter moon, and will be visible with a good horizon in the south southwest.
- On the evenings of August 4th or 7th look out for the Straight Wall on the Moon, but be warned: it isn't a wall, and neither is it straight!
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during August 2015.
At the beginning of the month three bright planets appear low in the western evening sky soon after Sunset. Brilliant silvery Venus is the brightest and highest with golden Jupiter below and right. Mercury is well below the two bright planets on August 1st, but moves quickly up the sky, night to night, as Venus and Jupiter sink lower. On the 7th Mercury is just a full-moon's diameter to the right of Jupiter. Venus is left of the close pair of planets, and all three set about 70 minutes after the Sun.
After passing between us and the Sun mid-month, Venus will appear in the eastern dawn twilight. By August 20th it will be rising in the east an hour before the Sun. Venus will remain the 'morning star' for the rest of the year.
Mercury continues its ascent of the evening sky through August while Venus and Jupiter disappear in the twilight. By month's end Mercury is setting due west after 8 pm, making its best evening sky appearance of the year. The bright orange star Arcturus is setting in the northwest, well to the right of Mercury, often flashing red and green as it goes.
Saturn is the only bright planet in the late-evening sky. A small telescope shows Saturn's ring system and biggest moon, Titan, looking like a star about four ring-diameters from the planet. More powerful telescopes should reveal faint banding in the planets atmosphere along with gaps and variation in colour of the rings.
In the north, to the left side of the Milky Way is Vega, the fifth brightest star in the sky, which forms part of the constellation of Lyra that represents an ancient stringed instrument. Opposite Vega, in the south, Canopus is the second brightest star in the night sky and twinkles with a yellow tint. To the Polynesians this star is Atutahi, the navigator, considered by Māori as the chief of all the stars in the sky. Canopus was also the navigator of Argo Navis, the ship in which the argonauts searched for the Golden Fleece. Argo Navis, once the biggest constellation in the sky, was subdivided into Carina (the keel, or the hull, of the ship), Puppis (the poop deck, or stern), and Vela (the sails). These constellations now hold the asterisms known as the false and diamond crosses which are adjacent to Crux, the Southern Cross.
Above Crux are Alpha Centauri, the third brightest star, and Beta Centauri, the 11th brightest star in our night sky, which point you towards the Southern Cross and appear to follow it around the sky. To the north of Beta Centuri lies the brightest globular cluster, Omega Centuri, which can be seen as a fuzzy star. With a small telescope the cluster becomes a glowing, shimmering ball of stars, with many individual stars visible towards the outskirts of the cluster.
Sitting about half way above the southern horizon as the Southern Cross sinks towards its lowest position in the sky is the faint constellation of Tucana, the Toucan. Alpha Tucanae is a magnitude +2.8 star about 200 light years away. Beta Tucanae is a loose group of 6 gravitationally bound stars approximately 140 light years away. The two exceptional objects in the Toucan are the Small Magellanic Cloud (SMC) and 47 Tucanae the second brightest globular cluster in our sky.
The SMC is a dwarf galaxy visible to the unaided eye as a cloudy smudge in the sky. The secret to viewing it properly is to use peripheral vision to bring out more detail. Peripheral vision is a trick that visual astronomers use to spot very faint objects such as nebulae, clusters or galaxies. Try to look at the object with the tip of the eye rather than directly at it, as if you are looking just to side of it, and you should be able to see much more. The Small Magellanic Cloud is best viewed from a dark location and it is bright enough to be seen from many suburban locations as long as the Moon and local lighting are not too bright.
There is another larger and brighter cloud to the right of the SMC. This is the Large Magellanic Cloud, another of our galactic neighbours lying just 160,000 light years away. The Magellanic Clouds, the crosses, alpha and beta centauri and all the beautiful clusters in the south are objects that can always be seen in our southern night sky as they are circumpolar, meaning they never set below our horizon.
A Final Note From Claire...
Thank you for listening to the August jodcast. I will shortly be heading off on maternity leave so our new Curator of Science, Haritina Mogosanu will be stepping in to produce the Southern skies section over the next few months. I look forward to catching up with you all again when I return in the New Year.
Odds and Ends
After nine years in transit, New Horizons finally reached Pluto this month. Speeding past the dwarf planet at a relative velocity of 13.78 km/s (49,600 km/h), New Horizons did not go into orbit, but instead took many hundreds of photographs and other scientific measurements as it flew past. At closest approach on July 14th it was some 12,500 km above the surface of Pluto, and is now returning spectacular images of the surface showing fractured nitrogen ice fields, many mountain ranges, and numerous other interesting geological features. Surprisingly, the surface shows fewer craters than were expected, suggesting a younger surface, or more extreme weathering processes, than were thought. The spacecraft can only transmit data back to Earth at a rate of 1-2 kbps, so returning all the data taken during the encounter will take another 16 months as New Horizons continues its journey on through the Kuiper Belt and eventually out of the solar system
Vitamin B3, otherwise known as niacin, may have originated in space! Researchers at the NASA Goddard Space Flight Center have been building on work in which they found traces of Vitamin B3 in a sample of Carbon-rich meteorites. Since then they have found the simpler organic molecule it can be created from and have been simulating various space-like scenarios on the mixture by adding different levels of water ice and exposing it to a bombardment of energetic photons. All of their results have so far matched real life samples. Vitamin B3 is a crucial ingredient for assisting with metabolism and is thought to have ancient origins, which may well be from the arrival of a meteorite or comet to Earth. The full story can be found here.
|Interview:||Dr. Amanda Karakas and Charlie Walker|
|Night sky:||Ian Morison and Claire Bretherton|
|Presenters:||Josie Peters, Megan Argo and Monique Henson|
|Editors:||Adam Avison, Charlie Walker and Monique Henson|
|Segment Voice:||Iain McDonald|
|Website:||Sally Cooper and Stuart Lowe|
|Cover art:||Portrait of Pluto and Charon CREDIT: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute|