A very happy New Year to all our Members!

 

 

COMMITTEE MEETING

 

        Members of the Committee are respectfully reminded that there is a meeting of the Committee at 1930 on Tuesday January 10th 2012.  The meeting will be held at Phil Berry’s house.

        Any member of the Society is very welcome to come along, but please do let Phil know beforehand.

 

MEETINGS

 

DECEMBER  MEETING

 

        The talk at the December meeting was given by one of our members who has spoken to members a number of times before.

 

Relatively Einstein

Paul Treadaway

 

        Right at the beginning of his talk, Paul warned there was a limited amount of straightforward maths, and if his audience understood his talk, he hadn’t explained it correctly…

        Paul began by looking at Newton’s theories.  His mechanistic approach made possible Neptune’s discovery from Uranus’s orbital irregularities.  However when it came to using this approach on Mercury’s perihelion precession there was a 7.8% error and it was not until Einstein produced his Theory of General Relativity that this discrepancy could be explained.

 

        We quickly went through co-ordinate systems.  The X, Y, Z system with the three scalars at right angles to each other is ideal for describing the position of something relative to a common junction of the scalars when describing say a building or something.

        For navigation, a better system is to use longitude, latitude and altitude.  Then again, in astronomy we use Declination, Right Ascension and Distance.

        But there is a fourth co-ordinate; - Time.  As Paul explained this makes it possible to measure velocities and acceleration and keeps things from happening all at once.

        In the classical co-ordinate system, with the Earth as a fixed reference point, stars at billions of light years away would circle in 24 hours; clearly not the case.

        Paul referred to Einstein’s “man walking inside a train in the direction of the train’s travel”.  An observer on the embankment would be expected to see the man travelling at the velocity of the train plus his velocity relative to the train.  Now it has been proved by observing binary stars that the velocity of light is a constant in a vacuum and not dependant on the motion of the source.

        Bearing this in mind, if a ray of light replaced the man on the train, then from the embankment it is travelling at the speed of light; on the train the leading edge of the ray cannot be the speed of light less the speed of the train; so this leads to the conclusion that the train has changed length in the direction of travel.

        Next Paul considered two simultaneous lightening strikes, each hitting a separate power pole along the side of the track of the train.  The observer on the embankment sees both events occurring at the same instant.  However, to an observer on the train, lightening strikes the pole towards the front of the train fractionally earlier that it does at the pole towards the rear.

        More generally each reference body has its own time frame.

        If it was possible for the two observers to measure the length of the train and then comparing their results they would conclude that the train would appear shorter to the observer on the embankment.

        Paul introduced the mathematical approach, first looking at the problem using the classical Galilei Transformation where the speed of light is assumed to be infinite.  But as we now know, the speed of light is not infinite.

        Both the relative time and distance is different for the moving frame of reference.

        Mathematician, Lorentz produced a method of transformation which takes into account the relativistic effects on time and distance.

        Paul showed from the formulae that length in the direction of travel decreases and a clock will slow down when in relative motion.

        We saw by using imaginary numbers that we can represent the three dimensional special coordinates and now the time coordinate as well can be represented, although this throws up the thought that we can move forwards and backwards through time as well as space!

        This is covered by Special Relativity.

        Now Paul moved to General Relativity which looks at the effects of rotation and gravity.

        We were reminded of the inhabitants of Terry Pratchet’s disk world; a flat rotating disk in space.  Two identical clocks are compared; one in the centre and one at the edge.  As Paul showed from Special Relativity, clocks in motion run at different speeds from those that are not.  Also if an inhabitant on disk world measures the circumference and diameter, dividing his circumference by his diameter his result will not be ‘pi’.  General Relativity addresses this.

        Consider a man in a lift, not moving but suspended in a shaft on Earth.  He feels his own weight; it is Christmas so he hangs decorations from the ceiling but drops one which falls to the floor.  Looking up through a hatch he sees the support wire.

        A second man in a lift, this time in space, is being accelerated towards a destination.  He feels his own weight; it is Christmas and also hangs decorations from the ceiling but drops one which falls to the floor.  Looking up through a hatch he sees the support wire.

        Paul said Einstein deduced from this situation that accelerating frames of reference experience a gravitational field.

        Back to the train scenario the man on the train is replaced with a ray of light, if the train is accelerating the observer on the embankment sees a ray of light travelling in a straight line, however viewed from the accelerating train; it travels in a curved path!  General Relativity predicts that light will follow a curved path in a gravitational field as was seen in 1924 when the apparent location of a star almost in line with the Sun was seen to be affected by the Sun’s gravity during an eclipse.

        It was Gauss who provided a way of looking at General Relativity by considering a coordinate system where the lines are neither straight nor parallel but arbitrary and it turns out that gravity associated with mass distorts space-time like pushing a finger into the surface of a jelly.

 

 

        Paul concluded by saying that may be light does indeed travel in straight lines, it is just that space-time is curved and that planets too are travelling around gravitational wells in space-time to arrive back where they started after their “year”.

 

        With apologies to Paul who showed his conclusions clearly using maths, but there hasn’t been room here to do justice.

 

 

John Wayte’s notes from the scientific world

 

      John Wayte talked about more notes he had found in the scientific world.

      Firstly he showed an artists diagram of the theory of the development of a black hole.

      A sun-like star is shown on an eccentric orbit near a super-massive black hole in the heart of a distant galaxy.

      Strong forces near the black hole increasingly distort the star and it begins to be ripped apart.

      Part of the star closest to the black hole is shown streaming towards it and forming an accretion disk with the rest of the star expanding into space.

      Near the black hole, magnetic fields power a narrow jet of particles moving near the speed of light.  Viewed head-on the jet is seen as a brilliant source of x-rays and radio waves.

      Then John showed the location of the oldest know object to be seen by the Hubble Space Telescope. It was 13.5 billion years old!

 

 

 

      John is away for the next couple of months, having an operation and we wish him every success and look forward to seeing him again in full health.

 

 

 

 

A method of timing an occultation

 

        Phil Berry showed the meeting a video of his first successful attempt to time an occultation using his Nexstar 5 telescope with a Watec 120N video camera recording at 25 frames per second with a GPS timed overlay.  It was on a 5.8 magnitude star named 40 Arietis occulted by the moon on December the 7th as mentioned by Brian Mills in the December Newsletter Sky Notes.

        By stepping through the video frame by frame it was possible to show the very faint star up to the point that the Moon “switched it off”.  The timing was recorded as 21 hours, 25 minutes and 19.552 seconds.

        Being a 5.8 magnitude star so close to the illuminated part of the moon, it was quite difficult to record.

        Subsequently, Brian has submitted the video to the occultation powers that be and the video and timing have been deemed valid.  So a very successful outcome!

 

JANUARY MEETING

 

        Wednesday 18th January 2012 – January is the month when we hold the Society’s Annual General Meeting.  This is then followed by a talk by Dr. Bob Seaney called “The Multiverse” during which Bob introduces us to an exciting look at the Universe.

        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 also 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)

        Anyone is welcome but on-members are asked if they wouldn’t mind contributing £2.

 

 

FUTURE  MEETINGS

       

        Wednesday 15th February 2012 – Sadly, Robin Durant is unable to be present at our February meeting due to illness and the Society sends him our best wishes for a speedy recovery.

        Our own Jan Drodz has very kindly stepped and is to give a talk entitled “Revolutions in Astronomy”.

 

        Wednesday 21st March 2012 – There will be a talk by Ben Ritchie called “The Life and Death of a Very High Mass Star”.

 

        Wednesday 18th April 2012 – Steve Richards talks about “Making Every Photon Count”.  He has written a book of the same name and is a beginner’s guide to Deep Space Astro –photography.

 

 

OTHER NOTES AND INFORMATION

 

 

SKY NOTES FOR JANUARY

 

Planets

 

Mercury is a morning object at the beginning of the month and may just be glimpsed above the south eastern horizon immediately before sunrise. It reached greatest western elongation at the end of December so is now drawing (apparently) closer to the Sun as it approaches superior conjunction on February 7th.

 

Venus is now becoming much more obvious in the south west. On the first of the month it sets at 1845h (2½ hours after the Sun), but by the end of the month this has become 2030, (3½ hours after the Sun). At magnitude -4 it moves from Capricornus into Aquarius and almost to the border with Pisces during the month. The map gives the position of Venus (with reference to Pegasus and Pisces) at 1700 on the dates shown, although please keep in mind that Pegasus is in the south on the 1st but has moved to the south west by the 31st.

 

 

 

 

Earth reaches perihelion (its closest to the Sun) on the 5th at 0100 when it will be at a distance of 91.3 million miles.

 

Mars is an evening object on the Virgo/Leo border, rising at 2130 by the middle of the month. By 2230 it has climbed to an altitude of 10° and is almost exactly due east. At month’s end it will rise at 2030 and shine at magnitude -0.5, brightening gradually as it heads for a March opposition. On the 24th it reaches its first stationary point before moving retrograde. Its angular size increases to almost twelve arc-seconds (12") by the end of the month.

 

 

Jupiter is still a brilliant evening object at magnitude -2.5 moving from Pisces into Aries, setting in the early hours of the morning. If you have a pair of tripod mounted binoculars (or some other way of holding them still) you will be able to see the four largest moons - Io, Europa Ganymede and Callisto. Their positions change relatively quickly as Io takes 1¾ days to make one orbit, and Callisto (the outer of the four) takes 16½ days. I have included the position of Jupiter on the “Venus” map.

 

Saturn is a morning object in Virgo, rising at 01.00hrs mid-month at magnitude +0.6. It spends almost the entire year in that constellation until in December it crosses into neighbouring Libra.

 

 

 

 

Lunar Occultations

In the table below I’ve listed events for stars down to magnitude 7.0 that occur before midnight although there are many others that are either of fainter stars or occur at more unsociable hours.  DD = disappearance at the dark limb and RD = reappearance at the dark limb.  Times are in GMT.

 

Jan

Time

Star

Mag

Ph

PA °

4th

2041

SAO 93394

6.9

DD

79

4th

2304

SAO 93412

6.8

DD

108

7th

2003

SAO 77813

6.9

DD

75

27th

1554

19 Piscium

4.9

DD

358

31st

1629

45 Arietis

5.7

DD

109

 

 

Phases of the Moon for January

 

First ¼

Full

Last ¼

New

1st

9th

16th

23rd

31st

 

 

ISS

Below are details of passes of the International Space Station (ISS) that occur before midnight and are brighter than magnitude -1. The details of all passes including those visible from other areas can be found at:

www.heavens-above.com

Please remember that the times and directions shown below are for when the ISS is at it’s maximum elevation, so you should go out and look a few minutes before. Times are in GMT.

 

Jan.

Mag

Time

Alt°

Az.

1st

-3.3

1621

88

S

1st

-1.6

1757

30

SSW

2nd

-2.3

1701

47

SSW

4th

-1.3

1644

31

SSW

 

Iridium Flares

The flares that I’ve listed are magnitude -2 or brighter although there are a lot more that are fainter, occur after midnight or at a lower altitude. 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 sometimes possible to see the satellite in advance of the “flare”, although of course it will be much fainter at that time.  Times are in GMT.

 

Jan.

Time

Mag

Alt°

Az.

2nd

1745

-8

56

NE

3rd

1739

-8

57

NE

4th

1733

-2

58

NE

11th

1659

-2

70

ENE

18th

1824

-3

49

NNE

19th

1816

-2

49

NE

20th

1812

-5

52

NE

26th

1742

-5

62

NE

28th

1730

-2

64

NE

31st

1714

-2

69

NE

 

 

Meteors

 

The Quadrantids - this shower is active from January 1st to 6th with maximum occurring on the 4th in the early hours, so the night of the 4th/5th would be the best time to look. The radiant is circumpolar although in the early evening/night it is fairly low down and close to due north.

The Night Sky in January (Written for 2200 GMT mid month)

 

In the north Ursa Minor points eastwards towards the Great Bear that now stands perpendicular to the horizon. The head of Draco is low down on the meridian, and just below it, if you have a good view north you may see the bright star Vega skimming the horizon. Just a little to the west and slightly higher you should be able to see another member of the Summer Triangle - Deneb in Cygnus the swan.

Looking east, Leo is fully risen and just below it lies the red planet Mars. Just west of Leo lies the faint constellation of Cancer which contains the open cluster known as the “Beehive” or the “Praesepe” that was catalogued by Messier as M44. Almost on the zenith is the bright star Capella in the constellation of Auriga.

In the south the brilliant winter constellations dominate the sky. Orion is on the meridian with Gemini to his north east, Taurus to his north west, Canis Minor to the east and Canis Major to the south east. As you can see from the map, Orion acts as an excellent signpost to the many other constellations that surround him.

If we turn to the west we see that the autumn constellations of Pegasus, Pisces and Cetus are close to setting. Whilst Perseus is due west, have a look with binoculars or a low power telescope, at the double cluster (NGC 869 and 884 to give them their correct name) in the sword handle. The square of Pegasus may appear in an unfamiliar pose as it will be standing on one corner, but can easily be identified from Cassiopeia as shown. The double cluster can be found either by using the two stars in Cassiopeia that point in approximately the right direction, or by using Pegasus and Andromeda to locate Perseus. Both options are shown on the map. The great spiral in Andromeda (M31) is also shown and worth a look as it is the most distant object visible to the naked eye.

 

 

Advanced Warning for February

February 10th - Venus and Uranus are in conjunction approximately twenty arc-minutes (20') apart in Pisces. Next month I’ll include a finder chart so that you can identify Uranus by using its much brighter neighbour. (Last month’s “Sky Notes” were in error when they said this occurred on the 2nd).

 

Brian Mills

 

DEFINITIONS OF TERMS USED IN ASTRONOMY

 

Angular Measurement. When we want to describe how close together two celestial objects appear (or how large/small they seem), it’s impossible to use conventional units of measurement so instead we use a system of angular measurement.

A full circle consists of 360 degrees (360°), each degree can be divided into sixty minutes (60') and each minute can again be sub-divided into sixty seconds (60"). More correctly we ought to refer to these as arc-minutes and arc-seconds. To give some idea of scale, the full Moon has an apparent angular diameter of roughly half of one degree (½°) or thirty arc-minutes (30') or indeed eighteen hundred arc-seconds (1800"), although it would never be expressed in such small units. You can see from this that during the conjunction of Venus and Uranus next month the two planets will be less than a Moon diameter apart. As I said above this system can be used to measure the apparent sizes of the planets but stars are too distant to be considered as anything other than point sources to the naked eye. The apparent sizes of celestial objects can vary significantly depending on their distances from us as shown in the table.

 

Object

Apparent

size

(furthest)

Apparent

size

(closest)

Sun

31.6'

32.7'

Moon

29.3'

34.1'

Mercury

4.5"

13"

Venus

9.5"

66"

Mars

3.5"

25.1"

Jupiter

29.8"

50.1"

Saturn

15"

20.8"

Uranus

3.3"

4"

Neptune

2.1"

2.3"

 

From this you can see how the apparent sizes of the Sun and Moon vary and why some solar eclipses are only annular - the Moon is not always large enough to fully obscure the solar disk so a ring of light (annulus) remains around the dark body of the Moon at the time of central eclipse.

We can also use angular measurement to say how far above the horizon (altitude) a celestial body is or will be - the ISS and Iridium Flare predictions are practical examples of this. If we treat the horizon as 0° and the zenith (overhead point) as 90°, it’s fairly easy to imagine sub divisions of  this to arrive at, for example 45° or 30°.

 

Brian Mills

 

NASA’S SPACE PLACE

 

Dawn Takes a Closer Look

By Dr. Marc Rayman

 

        Dawn is the first space mission with an itinerary that includes orbiting two separate solar system destinations. It is also the only spacecraft ever to orbit an object in the main asteroid belt between Mars and Jupiter. The spacecraft accomplishes this feat using ion propulsion, a technology first proven in space on the highly successful Deep Space 1 mission, part of NASA’s New Millennium program.

        Launched in September 2007, Dawn arrived at protoplanet Vesta in July 2011. It will orbit and study Vesta until July 2012, when it will leave orbit for dwarf planet Ceres, also in the asteroid belt.

        Dawn can manoeuvre to the orbit best suited for conducting each of its scientific observations. After months mapping this alien world from higher altitudes, Dawn spiralled closer to Vesta to attain a low altitude orbit, the better to study Vesta’s composition and map its complicated gravity field.

        Changing and refining Dawn’s orbit of this massive, irregular, heterogeneous body is one of the most complicated parts of the mission. In addition, to meet all the scientific objectives, the orientation of this orbit needs to change.

        These differing orientations are a crucial element of the strategy for gathering the most scientifically valuable data on Vesta. It generally requires a great deal of manoeuvring to change the plane of a spacecraft’s orbit. The ion propulsion system allows the probe to fly from one orbit to another without the penalty of carrying a massive supply of propellant. Indeed, one of the reasons that travelling from Earth to Vesta (and later Ceres) requires ion propulsion is the challenge of tilting the orbit around the sun.

        Although the ion propulsion system accomplishes the majority of the orbit change, Dawn’s navigators are enlisting Vesta itself. Some of the ion thrusting was designed in part to put the spacecraft in certain locations from which Vesta would twist its orbit toward the target angle for the low-altitude orbit. As Dawn rotates and the world underneath it revolves, the spacecraft feels a changing pull. There is always a tug downward, but because of Vesta’s heterogeneous interior structure, sometimes there is also a slight force to one side or another. With their knowledge of the gravity field, the mission team plotted a course that took advantage of these variations to get a free ride.

        The flight plan is a complex affair of carefully timed thrusting and coasting. Very far from home, the spacecraft is making excellent progress in its expedition at a fascinating world that, until a few months ago, had never seen a probe from Earth.

        Keep up with Dawn’s progress by following the Chief Engineer’s (yours truly’s) journal at:

http://dawn.jpl.nasa.gov/mission/journal.asp

and check out the illustrated story in verse of “Professor Starr’s Dream Trip: Or, how a little technology goes a long way,” at http://spaceplace.nasa.gov/story-prof-starr

 

 

 

 

 

 

 

This full view of the giant asteroid Vesta was taken by NASA’s Dawn spacecraft, as part of a rotation characterization sequence on July 24, 2011, at a distance of 5,200 kilometres (3,200 miles).  Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

 

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

 

 

 

 

 

 

 

 

 

 

 

CONTACTS

 

Chairman     John Vale-Taylor

                                                      pjvalet1@btinternet.com

 

Secretary & Events                 Phil Berry             01892 783544

                                                      philberryemail@gmail.com

 

 

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

 

Paul Treadaway                       01342 313799

                                                      paul_treadaway@btinternet.com

 

Wadhurst Astronomical Society website:

                                                      www.wadhurst.info/was/

 

SAGAS web-site                        www.sagasonline.org.uk

 

Any material for inclusion in the February 2012 Newsletter should be with the Editor by January 28th 2012