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znak.gif (3013 bytes)Primary school Preska, Medvode, Slovenija

Andrej Miklavcic, Alen Jambrošic in Miha Osredkar,

mentor, Tatjana Gulic, teacher of physic

Venus transit 2004

 

 

1.   Summary

In this seminary paper we have presented an interesting astronomical event, which occurred on June 8, 2004 of the Venus transit in front of the Sun.

We presented our group work on a model that introduced this event to students of our school.

We are also writing about how we made a projector for the Sun and instruments that we needed for the observation.

We also wrote same results of our measurements.

 

1.         Summary  2

2.         About us  3

3.         Our position  5

4.         About Venus  7

5.         Venus transit (Event theory)  8

6.         Time  9

6.1.__ Measuring of time_ 9

6.2.__ What is the universal time? 9

6.3.__ Exactly measuring or time_ 10

7.         Observation  11

7.1.__ Intention_ 11

7.2.__ Display of phenomenon to students 13

8.         Passage of Venus over Sun’s plane  15

8.1.__ Observation with telescope_ 15

8.2.__ Observation with projector for Sun_ 22

8.2.1._ Projector for the Sun_ 22

8.2.2._ How does projector for sun work_ 25

9.         Results of measurement 28

10.      Index of references  28

 

2.   About us

 

There are three thirteen year old boys in our group: Andrej Miklavcic, Alen Jambrošic and Miha Osredkar, and the mentor, the Physics teacher, Tatjana Gulic.

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Picture 01: Our group

Medvode is a town between Ljubljana and Kranj. Our school Part of  is in the village of Preska, near Medvode. Around 480 of  the students are driving to the school each day from more remote villages.

Every year the pupils take part in different competitions in the knowledge of mathematics, physics, chemistry, biology and Slovene, German and English languages. They are also successful in sports activities, such as badminton, basketball, volleyball, football and athletics.

School has two sub-branches, in villages of Topol and in Sora .

Headmaster of our school is Mr Primož Jurman, B.A.

We can participate in extra-curriculum subjects. Last year so we took classes in Astronomy. We were observing the Moon, the Sun and other planets on their ways around the Sun. One of our tasks was also to prepare the observation of an exceptional astronomical event: a transit Venus across the face of the Sun.

We prepared the observation of this event on our school playground. We presented the event to all students of our school and to other people, interested in this event.

We also joined the international net VT-2004 Observing Campaign, lead by ESO.

 

3.   Our position

 

State:

Slovenia

Town:

Medvode

Longitude:

14.41117 0 E

Latitude:

46.1324 0 N

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Picture 02: Where we are

 

The Observation took place during two magnificent sunny days on school playground.

Geographical position of our observation place was determined with the help of the Havens Above web site.

 

4.   About Venus

 

Venus is an inner planet, second closest to the sun in our solar system.

Entire surface of Venus is covered with clouds – coat of atmosphere. They are absorbing sun’s warmth, that is why Venus is the hottest planet in the solar system. This phenomenon is also known to us. On Earth, we call it the greenhouse effect. Surface temperature on Venus is around 480 0C.

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Picture 03: Venus

The interesting thing is, that Venus’ rotation is from east towards west, the opposite direction of the Earth’s rotation.

Revolution period is 224,70 days, Earth’s is 365,25 days. Venus’ distance from Earth is swinging from 43 million to 275 millions kilometres.

 

5.   Venus transit (the theoretical part)

 

To virtual passage of Venus over the Sun’s disk occurs, when Venus travels between the Sun and the Earth. If the orbit of Earth and Venus lies on the same plain, Venus is in the same line as the Sun with the Earth almost every 584 days. Viewed from the position of the Earth’s orbit, Venus’s orbit is inclined for 30244. That is why the passage of Venus over the Sun’s disk happens so rarely.

Transit can occur only in lower conjunction, when Venus is in the same side as Earth, regarding from the Sun. That is the time, when Venus is in a new moon phase for an observer on the Earth. The observers want to determine four moments of the transit. The transit starts with the first contact: the moment, when Venus’s disk touches the outside edge of the Sun’s disk. This moment is difficult to determine, we were unable to determine it. Second contact comes after approximately 20 minutes. It is the moment, when the Venus disk leaves the edge of the Sun. For approximately four hours and a half, Venus’s disk slowly moves over the Sun’s disk. The third contact is moment when Venus touches the opposite side of the Sun’s disk and the fourth, around 20 minutes later, when Venus’s disk leaves the Sun’s disk. 

The Maximum of transit is the moment when Venus disk is the nearest to centre of the Sun (minimum angle distance).

 

6.   Time

6.1.        Measuring of time

 

Every regularly repeating phenomenon can be used for time measuring. Nature has given our ancestors a few events, on which we based are unit for time. Exchange of day and night at rotation of Earth around the axe, serves the determination of one day. A Solar day lasts approximately four minutes longer than one rotation with respect to the stars.

One revolution of the Moon around the Earth was used for a month, one fourth for one week. Full moon, first quarter, new moon and last quarter are noticeable for everybody everywhere and the intervals are seven days and nine hours long. Months last for 29, 5 days (one day and a half more than four weeks).

 

One revolution of the Earth around the Sun is one year.

Life rhythm in biosphere is balanced also around seasons. It is a consequence of inclination of Earth’s axe regarding the ecliptic.

 

6.2.        What is the universal time?

 

The Time on our watches is determined by the rotation of the Earth. It is Noon, when the Sun is in the highest position on sky, in the zenith. A day starts at midnight (at 0.00 hours) and lasts 24 hours or 86400 seconds.

Earth is distributed in 24 time zones and in every time zone local time is for a certain numbers of hours different from the Greenwich Time. Every time zone includes 150 latitude, because 3600 divided 24 is equal 150. When it is noon in Greenwich (12.00), there are n time zones eastern (or west) from Greenwich, 12.00 plus (or minus) n hours. Slovenia, for example, is 1 time zone eastern of Greenwich that is why civil time in Slovenia is 13.00 when it is 12.00 in Greenwich.

 Because the speed of rotation of Earth is reducing, duration of a second is determined by the movement of the atoms and not by rotation of Earth around its axe. We know this time as Co-ordinated Universal Time, UTC. It is very precise, it disturbs only for one billion of a second per day. Because UTC isn’t different for more than 0, 9 seconds from the time defined by the rotation of the Earth, the change of one second per year is called a “leap-second”. This means, that a day is a   second longer than 24 hours.

 

6.3.        Exact measuring or time

For observing the Venus transit we must be up to 10 seconds exact as the appoint time. We can learn the exact time via telephone. GPRS too can shows us the universal time.

For the precise time we used a computer programme that is connected to the internet alone and takes care for accuracy with our computer watch.

We made one more check of the time one hour before the observation started.

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Picture 04: Computer display

 

7.   Observation

7.1   Intention

 

The intention of our observation of Venus transit was to calculate an astronomical unit; that is, the distance from Earth to Sun.

We can calculate it by parallax.

Calculations with parallax are still difficult for us to make with our knowledge, that is why the phenomenon was only observed and calculation summarised by ESO, which compared our recorded times with others and gave us our results.

 

Our intention was also to present the popular knowledge of astronomy and with to make our school friends and others interested in our surrounding.

The local TV station was also on the spot, recording a programme about the event.

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Picture 05: TV Interview with our teacher

 

7.1.        Presentation of phenomenon to students

 

We showed our school friends the rotation of the Earth, Venus and the Sun on a model that we made by ourselves, we each represented one planet

 

We introduced the Earth, Venus and the Sun. Orbits were circles, on which we put the pins. In order to make a better visual presentation to our school friends, we divided the Venus year into 7 earth months. On Earth’s track we put 12, on Venus’s 7 pins.

Earth and Venus move with the same speed, so the students who represented those two planets came from one to other pin in equal time. Student that represented Sun stood in the middle.

Venus’ orbit is shorter, that is why Venus circles the Sun in shorter time than the Earth. When Venus, Earth and the Sun were in the same line we stopped then. The pupils stood before the person who represented Earth, so they observed the ‘event’ from the Earth’s point of view, when Venus covered the Sun.

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Picture 06: The presentation to our school friends

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Picture 07: Pupils observe

 

8.   Passage of Venus over Sun’s plane

Observation started at 7.10 in the morning. To observation of the phenomenon was shown in two ways.

 

8.1.        Observation with telescope

 

With a telescope and a web camera, the phenomenon was observed on the computer screen.

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Picture 08: Telescope with web camera

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Picture 09: Telescope with camera, protected against the hot sun

 

We used telescope Celestron NexStar4. We used  the automatic mode of following. For the observation we used equatorial setting. On the objective lens of telescope we installed a foil made of mylar.

We fixed an eyepiece of telescope on a web camera (Logitech QuickCam Pro 4000). We installed the proper software for taking pictures and recording short clips.

We checked the universal time.

 

The approval of equatorial setting of the telescope came with the straight line of the transit. If the setting would be horizontal, the transit the line of the transit would be bent.

We proved the equatorial setting with taken photos. We printed photos on a foil and cropped them together as the pictures show.

We got a straight line. The picture, on which Venus is nearest to the Sun centre, was taken on 10.20 civil time or 8.20 of UTC, as predicted.

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Picture 10. The work on the photographs

 

Pictures that we got on the computer screen were shown to our school friends, so they could see the event safely.

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Picture 11: Observation was also fun

 

We fund out, when we compared pictures, that our pictures were turned upside down. That is because the telescope rotated around its own axe and the web cam rotated with it and the telescope itself flips the picture.

 

Some photographs with web camera:

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Picture 12: Some photographs that we took on the day of event

 

Animation of pictures:

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Picture 13: Animation

 

From clips and direct observation on the computer screen, we tried to define those four already mentioned parts of the transit.

 

8.2.        Observation with projector for the Sun

 

We observed the phenomenon with a projector for the Sun, which we also made ourselves. With its help, we projected the picture of the Sun and Venus on awhite paper in a shade. Every few minutes we marked the sun’s plane with a dark spot – Venus.

 

8.2.1.                 Projector for the Sun

 

We observed the sun safely and easily with the projector. With its help, we can even observe sun spots.

Projector is made with one mirror and two lenses which are put in two cylinders, which can be moved. A holder with the mirror and both cylinders is fixed on a stand.

Such projector was first described by an Indonesian physicist, Andrianto Handojo in Applied Optics, Oct 15, 1989.

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Picture 14: Preparing of projector for sun

 

8.2.2.                 How does the projector for sun work

 

Projector projects the sun with a mirror through lenses on a white base. We focus the picture by changing the distance between cylinders. White base must be in a shade, or in dark place, so the picture is more visible.

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Picture 15: Observation of the transit with the projector

 

9.   Results of the measurement

 

Measured times were determined with the observation of the phenomenon on computer screen. They are written down in UTC.

 

1st contact

not measured

2nd contact

05 h 39 m 10 s

3rd  contact

11 h 02 m 50 s

4th contact

11 h 22 m 45 s

 

Calculation of astronomical unit summarised by ESO, it compared our recorded times with other recorded times and gave us the results.

 

Our result: AU = 149816811 km

 

We finished the observation at 14.30.

 

10.         Index of references

 

Books:

 

Nicholas Harris; Neverjetno potovanje med planete; Tehniška založba Slovenije; 1. natis v Ljubljani; 2000.

 

Web pages:

 

http://www.fiz.uni-lj.si/venera2004/index.html

http://vt-2004.org/

http://www.heavens-above.com/selecttownquery.asp?Session=kebgcedpmdcimpnniolcpjij

http://www.algonet.se/~sirius/eaae/aol/market/collaboration/eclipse99/how_to_observe/how_to_observe.htm

 

Authors of  the photographs are members of our group.