April 19, 2019

AstroEvent: A Bright Dawn Comet.

 

Created with NASA/JPL Ephemeris generator).

Created with NASA/JPL Ephemeris generator).

 

   The dawn skies of October hold a special treat; a possible bright morning comet. 103/P Hartley 2 approaches perihelion on October 28, 2010. Earlier in the month sees it beginning its long dive through dawn skies. Northern hemisphere viewers will have the best view, as the comet passes through the constellations Cassiopeia, Perseus, Auriga, and Gemini in the month of October. Maximum predicted brightness is +4.5 on October 18th, and the comet will be circumpolar for much of the month and well placed for northern viewers. New Moon is October 7th, and Full is on October 23rd, meaning it will be washed out except for viewing from dawn skies on the dates in between. Comet 103P/Hartley 2 was discovered March 1986 by Malcolm Hartley on an observing run at Siding Spring, Australia. It is short period comet, with an orbit of 6.47 years and a perihelion of 1.06 AU and an aphelion of 5.89 AU. If that distance sounds familiar, that’s because it is; Comet Hartley had its orbit altered and shortened by the planet Jupiter on its discovery approach. Any object inbound to the inner solar system has about an estimated 40% chance of this occurring. Do set your alarm to welcome this cosmic visitor and new resident of the inner solar system to our dawn skies!    

The astro-term for this week is Ion Tail. As a comet approaches the inner solar system, its icy nucleus becomes subject to the intensifying solar wind and radiational pressure sublimating material and sweeping back a grand tail. The dust tail of a comet can be long and curved, while an ion tail may also be seen, straighter and pointing off in an anti-sunward direction. Less often, a spiky sunward anti-tail may be seen, pointing back towards the Sun. This can occur because our viewing geometry may actually allow us to peer around and see the dust tail streaming off from the other side. The ion tail particles tend to be charged by the solar winds, and follow the magnetic lines of force outward. Anyone who caught a glimpse of Comets Hyakutake and Hale-Bopp in the 90’s remembers the magnificent displays they produced as well as the glorious twin ion and dust tails they presented… Will Comet 103/P Hartley 2 give us another study in comet anatomy this fall?

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