MEETINGS

COMMITTEE MEETING

        Members of the Committee are respectfully reminded that there is a meeting of the Society’s Committee on Tuesday 12th of October beginning at 1930.  The meeting will be held at Phil Berry’s house and as always, any member of the Society is welcome to come along, although please let Phil know first.

SEPTEMBER MEETING

        The September meeting was introduced by Phil Berry who gave a short report on the success of this year’s Astro-barbecue as guests of Michael and Claire Harte.

        Owing to a change in the speaker, Phil now introduced himself to give a presentation:

Distances to the Stars
Phil Berry

        Phil’s talk introduced the different methods of measuring distances in Space from the size of the Earth’s orbit to the distance to the stars, galaxies and beyond, to the limits of the known Universe.   In 1672 Giovanni Cassini and his assistant, 4,000 miles away, compared the position of Mars seen at their respective locations and from the differences recorded, made a fairly accurate estimate of the Solar parallax and from this, the Earth to Sun distance.  Today the distance is measured very accurately using RADAR.  In the seventeenth century Cassini had only been out by 10%.
        The Earth-Sun distance is known as an Astronomical Unit, AU, and 2 x one AU gives the diameter of the Earth’s orbit; a suitable base line for triangulation to find the distance to the nearer stars.   Phil told us that in 1838, Bessell managed to measure the tiny parallax shifts of some local stars very carefully using the finest instruments available and determined their distances.
        Using the speed of light as a unit of measurement, the Sun is about 8 light-minutes away from Earth.  The orbit of the Earth is therefore 16 light-minutes and using triangulation, the nearest star is Proxima Centauri, a red dwarf at 4.2 light-years away.   Because of atmospherics on Earth, Phil explained that measurements from the ground limit accuracy but above the atmosphere, matters significantly improve.  From the 1990s the Hipparcos satellite has measured the shifts of about 120,000 stars with an accuracy of 1/1000th of an arc second.
        Gaia, Hipparcos’s successor, due to be launched soon, should achieve an accuracy of 20 millionth’s of an arc second – the thickness of a human hair seen 25 miles away!     Even so, this only enables local stars' distances to be measured.  Phil now explained how light intensity provides a versatile measuring method.  If the luminosity of a star is known, then using the Inverse Square Law it is possible to estimate distances.
        Delta Cepheus varies its brightness over a 5.3 day cycle and this type of star became the key to measuring greater distances.  In 1912, Henrietta Leavitt recognised that a Cepheid Variable star’s brightness had a tight relationship to the period of its cycle and used Cepheids whose distance had already been determined by parallax, to form a definite relationship.  Having discovered this relationship it was now possible to look at Cepheids in some of the closer galaxies and measure their distance in light years.  As Phil pointed out, measuring Cepheids variables in other galaxies was one of the key projects for the Hubble Space Telescope to a limit of about 65 million light years.  In fact it was Edwin Hubble who looked at Cepheid variable stars in the Great Andromeda Nebula and determined that it was a separate island galaxy well beyond our own mass of stars.
        In the 1970s, Tully and Fisher found a relationship between the rotation and luminosity of spiral galaxies.  Basically, big luminous galaxies rotate fast, while small low luminosity spirals rotate slowly.  This speed of rotation is determined by measuring the Doppler effect and the shift of the spectral lines on either side of the galaxy.   This enables astronomers to measure galaxy distances out to several hundred-million Light Years.
        It now became necessary to find something else to measure more distant objects and Phil said that astronomers needed to find something that is extremely luminous but also with known luminosity.  Within the last 10 years it has been found that White Dwarf Supernovae measure up to this class.  There are two qualities that make White Dwarf Supernovae ideal for distance measurement; They have almost exactly the same luminosity when they explode due to being of the same type of Thermo-nuclear device and they are extremely bright, so they can be seen out as far as 10 billion light-years.  They are only detectable for a very few days before they dim, but using a white dwarf supernova in a nearer galaxy whose distance has already been calculated from other means enables us to determine the distance to those seen at very great distances.  Often, the spectrum helps confirm the type of supernovae.
        Phil said that in a way we are looking back through time to about half the age of the Universe.   It was these distant objects that gave the first evidence that the expansion of the Universe is accelerating and also uncovered the existence of Dark Energy.
        Finally, Phil concluded his talk by mentioning a new method currently being explored using nearby galaxy NGC 4258.  This galaxy has a diameter of 1 light-year with a massive black hole at its centre.   Using radio telescopes to measure the movement of a cloud of gas travelling in a year it is now possible to measure the angle it moves although that angle may only be 10 millionths of an arc second!  So we now have an exceedingly skinny triangle but with modern techniques it should be possible to determine the distance.  As Phil says, the method hasn’t been fully developed but it will greatly improve and simplify conventional methods.
        All this leaves us wondering about past and future horizons due to the time light takes to travel; in fact events will have already happened but that information hasn’t reached us yet; - and may never reach us because of an accelerating expansion.
        An informative talk after which Phil then disappeared in a puff of smoke – to the pub…

OCTOBER MEETING

        Wednesday 20th October 2010 – Ian King is giving a talk with the intriguing title; “How Not to Build a Telescope”
        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 17th November 2010 – Society 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”.

OTHER NOTES AND INFORMATION

Finding your way round the night sky with just your hand

        There are often times when we are away from our telescopes and we want to locate something that may be visible for a short time such as a comet or an Iridium flare when we have an idea of its calculated position but need help finding it.
        The pole star, Polaris can be found easily by using the two stars at the back of the Plough, Dubhe and Merak.  We now have the direction of North.
        The horizon is often obscure by trees or hills.  Using a cup full of liquid and skimming the beam of a laser across the top will more or less provide an artificial horizon.
        Estimating angles is easily achieved using the hand.
        The little finger’s thickness is pretty well 1°, whilst the three middle fingers held together measure 4°.  A clenched fist gives a very convenient 10°, and an outstretched had measures 18°.
        Iridium Flares are reflections of the Sun from the highly polished flat surfaces of the aerials.  Because of their stable orbit it is possible to predict where that reflection falls on the surface of the Earth.  Such tables are given each month for Wadhurst in Brian Mills’ Sky Notes.  Although the reflections only last a few seconds they can have a magnitude of -8; brighter than Venus, but it is necessary to be prepared.  Using the artificial horizon and your hand, it should be possible to at least have some idea where to look.
        One method for locating M31, the Great Andromeda Galaxy is to “star-hop” starting with the two right hand stars in the easily found “W” in the constellation of Cassiopeia.  Using these as a pointer, look down 20° to the left hand of three bright stars in a line to the right.  These are in the constellation of Andromeda.  From the left star, Almach, the middle star, Mirach, is 12° to the right.  Then look above this by about 8° and the fuzzy blob you see is the diffused centre of the Andromeda Galaxy.  At over 2.5 million light years away it is the furthest object that can be seen with the naked eye.
        The centre of the galaxy is only 1/2° in diameter, but on a really clear night and with a pair of good binoculars it is possible to see the outer arms of the galaxy that stretch out as far as 2° either side and is very satisfying to see.                                                Geoff Rathbone

SKY NOTES FOR OCTOBER

Planets

Mercury is visible as a morning object at the very beginning of the month, but it is low in the east (at magnitude -1.1) just before sunrise. It suffers a superior conjunction on 17th October.

Venus is too close to the Sun for observation and passes through inferior conjunction on 29th October.

Mars is not suitably placed for observation this month.

Jupiter at magnitude -2.9 is unmistakable in the eastern sky rising around sunset at the beginning of the month. It is still travelling retrograde on the Pisces/Aquarius border below the square of Pegasus as shown in the diagram.

Saturn is not observable this month as it suffers a superior conjunction on the 1st.

Uranus is still close to Jupiter, but the apparent gap between the two is steadily increasing. The position of Uranus on October 15th is shown in the diagram.

Lunar Occultations
        In the table below I’ve only listed events for stars down to magnitude 7.0 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. Times are in BST.

Oct

Time

Star

Mag.

Ph

PA °

13th

20.41

SAO 186981

5.5

DD

135

14th

20.40

SAO 188123

7.0

DD

15

18th

23.59

SAO 146210

5.0

DD

34

24th

21.32

SAO 75810

4.9

RD

298

27th

21.22

SAO 77915

4.3

RD

340

     

 

   To aid identification I’ve included a graphic for two of the events in the table above. The first is for the disappearance on the 18th. The position of the star at the moment of occultation is shown and highlighted with the arrow.

 

 

 

       

The second diagram is for the event on the 27th. Again the position of the star at the moment it reappears is shown.

 

 

Phases of the Moon for October

Last ¼

New

First ¼

Full

1st

7th

14th

23rd

30th

 

ISS
        This month there is only one bright pass of the ISS that is visible before midnight and attains a reasonable altitude. 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 maximum elevation, so you should be able to see it for a few minutes before and after these times.  Time in BST.

Oct

Mag

Time

Alt°

Az.

30th

-2.5

19.03

30

SSE

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. 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 except for the last event.

Oct

Time

Mag

Alt°

Az.

16th

18.44

-2

60

NNE

17th

18.38

-4

61

NNE

18th

18.32

-3

63

NNE

19th

18.26

-4

64

NNE

20th

18.20

-8

66

NNE

21st

18.14

-5

67

NNE

22nd

18.07

-2

68

NNE

29th

19.30

-6

42

NNE

30th

19.23

-2

43

NNE

The event below is in GMT

31st

18.17

-4

45

NNE

 

 

Meteors
        The Orionid meteor shower is active from October 16th to 27th with maximum occurring on the 22nd when the ZHR is expected to be 25. The position of the radiant is shown in the diagram as a capital “R” circled, but bear in mind that it doesn’t rise until around 22.00 BST on the night of maximum.

 

Comet
        Comet 103P/Hartley looks as if it could become a naked eye object in the near future.

        The map shows the comet's position every fifth night (at 23.59) throughout October and the table below gives the expected magnitudes. It should be simple to interpolate where the comet will be on the nights in between. According to predictions (which are always difficult in the case of comets) it should be a naked eye object and therefore easy in binoculars. If you want to image it you will need to take short exposures because it is moving relatively quickly.

Oct

Mag

 

Date

Mag

1st

5.7

 

20th

4.4

5th

5.4

 

25th

4.5

10th

4.9

 

30th

4.7

15th

4.6

 

 

 

The Night Sky in October
        In the north Ursa Major is about as close to the horizon as it can get meaning that Arcturus has set, whilst Cepheus is almost overhead. As we look east the bright star Capella in Auriga is well above the horizon and Taurus is now fully risen. The fainter constellations of Aries, Triangulum and Pisces that are below Andromeda can now be more easily identified as their altitude increases. In the south Pegasus has nearly reached the Meridian so Fomalhaut should be easy to locate if you extend a line through the square’s two rightmost stars and continue it towards the horizon. In the West the Summer Triangle is still prominent although Hercules and Corona Borealis are both close to setting.

Reminder
        Don’t forget that British Summer Time ends on October 31st at 02.00.

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.

Comets
With the impending close approach of 103P/Hartley, it seems a suitable time to look at what they actually are.

        A comet consists of a solid nucleus (sometimes called the core) surrounded by a coma which could loosely be termed an atmosphere, plus a tail or two as shown in the diagram. The nucleus has often been described as a “dirty snowball” because it was thought to be made up of frozen particles of dust, water and other substances such as methane, ammonia and carbon dioxide. It now seems likely that the nucleus is to a large extent rocky with only a minimal amount of ice. Comets travel in very elliptical orbits but as they get close to the Sun they are heated and some of their matter is vaporised to form the coma. The solar wind (the stream of charged particles emitted from the Sun) take some of the coma with them as they pass the comet and these produce the tails. The dust particles form the dust tail and the gas particles are ionised by the solar wind and form the ion tail. Because they are driven by the solar wind a comets ion tail will always stream away from the Sun whilst the dust tail lags a little behind. Any tail that there is actually moves ahead of the nucleus after it has passed the Sun and returns to the more distant parts of the solar system. The nucleus can vary in size from a few tens of kilometres up to thousands of kilometres. It has been suggested that it was an encounter with a passing comet that brought water (and other carbon based molecules essential for life) to the Earth originally. Due to the irregular shape of a comets nucleus they are now termed as “Small Solar-System Bodies” according to a ruling made by the International Astronomical Union (IAU) when they met in 2006 and reclassify Pluto as a dwarf planet.

Meteors
        Meteors are generally Solar System debris similar in size to grains of sand (though some are larger) that by coincidence strike the Earth’s atmosphere and burn up due to friction with the air causing the familiar streak of light. They occur at altitudes around 75 to 100 kilometres. It is difficult to quantify what size of body qualifies as a meteor because different astronomical groups use different criteria. If the meteor is large enough for it to survive the journey through the atmosphere and reach the ground it is then called a “Meteorite”. We know that debris left in the wake of a comet can cause meteor showers when the orbit of the Earth passes through it. In these cases meteors appear to radiate from one particular area of the sky (called the radiant) in exactly the same way that snow does if you’re driving in a snowstorm. Meteors that reach a magnitude of -4 or brighter are termed “Fireballs”, and any that reach -14 and upwards are called “Bolides”.

Brian Mills

NASA’S SPACE PLACE

The Hunt is On!     by Carolyn Brinkworth

        The world of astronomy was given new direction on August 13, 2010, with the publication of the Astro2010 Decadal Survey. Astro2010 is the latest in a series of surveys produced every 10 years by the National Research Council (NRC) of the National Academy of Sciences. This council is a team of senior astronomers who recommend priorities for the most important topics and missions for the next decade.
        Up near the top of their list this decade is the search for Earth-like planets around other stars—called “extrasolar planets” or “exoplanets” —which has become one of the hottest topics in astronomy.
        The first planet to be found orbiting a star like our Sun was discovered in 1995. The planet, called “51 Peg b,” is a “Hot Jupiter.” It is about 160 times the mass of Earth and orbits so close to its parent star that its gaseous “surface” is seared by its blazing sun. With no solid surface, and temperatures of about 1000 degrees Celsius (1700 Fahrenheit), there was no chance of finding life on this distant world. Since that discovery, astronomers have been on the hunt for smaller and more Earth-like planets, and today we know of around 470 extrasolar planets, ranging from about 4 times to 8000 times the mass of Earth.
        This explosion in extrasolar planet discoveries is only set to get bigger, with a NASA mission called Kepler that was launched last year. After staring at a single small patch of sky for 43 days, Kepler has detected the definite signatures of seven new exoplanets, plus 706 “planetary candidates” that are unconfirmed and in need of further investigation. Kepler is likely to revolutionize our understanding of Earth's place in the Universe.
        We don't yet have the technology to search for life on exoplanets. However, the infrared Spitzer Space Telescope has detected molecules that are the basic building blocks of life in two exoplanet atmospheres.  Most extrasolar planets appear unsuitable for supporting life, but at least two lie within the “habitable zone” of their stars, where conditions are theoretically right for life to gain a foothold.
        We are still a long way from detecting life on other worlds, but in the last 20 years, the number of known planets in our Universe has gone from the 8 in our own Solar System to almost 500. It's clear to everyone, including the Astro2010 decadal survey team, that the hunt for exoplanets is only just beginning, and the search for life is finally underway in earnest.
        Explore Spitzer’s latest findings at:
http://www.spitzer.caltech.edu
        Kids can dream about finding other Earths as they read “Lucy’s Planet Hunt” at:
http://spaceplace.nasa.gov/en/kids/storybooks/#lucy.

        This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
 
 alien-atmosphere.jpg

 

     Artist’s rendering of hot gas planet HD209458b. Both the Hubble and Spitzer Space Telescopes have
    detected carbon dioxide, methane, and water vapour—in other words, the basic chemistry for life—in the
    atmosphere of this planet, although since it is a hot ball of gas, it would be unlikely to harbour life.

 

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 November 2010 Newsletter should be with the Editor by October 28th 2010