Permission to Dream
Mission 5: Venus, Earth's Twin?
Teacher's Guide
Dear Teachers,
As always, thank you for taking part in Permission to Dream's international
astronomy program. Our fifth mission is based on the planet Venus, and the qualities that
make it different from Earth. The goal of this Venus mission has many parts:
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Use the Permission to Dream telescope to locate and examine Venus,
noting its phases over a period of two weeks.
Explain the phases of the planet Venus.
Give factual physical information about Venus.
Introduce the students to the mythological character of
Venus/Aphrodite.
Introduce the students to Carl Sagan, who is not only a noted scientist,
but also a great educator.
We are providing you with extra background information and the answers to some of the
more concrete questions that we pose in the mission. Thanks very much.
Sincerely,
Permission to Dream Team
Selected Answers to Mission 5 Questions
*Disclaimer: We created our questions to allow for a great deal of creativity. Other answers (not seen
below) to our questions are not necessarily incorrect.
1. Why is Venus the brightest planet in the sky?
The clouds that cover the entire planet of Venus reflect sunlight, and this makes
Venus the brightest planet in the sky.
2. Why hasn't anyone landed on Venus?
Extreme temperatures and pressure are the two main items preventing us from
landing on the surface of Venus. Temperatures reach over 400 degrees Celsius
and the surface pressure is 90 times greater than that of Earth. When we send
probes to Venus, they only last several hours before the intense pressure crushes
them.
3. Mercury is the closest planet to the sun. Even so, it is not as hot as Venus, where lead
melts on the surface. Explain why Venus is hotter than Mercury, even though it’s
farther away from the sun.
Venus harbors something called a “greenhouse effect.” The extremely dense
atmosphere lets the sun’s heat in, but doesn’t let the heat escape the planet. Due
to the greenhouse effect, Venus’ surface is hotter than Mercury’s, even though
Venus is more than twice as far away from the sun.
4. Explain why we see Venus in different phases.
Venus travels around the Sun like all planets do. Since its orbit is smaller than the
Earth's, Venus can go through dramatic phases just like the Moon does. When
Venus is on the far side of the Sun, we see the entire near side lit by the Sun. But
then it is as far away as it gets, nearly 300 million kilometers away. When it is on
the near side of the Sun, it shows a beautiful thin crescent, because it is between
the Sun and us and we see the mostly unlit dark half. Even though less of Venus is
lit percentage-wise when it is a crescent, it is over six times closer to the Earth at
this point, so it looks much bigger. At a mere 50 million kilometers away, the
amount of lit planet we actually see is much larger then when it is full, and so it
appears brighter.
To see this for yourself, draw a circle one centimeter across, then, next to it, draw
a circle 6 centimeters across. The small circle represents Venus when it is on the
far side of the Sun, and the big circle is when it is nearby. Now draw an arc inside
the big circle so that it looks like a crescent Moon, making the thickest part of the
crescent one centimeter thick. Compare the area of the crescent with the area of
the small circle. You can see why Venus is so bright right now! Much more
apparent area of it is lit and so it looks brighter.
Related Links:
http://www.badastronomy.com/bitesize/venus_phase.html
http://www.badastronomy.com/bitesize/solar_system/venus.html
http://solarsystem.nasa.gov/features/planets/venus/venus.html
http://www.mythweb.com/encyc/entries/aphrodite.html
http://www.seds.org/billa/tnp/venus.html
http://amesnews.arc.nasa.gov/releases/2002/02_60AR.html
http://www.geocities.com/ResearchTriangle/System/8870/books/WashPostR.html