The half that can be seen refers to the local sky (seen from wherever you may be
Boundary between earth and sky defines horizon. Perpendicular to that is the Zenith.
Meridian, is an imaginary half circle stretching from the horizon due south, through the
zenith, and the horizon due north
Can pin point position of any object by stating the direction and altitude.
Angular Sizes and Distances:
Lack of depth perception means you can’t justify the true size or distance between objects
in the sky, however the angular sizes can be described
Angular size also depends on distance. Ex. The sun is 400 times the size of the moon yet
it has the same angular size because, is still about 400 times farther away like the moon
The angular distance between a pair of objects in the sky is the angle that appers to
To be more precise, each degree is subdivided into 60 arcminutes and each aricminute is
subdivided into 60 arcseconds
Why do Stars Rise and Set?
Sun, moon, plants, and stars move across the sky because the earth rotates, not the other
Stars relatively near the north celestial pole remain perpetually above the horizon. They
don’t rise or set, they instead circle around the north celestial pole counter clockwise.
Stars relatively near the south celestial pole never rise above the horizon at all
All other stars have circle daily but are partly above and below the horizon. Since earth
rotates counter clockwise( west – east), stars appear to rise in the east and set in the west
Why do the constellations we see depends on the latitude and time of year?
Constellations that can be seen change depending on where you are
Variation with Latitude:
Latitude affects the constellation we see because it affects the locations of the horizon
and zenith relative to the sphere.
Sky varies with latitude but longitude. Ex. People in people in Charleston and Sandiego
are about the same attitude so they see the same constellations at night.