LtE in CMO #250

From Richard SCHMUDE

@. . . . . . Thank you for continuing to send me the CMO newsletters.

Enclosed are copies of more Mars drawings that I have made during the past month. It appears that the dust has now covered the entire planet. My observation last night shows that the dust storm May be beginning to clear in the areas south of ~20S. The dark areas in this area were darker than Syrtis Major last night but this was not the case a month ago.

I have continued to make photometric measurements of Mars and that planet remains about 0.3 magnitudes brighter than predicted in the Astronomical Almanac. Mars has also about 10-20% redder than what is predicted. The B-V value for August 23 and August 24 were +1.69 and +1.79. The B-V is Blue magnitude minus the Visual (green) magnitude; a positive B-V value means that Mars is brighter in the Visual filter than in the Blue filter. If Mars did not have any dust then the B-V value would be around +1.55.

Finally I have begun making whole-disc polarimetric measurements of Mars. My measurement on August 22 was +0.860.08%, which is much lower than the +2.9% that a dust-free Mars would have at the solar phase angle of 44. Audouin Dollfus measured a value of +0.9% polarization for Mars at a solar phase angle of 41during the great dust storm of 1971. These polarization results suggest that the 2001 dust storm May have been as intense as the 1971 dust storm.

In spite of the size of the current dust storm, I have been able to see the classical dark areas on Mars with my 4-inch refractor and a W15 yellow filter. The yellow filter has helped me see the dark areas better.

I hope that this report helps you. Have a good week.

(24 August 2001)

Richard W SCHMUDE Jr ( GA , USA)

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