Published on November 13, 2007
Motions of the Celestial Sphere: Motions of the Celestial Sphere Constellations: Constellations Sky looks like a dome with the star painted on the inside. 88 constellations such as Ursa Major, Orion, etc. Asterisms are not constellations for example the Big Dipper, the Teapot, etc. Descriptions of Celestial Sphere: Descriptions of Celestial Sphere Zenith-directly overhead Meridian – imaginary line running north & south through the zenith Horizon – where the sky appears to intersect the ground. Altitude – height of a star above horizon (degrees). The sky appear like a dome overhead. Descriptions of Celestial Sphere: Descriptions of Celestial Sphere North Celestial Pole (NCP) – extension of Earth’s rotation axis onto the sky. South Celestial Pole - ditto Celestial Equator – extension of Earth’s equator onto the sky. Ecliptic – apparent yearly path of Sun. Stars are not a same distances. So, constellations are not real places. Rising and Setting of the Stars: Rising and Setting of the Stars The stars, sun, moon and planets all appear to rise in the east and set in the west. Reflection of Earth’s rotation from west to east. Local Rising and Setting of the Stars: Local Rising and Setting of the Stars We live on the side of the Earth. NCP’s altitude equals your latitude. Circumpolar stars never rise or set but circle the NCP Our view of Celestial Sphere: Our view of Celestial Sphere We live on the side of the Earth. Sky appears tilted at an angle equal to our latitude. Stars appear to move in arcs across the sky that are not perpendicular to horizon. Our view of Celestial Sphere: Our view of Celestial Sphere The sky appears to rotate around NCP. Altitude of NCP is always equal to your latitude on Earth's surface. Slide9: A space ship lands on an unknown planet. The occupants notice that the stars never rise or set but appear to move in circles parallel to the horizon. Where on the planet did the space ship land? At the equator. At 45 degrees latitude. At one of the celestial poles. Cannot be determine. Slide10: Atlanta has a latitude of about 33 north degrees. The star Polaris is very close to the Celestial North Pole. What is the altitude of Polaris when viewed from Atlanta? 33 degrees 45 degrees 57 degrees 90 degrees Slide11: This picture is a time exposure of the night sky showing star trails as the stars appear to rotate around the NCP. What is the name of the bright star near the center of the rock arch? Where are the circumpolar stars?