Results of analysis of Mercury transit data

		of November 15, 1999

			for the

		Mees White Light telescope

The MWLT was run at 1 minute cadence during the transit.  A total
of 39 images have the disk of Mercury fully on the solar disk and
well measured.

All known systematic effects have been included in the analysis,
including parallax and differential refraction.


	IMAGE SCALE   -----------------------------------------------------

There are 3 measures of the image scale:

	1) Solar radius 

	This method is "absolute" and sensitive to limb definition.
From 52 images, the scale is 

		2.3409 (+/- 0.0002) arc sec per pixel

The error quoted is only from random error fromthe scatter of the radius value.


	2) Rate of Mercury-Sun motion

	This method is differential, so a systematic in the limb
definition should be less important.  The result is

		2.3268 (+/- 0.004) arc sec per pixel

The error quoted is only from random error in the positions of Mercury.

	3) Mercury-Sun separation

	This is also differential.  The result is

		2.3322 (+/- 0.0007) arc sec per pixel

The error quoted is only from random error in the positions of Mercury.


	A weighted average of the differential methods gives

		2.332 arc sec per pixel  ***********

and implies a systematic error of the limb definition by about 1 part
in 260, or about 1.5 pixels.

	
	ROLL ANGLE   -----------------------------------------------------

There are 2 measures of the roll angle:

	1) Angle of the Mercury track measured N from W (CCW)

	The EW, NS motions were fit linearly over time and 
the angle of the fitted velocity found.  The result for the
difference angle is

		0.00324 (+/- 0.001 )  radians

measured east from Earth north to instrument north. The quoted error
is from random error in the observed angles only.



	2) Angle of Mercury measured N from W (CCW)

	The angle of Mercury from the ephemeris was fit to
a quadratic and compared to the angle in the instrumental system.
The result is

		-0.00343 (+/- 0.0002 ) radians

measured east from Earth north to instrument north.  The quoted error
is from random error in the observed angles only.


	A weighted average of the two methods gives

		-0.00318 radians  ***************

or about 12 arc min.



	SUMMARY   -------------------------------------------------------

	The direct measurements of the track of Mercury give limited
precision because the track was short.  The measurements of the
track location relative to disk center work better because that
distance is longer.

	The results of this analysis have been incorporated into the
IDL procedures MWLT_PIXEL_SCALE and MWLT_ROLL_ANGLE.


Barry LaBonte 
November 29, 1999

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