During a magnetic storm charged particles can be deflected from the outer magnetosphere directed along field lines into Earth s ionosphere where atmospheric atoms can be excited and ionized causing the aurora Orbit and rotationRotationMain article Earth s rotation Earth s axial tilt or obliquity and its relation to the rotation axis and plane of orbitEarth s rotation period relative to the Sun—its mean solar day—is seconds of mean solar time SI seconds Because Earth s solar day is now slightly longer than it was during the th century due to tidal deceleration each day varies between and SI ms longer Earth s rotation period relative to the fixed stars called its stellar day by the International Earth Rotation and Reference Systems Service IERS is seconds of mean solar time UT or h m s n Earth s rotation period relative to the precessing or moving mean vernal equinox misnamed its sidereal day is seconds of mean solar time UT h m s as of update Thus the sidereal day is shorter than the stellar day by about ms The length of the mean solar day in SI seconds is available from the IERS for the periods – and – Apart from meteors within the atmosphere and low orbiting satellites the main apparent motion of celestial bodies in Earth s sky is to the west at a rate of ° h min For bodies near the celestial equator this is equivalent to an apparent diameter of the Sun or the Moon every two minutes from Earth s surface the apparent sizes of the Sun and the Moon are approximately the same OrbitMain article Earth s orbit Earth orbits the Sun at an average distance of about million kilometers every mean solar days or one sidereal year This gives an apparent movement of the Sun eastward with respect to the stars at a rate of about ° day which is one apparent Sun or Moon diameter every hours Due to this motion on average it takes hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian The orbital speed of Earth averages about km s km h which is fast enough to travel a distance equal to Earth s diameter about km in seven minutes and the distance to the Moon km in about hours The Moon and Earth orbit a common barycenter every days relative to the background stars When combined with the Earth–Moon system s common orbit around the Sun the period of the synodic month from new moon to new moon is

days Viewed from the celestial north pole the motion of Earth the Moon and their axial rotations are all counterclockwise Viewed from a vantage point above the north poles of both the Sun and Earth Earth orbits in a counterclockwise direction about the Sun The orbital and axial planes are not precisely aligned Earth s axis is tilted some degrees from the perpendicular to the Earth–Sun plane the ecliptic and the Earth–Moon plane is tilted up to ± degrees against the Earth–Sun plane Without this tilt there would be an eclipse every two weeks alternating between lunar eclipses and solar eclipses The Hill sphere or gravitational sphere of influence of Earth is about Gm or km in radius n This is the maximum distance at which the Earth s gravitational influence is stronger than the more distant Sun and planets Objects must orbit Earth within this radius or they can become unbound by the gravitational perturbation of the Sun Earth along with the Solar System is situated in the Milky Way and orbits about light years from its center It is about light years above the galactic plane in the Orion Arm Axial tilt and seasonsMain article Axial tilt § Earth Due to Earth s axial tilt the amount of sunlight reaching any given point on the surface varies over the course of the year This causes seasonal change in climate with summer in the northern hemisphere occurring when the North Pole is pointing toward the Sun and winter taking place when the pole is pointed away During the summer the day lasts longer and the Sun climbs higher in the sky In winter the climate becomes generally cooler and the days shorter In northern temperate latitudes the Sun rises north of true east during the summer solstice and sets north of true west reversing in the winter The Sun rises south of true east in the summer for the southern temperate zone and sets south of true west Above the Arctic Circle an extreme case is reached where there is no daylight at all for part of the year up to six months at the North Pole itself a polar night In the southern hemisphere the situation is exactly reversed with the South Pole oriented opposite the direction of the North Pole Six months later this pole will experience a midnight sun a day of hours again reversing with the South Pole By astronomical convention the four seasons can be determined by the solstices — the points in the orbit of maximum axial tilt toward or away from the Sun — and the equinoxes when the direction of the tilt and the direction to the Sun are perpendicular In the northern hemisphere winter solstice currently occurs around December summer solstice is near June spring equinox is around March and autumnal equinox is about September or In the southern hemisphere the situation is reversed with the summer and winter solstices exchanged and the spring and autumnal equinox dates swapped The angle of Earth s axial tilt is relatively stable over long periods of time Its axial tilt does undergo nutation a slight irregular motion with a main period of years The orientation rather than the angle of Earth s axis also changes over time precessing around in a complete circle over each year cycle this precession is the reason for the difference between a sidereal year and a tropical year Both of these motions are caused by the varying attraction of the Sun and the Moon on Earth s equatorial bulge The poles also migrate a few meters across Earth s surface This polar motion has multiple cyclical components which collectively are termed quasiperiodic motion In addition to an annual component to this motion there is a month cycle called the Chandler wobble Earth s rotational velocity also varies in a phenomenon known as length of day variation In modern times Earth s perihelion occurs around January and its aphelion around July These dates change over time due to precession and other orbital factors which follow cyclical patterns known as Milankovitch cycles The changing Earth–Sun distance causes an increase of about n in solar energy reaching Earth at perihelion relative to aphelion Because the southern hemisphere is tilted toward the Sun at about the same time that Earth reaches the closest approach to the Sun the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year This effect is much less significant than the total energy change due to the axial tilt and most of the excess energy is absorbed by the higher proportion of water in the southern hemisphere HabitabilityA planet that can sustain life is termed habitable even if life did not originate there Earth provides liquid water—an environment where complex organic molecules can assemble and interact and sufficient energy to sustain metabolism The distance of Earth from the Sun as well as its orbital eccentricity rate of rotation axial tilt geological history sustaining atmosphere and protective magnetic field all contribute to the current climatic conditions at the surface BiosphereMain article Biosphere Coral reef and beachA planet s life forms inhabit ecosystems whose total is sometimes said to form a biosphere Earth s biosphere is thought to have begun evolving about Gya The biosphere is divided into a number of biomes inhabited by broadly similar plants and animals On land biomes are separated primarily by differences in latitude height above sea level and humidity Terrestrial biomes lying within the Arctic or Antarctic Circles at high altitudes or in extremely arid areas are relatively barren of plant and animal life species diversity reaches a peak in humid lowlands at equatorial latitudes


abby-lane abby-rode abigail-clayton ada-tauler addie-juniper addison-cain adele-wiesenthal adeline-lange adeline-pollicina adriana-amante adrianna-laurenti adrianna-russo agnes agnes-ardant agnes-zalontai aimee-addison aisha-sun aja aleena-ferari alessandra-schiavo aletta-ocean alexandra-nice alexandria-cass alexa-parks alex-dane alex-foxe alexia-knight alexis-devell alexis-firestone alexis-greco alexis-payne alexis-x alex-storm alex-white aliana-love alice-springs alicia-alighatti alicia-monet alicia-rio alicyn-sterling alighiera-olena ali-moore aline-santos alissa-ashley allysin-chaynes alysin-embers alyssa-love alyssa-reece amanda-addams amanda-blake amanda-blue amanda-jane-adams amanda-rae amanda-stone amanda-tyler amber-hunt amberlina-lynn amber-lynn amber-michaels amber-peach amber-wild amber-woods ambrosia-fox amia-miley ami-rodgers amy-allison amy-brooke amy-rose amy-starz anastasia-christ anastasia-sands andrea-adams andrea-brittian andrea-lange andrea-true andy angel angela-baron angela-summers angel-barrett angel-cash angel-cruz angel-cummings angel-ducharme angelica-sin angelika-reschner angelina-brasini angelina-korrs angelina-valentine angel-kelly angel-long angel-west angie-knight anita-andic anita-blond anita-cannibal anita-dark anna-belle anna-malle anna-nikova anna-pierce anna-ventura anna-veruska anne-bie-warburg anne-libert anne-magle anne-sand annette-haven annie-sprinkle ann-kiray ann-marie-michelle antonia-dorian april-flowers april-may april-west arcadia-lake ariana-bali ariana-jollee arlana-blue ashley-anne ashley-brooks ashley-coda ashley-fires ashley-lauren ashley-long ashley-marie ashley-nicole ashley-perk ashley-renee ashley-robbins ashley-welles ashley-wells ashley-winger ashlyn-gere astrid-bone athena-star aubrey-nichols aurora aurora-snow autumn-bliss autumn-rayne ava-devine ava-lauren avalon ava-marteens avy-lee-roth bailey-monroe bambi-allen barbara-bourbon barbara-boutet barbara-dare barbara-doll barbara-moose barbarella barbie-angel barbie-doll barett-moore bea-fiedler beata beatrice-poggi beatrice-valle becky-savage becky-sunshine belinda-butterfield bella-donna bethany-sweet beverly-bliss beverly-glen biggi-stenzhorn bionca black-widow blond-cat blondi blue-angel bobbi-bliss bobbi-dean bobbie-burns bonnie-holiday brandee brandi-edwards brandy-alexandre brandy-dean brandy-lee brandy-smile brandy-wine bree-anthony breezy-lane brenda-basse briana-blair bridgette-belle bridgette-monet bridgette-monroe bridget-waters brigitte-lahaie brigitte-monnin brigitte-verbecq brittany brittany-stryker britt-corvin britt-morgan bronze brooke-bennett brooke-fields brooke-haven brooke-west brook-van-buuren buffy-davis bunnie-blake bunny-bleu bunny-hatton busty-belle cali-caramel calisyn-heart cameo cameron-love camila-sampaio camilla-rhodes camille-morgan camrie-foxxx candace-daley candi candida-royalle candie-evens candi-summers candy-apples candy-barr candy-hill candy-samples candy-stanton cara-lott caressa-savage carmel-nougat carmen-blonde carmen-de-la-torre carmen-moore carmen-rose carol-connors carol-cross carol-cummings carole-dubois carole-gire carole-pierac carol-titian carolyn-connoly carolyn-monroe carrie-cruise cassandra-leigh cassidy cassie-courtland cataline-bullock catherine-count catherine-crystal catherine-ringer catherine-tailleferre cathy-delorme cathy-menard cathy-stewart celeste-fox celine-gallone chanel-preston chanel-price chantal-virapin chanta-rose chantelle-stevens charisma charisma-cole charlie-latour charlie-waters charlotte-de-castille charmane-star chasey-lain chayse-manhattan chaz-vincent chelsea-sinclaire chennin-blanc cheri-janvier cheri-taylor cherry-hill chessie-moore cheyenne-hunter cheyenne-silver china-lee china-leigh china-moon chloe-cruize chloe-dior chloe-kez chloe-stevens chris-collins chris-jordan chris-petersen chrissie-beauchamp christa-abel christa-ludwig christie-ford christi-lake christina-berg christina-blond christina-evol christina-skye christine-black christine-chavert christine-neona christine-rigoler christy-canyon cicciolina cindi-stephens cindy-carver cindy-crawford cindy-more cindy-shepard cindy-wong cinthya-marinho clair-dia claire-robbins claude-janna claudia-jackson claudia-jamsson claudia-mehringer claudia-nero claudia-van-statt claudia-zante claudine-beccarie clea-carson cleo-nichole cleo-patra cody-lane cody-love cody-nicole coffee-brown colleen-brennan connie-bennett connie-peterson constance-money copper-penny coreena corey-everson corinne-lemoine corneliah cory-everson cory-wolf courtney courtney-cummz courtney-james cris-cassidy crissy-moran cris-taliana crystal-breeze crystal-dawn crystal-holland crystal-knight crystal-lake crystal-lovin crystal-sync csilla-kalnay cuban-bee cynara-fox cyndee-summers cynthia-black cynthia-brooks cynthia-hammers cynthia-lavigne dagmar-lost daisy-layne dallas-miko dana-dylan dana-lynn danica-rhea daniela-nanou daniela-schiffer daniele-troeger daniella daniella-schiffer danielle danielle-foxxx danielle-rodgers danny-ricci danyel-cheeks daphne daphne-rosen darby-lloyd-rains darla-crane darla-delovely davia-ardell dayton-rain debbie-northrup debbie-revenge debbie-van-gils debi-diamond debi-jointed debra-lynn deidra-hopkins deidre-holland delania-raffino delia-moore delphine-thail delta-force delta-white demi-moor denice-klarskov denise-derringer denise-dior denise-sloan desiree-cousteau desiree-foxx desiree-lane desiree-west deva-station devin-devasquez devinn-lane devon-shire dia diana-holt diana-kisabonyi diana-siefert diana-stevenson diane-dubois diane-richards diane-sloan diane-suresne dido-angel dillan-lauren dina-deville dina-jewel dina-pearl ditty-blue diva divinity-love djiana dolly-darkley dominique dominique-dewitt dominique-saint-claire donna-hart donna-marie dorle-buchner dorothy-lemay dorothy-onan drea drimla dru-berrymore dusty-rose dyanna-lauren ebony-ayes edina-blond edita-ungerova edwige-faillel eileen-wells elaine-southern elena-berkova elena-maria-ricci eleonore-melzer elisabeth-bure elis-black elise elise-di-medici elle-devyne elle-rio elodie-delage elsa-maroussia elza-brown emili-doll emily-evermoore emily-george emily-jewel emmanuelle-pareze envy-mi erica-boyer erica-eaton erica-havens erica-idol erica-lauren erika-bella erika-cool erika-heaven erika-lockett esme-monroe eva-allen eva-angel eva-dionisio eva-gross eva-kleber eva-lux eva-uettori eve-laurence evelyne-lang evie-delatosso fabiana-venturi faith-stevens fallon fanny-garreau fanny-steel faye-runaway flame flick-shagwell flore-soller flower france-lomay france-quenie francoise frankie-leigh gabriella gabriella-mirelba gabriella-vincze gail-force gail-palmer gail-sterling georgette-saunders georgia-peach georgina-spelvin gia-givanna gianna-lynn gili-sky gina-carrera gina-gianetti gina-janssen gina-lee gina-martell gina-valentino ginger-jay ginger-lee ginger-lynn ginny-noack giovanna gisela-schwarz giselle-monet gladys-laroche gloria-leonard gloria-todd golden-jade greta-carlson greta-milos guia-lauri-filzi gwenda-farnel hare-krane harley-raine hayley-jade hazel-young heather-deeley heather-ellis heather-hart heather-lere heather-lyn heather-manfield heather-thomas heather-torrance heather-wayne heather-young helen-madigan helen-thomas helga-sven helga-wild hillary-summers holly-hollywood holly-joy holly-page holly-ryder honey-winter hottie-hollie hyapatia-lee ida-fabry ildiko-smits illana-moor ines-ridere ingrid-choray isabella-dior isabella-soprano isabelle-allay isabelle-brell isabelle-marchall isobel-wren iveta ivette-blanche jackie-right jacqueline-lorians jacy-allen jada-stevens jade-east jade-hsu jade-marcela jade-summers jade-wong jahn-gold jamie-brooks jamie-james jamie-summers jana-irrova jana-mrazkova jane-baker jane-darling jane-iwanoff jane-lindsay jane-lixx janet-jacme janey-robbins jasmine-delatori jayden-simone jaylyn-rose jayna-woods jazella-moore jazmin-luna-gold jean-afrique jeanette-littledove jeanie-marie-sullivan jean-jennings jeanna-fine jeannie-pepper jenna-jameson jenna-jane jenna-presley jenna-wells jennifer-haussmann jennifer-janes jennifer-jordan jennifer-morante jennifer-noxt jennifer-stewart jennifer-welles jennifer-west jenny jenny-feeling jenny-fields jenny-wings jersey-jaxin jesie-st-james jesse-capelli jessica-bangkok jessica-bogart jessica-darlin jessica-fiorentino jessica-gabriel jessica-laine jessica-may jessica-road jessica-wylde jessi-foster jill-ferari jill-kelly joana-redgrave joan-devlon joanna-storm joanna-sweet jody-maxwell joelle-lequement joelle-petinot johnni-black jordana-james jordan-green jordan-nevaeh jordan-star josephine-carrington joslyn-james julia-chanel julia-dal-fuoco juliana-grandi julia-paes julia-parton julia-perrin julia-swen julia-thomas julie-meadows julie-rage julie-simone juliet-anderson juliet-graham juliette-carelton kacey-jordan kagney-linn-karter kaitlyn-ashley kalena-rios kami-andrews kamila-smith kandee-licks kandi-barbour kapri-styles kara-nox karen-summer kari-foxx karine-gambier karin-schubert karli-sweet karmen-kennedy karol-castro kascha kassi-nova kat kate-frost kate-jones kathia-nobili kathleen-gentry kathleen-white kathy-divan kathy-harcourt kathy-heart kathy-kash katie-cummings katja-love kat-langer katrina-isis katrina-kraven katy-borman katy-caro kaycee-dean kayla-kupcakes kay-parker k-c-valentine keama-kim keira-moon keisha keli-richards kelli-tyler kelly-adams kelly-blue kelly-broox kelly-hearn kelly-kay kelly-kline kelly-nichols kelly-royce kelly-skyline kendra-kay kenzi-marie keri-windsor ketthy-divan kianna-dior kiley-heart kim-alexis kimber-blake kimberly-carson kimberly-kane kimberly-kyle kim-de-place kim-holland kimi-gee kimkim-de kim-kitaine kimmie-lee kimmy-nipples kina-kara kira-eggers kira-red kirsty-waay kitty-langdon kitty-lynxxx kitty-marie kitty-shayne kitty-yung kora-cummings kris-lara krista-lane krista-maze kristara-barrington kristarah-knight kristi-klenot kristina-blonde kristina-king kristina-klevits kristina-soderszk kristine-heller kristin-steen krisztina-ventura krystal-de-boor krystal-steal kylee-karr kylee-nash kylie-brooks kylie-channel kylie-haze kylie-wylde kym-wilde kyoto-sun lachelle-marie lacy-rose lady-amanda-wyldefyre lady-stephanie laetitia-bisset lana-burner lana-cox lana-wood lara-amour lara-roxx lara-stevens lataya-roxx latoya laura-clair laura-lazare laura-lion laura-may laura-orsolya laura-paouck laura-zanzibar lauren-black laurence-boutin lauren-montgomery laurien-dominique laurien-wilde laurie-smith lauryl-canyon lauryn-may leah-wilde lea-magic lea-martini leanna-foxxx lee-caroll leigh-livingston leilani lenora-bruce leslie-winston lesllie-bovee letizia-bruni lexi-lane lexi-matthews lezley-zen lia-fire liliane-gray liliane-lemieuvre lili-marlene lily-gilder lily-labeau lily-rodgers lily-valentine linda-shaw linda-vale linda-wong linnea-quigley lisa-bright lisa-de-leeuw lisa-k-loring lisa-lake lisa-melendez lisa-sue-corey lise-pinson little-oral-annie liza-dwyer liza-harper lizzy-borden logan-labrent lois-ayres lola-cait long-jean-silver loni-bunny loni-sanders loona-luxx lorelei-lee lorelei-rand lorena-sanchez lori-alexia lori-blue lorrie-lovett luci-diamond lucie-doll lucie-theodorova lucy-van-dam lydia-baum lynn-franciss lynn-lemay lynn-ray lynn-stevens lynx-canon lysa-thatcher madelina-ray madison-parker magdalena-lynn maggie-randall mai-lin mandi-wine mandy-bright mandy-malone mandy-may mandy-mistery mandy-starr marcia-minor maren margit-ojetz margitta-hofer margo-stevens margot-mahler mariah-cherry marianne-aubert maria-tortuga marie-anne marie-christine-chireix marie-christine-veroda marie-claude-moreau marie-dominique-cabannes marie-france-morel marie-luise-lusewitz marie-sharp marilyn-chambers marilyne-leroy marilyn-gee marilyn-jess marilyn-martyn marilyn-star marina-hedman marion-webb marita-ekberg marita-kemper marlena marlene-willoughby marry-queen martine-grimaud martine-schultz maryanne-fisher mary-hubay mary-ramunno mary-stuart mascha-mouton maud-kennedy mauvais-denoir maxine-tyler maya-black maya-france megan-leigh megan-martinez megan-reece mei-ling melanie-hotlips melanie-scott melba-cruz melinda-russell melissa-bonsardo melissa-del-prado melissa-golden melissa-martinez melissa-melendez melissa-monet mercedes-dragon mercedes-lynn merle-michaels mesha-lynn mia-beck mia-lina mia-smiles michele-raven michelle-aston michelle-ferrari michelle-greco michelle-maren michelle-maylene michelle-monroe micki-lynn mika-barthel mika-tan mikki-taylor mimi-morgan mindy-rae ming-toy miranda-stevens miss-bunny miss-meadow miss-pomodoro missy missy-graham missy-stone missy-vega misti-jane mistress-candice misty-anderson misty-dawn misty-rain misty-regan mona-lisa mona-page moni monica-baal monica-swinn monika-peta monika-sandmayr monika-unco monique-bruno monique-cardin monique-charell monique-demoan monique-gabrielle monique-la-belle morgan-fairlane morrigan-hel moxxie-maddron mulani-rivera mysti-may nadege-arnaud nadia-styles nadine-bronx nadine-proutnal nadine-roussial nadi-phuket nanci-suiter nancy-hoffman nancy-vee natacha-delyro natalia-wood natalli-diangelo natascha-throat natasha-skyler naudia-nyce nessa-devil nessy-grant nesty nicki-hunter nicky-reed nicole-berg nicole-bernard nicole-black nicole-grey nicole-london nicole-parks nicole-scott nicole-taylor nicolette-fauludi nicole-west nika-blond nika-mamic niki-cole nikita-love nikita-rush nikki-charm nikki-grand nikki-king nikki-knight nikki-randall nikki-rhodes nikki-santana nikki-steele nikki-wilde niko nina-cherry nina-deponca nina-hartley nina-preta oana-efria obaya-roberts olesja-derevko olga-cabaeva olga-conti olga-pechova olga-petrova olivia-alize olivia-del-rio olivia-flores olivia-la-roche olivia-outre ophelia-tozzi orchidea-keresztes orsolya-blonde paige-turner paisley-hunter pamela-bocchi pamela-jennings pamela-mann pamela-stanford pamela-stealt pandora paola-albini pascale-vital pat-manning pat-rhea patricia-dale patricia-diamond patricia-kennedy patricia-rhomberg patrizia-predan patti-cakes patti-petite paula-brasile paula-harlow paula-morton paula-price paula-winters pauline-teutscher penelope-pumpkins penelope-valentin petra-hermanova petra-lamas peyton-lafferty phaedra-grant pia-snow piper-fawn pipi-anderson porsche-lynn porsha-carrera precious-silver priscillia-lenn purple-passion queeny-love rachel-ashley rachel-love rachel-luv rachel-roxxx rachel-ryan rachel-ryder racquel-darrian rane-revere raven reagan-maddux rebecca-bardoux regan-anthony regine-bardot regula-mertens reina-leone reka-gabor renae-cruz renee-foxx renee-lovins renee-morgan renee-perez renee-summers renee-tiffany rhonda-jo-petty rikki-blake riley-ray rio-mariah rita-ricardo roberta-gemma roberta-pedon robin-byrd robin-cannes robin-everett robin-sane rochell-starr rosa-lee-kimball rosemarie roxanne-blaze roxanne-hall roxanne-rollan ruby-richards sabina-k sabre sabrina-chimaera sabrina-dawn sabrina-jade sabrina-johnson sabrina-love-cox sabrina-mastrolorenzi sabrina-rose sabrina-scott sabrina-summers sacha-davril sahara sahara-sands sai-tai-tiger samantha-fox samantha-ryan samantha-sterlyng samantha-strong samueline-de-la-rosa sandra-cardinale sandra-de-marco sandra-kalermen sandra-russo sandy-lee sandy-pinney sandy-reed sandy-samuel sandy-style sandy-summers sara-brandy-canyon sara-faye sarah-bernard sarah-cabrera sarah-hevyn sarah-mills sarah-shine sara-sloane sasha sasha-hollander sasha-ligaya sasha-rose satine-phoenix satin-summer savannah-stern savanna-jane scarlet-scarleau scarlet-windsor seka selena serena serena-south severine-amoux shana-evans shanna-mccullough shannon-kelly shannon-rush shantell-day sharon-da-vale sharon-kane sharon-mitchell shaun-michelle shawna-sexton shawnee-cates shay-hendrix shayne-ryder sheena-horne sheer-delight shelby-star shelby-stevens shelly-berlin shelly-lyons sheri-st-clair sheyla-cats shonna-lynn shyla-foxxx shy-love sierra-sinn sierra-skye sigrun-theil silver-starr silvia-bella silvia-saint silvie-de-lux silvy-taylor simone-west sindee-coxx sindy-lange sindy-shy siobhan-hunter skylar-knight skylar-price skyler-dupree smokie-flame smoking-mary-jane solange-shannon sonya-summers sophia-santi sophie-call sophie-duflot sophie-evans sophie-guers stacey-donovan stacy-lords stacy-moran stacy-nichols stacy-silver stacy-thorn starla-fox starr-wood stefania-bruni stella-virgin stephanie-duvalle stephanie-rage stephanie-renee stevie-taylor summer-knight summer-rose sunny-day sunset-thomas sunshine-seiber susan-hart susanne-brend susan-nero susi-hotkiss suzanne-mcbain suzan-nielsen suzie-bartlett suzie-carina suzi-sparks sweet-nice sweety-pie sybille-rossani sylvia-benedict sylvia-bourdon sylvia-brand sylvia-engelmann syreeta-taylor syren-de-mer syvette szabina-black szilvia-lauren tai-ellis taija-rae taisa-banx talia-james tamara-lee tamara-longley tamara-n-joy tamara-west tami-white tammy tammy-lee tammy-reynolds tania-lorenzo tantala-ray tanya-danielle tanya-fox tanya-foxx tanya-lawson tanya-valis tara-aire tasha-voux tatjana-belousova tatjana-skomorokhova tawnee-lee tawny-pearl tayla-rox taylor-wane teddi-austin teddi-barrett tera-bond tera-heart tera-joy teresa-may teresa-orlowski teri-diver teri-weigel terri-dolan terri-hall tess-ferre tess-newheart thais-vieira tia-cherry tianna tiara tiffany-blake tiffany-clark tiffany-duponte tiffany-rayne tiffany-rousso tiffany-storm tiffany-towers tiffany-tyler tiger-lily tigr timea-vagvoelgyi tina-blair tina-burner tina-evil tina-gabriel tina-loren tina-marie tina-russell tish-ambrose tommi-rose tonisha-mills topsy-curvey tori-secrets tori-sinclair tori-welles tracey-adams traci-lords traci-topps traci-winn tracy-duzit tracy-love tracy-williams tricia-devereaux tricia-yen trinity-loren trisha-rey trista-post trixie-tyler ultramax ursula-gaussmann ursula-moore uschi-karnat valentina valerie-leveau valery-hilton vanessa-chase vanessa-del-rio vanessa-michaels vanessa-ozdanic vanilla-deville velvet-summers veri-knotty veronica-dol veronica-hart veronica-hill veronica-rayne veronica-sage veronika-vanoza via-paxton vicky-lindsay vicky-vicci victoria-evans victoria-gold victoria-knight victoria-luna victoria-paris victoria-slick victoria-zdrok viper virginie-caprice vivian-valentine vivien-martines wendi-white wendy-divine whitney-banks whitney-fears whitney-wonders wonder-tracey wow-nikki xanthia-berstein yasmine-fitzgerald yelena-shieffer yvonne-green zara-whites zsanett-egerhazi zuzie-boobies

Natural resources and land useMain articles Natural resource and Land use Estimated human land use Land use Mha Cropland – Pastures – Natural forests – Planted forests – Urban areas – Unused productive land – Earth has resources that have been exploited by humans Those termed non renewable resources such as fossil fuels only renew over geological timescales Large deposits of fossil fuels are obtained from Earth s crust consisting of coal petroleum and natural gas These deposits are used by humans both for energy production and as feedstock for chemical production Mineral ore bodies have also been formed within the crust through a process of ore genesis resulting from actions of magmatism erosion and plate tectonics These bodies form concentrated sources for many metals and other useful elements Earth s biosphere produces many useful biological products for humans including food wood pharmaceuticals oxygen and the recycling of many organic wastes The land based ecosystem depends upon topsoil and fresh water and the oceanic ecosystem depends upon dissolved nutrients washed down from the land In Mha million km of Earth s land surface consisted of forest and woodlands Mha million km was grasslands and pasture and Mha million km was cultivated as croplands The estimated amount of irrigated land in was square kilometres sq mi Humans also live on the land by using building materials to construct shelters Natural and environmental hazards A volcano injecting hot ash into the atmosphereLarge areas of Earth s surface are subject to extreme weather such as tropical cyclones hurricanes or typhoons that dominate life in those areas From to these events caused an average of human deaths per year Many places are subject to earthquakes landslides tsunamis volcanic eruptions tornadoes sinkholes blizzards floods droughts wildfires and other calamities and disasters Many localized areas are subject to human made pollution of the air and water acid rain and toxic substances loss of vegetation overgrazing deforestation desertification loss of wildlife species extinction soil degradation soil depletion and erosion According to the United Nations a scientific consensus exists linking human activities to global warming due to industrial carbon dioxide emissions This is predicted to produce changes such as the melting of glaciers and ice sheets more extreme temperature ranges significant changes in weather and a global rise in average sea levels Human geographyMain articles Human geography and World The seven continents of Earth North America South America Antarctica Europe Africa Asia Oceania v t e A composite picture consisting of DMSP OLS ground illumination data for placed on a simulated night time image of Earth Cartography the study and practice of map making and geography the study of the lands features inhabitants and phenomena on Earth have historically been the disciplines devoted to depicting Earth Surveying the determination of locations and distances and to a lesser extent navigation the determination of position and direction have developed alongside cartography and geography providing and suitably quantifying the requisite information Earth s human population reached approximately seven billion on October Projections indicate that the world s human population will reach billion in Most of the growth is expected to take place in developing nations Human population density varies widely around the world but a majority live in Asia By of the world s population is expected to be living in urban rather than rural areas It is estimated that one eighth of Earth s surface is suitable for humans to live on – three quarters of Earth s surface is covered by oceans leaving one quarter as land Half of that land area is desert high mountains or other unsuitable terrain The northernmost permanent settlement in the world is Alert on Ellesmere Island in Nunavut Canada ° N The southernmost is the Amundsen–Scott South Pole Station in Antarctica almost exactly at the South Pole °S Independent sovereign nations claim the planet s entire land surface except for some parts of Antarctica a few land parcels along the Danube river s western bank and the odd unclaimed area of Bir Tawil between Egypt and Sudan As of update there are sovereign states that are member states of the United Nations plus two observer states and dependent territories and states with limited recognition Historically Earth has never had a sovereign government with authority over the entire globe although a number of nation states have striven for world domination and failed The United Nations is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations thereby avoiding armed conflict The U N serves primarily as a forum for international diplomacy and international law When the consensus of the membership permits it provides a mechanism for armed intervention The first human to orbit Earth was Yuri Gagarin on April In total about people have visited outer space and reached orbit as of July update and of these twelve have walked on the Moon Normally the only humans in space are those on the International Space Station The station s crew made up of six people is usually replaced every six months The farthest that humans have travelled from Earth is km achieved during the Apollo mission in MoonCharacteristics Diameter km Mass × kg In astronomy and navigation the celestial sphere is an imaginary sphere of arbitrarily large radius concentric with Earth All objects in the observer s sky can be thought of as projected upon the inside surface of the celestial sphere as if it were the underside of a dome or a hemispherical screen The celestial sphere is a practical tool for spherical astronomy allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant Contents Introduction Celestial coordinate systems History Star globe Bodies other than Earth Proper motion is the astronomical measure of the observed changes in apparent positions of stars in the sky as seen from the center of mass of the Solar System as compared to the imaginary fixed background of the more distant stars It was first physically measured individually in both seconds of time in right ascension RA or a and seconds of arc in declination Dec or d whose calculated combined value is the total proper motion µ expressed in seconds of arc per year arcsec yr or per century arcsec yr where arcseconds equal one degree Because most proper motions are much less than one arcsec per year most modern catalogues like the Hipparcos Index Catalogue HIP now express proper motion in terms of milliarcseconds per year mas yr where mas equals one arcsecond This measured sky motion is separate from the radial velocity measured in kilometres per second km s being the velocity moving toward or away from the observer as usefully obtained by the small Doppler shifts seen in starlight when using astronomical spectroscopy Knowledge of the proper motion and Doppler shift allow approximate calculations of a star s true motion in space in respect to the Sun Proper motion is not entirely proper that is intrinsic to the star because it includes a component due to the motion of the Solar System itself Due to the finite speed of light that is also constant without regard to whatever is the velocity of the emanating or reflecting source the instantaneous velocities of distant stars cannot be observed the observed proper motion reflects the velocity of a star relative to the Solar System at the time the light was emitted from that star Contents Introduction Examples Usefulness in astronomy History Stars with high proper motion Software See also References External links Introduction edit Over the course of centuries stars appear to maintain nearly fixed positions with respect to each other so that they form the same constellations over historical time Ursa Major or Crux for example looks nearly the same now as they did hundreds of years ago However precise long term observations show that the constellations change shape albeit very slowly and that each star has an independent motion This motion is caused by the movement of the stars relative to the Sun and Solar System The Sun travels in a nearly circular orbit the solar circle about the center of the Milky Way at a speed of about km s at a radius of ± kPc from the center which can be taken as the rate of rotation of the Milky Way itself at this radius The proper motion is a two dimensional vector because it excludes the component in the direction of the line of sight and is thus defined by two quantities its position angle and its magnitude The first quantity indicates the direction of the proper motion on the celestial sphere with degrees meaning the motion is due north degrees meaning the motion is due east and so on and the second quantity is the motion s magnitude expressed in seconds of arc per year Components of proper motion on the Celestial sphere The celestial north pole is CNP the vernal equinox is V the star path on the celestial sphere is indicated by arrows The proper motion vector is µ a right ascension d declination position angle Proper motion may alternatively be defined by the angular changes per year in the star s right ascension µa and declination µd On the celestial sphere the coordinate of a corresponds to celestial longitude where all right ascensions are measured from the vernal equinox V the point on the sky where the Sun crosses the celestial equator on near March d corresponds to celestial latitude The components of proper motion by convention are arrived at as follows Suppose in a year an object moves from coordinates a d to coordinates a d with angles measured in seconds of arc Then the changes of angle in seconds of arc per year are The magnitude of the proper motion µ is given by vector addition of its components where d is the declination The factor in cos d accounts for the fact that the radius from the axis of the sphere to its surface varies as cos d becoming for example zero at the pole Thus the component of velocity parallel to the equator corresponding to a given angular change in a is smaller the further north the object s location The change µa which must be multiplied by cos d to become a component of the proper motion is sometimes called the proper motion in right ascension and µd the proper motion in declination If the proper motion in right ascension has been converted by cos d into either arcsecond or milliarcsecond the result is expressed as µa mu alpha asterisk i e the proper motion results in right ascension within the Hipparcos Catalogue HIP are expressed in the right ascension mas yr and therefore have already been converted Hence the individual proper motions in right ascension and declination are made equivalent for straight forward calculations of various other stellar motions Position angle is related to these components by Examples edit For the majority of stars seen in the sky the observed proper motions are usually small and unremarkable Such stars are often either faint or are significantly distant have changes of below milliarcseconds per year and do not appear to move appreciably over many millennia A few do have significant motions and are usually called high proper motion stars Motions can also be in almost seemingly random directions Two or more stars double stars or open star clusters which are moving in similar directions exhibit so called shared or common proper motion or cpm suggesting they may be

gravitationally attached or share similar motion in space Barnard s Star showing position every years – Barnard s star has the largest proper motion of all stars moving at seconds of arc per year Large proper motion is usually a strong indication that a star is relatively close to the Sun This is indeed the case for Barnard s Star located at a distance of about light years After the Sun and the Alpha Centauri system it is the nearest known star to Earth Because it is a red dwarf with an apparent magnitude of it is too faint to see without a telescope or powerful binoculars A proper motion of arcsec per year at a distance of light year corresponds to a relative transverse speed of km s Barnard s star s transverse speed is km s and its radial velocity is km s which is at right angles to the transverse velocity which gives a true motion of km s True or absolute motion is more difficult to measure than the proper motion because the true transverse velocity involves the product of the proper motion times the distance As shown by this formula true velocity measurements depend on distance measurements which are difficult in general Currently the nearby star with the largest true velocity relative to the Sun is Wolf which moves at km s or of the speed of light In Rho Aquilae became the first star to have its Bayer designation invalidated by moving to a neighbouring constellation – it is now a star of the constellation Delphinus Usefulness in astronomy edit Stars with large proper motions tend to be nearby most stars are far enough away that their proper motions are very small on the order of a few thousandths of an arcsecond per year It is possible to construct nearly complete samples of high proper motion stars by comparing photographic sky survey images taken many years apart The Palomar Sky Survey is one source of such images In the past searches for high proper motion objects were undertaken using blink comparators to examine the images by eye but modern efforts use techniques such as image differencing to automatically search through digitized image data Because the selection biases of the resulting high proper motion samples are well understood and well quantified it is possible to use them to construct an unbiased census of the nearby stellar population — how many stars exist of each true brightness for example Studies of this kind show that the local population of stars consists largely of intrinsically faint inconspicuous stars such as red dwarfs Measurement of the proper motions of a large sample of stars in a distant stellar system like a globular cluster can be used to compute the cluster s total mass via the Leonard Merritt mass estimator Coupled with measurements of the stars radial velocities proper motions can be used to compute the distance to the cluster Stellar proper motions have been used to infer the presence of a super massive black hole at the center of the Milky Way This black hole is suspected to be Sgr A with a mass of × M where M is the solar mass Proper motions of the galaxies in the Local Group are discussed in detail in Röser In the first measurement was made of the proper motion of the Triangulum Galaxy M the third largest and only ordinary spiral galaxy in the Local Group located ± Mpc beyond the Milky Way Although the Andromeda Galaxy is known to move and an Andromeda–Milky Way collision is predicted in about – billion years the proper motion of the Andromeda galaxy about kpc distant is still an uncertain matter with an upper bound on its transverse velocity of ˜ km s Proper motion of the NGC M galaxy in the M group of galaxies was used in to find an accurate distance to this object Measurements were made of the radial motion of objects in that galaxy moving directly toward and away from us and assuming this same motion to apply to objects with only a proper motion the observed proper motion predicts a distance to the galaxy of ± Mpc History edit Proper motion was suspected by early astronomers according to Macrobius AD but proof was provided in by Edmund Halley who noticed that Sirius Arcturus and Aldebaran were over half a degree away from the positions charted by the ancient Greek astronomer Hipparchus roughly years earlier The term proper motion derives from the historical use of proper to mean belonging to cf propre in French and the common English word property There is no such thing as improper motion in astronomy Stars with high proper motion edit The following are the stars with highest proper motion from the Hipparcos catalog See List of stars in the Hipparcos Catalogue It does not include stars such as Teegarden s star which are too faint for that catalog A more complete list of stellar objects can be made by doing a criteria query at http simbad u strasbg fr simbad Proper motion of Cygni in one year intervals Highest proper motion stars Star Proper motion Radial velocity km s Parallax mas µa cos d mas yr µd mas yr Barnard s star Kapteyn s star Groombridge Lacaille Gliese CD GJ HIP — Cygni A B Lalande Epsilon Indi Software edit There are a number of software products that allow a person to view the proper motion of stars over differing time scales Two free ones are HippLiner – Freeware – Windows Moderately sophisticated with some pretty displays Still under development needs some more navigation and configuration features XEphem – Freeware – Linux and Apple OS X – complete astrometry package can view a region of the sky set a time step and watch stars move over time See also edit Radial velocity Peculiar motion Solar apex Leonard Merritt mass estimator Very Long Baseline Interferometry Galaxy rotation curve Celestial coordinates Milky Way See also The rotation curve of a disc galaxy also called a velocity curve is a plot of the measured magnitude of the orbital velocities i e the speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy s centre and typically rendered graphically as a plot The measured rotation rates of those stars do not match the calculated rates which calculation is based on well known laws of physics A general feature of the galaxy rotation curves is that the orbital speed of stars and gas rises or is almost constant as far from the galactic centre as it can be measured that is stars are observed to revolve around the centre of the galaxy at increasing or the same speed over a large range of distances from the centre of the galaxy Given the observed mass distributions in galaxies the orbital speed should decline at increasing distances in the same way as do other systems with most of their mass in the centre such as the Solar System or the moons of Jupiter The rotation curves of spiral galaxies are also known to be asymmetric The observational data from each side of a galaxy are generally averaged Rotation curve asymmetry appears to be normal rather than exceptional The galaxy rotation problem is the discrepancy between observed galaxy rotation curves and the theoretical prediction assuming a centrally dominated mass associated with the observed luminous material When mass profiles of galaxies are calculated from the distribution of stars in spirals and mass to light ratios in the stellar disks they do not match with the masses derived from the observed rotation curves and the law of gravity A solution to this conundrum is to hypothesize the existence of dark matter and to assume its distribution from the galaxy s center out to its halo Though dark matter is by far the most accepted explanation of the rotation problem other proposals have been offered with varying degrees of success Of the possible alternatives the most notable is Modified Newtonian Dynamics MOND which involves modifying the laws of gravity Contents History and description of the galaxy rotation problem Halo density profiles Further investigations Alternatives to dark matter See also Footnotes External links Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but would account for most of the matter in the universe The existence and properties of dark matter are inferred from its gravitational effects on visible matter on radiation and on the large scale structure of the universe Dark matter has not been detected directly making it one of the greatest mysteries in modern astrophysics Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level According to the Planck mission team and based on the standard model of cosmology the total mass–energy of the known universe contains ordinary baryonic matter dark matter and dark energy Thus dark matter is estimated to constitute note of the total matter in the universe while dark energy plus dark matter constitute of the total mass–energy content of the universe Astrophysicists hypothesized the existence of dark matter to account for discrepancies between the mass of large astronomical objects determined from their gravitational effects and their mass as calculated from the observable matter stars gas and dust that they can be seen to contain Their gravitational effects suggest that their masses are much greater than the observable matter survey suggests Dark matter was postulated by Jan Oort in albeit based upon insufficient evidence to account for the orbital velocities of stars in the Milky Way In Fritz Zwicky was the first to use the virial theorem to infer the existence of unseen matter which he referred to as dunkle Materie dark matter More robust evidence from galaxy rotation curves was discovered by Horace W Babcock in but was not attributed to dark matter The first hypothesis to postulate dark matter based upon robust evidence was formulated by Vera Rubin and Kent Ford in the s– s using galaxy rotation curves Subsequently many other observations have indicated the presence of dark matter in the universe including gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster the temperature distribution of hot gas in galaxies and clusters of galaxies and more recently the pattern of anisotropies in the cosmic microwave background According to consensus among cosmologists dark matter is composed primarily of a not yet characterized type of subatomic particle The search for this particle by a variety of means is one of the major efforts in particle physics today Although the existence of dark matter is generally accepted by the mainstream scientific community some alternative theories of gravity have been proposed such as MOND and TeVeS which try to account for the anomalous observations without requiring additional matter However these theories cannot account for the properties of galaxy clusters Contents Overview Baryonic and nonbaryonic dark matter Observational evidence Galaxy rotation curves Velocity dispersions of galaxies Galaxy clusters and gravitational lensing Cosmic microwave background Sky surveys and baryon acoustic oscillations Type Ia supernovae distance measurements Lyman alpha forest Structure formation History of the search for its composition Cold dark matter Warm dark matter Hot dark matter Mixed dark matter Detection Direct detection experiments Indirect detection experiments Alternative theories Mass in extra dimensions Topological defects Modified gravity Fractality of Spacetime Popular culture See also Notes References External links Overview edit Estimated distribution of matter and energy in the universe today top and when the CMB was released bottom Dark matter s existence is inferred from gravitational effects on visible matter and gravitational lensing of background radiation and was originally hypothesized to account for discrepancies between calculations of the mass of galaxies clusters of galaxies and the entire universe made through dynamical and general relativistic means and calculations based on the mass of the visible luminous matter these objects contain stars and the gas and dust of the interstellar and intergalactic medium The most widely accepted explanation for these phenomena is that dark matter exists and that it is most probably composed of weakly interacting massive particles WIMPs that interact only through gravity and the weak force Alternative explanations have been proposed and there is not yet sufficient experimental evidence to determine whether any of them are correct Many experiments to detect proposed dark matter particles through non gravitational means are under way One other theory suggests the existence of a Hidden Valley a parallel world made of dark matter having very little in common with matter we know and that could only interact with our visible universe through gravity According to observations of structures larger than star systems as well as Big Bang cosmology interpreted under the Friedmann equations and the Friedmann–Lemaître–Robertson–Walker metric dark matter accounts for of the mass energy content of the observable universe In comparison ordinary baryonic matter accounts for only of the mass energy content of the observable universe with the remainder being attributable to dark energy From these figures matter accounts for of the mass energy content of the universe and of the matter is dark matter Dark matter plays a central role in state of the art modeling of cosmic structure formation and galaxy formation and evolution and has measurable effects on the anisotropies observed in the cosmic microwave background CMB All these lines of evidence suggest that galaxies clusters of galaxies and the universe as a whole contain far more matter than that which is easily visible with electromagnetic radiation Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation some alternative theoretical approaches have been developed which broadly fall into the categories of modified gravitational laws and quantum gravitational laws Baryonic and nonbaryonic dark matter edit Play media Fermi LAT observations of dwarf galaxies provide new insights on dark matter There are three separate lines of evidence that suggest the majority of dark matter is not made of baryons ordinary matter including protons and neutrons