The Sky from EarthThe Sky from Earth

(Planetarium)(Planetarium)

PSC 203PSC 203

OverviewOverview

� In this section:In this section:� What do we see from Earth?What do we see from Earth?

� How do objects in the sky move daily?How do objects in the sky move daily?

� How do objects in the sky move yearly?How do objects in the sky move yearly?

� How do things change at other locations?How do things change at other locations?

The celestial sphereThe celestial sphere

� For objects such as the Sun and stars, we For objects such as the Sun and stars, we

cannot directly perceive their distancecannot directly perceive their distance

� Historically the sky was perceived as a Historically the sky was perceived as a

sphere with little lights on itsphere with little lights on it

� We still use the same vocabularyWe still use the same vocabulary

The celestial sphereThe celestial sphere

VocabularyVocabulary

� Horizon – the horizontal circle separating Horizon – the horizontal circle separating

the sky from the groundthe sky from the ground

� Zenith – the point straight overheadZenith – the point straight overhead

� Meridian – line from North to south Meridian – line from North to south

through zeniththrough zenith

CoordinatesCoordinates

� Just like the curved surface of the earth Just like the curved surface of the earth

has a coordinate system …has a coordinate system …

� So does the sky, 2 systems in factSo does the sky, 2 systems in fact� Altitude and AzimuthAltitude and Azimuth

� Right Ascension and DeclinationRight Ascension and Declination

� These will be studied in the planetariumThese will be studied in the planetarium

Altitude and AzimuthAltitude and Azimuth

� Altitude – how far above the horizonAltitude – how far above the horizon� 0 on horizon0 on horizon

� 90 at zenith90 at zenith

� Azimuth – how far around horizonAzimuth – how far around horizon� 0 at north0 at north

� 90 at east, 180 at south, 270 at west90 at east, 180 at south, 270 at west

Altitude and AzimuthAltitude and Azimuth Celestial coordinatesCelestial coordinates

� Project Earth’s coordinates out into spaceProject Earth’s coordinates out into space

� →Equator Celestial equator→Equator Celestial equator

� →Poles Celestial poles→Poles Celestial poles

� →Longitude Right Ascension→Longitude Right Ascension

� →Latitude Declination→Latitude Declination

Celestial coordinatesCelestial coordinates

Overview of SCOverview of SC North PoleNorth Pole

Overview of SCOverview of SC EquatorEquator

Motion of the starsMotion of the stars

Motion of the StarsMotion of the Stars

� Depends on location, we will look at South Depends on location, we will look at South

Carolina first (SC)Carolina first (SC)

� Latitude ~35 NLatitude ~35 N

SC, looking southSC, looking south

� Stars rise SEStars rise SE

� Have low altitude at Have low altitude at

the meridianthe meridian

� Set in SWSet in SW

SC, looking eastSC, looking east

� Stars rise along Stars rise along

eastern horizoneastern horizon

� Move up in at an Move up in at an

angle towards the angle towards the

southsouth

SC, looking westSC, looking west

� Move down towards Move down towards

the western horizon the western horizon

an angle from the an angle from the

southsouth

SC, looking northSC, looking north

� Some star rise is NE Some star rise is NE

and set in NWand set in NW

� Others circle around Others circle around

the north celestial the north celestial

pole (circumpolar)pole (circumpolar)

Overview of SCOverview of SC Star pathsStar paths

� The path of stars are different in different The path of stars are different in different

locationslocations� We will look atWe will look at

� Equator – latitude 0Equator – latitude 0

� South Africa – latitude ~40SSouth Africa – latitude ~40S

� Alaska – latitude ~60NAlaska – latitude ~60N

� North Pole – latitude ~90NNorth Pole – latitude ~90N

EquatorEquator

� Stars move from east to west more Stars move from east to west more

directly overhead directly overhead � (instead of arcs towards the southern horizon)(instead of arcs towards the southern horizon)

� There are no circumpolar starsThere are no circumpolar stars

� Celestial poles are on the horizonCelestial poles are on the horizon

EquatorEquator

North PoleNorth Pole

� North celestial pole at zenith (overhead)North celestial pole at zenith (overhead)

� Stars are all circumpolar and move around Stars are all circumpolar and move around

at constant altitudes at constant altitudes

North PoleNorth Pole

South AfricaSouth Africa

� Star move from East to West along an arc Star move from East to West along an arc

towards the northern horizontowards the northern horizon� (instead of towards the southern horizon)(instead of towards the southern horizon)

� Stars in the south are circumpolar around Stars in the south are circumpolar around

the south celestial pole the south celestial pole � (north celestial pole not visible)(north celestial pole not visible)

AlaskaAlaska

� Stars move in very low arcs from east to Stars move in very low arcs from east to

west along the southern horizonwest along the southern horizon

� Most stars in the sky are circumpolarMost stars in the sky are circumpolar

� North celestial pole is high in sky North celestial pole is high in sky

AlaskaAlaska

� My figureMy figure

Motion of the SunMotion of the Sun

Sun motion Sun motion

� Depends on location and seasonDepends on location and season

� We will first look at South Carolina’s view We will first look at South Carolina’s view

in each season…in each season…

SC, winterSC, winter

� Rises in SERises in SE

� Reaches low altitude at noon Reaches low altitude at noon

� Sets in SWSets in SW

� Night longer than dayNight longer than day

SC, springSC, spring

� Rises in ERises in E

� Reaches mid altitude at noon Reaches mid altitude at noon

� Sets in WSets in W

� Day and night equalDay and night equal

SC, summerSC, summer

� Rises in NERises in NE

� Reaches high altitude at noon Reaches high altitude at noon

� Sets in NWSets in NW

� Day longer than nightDay longer than night

SC, fallSC, fall

� Rises in ERises in E

� Reaches mid altitude at noon Reaches mid altitude at noon

� Sets in WSets in W

� Day and night equalDay and night equal

SCSC EquatorEquator

� Sun always moves more overheadSun always moves more overhead

EquatorEquator South CarolinaSouth Carolina

AlaskaAlaska North PoleNorth Pole

South AfricaSouth Africa

� My diagramMy diagram

Ecliptic verses equatorEcliptic verses equator

� In March, ecliptic on celestial equatorIn March, ecliptic on celestial equator

� In June, ecliptic north of celestial equatorIn June, ecliptic north of celestial equator

� In Sep, ecliptic on celestial equatorIn Sep, ecliptic on celestial equator

� In Dec, ecliptic south of celestial equatorIn Dec, ecliptic south of celestial equator

Ecliptic verses equatorEcliptic verses equator