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# Planets of the Solar System

## The eight planets of the solar system with increasing distance from the sun have larger orbits.

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Transit of Venus

### Transit of Venus

Credit: Gestrgangleri
Source: http://en.wikipedia.org/wiki/File:20040608_Venus_Transit.JPG
License: CC BY-NC 3.0

Very rarely, Venus comes between Earth and the Sun. This is like a solar eclipse except that Venus is so small not much of the Sun is covered.

#### Why It Matters

Credit: NASA
Source: http://en.wikipedia.org/wiki/File:Venuspioneeruv.jpg
License: CC BY-NC 3.0

Venus's clouds - Ultraviolet image taken by Pioneer Venus Orbiter (1979) [Figure2]

• Viewed from Earth, Venus usually passes above or below the Sun.
• Johannes Kepler calculated the distances of the planets to the Sun relative to Earth’s distance. He called this one AU. However, he didn’t know the value of one AU.
• Edmund Halley used the transit of Venus to calculate one AU. Using this information, the distances of the planets from the Sun could be calculated.
• The first of two transits was in 2004, the second in 2012. The next transit will not be until 2117.

#### Explore More

With the links below, learn more about Venus. Then answer the following questions.

1. Why don’t we see a transit of Venus each time that planet comes between us and the Sun?
2. How frequently do we see transits of Venus?
3. How did early astronomers determine that Venus has an atmosphere?
4. What did Halley need to know to calculate the value of one AU?

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### Image Attributions

1. [1]^ Credit: Gestrgangleri; Source: http://en.wikipedia.org/wiki/File:20040608_Venus_Transit.JPG; License: CC BY-NC 3.0
2. [2]^ Credit: NASA; Source: http://en.wikipedia.org/wiki/File:Venuspioneeruv.jpg; License: CC BY-NC 3.0

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