. . . using URSA MAJOR
By Bert Lineham
A dozen double stars are listed in Nortons Star Atlas, with mags. of primaries from 2.0 — 6.0; Comes from 5.0 - 11.6; separations from 0.5" - 43" of arc.
These stars are now grouped into three lists;
Decreasing Order Decreasing Order Increasing Order
of Primary Brightness of Separations of Magnitude Diff.
Zeta Mags. 2-4 Σ1195 43" Phi ½
Iota " 3-1O½ 23 23" Xi ½
23 " 4-9 Σ1415 17" Σ1415 1
Nu " 4-10 Zeta 14.5" OΣ235 1½
Xi " 4½-5 Iota 7.5" Zeta 2
Phi " 5-5½ Nu 7" Σ1193 3
57 " 5-8 57 5.5" 57 3
Sigma2 " 5-9 Xi 3" Sigma2 4
Σ1415 " 6-7 Hu1136 2" 23 5
OΣ235 " 6-7 Sigma2 1.5" Hu1136 5½
Σ1193 " 6-9 OΣ235 1" Nu 6
Hu1156 " 6-11½ Phi 0.5" Iota 7
Double stars that tend to the top of the lists are easiest to observe and vice versa. The third mag. Iota, with a separation of 7½" has the largest difference in magnitudes. Norton gives it as a test for a 4" telescope. Σ1415 between the Pointers of the Plough, has a similar double, Σ1603, between Delta and Gamma on the other side of the Bowl. OΣ235 is a binary with varying separation during its 72 year period.
(Eds. note: Bert Lineham co-founded the Northampton AS, which functions within the Northants Natural History Society back in the fifties. A friend and mentor to more than one young astronomer, he now lives in quiet retirement with his 4" refractor.)
The Amateur Astronomy Centre
By Peter Drew
As a long term commitment to the furtherance of Amateur Astronomy, Bedford Astronomical Supplies intend to found and build a major astronomical Centre expressly for the use of U.K. amateurs. In addition to instrumentation capable of serious photographic and visual observation of all classes of study, we plan educational facilities for the encouragement and enlightenment of the uninitiated, demonstrations of various scientific phenomena and basic catering services.
We have purchased, with planning permission, some 12 acres of land, bordering both sides of the A681 Bacup to Todmorden road in West Yorkshire. (O.S. grid ref. 899257)
The site is 1150 feet above sea level and has relatively unrestricted horizons, the best being E,S & W down to -27 degrees South. The area lies in a large basin surrounded by distant hilltops 150 feet higher, affording considerable weather protection and obscurant from any troublesome sky glow caused by the nearest towns. Optical field testing has so far yielded steady seeing conditions with excellent sky transparency.
The nucleus of the Centre will be a 20'x50' observatory building incorporating a 25' hemispherical dome housing a 40" aperture reflector.
The 40" telescope will be a Cassegrain/Newtonian design operating at F4 primary ratio and F16 Cassegrain effective ratio. The mount will be an electrically driven equatorial fork. The overall telescope construction will be similar to the designs favoured by the world's major professional observatories.
In addition to the main telescope there will also be 30" and 17" Newtonian's, a Schmidt camera, a 5" apochromatic Solar refractor, 120mm binoculars, Camera Obscura, Planetarium, Library and as many small portable telescopes as can be conveniently deployed. (Ed. note: All this equipment apart from the 40" mirror and Planetarium is already assembled.)
The purchase of the land and provision of a large proportion of the instrumentation is being financed by Bedford Astronomical Supplies. Additional funds for the remainder and future running costs will hopefully be raised by subscription membership to the Centre from the amateur astronomers of the U.K. We envisage a membership fee of £2.50 per annum (schoolchildren free). The fee will permit a member free access to and use of the equipment at the Centre. The general public will be admitted at convenient times and at special functions organised to be of interest to them.
It is intended to arrange conducted tours and observing sessions for individual Societies on a regular basis. In addition there will be at least four special weekend meetings for members per year, based on the highly successful American "Star Party" format.
We are particularly mindful that, as the Centre will take around two years to build, early subscribers should receive some recognition for their support other than the satisfaction of having made the project possible. We propose that any pre-inauguration Member will be considered a Founder Member, and as such will enjoy privileges such as inclusion in a special register on display as testimony to their support and priority consideration for special events and services. In addition. Founder Members may, at their discretion, receive free subscription after inauguration for a period equal to their pre-inauguration membership.
Progress bulletins will be published at regular intervals.
We consider this to be a great opportunity for all of us to take a national initiative to establish an unrivalled practical Astronomy Centre for amateurs. The degree of success and timescale of the project is very largely dependent upon collective financial support as soon as possible.
For membership, please send a S.A.E. with £2.50, payable to "The Amateur Astronomy Centre" to Peter Drew (Project Manager).
DEEP SKY NOTES
By Rob Moseley
NGC 7662 Andromeda
If you asked people to name their favourite planetary nebula, I think that a lot would go for M57, the celebrated "Ring" nebula in Lyra. No doubt the "Owl", the "Saturn" and the "Dumb-bell" would each have their devotees. Fair enough. All are fascinating characters - yet, needless to say, there are many more to hunt out.
NGC 7662 (or Herschel IV 18, as it is given,in Norton's) is one of my favourites. I renewed our acquaintance recently - on the 23rd and 27th Oct 1982, two of the very few clear nights this Autumn.
It is a surprisingly bright object - far easier to pick up with a small aperture than M57. Magnitude values that I've seen in print vary, but I'd put it at around 7.5, certainly no lower than 8. Three stars of roughly equal brightness appear in a ½ degree field and reveal its nature instantly at x60. With a very low power the nebula could easily be passed over as a star. It is on the smallish side - at 32x28" well under half the size of the "Ring". In my 6" reflector its slight elliptically is barely perceptible and it has perhaps a very faint, blue/green tinge. I have once seen its dark centre, for it too is a "ring" - but this was using a 12" reflector, out in the sticks on an exceptional night.
Unlike a lot of planetary nebulae this fellow is no problem to find as Lambda, Kappa and Iota Andromedae are convenient 4mag guide stars.
It may not have a fancy name, but NGC 7662 is well worth looking up.
AGM, - held at the Angel Hotel, Northampton. Nov 6th 1982
Since its founding in 1964 "The Astronomer" has become.much more than a fast news service. Today it functions as an organising body for many of the most dedicated amateur observers worldwide, especially in the areas of comet, variable star and nova search work.
The annual AGM at Northampton is always an eagerly anticipated event. This year was no exception. Around 70 subscribers crammed in to enjoy an equally packed programme lasting from 10am to nearly 7pm.
Prominently displayed was the usual selection of superb photographs and drawings submitted during the past year. Of special note were spectacular aurorae shots by the Finnish amateur Pekka Parviainen, supernova search work by Alan Young and observations of Comet Austin by the two French aces Merlin and Verdenet.
After the annual report and accounts by the editor, Guy Hurst (who we were fortunate to have speaking at the November meeting of the C&WAS), nine addresses were given. Original techniques were outlined by Mike Maunder (post exposure hypo methods using mercury vapour) and Terry Platt (telescopic video systems utilising ex-Govt. light intensifiers). Other subjects included large aperture photographic programmes, asteroids, multiple and variable stars - and astronomy in the Antarctic!
Mr R Johnson (Exhibition) and Alan Young (Cover Contributions) received the annual TA Awards.
Compiled by Geoff Johnson
New Light on T Tauri
T Tauri, the prototype of a class of young stars has recently been re-examined with the Mauna Kea 2.2 metre telescope. Using a relatively new technique of infrared speckle interferometry a companion has been found which accounts for the excess infrared brightness. The separation of the components was found to be 0.61 arc seconds - which corresponds, to 150 astronomical units at a distance of 520 light years.
Do Neutrinos Have Mass?
The neutrino interacts so weakly with ordinary matter that it can pass through light years of lead. Until recently this particle was considered to have zero mass, just like a photon of light. Indication that neutrinos do have finite mass have come from a number of sources. If they do it could clear up a few vexing astronomical problems. The particles might have enough mass to "close" the universe and prevent infinite expansion.
They might also account for the unseen "missing" mass in clusters of galaxies indicated by dynamical studies. It might also solve the problem of the lower than predicted emission rate of solar neutrinos.
Recently an international team of physicists set up a sensitive detector in Switzerland which records neutrinos from an atomic reactor. Their results, however, suggest that neutrinos do not have a rest mass which differs substantially from similar experiments carried out in America.
Jewitt and Danielson, of Palomar, report that they have recovered this comet as follows: 1982 October 16.4 RA 7h 11m Dec. + 9°33' (NW of Procyon).
The comet was magnitude 24.2 and of stellar appearance. Perihelion should occur on 1986 Feb. 9.3.
New Minor Planets
Recently Edward Bowell of Lowell Observatory, Flagstaff, discovered two new minor planets. Official acceptance of the names was notified in the Minor Planet Circular for 1982 Aug. 4.
(2602) MOORE — 1982 BR Discovered 1982 Jan. 24 is named after Patrick Moore, the well-known astronomer, writer and broadcaster.
(2603) TAYLOR — 1982 BWI Discovered 1982 Jan. 30 is named after Gordon Taylor, astronomer at the Nautical Almanac Office, RGO. Mr.Taylor has been director of the Computing Section of the BAA since 1974. His research has centred on predictions of occultations of stars by solar system objects. His work has lead to determination of asteroid sizes and the Uranian rings.
Observing the Sun with the Naked Eye
This month there is a partial eclipse of the Sun (Dec 15), and despite the very low altitude of the Sun at the time of eclipse it would be quite possible to damage the eyes without adequate protection.
In an article in the Oct. BAA J, JCD Marsh drew attention to this danger and analysed some common methods in use to attenuate the Sun's brightness.
Sunglasses - definitely unsafe. Exposed B&W film - this could be safe if a piece of fully exposed, developed film is used. Old negatives are un-satisfactory, Photographic filters - a combination of filters may be safe but would need to be chosen by someone with a good knowledge of solar radiation. Smoked glass - generally unsafe as the density of the sooty film deposited can be variable. Welders goggles - even with a high shade number they cannot guarantee protection in the infrared, being designed to cut out the ultraviolet wavelengths.
The only really safe method is projection, using either a telescope or failing that a pinhole.
By Rob Moseley
The Moon may well repay close attention by even the most casual observer at the moment. Some very odd things have been happening recently.
Aristarchus (the most event prone formation on the Moon) has been misbehaving badly - showing marked albedo variation, vivid colour displays of green, blue and red, and even a series of brilliant flashes in an area just to the SE. In the early hours of Nov. 28 1982 I was lucky enough to witness an abnormal brightening of the illuminated interior - which was widely reported. In January the BAA TLP team noted extremely low albedo in earthshine. Anyone taking whole Moon photographs exposed for earthshine on a regular basis can provide valuable data here.
Jan. 29 was "The Night the Moon went Mad" according to BAA TLP co-ordinator Peter Foley. The obscure 4 mile crater Toricelli B situated in the southern reaches of the Mare Tranqillitatis, put on a truly astounding performance. It brightened to an unprecedented level for any lunar formation - far outshining Aristarchus with a brilliant blue fluorescence. It continued to be easily visible in earthshine when only two or three days from the evening terminator.
On the same night it seems that the celebrated Linne controversy was reopened when observers reported a very definite crater instead of the normal white patch!
So - dust off the telescope and take a look. You might be missing something!
M 78 (NGC 2068) in Orion is perhaps something of a backwater of -the Messier List - being overshadowed by other, more spectacular objects in the constellation.
It is a true nebula, gaseous and diffuse, belonging to the great Orion Cloud. However, unlike M42 it is not self luminous but shines by the light of stars within.
I've made two recent observations of this object. On the first occasion (Nov 18 1982) my logbook entry runs as follows:
"UT 01.10 Picked up M 78 while sweeping N of Orion's Belt. A fascinating object. Noted first as a rather wide fuzzy double with an estimated separation of 40" (50" according to Burnham). The two stars are around m9 and I suspected a third. The stars are involved in faintish nebulosity, elliptical in shape and elongated N-S, with a suspicion of curvature. Dimensions were estimated as 6'x4'."
In fact the nebula is rather larger than this, but with a 6" aperture in town conditions only the brightest condensation is seen.
In January, under better conditions, I expected to confirm the third star. But it was not there. Perhaps a variable?
Nearby are two other fainter gaseous nebulae, NGC 2071 and 2067 - but these are difficult objects. I didn't expect to find them.
As an added bonus the double star Σ782 proceeds M78 by about a degree. Two pure white components of 8m with a separation of 36" (Webb).
The newly formed Deep Sky Section of the BAA produce a newsletter called "Deep Sky Diary". In it a recent article by Don Miles describes for beginners the theory of position angle, vital knowledge for everyone, but double star observers in particular.
Position Angle is measured in degrees from North (0° or 360°) through East (90°) South (180°) and finally West (270°). That might sound simple enough, but discovering how this works out at the eyepiece can be involved. It would be possible to write reams about field orientation depending on the optical train in use. Most astronomical books rush to the assumption, often without specifically saying so, that you are using a Newtonian reflector - and that you are not using a diagonal.
Many amateurs use binoculars, refractors and, increasingly these days, catadioptric (mirror-lens combination) types, all of which can present a different field orientation. You may also favour the use of a diagonal which again affects the field.
At the telescope the simplest direction to find is East-West. Whether or not your telescope is equatorially mounted, it is easy to detect in which direction the stars are drifting due to the Earth's rotation. Do turn off the drive if you are using one! The stars drift from East to West. It has been customary for many observers to modify these expressions and refer to "proceeding" and "following" - in the sense that "a second magnitude-star proceeds the galaxy", meaning that it is to the West of the galaxy and thus drifts through the field of view before the galaxy. If you are not already firmly committed to either nomenclature then East/West rather than proceeding/following is the more modern convention and should be adopted.
Having discovered which is East and West in your field of view, move the telescope at right angles to this direction and approximately towards the Pole Star. It is not necessary to do this precisely, since you know that North/South must be at exactly 90° to the East/West line you have already determined. By watching through the-telescope as you move it, you will discover which way is North.
The above procedure is quite adequate for making drawings of Deep Sky objects. If you wish to be more precise, then use an eyepiece with a cross-hair. By orientating one line along the East/West direction it is possible to estimate the position angle of a double star to about 5 simply by eye. You will probably not require greater accuracy than this unless, specifically making double star measures.
One word of warning. If your telescope is altazimuth mounted, the orientation of the field is slowly changing all the time, or will appear different if the telescope is moved to a different part of the sky. It is a simple matter, however, to watch the drift and repeat the procedure once in a while, or if you start observing a different object.
Field Orientation for the Naked Eye - your telescope will almost certainly NOT give a field this way up and this way round, but...
... the diagram serves to illustrate how the 360° circle corresponds with the "compass" points, and also the use of the terms "North following" etc. which, are often found, in the literature.
If your telescope is mounted equatorially, why not draw a similar diagram to that above but mark in the points as you find them to be in your particular circumstances - but beware of changing the light path at all! If you do - check again!
You think you've got it? Try observing a few doubles that your telescope can easily split. Estimate the PA by eye and check with "Burnham's Celestial Handbook" or a similar source. You wont be spot on, of course, except by fluke (and anyway, some of the published measures are rather old) - but if you're in the wrong quadrant... better check again. The important thing with this exercise is not to know the P.A. before you start or you are immediately biased. If you get 10 out of 10 in the right quadrant, then P.A. should give you no trouble. If you didn't... back to the drawing board!
BAA LUNAR SECTION MEETING
Hawkstone Hall, Lambeth Feb 12 1983
A well attended meeting, despite the snow, started with a rousing pep-talk to the troops from Patrick Moore. After nearly 50 years with the Section Patrick was still looking ahead. He pointed out that there remained a vast amount of work to be done by amateurs - and compared the stultifying effects of the Apollo programme to the publication of Beer and Madler's "Der Mond" in 1858.
Progress reports were given by the sub-section co-ordinators (TLP, Topographic and Occultation), and TLP chief Peter Foley had some real fun and games to report with recent spectacular events occurring in Aristarchus, Toricelli B and Linne. An image processor applied to the Moon was demonstrated by Jeremy Cook.
Light relief was to be gained by spotting how many times Patrick's monocle fell out.
ASTRONOMICAL NEWS ROUNDUP
Compiled By Geoff Johnstone
Neptune, the smallest of the gas giants, has a diameter nearly four times that of the Earth, and a mass 17 times greater. Orbiting the Sun at a distance of about 30 astronomical units, it is so small as seen by Earth based observers that its rotation period is uncertain — 15 - 20 hours being the range usually quoted. Now a study by Belton, Wallace and Howard of Kitt Peak National Observatory has produced a new estimate. Using the 2.24 metre reflector and the 1.3 metre reflector at Kitt Peak, 300 infrared measurements have been made. The result comes from a study of the period implied by the light curve. Neptune is now thought to rotate in 18 hrs 12 mins, with an uncertainty of plus or minus 24 mins.
The Observable Universe
The most distance galaxy lies at a distance of 10000 million light years, assuming Hubble's constant to be 50 kilometres per second per megaparsec. This figure has been obtained from red-shift measurements.
In 1964 Hannes Alfuen noted that except the Sun, all bodies in the Solar System which have not undergone tidal breaking spin roughly at the same rate — about 2 revelations in 24 hrs. Asteroids should therefore behave in a similar manner.
The most repent assessment of rotation periods for main belt asteroids has now been reported, following studies of timed photoelectric light curves.
The rotation rate of medium sized asteroids changes in direct proportion to size ie the larger the asteroid the faster it rotates. Smaller objects, 60 km diameter, turn on average 2.1 times per day, whereas one 230 Km. across might manage 3.7 revolutions. It was also found that the very dark carbonaceous asteroids rotate more slowly than the lighter silicacious types — which in turn rotate slower than the metal rich types. A theoretical basis for these statistical results has yet to be found.
Writing in the Journal of the BAA RJ Livesey comments on the observability of the Aurora Borealis.
The probability of seeing aurorae is increased the farther north one travels. Many auroral events are not spectacular and may consist of quiet glows, homogeneous arcs or rays related to auroral storms below the observers horizon. In the UK auroral activity is most probable at about 22.00 hours. However, activity may wax and wane several times in the course of a night. The best period is following sunspot maximum, but in cycles of low sunspot activity auroral counts can be very low in this country.
The critical value of a star's mass is 8.5% that of the Sun. Above this amount an object contracts along a "Hayashi Track" on the Hertzsprung-Russell diagram until it reaches the main sequence, at which point nuclear fusion begins. A star with half the Sun's mass would be a red dwarf and would have a long stable life, remaining essentially unchanged for a time longer than the current age of the Galaxy. An object with less than the critical mass would contract along the "Hayashi Track", but the temperatures of these "black dwarfs" can never be high enough to ignite the hydrogen. The radii remain constant as the black dwarf cools. Eventually they can only be detected using an infra~red telescope. No black dwarfs have been observed with certainty, although according to estimates, there could be as many as 2000 per square degree. If these objects are found it could solve the problem of the missing mass in the Solar neighbourhood - and if these stars do exist the Space Telescope should be able to find them.
Effects of Gravitational Resonances on the Rings of Uranus
In 1977 several observatories took part in the observation of the occultation of the star SAO 158687 by Uranus. The data acquired indicated the presence of five rings, four of which were circular and the other either elliptical or inclined to the equatorial plane. A further occultation in 1978 confirmed the presence of the five rings and added a further four. In 1980 yet another, occultation confirmed the presence of all nine rings.
If a planet has a system of particles in free-orbit in the form of a ring this ring will be disturbed by the presence of the satellites. This disturbing gravitational effect is known as gravitational resonance and causes collisions of ring particles - which has the effect of removing the particle from the resonance orbit. In time this leads to a particle free 'zone' and a whole system of rings.
GA Steigman of Hull University finds close agreement between the radii of the rings and the resonances of the inner satellites, and proposes the existence of an as yet undiscovered satellite, Uranus 6, with an orbital distance of 105,221 Km. and a period of just over one day.
The Largest Refractor - 1852
A recent article in "Sky & Telescope" describes the little known Craig telescope of 1852. It was built at Leamington Priors, south of Coventry, and consisted of a refractor of 24" aperture. The largest refractor in the world at that time was only 15" although Lord Posse's 72" reflector was in use in Ireland.
The mounting of the telescope consisted of a brick tower 64 feet high and 24 feet in diameter, from which the cigar shaped tube was slung. The tube was of riveted boiler plate, 76 feet in length and weighing 3 tons. The whole assembly could rotate round the tower with the eyepiece end fixed on a small wooden dolly which ran on a circular rail 52 feet from the tower's centre.
Unfortunately the telescope proved to be unsatisfactory. The elements of the lens were made of flint and plate glass rather than the more optically satisfactory flint and crown. It was reported in the press that one part of the lens was too flat by one five thousandth of an inch. Although Craig, the vicar of Leamington Priors, did report confirming the existence of Saturn's Crepe ring, it seems that the telescope was dismantled by 1858.
Richard McKim, Mars co-ordinator for the Terrestrial Planets Section of the BAA recently wrote in the BAA J of the need for systematic observations of Mars by amateurs with suitable instruments. The eventual aim of the Section is to produce, from published and archival Section material a yellow cloud catalogue from 1882 to date, and regression curves for the Polar Caps. It has been suggested that residua volcanic activity may act as a triggering mechanism for global dust storms.
Recent Research at Siding Springs
The main part of the first major optical survey of the Southern Skies, directed from the Royal Observatory Edinburgh, has been completed using the 1.2m Schmidt at Siding Springs. The whole project is run jointly with the European Southern Observatory in Chile. A total of more than 1000 photographs have been taken. About 600 of these are being used in a ESO/SRC atlas of the Southern Skies.
FORE-RUNNERS OF THE SPACE-SHUTTLE
By Paul Porter
The North American X-15
In one of the most spectacular research programmes ever carried out in the USA, 3 X-15 aircraft achieved such extremes of speed and altitude that the unofficial records they set have never been beaten by a manned aircraft. In fact, the heights attained enabled some of their pilots to be termed "astronauts".
The programme started in 1955 when the USAAF & Navy, together with NACA, gave the "North American" Company a contract to build 5 aircraft capable of flying at Mach 7 and an altitude of 264,000 feet. The idea was not simply to build fast aircraft, but to gain vital information on structure, heating control and stability, problems at hypersonic speeds during entry to and return from the upper atmosphere. For this the aircraft had to be built mainly from titanium and stainless steel, with an armoured skin covering to withstand both very high and low temperatures.
Although the X-15s were rocket powered and were designed to be air launched from a B-52 bomber, conventional landing was necessary.
The first X-15 became airborne in March 1959 but was not released - the flight being an aerodynamic test. This was followed by an unpowered flight. On 17th Sept 1959 the rocket engine was switched on, but speeds were still kept low for testing purposes.
In May 1960 an X-15 achieved a speed of Mach 1.19, raised to Mach 4.9 the following year. By Oct 1967 an X-15 made Mach 6.72 (4,552mph). The greatest altitude reached was 354,000 feet in 1963.
There were accidents on the way. The second craft was damaged in 1962 and rebuilt to improved specifications. The third was destroyed in Nov 1967.
In all, 199 flights had been made by the X-15s when the project was terminated in 1968.
BUILDING LARGE TELESCOPES
By John Wall FRAS (Optical Engineer, Old Royal Obs., Greenwich)
There are many who wish to up-grade their observing capability, but are not too sure that a large telescope can be built. Financial and technical competence are large factors to be considered.
These factors will, of course, influence the size of telescope to be undertaken. If a mirror is to be purchased, then purely financial restraints will apply. A moderate aperture of, say, up to 45cm (18") will result. However, if the constructor opts to grind the mirror himself, 45cm can be a kick-off size.
A good aperture range for a large amateur telescope is from 45cm (18") to 60cm (24") - and the engineering problems of mounting them will not be formidable. I may add here that the amateur can go much higher than this these days, pushing the aperture up to 81cm (30") - if he accepts the new concept of very thin mirrors current in the USA.
A word about mirrors. Buying a large mirror is extremely expensive. A good professional mirror is of course an asset if the telescope is to be used for conventional observations, such as fine planetary detail. If however, the modern approach to telescopes is adopted, whereby the aperture will be used to feed light to an image photo-multiplier coupled to a micro-processor, then all that is required is that the mirror be good enough to form a small image on the spatial filter (or, in lay parlance, the pinhole in front of the photo-multiplier tube). A thin mirror can be used for this work, and the problem of flexure can be alleviated by correctly designing the flotation system for it. Such a mirror will yield splendid views of deep sky objects to boot, and can be used visually for this kind of work without detecting any degradation of the image... if it exists. But trouble will occur if the mode is used incorrectly by trying to crack on very high powers to observe planetary detail. A green plate glass mirror, 25 - 50mm thick will not be up to it. If that is what is required then forget it.
The problem of grinding a large mirror by hand is not so terrible as one might think. The blank can be a piece of green plate glass ordered through, your local builders merchant, and cut to a disc beforehand. This is placed on a flat table with a pumped up cycle inner tube between. This acts as an air-bag support. Edge supports can be screwed to the table to stop the mirror sliding sideways,
Grinding and polishing can be done with a sub diameter tool, working onto the mirror which lays face up. The initial tool must be at least half the aperture to start with. Smaller tools for zonal polishing can be used later during the figuring stage.
Using a sub tool removes the colossal effort required to shove a 24" mirror about, when using the standard method. A thin mirror can be raised by one person, and propped into the test stand - which must be adjacent. For a thin mirror it is useless to try any greater correction than the standard 1/8 wave.
One can try, of course, to make the mirror as fine as possible, and some will achieve excellent figures. But remember, large apertures in indifferent sitings do not yield the images that a good 10" will on most average nights. Hence the bias towards using large apertures in conjunction with photometric, equipment. In fields such as variable star monitoring data can be collected which is of great value to professional astronomers.
(In the next issue of "MIRA" John Wall continues this article with a look at engineering problems involved in mounting large telescopes.
John was responsible for the superb 24" built for Crayford Manor House AS. He has recently completed a 30")
By Richard Barrett
(Part 1 of an observational survey)
Of the 130 or so planetary nebulae mentioned in "Burnham's", the vast majority are fairly insignificant objects, being either faint or having very small angular diameters. There are a few planetaries, however, which are bright, large and visible in quite modest amateur telescopes.
With my 4" F8 reflector (which is not of particularly good quality) I have seen only perhaps five or six — although I am sure that it would be possible to see at least 15. It is simply a matter of getting round to searching for them!
The ease with which planetaries can be seen, as with all nebulous objects, depends not only on magnitude, but also on angular size. A prime example of this is the' Helix' planetary nebula (NGC 7293) in Aquarius, which has an integrated (total) magnitude of about 6.5 - the brightest of all planetaries. But owing to its extremely large size of 12'x16', this is rather a low surface brightness object, best seen in binoculars or a rich field telescope under very low powers.
Not so the "Saturn" nebula (NGC 7009), also in Aquarius, which is a fairly snail object (50") of mag 8, located just over a degree W of Nu Aquarii. Although I have never seen it, I am reliably informed that it is a reasonably easy object for a 4" telescope or larger. Once located, fairly high powers should be used to show the nebulous nature of the object (with low powers planetaries of this size appear rather like stars). Incidentally, this planetary got its name because of two rays (ansae) projecting from opposite sides of the disc, giving it the appearance of having edge-on rings. Unfortunately these ansae are too faint to be seen in the average amateur telescope.
Several interesting examples are to be seen in Summer skies. Probably the most famous planetary is the "Ring" nebula in Lyra. The magnitude given for the "Ring" (M 57 or NGC 6720) of about 9, combined with its fairly large size of 80x60", would tend to suggest that it is a difficult object with small telescopes. Fortunately, this is not the case - indeed, I have seen it in a 60mm (2½") refractor with no difficulty whatsoever.
M 57 can be, found about halfway between Beta and Gamma Lyrae.
Through my telescope the "Ring" nebula appears, even at low powers, as a small "fuzzy" object at the apex of a triangle of stars about a degree in size. At x133 I can just suspect the "hole" in the centre of the ring, but at this magnification the nebula, is quite faint and is best seen using averted vision. When so viewed the nebula comes into its own, and with ideal conditions the dark centre may just be glimpsed. I find this nebula one of the most enjoyable objects for the small telescope, being both bright and large, showing clear nebulous qualities, perhaps this is the reason for its fame.
In Ursa Major (The Plough) there is another planetary, but this is a large, faint object. It may just be seen in a 4" telescope under exceptional conditions, but needs a large instrument to bring out the details. M 97 (NGC 3587) is called the "Owl" nebula because it has two darker circles in the disc, creating the impression of two owl-like eyes. The effect was first noticed by Lord Rosse in 1848.
The 11th magnitude nebula can be located some 2½° degrees SE of Beta Ursae Majoris (the more southerly of the Pointers) and its exact position can be identified by three quite bright stars which form a kite shape with the nebula.
(Neither Richard or I have been able to pick up M 97 from Coventry so far.) Ed.
Amongst the finest planetaries in the sky is M 27 - the "Dumb-hell" nebula in Vulpecula. This is a bright, large object, clearly visible even in binoculars, appearing as a circular nebulous patch about 3.3° degrees N of Gamma Sagittae (the tip of the Arrow). Its name is derived from the nebula's two lobes on either side of the central star, which creates a dumb-bell like appearance. To find the nebula, look about 4° degrees N of Gamma Sagittae and locate 14 Vulpeculae. This is in the middle of the base of a trapezium formed by the stars 12, 13, 16 & 17 Vulpeculae.
Probably the best way to find this object with a telescope is to first use binoculars to familiarise the field, hence making star-hopping that much easier. This is necessary because there are a number of stars in the area of the "Dumb-bell" of about equal magnitude to the Flamsteed numbers just mentioned, and could easily be confused in the telescope.
M 27 is one of the largest planetaries in the sky (8'x5') and its brightness makes it one of the easiest to see. In large apertures it is a magnificent object.
Along with these few well known planetaries are several others which are rarely mentioned in text-books, despite the fact that they are just as bright. One of these is NGC 6826 in Cygnus. It is often called the "Blinking" planetary, because it highlights a trick used by observers to distinguish the central star from the surrounding nebula when they are of equal brightness. The procedure involves staring directly at the central star for a moment, which will make the nebula seem to disappear - hence revealing the star clearly. Then averted vision is used (ie the nebula is not looked at directly) while attention is focussed on the area of the nebula which often masks the central star. Alternating between the two rapidly causes the nebula to blink - an effect which is particularly noticeable in NGC 6826.
This planetary can be located about 10 degrees NW of Deneb, ½° degree E of the mag. 5 double star 16 Cygni.
Early in the Summer also look for NGC 3242 in Hydra, a 40"x55" glowing disc of about mag. 9, 2° degrees S of Mu Hydrae.
There is also a good planetary in Hercules, NGC 6210, of mag. 9.7 and diameter 20"x16" NE of Beta Herculis (close to two mag. 7 stars.)
M 57 The Ring M 27 1968 July 27
4" Spec x32 1° Field 4" Spec x30 1° Field
Obs R Barrett Obs R Moseley
Lunar & Planetary Notes
By Rob Moseley
A recent drawing of Jupiter has been provided by Paul Porter.
The SEB is the dominant feature on the disc, and the NEB & STB are also recorded - as well as a suspicion of the elusive Equatorial Band.
Note also the close proximity of two moons. To the W; (ie left) is Io, about to be eclipsed by Jupiter's shadow. But more intriguing is the object to the E. At the time of the drawing both Europa & Ganymede were approaching the disc prior to transit. However, Paul could detect only one point of light. It would be nice to think that he had observed a mutual eclipse/occultation. Peek, in his classic "The Planet Jupiter" describes such phenomena as "...not at all rare... when the Sun & Earth are near the plane of Jupiter's equator." This occurs every 5.95 years, and according to my calculations, last took place in 1980. So it would seem that the two bodies were so close that Paul's instrument could not split them. Interesting though.
Jupiter 1983 April 7 04.30 UT
2.4" OG x100
Obs P Porter
On March 21, with a 6½ day Moon I was fortunate to get a spectacular view of Cassini, near the terminator. The low angle of illumination turns a normally rather vague and indistinct formation into a breathtaking sight. It is of particular interest to Coventrians! Notice the "Three Spires" it casts onto the dark floor of the Mare Imbrium.
Cassini at Sunrise 1983 March 21
6" Spec x175
Obs R Moseley
ASTRONOMICAL NEWS ROUND-UP
Compiled by Geoff Johnstone
Extragalactic Star Cluster
Recently, while studying plates taken with the UK Schmidt telescope at Siding Springs, Australia, a mistake was made in setting the viewing microscope. Instead of the expected galaxy, astronomers saw a tiny cluster of a few dozen stars.
Some extragalactic clusters were found in the 195Os by George Abell. If the brightest stars in the cluster are red giants, then 7 the distance would appear to be 700,000 lyrs - one third the distance to the Andromeda Galaxy.
From this newly discovered "dwarf galaxy" (AM-4) the Milky Way would appear 9 X 35 - a magnificent naked eye object. Yet the Sun would be at least mag. 27!
Observations of Halley's Comet
At a meeting of the IAU in Greece last August, a new organisation was announced called the International Halley Watch (IHW)
The intention of the organisation (based at the JPL, Pasadena) is to observe the comet as part of a co-ordinated programme when it approaches the Earth in 1986. All comet observers, professional and amateur, are invited to share their results with the IHW network.
Observations will come from ground based, balloon, airborne and Earth orbital instruments, and will form the largest collection of data ever produced on a single comet.
Japan, the USSR and the European Space Agency are each sending spacecraft to encounter the comet in 1986. Teams supported by the IHW will study the comet using a variety of techniques.
1) Wide angle photography of the comet's tails.
2) Studies of the nucleus by high resolution photography and electronic imaging.
3) Spectroscopy of the nucleus and tail.
4) Determination of the quantity of volatile and non-volatile components of the coma and tail.
5) Photometric measurements of light variations.
6) Determination of size, composition and temperature of dust particles by infra-red spectroscopy.
7) Positional studies to provide information on the comet's orbit.
Amateur visual and photographic observations will be compared with those of the 1910 apparition. Amateur studies of meteors will be particularly helpful - as the Eta Aquarid shower in May and the October Orionids are thought to have originated from Halley.
Crossing the bright galaxy NGC 5128 is a thick dust lane noted by observers such as John Herschel. JG Bolton discovered a strong radio source in this galaxy which is situated well south of the equator in the constellation of Centaurus. It became known as Centaurus A.
One theory as to the nature of the source involved the collision between a spiral and an elliptical galaxy. This now seems unlikely as radial velocity measurements indicate a smooth recession and rotation.
French astronomers reject a complex explanation but believe it to be a normal galaxy of So or Sa type, composed of a bright bulge and thick disc. The disc is still under formation, undergoing accretion of dust and gas and slowly settling down. The continuing formation of this disc could explain the powerful radio activity of NGC 5128.
Advances in Telescope Design
A reflector of 2.4m (95") aperture will shortly be constructed by Massachusetts Institute of Technology at Kitt Peak. Features such as a fast, thin primary mirror, weighing only 2000 Kg - together with computer controlled tracking - enables a simple inexpensive instrument to be built.
Yet even with a thin mirror there is a limit to the size of telescope that can be constructed on a conventional design due to increasing weight, thence cost.
It seems however; that we are on the verge of a new era in telescope building - according to an article in a recent edition of "Popular Astronomy".
Designers are turning towards instruments with thinner, lighter optics consisting of several elements, each of which can be adjusted by a computer to keep the combined image sharp. Another cost saving device is to use altazimuth mounts. These are more compact, cheaper to manufacture and easier to handle than equatorials. In the USA three large new generation telescopes are at the advanced design stage. The smallest aperture of 7.6m (300") will be located in Texas. The University of California has been studying a 1Om (394") for Mauna Kea in Hawaii. Its mirror will be made up of 56 segments each 2m in diameter.
The largest telescope under study at Kitt Peak will have an aperture of 15m (590") and will either have a mosaic of 90 hexagonal segments or 6 individual mirrors arranged in a circle.
Europe too is to have a multi—mirror telescope at La Palma in the Canary Islands. It will have an aperture of 15m and is expected to be built about ten years from now.
Solar Activity and the Earth's Climate
Recent studies suggest that there is a relationship between solar activity and the Earth's climate Cycles other than the commonly known ones of 11 or 22 years are indicated.
The first major piece of evidence came when two periods of no sunspot activity (the so-called "Maunder minima") of 1645 - 1715 and 1420 - 1570, were found to coincide with "Little Ice Ages" - when the average temperature of Europe dropped by a degree.
The study of solar-terrestrial climatic effects can be extended back in time by examination of tree rings. These are linked with atmospheric production of Carbon 14. The rate of Carbon Ih production was higher during the "Maunder minima". Eddy found that Carbon 14 studies agreed with records of sunspot activity very accurately. By studying the size and thickness of Alpine glaciers, records can be extended back 7,000 years.
JM Mitchell has found detailed agreement between sunspot maximum and the size of the Great American Desert.
Other cycles apart from that of 22 years have been suggested from statistical analysis of sunspot numbers. There is some evidence for an 85 year cycle, but this is bound to be uncertain after only 250 years of systematic records.
Study of geological records such as annual layering of siltstone Australia strongly confirms 11 and 22 year cycles - and possible cycles of 90, 145 and 290 years. This record dates back to pre-Cambrian times, about 680 million years ago.
Caution has to be exercised in interpreting the results, as the periods might not be solar in origin but could be caused by variations in the Earth's magnetic field - of which little is known.