The Celestial Sphere

The Celestial Sphere

•The “Celestial Sphere” is an ancient concept dating back to the time
when we thought the earth was the center of universe

•It is a “gigantic” sphere glued to the stars

•Stars appear to rotate because sphere is rotating

•Sun, Planets, Comets, Asteroids all move on surface of sphere

Images taken from http://zebu.uoregon.edu/~imamura/121/images/sphere.gif

​The right shows our view of the celestial sphere on the left. We will focus on OUR view of the celestial sphere.

Celestial Sphere “Parts” You are reviewing today

▪ Meridian
▪ Celestial sphere
▪ Zenith
▪ Nadir
▪ Celestial poles
▪ Azimuth
▪ Altitude

Zenith

▪If you place yourself in the middle
of the celestial sphere, the zenith
is directly above you….90° above
your head

Horizon

▪The intersection of the celestial
“dome” and earth….

Note your cardinal directions….

But WHERE is the NCP and
the SCP?


It is the geographical latitude
latitude of the observer.

In Pocatello, you are a latitude of 42.9°. What is the degree of the Celestial North Pole (CNP)?

​42.9

Altitude of NCP is always equal to your latitude on Earth's surface.

RIGHT NOW…your celestial
north pole happens to be a star
called Polaris.

The sky appears to rotate around NCP.

Celestial Equator – imaginary circle
cutting the meridian in two equal
parts going through the observer
and the meridian.

Now you know the celestial sphere
terms….What do you do with them now?

▪FIND PLACES!!!

▪Latitude, altitude and azimuth
are measured in degrees.

▪There are 360° in a circle and
each degree can be further
equally subdivided

Limitations of Local Coordinates

• For an observer, all stars and objects in

sky besides North and South Pole stars
have Altitude and Azimuth that are
constantly changing

• Two people at different spots on earth

will disagree about Altitude and
azimuth coordinates even if they are
looking at the same object at the same
time