Vesta and Saturn on the Move



It so happened that on 19th March 2002 the asteroid Vesta was in near conjunction with the planet Saturn. Even though the two are at enormously different distances from us, Saturn at some 1200 million km and Vesta at around 400 million km, from our point of view they looked as if they were almost hailing each other. Good photo opp! All the images below were taken with a Canon EOS D30 digital SLR camera and a Celestron Ultima 2000-8" telescope, at prime focus (2030 mm, f10). Exposure was 4 seconds at ISO 1600. To get a good feel of the "dance of the spheres", I wished to capture the motion of the planet, its many moons and Vesta, all against the star background. Recall that the stars themselves rise and set, just to complicate life! In three hours they trace a 45 degree arc across the sky. Consequently the telescope had to be mounted in equatorial mode, tracking the sky. Next we have to determine our desired "fixed" frame of reference. Unfortunately Saturn and Vesta just happened to be in a part of the sky with no bright stars. The nearest were a couple of magnitude 9 stars. The numbers next to the two stars below are their magnitudes:

 Luckily the 4 second exposure was enough to show them clearly. These stars were therefore included in all the photos (later cropped off) and constituted the reference origin. So here below are the spheres dancing between 1918 and 2200 Oman Time (1518 and 1800 UT). Interesting that even over such a brief, 3-hour period there is quite perceptible movement of Saturn and its moons against the star background. As for Vesta, it's whizzing by!  The edges of the animation represent the fixed star background:

Saturn has a great many moons but only the brightest ones have been captured in the above photos. Brightness magnitudes are shown next to the moons' names. Vesta is the brightest known asteroid and was the fourth to be discovered. Saturn itself is extremely bright at magnitude -0.3. Consequently it is hopelessly over-exposed.

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