A19N_Unit1_Lec02.pdf - Unit 1 Cosmology Lecture 02 Douglas...

This preview shows page 1 - 13 out of 39 pages.

Unit 1CosmologyLecture 02Douglas EdmondsPenn State Hazleton
Observing the Sky
Cosmologyfrom Greekkosmos‘order, world’+logia‘discourse’n. an account or theory ofthe origin of the universe.The stories we tell about theworld and universe aroundus, and our collective selves:How we came to be here(our past), how we aremeant to be (our present),and where we are going(our future).
Flat or Spherical Earth?Spherical Earth postulated by Aristotle (384–322 B.C.)Evidence: curved shadow Earth casts on the Moon (Lunareclipse)Additional evidence: New stars seen when sailing southSpherical nature of Earth widely believed since AristotleColumbus set out to prove the world is round?Amythcreated by fictional biography of Columbus byWashington Irving
Flat or Spherical Earth?Measuring Earth’s size: Eratosthenes (ca. 276–195 B.C.),Librarian of the Great Library at AlexandriaTraveler’s tales of the well at Syene (due south of Alexandria) –no shadow at noon on summer solsticeHence Sun’s altitude in Alexandria = Angular separation fromSyene
The Celestial Sphere:A Map of the Sky
ConstellationsConstellationsare patterns ofstars that the eye picks out.The stars are usually not neareach other; they just lie in thesame direction.Historically, the brightest starsare stars of the 1stmagnitude.The next brightest are stars ofthe 2ndmagnitude.The fainteststars one can see by eye are 6thmagnitude.(The biggesttelescopes can reachm = 24 orso.)
Orion, the HunterLeo, the LionCygnus, the SwanScorpius, the ScorpionAntlia, the Air PumpPuppis, the Stern
#1. Daily MotionEarth’s axis of rotationdefines some places on thecelestial sphere.Thecelestial North poleisover Earth’s north pole.There happens to be abright star near it, which iscalled Polaris, or theNorthStar.Thecelestial equatoris theextension of Earth’s equator.
#1. Daily MotionEach day, Earth completesone rotation (west-to-east)on its axis. This causes us toface different directions. Asthe Earth turns us around,we see most stars, planets,and the Moon and Sunriseandseteach day. Thesedaily (diurnal) motionsreflect Earth’s spin.
Stars appear to rotate about theNorth & South celestial poles
#2. Yearly MotionIn addition to rotating, the Earth alsorevolvesabout the Sun.

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 39 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Fall
Professor
ERACELOUS
Tags

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture