The Celestial Sphere (The sphere should really be rotating, not Earth)

An Ancient Greek Idea Imagine the universe to be a hollow sphere with the Earth at the center –The Celestial Sphere Idea based upon how things _________ to be –The pattern of stars in the sky ________________ Stars ‘embedded’ on the _________ –Pretend the stars are painted on a giant ‘bubble’ around Earth Geocentric (________________) model appear does not change inside Earth centered

Celestial Sphere: Extension of the Earth’s Coordinate System Celestial sphere N/S celestial poles ____________ Celestial equator ____________ Declination ____________ Right Ascension ____________ Like a clear bowl over your head! Latitude Longitude Equator N/S Poles

The Celestial Sphere Earth NCP SCP Celestial equator Earth’s spin axis The celestial sphere

SE AE SS WS Earth Celestial Sphere Ecliptic Celestial equator  Ecliptic = apparent annual path of Sun on the CS NCP Path of Sun during the year SCP Ecliptic (2) Ecliptic (2) = _____________________________________________

North South Right Ascension (hours) Celestial Equator Ecliptic Sun’s Path East Declination (degrees)

Key terms Celestial sphere: –_________ sphere of the sky (what it looks like) Celestial poles joined by line that runs through the Earth’s north and south poles (this line is, in fact, the Earth’s spin axis) NCP is directly above _______________ –Point about which the stars appear to rotate Celestial equator: –___________ of Earth’s equator onto the CS Apparent Earth’s North Pole Projection

Apparent motion: Earth’s rotation As Earth ________, it looks as if the celestial sphere is _________ around us In the north, the center of the rotation is the _______________________________ In the south, the center of the rotation is the _______________________________ The celestial sphere appears to rotate once every _________ rotates rotating North Celestial Pole - Polaris South Celestial Pole – No pole star 24 hours

Where on Earth Definition: –Latitude ( ): The angle between the Observer, the center of the Earth and the Earth’s equator (Measured in degrees) = 0 o (Equator) = 90 o (North pole) = -90 o (South pole)

Earth Equator North pole South pole observer zenith  = 0 o )  = -90 o )  = 90 o ) horizon

The latitude of an observer is equal to the altitude of the visible celestial pole A B To NCP zenith horizon Earth B = 90 o - To CE A + B = 90 o latitude of observer = altitude of NCP = A

The final steps: (hold tight) By definition: angle A + angle B = 90 o But, angle B = 90 o -, so A + 90 o - = 90  And hence, A =

The Celestial Sphere

Precession In addition to its rotation and revolution, the earth’s axis also __________ (wobbles) like a top. The angle between the ecliptic and the equator remains at 23.5°, but the direction changes. The period of this precession of the equinoxes is about ____________. precesses 26,000 years

Polaris won’t always be the North Star Orion won’t always be a winter constellation Horoscopes are all wrong! Because of precession:precession