WADHURST ASTRONOMICAL SOCIETY

NOVEMBER NEWSLETTER 2008

INDEX: MEETINGS, OTHER NEWS, CONTACTS

MEETINGS

MEETINGS OCTOBER MEETING

        The October meeting was introduced by our Chairman, John Vale-Taylor who explained that this month we were viewing two lectures from an astronomical course as an introduction to Einstein’s Theories of Relativity.
        We would like to thank Alex and Cameron Brown for providing a laptop to replay the DVD at short notice after we developed an unexpected problem.

Astro Lectures
Einstein’s General Theory of Relativity
        In the first video, We were introduced to the idea of General Relativity and how time and space in reality are not linear when in the vicinity of gravitational fields, messing up the measurement of time and distances.
        To begin the video talk, the lecturer talked about Newton’s laws of gravity and how they had served well for three hundred years but then Einstein believed that Newton’s laws begin to break down when speeds approach that of light.
        Einstein claimed that acceleration produced the same effect on a body as uniform gravity did and using the idea of a man in a windowless elevator when looking at a torch shining light horizontally across the elevator he would see the light bend if they were accelerating close to the speed of light.  Einstein postulated that the same effect would occur if instead of accelerating, a source of gravity appeared beneath the elevator.  The man could not tell the difference.
        This effect of warping space was likened to an ant walking in a straight line across a flat rubber sheet.  Placing a weight in the centre of this sheet would cause it to distort and now the ant would take a very different path if trying to walk in a straight line.  If the sheet was considered to be time and space coordinates then their distortion would suggest the bending of time and space.
        In this analogy, the two dimensional sheet would be distorted, not by the earth’s gravity but by some fourth dimensional effect that man cannot visualise.
        In 1919 Arthur Eddington observed an eclipse of the Sun and during total darkness measured the position of certain stars close to the Sun as they became visible.  He found that their position had been affected by the Sun’s gravity.  (Today radio astronomy is used to measure the Sun’s gravitational effect during daylight)  The displacement was in line with Einstein’s predictions.
        An interesting experiment took place in 1963 in the Jefferson Tower at Harvard University.  A source of iron Fe 57 was placed at the bottom and radiated gamma rays at a precise wavelength.  This was to be detected by an absorber at the top of the tower, but because of gravity, the rays were red shifted and so were not absorbed.  By blue shifting the source by a calculated amount, the radiation was then able to be absorbed, so suggesting that Einstein was correct.
        The experiment was carried out with the source at the top of the tower.  This time the gamma rays were blue shifted and so by red shifting the source the wavelength was brought back so that it was again absorbed.
        Finally in this lecture, the lecturer described how the atomic clocks aboard the Global Position Satellites (GPS) had to be corrected by calculated amounts to correct for their speed and the effects of gravity.  Without these very tiny corrections, errors of many kilometres would appear on Earth.

Warping of Space and Time
        In the second video we looked more closely at the importance of correcting for errors in GPS navigation.  Special Relativity, which states that the speed of light is relatively the same whatever speed one is travelling at, causes the clocks in the GPS satellites to run 7 micro-seconds fast, whilst General Relativity, which states that gravity warps space, causes the clocks to run slower by 43 micro-seconds.  So the clocks have to be compensated for by correcting them by 38 micro-seconds.
        Since light travels by about a foot in a billionth of a second, in just a day, the GPS would create an error of several miles and be useless without the precise correction.
        The lecturer noted that this was the most obvious result of both the Special and General theories of Relativity.
        Looking again at the General Theory of Relativity, we looked at the precession of two orbiting pulsars whose orbits are very elliptical.  The warping of space and time meant that the point of aphelion precessed during time, but because the effect of gravity precession appeared at a different rate expected and could only be accounted for by applying the theory of general relativity.
        Gravity waves are being radiated by the orbiting pair and this takes energy out of the system, therefore as time passes, the pair’s orbit speeds up and the distance of the pulsars’ orbit has been calculated to be reducing by about 7 millimetres a year.
        This means that the precession is also changing and the angle at which it is speeding up can only be accounted for by general relativity.
        The video then led the discussion to the effect of gravity on the path of light, using the effect of a star’s gravity to bend light from a distant quasar that is in line but behind the star.  This causes the light to curve.  Many examples have been photographed in many parts of the sky.  The effect is called gravitational lensing.
        If the quasar is precisely in line behind the star, then a ring is seen around the star.  This is called an Einstein Ring because Einstein had predicted the effect, although he never thought it would ever be seen.
        Another effect is called micro-lensing where the gravity of a star “focuses” the light from a more distant star behind it, producing a brightening as the two come into line.  In fact quite recently a star was seen to produce this brightening and then shortly afterwards there was another short burst.  This was caused by a newly discovered huge planet orbiting the nearer star.
      These are just some of the ways in which the predicted effects have helped to confirm the theories of both General and Special Relativity.

NOVEMBER MEETING        

Wednesday 19th November 2008  During our meeting, we will be having a talk by John Murrell who is a very active member of the Croydon Astronomical Society. His talk is on “Gamma Ray Bursts”.  These are the most luminous electromagnetic events occurring in space since the Big Bang.

        The meeting begins at 1930 although members are invited to arrive anytime after 1900 as this is a good time to exchange ideas and discuss problems.

        The venue as always is 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  6AX)

FUTURE MEETINGS

        Wednesday 10th December 2008. Please note that as it is December, the Society meets on the Second Wednesday instead of the third as in other months.

        Paul Treadaway, who is a well known member of the Society gives a talk about “How Stars Work”.

        Members will remember the talk Paul gave us last year and will recall the intriguing scenarios he posed.

        Christmas is with us at the end of the month so there will be plenty of mince pies to be eaten during the meeting.

        Wednesday 21st January 2009 This is the Annual General Meeting.  That should not take too long and then Phil Berry gives a fascinating talk, bringing us up to date with the impressive progress he has achieved with his observatory following on from his previous talk earlier in the year.  This time Phil calls his talk “The Further Trials and Tribulations of an Amateur Astronomer”.

OTHER NEWS AND INFORMATION

WEB-SITE WINS SAGAS PRAISE

        SAGAS, the Southern Area Group of Astronomical Societies, have awarded our web-site, administered by Michael Harte with a top score of 5 stars for promoting and providing links to the SAGAS website.  Only one other group managed the full score.

        Congratulations to Michael.

SKY NOTES FOR NOVEMBER 

Planets

Mercury will be visible as a morning object for the early part of the month when it rises about one hour before the Sun. It is at superior conjunction on the 25th when it is around the far side of the Sun.

Venus is brightening as an evening object in the south west. By the middle of the month it will be at magnitude -4.0 when it will set two hours after the Sun.

Mars is not suitably placed for observation this month.

Jupiter is still in Sagittarius and low down in the south at magnitude -2.0. It becomes more difficult to observe during November despite setting two and a half hours after the Sun by the end of the month.

Saturn is a morning object at magnitude 1.1 rising some six hours ahead of the Sun by mid-month (that’s just after 01.00) so it will soon be an evening object. The ring system is moving towards an edge-on view as seen from Earth, which will occur during September 2009. Because of this Saturn’s satellite Titan will be visible in transit across the face of the planet and will also be seen to be occulted.

Lunar Occultations
        On the evening of November 13th the Moon’s passage across the sky takes it once again “through” the Pleiades star cluster. On the down side the Moon is just past full but on the plus side there are some bright re-appearances to see. The brightest is Alcyone at magnitude 2.8 which might be observed to disappear at the bright limb first. Next year Alcyone will be the subject of a graze occultation visible from the south east of England.
        As usual in the table I’ve only included events for stars down to around magnitude 7.5 that occur before midnight. DD = disappearance at the dark limb, DB = disappearance at the bright limb and RD = re-appearance at the dark limb. Although there are many re-appearances, only the very brightest are included here.
Times are all GMT.

Phases of the Moon for November 

New	First Quarter	Full	Last Qaurter
27th	6th	13th	19th

Meteors

The Taurids.
The Taurid meteor shower comes to maximum on the 3rd of this month and although the ZHR (zenithal hourly rate) is only 10 there are usually a high proportion of bright and slow meteors plus some fireballs. The maximum is known to be rather flat and extended unlike showers such as the Leonids or Perseids that show a sudden but brief period of increased activity. In 2005 the Taurids displayed unusually high activity and it is suggested that this could be repeated again this year. This shower which is known to have a double radiant in Taurus is associated with the comet 2P/Encke. It is well worth observing partly because the crescent Moon will be out of the way, having set before 20.00 on the night of maximum, and also because there is a chance of seeing something rather special.

The Leonids.
The Leonid meteor shower is active from November 15th to the 20th with maximum occurring on the 17th. Unfortunately a gibbous Moon will interfere with a ZHR of around 20 at maximum. The radiant does not rise until 23.00 which is only a few hours after the Moon. In the past this shower has seen some spectacular outbursts but unfortunately the predictions from those who model the shower’s activity suggest that this year will not be one of them.

ISS
There are a large number of passes of the ISS this month as seen from Wadhurst but many are low in the sky or occur in the early hours of the morning. I have only included those that are the brightest, attain reasonable altitude and occur before midnight. The information given is for when the ISS is at maximum altitude, so it is best to look some minutes before this time. Full details of all passes can be found at: - www.heavens-above.com
Times are all GMT. 

Iridium Flares
I thought I would include a few of these events because although they are of no scientific value, they can be quite spectacular with the very brightest reaching beyond magnitude -8. They are caused when an Iridium satellite briefly reflects sunlight from one of its 3 antennae onto a small area of the Earth’s surface. The name “Iridium” was used because there were originally going to be 77 of them (forming a communications network to cover the globe) and Iridium has the atomic number 77 in the periodic table. The predictions are specifically for the Wadhurst area because although the time, altitude and azimuth elements change very little (compared with my home in Hildenborough for example) the magnitude of the flare can vary considerably. I’ve only included the brightest and most easily visible – a full list is available at: www.heavens-above.com
It is possible to see flares in daylight if you know exactly where to look for them.

Advance Warning for December

Lunar Occultation of Venus
In the afternoon of December 1st Venus will be occulted by the dark limb of a thin crescent Moon and will later emerge on the bright limb. The disappearance should be a fairly easy event as Venus will be at magnitude -4.1 and the Sun will be setting around the time that the planet is occulted. One thing to bear in mind is that the Moon will be quite low in the sky (only 14° high at disappearance) so a good south western horizon is required.

Meteors
The Geminid meteor shower reaches maximum on December 13th although moonlight will interfere.
The Ursid meteor shower reaches maximum on December 20th but is more favourable as the Moon is between last quarter and new and doesn’t rise until 03.20

NASA SPACE PLACE

The Chemical Weather Report

        “Sunny tomorrow with highs in the mid-70s. There’s going to be some carbon monoxide blowing in from forest fires, and all that sunshine is predicted to bring a surge in ground-level ozone by afternoon. Old and young people and anyone with lung conditions are advised to stay indoors between 3 and 5 p.m.”
        Whoever heard of a weather report like that? 
        Get used to it. Weather reports of the future are going to tell you a lot more about the atmosphere than just how warm and rainy it is.  In the same way that satellite observations of Earth revolutionized basic weather forecasting in the 1970s and 80s, satellite tracking of air pollution is about to revolutionize the forecasting of air quality.  Such forecasts could help people plan around high levels of ground-level ozone—a dangerous lung irritant—just as they now plan around bad storms.
        “The phrase that people have used is chemical weather forecasting,” says Kevin Bowman of NASA’s Jet Propulsion Laboratory. Bowman is a senior member of the technical staff for the Tropospheric Emission Spectrometer, one of four scientific sensors on NASA’s Aura satellite.
        Aura and other NASA satellites track pollution in the same way that astronomers know the chemical composition of stars and distant planetary atmospheres: using spectrometry. By breaking the light from a planet or star into its spectrum of colours, scientists can read off the atmosphere’s gases by looking at the “fingerprint” of wavelengths absorbed or emitted by those chemicals. From Earth orbit, pollution-watching satellites use this trick to measure trace gases such as carbon monoxide, nitrogen oxide, and ozone.
        However, as Bowman explains, “Polar sun-synchronous satellites such as Aura are limited at best to two overpasses per day.” A recent report by the National Research Council recommends putting a pollution-watching satellite into geosynchronous orbit—a special very high-altitude orbit above the equator in which satellites make only one orbit per day, thus seeming to hover over the same spot on the equator below.  There, this new satellite, called GEOCAPE (Geostationary Coastal and Air Pollution Events), would give scientists a continuous eye in the sky, allowing them to predict daily pollution levels just as meteorologists predict storms.
        “NASA is beginning to investigate what it would take to build an instrument like this,” Bowman says. Such a chemical weather satellite could be in orbit as soon as 2013, according to the NRC report. Weather forecasts might never be the same.
        Learn more about the Tropospheric Emission Spectrometer at: tes.jpl.nasa.gov

        Kids can learn some elementary smog chemistry while making “Gummy Greenhouse Gases” out of gumdrops at: spaceplace.nasa.gov/en/kids/tes/gumdrops

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

Any material for inclusion in the December Newsletter should be with the Editor by 28th November 2008

CONTACTS

Chairman   John Vale-Taylor 

Phil Berry  01892 783544

Treasurer  Mike Wyles  01892 542863

Publicity & Website  Michael Harte  01892 783292

Newsletter Editor  Geoff Rathbone  01959 524727

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