“ Catch a star ! “









I- origin of the moon


Three theories are proposed to explain the origin of the Moon :


1 - The theory of Fission : The rotation of the Earth was 10 times faster than today and under the effect of the tides of the Sun, parts of the external layers would have been rejected and would have accumulated to form the Moon.


2 - The theory of capture: the Moon would have been formed by agglomeration of the matter of a protoplanetary disc in which metals were missing.


3 - The theory of collision:  a giant asteroid (8 times as large as the Moon) hit the Earth on its side. At the time of the "crash" parts of the earth’s crust was projected into space, forming the Moon, whereas the metal core of the asteroid agglomerated with that: of the Earth by fusion.


from” Astronomie et astrophysique”


The first historic observation :

The first man who really observed the Moon was Galileo because he observed the Moon with a refractor of 30 mm aperture.


II- Discovery of the Moon



The discovery of the moon was realised by observations from Earth and with space probes.


Mission’s name







By flight








Photographs of  hidden side of the moon



The United States

Photographs of  hidden side of the moon





First landing on the moon



The United States

First manned landing on the moon, return of  samples




Automatic  return of  samples




Lunokhod-1:remote controlled moon jeep





- single Natural satellite of the Earth 

Movement around the Earth:


- average distance to the Earth is of 384400km is approximately 0.0026 A.U.

 - orbital Eccentricity:  0.054°

- Period of revolution:  27.32 days

- Slope of the orbit:  5.1° in comparison with the Terrestrial orbit 

Rotational movement:


- the period of rotation of 27.32 days is the same one as its period of revolution

- relative flatness is 0.0006

- slope of the equator compared to the orbit:  2.6°

Mass, size and density:


- equatorial diameter:  3476 km

- volume:  2.20*10-3 km2

- mass:  7.35*1022kg

- fields gravitational:  1.57N/kg

- escape velocity:  2.4km.s-1

- true density:  3.36

- decompressed density:  3.35

- gravity has the equator 1.62m.s-2

Temperature on the surface:


- extreme:    day  : 127°C (400K)

                     night : -173 °C (1OOK )

- average:  0°C ( 273 K )





- none

Magnetic field: 

- none

Tourist information:

- time of radio transmission with the Earth is of approximately 1.3s


  IV - TIDES :


 Tides count among the most significant variations

 In the height of the sea. The combined attraction of the Moon and the Sun, is at the origin of this phenomena and its variations.

The Moon and the Sun attract the Earth and its oceans which become deformed. Water will

accumulate where attraction is maximum, i.e. at the

point of the sphere located closest to the star.

Moreover, thanks to the speed of movement, a centrifugal force opposite to attraction maintains the Earth on its orbit. This centrifugai force pushes back the water, which thus will accumulate contrary to the

Star. Moreover, one knows that the Moon is seldom in the equatorial plan of the Earth, thus, for the same

latitude, the amptude will not be the same for the

two daily tides. Sometimes there is only one tide per day.     






















 from” Astronomie et astrophysique”


V – Comparison with Titan :


Titan, the greatest satellite of Saturn, is very interesting because it can be compared to Earth at this origin.

The atmosphere is very rich, actually scientists suppose that consists of clouds of ammoniac, nitrogen and methane or could say “among over grasses”. They are waiting with impatience the landing of the Huygens spacecraft.

We can note that diameter and mass are similar at the moon but the principal difference is about atmosphere. The atmosphere of Titan is very important with organic molecules like N2 and CH4.


Principals characteristics of Titan and comparison with moon : 





Comparison with M oon


1 222 000 km  from Saturn

3,2 x distance Earth- Moon

Period of revolution

15,96 days

27,32 days


5150 km

1,48 x


7,2.1010 km3

3,3 x


1,3.1023 kg

1,77 x



0,57 x


- pressure

- temperature

- composition


1,5 bar

- 183 °C  ( 90 K )

90% of N2 ; 10% of CH4 ; clouds of hydrocarbures



- 173 °C  ( 100 K )







This image taken by Cassini's visual and infrared mapping spectrometer clearly shows surface features on Titan. It is a composite of false-color images taken at three infrared wavelengths: 2 microns (blue); 2.7 microns (red); and 5 microns (green). A methane cloud can be seen at the south pole (top of image). This picture was obtained as Cassini flew by Titan at altitudes ranging from 100,000 to 140,000 kilometers (88,000 to 63,000 miles), less than two hours before the spacecraft's closest approach. The inset picture shows the landing site of Cassini's piggybacked Huygens probe.



Credit: NASA/JPL/University of Arizona


VI- Experiments


1 - Procedure :  


After preparatory meetings we chose the

evening of October 21, 2004 to take our images. All the photographs were taken by us with the assistance of a professor of the club  of astronomy.

 This evening was not selected randomly, because to make a good lunar study in the evening, we needed to take pictures during the first quarter, while having a clear sky. This evening was “ideal”.


After having gathered the material in the course of the day, we began the evening at 19h00. After installing the material, we could begin the observation from 19h18. With material of a Perl Vixen refractor 150mm in diameter and 750mm focal distance, we observed the Moon. The webcam “toucam pro” was used to carry out the videos, several intermediaries were used, like the lens of Barlow 2X, a reducer of focal of 0.5X, a filter cantiniuum or a IR-UV filter, (it cuts infra-red and ultra-violet at the same time).




Pierre and the telescope

We encountered several difficulties that evening.

Given that this refractor is equipped with a motorised mounting aided by automatic follow-up, we first had to mount it, that is align the refractor’s axis of rotation with the earth’s. During the first observation we experienced a lot of turbulence which complicated the focusing. We also realised that focusing produced vibrations which were accentuated by the refractor zoom. Thus, the more we zoomed, the stronger the vibrations were (use of barlow). Furthermore, the wind created vibrations on the refractor. The turbulence was therefore stronger because, the moon being low caused the atmosphere to be thicker.


Webcam and this carry-eyepiece adapter

We produced a score of films of the moon that required formatting in order to be released.


The formatting

For this step we used a program called “registax V1.1beta” which is free and available on the internet. Formatting at a film file-type.avi is carried out in 4 stages:

  1. aligning of images
  2. quality optimization and sorting
  3. compilation of the best images
  4. wave processing of selected compilation

 Treatment of a film


2 - Observations


At the time of our observation, we could notice that there were various kinds of craters.  Some have a central peak located at the center of the crater, others have their crown in the shape of steps, others have an extremely flat bottom...  All these differences let suppose that all these craters have many different origins.  Thus we will raise some assumptions, which we will explain thereafter by comparing the results of our experiments with the craters of the Moon that we took.


We have observed that the moon  crater could have  various forms shown  on this photography:





 (Personnal picture)



On the small and the large craters (fig. 1 and 2 ) diameter d  is close to the diameter of its base D.  Moreover, on the craters on fig. 1 and 2 the diameter is much larger than their height.

One can notice that the crater on fig.2 has one central peak, they are not found only on craters of a significant diameter.

We noticed that some of the craters had an extremely flat bottom whereas with other are equipped with an irregular bottom.



We also observed long mountainous bands, those would be the vestiges of old giant craters (dating from the formation of the Moon) having been immersed by the magma resulting from the lunar era of vulcanicity (= 3.3 Gy).  They are the seas.


Some finals images after treatments :


( pictures took  by us )


3 - Assumptions


The lunar craters can have different origins.  That is seen by the diversity of their forms.  Here are  some assumptions concerning their origin:

1 - Volcanic origin:  flow of lava produced by the repression of a dome, which is dug by the aspiration of the magma.

2 - Meteoritic origin:  fall of meteorites which by contact on the lunar ground disintegrated by producing a violent explosion devastating a surface much larger than the size of the meteorite itself.

3 - Collapse:  once the era of vulcanicity was completed, certain bulky magmatic chambers could have been blocked causing a very significant local collapse.  That would result in a considerable drop of the level of the lunar ground.

These various assumptions are the fruit of our imagination.  Some can appear more realistic than others.  We will model thus them and observe their result in order to roughly deduce the origin of the various lunar craters.


4  - experimental Modeling



The first experiment consisted in reproducing on a small scale the formation of a crater of volcanic origin.  For that we used a polystyrene container (~ 8 L) which we equipped with a PVC pipe that we heated to give it a U shape (fig. 1).  We then ran concrete in this container up to the level of the head of the pipe, and then we let it dry for about two days.


Observations:  we obtained a crater of a very small raised diameter, broad, without jagged edges. 




The second experiment consisted in modelling the fall of meteorites and observing the results. To be done, we had to copy of the lunar crust in a container.  We then used plaster which we dampened so that it had an ideal consistency:  neither too soft, nor too hard, to be closest to the surface of the Moon.  Once the good compromise was found, we manufactured pellets of this plaster, of the same consistency, in order to copy on a reduced scale the meteorites.  We then propelled them against the plaster surface contained in the container and at this point in time some craters of various forms appeared.




Observations:  We obtained craters of various aspects but on the whole they have shredded edges, a low depth compared to the diameter and a bottom without a central peak.





The third experiment consisted in reproducing the effect of the collapse of an underground cavity (ex:  old lunar magmatic chamber).  For that, we used dry plaster with the consistency of corn flow again in which we put an inflatable balloon fitted with a valve than enable us to inflate and deflate it at will.





Observations:  we obtained flat-bottomed circular cavities, but without raised edges


 5 - Conclusion


           Experimental modelling to which we carried out have us to deduce the probable origin of certain craters:  smallest.

Indeed, those whose extreme diameters (bases and head of the crater) are almost equal and the height is low.  Their characteristics observed with the telescope correspond to the characteristics of the craters modelled in our experiment.  They are small craters which are also the most widespread on the lunar surface. 


The large craters with central peak were very difficult to model.  We were not able to produce one in our experiment. Was this the result of the consistency of our model not corresponding to the consistency on the lunar ground?  Or perhaps an insufficient launch speed?  Is our modelling adapted on a great crater scale?


            In the same way, to come up with a crater "of volcanic origin", we modelled a dome with a central hollow (fig 1).  Would this be the cause of a bad consistency of the material, or is because the retractation of cement is different from the lunar magma?



As for the craters whose origin would be a collapse, our experiments give only extremely cylindrical craters of which the depth varies according to the volume of the balloon after inflation. 


 We can think that on a large scale, a collapse would produce strong vibrations which would cause crumbling of the walls of the craters. The final result would be a crater in the shape of steps with a more

or less conical total form (fig 2).


The results of these experiments are rather disappointing because they can explain only one kind of craters: those of modest size. But the difficulty of modelling these phenomena in addition teaches us difficulties to model and the importance of the side effects of these phenomena (vibrations) and all their details to be taken into account. 


VII Conclusion :


We find this experiment to be harder than expected, but very interesting nonetheless. It enabled us to discover more about the mysteries of our satellite, the Moon.

As the project went on, our problems multiplied. However, we were not discouraged. The fact that this was such a challenging experiment made the results we achieve through our experiments all the more satisfying.

First of all, producing the images proved rather difficult. Even though we experienced good weather, the unfortunate presence of turbulence made it hard to take clear picture. We are therefore very proud of our images. They took a long time to take because we had to make many attempts before we succeeded.


VIII. References :


 Bibliography :

« astronomie et astrophysique » Seguin et Villeneuve.

« astronomie et webcam » Christophe Béthune.


Internet sites :








Antoine et Pierre.


CLENET Antoine ( 18 years ) ,


DABRETEAU Pierre ( 17 years )


and Jean-Jacques RIVES ( teacher )


From :    Lycée Léonard de Vinci

                               Rue du fromenteau

BP 369

85603 MONTAIGU Cedex




Thanks to M.GAUTHIER ET Mr Richard for the help to traduce this document.