Mike Frost writes:

?. . taking up Vaughan's challenge to find unconventional ways of observing.  I'm currently embroiled in a discussion on whether or not stars can be seen in daylight from the bottom of mineshafts or chimneys.
I wish to raise the important issue of Underwater Astronomy.  [This copy] from last November?s issue of Sky & Telescope of a article by Kevin J. McCarthy of Plaistow, New Hampshire, discovered that, by lying at the bottom of his swimming pool, he could see the night sky just as clearly as from the surface, but with out the mozzies.

I?d like to be able to add a few personal observations to this, as I have made night scuba dives on a few occasions (which solves the breathing problem!).  However, although I have dived with clear skies and bright planets overhead it has always been into the sea and the effect of surface waves is to introduce ?bad seeing? which essentially destroys the star images.

So Hale-Bopp is finally here, after proberly the longest time ever from discovery until perihelion, it is now a naked eye object from a dark sky.  1996 looks like being the year of the comets with first Hyakutake then Tabur and now the big one, Hale-Bopp.  But where are they coming from?
It is now known that there are two distinct types of comets; they are the short period and the long period comets and both types have very different orbital characteristics.  Lets first look at the short period comets.
These are mostly in orbits within the orbit of Jupiter with periods of between one and ten years.  The orbits of this class of comets will be wide elliptical orbits sweeping from out side the orbit of Mars in towards the orbit of Mercury.  All of these objects orbit close to the ecliptic, the plane of the orbits of all the planets in the solar system and all travel around the sun in the same direction as the planets.  One of the problems with short period comets is why we can see them at all.

All comets are now known to consist of various kinds of ice and dust.  Most of the ices are a mixture of water ice with other elements mixed in and the description of them, as a dirty snowball, is most apt.  The sun warms the surface  of the comet as they rotate, Halley takes 7.4 days.  Moving closer in towards the sun along their orbit, the tempreture of the dark surface, only 4.5% to 5% reflectance, reaches the melting point of water, the ice, with no atmospheric pressure to hold in the molecules as a liquid, sublimates straight into a gas.  The gas streaming off is mostly water vapour (80%) and carbon monoxide (nearly 20%) with a small amount of carbon dioxide and other elements, it is ionized by the suns ultraviolet light and blown along on the solar wind.
All of this out gassing is what makes comets so beautiful to see, this is what forms the coma and the tail.  The gas escapes into space with a speed of about 2,000 mph and in doing so takes with it any dust trapped in the ices.  Most of the dust particles are so small, similar in size to cigarette smoke, that the pressure of sunlight on them is enough to push them away from the sun.  The larger grains are more like sand size and mostly stay near the orbit of the comet.  If they come near a body such as the Earth they will hit the atmosphere and burn up as a meteor.

The tale of a comet can stretch for many millions of miles and is the nearest thing to nothing you can ever see!  The air at sea level is 300 billion times denser than the inner coma of a comet.
The gravitational pull of such small bodies of 1km, to say, 50 km across is almost non existence, if you stood on the surface and gave a good jump (even with a space suit on) you would have to radio for help, and be rescued before you vanished into space.
As most campers know water is heavy stuff and comets are quite small bodies, so after a comparative small time scale astronomically speaking, a comet will be reduced to a small collection of rubble.  Each day Halley?s comet lost gas and water at around 25 tons a second with 3 tons of dust ejected a second ? boiled away by the sun?s heat from jets which covered 10% of its surface.  After a few hundreds of passes by the sun it will be shrunk to a shadow of its former self, what little volatilise are left will be deep beneath the surface covered by a thick layer of dirt and debris protected from the suns warmth.

So how long will a short period comet last?  This will of cause depend on its initial size, density, composition and most importantly how close it approaches the sun.  Even if all the short period comets were as large as Halley?s to start with, about 16x8x7.5km, it would not take many passages close to the sun to boil away its water ices.  So after a few thousand years it would be dead.  Because of planetary gravity fields, comets will not stay forever in their orbits but will be perturbed and will eventually ether; 1/ hit something, ie., us, the Moon or another planet or the sun, or 2/ it will be expelled from the solar system by a close pass of a planet.  Then it?s lost.
In recent years we have found many small bodies crossing the path of Earths orbit and many of these may be long defunct comet cores.  Every close encounter to any other body will slightly change their orbit.  Some times fatally.

So if short period comets only have lives of a few thousands of years they must be replaced from some where or we would not have any now.  This problem of replacement has been solved recently with the discovery of the Kuiper belt objects orbiting beyond Pluto.  These bodies of which 37 are known (as of Sept 96) orbit outside Neptune?s orbit and extend out into space for up to possible 200 AU.  All of the first 27 objects to be found are at least 100km in diameter but the latest are in the 6km to 12km range.  It is estimated that there could be 10 billion objects orbiting the sun in the Kuiper Belt with an estimated total mass of two or three Earth?s.
To find such small bodies as these is no mean task as they have a magnitude greater than mag 21 (very faint indeed).  To find them a search is made of the sky opposite the sun, so they are as bright and as near as possible.  Also areas of the sky such as the Milky Way are avoided because they contain far too many star images.

With the camera tracking on the stars for an hour or two, any Kuiper Belt objects in the field of view will then show small trails on the CCD fields.  Another exposure of the same area of sky is taken a few hours later.  If it contains a object, by comparing the magnitude and the length of the trail in the two exposures an estimate of the orbit and distance can be made.  Most of these bodies reflect very little light, a lump of coal reflects more, and with their great distance from the sun are difficult to find.  At this distance the sun?s power is down to the brightness of a full moon on Earth.
So what is the connection between Kuiper Belt objects and short period comets?  Well they are the same things.  It is believed that the disturbing influences of either Neptune or Pluto on their orbits causes one or two of them to fall in towards the sun every now and then.

What forces them into the inner solar system is the planet Jupiter.  Its gravity is second only to the sun?s and we all know what happens to comets who chance their luck with Jupiter?s gravity!!!
Jupiter stops the bodies from freely roaming the system by its huge gravitational pull.  It shepherds small bodies into controlled orbits or expels or devours them.  If a comet falls into a Jupiter crossing elliptical path it is in an unstable orbit and sooner or later will meet Jupiter and have its orbit changed.  What happens next depends on how it approached the giant planet.  If it gets placed into an inner planet crossing orbit it will not be long before it is destroyed by the sun or an impact as we have seen.

So where do long period comets come from?  The orbits of these are very different to the short period comets.  Most of them are big and bright and travel fast.  For a start they arrive from all sections of the sky, from every direction.  Not at all like the other short period comets, all going around the sun the same way.  These go all ways.  Some even travelling the ?Wrong Way* round the sun.  But the main difference is that these comets are coming in from the depths of space with orbits of thousands or millions of years.  They are from the Oort Cloud.
Comets arriving from the Oort Cloud have quite possible never been in to the sun before.  This cloud is the idea of a Dutch astronomer called Jan Oort, who reasoned that up to a light year out there could be pieces of the original star cloud which formed the solar system left slowly drifting around the sun as a cloud of particles in the depths of space.

This cloud does not circle the sun in the ecliptic plane but extends like a ball surrounding the sun in all directions.  Each one will be only a degree or two above absolute zero, orbiting a particular bright point of light, spending millions of years slowly orbiting within the feeble grasp of our sun.
Any slight disturbance of gravity, such as a close pass by another body or a nearby star getting closer will nudge it out of its orbit and send it in another direction.  Indeed many more must be lost into interstellar space as what eventually fall in towards the sun.  From that distance it must take many thousands of years before it reaches the sun?s warmth and starts to boil off its frozen ices.
The three big comets of this year have all travelled in from well out side our solar system.  Hyakutake passed only 10,000,000 miles over the north pole of Earth on its way in.  Just think if Hale-Bopp had arrived three months sooner or nine months later it would have missed Earth by less than 5 million miles and as it?s probable 10 to 20 times larger would have looked 1,000 times brighter on passing us!  As it is we shall be seeing Hale-Bopp from the side as it arcs over the sun to .91 AU at closest approach.  It will still be a great sight but think what it could have been.  And don?t forget this is twice as large as the body that wiped out the dinosaurs!

SOLAR SYSTEM EXPLORERS
THE NEXT GENERATION
TAKEN FROM ?CAPCOM*
THE NEWS LETTER OF THE MIDLANDS SPACEFLIGHT SOCITY
By Pam Draper

GALILEO ­ NASA Jupiter orbiter
Released atmospheric probe into Jupiter ­ data now relayed back to Earth.  Close flybys of the 4 largest Jovian moons: Io (Dec 95 and possibly at end of nominal mission).  Ganymede (July 96, Sept 96, Apr 97, May 98).  Callisto (Nov 96, June 97, Sept 97).  Europa (Dec 96, Feb 97, Nov 97).  2 years operation at Jupiter.

NEAR ­ NASA asteroid orbiter
NEAR (Near Earth Asteroid Rendezvous) was launched in Feb 96 on a Delta-2 rocket.  Flyby of asteroid Mathilde June 97.  Earth gravity assist Jan 98.  Enters orbit around asteroid Eros Jan/Feb 99.  One year of studies of asteroid with possible deliberate impact at end of mission.

MARS 96 ­ Russian Mars orbiter
Launch Nov 96 on a Proton rocket.  Will release 2 small surface stations to soft land and 2 penetrators to bury themselves under the surface upon arrival in Mars orbit Sept 97.  Studies of Martian surface, atmosphere, magnetosphere, 1 - 2 years use.

MARS GLOBAL SURVEYOR ­ NASA Mars orbiter
Launch Nov 96 on a Delta 2 rocket.  Carries 6 of the 8 instruments from the failed Mars Observer.  Enters orbit Sept 97, but 6 months of aerobraking follow (using the atmosphere to slow the space craft).  Will act as a data relay for Russian and US surface landers.  2 years use plus 3 more years as data relay.

MARS PATHFINDER ­ NASA Mars lander
Launch Dec 96 on a Delta 2 rocket. Direct landing on Mars July 97 without entering orbit.  Includes ?Sojourner Truth*, a Mars micro-rover to travel a short distance from the lander.  Surface studies in Aeria Vallis area (19.5° N, 32.8° W ).  Technology test-bed (eg. airbag landing system).

LUNAR­A ­ Japanese Lunar orbiter
Launch Aug 97 on M-5 rocket.  Will release 2 penetrators into the surface of the near side and 1 into the far side and then act as a data relay for them.  Studies of moon quakes and heat flow from the moon.

CASSINI­HUYGENS ­ NASA/ESA Saturn orbiter
Saturn orbiter / Titan probe.  Launch Oct 97 on a Titan 4­Centaur rocket.  Gravity assists from Venus (April 98, June 99), Earth (Aug 99) and Jupiter (Dec 2000).  Enters orbit around Saturn June 2004.  Releases Huygens probe into atmosphere of Titan Nov 2004.  Probe may survive to transmit from the surface for a short while.  Asteroid flyby to save propellants.  At least 4 years of operation at Saturn.

LUNAR PROSPECTOR ­ NASA Lunar orbiter
Launch Oct 97 on LMLV-2 rocket.  1 ­ 3 years use of surveying the moon?s resources; minerals possible ices and any outgassing.

DEEP SPACE 1 ­ NASA Asteroid/Comet flyby
Launch July 98 on LMLV­2 rocket.  Will flyby comet West­Kohoutec­Ikemura and asteroid McAuliffe in the course of a year.  First planetary mission to use Ion propulsion (solar powered).  Technology test-bed in the ?New Millennium* series.

PLANET-B ­ Japanese Mars orbiter
Launch Aug 98 on M-5 rocket.  Will study magneto-sphere and ionosphere of Mars after arrival in 1999.

MARS SURVEYOR 98 ORBITER ­ NASA Mars orbiter
Launch Dec 98 on Med-Lite rocket.  Arrival at Mars in 1999.  Includes 1 more instrument from the failed Mars Observer (using Russian components).

MARS SURVEYOR 98 LANDER ­ NASA Mars lander
Launch Jan 99 on Med-Lite rocket.  Arrival at Mars in 1999 and lands near polar region.  Uses robot arm to collect surface samples for analysis onboard.  Includes Russian instrument.  Releases 2 small penetrators (New Millennium technology tests) before entry into atmosphere.

STARDUST ­ NASA comet coma sample return
Launch Feb 99 on Med-Lite rocket.  After an Earth gravity assist it passes through the coma of comet Wild-2 in Jan 2004 and returns to Earth with cometary dust samples.  A re-entry capsule is dropped onto Utah desert in 2006.

MUSES-C ­ Japan Asteroid sample return
Launch Jan 2002 on M-5 rocket.  Lands on asteroid Nereus in 2003 and returns a sample to Earth in 2006.  Technology test vehicle.

ROSETTA ­ ESA Comet nucleus orbiter
Launch Jan 2003 on Ariane 5 rocket.  Gravity assists from Mars and Earth twice plus 2 asteroid flybys.  Arrives at comet Wirtanen in Aug 2011 and remains with it for at least two years as it approaches perihelion (closest approach to the sun).  Drops 2 landers onto the nucleus ~ Roland (German) and Champollion (French/NASA)

As you can see from the above, space is going to be a pretty busy place in the next few years and a really exciting time lies ahead for space science.  The shuttle will be busy constructing and servicing the Alpha space station.  The Hubble space telescope gets another service to update it and hopefully a new generation of rockets such as the DC-X now starting flight tests will bring us even more exciting achievements for the new millennium.

Ivor Clarke.

Recently it was the 30th anniversary of Star Trek, can I have been watching it for so long?  I remember when it first started being shown on a Saturday teatime and watching it in good ?ol black and white.  It was years before I knew what the colours of the jumpers were!  Then it was easy to spot who wasn?t coming back from beaming down to a planets surface, the guys in the red jumpers always copped it.  I must admit it, I loved it and while I?m not a Treckie and don?t dress up in Star Fleet uniforms and go to conventions and can?t speak Klingon; I have managed to watch just about every episode on the BBC.

Most amateurs astronomers I know have seen the Next Generation series and most have watched the first series with Captain Kirk and Spock.  These early shows always had very polystyrene looking rocks littering up the dust surface of the planets, none of which ever had blue skies.  And where did the oxygen to breath come from on a barren planet?   And why did distance change in every episode from parsec?s to light years to miles to kilometers and back?  And how, if they went where no one had gone before, there was always someone there who spoke English?

One of my favourite episodes in the Next Generation series was number 35 called ?A Measure Of a Man*.  In this story, a robotic scientist wanted to take Data (the android) to pieces to see how he worked.  Data objected to this as there was a good chance he would not recover from this invasion of his systems.  I should point out that Data was discovered on a distant planet and was built by advanced alien technology and was far in advanced of the existent technology of the day.  It was decided to try and prove that it was inadmissible to take a senescent being apart to build a race of slaves.  How can any thinking being be asked to kill himself just to satisfy the whim of another?  If a being can think and know of its own existence and can react to the present based on past memories, it is alive just as we are alive.  Needless to say Data wasn?t dissected and spent the next few episodes trying to understand human humour and jokes.

Ivor Clarke

TAURUS  The arrangement of stars which pre-dates history and well established by Egyptian and Tigris/Euphrates cultures of 2500BC.

PRINCIPAL STARS
a  Aldebaron
b  El Nath
d  Alheka
Hyades open cluster

ALDEBARON, (a) Alpha Tauri, lies at 68 ly, (light years), so the light we observe today was emitted in 1928.  To the eye it shines as a star of 0.8 mag with a strong orange red colour, also it?s a suspected irregular variable star with a range of 0.2 mag.  Through a small telescope however observers will notice Aldebaron has a faint companion of 11.2 mag and so approaches the detectable limit of a 3* refractor.  This star lies approximately 121* arc sec from Aldebaron and increasing the rate of separation by 13* a century, so a wide double.

EL NATH, (or ALNATH) (b) Beta Tauri, a star of 1.6 mag and lies approx 300 ly away.  Interesting feature of this star is that it use to belong to Aurigae and was designated g Aurigae, but when the I.A.U. years ago rearranged the constellation boundaries, the result of which Nath now resides in Taurus as b   Tauri but still retains its original name!

ALHEKA (d) Delta Tauri, a star of 3.0 mag which lies approximately 900 ly away.  To the unaided eye this star appears considerably fainter than the previous star Nath, but in reality its a star which is a 1,000 times more luminous than our sun and further to this, is a very active star as on occasions it throws off shells of material.  When these events happen the star brightens up slightly which can be detected with suitable equipment.

NAKED EYE DOUBLES
For the naked eye observer its an interesting excise to try and separate d Delta and 64 Tauri.  d Delta has a mag of 3.0.   64 Tauri has a mag of 4.8.  Another ­ try q1 Theta and q2.   q1 has a mag of 4 and q2 as a mag of 3.6 with a separation of 337 arc sec.

VARIABLES
l Lambda Tauri is an eclipsing binary star discovered by Joseph Baxenhall in 1848.  It is a 3.4 mag (usual) to 3.9 (or 4.1 if you read a different book  Ed.) at minimum every 3.95 days.  Eclipse lasts approximately 14 hours.  The following dates and times represent the forthcoming eclipses for Dec. 96

DATE START TIME  MID ECLIPSE
 Dec 12  20. 1 Dec13     03.1
 Dec 16  18.9 Dec17      01.9
 Dec 20  17.8 Dec 21     00.8
 Dec 24  16.7 Dec 24     23.7
 Dec 28  15.6 Dec 28     22.6

Use g Tauri as a comparison star, mag 3.6 to estimate the light change of l.

STAR CLUSTERS

HYADES  The V shaped asterism group of stars close to Aldebaron which covers approximately 5° of the sky and is the nearest star cluster to us, lies at around 150 ly away.  It is important to professional astronomers for it marks the first step in measuring the more remote objects in our galaxy.
It?s of interest to note that we ourselves, along with Aldebaron are situated close to the fringe of the cluster and although we are not members of this group we happen to be closer to the center of the Hyades than some of its outer lying members!  Even in completely different regions of the sky, Hyades members have been found moving towards the Hyades convergent point, this being towards the area of sky occupied by Betelgeuse in Orion with a velocity of 27.5 miles per second.
Only in 1942 when Baade began the first serious study of the Hyades, we have found approximately 350 stars, all of them being of an  age of 400 million years and slightly variable in magnitude.

PLEIADES  (M45)  The most spectacular star cluster in the heavens and best observed at low power, with binoculars.  In marked contrast to the Hyades, the Pleiades are a very young group of stars around 10 to 20 million years old.  This group which consists of over 250 members, lying 400 ly away, occupies an area of space 50 ly across.
An activity for amateur astronomers is to try and see as many naked eye stars as you can.  The Rev. William Rutter Dawes, the eagle eyed double star observer of the last century, could see 13 members with out optical aid!  Barham suggests there are at least 20 stars in the vicinity, through the brighter stars obscure the fainter.  Another activity for the telescope observer is to try and see the faint clouds of nebulosity associated with this group.  Very conspectus photographically, but obscure to the visual observer.  In fact this nebulosity, one of the few reflective nebula bright enough to be seen telescopically has developed its own folklore as to which type of instrument shows it off best.

The nebulosity was discovered in 1859 by the German astronomer Wilhelm Tempel with a 4* refractor at the Milan Observatory whilst searching for comets and describes the appearance as like the faint stain of breath on a mirror, 35? by 20? extending southwards from Merope.  For some years a controversy raged about its existence and that of other nebulosity in the Pleiades until photographs finally confirmed Tempel?s discovery.

Alcyone the brightest Pleiad, along with its other bright companions, are very hot stars rotating at unusually high speed of 94 miles a second at their equators.  Otto Struve discovered that Pleione has so rapid a rotation of once every 6 hours, that gaseous shells of material are thrown off.  An event which spectroscopically observed occurred between 1938 to 1952, when it faded beyond visibility.  Another episode occurred in 1972 when it brightened temporarily.  It may be of interest to know that Pleione is on the BAA variable star list and so requires close monitoring as it?s been known to vary from mag 4.8 to 5.5, so this variability is well suited to amateur astronomers.

NEBULA AND VARIABLE STARS

CRAB NEBULA  (M1, NGC 1952)  No surviving records, if any, made of this super nova event in the western world.  However we have records from the Chinese, Japanese and Korean sources which state that a bright star suddenly appeared close to d Delta Tauri on the 4th July 1054AD.  Eventually to shine at mag -5 at maximum luminosity, it was seen for 23 days in daylight and followed for 22 months in all.  Without optical aid the Crab became lost until 1731, where be chance, an amateur astronomer, John Bevis discovered a faint patch of luminosity, later rediscovered in 1758 by Messier who classified it as the first object in his catalogue.
Modern instrumentation has revealed that M1 is the same object that Oriental astronomers observed and is the remains of a super nova explosion which happened over 4,400 years ago and is still expanding at 1,300 km per sec (600 mps).
NGC 1647  mag 6.4, size 45?, a group of around 40 stars.

HINDS VARIABLE NEBULA  NGC 1554/5, in 1852 John Russell Hind first noticed nebulosity close to a 10th mag star.  In 1861, Heinrich Ludwig D?Arrest in Germany found that the nebula had almost disappeared, very large telescopes showed traces of it, but by 1868 it had completely gone.  So Hinds nebula was officially classed as missing.  Later in 1868 Otto Struve found nebulosity around a 14th mag star close to T Tauri and D?Arrest, who had previously looked carefully at the area was certain that the nebulosity was new.  It was recorded at various times until 1877, but then it too disappeared.  Then in 1890 Barnard and Burnhum using the 38* refractor at Lick Observatory, rediscovered Hind?s old nebula, but just a ghost of its former self and a difficult object even with this powerful telescope.  Late in 1895 it vanished again!  To reappear once again later.  Nowadays it is easily visible with large ?scopes, but it?s form is not the same as when Hind first reported it.

Moreover T Tauri itself is embedded in nebulosity and this nebulosity too is variable.  As an extra puzzle, it was found that Hind?s nebula yields emission lines, though T Tauri is a dwarf star not nearly hot enough to excite nebula gas to luminosity.  The nebula is much more variable than the star and it was suggested that changes in luminosity could be largely responsible.  In Hind?s day the gas was lit by T Tauri, but later some other material moved in around 1860 and cast, what could be regarded as a shadow.

COMETS
TAURIDS meteor shower from late October to mid November.  Not a very rich shower with only a ZHR (Zenith Hourly Rate) of around 10 but does produce many fireballs ? their speed of 17.5 mps being rather slow.

ENCKE'S COMET is responsible for this show which was first discovered by Mechain in 1788, and 9 years later independently discovered by Caroline Herschel in November 1795, who at the time didn?t realize it was the same comet as Mechain?s.  Only in 1819, when the comet computation by Encke proved that Mechain?s and Caroline?s comets were the same one.