Randy L. Phelps.

The following Applet was written and provided by Walter Fendt and is copyrighted by him. The right of commercial use remains with that author.

The purpose of this exercise is to illustrate the daily motions of stars/objects on the celestial sphere, as seen from intermediate latitudes, such as Sacramento. Be sure to complete all three exercises as described on the previous page.

Exploration

Anticipate the Results

Instructions/Sugestions to Help Answer These Questions

1. The Appearance of the Sky at intermediate latitudes

Where is the North Celestial Pole as seen by the observer?
Where is the Celestial Equator as seen by the observer?
What particular star, if any, is located near the zenith?

Set the latitude in the applet for that of Sacramento and hit the "Enter" key - Note: you must know what the latitude is for Sacramento and you must hit the "Enter" key after inputing into the applet!
Note the positions of the observer (O), the North Celestial Pole (NP), the celestial equator (the cirle on which the letter V is marked), the zenith (Ze), and a specified star (ST).

2. Circumpolar Stars

As seen from intermediate latitudes, what stars are circumpolar?
As seen from intermediate latitudes, are all objects north of the Celestial Equator visible at some time during the year?
As seen from intermediate latitudes, are all objects south of the Celestial Equator visible at some time during the year?
How does the fraction of the stars in the sky that are visible over the course of the year vary with latitude?
If a camera were pointed toward the zenith, and a time exposure photograph were take, what would the resulting picture look like?

Recall what circumpolar stars are...
Set the applet as described in Exploration 1 above, but rerun the whole set of simulations below with various latitudes between the Equator and the poles, including that for Sacramento.
Position the cursor over the "Rotation/Pause" icon, and click on it.
Note the motion of the indicated star (ST).
Stop the simulation by clicking "Rotation/Pause"
Change the "Declination" of the star from the default value (20^o) to a value from 0^o to 90^o. A value of 0^o corresponds to a star located on the Celestial Equator, while a value of 90^o corresponds to a star at the North Celestial Pole. Restart the simulation.
Repeat the simulation for stars with various "Declinations" between 0^o to 90^o, inclusive.
Repeat the exercise for "Declination" values from 0^o to -90^o. The minus indicates stars located south of the Celestial Equator.
In all cases, note how large the circle the star makes on the sky is at various distances from the celestial pole, and see if the star dips below the horizon.

Now try to explore the following. First think about the question, and then determine what parameters in the applet need to be changed to help you explore the concept.