A scientific model.  Why do we use the model of the celestial sphere when studying the night sky, even though it does not accurately represent three-dimensional.

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Presentation transcript:

A scientific model

 Why do we use the model of the celestial sphere when studying the night sky, even though it does not accurately represent three-dimensional space?  How can you locate constellations and other sky objects using the coordinate system of the celestial sphere?  Why are different constellations visible in the sky at different times of the year or from different places on Earth?

 An imaginary sphere used to help locate celestial objects.  The Earth is at the center and the celestial bodies (stars, planets, galaxies, etc) are “painted on” the surface of the sphere  It is considered a scientific model

 Horizon – the visual boundary between Earth and the sky (with cardinal points N, S, E, and W)  Zenith - Point on the celestial sphere directly overhead  Nadir -Point on the celestial sphere directly underneath the observer’s feet  Celestial equator - a projection of Earth’s equator onto the celestial sphere, always crosses the horizon directly East and West  Celestial Poles projection of Earth’s north and south poles onto the celestial sphere

From geographic latitude l you will see the celestial north pole ( l) degrees above the Northern horizon l Locating the Celestial North Pole and Celestial Equator in your sky zenith

The Celestial South Pole isn’t visible from the Northern Hemisphere. Celestial Equator is visible in the sky 90 o south of the CNP Horizon Looking North Celestial North Pole Example: New York City: l ≈ 40.7º Polaris Zenith (90 o above horizon) Same as latitude ( l )

 Latitude: (parallels) marks locations north and south of the equator  Longitude: (meridians) marks locations east and west of the Prime Meridian

 Declination (Dec): imaginary lines on the celestial sphere that show positions north and south of the celestial equator  +60 o is north and -60 o is south  Similar to latitude lines on the Earth  0 o declination is at the celestial equator

 Similar to longitude on Earth  Usually measured from 0 – 24 hours.  Right ascension is a unit of angle  As you face north, the stars will appear to rise (ascend) from the east (your right).  The celestial meridian (0 hour) is a semicircle connecting the celestial poles and passing through the vernal equinox on the celestial equator Right Ascension (RA): The E-W position of a celestial body

 Constellations, stars, galaxies, etc. can be given an “address” in the sky using RA and Dec.  Degrees of Declination (Dec) can be divided into 60 arcminutes and each minute of arc can be divided into 60 arcseconds.  Hours of Right Ascension (RA) can be divided into minutes and seconds as well.  So, the specific “address” for the star Antares is  Dec: -26 o 25’55”  RA: 16 h 29 m 30 s

The Sun’s apparent path on the sky is called the Ecliptic. OR The Ecliptic is the projection of Earth’s orbit onto the celestial sphere.



 Why do we use the model of the celestial sphere when studying the night sky, even though it does not accurately represent three-dimensional space?  How can you locate constellations and other sky objects using the coordinate system of the celestial sphere?  Why are different constellations visible in the sky at different times of the year or from different places on Earth?