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  • Combination of the pictures from German y and

    Nam ibia

    v s�� � � � �

    1E E

    E v v

    r r

    s s s r r r

    � � � � � �

    �� � � � � � � � � �

    „Shadow“ 2

    „Shadow“ 1

    Sun

    Venus

    Earth

    Observer 1

    Observer 2

    �� �

    v �

    s �

    s

    rErE rVrV

    v

    E

    r

    r

    w

    ��

    : linear distance between the observers

    : relative radius of Venus‘ orbit

    : angle of projection

    : parallactic displacement

    1

    sin w sin w 1 1E

    s � V

    r AU

    r�

    � � �� �

    � � � � � �

    �� ��

    w

    Observer 1

    Observer 2

    Venus

    Here the parallactic displacement of Venus becomes visible by

    combination of the above Germany and Namibia pictures

    Usual explanation: Both „shadows“ have positions on the sun

    with an angular difference of

    The following relation can easily be shown:

    ��.

    Because the relative distances of sun, Venus and earth are

    known the following relation holds:

    Internet Project

    Observing, Photographing and Evaluating the

    Transit of Venus, June 5/6th, 2012 Coordinated by U. Backhaus, Dep. of Physics, University of Duisburg-Essen, Germany

    http://www.venus2012.de

    The passage looks slightly different when observed from dif-

    ferent locations on earth. This so called parallax effect is due

    to the distance between Venus and earth or, more precisely,

    due to the different distances of the sun and Venus from the

    earth. Therefore, measurements of the parallax effect allow

    the derivation of the distance to the sun.

    But the angular differences are smaller than the apparent

    radius of Venus. They can be recognized only by exact

    measurements and by combinating simultaneously taken

    pictures. Therefore, as in 2004 an international cooperation

    between schools, amateur astronomers and universities has

    just started to prepare careful observations of the transit.

    Determination of

    * the geographical positions (latitude and longitude) of the

    participants,

    * the radius of the earth,

    * the orbital radius of Venus (without using Kepler's third law!)

    and

    * the siderical period of Venus.

    Projects for Preparation:

    If the linear distance between the observers and the angle

    of projection w are known, the distance r between the sun

    and the earth can be calculated by the following relation:

    � E

    Some theory:

    Daylight side of the earth when

    Venus leaves the sun:

    From this part of the world the

    3rd and 4th contact can be

    observed.

    The main goals of the project are:

    * to form new contacts between schools,

    amateur astronomers and universities,

    * to get acquainted with internet collaboration,

    * to gather information due to transits of Venus

    in history,

    * to learn photographing the sun and determi-

    ning the exact orientation of the pictures,

    * to learn determining the exact position of an

    object on the sun's disc,

    * to learn the mathematical methods of evalu-

    ating observations made from different loca-

    tions and, finally,

    * to get an impression and an own measure for

    the distance to the sun.

    Daylight side of the earth when

    Venus enters the sun:

    From this part of the world the

    1rst and 2nd contact can be

    observed.

    Pictures simultaneously taken 2004 from Essen (U. Backhaus),

    Germany (left), and Namibia (E. v. Grumbkow) (right)

    On June 5/6th, 2012 Venus will pass the sun's disc - an

    extremely rare event which happened already in 2004 but will

    not rerun until 2117. Those so called Venus transits played an

    important role for the determination of the distance between

    the sun and the earth, the so called Astronomical Unit (AU).