Astronomical Unit

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DETAILED DEFINTION

 Did you know that the distance between the Earth and the Sun is approximately equal to 1 astronomical unit? Atsronomical units are very useful when it comes to measuring very far distances in space. In case you still don't understand how long 1 A.U. (astronomical unit) is I will give you another comparison. 1 A.U. is equal to 149,598,000 kilometers!

    Originally, the AU was defined as the length of the (1)semi-major axis of the Earth's elliptical orbit around the Sun. In 1976, the International Astronomical Union revised the definition of the AU for greater precision, defining it as the distance from the center of the Sun at which a particle of negligible mass, in an unperturbed circular orbit, would have an orbital period of 365.2568983 days one Gaussian year. 

1.The semi-major axis is one half of the major axis, and thus runs from the center of the planet, start, etc., and to the edge of the ellipse.

HISTORY

 The astronomical unit has an interesting history. It started with Tycho Brache estimating the distance between the Earth and Sun as 8 million km. Later on the AU was estimated as 24 million kilometers by Johannes Kepler. Even though these estimates were far off they still greatly contributed to the accurate answer. In 1672, Giovanni Cassini made a closer estimate of 140 million km by observing Mars from Paris and having a colleage, Jean Richer, also observe in the French Guiana. This helped because it allowed them to determine the parallax of Mars with enabled them to calculate the distance from Earth to Mars then Earth to the Sun. Soon after new methods were devloped which is why we have an exact calculation today.

WANT TO KNOW MORE? (so what section)

 An astronomical unit is a measurement that is used for measuring great distances in space. This term is very useful to us while we our doing this unit because we are studying the solar system. When studying the solar system you should know roughly how far the planets are from each other. When you  use astronomical units it is easy to understand the distances in space because one astronomical unit is about equal to 150,000,000 kilometers and we are very familiar with kilometers. The solar system unit will help us to understand this word because we will be seeing this word in our textbooks when we are reading about the solar system and we should be able to understand what we are reading. NASA uses the astronomical unit as well because they need to know the distances between each of the planets especially when they are sending rovers to Mars. It is useful to understand astronomical units because they are used every day in the subject of space and the solar system.

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BIBLIOGRAPHY

 (This site is useful for finding out how to calculate the astronomical unit)

Ask an Astrophysicist. NASA.January 22, 1998. David Palmer. April 30, 2008

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980122b.html

(this site is useful for finding a wide range of info. on the AU)

Astronomical Unit. Wikipedia. May 5, 2008

http://en.wikipedia.org/wiki/Astronomical_unit

(this site also gives a wide range of info. on the AU)

Astronomical Unit. NASA. May 6, 2008. Site Manager: Don Yeomans. May 6,2008

http://neo.jpl.nasa.gov/glossary/au.html

(I found a nice example of the AU on this site)

Measuring Angular and Physical Sizes. Aeree's and Ben's Astronomy Lab. December 3, 2001. Aeree Chung Ben Johnson. April 29,208

(exact image)http://www.astro.columbia.edu/~archung/labs/fall2001/images/parallax.jpg

(webpage image is showed on)

www.astro.columbia.edu/archung/labs/fall20001

(this site was useful because it provided a basic, easy to understand image)

The Great Pyramid: metamorphose of the architexture. Archiseek online architexture resources. November 13, 2006. Vidusa-website member. April 30, 2008

(web page image is showed on)

www.olemiss.edu/astronomicalunit

(this textbook provides a good defintition and more info.)

Leigh Ann Garcia. Holt Science and Technology. Orlando, Fl. Holt, Rinehart and Winston. 2006

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