26meteorite Meteor shower A chunk of metal or rock that reaches Earth from spacemeteorite
27MeteoroidA meteoroid is a chunk of rock, metal, or dust in space.
28A Meteor: “A shooting star” Shooting stars are not actually stars. These flashes of light across the sky are small bits of rock burning up in the Earth’s Atmosphere.
29MeteoriteMeteoroids that survive as they pass through the atmosphere and hit Earth’s surface are called meteorites.
30There are three major types of meteorites: stone, iron and stony-iron. There are three major types of meteorites: stone, iron and stony-iron.
31Barringer Meteor Crater, Arizona A meteorite can make a hole, or crater, in the ground when it hits it. The larger the meteorite, the bigger the hole.
32METEOROID: A piece of stone or metal that travels in outer space. METEOR: An object from space that becomes glowing hot when it passes into Earth's atmosphere.METEORITE: A piece of stone or metal from space that falls to Earth's surface.
33cometsLumps of ice and dust that periodically come to the center of the solar system from the outer reaches.
34Dirty Snowballs Comets are dusty chunks of ice During each orbit around the sun they partially vaporizeHave elliptical orbitsThey are about the size of an earth mountain. (dirt and ice)Comets’ orbits are usually very long, narrow ellipses.They produce tails of gas and dust when they approach the sun.Courtesy: Calvin J. Hamilton
35HistoryUnlike the other small bodies in the solar system, comets have been known since antiquity. There are Chinese records of Comet Halley going back to at least 240 BC. The famous Bayeux Tapestry, which commemorates the Norman Conquest of England in 1066, depicts an apparition of Comet Halley.As of 1995, 878 comets have been cataloged and their orbits at least roughly calculated. Of these 184 are periodic comets (orbital periods less than 200 years); some of the remainder are no doubt periodic as well, but their orbits have not been determined with sufficient accuracy to tell for sure.
36Comets have been regarded as omens, even as recently as 1986. The history of comet watching dates back to 1000 BC from the Chinese records and Chaldea, a place in present Iraq.Comets have been regarded as omens, even as recently as 1986.Battle of HastingsToday astronomers study comets from scientific perspectives, and our understanding of these fascinating objects have grown tremendously.
37Structure of a Comet Solar heat vaporizes the nucleus to produce Coma - Hydrogen gas EnvelopeDust tailIon tailCourtesy: Deep Impact - NASA & JPL
38Parts of a CometWhen they are near the Sun and active, comets have several distinct parts:nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids;coma: dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus;hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen;dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye;Ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind.
39Comet Nucleus (plural: Nuclei) A drawing of what the surface of a comet might look like.The nucleus of a comet is the central portion of the head of a comet. It is a solid part of the comet, made of a special sort of dust which is called "fluffy" because it could be as light weight and full of holes as a sponge. The holes of this "sponge" are filled with ices like water, carbon dioxide (dry ice), and carbon monoxide (what comes out of your car).
40ComaThis cloud, called the coma, is the atmosphere of the comet and can extend for millions of miles. The cloud is very thin, however, 10,000 times thinner than a cloud in the Earth's atmosphere!The neutral particles that are in the coma can actually become excited by the solar wind causing the particles to become ions. A continual stream of neutral particles is produced as long as the nucleus is evaporating, and these neutral particles are continually converted to ions. These ions are what help form the comet tail.
41TailsA comet generally has two tails, not one. One tail is due to the comet's dust particles, the other is due to ionized gas from the comet coma. Dust particles form the first tail. This comet tail generally points back along the comet path (so if the comet is traveling right, the dust tail extends to the left).Ions (electrically charged particles), which first come from the nucleus as (neutral) gaseous particles, are swept into the second comet tail. Because of the special interaction with the Sun's magnetic field, this tail always points directly away from the Sun.
42Schematic of a CometThis image is a schematic of a comet. The center part of the comet, or nucleus, is represented by the flame. The solar wind particles are shown as green dots with arrows. And the ionized particles are shown as green/red dots with arrows. Neutral particles are shown by the other dots (without arrows).
43Orbits of Comets Aphelion distance Comet Sun Earth Perihelion distance Elliptical in ShapeRandomly orientedAphelion distanceCometSunEarthPerihelion distance
44Comet HuntersComet are named by International Astronomical Union (IAU) after the person who first discovers them.Many comets are discovered by amateur astronomers.Charles Messier, E. E. Bernard, Shoemaker and Levy, Hale and Bopp, Ikeya, Seki and Hayakutake are popular comet hunters.
45Origins of CometsComets are thought to be the left over debris from during the time of formation of the solar system.The elliptical orbits of comets suggest that they underwent gravitational pull from the giant planets.This all lead us to infer two possible locations where comets could start their journey towards the sun.
46Possible Homes for Comets Kuiper BeltOort CloudCourtesy - Deep Impact - NASA - JPL
48Kuiper Belt Discovered by Gerard Kuiper in 1951 The belt is 30 to 500 AU from the SunThe plane of the belt is close to the eclipticProbably contains more than 100,000 objectsSome of these objects are 100 km or larger in diameter
49Oort Cloud Hypothesized by a Dutch Astronomer Jan Oort in 1950. Shape is spherical distribution around the Sun.50,000 AU from the Sun.May contain 5 trillion objects.Probably created 4.6 billion years ago.
50Comets and their Spectra Spectroscopy is a technique in which light is broken into its component colors. Each chemical element show their fingerprint in the spectrum of the object.We can thus find the composition of comets by identifying the fingerprints.Most of the information on comets comes from infrared radiation, because comets are cold objects they radiate strongly at infrared radiation.
51Comet CollisionsComet collisions with Earth can bring devastation to life on Earth.Jupiter in our solar system is the largest planet and thus exerts greater gravitational pull on incoming Comets.Study of Shoemaker-Levey collision with Jupiter gave us important facts about Comet collisions.
55Winter and early spring of 1997 Comet: Hale-BoppWinter and early spring of 1997Next sighting: 4380
56FactsComets are invisible except when they are near the Sun. Most comets have highly eccentric orbits which take them far beyond the orbit of Pluto; these are seen once and then disappear for millennia. Only the short- and intermediate-period comets (like Comet Halley), stay within the orbit of Pluto for a significant fraction of their orbits.
57Approaching the SunAs a comet approaches the Sun, it begins to evaporate, forming the coma and a spectacular comet tail.Evaporation is not quite the correct term to describe what happens to a comet as it approaches the sun. The correct term is sublimation. The term describes what happens when a frozen material changes to gaseous form. (Evaporation describes what happens when a liquid changes to a vapor).
58SublimationThe most common example of sublimation is that of dry ice, which is the common name of frozen CO2. When dry ice is exposed to the air it begins to sublimate, or change to vapor, before your very eyes. This happens to dry ice because at room temperature the frozen gas would rather be a gas than frozen solid.
59Long Period CometsA comet with an orbital period of more than 200 years.
60Short Period CometsA comet with an orbital period of less than 200 years.Short period fade over time as more and more of their ices melt with each passage of the Sun.Examples: Comet Halley, 76-year orbit; Comet Encke, 3.3-year orbit; Comet Wild 2, 6.2 year orbit.
61orbit The path a planetary body makes as it revolves around the sun The orbit of a comet tends to be far more elliptical than planet’s orbits.
62CircleA geometric shape where all points on a plane are the same distance from the center
63ellipseA geometrical shape where all the points on a curve is the constant sum of the distances from two fixed points, called focal points.
64PerihelionThe point where an object orbiting the Sun is closest to the Sun
65Astronomical unit (AU) One AU is equal to the average distance between the Sun and Earth, approximately 150 million kilometers (93 million miles)
66EjectaThe debris that is ejected from the site of impact when a crater forms
67Gravity Force of attraction between two objects Just as Earth pulls on you, you pull on Earth with the exact same amount of force.
68mass The amount of matter in an object The measure of an object’s inertia.Mass is not the same as weight, which measures the gravitational force on an object.Your mass is the same everywhere, whether you are at home, on the Moon, or floating in interplanetary space.
119Life Support: pHA number which tells how acidic or basic a liquid is
120Life Support: ppm(parts per million); the units attached to the number determined by the TDS meter
121Life Support: Solar Energy Energy provided by the sun
122Life Support: TDS(total dissolved solids); a number telling how much solid material is dissolved in water, measured by the TDS meter
123Life Support: ValveA device used to control the flow of air or water
124Navigation Team: Angle The point formed by the joining of two lines
125Navigation Team: Detector A device used to gather information
126Navigation Team: GridA system of X and Y coordinates used in launching detectors
127Navigation Team: Initialize To begin or name something
128Navigation Team: Particle density A number telling how tightly packed the material in a comet is
129Navigation Team: Star Chart A paper map of the stars
130spectrometerAn instrument used to obtain and record a spectrum of an astronomical objectA spectrum is a series of colors that is produced when light is spread out in order of wavelength.
131Navigation Team: Starfield A group of stars in view of the spacecraft’s camera
132Navigation: DensityMass of a substance contained per unit of volume
133Navigation: ComaThe atmosphere of a comet, which surrounds the nucleus
134Navigation: NucleusThe solid part of a comet made up of rocks, dust, gas and ice (dirty snowball)
135Navigation: TailThe longest part of the comet caused by solar wind
136Navigation: Constellation A group of stars that form a pattern in the sky
137Navigation: Declination The label for the Y-axis on a star chart. The declination of an object is its distance in degrees above or below the celestial equator. Decline numbers range from 0 degrees to +90 degrees and 0 degrees to -90 degrees. It is similar to latitude on Earth
138Navigation: Right Ascension The label for the X-axis on a star chart. The right ascension of an object in the sky is its position, simply put relative to the vernal equinox. It is measured in hours minutes and seconds from 0 hours, 0 minutes and 0 seconds of right ascension at the starting point (vernal equinox), to 23 hours, 59 minutes of right ascension. Right ascension is equivalent to longitude.
139Navigation: Eccentricity A numerical value for the shape of an orbit ranging from 0, which equals a circular orbit, to 1 which equals a flattened, elliptical orbit. Planets , moons, asteroids and short period comets have eccentricity values close to 0. long period comets have eccentricity values of 0.5 or more
140Navigation: Short Period Comet A comet with an orbital period of less than 200 years. (Comet Halley is 76 years and comet Encke is 3.3 years.
141Navigation: Long Period Comet A comet with an orbital period of more than 200 years. (Hale-Bopp is 2425 years and Hyakutake is 15,000 Years)
142Navigation: Magnitude A numerical value for the brightness of a celestial object. The brighter an object appears in the sky, the smaller its magnitude the dimmer an object appears in the sky, the larger its magnitude.
143Navigation: Stellar Object A celestial object that produces its own light (the sun)