Letters to the Editor
From Vaughan Cooper
I would be particularly interested to hear from any members who may have been observing the Sun on Saturday 22nd July at approximately 9.30 BST as I recorded a very small spot slightly NW from the center of the disc. As the seeing at the time wasn't very good I returned a few hours later at approximately 12 noon BST for a further examination of the spot, but by this time the feature had vanished. I'm aware that sunspots evolve and change their structure from day to day, but I've never recorded a sunspot, however small, to disappear in such a short time of only a couple of hours. This leads me to conclude I may have made an error of judgement of interpreting this feature, what-ever it was, to be a sunspot. If it was a spot I'm surprised that it disappeared so quickly. In conversation with Geoffrey Johnstone a few days later he mentioned observing the Sun during the same morning in question and observed a blank disc, hence my uncertainty of my earlier observation.
Solar activity has declined quite markedly since last year, however July had a few isolated groups visible, but declining further towards the end of the month and into August with the odd one or two very small spots. Solar activity is becoming progressively less as since the 9th of the month the Sun has remained blank for 16 consecutive days up to the time of writing, so indicating a steady decline to minima, scheduled I believe sometime in 1996/97 if taking the accepted value of 11.2 years as the average cycle which isn't always regular from cycle to cycle. The last minima occurred in June 1986 followed by maxima in June 1989, thus my reason for predicting the next minima may be in 1996/97. We will have to wait and see.
From Clive Rogers
In issue 35 of MIRA I wrote an article on Light Pollution (astronomers worst nightmare). In the article I suggested some ways of cutting down on wasted light. To that end I wrote to the Coventry Evening Telegraph, Councillors, MP's and MEP's to ask their help to eliminate lighting up the night sky with the orange glow.
Since that article the Coventry City Council have taken down the 2 bulk head lights (orange security lights attached to the block of flats) and replaced them with low level lights. These lights are white and shed light in all directions including up. I re-wrote to the council to draw their attention to the error of their ways but to no avail. So, out came the ladder and sticky tape, the tape was put on top of the lights to put the light where it belongs, down on the ground.
I have also written to Graham Crabtree (Street Lighting Officer) to ask why the new street lighting, the LTI (Low Threshold Increment) lanterns are so high? Why is light allowed to shine through the white plastic top of each lantern? Why is there a 5° uplift on the front of each lantern, is this allowing light upwards? After all, when the contractors built the flats they put light switches on the wall so I could put a light on when necessary so why light my home from the outside?
The answers came back as follows:
If the LTI lanterns were not so tall more street lamps would have to be used. The 5° uplift on the front of each lamp is to light the opposite side of the road better.
Mr. Crabtree was not aware that light shone through the white plastic top of the lantern and was going to look into the matter. As far as lighting up my rooms from the outside, nothing can be done about that (as yet!). If anyone has any success stories reference their fight against Light Pollution please let me know. All success stories (and failures) will be transmitted to Mr. Bob Mizon, the Coordinator of CfDS.
Keep up the good work Clive, reducing sky glow means keeping light where it belongs and not wasting energy (ie. our money) lighting up the sky. ED.
The 6 1/2" Cooke Refracter Finds a New Home
By Stephen and Pam Draper
At 9.30am, on Saturday 20th May 1995, Vaughan Cooper, Pamela and Stephen Draper, Iain Jenks, Ted Nicholls and Graham Smith all met in the CoventryTechnical College for an early start that day. Dr Mike Inglis and a Safety Officer (sorry, but we can't recall his name) from Warwick University arrived and we were all introduced.
We then proceeded in a very compact lift up to the roof of the college. It was a cold grey windy day, especially 80ft up. Our first sight of the observatory, some distance away from the door onto the roof, told us straight away what awesome problems faced us. Once inside the observatory we all had a chance to view the dismantled telescope and choose our first move.
Ted was already inside the dome, busy chiselling away at the concrete within the bell housing which forms the base of the Cooke, to make it more accessible for lifting and moving. We had brought two trolleys to aid us, all with wonky wheels. From the door onto the roof, a flight of stairs led down to the first landing, then another flight after this to where the lift was situated. And then down two more floors using the lift or stairs to the ground. Boxes of books and magazines were moved to the lift landing, many of these being of good age, but neatly kept. Pam carried what she could manage, a couple of lighter weights and the R.A. and DEC fine adjustment levers.
Meanwhile we realised we needed a plank to slide some of the too heavy to carry smaller parts of the telescope down the stairs. It just so happened that across the Technical College roof, builders had left some construction planks. Vaughan and Steve borrowed one and took it to the first stairway. T he safety officer keeping an eye on things and offered advice on many ways of proceeding.
At this point Pam went down and stood a lonely vigil over the growing number of telescope parts on the ground below. While upstairs, piece by piece, the telescope came down in the lift as several swear words echoed down from the stairways above.
Later, after much sweat and effort, the final piece came down, the enormously heavy and large cast iron bell housing base of the Cooke. This was tied to a trolley then lowered gingerly down stairs on ropes to the lift entrance and pushed inside. Once downstairs all the pieces were placed in the van, including the bell housing, which had the possibility of giving several people nasty accidents. An almighty effort was needed to pull it up the ramps and into the back of the van.
Once at Warwick University the strain showed as Steve and Pam, Iain and Graham went on a grand tour of the Science Park, the National Grid and several other car parks trying to find the Physics Department. Finally a student was accosted who climbed in our car, and in convoy showed us the way.
The university van then arrived and the telescope pieces removed with the help of a wheel and pulley system taking the strain, before finally finishing about 2pm. It was exceptionally hard work, but thankfully safely done with good humour. A day I don't think any of us will ever forget. . . .
Well done to all concerned with the dismantling and move. Let us all hope that this move to the Warwick University site will prove to be the best yet for both the Society and the number of members who will be able to use this facility in the future. Now that the telescope has finally left the Technical College, we can say that a new era for the C&WAS has began. ED
History of Astronomy
I've found a book which lists all sorts of information about astronomy, so I have injected a bit of fun into the results below . . .
9000 - 8000 BC A bone, found in what is now Zaire and marked with what looked like a crude record of months and lunar phases properly dated back to this time.
5000 - 4000 BC The Egyptian calendar based on 365 days starting with the day Sirius (the Dog star) rose in line with the sun was instituted as early as 4212 BC. This told them when to put their macs on, as it coincided with the annual flood.
2600 - 2500 BC A Chinese person stuck a straight stick in the ground and found that the shadow roughly reached the same place every day. Unfortunately it was not velly good at night.
1880 - 1750 BC Star catalogues, (no, they weren't for sale) and planetary records were started in Babylonia.
1500 - 1451 BC Thutmosis III erected Cleopatra's Needle as a huge sundial. It now stands on the north bank of the Thames in London, close to Big Ben (which is much better at giving the time).
800 - 750 BC The sun got turned off in Babylonia and they recorded their first solar eclipse. On May 28th.
585 BC during a battle between the Medes and the Lydians an eclipse frightened them so much they forgot to carry on fighting.
440 - 430 BC Meton of Athens decided to invent the Metonic cycle. Not to ride on but to explain the 19 year period in which the sun and the moon came together. This was used to predict eclipses and forms the basis of the Jewish and Greek calendars.
380 - 370 BC The Chinese see the first supernova but didn't know what it was.
270 - 260 BC Aristarchus of Samos challenged Aristotle by saying that the sun was in the middle of our solar system.
240 - 230 BC Eratosthenes of Cyrene put a tape around the Earth and announced that it was 28,500 miles (its really 24,822 miles). Halley's comet was seen over China for the first time.
130 - 120 BC Hipparchus waited for a total eclipse to measure the size of the Moon. I'm surprised that he could have written anything down, it would have been dark.
AD 140 - 150 Ptolemy wrote an important manuscript which helped scientists to believe that planets went round the Earth. Big mistake.
AD 630 - 650 The Chinese made a clear statement that the tail of a comet always points away from the sun.
AD 660 - 680 The first English sundial was built in Newcastle. Its a pity because they don't get much sun up there.
AD 1000 - 1010 A calendar of 365 days divided into twelve months of 27 or 28 days was introduced into India. Because this fell short of the correct year, they pushed in an extra month every now and then. A ten day week must have been getting them a bit tired so they shortened it to 7 days.
AD 1066 A large comet (Halley's comet although they did not know it at the time) was seen over England.
AD 1250 Alfonso X ordered the Alphonsine Astronomical Tables. They were used for almost 300 years but were not in print until 1483.
AD 1430 - 1439 Ulugh Beg, a Mongol astronomer, published a new table of star positions and a map. It was an improvement on Ptolemy's maps. Master Beg begged to differ and assassinated him a few years later.
AD 1440 - 1450 Nicholas of Cusa wrote a book containing the idea of a continues universe and reckoned that all heavenly bodies were alike . . . (shock, horror) and would you believe that he thought that the Earth revolved around the sun. He's obviously a total nutter. Most Astrologers of the day thought the same and thought he was off his trolly, but they were finding it difficult to live with the old way of thinking.
AD 1497 Nick Copernicus, the Polish astronomer described and recorded how a star could be hidden by the Moon (seems pretty obvious to me).
AD 1504 Chris Columbus sent the willys up a group of angry natives by predicting a total eclipse of the sun, got himself out of a tight spot too!
AD 1543 Copernicus's new book on the "Revolutions of Celestial Bodies" backed up by poor Nicholas of Cusa's theory that the planets DID in fact go round the sun.
AD 1572 Tycho Brahe, a Dane, saw a new star which he called "Nova", which means new. In 1574 he went on to compare parts of the human body with the universe; a little off track I think!
AD 1580 The King of Denmark was well impressed with Tycho, so he built him a spiffing new observatory on the island of Hlveen.
AD 1584 Giordado Bruno put himself on record as a follower of the Copernicus fashion. "The universe is infinite and the Earth goes round the sun" he said. (Not the sort of thing you said then during the Inquisition.) He was burned at the stake.
AD 1597 Galileo wrote a letter to Kepler (grudgingly) indicating that he'd come to agree with Copernicus scheme of the solar system. What would he think if he lived today?
AD 1598 Tycho moved in with the Holy Roman Emperor Rudolph II in Prague. Two years later he died and Kepler got his job but not the living quarters. Just to keep in with the master he produced two more nova by 1604.
AD 1609 Galileo finally showed off his new toy called a telescope, it changed astronomy for ever. With 30 times magnification he proved Copernicus right. Earth shine was observed.
AD 1610 Galileo's big time. His series of newsletters was published called "Starry Messengers" describing his sightings of Saturn, Jupiter, the Milky Way and Venus. A message he sent to Kepler was like this;
"SMAISHEMPTROFIAAVTEHOAOAIBSRELROVEDTHDESTPTNFLNETVTOE " In those days scientists used to send each other impossible anagrams of their discoveries so that the recipient couldn't ever claim the discovery for themselves. This one decoded reads:- "I have observed the most distant of planets to have a triple form." What he had seen was the large planet Saturn with two bits on either side which turned out to be the rings. Silly Billy.
AD 1616 Cardinal Bellarmine rapped Galileo's knuckles over the old Earth-round-the-sun business. Remember what happened to Bruno? Kepler's "Rudolphine Tables" told the world where to find 1005 stars and calculated the movements of the planets.
AD 1632 Galileo introduced relativity to physics by pointing out that experiments made in a closed cabin couldn't be used to tell whether the ship was moving or not. Silly man, why did he not open the porthole?
AD 1633 Galileo was summoned by the Inquisition crowd who accused him of mickey taking of Pope Urban VIII and not throwing Copernicus ideas into touch. He had been warned and shown the red card before! He told a few white lies, kept his fingers crossed but was kept under house arrest.
AD 1656 Christian Huygens from Holland discovered that the "Triple Form" Galileo raved about was really rings. He also found Titan.
AD 1659 Huygens becomes the first to spot surface features on Mars. He also realised it wasn't made of chocolate.
AD 1665 Top boffin Isaac Newton escapes Cambridge and the plague by running back to mum in Woolsthorpe.
AD 1660 Isaac Newton wrote "Principia" which was to the principal physics work for 200 years. When Newton found that one law explained most things on Earth as well as in space, people started to get it into their thick heads that 'celestial bodies', ie. stars, weren't of a divine nature. Edmond Halley's prediction of the return in 1682 and 1756 of the comet based on his math calculations put the lid on Newtons theory of gravity.
His three best ideas were;
1/ If an object is just sitting around or moving at a steady pace nothing will change unless something else comes along to change the situation.
2/ Force is something that causes a body to move. Don't you need force to get yourself out of bed and from the horizontal to the vertical?
3/ For each action there is an equal and opposite reaction, ie. if you kick a dog it bites your leg or, being serious, the power coming out of the back end of a rocket will make it go the other way. What goes one way pushes what ever it is in the opposite direction.
From the apple falling on his head he deduced that all the bodies in the universe areaffected by a force varying inversely with the distance between them. He called the force (yes, you've got it), gravity. Clever wasn't he?
AD 1704 Newton wrote his book called "Optics"
AD 1744 Jean Phillippe Loys de Cheseaux was puzzled over the darkness of the night sky. Loss of light in space was the general idea.
AD 1761 Loads of Joseph Delisle mates looked at Venus from around the globe. A lot of cloud stopped observations but from the ones he did get he determined the solar parallax and the distance from the sun to Earth.
AD 1782 The first explanation of the variation in the light from the star Algol was made by a 17 year old deaf mute called John Goodriche. He realised that it was an invisible companion to Algol doing the mischief.
AD 1820 John Herschel and Charles Babbage decided to have a little get together every now and then and the Royal Astronomical Society was born.
AD 1826 Heinrich Olbers came up with a real puzzle. If the stars are evenly distributed in space, why is the sky as black as sitting in a black bag? The question became known as Olbers Paradox.
AD 1830 Mary Fairfax Somerville wrote "The Mechanisms of the Heavens", which was an easier to follow translation of Laplace's "Mecanique Celest" Laplace declared that she was the only woman to understand his book. Was she the only woman who wanted to read it?
AD 1835 Halley's comet came back as predicted. It was first seen over Rome.
AD 1837 Johann Franz Encke discovered just a small gap in Saturn's rings and became famous overnight. Remembered for a gap.
AD 1838 Friedrich Bessel was the first to find a way of measuring how far away stars are. While doing this he also discovered that the star Sirius must have an unseen companion, later called Sirius B, which was the first of what became to be known as a White Dwarf (caved in star).
AD 1842 A gentleman called Majocci tried to take the first photograph of a total eclipse. He didn't have his flash with him.
AD 1846 A German called Johann Galle discovered the most distant planet Neptune, only 2,794,000,000 miles away (give or take a little bit).
AD 1850 William Cranch Bond, an American astronomer, discovered another ring inside the B ring surrounding Saturn. After much thought he called it the C ring.
The next Issue of MIRA will continue this fascinating look at the history of astronomy and bring the story up to date. I can't wait. ED
The rest of you may have been leading happy, fulfilled lives, meeting communally once a month to refresh your passion for astronomy. Me, I've been relentlessly finding out
Everything you ever wanted to know about but were afraid to ask
By Mike Frost
The camera obscura (literally "dark chamber") was the Victorian equivalent of the virtual reality simulator. Visitors to seaside resorts would pay to enter a darkened room into which was projected an image of the outside world - they were, literally, on the inside of a pinhole camera - this is where the word "camera" comes from. As you'll see, several of the old cameras have survived to the present day, monuments to the golden years of seaside holidays. However, a new generation of cameras obscura has emerged, proving that even in these days of 3-D stereograms. Mortal Kombat and MTV videos, the subtle beauty of the projected image can still be appreciated.
What started off my interest in cameras obscura was a visit to the Foredown Tower in Hove in 1993, and in April this year I paid a return visit. At Foredown there is a camera obscura originally built for the Gateshead garden festival of 1990. In 1991 it was transferred into the Tower, originally the water tank for an isolation hospital on the South Downs. Foredown Tower countryside centre features the camera obscura as its showpiece, but also features displays on the history of the isolation hospital (now demolished) and the ecology of the down lands. For astronomers, there's a dedicated satellite dish to receive weather pictures, and they are hoping to open a heliostat to project solar images.
I had a long chat with Mike Feist, who runs the Foredown Tower. He has used the camera obscura to observe the sun (at low azimuth) and moon - he believes it should certainly be possible to observe Venus and probably Jupiter too in the twilight. He's a great enthusiast for observing atmospheric effects:- rainbows, sun and moon halos, sundogs etc. Not surprisingly, he is also very interested in finding out about cameras obscura elsewhere in the U.K. and abroad, and is compiling a directory, which he very kindly let me have a copy of, and which I am quoting substantially from.
He was, I think, astonished, that I could name two British cameras he didn't know about! Namely those in Llandudno (see my last article) and at the Astronomy centre, Todmorden, which Vaughan brought to our attention. I was less surprised that he could name two I had not previously come across.
Nearest to us in Warwickshire is the camera in the Boneswaldthorpe Tower on the northwest city wall of Chester, which forms part of Chester's Grosvenor museum. Perhaps somewhere to stop off on a day trip to Jodrell Bank? A lot further north is the camera in the Barrie Cricket Pavilion at Kimemuir, Forfar. This was a present to the town of Kirriemuir by J.M.Barrie, author of "Peter Pan". Apparently archival film exists of the author opening the pavilion in the 1930's. Unfortunately the camera is only open a few days a year, due to a lack of volunteers to run it.
Several members of the society told me they had visited two other Scottish cameras, in Dumfries and Edinburgh. The Edinburgh camera, dating from 1853 but renovated in 1947, stands on Castle Hill and overlooks the city - it sounds a splendid sight. The focal ratio of F67.5 means that the Edinburgh camera has an unusually large depth of field. The Dumfries camera is older still, built in 1836 for the Dumfries and Maxwelltown astronomical society to observe sunspots. It occupies a converted windmill, and forms part of Dumfries museum. Should any of the society find themselves having to entertain President Yeltsin, never fear, I have a tourist guide in Russian for the Dumfries camera!
The Isle of Man camera at Douglas is currently under renovation by the Manx government. Instead of a the rotating aperture (the "pinhole") which generally tops most commercial cameras, Douglas has 11 separate stationary turrets, each with its own lens and mirror.
Llandudno, as I mentioned last year, is a small construction on the site of the old camera, which was burned down by vandals in 1966. Abervstwyth, which re-opened in 1985, is a much grander construction, a two storey building on Constitution Hill featuring an 14 inch diameter lens (stopped down to 12.5") consisting of three elements. The Powys County observatory on the Welsh/English border at Knighton opened last year and has a 13" aperture, using the spare lens blank which wasn't needed for the main telescope in the observatory. Portmeirion Italian village is alleged to have a camera but no-one there owns up to knowing anything about it.
The remaining English cameras occupy spectacular sites. The Bristol camera, built in 1829, overlooks Clifton suspension bridge. It occupies a former snuff mill. Finally, and I think most recently, the old Greenwich observatory has added a camera obscura to its attractions. It is adjacent to Flamsteed house, and offers a view north over the Thames.
As far as we know, the above constitutes a definitive list of extant outdoor British cameras. Many science centres and museums feature smaller scale indoor cameras to demonstrate the principles of pinhole photography. Museums of photography often include portable cameras obscura, used by artists to help them to sketch outdoor scenes; not to mention the camera obscura's cousin, the camera lucida, which is another portable artist's aid, creating a virtual image by means of a prism rather than a projected image by means of a pinhole. And almost every seaside resort can boast an ex-camera. Brighton, Margate, Ramsgate, Folkestone, Eastbourne and Colwyn Bay all certainly used to have one. As regards future cameras, the designer of the Greenwich camera, Peter Drew, also built the Todmorden camera, and plans new cameras for Edinburgh, Liverpool and San Francisco.
Which of course opens up a new list... cameras international! Mike Feist knows details of a number across the world. Point Lobos camera obscura at the north end of Ocean Beach in San Francisco was opened in 1949, nearly closed in 1978 but was saved by a petition containing 10 000 signatures! The Griffith observatory in Los Angeles has a camera obscura overlooking Mt Hollywood, built in 1953 and renovated in 1980. There are also reports of American cameras in Colorado Springs, Chattanooga and Santa Monica.
Down Under there is one confirmed sighting, at Picnic Point in Toowomba, Queensland. Instead of the aperture revolving, the entire building rotates! There are probably working cameras in Ultimo, New South Wales (a suburb of Sydney) and Darlingshurst NSW, but the seaside camera at Manly beach (like Bondi, only nicer) has gone, along, probably, with those in Brisbane, Adelaide and Melbourne. A Kiwi Kamera at Napier on the North Island of New Zealand is strongly rumoured.
Asia is under represented for cameras obscura, and Africa can currently muster just one, Grahamstown in South Africa.
In Europe, Cadiz at the bottom of Spain, opened in 1994 in a watch tower overlooking the city, and is virtually a twin of the Hove camera. Oybin, which sits almost at the point where Germany, Poland and the Czech Republic meet, has had a camera obscura since 1852. It was
demolished in 1980 but rebuilt by students from the Gorlitz technical school.
You might think I was at a disadvantage searching for international cameras, not having many international visitors, but I do have one advantage over Mike and the commercial cameras obscura - an Internet connection! I did a search for "camera obscura" when I was surfing the Net the other day and came up with a picture of a camera obscura in the Gellertmuseum in Hainichen, Saxony, but as the accompanying text was in German I wasn't able to find out much more! (I've since been told J.S. Gellert was a writer). Better still, I was able to check on locations where Mike had reported an unconfirmed sighting. Which was how I came to have an e-mail correspondence with a surrealist artist from Parma, Italy, by the name of Diego Cuoghi, who was unwise enough to include the words "camera obscura" in the middle of a passage of Italian. Mercifully Diego understood English, and was able to tell me about a camera dating from the turn of the century in the Rocca de Fontanellato, a medieval castle near Parma. The camera is in one of the towers of the castle and using it one can view the square in front of the castle and the church of San Croce.
There are, however, still a number of unconfirmed sightings around Europe; so if you haven't yet made your minds up where to go for your summer hols, may I suggest... Mont St Michel, Normandy (I have been there myself, never saw anything!); in the Bois de Boulogne, Paris; Egger, Hungary; Gotha Castle, Germany.
What are you waiting for? Get out there and start ticking off those lists! I particularly recommend the Foredown Tower and the Powys County Observatory in Knighton.
Let me know how you get on!
Cameras Obscura - Specifications
Country Location Date Aperture Focal Ratio Location
England Bristol 1829 5" Clifton Suspension Bridge
England Chester 1856 5" Boneswaldthorpe Tower
England Greenwich 1994 8" f34 Greenwich Observatory
England Hove 1991 12" f18 Foredown Tower
England Todmorden Recent 5" Astronomy Centre
Wales Aberystwyth 1985 12.5" f20
Wales Llandudno Recent 4" Great Orme
Wales Knighton 1994 13" Powys Observatory
IOM Douglas 1880's
Scotland Dumfries 1836 9" f16 Dumfries Museum
Scotland Edinburgh 1853 10" f68 Castle Hill
Scotland Kirriemuir 1929 7" f15 Kirriemuir Cricket Club
Australia Toowomba 1996 6" f13
Germany Oybin 1980
Germany Hainichen The Gellert Museum
Italy Parma Rocca de Fontanellato
S. Africa Grahamstown 5"
Spain Cadiz 1994 12" f17
USA Los Angeles 1953 10" f12 Griffith Observatory
USA San Francisco 1949 8" f19 Point Lobos, Ocean Beach
A little while ago I received a note from Vaughan Cooper about this subject, he says in his letter: "The late Horace Dell had one installed in the roof space of his house in Luton. I visited Horace once, a few years ago and saw it in action. - Whats happened to it now I have no idea." ED
ECLIPSING VARIABLE β LYRA
By Vaughan Cooper
With a view to develop and extend your knowledge, in depth and breath of the night sky, in a simple and practical way and without the expenditure of expensive equipment, try nightly naked eye estimates of the variable star β Lyra (Sheliak)
The experience of this will benefit you on many levels. You will learn in greater depth, the names or designated Greek letter of many stars, along with their fixed magnitudes which you wouldn't ordinarily bother with and have first hand experience of the many subtle changes the night sky has to offer. This knowledge will prove invaluable when you are trying to find variables with binoculars or telescopes - and last, you will learn perseverance. To this effect I offer you β Lyra, a star that regularly changes in brightness, just a little under one magnitude over approximately a two week period, so results of the project should be achieved in a reasonable time. This I feel, is an important consideration to maintain ones interest in the project before moving on to more difficult and demanding stars.
With reference to the diagram of Lyra and the annotation of the fixed magnitudes of the comparison stars in Hercules, make nightly estimates of β, from this you will notice the subtle changes of β Lyra. During its brightest phase, β will be approximately equal to γ Lyra at 3.2 while during its faintest phase will equal δ Lyra at 4.3 (the official magnitude range of β Lyra is 3.3 to 4.2 with a period of 12.95 days).
Although the complete cycle of variability of β has a period of just a little under two weeks and should offer you quick results to maintain your interest. I do suggest through, to continue the programme of observations over a couple of months as it's unlikely that every night will be clear or free of moon light.
Give yourself a chance to develop your observing skills to recognise the subtle changes in magnitude - this is where your persevering comes in!
From your observations and the notes draw up a simple graph, as this will reveal in graphic form that β Lyra has during its 12.95 day cycle two unequal minima separated by two equal maxima.
The cycle of variations in magnitude is due to the mutual eclipse of the two unequal bright stars which lie very close together at only 22 million miles from centre to centre and as a result, the stars have been flattened into an ellipsoid in shape, due to their rapid rotation and mutual gravitation tidal action. They are so close together that a jet of hot material passes continuously, at 180 meters per second from the giant class B8 star which has a diameter of about 19 times and luminosity of 3,000 that of the sun, to its cooler companion being a late type A or early F sub-giant whose diameter is about 15 times that of the sun. Also a cool stream of gas from the cooler star F passes to the B star. As a consequence of the two stars ellipsoidal shape and revolving around their mutual centre of gravity, we observe a difference in the surface area presented to us during the stars 12.95 day period of revolution; thus the changes in brightness β Lyra presents to us.
β Lyra is the standard of an important type of eclipsing variables whose components are very close together, from it astronomers have learnt much about stellar evolution since John Goodricke discovered the variability of β Lyra on September 10th 1784. One of which is, the period of revolution of the two stars are gradually shortening due to loss of mass, so the 12.95 days is todays current value and this will change in the future. However, we are still uncertain about the distance of β Lyra from us, because it is too remote for a determination of its trigonometric parallax, although a distance of 860 l.y. is offered by Sandage.
The evening of the 10th Sept. 1784 marks a special day for variable star astronomy, because not only did John Goodricke discover the variability of β, his second after Algol, but also by coincidence, John's near neighbour and good friend Edward Pigott discovered η Aquilae.
For the more ambitious member you might wish to try your observing skills on R Lyra, a semiregular variable with a rough period which is not always present of 46 days with a change of magnitude from 3.9 to 5.0. As this is approaching the effective limit of naked eye variable star observing, particularly in an urban environment you will probably experience great difficulty in observing this star and it may be better to use binoculars, however comparison stars are listed below:
γ Lyra 3.23 For positions refer to
μ Her 3.42 Nortons Star Atlas
η Cyns 3.89 or Tritons' Sky Atlas 2000
ζ Lyra 4.09
κ Lyra 4.34
16 Lyra 5.01
Many of the naked eye variables, which are neglected by the main variable star organisations, a total of around 34 in number which reach mag. 4 or brighter, so there plenty of work to do provided you have patience and perseverance. For further naked eye variables to study during the following months.
Chi Cygni 3.3 max to 14.2 min. period 408 days. This star is a presently fading as max was July 13 and min should be Jan 27.
P Cygni 3.0 max to 6 min. period not known. Massive hot luminous star that rose to 3 mag. around 1600 and first thought to be a nova. Since the 18th Cent. it has varied between 4.6 and 5.6 - so again may be a little difficult for effective naked eye observing.
ε Peg Usual mag 2.5. Period not known. Doubtful variable. A unconfirmed observation recorded when this star flared to mag 0.7 during 26/27 Sept. 1972