3rd April 2006 EAAS Meeting Report
Lights, Camera, Action! Observing time variable phenomenae in the Solar System

Neil McKeown started the meeting by giving a short talk about the Total Solar Eclipse in Turkey which he attended with the IFAS Trip and showed his photos of the event and gave views on what was a magnificent event.

Mark Stronge then introduced the main speaker Dr. Apostolos Christou, research astronomer at the Armagh Observatory, or Tolis as he prefers. His talk was on  “Lights, Camera, Action: Observing time-variable Phenomena in the Solar System” which dealt with eclipses, occultations and transits. He opened his talk by speaking about his professional work - orbital trajectories. He then explained how there are many different types of bodies constantly in motion in the solar system - planets, satellites, asteroids and comets and how the interaction of these bodies causes events such as eclipses, occultations and transits.

Apostolos then explained his motivations for doing what he does. Firstly he thinks it fun and showed an excellent picture of the occultation of Saturn by the moon in 2002 and secondly there is real scientific value to such events, for instance astronomers were able to determine the size of Charon, one of the moons of Pluto and the upper limit of the size of its atmosphere. He then went on to explain how results such as the one above are achieved through the use of a network of observers recording the event from different locations. Each person records the ingress and exgress times - the appearance and reappearance of the further body interacting with the nearer body. Such measurements can determine the size and/or shape of a body such as an asteriod or detect the presence of an atmosphere on a body such as the Charon example above. He went onto explain that such measurements are more robust than a simple magnitude measure especially for asteroids where assumptions of the albedo have to be made. The albedo measures how much light from the sun a body such as an asteriod reflects.

The next bit of the lecture dealt with mutual events. These occur at the time of the equinox when the sun is at the equator on a planet. For the gas giants in the outer solar system this means that their moons can hide each other from view from the perspective of an observer on the Earth. Such events include eclipses and transits. We were then showed videos of events in the Jovian system between 2002-03. 17 events were captured with the interaction of the 4 main moons - Io, Europa, Callisto and Ganymede. He went onto outline the next time for such interactions this time at Uranus. It goes through the equinox every 42 years and the period for mutual events starts later this year and lasts until 2009. It has 5 large satellites - Miranda, Ariel, Umbriel, Oberon and Titania. Obviously due to the long intervals between the times when Uranus is in the right position for such events, they have never been observed before. His predictions for the events can be found at www.arm.ac.uk/~aac/uranus . These events will be hard to observe as the brightest of the 5 moons is at 14th mag and Miranda is at 16th mag. Additionally the moons orbit reasonably close to the planet compared to Jupiter and their proximity to the planet makes observing the events harder.

The next stage dealt with how to actually observe these mutual events. It is a CCD only event, its too faint for visual observing. Apostolos then moved onto another area of interest to him - meteor observing. The observatory has a meteor station on its roof with 3 cameras - 1 medium angle and 2 wide angle lenses.  These cameras are used in collaboration with Robert Cobain’s camera in Bangor as a double station. The double station uses the fact that the same meteor can be observed from different locations and its orbit and radiant can be determined and to what shower the meteor belongs or whether it is a sporadic. Since June 2005, 1133 meteors have been observed by the cameras with 277 being observed by the double station. He then went on to explain that the sporadic rate tends to be lower in the winter and spring compared to the summer and autumn. We were then shown some lovely footage of the some meteors caught on the cameras. This was a very interesting lecture and many questions followed.

With the end of lecture, a short observing session occurred in the grounds of the school with a couple of telescopes being available to view the moon and other objects such as the Pleiades.

Until Next Month Clear Skies

Neill McKeown



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