Extra-Solar Planets · 2012-05-30 · Edge Of The Universe (2003) Part 2. Death Trap Planets "Edge...

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SOCIETY JOURNAL

February 2007

The society meeting this month will be a video presen-tation. The video follows the hunt for extra-solar plan-ets and makes extensive use of special effects and graphics to illustrate this search.

Extra-Solar Planets

AAS Journal 2 February 2007

President: Steve Calveley 412-9770

Vice President: John White 486-2398

Treasurer: Desmond Heath 575-7750

Secretary: Tim Natusch 838-8938

Curator of Instruments: Dave Moorhouse 0274 819089

Librarian: Helen McRae 021 494418

Editor: Phil Foster 378-9312

Councillor: Mark Cannell 520-1123

Councillor: Martin Thomas 482-2917

Councillor: Nick Moore 576-6060

THE SOCIETY COUNCIL

JOURNAL OF THE AUCKLAND ASTRONOMICAL SOCIETY

The aim of this publication is to promote and foster the science of astronomy, and to encourage the association of astronomical observers and other persons interested in astronomy.

11 issues per year.

Auckland Astronomical Society, Inc., P O Box 24-187 Royal Oak, Auckland 1345, New Zealand

Email : [email protected] Internet : www.astronomy.org.nz

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February 2007 3 AAS Journal

MONDAY 12th FEBRUARY 2007 8.00 PM AT THE STARDOME OBSERVATORY

MONTHLY MEETING

Video Evening

Friends and visitors are welcome. The Library will be open from 7:30pm and after the meeting a light supper will be provided.

Edge Of The Universe (2003) Part 2. Death Trap Planets

"Edge Of The Universe" explores the most terrifying and mysterious phenomena in the known universe. This three part series investigates death trap planets, lethal asteroids and comets, and extraordinary new discoveries about the shape and structure of the Universe and what lies beyond its edge. Using stunning special effects and graphics this series will reconstruct the inaccessible and visualise the unseeable. The world's leading astronomers and cosmologists reveal how they are pushing back the frontiers of knowledge using the world's largest telescopes and ambitious missions into space.

This episode describes the hunt for extra-solar planets and the challenges these discover-ies have presented to our understanding of how planets form and evolve.

SOLUTION TO THE DECEMBER CROSSWORD Across: 3 Dobsonian, 5 Irregular, 6 Cernan, 7 Cape Town, 10 Gegenschein, 11 Emission, 13 Conjunction.

Down: 1 Herschel, 2 Barlow Lens, 4 Night Eyes, 5 Inclination, 8 Procyon, 9 Cygnus, 10 Gnomon, 12 Chi.


Calendar of Society Events

February 2 Friday 7:30 PM Young Astronomers Group Margaret Arthur 5 Monday 8:00 PM Beginner's Guide to the Sky at Night The Hunter and his Dog Martin Thomas 8 Thursday 7:30 PM A.A.S. Council Meeting 12 Monday 8:00 PM Society Monthly Meeting Video Evening: Extra-Solar Planets 16 Friday 7:30 PM Night Eyes Have You Seen it Yet? David Britten 26 Monday 8:00 PM Introduction to Astronomy World's New Large Telescopes – the State of the Game 2007 Steve Calveley

March 2 Friday 7:30 PM Young Astronomers Group Margaret Arthur 5 Monday 8:00 PM Beginner's Guide to the Sky at Night Martin Thomas 8 Thursday 7:30 PM A.A.S. Council Meeting 12 Monday 8:00 PM Society Monthly Meeting TBA 16 Friday 7:30 PM Night Eyes David Britten 19 Monday 7:00 PM Burbidge Dinner 26 Monday 8:00 PM Introduction to Astronomy TBA

Young Astronomers

Coordinator: Margaret Arthur

If you are interested then come along and join us on the first Friday of the month

Friday 2nd February 7.30pm at the Stardome Observatory


New eyepieces, two-beam collimators, new Dobs and great new prices. More available online.

New Telescope Models 8" Dobsonian NOW $ 819 Pyrex option $1069

10" Dobsonian NOW $1269 Pyrex option $1479 or with Cooling Fan $1309

12" Dobsonian NOW $1859 (Pyrex option) $2589 (or with Cooling Fan) $1919

Newtonian Laser Collimators Single target NOW $ 49 NEW 2 target model $ 89

New 2” Star Diagonals $ 119 35mm Camera Adapters $ 29

PLUS … New 2” Eyepieces

26mm Kellner 3 element $ 89 32mm Kellner $ 99 40mm Kellner $ 109 30mm Superview 5 element $ 114 42 or 50mm Superview $ 124 New 2” Barlow Lenses $ 109

Plus a full range of Focusers Drive Systems, Filters and Finders

NEW COMPONENTS including Mounts, Mirrors, Filters Tube Rings, Drive system

www.ASTRONOMY.co.nz

New ASTRONZ Products

See the all the new products and order online today

Astronomy New Zealand Limited, PO Box 39-496, Howick, Auckland email [email protected]

Burbidge Dinner

Parnells on the Rose Garden 85 Gladstone Road Parnell 19th March 2007 7pm onwards seated by 8pm $65 per head, wine included

After last year’s successful event, the venue and overall format for the Burbidge Dinner will remain the same. The Beaumont and Astrophotography prizes will be awarded at the dinner. The speaker for the dinner has yet to be confirmed.

Contact Helen McRae for tickets 09 6241815/09 3022268 email: [email protected]


Introduction to Astronomy

The ‘Introduction to Astronomy’ is a new event looking at general topics of interest to those with a new interest in astronomy. These meetings cover all aspects of astronomy in a low key informative way.

‘Introduction to Astronomy’ also provides a good opportunity to meet other members and feel free to ask any questions you may have. See you there !!

Coordinator: Steve Calveley (ph: 412-9770)

The Night Eyes junior group first meeting for 2007 starts at 7:30pm in the Observatory Sun Room on Friday 16 February. The main topic for the meeting will be: Have You Seen it Yet? Parents, friends and other Society members are very welcome to attend.

Night Eyes February Meeting

Coordinator: David Britten Friday 16th February 7.30pm at the Stardome Observatory

For further information please contact: David Britten at [email protected] (ph. 846-3657).

World's New Large Telescopes – the State of the Game 2007

Steve Calveley Monday 26th February 2007

8:00pm at the Stardome Observatory


The Sky This Month

CosMos

DATE TIME RISE SET Full Moon 02 Feb. 07 1846 2043 0602 Last Quarter 10 Feb. 07 2252 0000 1401 New Moon 18 Feb. 07 0515 0702 2037 First Quarter 24 Feb. 07 2057 1425 2353

DATE RISE SET Mercury 01 Feb. 07 0755 2122 Mercury 22 Feb. 07 0719 1958 Venus 01 Feb. 07 0829 2143 Venus 22 Feb. 07 0914 2124 Mars 01 Feb. 07 0407 1846 Mars 22 Feb. 07 0359 1824 Jupiter 01 Feb. 07 0217 1641 Jupiter 22 Feb. 07 0106 1533 Saturn 01 Feb. 07 2102 0736 Saturn 22 Feb. 07 1935 0605 Uranus 01 Feb. 07 0911 2159 Uranus 22 Feb. 07 0754 2040 Neptune 01 Feb. 07 0715 2054 Neptune 22 Feb. 07 0556 1933 Pluto 01 Feb. 07 0336 1723 Pluto 22 Feb. 07 0216 1603

DATE RISE SET 01 Feb. 07 0636 2033 14 Feb. 07 0650 2020 28 Feb. 07 0704 2002

All times in NZDT (UT + 13hrs) and are for Auckland.

Mercury sets around three hours after the Sun as February begins, its magnitude –0.9 disk 6.0: in diameter. Look for the fleet footed one to the left and below brilliant Venus. These two move together through Aquarius the first week then Mercury tires and drops away, sliding towards the horizon as the month progresses and declining in brightness before being lost to observers around midmonth.


Saturn is well placed in the February sky, rising just after 2100 hrs on the 1st. Saturn’s disk spans 20.3” in diameter and resides in Leo the ‘Lion’ all month. A near Full Moon lies near on the 3rd. By the 28th, Saturn is rising almost two hours earlier at 1910, easily placed for observers to explore this dynamic ringed planet with its retinue of satellites headed by orange-hued Titan.

Mars rises at 0407 hrs on the 1st, around 2.5 hours before the Sun rises. Look for it below the ‘teapot’ asterism in Sagittarius, around halfway be-tween the faint globular cluster NGC 6717 and the glorious and eye-opening globular M22. By the end of the month, Mars lies above and to the right of beta Capricorni, near the globular cluster M75. Mars’ disk never gets above 4.5” in diameter.

Jupiter rises at 0215 hrs on the 1st, blazing away at magnitude –1.9, its 38.8” disk lying below and to the left of Antares, the ‘heart’ of the scor-pion midmonth. In Ophiuchus all month, it lies in the region of globular cluster NGC 6287 at months end. A waning crescent Moon passes on the 13th.

Venus leads Mercury across Aquarius before the latter drops away, leaving our magnificent –3.9 magnitude beacon to dominate the western evening sky. On the nights of the 19th and 20th, Venus lies in Pisces where she is joined by a slim crescent Moon. By the 28th, Venus is setting at 2118 hrs, having lost none of her dazzling brightness.

Uranus shines at magnitude 5.9, seen with the naked eye from under a dark sky. It’s tiny 3.3” disk sets at 2200 hrs as February begins, residing in Aquarius. Venus moves past on the 7th. By the end of the month, Ura-nus is setting at 2018 hrs.

Neptune sets at 2055 hrs, unavailable to observers this month. Moving into the morning sky, its 8.0 magnitude 2.4” disk is better placed later in April.

Pluto is now climbing higher in the morning sky but is best left until later in the year.

References Astronomy Lab 2


P eople worry about asteroids. Being hit by a space rock can really ruin your day. But that’s nothing. How would you like to be hit by a whole galaxy?

It could happen. Astronomers have long known that the Andromeda Galaxy is on a collision course with the Milky Way. In about 3 billion years, the two great star systems will crash together. Earth will be in the middle of the biggest wreck in our part of the Universe.

Astronomer John Hibbard isn’t worried. “Galaxy collisions aren’t so bad,” he says. A typical spiral galaxy contains a hundred billion stars, yet when two such behemoths run into each other “very few stars collide. The stars are like pinpricks with lots of space be-tween them. The chance of a direct hit, star vs. star, is very low.”

Hibbard knows because he studies colliding galaxies, particularly a nearby pair called the Antennae. “The two galaxies of the Antennae system are about the same size and type as Andromeda and the Milky Way.” He believes that the Antennae are giving us a preview of what’s going to happen to our own galaxy.

The Antennae get their name from two vast streamers of stars that resemble the feelers on top of an insect’s head. These streamers, called “tidal tails,” are created by gravitational forces – one galaxy pulling stars from the other. The tails appear to be scenes of incredi-ble violence.

But looks can be deceiving: “Actually, the tails are quiet places,” says Hibbard. “They’re the peaceful suburbs of the Antennae.” He came to this conclusion using data from GALEX, an ultraviolet space telescope launched by NASA in 2003.

The true violence of colliding galaxies is star formation. While individual stars rarely collide, vast interstellar clouds of gas do smash together. These clouds collapse. Gravity pulls the infalling gas into denser knots until, finally, new stars are born. Young stars are difficult to be around. They emit intensely unpleasant radiation and tend to “go super-nova.”

GALEX can pinpoint hot young stars by the UV radiation they emit and, in combination with other data, measure the rate of star birth. “Surprisingly,” Hibbard says, “star forma-tion rates are low in the tidal tails, several times lower than what we experience here in the Milky Way.” The merging cores of the Antennae, on the other hand, are sizzling with new stars, ready to explode.

A Great Big Wreck Dr. Tony Phillips


This GALEX UV image of the colliding Antennae Galaxies shows areas of active star formation, which is not in the tidal tails as one might expect.

So what should you do when your galaxy collides? A tip from GALEX: head for the tails.

To see more GALEX images, visit http://www.galex.caltech.edu. Kids can read about galaxies and how a telescope can be a time machine at http://spaceplace.nasa.gov/en/educators/galex_puzzles.pdf. This article was provided by the Jet Propulsion Laboratory, California Institute of Tech-nology, under a contract with the National Aeronautics and Space Administration.

This section is provided by NASA’s Space Place. They have a good website at http://www.spaceplace.nasa.gov with fun and interesting resource for children and teachers.


News Feed

Magellanic Clouds May Be Just Passing Through

The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are two of the Milky Way's closest neighbouring galaxies. Both are visible only in the southern hemi-sphere. By studying their orbits, astronomers can learn about both the histories of the Clouds and the structure of the Milky Way (from its influence on the Clouds' motions). Astronomers Nitya Kallivayalil and Charles Alcock (Harvard-Smithsonian Center for Astrophysics) and Roeland van der Marel (Space Telescope Science Institute) have made the most accurate measurements to date of the three-dimensional velocities through space of the LMC and SMC.

Their surprising results hold profound implications for both the Milky Way and its com-panions. They found that the velocities of the LMC and SMC are unexpectedly large -- almost twice those previously thought. The radial velocities (motion along the line of sight) for both Clouds are well known and relatively easy to measure. Much more diffi-cult to measure is the proper motion (motion across the sky), requiring extraordinary pre-cision over the course of several years. Both proper motion and line-of-sight motion must be known to calculate the true 3-D velocity.

By making two sets of observations two years apart with NASA's Hubble Space Tele-scope, astronomers calculated accurate proper motions for the LMC and SMC. By com-bining proper motions and radial velocities, they found that the LMC speeds through space at 378 km/sec while the SMC has a speed of 302 km/sec. There are two possible explanations for these high speeds:

The mass extent of the Milky Way is larger t h a n p r e v i o u s l y thought. If the Clouds are gravitationally bound to the Milky Way, then the Milky Way must be much more massive than pre-vious data suggested. The excess mass would pull on the


Two years ago the Huygens descent module drifted down through the hazy atmosphere of Saturn's moon Titan, beaming its data back to Earth via the Cassini mothership. To-day, Huygens's data are still continuing to surprise researchers. Titan holds a unique place in the Solar System as the only moon covered in a significant atmosphere. The at-mosphere has long intrigued scientists as it may be similar to that of the early Earth but the deeper mystery was: what lies beneath the haze? The European Space Agency built the Huygens spacecraft to find out.

The probe, carrying scientific investigations involving both sides of the Atlantic, hitched a ride on NASA's Cassini spacecraft. Together Cassini and Huygens make an unprece-dented joint space mission – as a major milestone, Huygens parachuted to the surface of Titan on 14 January 2005. While Cassini keeps flying by this moon of Saturn collecting new data, one can say that the data collected by Huygens's six instruments during its 2.5-hour descent and touch-down have provided the most spectacular view of this world yet and first dramatic change in the way we now think about it.

The Descent Imager/Spectral Radiometer (DISR) pictures were an enormous surprise to astronomers. Instead of the expected smooth terrain, they saw a varied landscape of channels that had been formed by some kind of flowing liquid. The landing site itself was covered in rounded ice pebbles. The Surface Science Package (SSP) provided the final piece in this particular puzzle. The impact it detected when Huygens touched down indicated that the spacecraft had come to rest in compacted gravel.

The data indicate that Huygens landed in an outflow wash. The Gas Chromatograph and Mass Spectrometer (GCMS) instrument confirmed the nature of the liquid that shapes the surface of Titan. It detected methane evaporating from the Huygens landing site. Meth-ane on Titan plays the role that water plays on Earth. But there are still mysteries. It is not yet clear whether the methane falls mostly as a steady drizzle or as an occasional del-uge.

Huygens's Second Landing Anniversary -- The Surprises Continue

ESA News

Clouds, keeping them "close at hand."

The Magellanic Clouds are not gravitationally bound to the Milky Way. If previous cal-culations of the Milky Way's mass are accurate, then the Galaxy is not massive enough to hold onto its companions. In a few billion years, they will escape from the Milky Way.

The Magellanic Clouds may not be true companions of the Milky Way - they may be travellers just passing through the neighbourhood. The velocities of the Magellanic Clouds relative to each other also are surprisingly high. This suggests that the Magellanic Clouds may be coincidental companions and are not gravitationally bound to each other. Alternatively, their high velocities may explain why these two galaxies, if bound, did not merge with each other long ago. Future measurements of the Magellanic Stream – a long streamer of hydrogen gas trailing behind the Clouds – may clarify the previous paths of the Clouds and their relationships with each other and with the Milky Way.


The GCMS also detected two isotopes of argon. Both have important stories to tell. The Ar40 indicates that the interior of Titan is still active. This is unusual in a moon and indi-cates that perhaps an insulating layer of water ice and methane is buried in the moon it-self, close to the surface, trapping the heat inside it. Occasionally, this heat causes the so-called cryo-volcanoes to erupt. Icy 'lava' flows from these cryo-volcanoes have been seen from the orbiting Cassini spacecraft. Because Ar40 is so heavy, it is mostly concentrated towards the base of the atmosphere, so having Huygens on the surface was essential for its detection. Daniel Gautier, Observatoire de Paris, France, thinks that the other isotope, Ar36, is telling scientists that Titan formed after Saturn, at a time when the primeval gas cloud that became the Solar System had cooled to about 40K (-233°C).

The atmosphere of Titan held surprises too. At an altitude of around 60 kilometres, the wind speed dropped, essentially to zero. Explaining this behaviour presents a challenge for theoreticians who are developing computer models of the moon's atmospheric circu-lation. The Huygens Atmosphere Structure Instrument (HASI) provided the temperature of the atmosphere from 1,600 kilometres altitude down to the surface. Huygens also measured the composition profile of the atmosphere to be a mixture of nitrogen, methane and ethane. The methane and ethane provide humidity, as water does in Earth's atmos-phere. At the surface of Titan, Huygens measured the temperature to be 94K (-179°C) with a humidity of 45 percent.

Even though the Huygens data set is now two years old, the discoveries have not yet stopped. In addition, Huygens gives planetary scientists a wealth of 'ground-truth' to complement and help interpret the observations still coming from Cassini. At the begin-ning of 2007, Cassini showed that liquid methane is present on Titan in lakes. Cassini will make another 21 fly-bys of Titan between now and the end of its scheduled mission in the middle of 2008. The Cassini-Huygens scientists are discussing their options to ex-tend the mission.

Unexpected Cooling Effect in Saturn's Atmosphere University College London London, U.K.

In the hunt for interplanetary answers to how atmospheric temperatures are maintained, UCL researchers have ruled out a long held theory. They've found that the hotter than expected temperature of Saturn's upper atmosphere -- and that of the other giant planets -- isn't due to the same mechanism that heats the atmosphere around the Earth's Northern Lights. A simple calculation to give the expected temperature of a planet's upper atmos-phere balances the amount of sunlight absorbed by the energy lost to the lower atmos-phere. But the calculated values don't tally with the actual observations of the Gas Gi-ants: they are consistently much hotter.

It has long been thought that motion within the electrically charged part of the atmos-phere, the ionosphere, is driven by the planet's magnetic field, or magnetosphere, was the culprit behind this heating process. Now writing in the journal Nature, researchers reveal, using numerical models of Saturn's atmosphere, that the net effects of the winds driven by polar energy inputs is not to heat the atmosphere but actually cools it. Professor Alan


Aylward, of the UCL Department of Physics & Astronomy, and an author of the study, explains: "The aurora has been studied for over a hundred years, yet our discovery takes us back to first principles. We need to re-examine our basic assumptions about planetary atmospheres and what causes the observed heating." "Studying what happens on planets such as Saturn gives us an insight into what happens closer to home. Planets can lose their atmospheres as we see with Mars. Do we completely understand how this happens? Are there mechanisms heating the gas and causing it to escape that we do not yet fully understand? By studying what happens in other atmospheres we may find clues to Earth's future."

Comet McNaught (C2006/P1)

For those who did not get to see Comet McNaught, here is a photograph of it in the Auckland sky. Photograph taken by David Roos.


Book Reviews

Utilization of Space – Today and Tomorrow

Authors: Berndt Feuerbacher and Heinz Stoewer (Editors)

Publisher: Springer, 2006

T his handsome 400 page hard-back volume is a collection of fourteen review articles by

twenty mainly European authors. The articles are organised into six sections covering general aspects of access to space, observing Earth, looking up at the stars and planets, Earth communi-cations and spacecraft navigation, space as a laboratory and future chal-lenges.

The articles are not easy reading re-views in the style of Scientific Ameri-can or Sky & Telescope – they are written by technical specialists for a technically orientated readership who will be less concerned about the den-sity of the prose, and more concerned with the content. The book is heavily illustrated throughout with colour im-ages and graphics, adding to the qual-ity feel, although jpeg artefacts are evident in a few.

Although definitely technically orientated, mathematics is minimal in most articles. Each article has a comprehensive list of references plus web references where relevant. The book is complete with a comprehensive list of acronyms from ACES (Atomic Clock En-semble in Space) to XMM (X-Ray Multi-Mirror), and an index.

Two articles are directly about astronomy. The first (27 pages), “Astronomy and Astro-physics from Space” reviews the problems with surface-bound observing that can be eliminated by a space-based platform and some of the limitations of the space environ-


ment (such as exposure to cosmic rays and charged particles, magnetic torques on space-craft, etc). The use of space to study aspects of cosmology and structure formation, black holes and compact objects, star and planet formation is briefly reviewed. Current space based astronomy missions are discussed in terms of optical, UV, infrared, far infrared / sub-mm, microwave, x-ray and gamma ray capabilities. Future missions are reviewed including the HST-replacing James Webb Space Telescope, the astrometric GAIA mis-sion, space based interferometry projects, planet hunting missions and the next genera-tion of X-ray telescopes.

The second astronomy-related article (29 pages), “The Solar System” covers the history and current status of space-based exploration of the solar system and our broad under-standing of the planetary systems and their satellites. Other than for the Huygens landing, it is effectively pre-Cassini and presents none of the recent discoveries about Saturn and its moons, particularly Titan. A table of planetary properties lists Jupiter and Saturn as having 16 and 33 known satellites respectively. This reflects the use of decade-old sources of information (mid-1990’s) by the authors, in an area where discoveries have been frequent and numerous. The authors also review the orbital dynamics of the planets and their satellite systems, their composition and interior structure, surfaces and atmos-pheres, energy balance and evolution, magnetic fields and field generation and the origin of the solar system.

A third article perhaps is relevant to aspects of astronomy, “Fundamental Physics”. The author concentrates primarily on planned missions to test aspects of special relativity, general relativity, quantum physics, statistical physics, cosmology and high energy phys-ics. The current state of Earth-based measurement and the expected improvement from space-based experiments is emphasised.

A few minor production problems are evident such as references to graphics that do not exist, or captions that refer to colour graphs or figures that are actually reproduced in monochrome. Factual errors also exist. For example, dark matter and dark energy are stated to contribute ~70% and ~25% of the critical density (of the universe), respectively. The opposite is true. These blemishes are minor.

Given that only two or three of the articles are directly or indirectly related to astronomy, what value is this book to an amateur astronomer? A well read astronomy enthusiast who keeps up with the news would find little totally new material about astronomy, whereas a newcomer would find a comprehensive review of the importance of space based explora-tion on our understanding of the solar system and our Universe. Perhaps the well read astronomy enthusiast would gain more from the articles with a non-astronomical orienta-tion?

This is not a text book. Neither is it a collection of articles aimed at novice readers. Read-ers should have some scientific or technological background to be able to better appreci-ate the broad scope of the content, and hopefully appreciate those aspects outside their direct realm of experience or interest.

Roger Feasey


“When the Pleiads, Atlas’ daughters, start to rise Begin your harvest; plough when they go down. For forty days and nights they hide themselves, And as the year rolls around, appear again When you begin to sharpen sickle-blades; This law holds on the plains and by the sea, And in the mountain valleys, fertile lands Far from the swelling sea.”

Works and Days – Hesiod (8th century BC)

O ne of the highlights of Taurus and indeed the whole sky is the glorious open clus-ter M45. I have often stood beneath the summer celestial sphere and gazed long-ingly at the small misty glow within the ‘bull’s’ body, my imagination captured

by this cosmic ‘cloud’ of hot young suns who collectively form the stellar family ‘Pleiades’ or ‘Seven Sisters’. Even the immortal poet Tennyson was captured by their sheer beauty, writing:

“…Many a night I saw the Pleiads, rising thro’ the mellow shade, Glitter like a swarm of fireflies Tangled in a silver braid.”

This fine group has been revered by humankind since antiquity. Titles like ‘Virgin’s of Spring’, ‘Stars of Abundance’ and ‘Stars of the Season of Blossoms’ were enshrined with the Pleiades. Chinese women worshipped them as the ‘Seven Sisters of Industry’. The Maori of New Zealand revered it as Matariki and greeted its rising with laments for those who had recently died. An important task of Matariki was to keep moving in a cluster through the heavens so that it could predict lean and fat seasons and bring food supplies to the Maori. Offerings of their first sweet potatoes (kumara) of the season were made to Matariki.

There was a universal vision of a hen and her chicks amongst many, the Russians calling this group the ‘Sitting Hen’, the Danes referred to it as ‘Eve Hen’. The French and Ital-ians called it the ‘Pullets’ and the Hungarians saw it as ‘Hen With Fledglings’.

Amongst Mediterranean peoples, the rising of the Pleiades heralded the beginning of the season for navigation. Manilius called this group ‘Narrow Cloudy Train of Female Stars’. The Finns and Lithuanians called it a ‘Sieve’ whilst some French peasants thought it a ‘Mosquito Net’.

TAURUS The “Bull”

CosMos


Open Cluster M45, aka Pleiades, Matariki ... Photo Credit: Robert Gendler


One of the well known myths surrounding these seven daughters of Atlas and Pleione has them harassed by the amorous Orion. Disturbed by Orion’s lustful advances towards his daughters, Zeus intervened and turned them into doves where they flew off into the heavens to escape. Orion has been placed in the sky just out of reach of the fair maidens, forever destined to have one eye on the maidens and one eye cast towards his rear where his arch-nemesis the scorpion (Scorpius) stalks him across the sky.

The Aborigines of Australia have a delightful legend around a missing Pleiad. It appears that the missing Pleiad was once a beautiful queen, far more radiant than her six hand-maidens. Waa the ‘Crow’ became infatuated with her heavenly beauty and decided to take her for his bride. Disguising himself as a white grub, he hid himself within the bark of a tree. The Queen and her handmaidens came down to Earth to search for grubs to eat. Suddenly, Waa leapt out and grabbed the queen, having reverted back to his former self, and kidnapped the beauty.

To the naked eye from a reasonably dark site, six are easily seen though upwards of nine-teen have been reported. I have, under a very dark sky and with good atmospheric seeing, seen 11 stars (admittedly when I was younger) but the closeness of the members them-selves makes resolution something of a trial.

With binoculars, the cluster comes alive and with greater optical power, literally hun-dreds of stars are seen. Riccioli in 1651 caught the flavour when he wrote:

“…a first rate field-glass, taking in 3 ¼° and magnifying seven diameters, shows 57; Hooke, in 1664 saw 78 with the best telescope of his day; Swift sees 300 2ith his 4 ½ inch, and 600 with his 16 inch.”

Modern estimates put the membership of the Pleiades at around 300 to 500 stars. There are no bright red or yellow stars within the cluster, the brighter members being of spec-tral types B through to F. In contrast though, there are a few faint red dwarf variable stars, similar to the flare stars inside the Orion Nebula. They typically have a luminosity (brightness) only 1/100th that of the Sun and shine between 13.3 and 16.9 magnitudes. In 1963, G. Haro studied 7 of these stars and found them to have light variations of around 0.8 to 3.7 magnitudes within a period of several minutes to three hours.

It was in 1767 that Rev. John Michell calculated the probability of finding such a group of stars as the Pleiades by chance alignment. His calculations showed a chance of 1/496,000. It was this calculation along with the commonality of such clusters in the sky that lead him to believe that these clusters are in fact physical groups.

The Pleiades group lies around 380 light years away from our Sun, as measured by the satellite Hipparcos. The members are thought to be around 100 million years old, young on a cosmic scale.

The brightest member star and the most centrally located is Alcyone (eta), a B-type sub-giant of magnitude 2.86 with a luminosity of 2300 Suns. Its diameter is probably no more than ten times our Sun and its mass around 5 Suns. Alcyone is the most massive of the member stars. Archibald Lampman wrote of Alcyone:


“…the great and burning star, Immeasurably old, immeasurably far, Surging forth its silver flame Through eternity,…Alcyone!”

The early Arabs called Alcyone the ‘Walnut’, the ‘Central One’ and the ‘Bright One’. A telescope centred on this beauty will show three faint stars forming a beautiful triangle close by.

Maia is the first born and the most beautiful sister of all. Shining at magnitude 3.9, this B-type giant star has a connection with out current calendar. The month of May is de-rived from Maia.

Electra is a magnitude 3.7 B-type giant and Celaeno is a B-type subgiant of magnitude 5.5. Taygeta is a similar B-type star shining at magnitude 4.3 and may be a spectroscopic binary. There is also a companion of magnitude 8.10 with a 68.8” separation first discov-ered by Sir John Herschel. Sterope is a pair of widely separated stars of magnitude 5.8 and 6.4. This pair is also sometimes known as Asterope.

Merope is the only sister to marry a mortal and therefore hides her face in shame. She is immersed in a diffuse wispy nebulosity, discovered by Tempel in 1859. This nebula is part of a huge cloud (NGC 1435) that pervades this whole region. Merope shines at mag-nitude 4.2, another B-type subgiant. This great cloud of illuminated dust and gas was thought to be the nursery from which the Pleiades were born. However, clusters the age (20 million) of the Pleiades should have long ago dissipated their original pre-natal gas. Obviously this is not so here so further study was needed to unlock the mystery.

Recent evidence shows that the Pleiades have burrowed through a non-related cloud of gas and dust on their journey around the Galaxy. The stars are not hot enough to ionise this gas, except for the gas very nearby, so what we see is in fact starlight reflected off the grains of dust, giving rise to the blue colour of this nebula in photographs. This find-ing is further evidenced by the fact that the Pleiades and the nebula NGC 1435 do not share a common motion across the sky.

NGC 1435 can be extremely difficult to discern in the telescope, sometimes missed in large mirrors and seen in smaller. Sky conditions and optics all play a part but once ex-perienced, never forgotten. Walter Scott Houston, using a 20cm reflector in 1974 was surprised when he:

“…looked into the eyepiece, expecting to see a few faint wisps, the field was laced from edge to edge with bright wreaths of delicately structured nebu-losity…”

The brightest region of NGC 1435 lies about Merope, discovered by Ernst Tempel on October 19, 1859 using a 10cm refractor from Italy. A faint extension was discovered about Maya in 1875 (NGC 1432). The rest of the faint nebulosity about Alcyone, Ce-laeno, Electra and Taygeta was discovered five years later.

Next to Merope lies IC 349, a reflection nebula first seen by E.E. Barnard in 1890 using the Lick Observatory 36 inch. Named Barnard’s Merope Nebula, it lies close to its illu-


The Hunter and his Dog

Beginner’s Guide to the

Sky at Night

These informal meetings are designed for people with little or no observing experience, and those who wish to learn their way around the night sky. The sessions are interactive, so feel free to ask questions and generally join in. Also, bring along any “optical aids” you may have (binoculars or telescopes) and hopefully Auckland’s weather will be kind to us, and we can go outside and observe what we’ve been discussing!

Monday 5th February 8pm at the Stardome Observatory

Coordinator: Martin Thomas

minating star with a separation of 0.06 light years or for comparison, 3500 times the Earth/Sun separation.

Pleione and Atlas, mother and father of the Pleiads, are indeed joined in wedlock, these two stars forming a binary system with an apparent separation of 5’.0. A marriage made in heaven. Atlas is a magnitude 3.8 B-type giant catalogued as a double by F. Struve in 1827. The very close separation of this pairing at 0.4” and magnitude difference of 3 makes resolution difficult in the largest of telescopes.

Pleione is a 5th magnitude B-type main sequence star with a manic rotation, around 100 times that of our Sun. This causes it to eject a series of expanding gaseous shells outward from the equatorial region. Known as BU Tauri, this variable stars brightness range has only been slight in recent years.

Around 36.0” north northeast of Merope lies a fascinating variable star T-Tauri. T-Tauri is immersed within a fascinating faint reflection nebula, Hind’s Variable Nebula discov-ered by Hind in the 1850’s. This nebula changes its brightness over time, presumably because of passing dust obscuring then releasing the nebula’s light. A small nebula, NGC 1554, was discovered nearby by Struve in 1868 but it seemingly disappeared. Dreyer found no sight of it in 1877 whilst using Lord Rosse’s large telescope. A 14th magnitude star lies at this position, 4.4’ west southwest of T Tauri.

A tiny nebula 4.0’ southeast of T-Tauri has also disappeared, one only observation re-corded by Bigourdan in 1890. This region deserves constant monitoring for changes though currently NGC 1555 is rather small and faint.

Clear skies and good hunting


TRADING POST

If you would like to advertise any astronomical equipment in the Journal, please email [email protected].

Southern Sentinel Observing List JOG observers astronomical objects

to observe in February

Medium Objects requiring more aperture. A 6 - 8 Inch telescope recommended

Hard Objects difficult to see or find. A 10 Inch + telescope recommended

Easy Objects easy to see or find in small telescopes or binoculars

M 35 OC Gemini M 41 OC Canis Major M 46 OC Puppis M 47 OC Puppis M 48 OC Hydra M 50 OC Monoceros M 93 OC Puppis

NGC 2239 OC Monoceros NGC 2264 OC Monoceros NGC 2362 OC Canis Major NGC 2451 OC Puppis NGC 2477 OC Puppis NGC 2516 OC Carina Saturn Planet Gemini

Mel 66 OC Puppis Mel 71 OC Puppis NGC 2158 OC Gemini NGC 2169 OC Orion NGC 2237 BN Monoceros NGC 2238 BN Monoceros

NGC 2266 OC Gemini NGC 2298 GC Puppis NGC 2346 PN Monoceros NGC 2359 BN Canis Major NGC 2440 PN Puppis

NGC 2207 G Canis Major NGC 2217 G Canis Major NGC 2292 G Canis Major NGC 2293 G Canis Major NGC 2295 G Canis Major NGC 2310 G Puppis NGC 2339 G Gemini

NGC 2371 PN Gemini NGC 2419 GC Lynx NGC 2434 G Volans NGC 2438 PN Puppis NGC 2442 G Volans Abell 20 PN Canis Minor Abell 21 PN Gemini

PN - Planetary Nebula G - Galaxy OC - Open Cluster GC - Globular Cluster BN - Bright Nebula DN - Dark Nebula SN - Supernova Remnant Gal G - Galaxy Group


Southern Sentinel Crossword February 2007 Edition

The solutions to the December crossword are on page 3.

1 2

3 4

5 6

7

8 9

10

11

12 13

Across 5 An astronomer who is obsessed to own

telescopes of ever larger aperture is known to suffer what (8,5)

7 Eruptions in the outer part of the Sun's atmosphere (5,6)

8 Colourful displays in the atmosphere which occur when molecules are energized by particles in the solar wind (6)

11 Brightest Star in Canis Minor (7) 12 A star that suddenly expels a huge

amount of energy, becomes brighter, and which slowly fades back to its initial state (5)

13 A method of evaluating optics by pointing a telescope at a bright star (4,4)

Down 1 One of 88 divisions in the night sky,

each containing an asterism of stars (13)

2 Computer star charting program (5) 3 A system of millions or billions of stars,

gases held together by gravity. (6) 4 Standard measure of time on earth

used by astronomers (9,4) 6 The phase of the Moon in which it is

fully illuminated and rises at sunset and sets at sunrise. (4,4)

8 Last name of the Lunar Module Pilot of Apollo 11 (6)

9 High energy radiation. (1,3) 10 The small particles which occupy the

interstellar medium. (4)

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