AN INVITATION TO WINCHESTER PLANETARIUM

        Members of the Wadhurst Astronomical Society have received the following invitation to an Astronomy Day at Winchester in December.  Members Interested in going should let one of our Committee members know before or at our next meeting on the 15th of September 2010.

Astronomy Day, Sunday 5th December, 1030 -1630.
AS Tickets just £12 for the full day!
 
Programme includes:
 A History of the Universe – 1 hour lecture, Robin Catchpole (Cambridge University)
A Tour of the night sky – 30 min planetarium show, Ninian Boyle (BBC Sky at Night team)
TBC – 1 hour lecture, almost certainly by Daniel Thomas (Portsmouth University)
Light is the messenger of the Universe – 30 min workshops/discussion, Robin Catchpole
Astrophotography for beginners – 30 min workshops, Lilian Hobbs
Guide to Equatorial mounts – 30 min workshops, Ninian Boyle
LOFAR telescope – 30 min workshops, SEPnet/LOFAR team
A Flight through the Universe – 40 min planetarium show, Jenny Shipway (INTECH)
We are Astronomers – 24 min planetarium film show
 
        Workshops are repeated to increase capacity and give flexibility in scheduling.  We should have academic display stands to explore and you can also book for either of the family planetarium shows we are running for our public visitors this day. Note we won't have any AS stands (although you're welcome to display leaflets/flyers) as I don't want to see any of you missing out on the events!
 
Bookings: no hassle for your AS
 
Tickets will be paid for individually on the day.  All your AS needs to do is send me a list of names of interested members a week or so in advance and this will be used on the door to indicate who is eligible for the cheap deal.
                Tickets (including individual event tickets) will be available to public visitors on the day, but at a significantly higher price (tbc).  Astro Soc members get early entry (0930 vs 1000 for public visitors) so get first choice of event tickets.  A final programme will be made available well before the date to allow forward planning.
                Please do encourage your members to save this date as I will make a loss if we don't get enough people in!!  I'm hoping this can be an annual event if successful this year (and if we do make a profit then I will drop the AS price next year).
  
Best wishes,
Dr Jenny Shipway,
Planetarium Manager
INTECH Science Centre & Planetarium
Telegraph Way, Morn Hill
Winchester, SO21 1HZ
Telephone: 01962 891916
Website:http://www.intech-uk.com

ASTRO-BARBECUE

        This year’s Astro-barbecue was held by kind invitation of Michael and Claire Harte on Saturday the 28th of August.  Over ten members, family and friends came along and the sky was clear.  Two telescopes; a Nexstar 5 and a 5-inch refractor where available to observe Jupiter with its equatorial belts and four of the Jovian satellites.
        The Moon was well placed and it was possible to see surface features particularly along the terminator.  That evening, there was an occultation, although the Moon was extremely bright.  Even so, Phil Berry made a video recording of the event, but because of the contrast it wasn’t too successful.
        An impressive large pair of binoculars made it possible to discern some of the millions of stars making up the Milky Way.
        Some of the young visitors present were enthralled when the International Space Station made a couple of passes and also when an Iridium Flare occurred after being predicted in the Sky Notes.

 

MEETINGS

        Wednesday 15th September 2010 – Our own Phil Berry gives a talk entitled “Distances to the Stars”.
        Meetings begin at 1930 although members are invited to arrive anytime after 1900 as this is a good time to exchange ideas and discuss problems and relax before the meeting.
        The venue as always is held in the Upper Room of the Methodist Church at the east end of Wadhurst Lower High Street, opposite the entrance to Uplands College.  (For those with SatNav – the post code is TN5  6AT)

 

FUTURE MEETINGS

        Wednesday 20th October 2010 – Ian King is giving a talk with the intriguing title; “How Not to Build a Telescope”

        Wednesday 17th November 2010 – Member Trevor Grey will be giving a talk entitled “It Is Rocket Science”.

        Wednesday 15th December 2010 – Brian Mills gives a very appropriate talk about “The Star of Bethlehem”.

 

SKY NOTES FOR SEPTEMBER

Planets

Mercury suffers an inferior conjunction on September 3rd after which it moves west of the Sun meaning that it becomes a morning object. In other words it rises ahead of the Sun but sets before it. For early risers this is the best morning apparition of Mercury during 2010. Greatest western elongation (18°) occurs on the 19th when Mercury rises at 05.00 BST with sunrise occurring at 06.40. The planet will be approximately 12° above the eastern horizon at magnitude -0.2 with the Sun 6° below the horizon at the start of civil twilight (see the note in “Definitions”). One advantage of a morning apparition at this time of year is that the ecliptic makes an angle of around 60° with the horizon so the planet climbs steeply away from the horizon.

Venus is to all intents and purposes unobservable to us. Despite being some angular distance from the Sun it sets not long after it because of the shallow angle that the ecliptic makes with the horizon during the evenings at this time of year.

Mars is no longer observable as it sets an hour after the Sun.

Jupiter at magnitude -2.9 is moving retrograde in the constellation of Pisces. It reaches opposition on the 21st and on that date rises a few minutes after sunset. This is one of the closest oppositions for some time with the planet subtending an arc of almost 50”. The apparent size varies because the orbits of both the Earth and Jupiter are ellipses so it depends where the planets are on those ellipses when opposition occurs. Anyone who was watching the Perseid meteor shower during August cannot have mistaken the brilliant planet rising in the east. Its location is shown in the diagram below.

 

 

Saturn is too close to the Sun for observation this month and suffers a conjunction with the Sun on October 1st.

Uranus is not usually mentioned in the sky notes because it is at the limit of naked eye visibility but at the moment it lies close to Jupiter and comes to opposition on the same date. It’s exact position is shown in the diagram for September 19th (instead of the 21st) because the Moon is much closer on the 21st and will make identification more difficult. The passage of the two planets is quite slow and a few days either side of opposition will make very little difference to their positions. Currently Uranus is magnitude 5.7 and would be difficult to find in normal circumstances but the close proximity of Jupiter acts as a very useful signpost, meaning that with binoculars it should be an easy target. The Moon is shown to scale to give an idea of the angular distances involved. If seeing conditions are good you may just be able to discern that Uranus has a blue/green hue, and in a telescope it should be possible to resolve it as a small disk. Whatever you use to look for Uranus, don’t forget to take a look at Jupiter and the four main moons which will appear as shown below at 22.00BST on the 19th.

 


 

Lunar Occultations
        In the table below I’ve only listed events for stars down to magnitude 7.5 that occur before midnight although there are others that are either of fainter stars or occur in the early hours.
DD = disappearance at the dark limb whilst RD = reappearance at the dark limb. Note that on September 20th there is a disappearance and reappearance of the same star less than 15 minutes apart. Times are in BST.

Sept

Time

Star

Mag.

Ph

PA °

13th

21.02

SAO 184075

6.2

DD

118

16th

23.15

SAO 187468

5.9

DD

76

19th

19.47

SAO 164279

6.4

DD

48

19th

21.17

SAO 164303

6.9

DD

54

20th

20.43

SAO 145833

7.3

DD

27

20th *

21.43

SAO 145849

7.3

DD

139

20th *

21.57

SAO 145849

7.3

RD

158

 

Phases of the Moon for September

Last ¼

New

First ¼

Full

1st

8th

15th

23rd

ISS
        This month I’ve included passes where the ISS is magnitude -2 or brighter, all of which occur in the first half of the month. The details of all passes can be found at www.heavens-above.com Please remember that the times shown below are for when the ISS is at its maximumelevation, so you should be able to see it for a few minutes before and after these times.  Times are all BST.

Sept

Mag

Time

Alt°

Az.

1st

-3.6

20.16

78

SSE

1st

-3.6

21.51

79

N

2nd

-3.5

20.42

79

N

2nd

-2.0

22.16

33

W

3rd

-3.6

21.09

81

N

4th

-3.5

20.00

78

N

4th

-3.7

21.35

72

SSW

5th

-3.6

20.26

83

NNE

6th

-3.5

20.53

68

SSW

7th

-3.5

19.44

85

N

7th

-2.5

21.19

34

SSW

8th

-3.4

20.10

63

SSW

9th

-2.3

20.36

32

SSW

11th

-2.0

19.53

29

SSW

Iridium Flares
        The flares that I’ve listed are magnitude -2 or brighter although there are a lot more that are fainter or occur after midnight. One or two are at low altitudes but have been included because of a shortage of events for this month. If you wish to see a complete list, or obtain timings for somewhere other than Wadhurst, go to www.heavens-above.com Remember that when one of these events is due it is often possible to see the satellite in advance of the “flare”, although of course it will be much fainter at that time.  Times are all BST. 

Sept

Time

Mag

Alt°

Az.

1st

21.16

-2

21

N

4th

20.51

-2

28

N

15th

19.42

-6

47

N

16th

19.34

-2

49

N

22nd

22.11

-3

11

NE

23rd

21.07

-4

17

N

23rd

22.06

-6

12

NE

24th

21.01

-2

19

N

The Night Sky in September
        In the north Ursa Major is almost on the meridian and therefore close to the lowest point in the sky that it can reach whilst Cepheus is also close to the meridian but is at its greatest altitude. The bright star Capella in Auriga is climbing as is the constellation of Perseus whilst the head of Draco is ideally placed for identification close to Hercules.
        In the east Pegasus, Andromeda and Perseus are well above the horizon meaning that the Double Cluster and M31 are available for viewing. The fainter constellations that lie below Andromeda and Pegasus (Triangulum, Aries and Pisces) can also be quite easily located.
        Looking south the Summer Triangle is still prominent with Deneb in Cygnus being almost overhead. The smaller constellations of Delphinus, Equules and Sagitta that lie close to the lower end of the triangle are ideally positioned for identification.

 

 

       

Looking west the bright star Arcturus in the constellation of Böotes is close to the horizon and will be lost in a months time. Hercules and Corona Borealis though can still be found between Arcturus and Vega.

 Brian Mills

DEFINITIONS OF TERMS USED IN ASTRONOMY

        For the last few months we have looked at some definitions of astronomical terms, and this month I’ve included a few more.

Twilight
        Twilight comes in three different flavours depending on your preference. Once the Sun has set it is said to be civil twilight until it reaches 6° below the horizon. From 6° to 12° is classed as nautical twilight and then from 12° to 18° it is termed astronomical twilight. Once the Sun is more than 18° below the horizon we enter true night. This is something that doesn’t happen between the end of May and mid-July hence we say that twilight lasts throughout the night.

Magnitude
        Depending on which book you read you will find that the method we use for quantifying star brightness is attributed to either Ptolemy or Hipparchus, making the system in the order of two thousand years old. Ptolemy certainly popularised it is his book “The Almagest” or “The Great Compilation” in English, which was written in the second century. The system said that the brightest stars are 1st magnitude and the faintest the human eye can see are 6th magnitude, although it didn’t attempt to quantify the magnitude of the Sun! Incidentally, we ought to add a “+” sign to these to show that these are positive numbers, but there was no need for that distinction to be made originally. Using this system it was decided that a first magnitude star was 100 times brighter than a sixth magnitude star using a logarithmic scale that said each magnitude was 2.51 times brighter or dimmer that the one above or below. The table below may help to explain this.

Mag 1 star is 100  times brighter than a mag 6 star     or    (2.51 x 2.51 x 2.51 x 2.51 x 2.51)
Mag 2 star is 39.8   “           “               “               “               “                (2.51 x 2.51 x 2.51 x 2.51)
Mag 3 star is 15.8   “           “               “               “               “                (2.51 x 2.51 x 2.51)
Mag 4 star is 6.3     “            “               “               “               “                (2.51 x 2.51)
Mag 5 star is 2.51   “           “               “               “               “                (2.51 x)
Mag 6

        In modern times of course the system had to be extended to accommodate, for example, the bright star Sirius at mag. -1.44 and the Sun at -26.7, or in the other direction down to mag. +30 for objects viewed by orbiting telescopes.

        The above method of describing brightness is known as apparent magnitude and is quite simply a measure of the brightness of an object as seen from Earth. There is however another way of quantifying brightness and that is known as absolute magnitude.
        This system takes account of true luminosity by placing all objects at a distance of 10 parsecs before calculating their brightness. This provides a meaningful comparison for bright objects that appear dim because they are extremely distant, and objects that only seems bright because they are very close to us. To demonstrate this, compare the apparent and absolute magnitudes below. You can see how the Sun at 10 parsecs would become a very ordinary star, demonstrating it is simply its closeness that accounts for its apparent brightness.


Star

Apparent mag.

Absolute mag.

The Sun

-26.7

+4.8

Sirius

 -1.44

+1.45

Spica

+1

-3.6

 

        However when we discuss magnitude, amateur astronomers will always be talking about the apparent magnitude unless they specify otherwise.

Parsec
        The Parsec is an astronomical unit of measurement that is equal to 3.26 light-years or 19 million million miles. As you can see in the diagram a nearby star can be seen to move slightly when compared to much more distant stars as the Earth travels around the Sun. If over the course of half the Earths orbit the star appears to move by one arc second, then it said to be one parsec away.

Brian Mills

NASA’S SPACE PLACE

The Turbulent Tale of a Tiny Galaxy by Trudy Bell and Dr. Tony Phillips

                Next time you hike in the woods, pause at a babbling stream. Watch carefully how the water flows around rocks. After piling up in curved waves on the upstream side, like the bow wave in front of a motorboat, the water speeds around the rock, spilling into a riotous, turbulent wake downstream. Lightweight leaves or grass blades can get trapped in the wake, swirling round and round in little eddy currents that collect debris.
Astronomers have found something similar happening in the turbulent wake of a tiny galaxy that is plunging into a cluster of 1,500 galaxies in the constellation Virgo. In this case, however, instead of collecting grass and leaves, eddy currents in the little galaxy’s tail seem to be gathering gaseous material to make new stars.
                “It’s a fascinating case of turbulence [rather than gravity] trapping the gas, allowing it to become dense enough to form stars,” says Janice A. Hester of the California Institute of Technology in Pasadena.       
The tell-tale galaxy, designated IC 3418, is only a hundredth the size of the Milky Way and hardly stands out in visible light images of the busy Virgo Cluster. Astronomers realized it was interesting, however, when they looked at it using NASA's Galaxy Evolution Explorer satellite.  “Ultraviolet images from the Galaxy Evolution Explorer revealed a long tail filled with clusters of massive, young stars,” explains Hester.   
Galaxies with spectacular tails have been seen before. Usually they are behemoths—large spiral galaxies colliding with one another in the crowded environment of a busy cluster.  Tidal forces during the collision pull gas and stars of all ages out of these massive galaxies to form long tails. But in IC 3418, the tail has just young stars. No old stars.
“The lack of older stars was one tip-off that IC 3418’s tail isn’t tidal,” says Hester. “Something else must be responsible for these stars”
Hester and eight co-authors published their findings in the June 10, 2010, issue of The Astrophysical Journal Letters.  The team described the following scenario: IC 3418 is speeding toward the centre of the Virgo cluster at 1,000 kilometres per second. The space between cluster galaxies is not empty; it is filled with a gaseous atmosphere of diffuse, hot hydrogen. Thus, like a bicyclist coasting downhill feels wind even on a calm day, IC 3418 experiences “a stiff wind” that sweeps interstellar gas right out of the little galaxy, said Hester—gas that trails far behind its galaxy in a choppy, twisting wake akin to the wake downstream of the rock in the babbling brook. Eddy currents swirling in the turbulent wake trap the gas, allowing it to become dense enough to form stars.
“Astronomers have long debated the importance of gravity vs. turbulence in star formation,” Hester noted. “In IC 3418’s tail, it’s ALL turbulence.”
To many astronomers, that’s a surprising tale indeed.
See other surprising UV images from the Galaxy Evolution Explorer at: http://www.galex.caltech.edu
Kids (and grownups) can play the challenging new Photon Pileup game at: http://spaceplace.nasa.gov/en/kids/galex/photon/

ic3418-uv-vis-150dpi.jpg

Caption:
In the ultraviolet image on the left, from the Galaxy Evolution Explorer, galaxy IC 3418 leaves a turbulent star forming region in its wake. In the visible light image on the right (from the Sloan Digital Sky Survey), the wake with its new stars is not apparent.

 

CONTACTS

Chairman John Vale-Taylor
pjvalet1@btinternet.com

Secretary & Events Phil Berry 01892 783544
phil.berry@tiscali.co.uk

Treasurer Mike Wyles 01892 542863
mike31@madasafish.com

Editor Geoff Rathbone 01959 524727
geoff@rathbone007.fsnet.co.uk

Director of Observations Brian Mills 01732 832691
Brian@wkrcc.co.uk

Wadhurst Astronomical Society website:
www.wadhurst.info/was/

SAGAS web-site www.sagasonline.org.uk

Any material for inclusion in the October 2010 Newsletter should be with the Editor by September 28th 2010