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AAS Journal 24 May 2007

Southern Sentinel Crossword May 2007 Edition

The solutions to the April crossword are on page 23.

1 2 3

4

5 6

7

8

9 10 11

12

13

14

Across 2 Force of attraction between two

massive objects (7) 7 A telescope design which includes a

large primary mirror and a small convex secondary mirror to form the image (10)

8 The mechanical support that grips a lens or mirror (4)

10 The constellation 'The Flying Fish' (6) 13 Last name of the Commander of Apollo

17 (6) 15 An instrument used to separate the

incoming light from objects into component frequencies (12)

Down 1 The collective term for the phases of a

celestial body when it is less than 50% illuminated (8,5)

3 The natural glow of the night sky (7) 4 A measure of the amount of material of

an object (4) 5 The approximately 11-year frequency

of solar activity (5,5) 6 Optical systems which use both lenses

and mirrors to form the image (12) 9 Aberrations of optical system in which

the problem is that different things happen to different colors of light (9)

11 A galaxy with arms which originate from the central galactic bulge. (6)

13 Name of a quantum of light. (6)

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SOCIETY JOURNAL

May 2007

At the May Society meeting, Prof. Mark Cannell will de-scribe some of the gems of the constellation Sagitta-rius and also delve into its mythology to discover the origin of the Centaur.

Who Was The Centaur?


President: Henk Stolk 0274 878655

Vice President: John White 486-2398

Treasurer: Helen McRae 021 494418

Secretary: Jennie McCormick 624-1246 Curator of Instruments: Rob Beck 021-442135

Librarian: Olga Brochner 625-9444

Editor: Phil Foster 378-9312

Councillor: Mark Cannell 520-1123

Councillor: Andrew Goodfellow 524-4369 Councillor: Glenn Urquhart 269-5808

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.

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Contact Us :

May 2007 23 AAS Journal

SOLUTION TO THE APRIL CROSSWORD Across: 3 Spacehab, 5 Etx, 6 Equatorial, 8 Jewel Box, 10 Polar, 12 Leo, 13 Matter, 14 Mir. Down: 1 James Dunlop, 2 Six, 4 Helix Nebula, 7 Open Cluster, 9 Arizona, 10 Parsec, 11 Eta.

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Southern Sentinel Observing List JOG observers astronomical objects

to observe in May

Object Type Constellation M 49 Galaxy Virgo M 53 Globular Cluster Coma Berenices M 58 Galaxy Virgo M 59 Galaxy Virgo M 60 Galaxy Virgo M 61 Galaxy Virgo M 63 Galaxy Canes Venatici M 64 Galaxy Coma Berenices M 84 Galaxy Virgo M 85 Galaxy Coma Berenices M 86 Galaxy Virgo M 87 Galaxy Virgo M 88 Galaxy Coma Berenices M 89 Galaxy Virgo M 90 Galaxy Virgo M 91 Galaxy Coma Berenices M 94 Galaxy Canes Venatici M 98 Galaxy Coma Berenices M 99 Galaxy Coma Berenices M 100 Galaxy Coma Berenices Mel 111 Open Cluster Coma Berenices NGC 4244 Galaxy Canes Venatici NGC 4449 Galaxy Canes Venatici NGC 4559 Galaxy Coma Berenices NGC 4565 Galaxy Coma Berenices NGC 4631 Galaxy Canes Venatici NGC 4889 Galaxy Coma Berenices NGC 5005 Galaxy Canes Venatici

This month we have a very comprehensive list to observe. We are having a look specifically at the Virgo, Coma Berenices & Canes Venatici region of the sky, squeezed between 12 hours RA and 13 hours 30 minutes RA. Over 110 objects spread over 45o in declination are found in our full list, so we have limited the list here to the easier objects. You can find the full list at:

http://homepages.ihug.co.nz/~michellekemp/JOG/May.htm


MONDAY 14th MAY 2007 8.00 PM AT THE STARDOME OBSERVATORY

MONTHLY MEETING

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

T his month’s talk will look at the constellation Sagittarius which hides many treas-ures and which is coming into ideal position for observing. This constellation honoured the death of a wise hunter Chiron, who is often described as a centaur.

However, looking into ancient literature and pottery suggests that this description may be confused, Chiron had the legs of a man and the hindquarters of a horse whereas centaurs have only horse’s legs. Hyginus in 50B.C. may give one solution: Sagittarius may have been Crotus the son of Pan who was a skilled hunter. It was Zeus who placed his image among the stars with artistic license, giving him a horse’s flanks to reflect his swiftness in the hunt. More modern views of Sagittarius have shown that this constellation also contains the centre (centaur?) of our galaxy where careful images analysis has shown the presence of a relatively quiet, but massive, black hole. Sagittarius has also provided dis-coveries which have given rise to modern cosmology. In this richly illustrated talk, Prof. Mark Cannell will give his perspective on this large constellation describing the creation of the constellation from early times, how to find it in the sky and some of the amazing objects it contains.

Looking at Sagittarius and the Centre of the Milky Way

Prof. Mark Cannell


Calendar of Society Events

June 1 Friday 7:30 PM Young Astronomers Group Margaret Arthur 4 Monday 8:00 PM Beginner's Guide to the Sky at Night 7 Thursday 7:30 PM A.A.S. Council Meeting 11 Monday 8:00 PM Society Monthly Meeting 15 Friday 7:30 PM Night Eyes David Britten Waharau Dark Sky (page 6) Continues until 17th 25 Monday 8:00 PM Introduction to Astronomy TBA

May 4 Friday 7:30 PM Young Astronomers Group Margaret Arthur 7 Monday 8:00 PM Beginner's Guide to the Sky at Night 10 Thursday 7:30 PM A.A.S. Council Meeting 14 Monday 8:00 PM Society Monthly Meeting Looking at Sagittarius and the Centre of the Milky Way Prof. Mark Cannell 18 Friday 7:30 PM Night Eyes The Light in the Dark David Britten 28 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 4th May 7.30pm at the Stardome Observatory


Topic to be advised

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 7th May 8pm at the Stardome Observatory

Coordinator:

The Night Eyes junior group meeting for May starts at 7:30pm in the Observatory Sun Room on Friday 18 May. The main topic for the meeting will be:

The Light in the Dark

Parents, friends and other Society members are very welcome to attend.

Night Eyes May Meeting

Coordinator: David Britten Friday 18th May 7.30pm

at the Stardome Observatory

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


References The eta Chamaeleontis Cluster: A Remarkable New Nearby Young Open Cluster - The Astrophysical Journal, Volume 516, Issue 2, pp. L77-L80 (Mar. 1999). Authors: Mama-jek, Eric E.; Lawson, Warrick A.; Feigelson, Eric D. Article on web: http://adsabs.harvard.edu/abs/1999ApJ...516L..77M

Chamaeleon: Poem by Andrei Dorian Gheorghe, founder and director of the Cosmopo-etry Festival of the Romanian Society for Meteors and Astronomy-SARM

http://www.blackskies.org/: Neat Southern Planetaries - A series of articles by Andrew James, Astronomical Society of New South Wales.

Yes, the Chamaeleon lies very patient and still as Musca buzzes above, waiting to pounce. With not much in the way of tasty morsels in this region, who can blame the chamaeleon's indulgence.

Chamaeleon is one of Pieter Keyser and Fredrick de Houtman's constellations, appearing along aside Musca on Johann Bayer's Uranometria. Only 132 sq.° in size, the stars here are rather faint, the brightest being alpha at magnitude 4. Lying around 78 light years dis-tant, this F6 subgiant appears creamy in colour.

Gamma is a red star of spectral class M, shining at magnitude 4.1 and lying around 250 light years away. Of more interest is delta¹ and delta². Delta¹ is an orange giant of magni-tude 5.4 and has a computed distance of 360 light years. It is a double star of magnitudes 6 and 6.5, however the separation is very close at 0.6" so is very difficult. Delta² is an optical companion only but with a blue-white hue of magnitude 4.6, it is in lovely con-trast to delta¹.

NGC 3195 is a planetary nebula discovered by Sir John Herschel in 1835. It appears to the eye as a bluish and evenly lit round glow, spanning 30" in diameter, similar in size to Jupiter.

An open cluster of faint scattered stars was discovered through x-ray observations about the star eta in 1999. Named Mamajek 1 or the eta Chamaeleontis Cluster, it is around 316 light years from our Sun, the 4th in distance behind the Ursa Major, Hyades and Coma Berenices clusters. In their article published in The Astrophysical Journal, the authors wrote,

". the eta Cha cluster is far from any significant molecular cloud and thus has mysterious origins. The cluster appears to share proper motions with other young stars in the Chamaeleon region and may be a compact exten-sion of the Sco-Cen OB association."

Don't expect to see much here as the stars are faint and only mentioned here for interest sake.

Clear skies and good hunting.


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:

Topic to be confirmed Monday 28th May 2007

8:00pm at the Stardome Observatory

At the time of going to press, the topic for the May Introduction to Astronomy was not confirmed. Watch other sources for details.

We are delighted to warmly welcome the following new

members to the Society.

We would like to extend a welcome to these people who have recently joined the society. Hope to see you at our regular meetings.

Senior Membership Mark Williams, Wade Smith, Sam Subramanian, Sheila Pasini, Noel Hendry, Pat Gib-bins, Phil Haynes, Alison Simpson Family Membership Philip Allen, Paulette Tinsel, Desmond Vessaokar


The Auckland Astronomical Society is organising another wonderful, informal and fun astronomical get-together weekend. This will be held at the Waharau Outdoor Centre located in the regional park north of Kaiaua on the Firth of Thames. The weekend is an ideal way for both new and existing members to become more famil-iar with telescopes and to meet other members. Even if you just want to look through a telescope or learn more about the night sky, then this weekend is a must. There are all variety of different flavours of telescopes brought by experienced members who are al-ways happy to show you the sky. The centre includes a lodge, five chalets (88 bunks) and an ablution block. There is a large courtyard in front of the lodge for telescope viewing and the chalets are nicely nes-tled in native bush. There are many pleasant bush walks, glow-worms, a bird life sanctu-ary within walking distance (sort of !!) Miranda hot pools are approx 20km from the camp and are a great relaxant.

Bookings and Enquiries

For all enquiries contact Dean: phone 021 706 912 email: [email protected] Bookings can be made through Dean or via the AAS website www.astronomy.org.nz. To minimise cost, the weekend will not be catered. However there is a large fully equipped kitchen area for cooking needs complete with walk-in freezer and fridges. Tea/coffee/sugar/biscuits will be provided by the AAS. There is a local Hotel, a Fish & Chip shop and small Dairy located 8km from the camp, in Kaiaua.

Cost $25 per person for the weekend. Single night stay will be $15. Payments can be sent to AAS, PO Box 24-187, Auckland or paid on site.

Note: staying beyond sunset is the point at which a nights stay payment is due.

Waharau Dark Sky Weekend Winter 2007 Friday 15th June to Sunday 17th June


The brightest object westward of NGC 5128 is a lovely yellow double star LDS 444. Dis-covered by J. Luyten, it can be resolved in 20cm telescopes, the components of magni-tude 8.6 and 8.9 separated by 2.9".

Another planetary nebula worth finding is MyCn 18, the Hourglass Nebula. Lying 1.5° to the south southeast of NGC 5189, a 20cm aperture will struggle somewhat with this small and faint glow. Lying 8,000 light years distant, it was discovered by Annie Jump Cannon and Margaret W. Mayall whilst working on an extension to the Henry Draper Catalogue.

Born from a sun-like star whose nuclear resources have been exhausted, the outer layers of this once vibrant star have been pushed off into the surrounding cosmos to fleetingly enrich the imagination of astronomical observers throughout the galaxy.

It took the Hubble Space Telescope to unlock the secret beauty of this particular celestial 'jewel'. Raghvendra Sahai and John Trauger uncovered the now distinct 'hourglass' shape whose photograph ran rampant throughout the world's media. National Geographic probably captured the thoughts of many when they featured it on the cover of their April 1997 edition with the description,

"Astronomers looked 8,000 light years into the cosmos with the Hubble Space Telescope and it seemed that the eye of God was staring back."

Musca does not have many enemies though one does provide enough menace to put the little fly on edge. Careful flight is a must as Musca flies through this region for the heav-enly lizard lies in wait.

Planetary nebula NGC 3195


Sir John Herschel discovered an unusual gaseous nebula in 1835 which he called "a very strange object". Lying in the northeastern corner of Musca, close to neighbouring Cir-cinus and Centaurus, the star field here is very beautiful and the object itself, NGC 5189, appears pretty bright with some structure evident. Telescopes in the 30cm plus range will show a gaseous 'S' shape with a distinct blue or green-blue colour to the overall nebula

Classified for many years as a gaseous nebula, it is now catalogued as a planetary nebula residing some 3,000 light years from our Sun. There are 4 stars seemingly immersed within the 0.45 solar mass nebula including the star that gave rise to NGC 5189. This off centre central star is a WC8 Wolf Rayet type with a possible extremely close companion that may explain NGC 5189's structure.

Staying within sight of NGC 5189, there are a couple of double stars nearby. Andrew James (see references below) writes,

"Just outside the planetary's outer boundary, are two uncatalogued but dis-tinctly wide 10th and 11th magnitude pairs west and north of the centre of the planetary by c.5' and 8' min.arc., respectfully. The magnitude of the most-distant pair, 'Pair 1', is 10.7/12.0 47"sec.arc. PA 55°. 'Pair 2' is 11.1/12.0 51"sec.arc PA 351°."

MyCn 18, the Hourglass Nebula. The insert shows a close-up of the eye


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The Sky This Month

CosMos

DATE TIME RISE SET Full Moon 02 May 07 2211 1706 0636 Last Quarter 10 May 07 1628 - 1329 New Moon 17 May 07 0729 0731 1712 First Quarter 24 May 07 0903 1315 -

DATE RISE SET Mercury 01 May 07 0646 1730 Mercury 29 May 07 0917 1836 Venus 01 May 07 1031 1950 Venus 29 May 07 1050 2019 Mars 01 May 07 0248 1528 Mars 29 May 07 0241 1431 Jupiter 01 May 07 1942 1014 Jupiter 29 May 07 1741 0810 Saturn 01 May 07 1400 0025 Saturn 29 May 07 1213 2237 Uranus 01 May 07 0244 1521 Uranus 29 May 07 0058 1333 Neptune 01 May 07 0038 1411 Neptune 29 May 07 2245 1222

DATE RISE SET 01 May 07 0700 1736 15 May 07 0712 1723 31 May 07 0724 1713

All times NZST (UT +12 hrs) and are for Auckland.

Mercury opens the month in Aries but lies too close to the rising Sun to observe. Moving in to the evening sky and occupying Taurus later in the month, Mercury sets around 1.5 hours after the Sun on the 31st. At this time, Mercury's 0.3 magnitude 7.7" disk lies in the region of the large and rich open cluster M35 (NGC 2168).


Another fine double star with a similar colour contrast is theta Muscae, it too lies in a rich field of stars. Their respective magnitudes are 5.7 and 7.7 and the spectral classes are B0 and WC6.

There are two globular clusters in Musca, one fairly difficult because of its faintness and loose concentration. Starting with the easier of the two, NGC 4833 is fairly compact but easily resolved, many of the stars appearing in small curves and arcs. A magnitude 8.7 foreground star lies on the northern edge. Look for this cluster 42' to the north northwest of delta Muscae.

By contrast, search for NGC 4372. Discovered by James Dunlop on April 30, 1826, this 'shy' and unobtrusive globular cluster is difficult to detect at a cursory glance. The diffi-culty is that obscuration by interstellar dust is rather heavy in this region, therefore the stars are rather faint. The bright star HD 107947 of magnitude 6.8 lies close to NGC 4372 and does the observer no favour, its dazzling glare all but overwhelming the cluster. If this star is put out of the eyepiece field of view, then the globular may be seen to the south as a large scattering of loosely structured stars, reminiscent of an open cluster.

IC 4191 is a small planetary nebula that can be picked out from the stars because of its bright blue disk. There is an orange star of magnitude 6.4 nearby to the south as a guide.

NGC 5189, showing its ‘S’ shape.


"I know you have fallen in love with the proud star Canopus of Carina. You hope to become nicer, that is the reason you always change your colors. Sorry for your illusions, I must be sincere: you are just a starry lizard, and Canopus will always be above you. But ... dream, poor Chamaeleon! Who knows ...?"

Chamaeleon by Andrei Dorian Gheorghe (2003)

M usca appeared on Lacaille's chart of 1763, having originally been designated as Apis 'The Bee' by Bayer 160 years earlier. It was invented by Pieter Keyser and Fredrick de Houtman after 1595. Lying directly south of Crux, it is made

up of a group of prominent stars, the brightest alpha of magnitude 2.7. Though a rela-tively small constellation at 132 sq.°, it has a number of interesting double stars and deep sky objects.

Alpha is a hot B2 type subgiant lying around 430 light years away. It has a computed luminosity of 1200 Suns and appears to be slightly variable, ranging from magnitude 2.66 to 2.73.

Southeast of alpha lies the Cepheid variable star R Muscae. This yellow star fluctuates in brightness from magnitude 5.93 to 6.73 within a period of 7.5 days.

Beta Muscae is a blue-white star, shining prominently at 3rd magnitude. High power will split this star into two equal components of 4th magnitude, separated by a relatively close 1.6". Distance figures vary from 290 to 470 light years. If the last figure is taken, then beta has a computed luminosity of around 580 Suns.

Epsilon is a 4th magnitude red giant star and marks the fly's 'right wing' while the 'left wing' is represented by magnitude 3.6 delta, an orange giant star. Completing this field is magnitude 3.8 gamma, a B-type main sequence star marking Musca's 'tail'.

The lovely double star h4498 with components of magnitude 7.0 and 8.0 lies in a busy field of stars. They appear yellow and white, in fine contrast with one another. The brighter member has a very close companion unresolved with amateur telescopes at 0.1" separation.

MUSCA “The Fly” and “The Chamaeleon”

CosMos


The red planet Mars rises around 0248 hours on May 1st, its small 5.3", 1.0 magnitude, disk lying in the "Water Carrier" Aquarius. Moving into Pisces on the 10th, a crescent Moon approaches on the 13th. Continuing on into Cetus on the 25th, Mars ends the month with a slightly larger disk of 5.7".

Jupiter currently sits amongst the spread out star field of Ophiuchus, domicile of many bright globular clusters. Jupiter is gloriously displayed below the large shape of Scorpius all month, as it has been for quite some time. Rising at 1942 hours on the 1st May, Jupiter's 43.7" disk shines brightly at magnitude -2.5. The Moon is nearby on the 5th. Jupiter contin-ues its slow crawl through Ophiuchus as the month progresses, only slightly growing in size and brightness. Jupiter lies near the globular clus-ter NGC 6287 all month.

Venus blazes away at magnitude -3.7 in Taurus as the month begins, it's 16.6" disk setting well after the Sun. Moving into neighbouring Gemini on the 9th, its disk continues to grow and brighten. By the 31st, Venus shines at magnitude -3.5 and measures 21.5" in diameter. Look for this beautiful beacon above beta Geminorum. A crescent Moon resides with Venus on the 20th.

Saturn sets at 0020 hours on May 1st amongst the stars of Leo, shining at magnitude 0.8. It's 18.5" disk lies high in the north northeastern sky as darkness begins. A near First Quarter Moon lies close over the nights of the 22nd and 23rd. Look for Saturn's brightest moon Titan to the west of Saturn on the 14th and to the east on the 23rd.

Uranus rises around 0244 hours as the month begins, its tiny 3.3" disk shining at magnitude 5.9. Uranus lies northwest of Mars though Mars pulls away quickly, leaving Uranus alone in a poor Aquarian star field. Look for Mars southwest of 4.2 magnitude phi, an M-type orange giant. On the 31st, Uranus lies north of 96 Aquarii, a magnitude 5.6 white star of spectral type F.

Neptune rises on May 1st at 0038 hours, lying amongst the stars of Capri-cornus the "Goat". Shining at magnitude 7.9, binoculars will pull in this tiny 2.4" planet with care. A one day past Last Quarter Moon passes on the 11th.

References Astronomy Lab 2 Cartes du Ciel – version 2.76 Stellarium 0.8.2


D uring the summer and fall of 2006, U.S. Coast Guard planes flew over the North Pacific in search of illegal, unlicensed, and unregulated fishing boats. It was a tricky operation – in part because low clouds often block the pilots' view of any-

thing floating on the ocean surface below.

To assist in these efforts, they got a little help from the stars.

Actually, it was a satellite – CloudSat, an experimental NASA mission to study Earth’s clouds in an entirely new way. While ordinary weather satellites see only the tops of clouds, CloudSat’s radar penetrates clouds from top to bottom, measuring their vertical structure and extent. By tapping into CloudSat data processed at the Naval Research Laboratory (NRL) in Monterey, CA, Coast Guard pilots were better able to contend with low-lying clouds that might have otherwise hindered their search for illegal fishing activ-ity.

In the past, Coast Guard pilots would fly out over the ocean not knowing what visibility to expect. Now they can find out quickly. Data from research satellites usually takes days to weeks to process into a usable form, but NASA makes CloudSat's data publicly avail-able on its QuickLook website and to users such as NRL in only a matter of hours – mak-ing the data useful for practical applications.

"Before CloudSat, there was no way to measure cloud base from space worldwide," says Deborah Vane, project manager for CloudSat at NASA's Jet Propulsion Laboratory.

CloudSat’s primary purpose is to better understand the critical role that clouds play in Earth's climate. But knowledge about the structure of clouds is useful not only for scien-tific research, but also to operational users such as Coast Guard patrol aircraft and Navy and commercial ships at sea.

“Especially when it's dark, there’s limited information about storms at sea,” says Vane. “With CloudSat, we can sort out towering thunderclouds from blankets of calmer clouds. And we have the ability to distinguish between light rain and rain that is falling from severe storms.” CloudSat’s radar is much more sensitive to cloud structure than are radar systems operating at airports, and from its vantage point in space, Cloudsat builds up a view of almost the entire planet, not just one local area. “That gives you weather information that you don't have in any other way.”

There is an archive of all data collected since the start of the mission in May 2006 on the CloudSat QuickLook website at http://cloudsat.atmos.colostate.edu. And to introduce

Clouds from Top to Bottom Patrick L. Barry


Star map showing the Milky Way From Starry Night Pro 3

With a clear dark sky, a pair of binoculars and a good friend, an exciting space journey to the stars is just a glimpse away.

Foot Note Light travels at 300,000 kilometres per second so, one light year is equal to a distance of 9.6 trillion kilometres.

One solar (Sun) mass is equal to 1.98892 × 1030 kilograms.

Stardome Observatory is open for telescope viewing during May. Dates and times of shows can be obtained by ringing Stardome Observatory reception on (09) 624.1246 ex 0 or by visiting the website http://www.stardome.org.nz

Beaumont Prize Articles submitted to the journal are eligible for the Beaumont Prize 2008 of $300. To be eligible an article must be original, 1000 words or more in length and be written by a current, paid-up society member. So put your thinking caps on, put your fingers on the keyboard and best of luck for next year.


O ur home in the Universe is almost as old as time itself and dates back to an im-pressive 13.6 billion years, give or take a few billion here and there.

The home I am referring to is not the Solar System or planet Earth, but some-thing much more massive, stretching nearly 100,000 light years in diameter. Our home contains all the stars we see in the night sky including some 300 billion more. In fact, it is so immense that there is no hope of ever leaving it.

The Milky Way Galaxy is Earth’s home in the Universe. It is a vast city of stars, planets, gas, dust and life, shaped like a huge Catherine wheel and it is just one galaxy among trillions in the Universe. To give you some idea as to the relative physical scale of the Milky Way; if we were to reduce the galaxy to 130 km in diameter, our Solar System would be a mere 2 mm wide; a truly tiny speck in a vast diverse Universe!

The Milky Way is now classified as a Barred Spiral. In earlier times it was thought to be an ordinary spiral but in the early 1980s astronomers found a central bar 27,000 light years long running through its centre. It is from this bar that several loosely wound arms emerge producing the huge spiral shaped system which we now know the galaxy to be. Our Solar System is buried deep within one of the outer arms of the galaxy, the Orion arm; we can liken our residence in the Milky Way Galaxy as being similar to living in the outer suburbs of a very large city.

At the heart of the Milky Way, named the Galactic Centre, some 30,000 light years dis-tant from the Sun, resides a supermassive black hole called Sagittarius A*. It is thought that this object is a 3.7 million solar (Sun) mass black hole. It is slowly consuming all surrounding material because of its huge gravitational influence. Astronomers now be-lieve that most galaxies in the Universe have their very own massive black holes at their centres.

The Milky Way in May May is a perfect month for discovering the wonders of our home galaxy. On any dark clear night this month, the sky overhead will reveal our astonishing place in space. Stretching from the eastern horizon to the western, an iridescent river of star light, gas and interstellar dust highlights one of the spiral arms within the disc of our Milky Way Galaxy. Almost all the stars within this band are unresolvable to the naked eye; however a good pair of binoculars or a telescope will reveal individual stars, star clusters and star formation areas.

Keep a look out early in the evening for the bright planet Venus sitting low on the west-ern horizon and on the eastern horizon the giant planet Jupiter makes a colourful appear-ance for early evening observations throughout the winter months.

THE NIGHT SKY FROM WHERE WE SIT Jennie McCormick

Stardome Observatory – May 2007

OUR HOME AMONG THE STARS


A CloudSat ground track appears as a diagonal line overlaid upon a GMS-6 (a Japanese weather satellite) infrared image. CloudSat is crossing the north-central Pacific Ocean on a descending orbit (from upper-right to lower-left) near a storm front. The radar data corresponding to this ground track (beginning in the centre panel and continuing into the lower panel) is output in colour and shows a vertical cloud profile far more complex than the two-dimensional GMS-6 imagery would suggest.

kids to the fun of observing the clouds, go to http://spaceplace.nasa.gov/en/kids/cloudsat_puz.shtml. 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.


A stronomers have discovered the most Earth-like planet outside our Solar System to date, an exoplanet with a radius only 50% larger than the Earth and capable of having liquid water. Using the ESO 3.6-m telescope, a team of Swiss, French

and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbour a Neptune-mass planet. The astrono-mers also have strong evidence for the presence of a third planet with a mass about 8 Earth masses.

This exoplanet – as astronomers call planets around a star other than the Sun – is the smallest ever found up to now and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun. However, given that its host star, the red dwarf Gliese 581, is smaller and colder than the Sun - and thus less luminous - the planet nevertheless lies in the habitable zone, the region around a star where water could be liq-uid! The planet's name is Gliese 581 c.

It is estimated that the mean temperature of this super-Earth lies between 0 and 40 de-grees C, and so water would be liquid. Moreover, its radius is only 1.5 times the Earth's radius, and models predict that the planet should be either rocky – like our Earth – or fully covered with oceans.

The host star, Gliese 581, is among the 100 closest stars to us, located only 20.5 light-years away in the con-stellation Libra ("the Scales"). It has a mass of only one third the mass of the Sun. Such red dwarfs are intrinsically at least 50 times fainter than the Sun and are the most common stars in our Galaxy: among the 100 closest stars to the Sun, 80 belong to this class.

Red dwarfs are ideal targets Artist's impression of the planetary system around the red dwarf Gliese 581.

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Astronomers Find First Earth-like Planet in Habitable Zone

ESO 22/07 - Science Release 25 April 2007


for the search for low-mass plan-ets where water could be liquid This is because dwarfs emit less light and so the habitable zone is much closer to them than it is around the Sun. Planets lying in this zone are then more easily de-tected with the radial-velocity method, the most successful in detecting exoplanets.

Two years ago, astronomers found a planet around Gliese 581 with a mass of 15 Earth-masses, i.e. similar to that of Neptune, that orbits its host star in 5.4 days. At the time, the astronomers had al-ready seen hints of another planet. They therefore obtained a new set of measurements and found the new super-Earth. They also found clear indication of another 8 Earth-mass planet which com-pletes an orbit in 84 days. The planetary system surrounding Gli-ese 581 contains thus no fewer than 3 planets of 15 Earth masses or less, and as such is a quite re-markable system.

The discovery was made thanks to HARPS (High Accuracy Ra-dial Velocity for Planetary Searcher), perhaps the most pre-cise spectrograph in the world. Located on the ESO 3.6-m tele-scope at La Silla, Chile, HARPS is able to measure velocities with a precision better than one metre per second (or 3.6 km/h)! HARPS is one of the most successful in-struments for detecting exoplanets and holds already several recent records, including the discovery of another 'Trio of Neptunes'

Three-planet Keplerian model of the Gliese 581 ra-dial-velocity variations. The panels display the phase-folded curve of each of the planets, with points representing the observed radial velocities, after removing the effect of the other planets. Top panel refers to the 15 Earth-mass planet orbiting close to the star (5-d period), the middle one is the 5 Earth-mass planet in the habitable zone and the lower panel shows evidence for a third, 8 Earth-mass planet with a period of 84 days. The error on one measurement is of the order of 1 m/s.

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