PROJECT: Annular solar eclipse vs. the Venus transit

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Authors: Anicet Cosialls Manonelles, Aida Pallàs Ramos (16), Violeta Porta Alonso (16), Alícia Tiffon Calvet (16).

School: IES GUINDÀVOLS, Eugeni d´Ors s/n , 25196
- Lleida (SPAIN)

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We have intended to give  an answer  to the  questions mentioned below ,  after having taken the image of the annular eclipse of Sun on the 3rd October, 2005   by Josep Masalles  and the image of the Venus transit on the 8th June , 2004  by the pupils of  IES Guindàvols- the winners of  Catch a Star  2004.
  1. Which distance is the Moon from the Earth at the moment of  the eclipse?
  2. Which percentage of the solar disk is eclipsed by the Moon and by Venus in their corresponding eclipses?
Moreover, the weather changes of the intensity of the sunlight, the temperature, the dampness or speed of the wind during the annular eclipse, have also been studied, as well as the most important differential features among  the Venus transit and  the annular eclipse.


It is known that the orbit of the Moon around the earth is not circular, but eliptical, and for that reason the distance from the Earth changes constantly in its orbital movement. The minimum distance perigee is 363.300 km and the maximum apogee is 405.500 km.
There is a solar eclipse in a determinate place of the Earth, when the Moon hides the Sun, at that spot of the Earth. This can only happen during the New Moon (Sun and Moon in conjunction) and  it is presented different types of solar eclipse:
The disks of the Sun and of the Moon, seen from of the Earth, are almost equal. Both of them hardly surpass half  degree.  The Sun disk is 400 times bigger than the moon disk, although, the sun is 400  times farther from the Moon.

In order to have a total eclipse of Sun in a determinate place of the Earth  the three following conditions must be simutaneously fulfilled:
  1. The Moon has to interpose between the Earth and the Sun.
  2. The Moon has to be at a distance of 357.550 km of distance from the Earth.
  3. The Moon, the Earth and the Sun have to coincide in the same level.

annular eclipse zone
Figure 1. Spain annular eclipse zone

                                                   Solar eclipse animation

Formulation of the problems

In this research essay we have intended to give answer to the following questions formulated both in the observations of the annular eclipse of Sun in Lleida (03-10-2005) and the Venus transit in Lleida too (08-06-2004):
  1.  Which procedures do we have within our reach to observe the eclipse?
  2. Which distance must  the Moon be situated from the Earth in order to produce a total eclipse of Sun in a detreminate point of the Earth?
  3. How can we determine experimentally, from the observation of the annular eclipse of Sun on 3rd  October, 2005, the distance to the moon from the earth?
  4. How does the temperature change during  the eclipse? How does the intensity of the sunlight change during  the eclipse?
  5.  How do dampness and speed wind change during  the eclipse?
  6. Which maximum percentage of the surface of the Sun overshadows the Moon during the eclipse?  
  7. Which particular differences are there between the annular eclipse (03-10-2005) and the Venus transit (08-06-2004) ?
  8. How can the data of the profile of the Moon surface during an annular eclipse  be obtained using the telescope VLT of Paranal (Chile).

Solutions of the problems
  1. Which procedures do we have within our reach to observe the eclipse?
- You must NEVER look at the sun without any protection; it is very pernicious for the sight.  The eclipse does not even have to be looked at when it is in an advanced period and the sunlight is reducing since serious ocular damages could happen. To observe the  solar eclipse five different methods have been used:
-  Special glasses, which are made out of standardized filters, which prevent from the harmful sunbeams, and a  cardboard contour. This can be seen in  fig.2.
- Video camera  protected with a number 14 lead base soldering filter, which has the same function as  the glasses of standardized filter. This can be seen in  fig.3.  
looking at the eclipse
video camera
Fig. 2 Some pupils looking at the eclipse
Fig. 3 Video camera protected with a solar filter
-  Thermoplastic soldering mask, which is composed of a  fixed, small and rectangular window with a special glass which absorbes the ultraviolet radiation. This can be seen in fig.4.
- If we do not have either any glasses or any system, two sheets of cardboard can be used instead. In one of them a small hole must be made and the light of the Sun that passes through this small hole has to be projected on the other sheet. This can be seen in fig.5.

Mechanical students
Eclipse on paper
Ecplise trough the leaves
Fig. 4 Mechanical students with soldering masks
Fig. 5 Method with cardboards
Fig. 6 Projection of the eclipse through the leaves of the school playground trees.

First contact
2nd eclipse
3rd eclipse
4th eclipse
Sequence of the annular eclipse - Sony Digital Video Camara - LLeida (41º 37' 37'' N, 0º 36' 52´´ E, 170 m)

2. Which distance must  the Moon be situated from the Earth in order to produce a total eclipse of Sun in a detreminate point of the Earth?

- In order to answer this question, we’ll suppose that the moon is aligned between the Earth and the Sun and in the same plane. Furthermore we’ll suppose that the sunlight propagates in the space in straight line).
Sun’s radius (S) = 696 000 km
Moon’s radius (L) = 1738 km
Average distance from the Earth to the Sun (ds) = 149.600.000 km

Figura 7.  Relative position of the Earth, the Moon and the Sun in a total  Sun’s eclipse

 Applying the Thales’ theorem:

The distance where the moon has to be  from the Earth at the moment  the total eclipse is produced  can be calculated .

dl = 373.570 km

If the moon is situated near  the apogee (405.500 km), the eclipse will be annular.

3. How can the distance to the Moon from the Earth be  experimentally determined -from the observation of the annular eclipse of Sun on 3rd  October, 2005?

-  To determine  experimentally the distance to the Moon  from the Earth the eclipse’s day, we will base upon the shot taken by Josep Masalles Roman at Villagordo del Cabriel (39º33'10" N - 1º28'26" W - 699 m) (fig.8). This photograph was taken by fitting together one Reflex camera to a telescope Meade ( D:125 mm,  F:1250 mm).

Figure 8. Annular eclipse
Figure 9. Meade Telescope

- Doing a picture treatment with the Paint Sho Pro program we can obtain the percentage of the Sun’s diameter eclipsed by the moon.
Figure 10. Image treachment with  Paint Shop Pro program

- Now we’re going to measure the apparent diameters of the Sun and the Moon from the differences of the axis (x, y)  of the extreme points.
- The obtained results are:

Apparent radius (length’s units)

Annular eclipse  
Figure 11. Moon’s position in a total Sun’s eclipse

Annularl eclipse
Figure 12. Moon’s position in an  annular solar eclipse

Applying again the Tahles’ theorem on the figures number 11 and 12 the following equalities are obtained:


The following conclusion can be inferred:
    dl =390.766 km

 4. How does the temperature change during  the eclipse? How does the intensity of the sunliht change during  the eclipse?

The material used in this practice  at  the  schoolplayground  is:
  •  Temperature sensor with a sensibility of 0,001 ºC
  •  Light sensor with a sensibility of 0,001 Klx
  •  MultiLog PRO keyboard
  •  Two supports with nuts and two tweezers
  •  In the classroom .
  •  A computer with the MultiLab program is required
The assembly of all the device has  to be done on this way:
    1st: In order to fasten the sensors, they have to be fixed by an adjusting nut, and all this  must be fixed  too  to the  tweezers which will be tied up to a base.(fig.1)
    2nd:- Connect two sensors with the MultiLog PRO  keyboard
    3rd: -Turn on the keyboard and select the capture mode, in this case, one sample per each second during 10.000 seconds.
          -Start measuring at the beginning of the eclipse and stop once it has finished.
    4th:-Download and analyse the data in the computer with the MutiLab progamm’s  help.


Figure 13.  Assembly Experience

- Data treatment:
Both, the  data of temperature and  light intensity must be downloaded and  checked.
- Taking into account that we started registering the  data at 07:41am, we can know the exact time  when the Moon  was totally opposite the Sun and thus when the annular eclipse was produced, at 09:01am . While commuting the first and the second cursor  at  the beginning and in the middle  of the eclipse the descent of the intensity of light and the descent of temperature produced can be measured. (Fig.14 and 15).

Figure 14. graphic 1
Figure 15. graphic 2

- (As far as the  light data   are concerned  we have to bear in mind that normally the light intensity is higher as the day  advances;and for this reason, after the eclipse there is more light than at the beginning.
Not too much care must be given to the temperature data  when wind gales are produced  because they  might cause some modifications on them)

- Sunlight intensity:
Maximum intensity: 9’315Klx
Minimum intensity: 1,215 Klx
Variations: Dllum = 8,1Klx => 87%                                

From  the beginning to the moment  when the annular eclipse took place , a descent in the intensity  of light was produced- that is to say-   a 87% less.

- Temperature:
Maximum temperature: 13,32 ºC
Minimum temperature: 11,799 ºC
Variation: Dt = 1,128 ºC => 8,47%

From the beginning to the exact moment of the annular eclipse the temperature has fallen  1,128ºC.  we are talking about a reduction of an 8,47%

5. How do dampness and speed wind change during  the eclipse?

- We have been able to observe that there was a reduction in the temperature and the intensity of light, and also in the dampness and the wind speed. The meteorological observatory of the city of Lleida gave us some information that was recorded during the eclipse. (Look at fig. 16a, 16b and 17).  The information had been taken in solar schedule,. -two hours less than the time established in our zone.

                                                  Fig.16a.  Dampness graphic        Fig.16b. Temperature graphic

- Figure 16 shows us the  air dampness  and temperature descent. Knowing that
these two factors were linked,  we already supposed that a decrease in the air’s dampness will be produced- since a reduction of 1 degree  took place during the eclipse.


In figure 17 we can see the wind speed during the annular eclipse. With this graph we can know that a reduction in the wind speed took place. This fact happens because the air moves quicker if the weather is hotter. However, as the temperature lowered an 8'47 % the air masses moved less and slowier.
Fig.17. Information about the wind speed


Comparison between an annular eclipse and the Venus transit

 6 -7.Comparison between an annular eclipse (03-10-2005) and theVenus transit (08-06-2004).


Fig. 18. Mercury transit. (Photo by theWinners of “Catch a Star 2004”)

Fig. 19. Venus transit (Photo by theWinners of “Catch a Star 2004”)

Fig. 20. Solar Eclipse.

Time of the first contact (TU)
Time of the fourth contact (TU)
Length (hh:mm:ss)
Surface eclipsed (%)

Reduction of the intensity of light (%)
Reduction of the temperature (ºC)

The Venus transit
Sun’s eclipse
                                                     Fig. 21. The annular eclipse versus the Venus transit

Observations with the ESO VLT telescope

8. How to obtain information about the  surface  of the Moon during an annular eclipse using the telescope VLT from Paranal (Chile).

The  VLT telescope is the best  one of the European astronomy at the moment and  the main one from the new observatory of ESO in Paranal. It is also the  one that has the most sophisticated devices  in the world.
The VLT does not only consists in one telescope.,  but  some interconnected. The main elements are 4 reflecting telescopes with primary mirrors of 8,2 m of diameter. The 4 telescopes are situated forming a trapeze. There are 4 more telescopes which   are mobile, measuring 1,8 m  able to see a man walking on the Moon.
- This telescope (fig.22) makes possible the observation of the Baily’s pearls (fig.24) during an annular . Baily’s pearls are the last rays of light going through valleys and mountains  in the Moon. Scientists highly appreciate to observe and chronometre with precision the first and the last instants of the first and last  pearls, because  this allows them to rebuilt exactly   the surface  of the Moon.
However, lhe annular eclipse couldn’t  be seen from “Cerro Paranal”

telescope VLT, Chile
telescope VLT, Chile
Baily's perls
Fig. 22. VLT Telescope, Chile
 Fig.23. Inside the Paranal observatory
 Fig. 24. Baily's pearls

Conclusions From the analysis and discussion of the results obtained we can say that:
  1. We can observe an annular eclipse in 5 different ways: Using special glasses, a video-camera protected with a  soldering filter, a soldering mask,  the projecting the solar  trough the  leaves holes of the trees, and using a fine cardboard.
  2. The Moon and the Earth have to be at 373.570 km in order to take place a total eclipse.
  3. The distance between the Moon and the Earth during the eclipse on October  3rd, 2005 was 390.766 km.
  4. The surface of the solar disk has been eclipsed a 91 %
  5. The time between the first and the last contact of the Venus transit was longer than the time during the annular eclipse.
  6. The temperature slowed down 1,128º C during the eclipse, and there was a reduction of about 87% of the intensity of the light and there was  also a relative dampness increase.
  7. The wind speed  diminished during the eclipse which  is a consequence of a decrease in the temperature.
A very special day for the educative community of Guindàvols High School was 3rd September, 2005. Althoug the scientiific commmunity had already lost their attention on solar eclipses, the event that took place on 3rd September was an excellent opportunity to introduce ourselves inside the worl of astronomy. Apart from that, we have achieved that the astronomical culture spread among all our students.

Photo Gallery
Soldering mask
Telescopi Meade

References Web sites

Personal webpage of Josep Masalles:

"8 th june ¡Let´s to observe!"  (Winners  of Catch a Star 2004):

Instituto Astrofísico de Canarias (IAC):

European Southern Observatory (ESO)