Published on January 16, 2008
AnnouncementsWed, Dec 6: Announcements Wed, Dec 6 Final exam update Reminder: Thurs (Dec 14) 9:45 am – 11:45 am LR 70 Format: 50% (75pts) conceptual, factual – closed book, 9:45am – 10:30am Hand in part 1 at 10:30am 50% (75 pts) computational, open book 10:30am – 11:45am I will gone all next week (Zach will proctor exam) Today’s lecture Comets, meteors Begin Millionaire astronomer review quiz: rules If reach $64,000, a contestant wins $6 Bruegger’s lunch card Anyone who answers the team reaches $1,000,000, gets a 100% on the final exam (must start below $64,000). Historical Comets: Comet Halley (period 76 yr-79 yr): Historical Comets: Comet Halley (period 76 yr-79 yr) Edmond Halley (1656-1741). He witnessed the comet in 1683, and predicted its return in 1705. Unfortunately he died before next the apparition in 1759. Halley’s Comet: Bayeaux Tapestry: Halley’s Comet: Bayeaux Tapestry Edward the Confessor in 1064, informing Earl Harold that he must leave for Normandy to pay homage to Duke William and to confirm the agreement made between Edward and William in 1051 that William shall be king of England on Edward's death. Bayeux Tapestry : part 2: Bayeux Tapestry : part 2 The day following the death of Edward the Confessor, Harold's coronation took place in Westminster Abbey, the first king to be enthroned there. This was completely in violation of Edward’s agreement with Duke William of Normandy. Bayeux Tapestry : part 3: Bayeux Tapestry : part 3 The news of Harold being crowned King of England angered and infuriated William. After persuading his Counts and Barons to join him on this crusade, of which he had also managed to acquire Papal support, he sets about constructing ships to invade England. This image shows the construction of those ships. Note how similar they are to Viking longboats Bayeux Tapestry : part 4: Bayeux Tapestry : part 4 William joining his fleet that would probably now be at St Valery sur Somme, awaiting ideal conditions to sail across the English Channel and the start of the invasion. Bayeux Tapestry: part 5: Bayeux Tapestry: part 5 Halley's comet, first seen on the 24th April 1066, and considered by the Saxons to be a bad omen. At right, King Harold is told of the sighting of the comet. Omens were taken very seriously in those days. © copyright Glen Ray Crack - Battle - East Sussex - United Kingdom Submitted 10th January 1998 1998 - 1999 - 2000 - 2001 - 2002 Bayeux Tapestry: part 6: Bayeux Tapestry: part 6 © copyright Glen Ray Crack - Battle - East Sussex - United Kingdom Submitted 10th January 1998 1998 - 1999 - 2000 - 2001 - 2002 The battle of Hastings, May 1066, showing King Harold (center) trying to remove an arrow from his eye. The Normans later found him dead and hacked up his body. Present (2006) position of Comet Halley: Present (2006) position of Comet Halley Comet Halley’ orbit: retrograde and Inclined: Comet Halley’ orbit: retrograde and Inclined Short-period comet (76 yr) Eccentricity 0.967 Perihelion 0.59 AU, aphelion 35 AU Probably originated in Kuiper belt Last apparition in 1986, next 2061 Orbital inclination 162 (implies retrograde orbit) Comet Halley: Nucleus: Comet Halley: Nucleus Giotto spacecraft (1986) showed jets of gas, dust from crack on sunlit side of nucleus Nucleus is 16x8x8 km (10x6x6 miles). Tail is 1.5•107 km long near perihelion Mass of nucleus is 1015 gm, Nucleus has low density (0.1gm/cm3) Nucleus is coverd by dark ‘soot’ (carbon) Comet Levy-Shoemaker 9 (SL9): Comet Levy-Shoemaker 9 (SL9) First detected by David Levy and Helen Shoemaker in March 1993 while searching for asteroids – ‘squashed appearance’. The comet had already had a near-miss with Jupiter in 1992. SL9: Collision course with Jupiter: SL9: Collision course with Jupiter In July 1994 the comet crashed into Jupiter There were over 20 fragments, the nucleus having been torn apart by tidal forces. Perilhelion 5.7 AU (very distant for a comet: detactable at Earth: no classic tail The 21 large fragments had diameters 1-3 km, traveling at 60 km/sec relative to Jupiter. Estimated energy of collision 6,000,000 megatons (600x entire world’s arsenal of atomic bombs) If collision was with Earth, all life would be destroyed immediately Impact! (HST image, fragment G): Impact! (HST image, fragment G) Shock waves SL9 Impact sites on Jupiter: SL9 Impact sites on Jupiter Movie of fragment R impact (Keck) Destruction of Sun-grazing comets(Images from LASCO camera on SOHO spacecraft studying Solar activity): Destruction of Sun-grazing comets (Images from LASCO camera on SOHO spacecraft studying Solar activity) Click movie1 Fragmentation of Comet LINEAR near perihelion: Fragmentation of Comet LINEAR near perihelion Each ‘cometesimal’ is only ~100 m in size Before perihelion After perihelion Meteor Showers: Meteor Showers Caused by debris from Jupiter-family and short period comets whose orbit crosses the Earth. Showers are named for the constellation the meteors appears to originate from Number of meteors highly variable from year to year- due to clumpy character of dust debris The peak of the 1997 Leonid meteor shower as seen from ABOVE, in Earth orbit, by the MSX satellite. 29 meteors were imaged over a 48 minute period entering the Earth's atmosphere. Great Meteor shower of 1833: Great Meteor shower of 1833 The Leonid shower of Nov 13, 1883 was especially bright (1,000’s per hour at peak) The Leonids are cause by intermediate period comet Temple-Tuttle (33 yr period), so peaks occur every 33yr (approximately), including Nov 2002. Many people were awakened by the brightness of the meteors through their bedroom windows A number of preachers declared the shower to be a sign of the ‘End Times’. Panic in some cities. The origin of meteors was not known. Here is a typical popular ‘explanation’: The Charleston Courier published a story on “how the sun caused gases to be released from plants recently killed by frost”. These gases, the most abundant of which was believed to be hydrogen, "became ignited by electricity or phosphoric particles in the air." Major Annual Meteor showers : Major Annual Meteor showers May be an ‘extinct’ comet with hard carbon ‘shell’ preventing outgassing Current positions of Comets 55P/Tempel-Tuttle (Leonids) and 109P/Swift-Tuttle (Perseids): Current positions of Comets 55P/Tempel-Tuttle (Leonids) and 109P/Swift-Tuttle (Perseids) Web applet Meteor Shower Radiants: Meteor Shower Radiants Meteors appear to originate from a point in the sky called the radiant The shower is usually named for the constellation in which the radiant is located For example, the Leonids originate in Leo (‘the lion’) Leonid meteor shower (5 min exposure): Leonid meteor shower (5 min exposure) Leonid shower showing radiant in constellation Leo: Leonid shower showing radiant in constellation Leo Meteors, Meteoroids, and Meteorites: Meteors, Meteoroids, and Meteorites A meteoroid is a small rock in space A meteor is a meteoroid which enters the Earth’s atmosphere and produces visible trail. A meteorite is a meteor which survives the descent through the atmosphere and lands on the Earth. Meteorites have three classes: Stony, 95% of meteorites, but difficult to identify. Often covered with dark ‘skin’ from fiery passage through atmosphere. Iron: rare, only 5% of meteorites, but majority of meteorite finds (easy to identify) Stony-iron very rare (1%) Iron and stony-iron meteorites result from fragmented asteroids which are large enough to have been differentiated Iron meteorite Stony meteorite Widmanstatten patterns: evidence of slow cooling: Widmanstatten patterns: evidence of slow cooling Widmanstatten patterns are seen in iron meteorites after they are sliced and etched with acid. The pattern is a crystalization process resulting from very slow cooling (~10K per million yrs) The rock was fragmented from the interior of a larger body, where the iron is original very hot and molten (>2,500 K). The Peekskill Meteorite: The Peekskill Meteorite This meteor was photographed on October 9, 1992. The Peekskill (stony) meteorite (12.5kg, ~7”) Peekskill meteor movie Meteorites for sale!: Meteorites for sale!