The Sky from Earth The Sky from Earth (Planetarium) (Planetarium) PSC 203 PSC 203 Overview Overview 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 sphere The celestial sphere For objects such as the Sun and stars, we For objects such as the Sun and stars, we cannot directly perceive their distance cannot directly perceive their distance Historically the sky was perceived as a Historically the sky was perceived as a sphere with little lights on it sphere with little lights on it We still use the same vocabulary We still use the same vocabulary The celestial sphere The celestial sphere Vocabulary Vocabulary Horizon – the horizontal circle separating Horizon – the horizontal circle separating the sky from the ground the sky from the ground Zenith – the point straight overhead Zenith – the point straight overhead Meridian – line from North to south Meridian – line from North to south through zenith through zenith
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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