| Date post: | 17-Dec-2014 |
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Grunt Productions 2007
Simple Astronomical Simple Astronomical PrinciplesPrinciples
(Introduction - The Celestial (Introduction - The Celestial Sphere)Sphere)
A brief by Lance GrindleyA brief by Lance Grindley
Grunt Productions 2007
CoveringCovering
Principles of the Celestial Principles of the Celestial SphereSphere
Movement of Heavenly BodiesMovement of Heavenly Bodies Simple astronomical definitionsSimple astronomical definitions Combined co-ordinate systemCombined co-ordinate system
Grunt Productions 2007
Celestial SphereCelestial Sphere
Viewed from Earth, the sky appears Viewed from Earth, the sky appears as an inverted bowl.as an inverted bowl.
The stars and other heavenly bodies The stars and other heavenly bodies appear to lie on this sphere, appear to lie on this sphere, irrespective of their actual distance.irrespective of their actual distance.
Radius of celestial sphere is infinite Radius of celestial sphere is infinite so position is always described in so position is always described in angular terms.angular terms.
Grunt Productions 2007
Relative Motion of the Relative Motion of the Celestial SphereCelestial Sphere
Earth rotates eastwards at one revolution Earth rotates eastwards at one revolution with respect to the sun every solar day.with respect to the sun every solar day.
Heavenly bodies appear to move Heavenly bodies appear to move westwards rising in the east and setting westwards rising in the east and setting in the west.in the west.
Rate of rotation and apparent movement Rate of rotation and apparent movement is 360is 360oo divided by 24 hours = 15 divided by 24 hours = 15oo per per hourhour
Angular east/west movement is Angular east/west movement is measured on the equator and called measured on the equator and called “hour angle”.“hour angle”.
Grunt Productions 2007
Southern HemisphereSouthern Hemisphere
South
Celestial Equator
90o - latitude
Grunt Productions 2007
Northern HemisphereNorthern Hemisphere
North
Pole Star (Polaris)
latitude
Grunt Productions 2007
Celestial SphereCelestial SphereNorth Celestial Pole
South Celestial Pole
CelestialEquator
Parallel ofDeclination
CelestialMeridian
CelestialMeridian
HourAngle
Hour Angle
Grunt Productions 2007
Positions on Positions on Earth/Celestial SphereEarth/Celestial Sphere
Positions are related to Equator Positions are related to Equator and Greenwich Meridianand Greenwich Meridian
Latitude and Longitude used on Latitude and Longitude used on Earth’s surfaceEarth’s surface
Declination and Greenwich Declination and Greenwich Hour Angle (GHA) used on Hour Angle (GHA) used on Celestial SphereCelestial Sphere
Grunt Productions 2007
Describing PositionsDescribing Positions
GHA
Dec
Lat
Longitude
Grunt Productions 2007
Earth’s Solar OrbitEarth’s Solar Orbit
Earth’s axis remains stationary in Earth’s axis remains stationary in spatial terms but is not perpendicular spatial terms but is not perpendicular to the plane of the orbit.to the plane of the orbit.
Inclined axis causes the position of Inclined axis causes the position of the sun to move in relation to the the sun to move in relation to the equator.equator.
Changing angle (declination) creates Changing angle (declination) creates the seasons in temperate latitudes. the seasons in temperate latitudes.
Grunt Productions 2007
EclipticEcliptic
First Point of Aries
Ecliptic
Grunt Productions 2007
SeasonsSeasons
Winter Solstice 22
Dec
Summer Solstice 21
Jun
Spring Equinox 21
Mar
Autumnal Equinox 23
Sep
Grunt Productions 2007
Northerly DeclinationNortherly Declination
N S
E
W
P
Grunt Productions 2007
Southerly DeclinationSoutherly Declination
N S
E
W
P
Grunt Productions 2007
ConclusionsConclusions Concept of Celestial Sphere allows Concept of Celestial Sphere allows
us to use spherical trigonometry to us to use spherical trigonometry to measure relative positions and solve measure relative positions and solve problems.problems.
A precise time is required to predict A precise time is required to predict the relative position of an the relative position of an astronomical body.astronomical body.
The changing declination of the sun The changing declination of the sun creates the seasons and changes creates the seasons and changes times of rise and set.times of rise and set.
