Pismp the Skysains

download Pismp the Skysains

of 28

Transcript of Pismp the Skysains

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 1

    The Sky

    Edward M. Murphy

    Space Science for Teachers2005

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 2

    Horizon and Zenith

    It is sometimes useful to think of thesky as a great dome over our heads.

    The horizon (ufuk) is where the domemeets the Earth.

    The zenith is the point directly overhead.

    As the Earth turns, this dome turns overour heads. It appears as if the sky is alarge hollow sphere centered on the Earth.

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 3

    Horizon and Zenith

  • 7/29/2019 Pismp the Skysains


    Defining the position of objects The are two common systems for

    defining position of astronomical bodies

    in the sky. The Azimuth-Altitude (Az/Alt) system, and

    The Right Ascension-Declination (RA/Dec)


  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 5

    Altitude and Azimuth

    The height of a star above the horizon iscalled the altitude.

    The direction to the star as measured fromtrue north is called the azimuth.

    Note: True north is not the same as magneticnorth. The magnetic north pole is not located in

    the same place as the true north pole. On maps, the legend will show you how to correct from

    magnetic north, as measured by a compass, to truenorth.

  • 7/29/2019 Pismp the Skysains


    The Az/Alt System

    Alt / Az system defines the position of an objectin the sky in terms of its:azimuth (0 to 359 degrees; N = 0o, E = 90o,S = 180o, W = 270o) along the horizon,

    its altitude above the horizon (0 to 90degrees; 0o = horizon, 90o = zenith)

    N Sa



    Az = a=70o

    Alt = b= 60o

    Observer (you)

    Object inthe sky

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 7

    Altitude and Azimuth

  • 7/29/2019 Pismp the Skysains


    Estimating Az and Alt:

    The Hand and Fist Method

    Your hand span, closed fist and fingers canbe used as a measure of angle to estimateangles.

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 9

    Measuring Angles in the Sky

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 10

    Angular Sizes and Distances

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 11

    Measuring Angles

    The Sun and Moon appear to be about degree in size.

    Your finger held at arms length is aboutone degree across.

    Your fist at arms length is about 10degrees.

    Your outstretched hand at arms length isabout 20 degrees across.

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 12

    Altitude and Azimuth

    The altitude and azimuth of a starchange during the course of night as

    the star rises and sets.Angles are measured using degrees,

    minutes of arc, and seconds of arc.

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 13

    Measuring Angles

    Angles in astronomy are measured indegrees, arcminutes and arcseconds.

    1 degree = 60 arcminutes

    1 arcminute = 60 arcseconds

    1 degree = 3600 arcseconds

    1 arcsecond is the size of a U.S. quarter asseen from 5 km (3 miles) or a penny asseen from 2.2 miles.

  • 7/29/2019 Pismp the Skysains


    The RA/Dec System RA / Dec system defines the position of an

    object in the sky in terms of its position onthe Celestial Sphere.

    The RA / Dec system is analogous to theLongitude / Latitude system of defining the

    location of places on the Earth, i.e., RA issimilar to lines of Longitude and Declination issimilar to lines of latitude.

    Units of RA are measured in hours, minutes

    and seconds. (00h:00m:00s -->23h:59m:59s)

    Units of Dec are measured in degrees northand south of the celestial equator. (-90S -->+90N)

  • 7/29/2019 Pismp the Skysains


    The North Celestial Polemark theposition of +90o degrees Dec;

    The South Celestial Polemarks theposition of -90o degrees Dec; and

    The Celestial equator is defined as

    0odegrees Dec.These positions are analogous to the

    North pole of the Earth (+90o Lat);

    South Pole (-90o

    Lat), and the equator(0o Lat)

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 16

    Celestial Coordinates

    Just as Earth has lines of longitude andlatitude, the celestial sphere has a system ofcelestial coordinates:

    Declination (dec): The north-south position of a staron the celestial sphere. Declination is measured indegrees, arcminutes, and arcseconds. The celestialequator is defined to have a declination of 0


    Right Ascension (RA): The east-west coordinates ofan object on the celestial sphere. R.A. is measuredin hours, minutes, and seconds of time. The springequinox is defined to be 0


  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 17

    Celestial Coordinates

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 18

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 19

    Celestial Coordinates


    RA 18h


    DEC +38o44

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 20

    Longitude and Latitude

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 21

    Longitude and Latitude

    Latitude: Your north-south position on Earth.The equator is defined to have a latitude of0

    o. The north pole is at 90

    oN and the south

    pole at 90


    S. Longitude: Your east-west position on Earth.

    An arbitrary point, the Prime Meridian inGreenwich, England marks a longitude of 0


    Leander McCormick Observatory is at: Longitude 78

    o31 19.8 W

    Latitude 38o01 58.2 N

    Altitude 264 meters

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 22

    Rotation ofthe Earth

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 23

    The stars move

    from east towest becausethe earth rotatesfrom west toeast.

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 24

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 25

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 26

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 27

    Classroom Exercise

    Find Orion in the night sky. Is it on theequator, the ecliptic, both, or neither.

    How long is Orion above the horizoneach day?

    Find Sagittarius. Is it north or south ofthe equator?

    How long is Sagittarius above thehorizon each day?

  • 7/29/2019 Pismp the Skysains


    2/28/2013 The Sky 28

    Classroom Exercise

    Find Taurus. Is it north or south of theequator?

    How long is it above the horizon each day? Find the Sun on December 21. Whichconstellation is it in? How long is it above thehorizon each day?

    Find the sun on June 21. Which constellationis it in? How long is it above the horizoneach day?