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<DIV><FONT face=Arial size=2>Dear All,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>This was done a little over a year ago in a
collaboration between the Garden Route Centre of the ASSA and the University of
Milan, the results were published in the European Journal of
Physics</FONT></DIV>
<DIV><FONT face=Times-Roman size=1>
<P><FONT size=3>Eur. J. Phys. </FONT></FONT><B><FONT face=Times-Bold>30
</B></FONT><FONT face=Times-Roman size=1><FONT size=3>(2009)
35–46</FONT></FONT></P>
<P><FONT face=Arial size=2>Kind regards</FONT></P>
<P><FONT face=Arial size=2>Case</FONT></P>
<P><FONT face=Arial
size=2>********************************************************<BR>Case
Rijsdijk
Tel: +27 44 877 11
80<BR>"Entilini"
Fax +27 0866 844 195<BR>1156 Langvlei
Ave. Cell: +27 83 444 24
94<BR>Kingfisher
Close
e-mail: <A
href="mailto:particles@mweb.co.za">particles@mweb.co.za</A><BR>Wilderness
6560<BR>South
Africa
"Enough is a
feast"<BR>********************************************************<BR></FONT></P>
<P> </P>
<P><FONT face=Arial size=2></FONT> </P>
<P><FONT face=Times-Roman size=1><FONT size=3></FONT> </P></FONT></DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=hettlage@saao.ac.za href="mailto:hettlage@saao.ac.za">Christian
Hettlage</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=astronet@mail.saasta.ac.za
href="mailto:astronet@mail.saasta.ac.za">astronet discussion group</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, October 06, 2009 11:20
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [AstroNet] Fwd: Measuring the
Astronomical unit by parallaxmeasurement on Mars</DIV>
<DIV><BR></DIV>
<DIV>Dear All,</DIV>
<DIV><BR></DIV>
<DIV>Please find below an opportunity for measuring the distance to Mars.
Please contact John directly in case you are interested. Thanks!</DIV>
<DIV><BR></DIV>
<DIV>Kind regards,</DIV>
<DIV><BR></DIV>
<DIV>Christian</DIV>
<DIV><BR></DIV>
<DIV>
<BLOCKQUOTE type="cite">
<DIV style="MARGIN: 0px"><SPAN
style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'"><B>Von: </B></SPAN><SPAN
style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'">"John Clark"
<><BR></SPAN></DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'"><B>Datum:
</B></SPAN><SPAN style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'">3.
Oktober 2009 14:53:32 GMT+02:00<BR></SPAN></DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'"><B>An: </B></SPAN><SPAN
style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'"><<A
href="mailto:assa@saao.ac.za">assa@saao.ac.za</A>><A
href="mailto:john.clark@johnclarkastronomy.co.uk">john.clark@johnclarkastronomy.co.uk</A><BR></SPAN></DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'"><B>Betreff:
</B></SPAN><SPAN
style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'"><B>Measuring the
Astronomical unit by parallax measurement on Mars</B><BR></SPAN></DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'"><B>Antwort an:
</B></SPAN><SPAN style="FONT-SIZE: medium; FONT-FAMILY: 'Helvetica'"><<A
href="mailto:john.clark@johnclarkastronomy.co.uk">john.clark@johnclarkastronomy.co.uk</A>><BR></SPAN></DIV><BR><O:SMARTTAGTYPE
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<DIV class=Section1>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Dear
Sir,<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">I am a UK-based amateur
astronomer with an interest in solar system measurements. I have spent
some time over the last few months estimating the length of the astronomical
unit by timing eclipses of Jupiter’s moon Io, essentially reversing an
observation by Roemer who discovered the finite speed of light by timing
such eclipses. I measured the speed of light in a university
laboratory, and back-calculated the AU from my own observations of Io over a
couple of years.<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">This method worked, but it is
difficult to get an accurate value. My value was 20% low compared to
the accepted value.<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">My impression is that the method
of Cassini and Richer (1672) is likely to be more accurate, but it requires
simultaneously measuring and comparing the position of Mars from two faraway
locations on Earth. This measurement would have to be done to within
at least one second of arc. This is not as hard as it sounds, but it
obviously isn’t trivial.<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">I wondered if there is anyone in
<ST1:COUNTRY-REGION w:st="on"><ST1:PLACE w:st="on">South
Africa</ST1:PLACE></ST1:COUNTRY-REGION> who is interested/crazy enough to
collaborate with me to try this measurement during the forthcoming
opposition of Mars? It would then be at its closest to Earth, so that
the parallax would maximise.<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Based on a rough estimate, it is
about 10,000 km from the <ST1:COUNTRY-REGION w:st="on"><ST1:PLACE
w:st="on">UK</ST1:PLACE></ST1:COUNTRY-REGION> to SA over the Earth’s
surface, so the chord length (straight line distance) is about 9,000
km. Mars will be at about 100,000,000 km away at its closest approach,
so we are looking for a parallax of 9,000 parts in 100,000,000 or about 18.6
arc seconds. A measurement good to 1 arc second would therefore have an
error of 1 in 18.6 or 5.4%. Obviously a measurement good to 0.5 arc
sec would have half that error. With good amateur equipment that
should be feasible. <O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">I can help with the maths needed
to post-process the photos.<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Yours
sincerely,<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">John.<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><O:P></O:P></SPAN></FONT></P>
<DIV>
<P class=MsoNormal><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma">Dr John D.
Clark<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><O:P></O:P></SPAN></FONT></P>
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face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma">323 Wootton
Road</SPAN></FONT></ST1:ADDRESS></ST1:STREET><FONT face=Tahoma color=blue
size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><ST1:PLACE w:st="on"><FONT face=Tahoma color=blue
size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma">King's
Lynn</SPAN></FONT></ST1:PLACE><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><O:P></O:P></SPAN></FONT></P>
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face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma">Norfolk</SPAN></FONT></ST1:CITY></ST1:PLACE><FONT
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<O:P></O:P></SPAN></FONT></P>
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style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma">England</SPAN></FONT></ST1:PLACE></ST1:COUNTRY-REGION><FONT
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style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma">PE30
3AX<O:P></O:P></SPAN></FONT></P>
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style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma">+44 1553
679378<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><A
href="x-msg://15/john.clark@johnclarkastronomy.co.uk">john.clark@johnclarkastronomy.co.uk</A>
<A
href="http://www.johnclarkastronomy.co.uk/">http://www.johnclarkastronomy.co.uk</A>
<O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><O:P></O:P></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><A
href="http://www.springer.com/astronomy/book/978-0-387-89560-4">Measure
Solar System Objects and their Movements for Yourself! by John D.
Clark</A><O:P></O:P></SPAN></FONT></P></DIV>
<DIV style="MARGIN: 0cm 0cm 0pt"><FONT face=Tahoma color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Tahoma"><O:P></O:P></SPAN></FONT></DIV>
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style="FONT-SIZE: 12pt"><O:P></O:P></SPAN></FONT></P></DIV></DIV></O:SMARTTAGTYPE></O:SMARTTAGTYPE></O:SMARTTAGTYPE></O:SMARTTAGTYPE></O:SMARTTAGTYPE></BLOCKQUOTE></DIV><BR>
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