Introduction to Astronomy
The Celestial Sphere
Presented by Robert Wagner
What is the Celestial Sphere?
•A way of visualizing the sky
•A geocentric (Earth-centered) model
•Stars, planets, and other astronomical objects appear to be positioned on
the celestial sphere
http://astro.wsu.edu/worthey/astro/html/im-sky/celestial-sphere-2.jpg
What is the Celestial Sphere?
The Celestial Sphere - Definitions
•Zenith: The point straight overhead for an observer
•Horizon: The circle where the celestial sphere meets the Earth
•Celestial Pole: The projection of the Earth’s pole to the celestial sphere
•Celestial Equator: The projection of the Earth’s equator to the celestial
sphere
•Ecliptic: The apparent path of the Sun on the celestial sphere
•Vernal Equinox: The intersection of the ecliptic and the celestial
equator, where the Sun is moving northward
Image Credit: https://commons.wikimedia.org/wiki/File:91_minutes_of_the_night_sky.jpg
Circumpolar Stars
•Stars close to the celestial pole will never set!
•Polaris is near the celestial pole
•Stars revolve in circles around the celestial poles
•Stars at greater distances will cross the horizon
Navigation Through Astronomy
•The altitude of the pole gives the latitude of the observer!
•The pole will be 40 degrees above the horizon for an observer at a
latitude of 40 degrees
•The pole will be on the horizon for an observer at the equator
•The pole will be at the zenith for an observer at the pole
•The north celestial pole will not be visible for an observer south of the equator!
