TuesdayOctober 16, 2012

(Comets; Meteoroids,

Meteors, and Meteorites)

The Launch PadTuesday, 10/16/12

Identify this object

. comet

The Launch PadTuesday, 10/16/12

Identify this object

. comet

The Launch PadTuesday, 10/16/12

Identify this object

.asteroids

The Launch PadTuesday, 10/16/12

Identify this object

. Winslow, Arizona meteor crater

Announcements

Happy Fall!

Assignment Currently Open

Summative or

Formative?Date Issued Date Due Date Into

GradeSpeed Final Day

Quiz 6 S1 10/5 10/5 10/19

Quiz 7 S2 10/12 10/12 10/26

WS – Asteroids F1 10/15 10/17 10/19

Recent Events in ScienceNASA Chat: Orionids, Planets, Constellations Brighten

October Skieshttp://www.nasa.gov/connect/chat/orionids2012.htmlRead All About

It!The 2012 Orionid meteor shower peaks on the

night of Oct. 20-21, and that night's almost-new moon favors a good show. The moon's absence from the pre-dawn sky during the

Orionids' peak also means that bright moonlight won't be a problem. 

In addition to Orionids, you'll see brilliant Venus, red Mars, the dog star Sirius and

bright winter constellations such as Orion, Gemini and Taurus. Even if you don't spy a

meteor, the rest of the sky is dynamite! 

Set your alarm, brew some hot chocolate and plan to enjoy the show with NASA astronomer Bill Cooke and his team from NASA's Marshall

Space Flight Center. They'll be answering your questions via live Web chat on Saturday,

Oct. 20 from 10 p.m. to 2 a.m. CDT. 

The origin of comets is not well known because

they form at great distances from the Sun.The most famous short-period comet is Halley’s comet, with a 76-year

orbital period and potato-shaped nucleus

(10 mi. by 5 mi.)

Halley’s Comet

Comets

CometsComets are often described as

large, dirty snowballs.Comets are composed of frozen gases and rocky,

metallic materials.The frozen gases vaporize when near the Sun, which

produces a glowing head called the coma.

Some comets may develop a tail that points away from Sun due to radiation pressure and

the solar wind.

Comet Hale-BoppIn 1997, Comet Hale-

Bopp's intrinsic brightness exceeded any comet since 1811. Since it peaked on the other side of the Earth's orbit,

however, the comet appeared only brighter than any comet in two

decades. Visible above are the two tails shed by Comet Hale-Bopp. The blue ion tail is composed of

ionized gas molecules, of which carbon monoxide particularly

glows blue when reacquiring electrons. This tail is created by the particles from the

fast solar wind interacting with gas from the comet's head. The blue ion

tail points directly away from the Sun. The white dust tail is created by bits of

grit that have come off the comet's nucleus and are being pushed away by the pressure of light from the Sun. This

tail points nearly away from the Sun.

Comet HalleyHalley's Comet or Comet Halley is the best-known of the short-period comets and is visible from Earth every 75–76 years. Halley is the only

short-period comet that is clearly visible to the naked eye from Earth, and thus the only naked-eye comet that might appear twice in a human

lifetime. Other naked-eye comets may be brighter and more spectacular, but will appear only once in thousands of years.

Comet KohoutekComet Kohoutek was first sighted on March

7,1973 by Czech astronomer Luboš Kohoutek. It attained perihelion on December 28th that

same year. Comet Kohoutek is a long-period comet; its previous apparition was about

150,000 years ago, and its next apparition will be in about 75,000 years. At its apparition in

1973 it had a hyperbolic trajectory due to gravitational perturbations from giant planets.

Due to its path, scientists theorized that Kohoutek was an Oort-cloud object. As such, it

was believed likely that this was the comet's first visit to the inner Solar System, which

would result in a spectacular display of out-gassing. Infrared and visual telescopic study

have led many scientists to conclude, in retrospect, that Kohoutek is actually a Kuiper-

belt object, which would account for its apparent rocky makeup and lack of out-

gassing.

Orientation of a Comet’s Tail as it Orbits the Sun

Figure 22.27

Meteoroids, Meteors, and MeteoritesA meteoroid is a sand- to boulder-sized particle

of debris roaming through the Solar System.

Meteoroids, Meteors, and MeteoritesThe visible path of a

meteoroid that enters Earth's (or

another body's) atmosphere is

called a meteor (shooting star or falling

star.)

Meteoroids, Meteors, and MeteoritesMany meteors appearing seconds or minutes apart

are called a meteor shower. A meteor shower occurs when Earth encounters a

swarm of meteoroids associated with a comet’s

path.

Meteoroids, Meteors, and MeteoritesIf a meteoroid reaches the ground and survives

impact, then it is called a meteorite.

Meteoroids are referred to as meteorites when they

are found on Earth. Meteorites are classified

by their composition:Iron Meteorites

Mostly iron5%–20% nickel

Stony MeteoritesSilicate minerals with

Inclusions of other minerals

Meteoroids, Meteors, and Meteorites

Meteoroids, Meteors, and Meteorites

Stony- Iron MeteoritesMixtures of iron and stone

Carbonaceous Chondrites A rare composition of

simple amino acids and other organic material.

These may give an idea as to the composition of

Earth’s core and the age of the solar system

Comets and MeteoroidsWorksheet

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