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Teaching Tips and National Science
Education Standards
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Other Things to Do and Notice
 |
| Here
are two people holding transparencies with marks representing
Venus. Their partners are directing them to move their transparencies
so that they can see a transit. (Click to download larger image.) |
•
How large does the paper plate seem to be when standing at
Earth’s position? The student representing Earth should
hold his/her arm straight out and compare the size of the paper plate
to the fingers of his/her hand. If you have constructed your model
accurately, the paper plate should be much smaller than the tip of
a pinkie. (For most people, the paper plate will be about the size
of half the tip of a pinkie.) The apparent size of this model is equal
to the size of the real Sun in the real sky. But don’t
try looking at the Sun to check your answer.
• When you've lined up the Sun and Venus using one eye,
try closing that eye and opening the other. You’ll
notice that the position of “Venus” against the “Sun”
has shifted. You may even find that Venus is no longer transiting
the paper plate.
• How far to the right and left (or up and down) can
the student holding Venus move the mark on the transparency and still
“transit” the distant paper plate representing the Sun?
In this model, 1 inch (2.5 cm) of movement = 96,850 miles (155,864
km).
What’s
Going On?
We don't see a transit of Venus every time Venus passes between Earth
and the
Sun, which happens about every 584 days or 1.6 years. That's because
Venus
does not orbit in the same plane as Earth. Compared to Earth's orbit,
Venus's orbit is inclined at about 3.5°. This takes Venus as much
as 3.3
million miles above the orbital plane of Earth—much too high
above Earth's orbital plane to transit the sun. To appear to transit
the sun, Venus has to nearly cross the Earth's orbital plane. That
happens about twice every century (usually a pair of transits eight
years apart), making a transit of Venus a very rare astronomical event
indeed.
Our
thanks to the wonderful teachers of Shasta County’s Project
ARISE for helping us pilot test this activity.
Going Further
Web Sites:
A great animation showing the transit of Venus can be found at the
following NASA site:
http://svs-f.gsfc.nasa.gov/%7Ewfeimer/SEC/Gen_SEC/IP/Transit.mpg
A really wonderful description of the importance of Venus transits
to astronomers (written by Edna Devore, SETI Director of Education
and Public Outreach) can be found at this Web site:
http://space.com/searchforlife/seti_transits_030904.html
A comprehensive list of Web sites devoted to Venus transits of the
past can be found at:
http://www.transitofvenus.org/historic.htm
An excellent description of the transit of Venus that will occur on
June 8, 2004 (written by Fred Espenak) can be found at this Web site:
http://sunearth.gsfc.nasa.gov/eclipse/OH/transit04.html
Here’s a link to a wonderful Venus transit activity that uses
a paper plate to create a model of the orbits of Earth and Venus around
the Sun:
http://analyzer.depaul.edu/paperplate/Transit%20of%20Venus/Introduction.htm
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