Analysis of past comet apparitions

96P/Machholz

2007


Comet 96P/Machholz, dynamically very interesting but always very difficult to observe, will pass perihelion at the beginning of April 2007. Expected to reach 2 mag it will then be much too near the sun to be observable from earth (but will pass the field of view of the SOHO satellite). Terrestrial observers could succeed around Apr. 15, when the comet will appear very low above the northeastern horizon at an expected brightness of about 7 mag. During the next weeks it will rapidly gain altitude (due to its movement from Pisces towards Pegasus), but will fade equally rapidly, reaching magnitude 10 during the first week of May.

During the days around perihelion comet Machholz was visible in the SOHO images as a small comet with a nice tail. Already on Apr. 10, Michael Jäger could take the first photograph, which not only showed a brighter narrow gas tail but also - near the coma - a broad dust tail.

Despite the unfavorable circumstances 7 visual observations by 3 members of the German Comet Section were received - mainly because of the very nice weather during the week when the comet appeared in the morning sky. Additional 55 international observations (including a greater number by Don Machholz himself) could be used for a first analysis. They show the expected rapid fading of the comet after perihelion according to the formula

m = 12.0m + 5×log D + 10.7×log r

yielding a perihelion brightness of about 2.5 mag and a terrestrially observable maximum brightness of 7.5 mag (Apr. 14). At the end of June the comet had already faded to 13.5 mag!

Total Brightness and Coma diameter

In parallel the coma diameter decreased from 4' (125.000 km) at the beginning of the apparition to only 0.8' (20.000 km) at the end. The same is true for the degree of condensation, which decreased from DC 5 to DC 0. During the first weeks the coma showed a significantly brighter inner part, which measured half of the entire coma diameter.

Andreas Kammerer

FGK observations


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