Our autumn almanac 15.10.2010 – 21.10.2010

The Orionid Meteor Shower
Late at night in this seven day period you will be able to see the star pattern Orion. Between 11 o’clock and midnight, if you look towards the east, and then a little to the south, you will see the constellation of Orion the Hunter rising over the trees and roof tops on your horizon. Some exciting astronomical events will start to happen in this part of the sky from October 15 – 25, a meteor shower, or shooting stars.

To find Orion in the clear night sky look for three stars in a row which marks the hunter’s belt. The shooting stars you might see this week are called the Orionid meteors, because they appear to come from the hunter’s club formed by a scattering of faint stars. The shooting stars of Orion are bright sparks of ice, dust and small stones burning as they pass through the Earth’s atmosphere. They are fragments left floating in space by a comet called Halley’s comet. If you are lucky enough to see a few of these shooting stars, you will see they glow with varied colours. Some make a long trail in the night sky. This is called the meteor’s train. Looking forward to the night of October 21 is a night when you can expect to see up to 30 shooting stars per hour, however the almost-full waxing gibbous moon makes 2010 an unfavorable year for watching this Orionid meteor shower, and the moon is leaving only a narrow window for observing Comet Hartley 2 at its brightest around now.

Comet 103P Hartley from as seen from a four inch telescope, October 6th, 2010.

The comet passed within 0.12 AU of the Earth on October 20, 2010, only eight days before coming to perihelion (closest approach to the Sun) on October 28, 2010. In early November the comet will be visible around midnight without interference from the Moon.

The Deep Impact spacecraft, which had previously photographed Comet Tempel 1, is now being reused by NASA to study Hartley 2. The initial plan was for a flyby of Comet Boethin. However, astronomers found that Boethin was too faint to be observed, and its orbit could not be calculated with sufficient precision to permit a flyby. NASA retargeted the spacecraft toward Hartley 2 instead.

Deep Impact is a NASA space probe launched on January 12, 2005. It was designed to study the composition of the comet interior of 9P/Tempel, by releasing an impactor into the comet. At 5:52 UTC on July 4, 2005, the impactor successfully collided with the comet’s nucleus. The impact excavated debris from the interior of the nucleus, allowing photographs of the impact crater. The photographs showed the comet to be more dusty and less icy than had been expected. The impact generated a large and bright dust cloud, which unexpectedly obscured the view of the impact crater.

The Deep Impact mission was planned to help answer fundamental questions about comets, which included what makes up the composition of the comet’s nucleus, what depth the crater would reach from the impact, and where the comet originated in its formation. By observing the composition of the comet, astronomers hoped to determine how comets form based on the differences between the interior and exterior makeup of the comet. Observations of the impact and its aftermath would allow astronomers to attempt to determine the answers to these questions.

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