- Nat. Reps. meeting in Garching p. 2
- Report on the Athens General Assembly p. 2
- Statutes submitted to Court p. 3
- Statutes accepted by Court p. 4
Working groups
- The "links with planetariums" group p. 4
Who, what and where?
- Divulgence of Astronomy in Oporto p. 5
Historical experiments
- Roemer and the finite speed of light p. 6
Observations
- Chasing the partial solar eclipse p. 9
Editorial
Well at last the third issue is ready! But the least that can be said is
that things didn't come out easy, when they did come out at all... The initial
deadline at been set to February 28., and, when the day came, your desperate
editor had received only one contribution for the Newsletter... A few
additional papers arrived in the following months, but then, of course, began
the worst period of the year (final exams, etc.) for an amateur part-time
editor
This to emphasise once more that a more active attitude from all the members is
crucial to allow the publication of this Newsletter which can act as a decisive
link in our network. The diffusion of the Internet version of this Newsletter
is also totally dependent on your contributions!
But enough with complaining. Looking back at the past six months, I can think
of two major events for the EAAE community: the first one, illustrated below,
is the spectacular comet Hyakutake which came as a total surprise in January.
Maybe some of you or of your students have material (photographic or texts)
which could enrich the next issue of our Newsletter... The second event, more
confidential, was the official birth of our association! Yes, the statutes and
by-laws were finally accepted by the German Court, after a procedure that
nobody had imagined so complicated... Roland Szostak, our former provisional
secretary, tells us more about this juridical adventure in the following
pages.
And now, the summer will allow us to think about the very exiting
"Astronomy On-line"
EAAE-ESO-EC project that should give the decisive kick to put the EAAE
on orbit, making it known to the largest possible audience, for the good of
Astronomy.
Enjoy your holidays and, if you get bored on the beach, write an article on the
Sun!...
Taken on March 23. by E. Pasche (CH)
Michael Reichen
LATEST NEWS
and Executive Commitee
meet in Garching.
Stefano Sposetti & Michael Reichen
What follows is a summary of a personal communication made to me by Stefano Sposetti, the Swiss national representative, after the meeting held in Garching from June 9. to June 11., which I could not attend myself. It lists the main points of the agenda with brief comments on each of those:
a) EAAE application form:
The idea is to gather the largest possible number of new members!
However, admission should be reserved exclusively to persons involved in
astronomy teaching (schools, planetariums, amateurs, etc.). Each new member
should be supported by an EAAE member who would testify that the candidate is
really involved in "teaching". Education is the keyword!
b) Annual fee:
Every six months or each year, the national representatives shall send
50% of the money to the EAAE treasurer, the other 50% being kept for "national"
purposes.
c) News statutes and by-laws:
See articles below written by Roland Szostak.
d) Next General Assembly:
Will be held in Sweden in 1998. There most likely won't be any money at
all to cover travel expenses of the participants...Start saving now!
e) The "Astronomy On-line"
project:
Each National Representative is in charge to diffuse the information
concerning this EAAE-ESO project for the fourth European week for scientific
and technological culture. Registration is open until October 1. It is
financially supported jointly by the European Commission (70%) and by ESO
(30%).
Each country has to have its NSC (National Steering Committee) to organise the
project at a national level. Each group of students or amateurs participating
to the project shall be under the guidance of a "project director" (teacher,
professional astronomer, etc.) and shall chose a project theme before November
1. The theme will then be presented on the Web through a national "homepage"
(in English...).
There will be three levels of difficulty (elementary, medium and advanced) to
classify the group projects.
It seems pretty obvious that an Internet connection is absolutely necessary to
get involved in this project. Each teacher or interested person not yet
connected should run to his/her local provider to try to get a connection at
low cost (why not talk about sponsoring, such a large scale project could be
potentially interesting for commercial purposes...).
As much advertisement as possible should be made in the media (newspapers,
television...). This could be a very efficient stimulus for the providers!
This "Astronomy On-line" project is a wonderful opportunity to let people know
about the EAAE, about ESO and about Astronomy and Astrophysics in Europe, from
the secondary schools to the professional observatories. Let's get the most out
of it!...
S.S. & M.R.
Report on the Constitutional General Assembly of the EAAE.
James G More (Secretary)
Participants of the assembly worked in groups to consider the proposed text of
the Statutes and By-
Laws
of the EAAE. Following two plenary sessions the content of both tests was
accepted unanimously. The formal signing took place on Saturday 25 November by
the following participants:
C. Brattas (Sweden), S. Gaitzsch (Germany), L. Gouguenheim (France), A.
Pickwick (UK), E. Ribeiro (Portugal), D. Simopoulos (Greece), F. Wagner
(Luxembourg).
All participants recognised the enormous debt of gratitude owed to Roland
Szostak for his framing of the statutes and he was thanked accordingly.
At this historic stage in the life of the EAAE Richard West was proposed and
elected as Honorary Life President of the EAAE. In the words of our new
President Dionysios Simopoulos we thank our "father snd mother" for his vision
which led to the formation of the EAAE.
The formal elections for the Executive Committee took place with the following
results:
President: Dionysios Simopoulos (Grcece)
Vice-
President:
Fernand Wagner (Luxembourg)
Secretary: James More (Scotland)
Treasurer: Friedrich Volck (Germany)
Editor: Michael Reichen (Switzerland)
Committee members:
Laura Abati (Italy),
Knud Jepsen (Denmark),
Lucienne Gouguenheim (France),
Robert Wielinga (Netherlands).
The representatives of each country elected a single member to act in the vitally important role of National Representative:
Austria: G. Rath
Belgium: J. Gusenberg
Denmark: M. Winther
Finland: M. Sarimaa
France: J. Sert
Germany: K.H. Lotze
Greesce: M. Metaxa
Ireland: P. O'Leary
Italy: L. Abati
Luxembourg: F. Wagner
Netherlands: R. Wielinga
Norway: F. Pettersen
Portugal: F. Martins
Spain: S. Garcia Garcia
Sweden: B. Lingons
Switzerland: S. Sposetti
UK: A. Cohen
Following this the real challenge of beginning the work of the EAAE took a
first step with the formation of 2 Standing Committees with respective
chairpersons:
1. Financial Support: R Buckland
2. Communications Network: A Vasterborg
Seven working groups were proposed with the chairpersons shown :
Astronomical Concepts: R.Gaitzsch
Didactic Materials: L. Gougenheim
Training Teachers: R.M. Ros
European Student Projects: M. Winther
Planetarium Links: M.Moutin
Research on Teaching Materials: F Petterson
Public Education: N. Matsopoulos
Guidance was given to chairpersons:
1. Draft aims for the group
2. Establish a membership list
3. Publish information
4. Inform executive council regularly
Following the Conference the members of the Executive Committee held a brief
meeting to discuss the way forward. Some of the points raised are noted
below:
1. Once the Statutes and Constitutional Assembly Record are complete, copies
will be sent to Committee Members, National Representatives and Working Group
Chairpersons.
2. An account will be established once the Statutes are accepted by the German
Court. In the meantime the Secretary will send Membership Forms to National
Reps asking them to accept provisional membership with finance details to be
arranged later.
3. The Socrates Programme will be one possible source of funding for the EAAE.
The Financial Support Committee must take this on board. All EAAE members must
explore projects which could forward the aims of the EAAE.
The process of establishing the EAAE as an active association will be a
challenging one. We all have our normal day to day tasks and must find the
commitment to put in extra hours to further the aims of the EAAE. It is
pleasing to report that the Didactic Materials group under Lucienne Gouguenheim
is already well organised with clear objectives. I look forward to hearing from
other groups in the near future.
J.M.
Roland Szostak (D)
Dear members,
one of the main topics of the Constitutional Conference in Athens was the
adoption of our Statutes, in order to establish the formal ingredients for the
juridical existence of the EAAE. So it was important that the participants of
this conference sat together and discussed the prepared text. This was done in
groups during one session. To my opinion one should have had more time for
examining all regulations profoundly. Nevertheless in the same afternoon the
plenum succeeded in going through the whole text, inserting all corrections and
additional ideas until finding acceptance for each single paragraph. To my view
it was good to have an interval of one more day for further critical inspection
and residual corrections until we carne to the final voting about the statutes.
So in the end the statutes were adopted unanimously in the same impressing way
as this had happened to the declaration of the workshop at Garching one year
before. I think this demonstrates, that all participants are motivated by the
same ideas.
Directly after the constitutional conference the preparation of the documents
for submission to court started. The Statutes, the By-
Laws
and the minutes of the constitutional session had to be translated into German.
In careful consultations by mail fax and phone with James More and Richard West
all details in these documents were completed and checked. Then I had to
contact a notary in Munich, who is obligatory for the formal procedure. When
all the necessary residual signatures were at hand, these documents were passed
to the notary. So in January the notary has submitted all documents to court,
and now we are waiting to hear from the court. The notary says, that in no case
a prediction can be made about any revisions, which may be wanted.
So we have to wait and trust, that all those corrections can be made without a
complicated procedure. You may remember that in the statutes and during the
constitutional session we tried to pay good attention to the point, that all
residual corrections can be made by one authorised person. I think we did our
best and should look ahead in good confidence: Computer freaks would say "plug
and pray".
As soon as the EAAE will be juridically accepted, the treasurer will be ready
to open the central bank account of the association. And the secretary will be
ready to start the official memberships. Let me finish these lines by
expressing my thanks to all of you, who have contributed to it so carefully.
R.S.
Official existence of EAAE has started
Roland Szostak (D)
Dear members,
when I wrote the preceding report "Statutes submitted to Court" in February, we
all expected, that we had to wait only one or two months more, until the
Statutes would have been registered in Garching, giving the EAAE its official
existence. The only aspect of fear in my mind was, that in the worst case we
might have difficulties to overcome some unforeseen juridical objections
without the necessity of a new constitutional conference. You remember, we had
been very careful in Athens. So all went well.
The corrections wanted by the court were really minor: a few marginal exchanges
of juridical expressions, which improved the precision of the text. But no
changes of our ideas. I think this confirms that the work done in Athens was
very good. The really major change was a strict formal separation of the By-
Laws
from the Statutes. This was necessary, because we want to have the By-
Laws
as a part of regulations which can be changed without being dependent on the
court. So in consequence only the Statutes are officially registered by court,
but the By-laws not. But the court said, that in this case no references to the
By-
Laws
were allowed at all in the text of the Statutes. So every little word or remark
about the By-
Laws
in the text of the Statutes had to be extinguished. It was possible to do this
and the text was accepted. Nevertheless the court -
we don t know really why -
wanted 7 new signatures, which shocked me considerably. But there was no demand
for a new constitutional conference. So within a few days the new signatures
were done and formally everything was o.k.
Two months later, when we expected to become informed about the official
registration, the court noticed, that still the question had to be clarified
that -
with respect to the international character of our association -
there were no other registration of such a company or a subdivision of it in
another country. Finally also this obstacle could be removed. So we learned
that bureaucracy is subtle and very accurate, taking considerably long time. In
the meantime the opinion had grown, that it would have been better to have
applied for registration in another country. But after all, now we have it !
So the EAAE exists officially from now. Let us be happy about the birth of our
association. Do you remember the nice drawing of the stork as the symbol of
birth, presented by Laura Abati ? May I suggest a little correction ? This had
been at that time rather the moment of conception. And now we have the moment
of birth. Juridically spoken. May we hope for a good future of the newborn
EAAE.
R.S
Roland Szostak is the provisional secretary of the EAAE, and has taken care
of the elaboration of the Constitution and By-laws for the Association.
WORKING GROUPS
The "Links with Planetariums" group
Marc Moutin (F)
At the end of the constitutional conference of the EAAE, in Athens last November, several working groups were defined, on different items.
As a few planetarium representatives were present, it seemed to be useful to
exchange ideas and experiences concerning the relationship between the
planetaria and the other educative structures such as schools. For example, to
help teachers to see better how the planetarium can offer interesting shows
complementary to education programs, and to help the Planetarians to understand
better teachers expectations and perhaps offer some new perspectives.
I'm sure that exchanging experiences on this special relationship of
Planetariums, pedagogy and school education, could first give good ideas to
other colleagues, then could open the eyes of many teachers on the
possibilities of the planetarium theatre in ways they couldn't have ever
imagined.
As I have been elected Chairman of the group "Links with planetariums" I take
the opportunity of this letter to invite you to think to this new vector of
communication and to imagine how it could work.
The task is huge and quite difficult !
How to begin ?
The Net is a good way to exchange and we could develop a news group on this
subject. Information, experiences could be delivered regularly on EAAE Home
page. But we have to think of all those who don't have access to the Net.
That's why we could regularly exchange information about experiences, contacts
and ideas in this letter .
What happened since last November ?
I informed the french Planetarium community by writing an article in the next
edition of the french magazine "PIanetariums" about EAAE ,its goals and the
existence of this working group, inviting my colleagues to join us and exchange
their experience concerning what they do with schools.
At the next conference of APLF(French Planetarium Speaking Association) in
Reims at the beginning of May, we will debate on how we could proceed to
communicate more on this subject with our European colleagues.
At the European Planetarium level, I wrote an article in the Europlanetarium
Newsletter asking for collaboration and if possible for national correspondents
in order to better coordinate the information. As these papers have not been
published yet, not so many people are at present really, involved in the
working group "Links with Planetariums", except the Planetarium people who were
present at the conference in Athens (list below)
By next summer, we should better know who in the European Planetarium group is
involved in this reflection and how we think to proceed to improve
communication between teachers and planetarians.
As you understand, things are beginning on the Planetarium side. But to keep a
real "link", the communication has to go in 2 directions...not only from
planetarians towards teachers, but also from teachers towards planetarians.
That's why I invite all of you that are not directly involved in Planetariums
but are interested in what they do and above all in what they could do to
better answer to what you need to join us and let us know what you wish and how
we could collaborate more closely.
Members of the group:
Johan Gysenbergs, Genk Europlanetarium (B)
Eddy Pirotte ,Genk Europlanetarlum (B)
Paul Venneman, Planetarium Heisel, Brussels (B)
Thomas Kraupe, Planetarium Forum der Technik, München (D)
Asuncion Sanchez, Planetario de Madrid (E)
Piet Smolders, Amsterdam Planetarium (NL)
Frank Pettersen, Northern Lights Planetarium, Tromsö (N)
Angela Turrichia, Aula Daaditta Planetario, Bologna, (Italy)
Marc Moutin, Planetarium La Villette, Paris (F)
Tel: 33,1.40.05.73.03 Fax : 33.1.40.05.71.18
E-
Mail:
moutin@worinet.net
M.M.
Marc Moutin is in charge of the planetarium of "La Cité des Sciences" in Paris.
WHO, WHAT, WHERE ?
Divulgence of astronomy at the Oporto University Observatory
Paulo Pinto (P)
For twenty years, at the Astronomical Observatory of Oporto University, we have been having visits from schools. The number of students has been growing constantly and presently about two thousand students visit the observatory, in more or less forty visits, every year. In the begginning visits consisted of exhibitions on astronomy, with the help from slides, answers to questions asked by students and finished with an exhibition and explanation of a camera, with an equatorial movement. In the last ten years we used a video film about astronomy, followed by a period of discussion concerning some astronomical points not well understood by the visitors. The points they question more frequently concern black holes, what will happen to the Earth when the Sun becomes a red giant, how the universe is expanding, how the stars are born and how they die, etc. Actually, since 1993 the camera has been substituted by a Newtonian reflector of 18", constructed by JMI, which works with a CCD ST6, from SBIG. This reflector is used to show the Moon and the planets, Mars, Jupiter and Saturn and sometimes galaxies, nebulae or star clusters. But to see these last objects it's necessary a transparent and dark atmosphere, which is very rare, because we have a great light pollution from the cities of Oporto, Gaia and Gondomar, since the Observatory is among them. As CCD images must be shown in a computer after being processed, we don't obviously use the CCD camera in the normal visits. The impact before this image processing is worse than the visual observation and we have no time, and not enough experience, to process the images, during the normal observations open to visitors. During some years after 1975, we gave courses on astronomy to school teachers. They are free courses and the teachers frequented them because they wanted to know something about astronomy. Nowadays, after September of 1992, they are obliged to learn astronomy, because this science was introduced in the curricula of some subjects. So, we are giving again courses on astronomy to the teachers of Natural Science, Physics and Mathematics to update their scientific knowledge, but now integrated in a national program, the "Programa FOCO", led by the Ministry of Education. We hope that these courses prepare the teachers to give the fundamental knowledge about the solar system, stars and galaxies evolution and the universe formation they need in their lessons. We also hope that they may serve as a guide to locate appropriately in all the structure of astronomy the knowledge they will possibly obtain in future readings on this subject.
P.P.
Paulo Pinto works as a professional astronomer at the Oporto University
Observatory in Portugal.
HISTORICAL EXPERIMENTS
Roemer and the finite speed of light (historical point of view)
Martine Bobin (F)
Abstract: the aim of this paper is to place in its historic context the
Roemer's fundamental experience (1676). I will try to prove the importance of
the theoretical presuppositions of the scientist in his interpretation of
observations and measures, and to make clear the conflict between Jean
Dominique Cassini and Olaus Roemer. Finally the consequences of this discovery
until 1729 (when it was confirmed by Bradley) will be explained.
The speed of light before 1676
Until the 17th century (invention of the telescope and the
clock), the sky was observed to the naked eye and no instrument was able to
measure very short lapses of time (<1 second).
Before the 17th century
In the antic world, the ancients were particularly interested in
understanding the question of vision (why and how people can see) Most of them
thought that light arrived instantly but they didn't agree about the nature of
this light ( local movement of something arriving suddenly or instant
modification of the environment).
The contribution of the Arabs in Optics was very important mainly owing to Al
Kindi (who died in 873) and Ibn al Haytam, better known as Alhazen (965 -
1039). He was the first one to systematise experimental proof. After many
observations and experiments, he suggested the following pattern: light is
concrete; it exists independently of vision (even if the eye is absent).It is
propagated in straight line (rays of light ) in all directions. Alhazen thought
that light moved with a great but finite speed.
In the Christian Middle Ages, oriental expeditions, from the 11th to the 13th
century, made the Arabs' works known and led to develop experimental science
and techniques. Robert Grossetête (1168 -
1253) explained that the straight propagation resulted from waves which made
the light vibrate. Roger Bacon (1214 -
1294) thought that sound too resulted from waves but far less rapid than light
(the vision of flash of lightning precedes the clap of thunder).
In the 17th century
In the 17th century a lot of scientists thought that light arose
instantly but they carried out experiments to elucidate the problem.
In his << Discorsi intorno a due nove scienze >>, Galileo (1564 -
1642) suggested the experience of the lantern: two men take place face to face;
one unmasks his lantern; as soon as he sees the light, the other unmasks his
own. The first observer can estimate the period which separates the moment when
he exposed his lantern from the moment when he has seen the light of the other
one. The two men take place at a greater distance and start the experiment
again. If the measured period is longer, we can conclude that the speed of
light is finite.
This experiment was too rough because Galileo didn't estimate the speed of
light properly but the problem was examined.
Descartes (1596 -
1650) found a better approach to this question: he suggested the experiment of
the eclipses of the Moon, considering astronomical distances:
If the light takes one hour to go from the Earth to the Moon:
t = 0: the Earth is in To, the Moon is in Lo, the light of the Sun arrives at
To.
t = lh: the light of the Sun arrives at the Moon which is in L1. It's the time
of the eclipse.
t = 2h: the light comes from the Moon and arrives at the Earth which is in
T2.
Then we could measure the angle q. But the eclipsed Moon always appears in line
with the Sun...
In 1638 he wrote to Mersenne: << Galileo's experiment to know if light
moves instantly is unnecessary because the eclipses of the Moon (corresponding
quite exactly to the calculations ) prove it much better than we could
test it on the Earth >>.
Just before Roemer's discovery some scientists were persuaded that the speed of
light was finite (Fermat (1601-
1665);
Grimaldi (1618-
1663);
Huygens (1629-
1695):
at least on Earth but he's not sure about the light of stars). They were ready
to accept favourably the experimental measures which would confirm this idea.
Roemer's discovery: the context
Paris' Observatory in the age of Roemer
Paris' Observatory, which was destined to welcome the astronomers of the
new << Académie Royale des Sciences >> was created in 1667.
At this time astronomy was prosperous: the << pendulum clock >> was
invented by Huygens in 1657, the << wire micrometer >> was
perfected by Auzout in 1666 and the big telescopes were improved a lot. Thus,
progress was expected on precision of measurements of time and angles. Before
1670, the Parisian astronomers succeeded in perfecting and using instruments
and techniques which would revolutionise the observation astronomy.
The most important astronomers who worked in Paris during the period 1667-
1676
were:
Jean Picard (1620-
1682),Adrien
Auzout (1622-
1691)
until 1668, Jean Dominique Cassini (1625-
1717)
after 1669, Jean Richer (1630-
1696),
Olaus Roemer (1644-
1710)
after 1672, and Christiaan Huygens (1629-
1695),
for his theoretical contribution.
The determination of longitudes with the help of the satellites of
Jupiter
At the end of the 16th century, the determination of longitudes were
very rough, because there was no <<garde temps >> (no way of
keeping tracks of time). Galileo thought of using the four large satellites of
Jupiter as time indicators: their moves are almost circular and regular, their
period is short enough and the moments of the eclipses don't depend on the
place of observation.
Galileo could not bring his plan to completion, the instruments were not
precise enough.
In 1668, Cassini published the <<Ephemerides Bononienses mediceorum
siderum>> where he explained the method for determining longitudes with
the simultaneous observation of a same eclipse from two different places. The
use and the perfection of Cassini's tables, the use of the clock, permitted to
realise a large program of determination of longitudes. Many expeditions were
arranged to that end by the astronomers of Paris's Observatory: Mediterranean
(16681669), Acadia (1670), Uraniborg (1671-
1672),
Cayenne (1672-
1673),
French coast line (1672-1674).
In July 1671, Picard went to Copenhagen and to Uraniborg to determine the
difference of longitude between Paris's Observatory and Tycho Brahe's, in
Hveen. He wanted to use the precious measures of the famous Danish naked eye
observer. The young Danish astronomer, Olaus Roemer, helped him. During Winter
1671 -
72,
observations of the eclipses of Io were made simultaneously by Roemer and
Picard in Uraniborg and by Cassini in Paris. The care they took in measuring
(and perhaps a fortunate coincidence too) permitted to obtain a very good value
of the difference of longitude between Uraniborg and Paris. Picard, who had
appreciated the work of Roemer came back to Paris with him during Summer 1672.
From this time on, Roemer took an active part in the work of the
<<Academie >> and continued the observations of the Jupiter's
satellites with Picard.
The measures of Cassini and Roemer
The precise determination of the positions of the satellites is very
difficult . The revolution of Jupiter around the Sun is neither circular nor
uniform (It is the first <<inequality>> with a period of about 12
years); the planes of the orbit of Jupiter and of the orbits of Galilean
satellites are inclined on the ecliptic plane. The equation of time has to be
considered (measures are made in true solar time). Today other <<
inequalities >> are known, due to the flattening out of Jupiter and to
the interaction between the different satellites and with the next planets
(notably Saturn). , For several years, the observers had been noticing a
<<second inequality >> (in the dates of the eclipses of Io) which
depended on the respective positions of the Moon, the Earth and
Jupiter.
On saturday August 22nd 1676, (1674? 1675? there is a problem of dates:
documents are lost or undecipherable) Cassini said, in a communication to the
<< Académie >>, that this second inequality seemed due to
the fact that light takes time to come from the satellite to us and it takes
ten minutes to cover a distance equal to half a diameter of the terrestrial
orbit.
In September 1676 (an event precisely dated), Roemer announced to the <<
Academie >> that the eclipse of Jupiter's first satellite, expected on
September 9th, would occur with a delay of ten minutes; this was confirmed by
later observations. The report of this session was published in the <<
Journal des Sçavans >> released on December 7th 1676.
Principle of Roemer's proof
T is the period of revolution of Io. If the speed of the light is c: the
difference of date between two consecutive eclipses (A and B) is T + (d'-
d)
/ c with (d'>d), and the difference of date between two consecutive eclipses
(C and D) is T -
(d-
d')
/ c with (d>d').
Roemer couldn't measure such a small difference but he thought that 40
revolutions of side C were appreciably shorter than 40 of side A.
Both explanations given by Cassini and Roemer are similar but Cassini will then
change his mind and will even contradict Roemer's arguments, and for many years
on, Roemer, for his part, will confirm his theory despite a lack of precise
measurements.
The Cassini- Roemer disagreement
Roemer: when we read Roemer's thesis, we can be surprised by the
weakness of his argumentation. There is no article written by Roemer
summarising the measurements of the speed of light. Roemer took few notes and
the fire of Copenhagen in 1728 damaged most of his registers where he put his
observations down and his manuscripts. A letter from Roemer to Huygens reveals
that his theory about the delay of light is exclusively based on observations
realised by Picard and himself. One of Roemer's manuscripts found in 1913 at
the library of the university of Copenhagen, and studied by K Meyer, contains,
along with a few calculations, a series of observations carried out between
1668 and 1677 on the satellite of Jupiter. The document enabled to piece the
analysis of Roemer together and to check his calculations. Roemer's conclusions
about the time light takes to course half the diameter of the terrestrial
orbit, fluctuate from 9,6 to 12 minutes. Given that the tables used are
uncertain, the agreement between the precision and the observation of the 10
minutes delay expected for the 9th of November seems to be extraordinary. K
Meyer writes on that subject "there is a great gap between this value of 10
minutes and that deduced from the observations realized in 1671,72 and 73".
Roemer seems to have given up this problem from 1678 on which he stopped
working for good. Delambre wrote in 1821, in his << histoire de
l'astronomie moderne >> : << The fact that Roemer didn't pursue
that research, that he didn't try to determine better the equation of the light
of the first satellite and show that this equation was the same for the four of
them, that fact is quite strange >>.
Cassini: two objections were given by Cassini and his sons as well as by
Maraldy (16651729).
The first objection assumes that the correction due to the light speed doesn't
suppress all the inequalities. As for the second, it assumes that the
hypothesis about the finite speed of light is not correct for the other
satellites of Jupiter. Contrary to Roemer, Cassini and Maraldy made a lot of
observations. In his treaty of 1693 << Les hypothèses et les
tables des satellites de Jupiter réformées sur les nouvelles
observations par M Cassini>>, Cassini insisted on the necessity of long
years of observations before being able to reach any good conclusions.
Maraldy stated in 1707: <<Hence it seems that there is a great number of
observations which can't be explained by the movement of light although there
are some for which that explanation is favourable; consequenly, that hypothesis
is not sufficient to explain the second inequality of satellites >>
Two contributions poles apart:
the aims and methods of both scientists, Roemer and Cassini, were
totally different. Roemer turned into a law a hypothesis given by Cassini and
his measurements were interpreted in order to demonstrate the finite speed of
light. Cassini who minutely studied the movement of Jupiter's satellites, tried
to understand all their inequalities. He was extremely precise and couldn't
accept a theory unless that one fitted, in a very satisfying approximation, the
observed phenomena. In those days measurements were not precise enough to allow
scientists to conclude without any hesitation.
This discovery was attributed to Roemer who proved to be more daring that
Cassini. But the latter, through his working method, enabled to raise the
problem of the inequality. The hypothesis of Roemer, for his part, enabled to
accept more easily, the theories about light of Huygens and Newton.
We can say that both scientists contributed in their own different ways to the
evolution of ideas as far as light speed is concerned.
The consequences of Roemer's discovery.
In France: on September 16, 1677, Huygens wrote to Roemer in order to
tell him that he read the english version of his communication dated November
21, 1676 in front of the Royal Academy of Sciences. Following the reasoning of
Descartes concerning the eclipses of the Moon he looked for the inferior limit
of the light speed so that the angle should be imperceptible. The limiting
value of is 6 minutes and to that angle corresponds a time course of 10 seconds
for the distance from Earth to Moon. He inferred that the speed of light was
100000 times superior the sound speed. The Roemer's discovery confirmed Huygens
in his opinion of finite speed of light which was necessary for his theory of
light.
In England : in June 1677, a accurate translation of Roemer's thesis was
published in the << Philosophical Transactions of the Royal Society
>>. Flamsted (1646-
1719)
<< Royal Astronomer>> since 1675 and working in Greenwich since
1676, had been interested in the Jupiter's satellites since 1672. He was
particularly interested in the distances between Sun and Earth and in the
<< elongations >> of Jupiter's satellites. His method for
determining longitudes was the use of the movement of the Moon. After Roemer's
discovery, he studied the eclipses of Io. In 1679, Roemer stayed in London,
where he met Hooke and Flamstead. The latter believed immediately in <<
Roemer's equation of light >> and, thanks to his influence, English
scientists (except Hooke) were favourable to this discovery. In 1674, Flamstead
wrote to Newton, speaking about the << Roemer's equation of light
>> and about his influence on the ephemeris of Jupiter's satellites. In
his <<Principia >>, Newton stated that he was now convinced of the
finite speed of light and that this idea was confirmed by the observations of
<< several astronomers >>.
In 1694, Halley (1656-
1742)
wrote a critical report of the tables of the first Jupiter's satellite
published by Cassini. He noticed that the latter didn't consider the ingenious
hypothesis of the finite light speed in his calculations. With the help of a
judicious use of Io's observations, Halley found that light took 8,5 minutes to
cover the Earth -
Sun distance. At the beginning of 18th century, there were more and more
English scientists who were convinced that the speed of light was finite and
that Roemer had proved it.
It was not necessary to try and find out another proof.
In 1729, Bradley (1693- 1762) suggested the idea of the aberration of light. This idea is based on the acceptance of the finite speed of light and confirms it quite obviously.
M.R.
Martine Robin is a mathematics teacher in Arpajon (near Paris), and is a member of the CLEA (Comité de liaison enseignants et astronomes), the french link between professional astronomers and teachers.
OBSERVATIONS
Chasing the partial Solar Eclipse by the EAAE on October 12th 1996
Josée Sert (F), Brian Stockwell (UK) and Mogens Winther (DK)
On Saturday October 12th will occur a quite rare phenomenon; a partial solar
eclipse. This eclipse will be visible from Northern Canada, all Europe and
Northern Africa.
We suggest that interested EAAE schools and Amateur Astronomers should follow
this phenomenon and in particular, try to perform the simple measurements
indicated below. When combined, these measurements may allow us (possibly for
the first time by schools) to give a reliable determination of the distance and
the size of the Moon.
When will it happen ?
Precise information and a time schedule for major cities will be given in the
next EAAE Newsletter (special issue, note from the editor).
Interested teachers with access to WWW internet, should however contact either
the EAAE homepage or
http://umbra.gsfc.nasa.gov/eclipse/predictions/eclipse-paths.html
An eclipse homepage edited by Nasa Fred Espenak is on
u32fe@lepvax.gsfc.nasa.gov.
Here you may find charts and animations provided by Frank Roussel (Frank
Roussel@univ-rennes1.fr) of the Université de Rennes (France).
The eclipse will however happen 1-3 hours after noon, on Saturday Oct. 12th
1996.
In Europe 30 to 70% of the Sun will become eclipsed. Please see the map
markings above.
Why do these eclipses occur ?
Occasionally, our moon passes in front of our planet and gives rise to a
shadow.
On October 12th this moon- shadow will rush across Northern Canada and the
European continent.
- At what time will this partial eclipse occur?
In Europe the eclipse will be at its maximum around
1300-1600hours depending on where you live. More details
will appear later.
- How do we observe such an eclipse ?
It is important to tell your students, never ever to look through an unshielded
telescope aimed at the Sun. Galileo did so and became blind. With our present
high transmission telescopes eye damage will occur within less than a second.
The tremendous heating power of sunlight is easily demonstrated using a
magnifying lens (a burning glass).
There are however quite a few, easy and safe methods available.
1. A simple and safe way to view the Sun
Some of the very first cameras contained no lenses but were only equipped with
a pinhole .
Strictly speaking , this camera is nothing more than a black box with one hole
in the front.
Light travels in straight lines and therefore rays from the sun will hit the
back of the box and create a perfect image of the Sun's disc. It is possible to
use this black box as a general camera, not only for photographing the Sun but
also for taking ordinary photographs when the exposure time would have to be
long because of the small aperture. This method was even used by French artists
painting miniatures during the 18th century. Imagine spending a whole day
painting miniature copies inside a warm black box like this!
Originally the Pin Hole Camera was invented by an English monk, Roger Bacon
(1220-1292). Roger Bacon's research was considered as being witchcraft and he
spent half his life in prison. In our project however, this camera is safe,
legal and simple.
The Sun's image inside our box will undergo all the phases of the eclipse, just
like the real Sun. At least, this method is safe and may even be carried out by
children in groups.
A few hints:
a)The light hole needs to be small in order to get a sharp image. Diameters
around 1 mm are sufficient.
b)The box needs to be about 0.6- 1 metre long in order to get a reasonably
large image.
During the EAAE Conference at ESO in 1994, the Spanish Group presented nice
results obtained with this Black Box Method. As a dark box, they had used huge
cardboard tubes. Such 4 metre long tubes may be picked up, often for free, at
storehouses selling carpets.
The size of the Sun's image will be around 1 percent of the box length. A 4
metre tube may thus give a most reasonable solar disc size of about 4cm.
This pinhole effect may be seen in nature. A leafy forest may absorb almost
all the sunlight, only leaving a few rays to pass through occasional holes. The
effect visible on the ground will be like shown on the next figure.
So during the EAAE eclipse you may observe eclipsed "solar discs" scattered all
around the forest floor.
During the month of October, these mini-Suns will have an elliptical shape. The
Sun is of course still circular, the elliptical shape is only an effect of the
projection. If sunlight came from straight above ("zenith"), the ground
projected images would all look perfectly circular.
How to observe the eclipse
Method 1. The Grinning Cat - Mirror Method".
Nasa researcher , Joe Jordan (NASA Ames Research Centre, Mountain View,
CA. USA), once wrote these comments : "...One of the best ways to observe a
partial solar eclipse is nice and simple: just take a mirror (like a standard
square pocket mirror) and reflect the sun's image onto a wall at least several
meters away. No poking holes or cutting and pasting cardboard, etc.! You'll
notice that the reflection looks inverted relative to the appearance of the
eclipsed sun in the sky."
This is actually a very interesting variation of Francis Bacon's 700 years old
Pin Hole Camera. Instead of letting the sunlight pass through a small hole,
this method reflects the light back, into for example, a northern, shady
classroom. Besides being totally safe, this method works well when long
distances are used. A small dentist-mirror, placed 10 metres away results in a
solar image which is approximately 10 cm in diameter. A larger mirror may still
be used if you cover unused parts with tape or paper.
Method 2 : Using Binoculars like a slide projector
Explain to your students that they must never aim an unshielded scope
directly at the sun! Don't leave the telescope unattended.
This binocular method will also give remarkable results.
For the October 12th eclipse make an accurate drawing when the eclipse is at
maximum.
It might help to sketch the Sun's circular outline on your paper before you
start (as an exercise a few days in advance, draw the ever present sunspots).
Method 3: Watching the Sun through negative film, welding glasses and filters
This method is often described in books and magazines but is still dangerous
for several reasons. Many years ago film plates used silver nitrate. An over
exposed film plate would thus give an effective metallic shield, similar to the
shield used by astronauts. Nowadays, however, most plastic films are made of
other materials and do not give any protection against solar infrared rays. The
same problem occurs on unauthorised welding glasses.
Sky & Telescope wrote (July 1991, p. 80): "One filter entirely safe for
direct solar viewing is a shade 14 rectangular welder's glass. It transmits
only 1 part in 370000 of the incident light and meets strict tolerances on
transmission of invisible infrared and ultraviolet as well." This costs only a
few dollars, but be sure you get the right item.
If you have a good school telescope, buy a proper optical solar filter. Mounted
correctly in front of a telescope this will give a most impressive picture.
Several brands are available and prices vary from $10 upwards.
Plastic Mylar filters are cheapest, but seem to be extremely fragile and they
only transmit a strange blue colour. Glass filters are available too, with
prices around $50. These transmit nice colours and beautiful photographs are
possible. For details of where to buy, take a look and compare prices in
astronomical magazines such as Astronomy or Sky & Telescope.
Warning : Do not use ordinary sun glasses in front of your telescope.
Some of these cheap filter glasses have 100% transmission in the invisible
infrared, again exposing your eye to lifelong damage.
Some companies sell solar filters designed to be mounted as an eyepiece. Avoid
these products. One of our students once mounted such an eyepiece solar filter
in his telescope. He aimed his instrument directly at the Sun. Forty seconds of
sunlight were enough and this eyepiece cracked into pieces!
History of eclipses
Solar and lunar eclipses have often been interpreted as bad omens. Several of
the preceeding eclipses, and the fear following these, actually changed world
history .
A well known Chinese example goes back to 1851. The old Manchu emperors were
about to fall, due to the so called Taiping Rebel Group. Western governments
tried to support the chinese emperor, sending modern weapons and British and
American officers. The General of this army was Charles Gordon, a military
genius. He suffered his first defeat in 1851. A rebel headquarter was to be
attacked on a moonlit night. Very unexpectedly, a lunar eclipse occurred
shortly before the assault. The superstitious Chinese soldiers interpreted this
as a most evil sign and lost their fighting spirit. As a result the attack
failed and there were high casualties...
Several years later General Gordon himself died, indirectly due to a solar
eclipse. In 1884-85 he led the defense of the Sudanese capital of Khartoum
against an attack by rebels. This time a solar eclipse demoralised Gordon's
native forces and the city was captured shortly before a British relief
expedition arrived. General Gordon was among those slaughtered (read the
magnificent article written by B.E.Schafer, Sky & Telescope, Dec. 1992, p.
639).
Another well known historical example dates back to Christopher Columbus. On
his fourth voyage to America in 1504, Columbus faced problems. His ships were
in poor condition due to shipworms and the vessels had to be beached in
Jamaica. A lot of his supplies had been stolen. Half his crew had mutinied and
now, while his ships were sitting like ducks on the beach, the Indians refused
to supply them with food. In this dire situation Columbus had a great idea.
Western European astronomers had calculated that a lunar eclipse would occur on
Sept. 14-15th 1494. Columbus now informed the Indians that, due to the Gods
being angry, the Moon would disappear during the following night. The lunar
eclipse appeared right on schedule, and Columbus finally got his supplies. R.W.
Sinnott had an interesting article on this project (see Sky & Telescope,
October 1992, p. 437).
Suggested Project in Maths / Science :
During all his lifetime Columbus did not believe that he had found a new
continent, but instead, believed he had discovered a new tradeway to India.
This Lunar Eclipse could however easily have shown Columbus that he was not
placed in India. However, due to a surprisingly simple mathematical error, he
miscalculated his position once again... Read and recalculate the data
mentioned in the article above.
Reference concerning pictures :
The pictures above appeared in "Holger Danske", a danish teaching magazine,
published in 1912. The Columbus picture dates back to 1892.
Drawings etc. may be reproduced, in case:
individual sources, the EAAE and this school project are mentioned.
Comments and/or suggestions for improvements are welcome!
J.S, B.S. & M.W.
Further planned :
1. Mathematical notes on eclipses ...
(Preliminary version already available on the EAAE homepage).
2. What happened at Golgatha ?
Mattheus mentions that the sky darkened, while Jesus was crucified at Golgatha.
According to some sources, this has been interpreted as another eclipse. Other
sources mention the possibility of sand storms. Recent research show the
Eastern period falls shortly after full moon, thus making the first explanation
- the solar eclipse - impossible.
Note from the editor: due to severe last minute file tranfer problems, some
figures are missing and others are of poor quality. These figures will be
published in better shape in the coming supplement on the solar eclipse. My
apologies to the authors.
Coming up next :
There will be a special issue early in September on the coming solar eclipse, with more material from the authors of the article presented here. Any contribution to this special issue is welcome and has to be turned in before
August 30., 1996
The next regular issue of the Newsletter (issue no. 4) should come out in November or early December. For that issue, the dead-line is
November 15., 1996
Please do not wait until the last minute if you think your article might need some "extra work" by the editor!
Miscellaneous
The report on the french national meeting prior to the Athens Constitutional Assembly that was published in Issue no.2 was written by Josée Sert, the elected french National Representative, and not by Lucienne Gougenheim. My sincere apologies to both of them for this confusion!
M.R.
Instructions to authors
In order to make the edition of the Newsletter somewhat easier (and faster!), the authors should try to keep in mind the following recommendations:
Text: - please write in English (ask you local English teacher for
corrections!)
- the Newsletter is published using Microsoft Word (5.1) on Macintosh, but any
other text editor on Mac or PC is OK... Always join a paper copy (good
quality!) of your article in case your diskette can't be read for one reason or
another.
Figs.: - if the figures are "ready to edit", please keep their dimensions to
something reasonable (use issue no.1 as an example) in order to save space in
the Newsletter for other articles!
- if the original figures are too large, I can scan them to adapt their size,
provided once again that the quality of the copy is of good.
- if pictures are to be included, think that the image has to be well
contrasted in order to get a satisfactory quality of the scan.
To facilitate contacts when needed, please give a fax or phone number at which you can easily be reached.
Send your articles to: Michael Reichen
home: 16, Avenue de Milan
CH - 1007 LAUSANNE
(tel: 21/616 75 82)
school: CESSOUEST
Route de Divonne 8
Case postale 2214
CH - 1260 NYON 2
(tel: +41 22/361 24 37)
(fax: +41 22/361 04 85)
My e-mail address is
michael.reichen@obs.unige.ch