Difference between revisions of "October 25, 2004"

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=Modeling Domes=
 
=Modeling Domes=
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<tr><td><div align="center" class="main_sm">Image Credit: [mailto:gibbidomine@libero.it Raffaello Lena] and Cristian Fattinnanzi, Fabio Lottero and KC Pau
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Image Credit: [mailto:gibbidomine@libero.it Raffaello Lena] and Cristian Fattinnanzi, Fabio Lottero and KC Pau
 
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<p align="left">Domes are one of the most difficult types of lunar objects to study quantitatively. Craters can have their diameters and depths measured fairly directly, but domes are such low and gently sloped features that it is very difficult to measure accurately their shadow lengths to derive topographic information. Members of the Geological Lunar Research Group have developed another way to approach this problem. They have mathematically investigated the relationship between how an ideal hemispherical dome's shadow length (R) varies with solar elevation and with its diameter (D) and height (H) ratio. The bottom part of the illustration shows the computed shadow lengths for various dome D/H ratios (and resulting slopes) against increasing solar elevation (alpha). The graph passes the common sense test - it shows that steep domes (D/H = 10) cast longer shadows and cast them at higher sun angles than low angle domes (D/H = 80). With this table you can estimate (or measure) which D/H value most matches a real dome. For the example of Milichius Pi (in the small excerpt from a KC Pau image taken when the sun was 1.2 degrees above Pi), the best fit is for D/H = 40, yielding a dome slope of 2.9 degrees and a height of about 200 m.</p>
 
<p align="left">Domes are one of the most difficult types of lunar objects to study quantitatively. Craters can have their diameters and depths measured fairly directly, but domes are such low and gently sloped features that it is very difficult to measure accurately their shadow lengths to derive topographic information. Members of the Geological Lunar Research Group have developed another way to approach this problem. They have mathematically investigated the relationship between how an ideal hemispherical dome's shadow length (R) varies with solar elevation and with its diameter (D) and height (H) ratio. The bottom part of the illustration shows the computed shadow lengths for various dome D/H ratios (and resulting slopes) against increasing solar elevation (alpha). The graph passes the common sense test - it shows that steep domes (D/H = 10) cast longer shadows and cast them at higher sun angles than low angle domes (D/H = 80). With this table you can estimate (or measure) which D/H value most matches a real dome. For the example of Milichius Pi (in the small excerpt from a KC Pau image taken when the sun was 1.2 degrees above Pi), the best fit is for D/H = 40, yielding a dome slope of 2.9 degrees and a height of about 200 m.</p>
 
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<p align="right">&#8212; [mailto:tychocrater@yahoo.com Chuck Wood]</blockquote>
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<p align="right">&#8212; [mailto:tychocrater@yahoo.com Chuck Wood]</p></blockquote>
 
<p align="left"><b>Related Links:</b><br>
 
<p align="left"><b>Related Links:</b><br>
 
[http://www.glrgroup.org/news/18.htm GLR Group]
 
[http://www.glrgroup.org/news/18.htm GLR Group]
 
<br>[http://www.glrgroup.org/domes/artificialdome.htm Lunar Domes and Artificial Domes: Two Tools for Lunar Observers (also published in <i>Selenology</i> vol 23 n.2; 2004)]
 
<br>[http://www.glrgroup.org/domes/artificialdome.htm Lunar Domes and Artificial Domes: Two Tools for Lunar Observers (also published in <i>Selenology</i> vol 23 n.2; 2004)]
<p align="left"><b>Tomorrow's LPOD: </b> Eclipse Preview</p>
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</p>
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<p><b>Yesterday's LPOD:</b> [[October 24, 2004|A Long, Cold Mare]] </p>
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<p><b>Tomorrow's LPOD:</b> [[October 26, 2004|Eclipse Preview]] </p>
 
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<p align="center" class="main_titles"><b>Author &amp; Editor:</b><br>  
 
<p align="center" class="main_titles"><b>Author &amp; Editor:</b><br>  
 
[mailto:tychocrater@yahoo.com Charles A. Wood]</p>
 
[mailto:tychocrater@yahoo.com Charles A. Wood]</p>
<p align="center" class="main_titles"><b>Technical Consultant:</b><br>
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[mailto:anthony@perseus.gr Anthony Ayiomamitis]</p>
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<p align="center" class="main_titles"><b>Contact Translator:</b><br>
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[mailto:pablolonnie@yahoo.com.mx Pablo Lonnie Pacheco Railey]  (Es)<br>
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[mailto:chlegrand@free.fr Christian Legrand] (Fr)</p>
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<p align="center" class="main_titles"><b>[mailto:webuser@observingthesky.org Contact Webmaster]</b></p>
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<p align="center" class="main_titles"><b>A service of:</b><br>
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[http://www.observingthesky.org/ ObservingTheSky.Org]</p>
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<p align="center" class="main_titles"><b>Visit these other PODs:</b> <br>
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[http://antwrp.gsfc.nasa.gov/apod/astropix.html Astronomy] | [http://www.msss.com/ Mars] | [http://epod.usra.edu/ Earth]</p>
 
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Latest revision as of 15:20, 15 March 2015

Modeling Domes

LPOD-2004-10-25.jpeg

Image Credit: Raffaello Lena and Cristian Fattinnanzi, Fabio Lottero and KC Pau


Modeling Domes

Domes are one of the most difficult types of lunar objects to study quantitatively. Craters can have their diameters and depths measured fairly directly, but domes are such low and gently sloped features that it is very difficult to measure accurately their shadow lengths to derive topographic information. Members of the Geological Lunar Research Group have developed another way to approach this problem. They have mathematically investigated the relationship between how an ideal hemispherical dome's shadow length (R) varies with solar elevation and with its diameter (D) and height (H) ratio. The bottom part of the illustration shows the computed shadow lengths for various dome D/H ratios (and resulting slopes) against increasing solar elevation (alpha). The graph passes the common sense test - it shows that steep domes (D/H = 10) cast longer shadows and cast them at higher sun angles than low angle domes (D/H = 80). With this table you can estimate (or measure) which D/H value most matches a real dome. For the example of Milichius Pi (in the small excerpt from a KC Pau image taken when the sun was 1.2 degrees above Pi), the best fit is for D/H = 40, yielding a dome slope of 2.9 degrees and a height of about 200 m.

Chuck Wood

Related Links:
GLR Group
Lunar Domes and Artificial Domes: Two Tools for Lunar Observers (also published in Selenology vol 23 n.2; 2004)

Yesterday's LPOD: A Long, Cold Mare

Tomorrow's LPOD: Eclipse Preview



Author & Editor:
Charles A. Wood


COMMENTS?

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